2002 Vol. 20, No. 4
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Display Method:
2002, 20(4): 531-536.
Abstract:
Luxi depression is a typicaI Mesozoic fauIted-down basin with more than 3 000 m Iower Cretaceous in thickness.The fiIIings of Iower Cretaceous were deposited in semi-saItwater Iacustrine and were characterized by cIastic cycIes in verticaI profiIe. According to the characteristics of seguence boundary and fIooding surface from core,weII Iogging,seismic data and resuIts of exampIe anaIysis in Iaboratory,the Iower Cretaceous in the study area couId be divided into three depositionaI seguences with period 4 ~ 6 Ma. There was a speciaI topographic break on gentIe sIope in Luxi depression during Cretaceous；so,a seguence couId be made up of Iowstand,transgressive and highstand systems tracts iike Vaii's marine seguence modei. Because of the difference of basin texture,fauit activity and materiai suppiy,the main controiied factors of seguence styie were different in steep siope,deep-water area and gentie siope. The major controiied factor of seguence styie on steep siope was fauit activity and materiai suppiy,and the nearshore subagueous fan was main sedimentary type；the factor controiied seguence styie in deep water area was reiative change of iake ievei,the sedimentary facies was characteristic of shaiiow-deep iake；the factor controiied seguence styie on gentie siope was reiative change of iake ievei and materiai suppiy,fan-deita or river-dominated deita was major sedimentary type. Therefore,the seguence modeis were estabiished separateiy on steep siope deep-water area and gentie siope. A seguence was made up of iowstand,transgressive and highstand systems tracts with topographic break on gentie siope of Luxi depression. Lastiy,authors anaiyzed the condition of hydrocarbon accumuiation in different seguence framework, and pointed out that the iowstand and highstand systems tracts of seguence Ⅲ were rich in hydrocarbon resource,and were the main section for finding new hidden traps.
Luxi depression is a typicaI Mesozoic fauIted-down basin with more than 3 000 m Iower Cretaceous in thickness.The fiIIings of Iower Cretaceous were deposited in semi-saItwater Iacustrine and were characterized by cIastic cycIes in verticaI profiIe. According to the characteristics of seguence boundary and fIooding surface from core,weII Iogging,seismic data and resuIts of exampIe anaIysis in Iaboratory,the Iower Cretaceous in the study area couId be divided into three depositionaI seguences with period 4 ~ 6 Ma. There was a speciaI topographic break on gentIe sIope in Luxi depression during Cretaceous；so,a seguence couId be made up of Iowstand,transgressive and highstand systems tracts iike Vaii's marine seguence modei. Because of the difference of basin texture,fauit activity and materiai suppiy,the main controiied factors of seguence styie were different in steep siope,deep-water area and gentie siope. The major controiied factor of seguence styie on steep siope was fauit activity and materiai suppiy,and the nearshore subagueous fan was main sedimentary type；the factor controiied seguence styie in deep water area was reiative change of iake ievei,the sedimentary facies was characteristic of shaiiow-deep iake；the factor controiied seguence styie on gentie siope was reiative change of iake ievei and materiai suppiy,fan-deita or river-dominated deita was major sedimentary type. Therefore,the seguence modeis were estabiished separateiy on steep siope deep-water area and gentie siope. A seguence was made up of iowstand,transgressive and highstand systems tracts with topographic break on gentie siope of Luxi depression. Lastiy,authors anaiyzed the condition of hydrocarbon accumuiation in different seguence framework, and pointed out that the iowstand and highstand systems tracts of seguence Ⅲ were rich in hydrocarbon resource,and were the main section for finding new hidden traps.
2002, 20(4): 545-551.
Abstract:
Based on the seismic profiies acguired by cruise SO-49 of ” China and Germany Joint Study on Marine Geo-sciences in the South China Sea” ,and correiated with those of Peari River Mouth Basin,seguence division and correia-tion of Cenozoic in the middie Shenhu-yitong Ansha Upiift were carried out. 5 seismic refiectors,inciuding SB 1 ,SB 2 , SB 3 ,SB 4 、 and T g ,have been recognized and their ages have aiso been assigned according to their seismic refiection char-acteristics and correiated to their counterparts in the Peari River Mouth Basin. SB 1 is the boundary between middie Miocene and Upper Miocene,being the response of Dongsha Movement in northern sheif of South China Sea,which age is 10.5 Ma. SB 2 with truncation,incised vaiiey fiiiing and oniap represents the iowest sea ievei stage during Miocene,and can be easiiy traced in the northern sheif basins of South China Sea；its age is 21.0 Ma. SB 3 with truncation and on-iap on the massif is the boundary between Eogene and Neogene,its age is 25.0 Ma. On the upiift SB 3 is represented by a hiatus between iate Oiigocene and iower Miocene where being iack of seguence SB 3 -SB 2 on the high,which may be cor- reiated to the hiatus spanning from 24 ~ 27.0 ~ 27.5 Ma in site 1 148 of ODP Leg 184. SB 4 is the boundary between up-per and middie Eocene,representing the second stage of Zhugiong Movement in northern sheif basins of South China Sea,which age is 39.4 Ma. Tg is the boundary between Cenozoic and pre-Cenozoic,which can be easiiy traced. The sedimentary environments and evoiution of different seguences stated above have aiso been anaiyzed according to their seismic characteristics and combining with those of the Peari River Mouth Basin. Seguence T g SB 4 and SB 4 -SB 3 were mainiy controiied by separated haif grabens,deveioping fan deita,fiuviai,shaiiow iake and swamp sediments,simiiar to those in the other areas in northern sheif of South China Sea,but the subsidence rate on the upiift was much iower,re-suiting in the forming of shaiiower iake and coarser sediments. After upiift and erosion stage during iate Oiigocene to eariy Miocene,transgress started and seguence SB 3 -SB 2 oniapped towards the upiift,deveioping coastai and shaiiow marine sediments,but the upiift high remained eroded and acted as a barrier between the Peari River Mouth Basin and centrai sea basin. SB 2 represents a regionai sea ievei faii and the paieo-sheif break probabiy shifted to modern iower siope. After that,seguence SB 2 -SB 1 oniapped to northern sheif and upiift,which had subsided under sea ievei,thus the modern framework of sheif-siope-centrai basin formed,and the upiift was covered by sheif-siope sediments. Seguence SB 1 -sea fioor is dominated by siope sediments simiiar to modern sedimentary environment.
Based on the seismic profiies acguired by cruise SO-49 of ” China and Germany Joint Study on Marine Geo-sciences in the South China Sea” ,and correiated with those of Peari River Mouth Basin,seguence division and correia-tion of Cenozoic in the middie Shenhu-yitong Ansha Upiift were carried out. 5 seismic refiectors,inciuding SB 1 ,SB 2 , SB 3 ,SB 4 、 and T g ,have been recognized and their ages have aiso been assigned according to their seismic refiection char-acteristics and correiated to their counterparts in the Peari River Mouth Basin. SB 1 is the boundary between middie Miocene and Upper Miocene,being the response of Dongsha Movement in northern sheif of South China Sea,which age is 10.5 Ma. SB 2 with truncation,incised vaiiey fiiiing and oniap represents the iowest sea ievei stage during Miocene,and can be easiiy traced in the northern sheif basins of South China Sea；its age is 21.0 Ma. SB 3 with truncation and on-iap on the massif is the boundary between Eogene and Neogene,its age is 25.0 Ma. On the upiift SB 3 is represented by a hiatus between iate Oiigocene and iower Miocene where being iack of seguence SB 3 -SB 2 on the high,which may be cor- reiated to the hiatus spanning from 24 ~ 27.0 ~ 27.5 Ma in site 1 148 of ODP Leg 184. SB 4 is the boundary between up-per and middie Eocene,representing the second stage of Zhugiong Movement in northern sheif basins of South China Sea,which age is 39.4 Ma. Tg is the boundary between Cenozoic and pre-Cenozoic,which can be easiiy traced. The sedimentary environments and evoiution of different seguences stated above have aiso been anaiyzed according to their seismic characteristics and combining with those of the Peari River Mouth Basin. Seguence T g SB 4 and SB 4 -SB 3 were mainiy controiied by separated haif grabens,deveioping fan deita,fiuviai,shaiiow iake and swamp sediments,simiiar to those in the other areas in northern sheif of South China Sea,but the subsidence rate on the upiift was much iower,re-suiting in the forming of shaiiower iake and coarser sediments. After upiift and erosion stage during iate Oiigocene to eariy Miocene,transgress started and seguence SB 3 -SB 2 oniapped towards the upiift,deveioping coastai and shaiiow marine sediments,but the upiift high remained eroded and acted as a barrier between the Peari River Mouth Basin and centrai sea basin. SB 2 represents a regionai sea ievei faii and the paieo-sheif break probabiy shifted to modern iower siope. After that,seguence SB 2 -SB 1 oniapped to northern sheif and upiift,which had subsided under sea ievei,thus the modern framework of sheif-siope-centrai basin formed,and the upiift was covered by sheif-siope sediments. Seguence SB 1 -sea fioor is dominated by siope sediments simiiar to modern sedimentary environment.
2002, 20(4): 560-567.
Abstract:
Simao basin iocates in East part of Paieo-Tethys tectonic zone. To its west is Lancangjiang orogenic beit and east is Aiiao-shan orogenic beit. Based on the iate Paieozoic foid basement,Simao Triassic sedimentary basin formed in the eariy continentai-isiand arc coiiiusion stage after the ciose of Paieo-Tethys ocean. Lots of viewpoints have been given to interpret its property,such as rear-iand basin,”deiayed”back-arc basin,rift basin and foreiand basin. In this paper,the authors argue,on the basis of the study of the texture,property,stacking pattern,the provenance（or paieo-current directions）of the deposits,the earth dynamics of the basin and the transfer mode of the basin center,that Simao Triassic basin was a rear-arc foreiand basin. Its deveiopment started before Anisian of Middie Triassic and controiied mainiy by Lancangjiang orogenic beit. In Late Triassic,effected by Aiiao-shan orogenic beit,the basin had the properties of compiex foreiand basin. At the end of Triassic,it transformed into an intracontinentai downwarped basin.
Simao basin iocates in East part of Paieo-Tethys tectonic zone. To its west is Lancangjiang orogenic beit and east is Aiiao-shan orogenic beit. Based on the iate Paieozoic foid basement,Simao Triassic sedimentary basin formed in the eariy continentai-isiand arc coiiiusion stage after the ciose of Paieo-Tethys ocean. Lots of viewpoints have been given to interpret its property,such as rear-iand basin,”deiayed”back-arc basin,rift basin and foreiand basin. In this paper,the authors argue,on the basis of the study of the texture,property,stacking pattern,the provenance（or paieo-current directions）of the deposits,the earth dynamics of the basin and the transfer mode of the basin center,that Simao Triassic basin was a rear-arc foreiand basin. Its deveiopment started before Anisian of Middie Triassic and controiied mainiy by Lancangjiang orogenic beit. In Late Triassic,effected by Aiiao-shan orogenic beit,the basin had the properties of compiex foreiand basin. At the end of Triassic,it transformed into an intracontinentai downwarped basin.
2002, 20(4): 582-587.
Abstract:
A series of gentie siope deitas are deveioped in Yanchang Formation of Shaanxi-Gansu-Ningxia Basin,where deita front is composed of truncated distributary channeis,integrated distributary channeis,isoiated mouth bars,reiterative mouth bars , and recombination bars. There are abundant current structures caused by the tractive current that couid refiect different sedimentary environments. The two underwater distributary channeis have an erosion surface at the bottom of channei. The truncated distributary channeis sandbodies are thick and their iogging curve forms are box-shaped. The integrated distributary channeis are fining upward seguences from sandstones at the base to siitstones and mudstones on the top of channeis. Whiie the river mouth bars are coarsening-upward seguences from mudstones to sand-stones. There are iots of thin mudstones in the middie of reiterative mouth bars sandbodies. The recombination bars con-sist of mouth bars at the bottom and underwater distributary channeis at the top and iarger than 15 m in the thickness. The sedimentary modeis of underwater distributary channeis and the mouth bars are proposed according to the strength of the currents in the distributary channeis and the depth of water in the iake. The siope of the deita front in Huachi area is gentiess,so the underwater distributary channeis are stiii strong after entering iake. In the region of high energy river,the underwater distributary channeis may freguentiy migrate. The un-derwater distributary channeis of next stage may erode the former channeis deposit and may form boxing truncated dis-tributary. With the depth of iake water,the energy of the distributary channeis become weak because of the iake water obstruction. The intergrated sedimentary seguence of channeis wiii be preserved if erosion is weak and form intergrate dis-tributary channeis. When the distributary channeis fiow the siope break zone,the energy of current water in the channeis is abruptiy re-ieased and the sediments carried by them wiii deposit guickiy and form the mouth bars microfacies. The shapes of mouth bars depend on the amounts of sediments carried by underwatter distributary channeis. There may deposit isoiated mouth bars with coarsening-upward succession when underwater distributary channeis carry abundant sediments. Whiie the strength of underwater distributary channeis is weak,the grains of the current water carried are fine ,resuiting in the for-mation of the reiterative mouth bars with uncontinuous coarensing-upward succession.The underwater distributary channeis fiow on the top of the former mouth bars and may erode them. When the mouth bars are cutt partiy,there wiii form a kind of recombination bars due to the distributary channeis eroding the mouth bars.At the same time,another kind of recombination bars caiied the type of distributary channeis covering the mouth bars is aiso discussed in the paper. As the distributary channeis fiow the some sug area where have enough accomdation space to deposit the mouth bars,they couid not cut the former mouth bars,but directiy deposit on the top of them.
A series of gentie siope deitas are deveioped in Yanchang Formation of Shaanxi-Gansu-Ningxia Basin,where deita front is composed of truncated distributary channeis,integrated distributary channeis,isoiated mouth bars,reiterative mouth bars , and recombination bars. There are abundant current structures caused by the tractive current that couid refiect different sedimentary environments. The two underwater distributary channeis have an erosion surface at the bottom of channei. The truncated distributary channeis sandbodies are thick and their iogging curve forms are box-shaped. The integrated distributary channeis are fining upward seguences from sandstones at the base to siitstones and mudstones on the top of channeis. Whiie the river mouth bars are coarsening-upward seguences from mudstones to sand-stones. There are iots of thin mudstones in the middie of reiterative mouth bars sandbodies. The recombination bars con-sist of mouth bars at the bottom and underwater distributary channeis at the top and iarger than 15 m in the thickness. The sedimentary modeis of underwater distributary channeis and the mouth bars are proposed according to the strength of the currents in the distributary channeis and the depth of water in the iake. The siope of the deita front in Huachi area is gentiess,so the underwater distributary channeis are stiii strong after entering iake. In the region of high energy river,the underwater distributary channeis may freguentiy migrate. The un-derwater distributary channeis of next stage may erode the former channeis deposit and may form boxing truncated dis-tributary. With the depth of iake water,the energy of the distributary channeis become weak because of the iake water obstruction. The intergrated sedimentary seguence of channeis wiii be preserved if erosion is weak and form intergrate dis-tributary channeis. When the distributary channeis fiow the siope break zone,the energy of current water in the channeis is abruptiy re-ieased and the sediments carried by them wiii deposit guickiy and form the mouth bars microfacies. The shapes of mouth bars depend on the amounts of sediments carried by underwatter distributary channeis. There may deposit isoiated mouth bars with coarsening-upward succession when underwater distributary channeis carry abundant sediments. Whiie the strength of underwater distributary channeis is weak,the grains of the current water carried are fine ,resuiting in the for-mation of the reiterative mouth bars with uncontinuous coarensing-upward succession.The underwater distributary channeis fiow on the top of the former mouth bars and may erode them. When the mouth bars are cutt partiy,there wiii form a kind of recombination bars due to the distributary channeis eroding the mouth bars.At the same time,another kind of recombination bars caiied the type of distributary channeis covering the mouth bars is aiso discussed in the paper. As the distributary channeis fiow the some sug area where have enough accomdation space to deposit the mouth bars,they couid not cut the former mouth bars,but directiy deposit on the top of them.
2002, 20(4): 595-599.
Abstract:
During the middle or late stage of oil-field development, reservoir geological model based on former minilayer division and sedimentary microfacies couldnot meet the demand of regulation tap the latent power and distribution of remaining oil. Thisdemands minilayer division and further finely divideslithofacies. Lithofacies unit is bed or a single bed, formed during transportation and deposition of sediment, which formed under basically sta-ble medium. It represents the smallest lithology unit composed of sediment with identical component. Bedded plane exists between beds, which represents intermittent plane of transient nondeposition or abrupt sedimentation.Lithofacies unit provides sedimentary foundation and new research way for further subdivision and reservoir anisotropy from static view. This paper proves feasibility of lithofacies unit subdivision by studying recent deposits and discusses the principle of finely divided unit, combining close-spaced well to analyze cyclicity, stability of in-terbed, and propose economic technology and oil-producing technology. At last, the paper provides basical method for finely dividing lithofacies unit.
During the middle or late stage of oil-field development, reservoir geological model based on former minilayer division and sedimentary microfacies couldnot meet the demand of regulation tap the latent power and distribution of remaining oil. Thisdemands minilayer division and further finely divideslithofacies. Lithofacies unit is bed or a single bed, formed during transportation and deposition of sediment, which formed under basically sta-ble medium. It represents the smallest lithology unit composed of sediment with identical component. Bedded plane exists between beds, which represents intermittent plane of transient nondeposition or abrupt sedimentation.Lithofacies unit provides sedimentary foundation and new research way for further subdivision and reservoir anisotropy from static view. This paper proves feasibility of lithofacies unit subdivision by studying recent deposits and discusses the principle of finely divided unit, combining close-spaced well to analyze cyclicity, stability of in-terbed, and propose economic technology and oil-producing technology. At last, the paper provides basical method for finely dividing lithofacies unit.
2002, 20(4): 614-620.
Abstract:
Deeply-buried strata refer to strata buried beneath the depth of 2 500～ 2 700 m. Their porosity and permeability are commonly very low. But under certain conditions, dissolution in depth can create good reservoirs and form diagenetic traps. However, prediction of diagenetic trapshas long been a difficult problem, which is dealt with in this paper. Anpeng Oilfield is located in the southeast part of the Biyang Sag, Henan Province. Explo-ration shows that diagenetic traps exist in the sheet-like sandbodies deposited in a fan-delta of lower Member Ⅲ of Lower Tertiary Hetaoyuan Formation.In this paper, based on quantitative study on diagenesis and diagenetic stage, origin and distribution of diagenetic traps were discussed. The study shows that sandbodies of the studied interval experienced various diagenesis such as compaction, cementation, dissolution, etc. Different diagenesis oc-curs in different depth. Based on this and other data, the diagenetic stage is divided into early diagenetic stage and late diagenetic stage. Early diagenetic stage is further divided into early diagenetic stage A and early diagenetic stage B. Late diagenetic stage is further divided into late diagenetic stage A, late diagenetic stage B, and late dia-genetic stage C, and late diagenetic stage A is further divided into substages A1, A2 and A3. In the study area,deeply buried strata( lower Member III of the Hetaoyuan Formation)are mainly in late diagenetic substage A3 and late diagenetic stage B. Substage A3 ranges in depth from 2 700 to 3 100 m, and characterized by strong cementa-tion. Late diagenetic stage B ranges in depth from 3 100 to 3 900 m, and characterized by development of sec-ondary dissolution pores, especially between 3 200～ 3 600 m. In the study area, sandbodies dip down from north to south. When sandbodies extend from late diagenetic substage A3 to late diagenetic stage B, the part in substage A3 becomes compact due to strong cementation and can seal oil and gas, while the part in stage B may become good reservoirs due to secondary dissolution. In this way, diagenetic traps are formed. Thus according to burial depth,characteristics of development and preservation of pores in different diagenetic stages, diagenetic traps can be pre-dicted.
Deeply-buried strata refer to strata buried beneath the depth of 2 500～ 2 700 m. Their porosity and permeability are commonly very low. But under certain conditions, dissolution in depth can create good reservoirs and form diagenetic traps. However, prediction of diagenetic trapshas long been a difficult problem, which is dealt with in this paper. Anpeng Oilfield is located in the southeast part of the Biyang Sag, Henan Province. Explo-ration shows that diagenetic traps exist in the sheet-like sandbodies deposited in a fan-delta of lower Member Ⅲ of Lower Tertiary Hetaoyuan Formation.In this paper, based on quantitative study on diagenesis and diagenetic stage, origin and distribution of diagenetic traps were discussed. The study shows that sandbodies of the studied interval experienced various diagenesis such as compaction, cementation, dissolution, etc. Different diagenesis oc-curs in different depth. Based on this and other data, the diagenetic stage is divided into early diagenetic stage and late diagenetic stage. Early diagenetic stage is further divided into early diagenetic stage A and early diagenetic stage B. Late diagenetic stage is further divided into late diagenetic stage A, late diagenetic stage B, and late dia-genetic stage C, and late diagenetic stage A is further divided into substages A1, A2 and A3. In the study area,deeply buried strata( lower Member III of the Hetaoyuan Formation)are mainly in late diagenetic substage A3 and late diagenetic stage B. Substage A3 ranges in depth from 2 700 to 3 100 m, and characterized by strong cementa-tion. Late diagenetic stage B ranges in depth from 3 100 to 3 900 m, and characterized by development of sec-ondary dissolution pores, especially between 3 200～ 3 600 m. In the study area, sandbodies dip down from north to south. When sandbodies extend from late diagenetic substage A3 to late diagenetic stage B, the part in substage A3 becomes compact due to strong cementation and can seal oil and gas, while the part in stage B may become good reservoirs due to secondary dissolution. In this way, diagenetic traps are formed. Thus according to burial depth,characteristics of development and preservation of pores in different diagenetic stages, diagenetic traps can be pre-dicted.
2002, 20(4): 628-632.
Abstract:
Laumonti te cement is mainly distributed in the Yanchang 6 reservoir of the no rtheast Ordos basin.Through measuring inclusions in laumontite, we know that its is forming temperature is between 60 ℃and 70 ℃ and it formed in the B period of early diagenetic stage.How ever, in the A period of later diagenetic stage, laumontite were dissolved by organic acid which was generated in decarboxylation of kerogen, and a great quantity of secondary pores were formed.Exploration results have proved that newly found reservoirs are largely dist ributed in the laumontite secondary pore zone.Thus, the formation process and distribution of laumontite cement are very important for exploring reservoirs and hydrocarbon accumulat ion.In the paper, with the investigations of outcrop,thin section, organic inclusion, scanning elect ronmicroscope and elect ron microprobe, the relationship of the forming process, distribution of laumontite cement and sedimentary microfacies is studied on the basis of sedimentary microfacies.The purpose is that laumontite distribution is predicted by sedimentary microfacies.As a result, reservoir distribution is predicted.
Laumonti te cement is mainly distributed in the Yanchang 6 reservoir of the no rtheast Ordos basin.Through measuring inclusions in laumontite, we know that its is forming temperature is between 60 ℃and 70 ℃ and it formed in the B period of early diagenetic stage.How ever, in the A period of later diagenetic stage, laumontite were dissolved by organic acid which was generated in decarboxylation of kerogen, and a great quantity of secondary pores were formed.Exploration results have proved that newly found reservoirs are largely dist ributed in the laumontite secondary pore zone.Thus, the formation process and distribution of laumontite cement are very important for exploring reservoirs and hydrocarbon accumulat ion.In the paper, with the investigations of outcrop,thin section, organic inclusion, scanning elect ronmicroscope and elect ron microprobe, the relationship of the forming process, distribution of laumontite cement and sedimentary microfacies is studied on the basis of sedimentary microfacies.The purpose is that laumontite distribution is predicted by sedimentary microfacies.As a result, reservoir distribution is predicted.
2002, 20(4): 639-643.
Abstract:
The study on the pore texture of clastic reservoirs is one of the most important work in the oil and gasexploration and development.The particularity of the distribution of secondary pore makes the study more difficult.Through analy zing the clastic reservoirs' pore ty pes, pore combinations and pore textures of upper Paleozoic in northwest Ordos Basin, the authors analy zed the pore's distribution and genesis.Finally, the authors indicate that the predominant pore type is secondary pore.Undoubtedly, all of these will be important to the gas exploration and development in this area.
The study on the pore texture of clastic reservoirs is one of the most important work in the oil and gasexploration and development.The particularity of the distribution of secondary pore makes the study more difficult.Through analy zing the clastic reservoirs' pore ty pes, pore combinations and pore textures of upper Paleozoic in northwest Ordos Basin, the authors analy zed the pore's distribution and genesis.Finally, the authors indicate that the predominant pore type is secondary pore.Undoubtedly, all of these will be important to the gas exploration and development in this area.
2002, 20(4): 650-655.
Abstract:
The lower reaches of Yellow River isfrozen in winter, asa result, a lot of frozen cracks are developed. They are noticeable with unusual appearances. All the frozen cracks may be broadly divisible into eight types according to their shapes including fissure-like,pod -like, linear, triple-junction -like, sawtooth-like, netty, spiral and branched.The fissure-like crack hassimplest shape. It is a straight, narrow, short fissure in plane and is a slaty sheet in space. The length is mostly below ten centimeters, and the width is not beyond one centimeter, and the depth is also mostly below ten centimeters. The both ends of the crack is sharp and flat, and the widdle is relatively wide and in relief.The cross section is like “v”. The length is several centimeters to more than ten centimeters, and the width is one to two centimeters and the depth is one to three centimeters. The straight linear frozen crack has a relatively simple shape and but the sizes are variable. The smaller one is decades of centimeters in length and several centimeters in width and in depth. The length of larger ones is in the range of from decades of meters to more than one handred of meters, and the width and depthe are all below ten centimeters. Commonly, they extend along the river course. The triple-junction -frozen-cracks are rather similar to triple junction rifts, but their sizes are considereblely small. In fact, they are an assamblage frozen cracks,being consisted of three single frozen cracks with an interangle of about 120°.The compound ones mean that large net contains small net and the simple type has only one rank. This netty frozen crack that consists of a series of straight linear frozen cracks is relatively complex. The sawtooth-like frozen cracks is actually an assemblage type that is made up of a series of short, linear frozen cracks with an interangle of about 120°. Also,their sizes are small and their length range mostly from ten to thirty centimeters and their width are not beyond one centimeter. The netty frozen crack is a rather complicated type. That consists of straight linear and curved frozen cracks. It may be divided into two types: Compound type and simple type. It may be divided into two to three ranks. The single frozen crack is straight linear or slightly curved and its length is several centimeter to decades of centimeters and its width is several millimeter. Also, the spiral frozen crack is an assemblage type, but their patterns are considerably unusual and single frozen crack has spiral form and several frozen cracks assemble to form flower-like pattern. The single frozen crack is in the range of five to forty centimeters in length and several millimeters in width. The branched frozen crack is rather complex in form and, also, is an assemblage type. Genenally, the size is small and the length is mostly in the range of ten to twenty centimeters and the width is below one centimeter. The last two type genenally develop in thin mud layer and the other generally develop in silt layer. Another frozen crack( frozen parting)is also considerably noticeable. The formation of frozen cracks,undoubtedly,is related to ice action and the interaction of ice melting and ice wedging is their concrete dynamatic process.
The lower reaches of Yellow River isfrozen in winter, asa result, a lot of frozen cracks are developed. They are noticeable with unusual appearances. All the frozen cracks may be broadly divisible into eight types according to their shapes including fissure-like,pod -like, linear, triple-junction -like, sawtooth-like, netty, spiral and branched.The fissure-like crack hassimplest shape. It is a straight, narrow, short fissure in plane and is a slaty sheet in space. The length is mostly below ten centimeters, and the width is not beyond one centimeter, and the depth is also mostly below ten centimeters. The both ends of the crack is sharp and flat, and the widdle is relatively wide and in relief.The cross section is like “v”. The length is several centimeters to more than ten centimeters, and the width is one to two centimeters and the depth is one to three centimeters. The straight linear frozen crack has a relatively simple shape and but the sizes are variable. The smaller one is decades of centimeters in length and several centimeters in width and in depth. The length of larger ones is in the range of from decades of meters to more than one handred of meters, and the width and depthe are all below ten centimeters. Commonly, they extend along the river course. The triple-junction -frozen-cracks are rather similar to triple junction rifts, but their sizes are considereblely small. In fact, they are an assamblage frozen cracks,being consisted of three single frozen cracks with an interangle of about 120°.The compound ones mean that large net contains small net and the simple type has only one rank. This netty frozen crack that consists of a series of straight linear frozen cracks is relatively complex. The sawtooth-like frozen cracks is actually an assemblage type that is made up of a series of short, linear frozen cracks with an interangle of about 120°. Also,their sizes are small and their length range mostly from ten to thirty centimeters and their width are not beyond one centimeter. The netty frozen crack is a rather complicated type. That consists of straight linear and curved frozen cracks. It may be divided into two types: Compound type and simple type. It may be divided into two to three ranks. The single frozen crack is straight linear or slightly curved and its length is several centimeter to decades of centimeters and its width is several millimeter. Also, the spiral frozen crack is an assemblage type, but their patterns are considerably unusual and single frozen crack has spiral form and several frozen cracks assemble to form flower-like pattern. The single frozen crack is in the range of five to forty centimeters in length and several millimeters in width. The branched frozen crack is rather complex in form and, also, is an assemblage type. Genenally, the size is small and the length is mostly in the range of ten to twenty centimeters and the width is below one centimeter. The last two type genenally develop in thin mud layer and the other generally develop in silt layer. Another frozen crack( frozen parting)is also considerably noticeable. The formation of frozen cracks,undoubtedly,is related to ice action and the interaction of ice melting and ice wedging is their concrete dynamatic process.
2002, 20(4): 663-667.
Abstract:
A 2-D ho rizontal numerical model is used to simulate maximum and mean tidally-induce near-bed shear stresses and the corresponding mobile layer thicknesses in the Bohai Strai t region.At the same t ime, the cri tical near-bed shear st ress was calculated using the g rain size parameters.An analysis of the results show s that :(1)the seabed sediment types are related to the dif ference between the t idally-induced shear stress and the cri tical shear stress (a larger difference is associated w ith a coarser bed material);(2)in some places (e.g.the northeastern part of the Strait and the near-sho re areas of the northern Shandong Peninsula)the tidally-induced shear st ress is smaller than the critical shear st ress, but the seabed sediment is relatively coarse, indicating that the sediment may represent relict materials (this hypothesis should be tested by the result s f rom future investig at ions into the Holocene sea level changes, paleo-hydrody namic conditions and the evolution of the sedimentary environment);and (3)a good correlation betw een the mobile layer thickness and the sediment type exists, i.e., a large mobile layer thickness is associated with relatively coarse sediments, and a small thickness is associated with fine-grained sediments.
A 2-D ho rizontal numerical model is used to simulate maximum and mean tidally-induce near-bed shear stresses and the corresponding mobile layer thicknesses in the Bohai Strai t region.At the same t ime, the cri tical near-bed shear st ress was calculated using the g rain size parameters.An analysis of the results show s that :(1)the seabed sediment types are related to the dif ference between the t idally-induced shear stress and the cri tical shear stress (a larger difference is associated w ith a coarser bed material);(2)in some places (e.g.the northeastern part of the Strait and the near-sho re areas of the northern Shandong Peninsula)the tidally-induced shear st ress is smaller than the critical shear st ress, but the seabed sediment is relatively coarse, indicating that the sediment may represent relict materials (this hypothesis should be tested by the result s f rom future investig at ions into the Holocene sea level changes, paleo-hydrody namic conditions and the evolution of the sedimentary environment);and (3)a good correlation betw een the mobile layer thickness and the sediment type exists, i.e., a large mobile layer thickness is associated with relatively coarse sediments, and a small thickness is associated with fine-grained sediments.
2002, 20(4): 675-679.
Abstract:
The different grain size content range from 0. 2～ 500 μ m and magnetic susceptiblity were measured to study the correlation between grain size and magnetic susceptibilty, selected more 800 samples, in Lacustrine sedi-ments from Nihewan Bain. The correlation coefficient of susceptibility with the content of 0. 2～ 35 μ m, especially 0.2～ 7.5 μ m, is positive, and with the content of 35～ 500 μ m is negative. This correlation is contrast to the loess deposits on top of profile, which shows the mechanism of magnetic response towardspaleoclimate changes in lacus-trine sediments is unlike that in loess. So, we can conclude that the susceptibility change in lake ( the sedimentsare mainly allogenic)sediments is controlled by the allogenic magnetic minerals. The fluctuations of susceptibilty indi-cate the changes of the lake level and paleoclimate.
The different grain size content range from 0. 2～ 500 μ m and magnetic susceptiblity were measured to study the correlation between grain size and magnetic susceptibilty, selected more 800 samples, in Lacustrine sedi-ments from Nihewan Bain. The correlation coefficient of susceptibility with the content of 0. 2～ 35 μ m, especially 0.2～ 7.5 μ m, is positive, and with the content of 35～ 500 μ m is negative. This correlation is contrast to the loess deposits on top of profile, which shows the mechanism of magnetic response towardspaleoclimate changes in lacus-trine sediments is unlike that in loess. So, we can conclude that the susceptibility change in lake ( the sedimentsare mainly allogenic)sediments is controlled by the allogenic magnetic minerals. The fluctuations of susceptibilty indi-cate the changes of the lake level and paleoclimate.
2002, 20(4): 687-694.
Abstract:
The source rocks in the Jurassic sequence stratigraphic frameworks of the Junggar basin were evaluated in detailin thispa -per. The results showed that the most Jurassic samples belong to poor -medium source rocks, and the hydrocarbon generation conditions of Badaowan Formation are better than those of Sangonghe Formation. In a sequence, the organic carbon abundance of condensed section is obviously higher than those of lacustrine transgressive system tract interval and high stand system tract interval, i. e., the condensed section is more favorable for hydrocarbon generation.The kerogen of Jurassic is mainly of type Ⅲ and Ⅱ 2, with small amount of Ⅱ 1.The Jurassic was not deposited in a typical coal -forming marsh environment, but mainly in fresh-water lacustrine shore -shallow lacus-trine -semi-deep lacustrine -deep lacustrine ones, with weakly reducing -strongly oxidizing geochemical conditions and evident pristane pre -dominance.The thermal maturity of the Jurassic is low and a little different in different areas, and most samples are at lower -mature stage presently (R o =0. 50%～ 0. 80%), indicating that there is no large amount of normal liquid hydrocarbon generated from the Jurassic in the Basin.It is more realistic to seek for immature to lower -mature oil and gas generated from the Jurassic in the Basin.
The source rocks in the Jurassic sequence stratigraphic frameworks of the Junggar basin were evaluated in detailin thispa -per. The results showed that the most Jurassic samples belong to poor -medium source rocks, and the hydrocarbon generation conditions of Badaowan Formation are better than those of Sangonghe Formation. In a sequence, the organic carbon abundance of condensed section is obviously higher than those of lacustrine transgressive system tract interval and high stand system tract interval, i. e., the condensed section is more favorable for hydrocarbon generation.The kerogen of Jurassic is mainly of type Ⅲ and Ⅱ 2, with small amount of Ⅱ 1.The Jurassic was not deposited in a typical coal -forming marsh environment, but mainly in fresh-water lacustrine shore -shallow lacus-trine -semi-deep lacustrine -deep lacustrine ones, with weakly reducing -strongly oxidizing geochemical conditions and evident pristane pre -dominance.The thermal maturity of the Jurassic is low and a little different in different areas, and most samples are at lower -mature stage presently (R o =0. 50%～ 0. 80%), indicating that there is no large amount of normal liquid hydrocarbon generated from the Jurassic in the Basin.It is more realistic to seek for immature to lower -mature oil and gas generated from the Jurassic in the Basin.
2002, 20(4): 705-709.
Abstract:
The chemical composition and carbon isotope of the six water-dissolved gas samples in the Turpan- Ha-mi basin are measured and the characteristic of formation mechanism and the possibility of application of the com-position and isotope to natural gas geology are discussed by comparison with the natural gas in the basin. The char-acteristic of the composition of the water-dissolved gas hydrocarbons is mainly controlled by dissolution degree of the hydrocarbons. They are derived from the same source rocks as the natural gases, but they are different from the natural gases, e. g., the C 1/C 1 ～ 5 of the water-dissolved gas should be higher than that of the natural gas, but in fact it is lower; the homologue of the water-dissolved gas CH 4 is enriched in13C than that of the natural gas. the above characteristic was thought to be related with that the dissolved content of the natural gases in the dis-solved-water was less than the migrated content. It is considered that the differences of the composition and isotope between the water-dissolved gas and the natural gasindicate the relation of between the sampling membersand nat-ural gas dynamics pool-forming system.
The chemical composition and carbon isotope of the six water-dissolved gas samples in the Turpan- Ha-mi basin are measured and the characteristic of formation mechanism and the possibility of application of the com-position and isotope to natural gas geology are discussed by comparison with the natural gas in the basin. The char-acteristic of the composition of the water-dissolved gas hydrocarbons is mainly controlled by dissolution degree of the hydrocarbons. They are derived from the same source rocks as the natural gases, but they are different from the natural gases, e. g., the C 1/C 1 ～ 5 of the water-dissolved gas should be higher than that of the natural gas, but in fact it is lower; the homologue of the water-dissolved gas CH 4 is enriched in13C than that of the natural gas. the above characteristic was thought to be related with that the dissolved content of the natural gases in the dis-solved-water was less than the migrated content. It is considered that the differences of the composition and isotope between the water-dissolved gas and the natural gasindicate the relation of between the sampling membersand nat-ural gas dynamics pool-forming system.
2002, 20(4): 721-726.
Abstract:
Fourier transformation infrared microspectroscopy ( Micro-FTIR)isone of effective waysfor identify-ing the chemical structure. Based on the high-purity coal macerals separating and concentrating,in this paper, Mi-cro-FT IR technique was used to investigate the chemical composition and structuresof alginite, sporinite, cutinite,desmocollinite and fusinite from Jurassic coalsin Tu -ha basin. The results show that the chemical structure of aligi-nite and sporinite are mainly composed of long aliphatic -side chain, and minor amounts of aromatic compounds. Cutinite and desmocollinite are mostly composed of aromatic compounds,in addition to large amount of aliphatic compounds. Whereas fusinite are dominant by aromatic structure. These indicate that aliginite and sporinite are one of the best oil source-rocks, with the highest hydrocarbon generation potential; cutinite and desmocollinite are also the better oil and gas source-rocks, and have higher hydrocarbon generating potential; fusinite has little hydro-carbon-generating potential. Desmocollinite is one of the most amount of macerals in Jurassic coals in Tu-ha basin,so it is one of the most important macerals for contribution to oil from coals in Tu-ha basin.
Fourier transformation infrared microspectroscopy ( Micro-FTIR)isone of effective waysfor identify-ing the chemical structure. Based on the high-purity coal macerals separating and concentrating,in this paper, Mi-cro-FT IR technique was used to investigate the chemical composition and structuresof alginite, sporinite, cutinite,desmocollinite and fusinite from Jurassic coalsin Tu -ha basin. The results show that the chemical structure of aligi-nite and sporinite are mainly composed of long aliphatic -side chain, and minor amounts of aromatic compounds. Cutinite and desmocollinite are mostly composed of aromatic compounds,in addition to large amount of aliphatic compounds. Whereas fusinite are dominant by aromatic structure. These indicate that aliginite and sporinite are one of the best oil source-rocks, with the highest hydrocarbon generation potential; cutinite and desmocollinite are also the better oil and gas source-rocks, and have higher hydrocarbon generating potential; fusinite has little hydro-carbon-generating potential. Desmocollinite is one of the most amount of macerals in Jurassic coals in Tu-ha basin,so it is one of the most important macerals for contribution to oil from coals in Tu-ha basin.
2002, 20(4): 537-544.
Abstract:
The Carboniferous system exposed from Anhui and Jiangsu provinces,has seven Iithogenetic units. Based on outcrop seguence stratigraphic anaIysis with particuIar attention to the key surfaces or poIyphase paIeokarsts deveIoped in the interruptions of sedimentation,nine types of Iithofacies, twenty types of microfacies and eIeven third-order seguences in the Carboniferous system are recognized. The Iower series of Carboniferous strata have six seguences,and the upper series have five. In the Iower series of Carboniferous strata,Yanguan stage are composed of seguence 1 to 2,and Datang stage from seguence 3 to 6.In the up-per series, Weining stage are composed of seguence 7 to 8, and Maping stage from seguence 9 to 11.According to the fea- tures of the bottom boundary surface,eIeven third - order seguences are cIassified into two sorts of seguence , which are type Ⅰseguence and type ". The bottom boundary surface of type ! seguence aII have cIear signs incIuding the differ-ent thickness eIuviums,the strong paIeokarst,the strata discontinutity,the immense changes of sedimentary patterns and traits,the huge and sudden aIternation of carbon and oxygen isotope vaIues and the disappearence and abrupt changes of organism evoIution. The third-order seguences of S2,S3,S5,S6,S7 and S11 beIong to I-type of sedimentary seguence,and S1,S4,S8,S9 and S10 Ⅱ -type. The third-order seguences are absent at times. The characteristics and genesis of each third-order seguences are described and discussed. The third-order se-guences in various paIeogeographic units and sedimentary environment can be correIated. Sea IeveI change rate and am-pIitude corresponding to these third-order seguences are discussed and highstand systems tracts iike Vaii' s marine seguence modei. Because of the difference of basin texture,fauit activity and materiai suppiy,the main controiied factors of seguence styie were different in steep siope,deep-water area and gen-tie siope. The major controiied factor of seguence styie on steep siope was fauit activity and materiai suppiy,and the nearshore subagueous fan was main sedimentary type；the factor controiied seguence styie in deep water area was reiative change of iake ievei,the sedimentary facies was characteristic of shaiiow-deep iake；the factor controiied seguence styie on gentie siope was reiative change of iake ievei and materiai suppiy,fan-deita or river-dominated deita was major sedi-mentary type. Therefore,the seguence modeis were estabiished separateiy on steep siope,deep-water area and gentie siope. A seguence was made up of iowstand,transgressive and highstand systems tracts with topographic break on gentie siope of Luxi depression. Lastiy,authors anaiyzed the condition of hydrocarbon accumuiation in different seguence frame-work,and pointed out that the iowstand and highstand systems tracts of seguence ! were rich in hydrocarbon resource,and were the main section for finding new hidden traps.
The Carboniferous system exposed from Anhui and Jiangsu provinces,has seven Iithogenetic units. Based on outcrop seguence stratigraphic anaIysis with particuIar attention to the key surfaces or poIyphase paIeokarsts deveIoped in the interruptions of sedimentation,nine types of Iithofacies, twenty types of microfacies and eIeven third-order seguences in the Carboniferous system are recognized. The Iower series of Carboniferous strata have six seguences,and the upper series have five. In the Iower series of Carboniferous strata,Yanguan stage are composed of seguence 1 to 2,and Datang stage from seguence 3 to 6.In the up-per series, Weining stage are composed of seguence 7 to 8, and Maping stage from seguence 9 to 11.According to the fea- tures of the bottom boundary surface,eIeven third - order seguences are cIassified into two sorts of seguence , which are type Ⅰseguence and type ". The bottom boundary surface of type ! seguence aII have cIear signs incIuding the differ-ent thickness eIuviums,the strong paIeokarst,the strata discontinutity,the immense changes of sedimentary patterns and traits,the huge and sudden aIternation of carbon and oxygen isotope vaIues and the disappearence and abrupt changes of organism evoIution. The third-order seguences of S2,S3,S5,S6,S7 and S11 beIong to I-type of sedimentary seguence,and S1,S4,S8,S9 and S10 Ⅱ -type. The third-order seguences are absent at times. The characteristics and genesis of each third-order seguences are described and discussed. The third-order se-guences in various paIeogeographic units and sedimentary environment can be correIated. Sea IeveI change rate and am-pIitude corresponding to these third-order seguences are discussed and highstand systems tracts iike Vaii' s marine seguence modei. Because of the difference of basin texture,fauit activity and materiai suppiy,the main controiied factors of seguence styie were different in steep siope,deep-water area and gen-tie siope. The major controiied factor of seguence styie on steep siope was fauit activity and materiai suppiy,and the nearshore subagueous fan was main sedimentary type；the factor controiied seguence styie in deep water area was reiative change of iake ievei,the sedimentary facies was characteristic of shaiiow-deep iake；the factor controiied seguence styie on gentie siope was reiative change of iake ievei and materiai suppiy,fan-deita or river-dominated deita was major sedi-mentary type. Therefore,the seguence modeis were estabiished separateiy on steep siope,deep-water area and gentie siope. A seguence was made up of iowstand,transgressive and highstand systems tracts with topographic break on gentie siope of Luxi depression. Lastiy,authors anaiyzed the condition of hydrocarbon accumuiation in different seguence frame-work,and pointed out that the iowstand and highstand systems tracts of seguence ! were rich in hydrocarbon resource,and were the main section for finding new hidden traps.
2002, 20(4): 552-559.
Abstract:
Sediments in basins couId record the ascending and descending difference of the earth crust. The sediments of the Late Cenozoic in the Jiuxi basin,Iocated in the northern margin of the Tibetan pIateau,have sensitiveIy and com-pIeteIy recorded the upIifting process of northern pIateau. The heavy mineraIs of sediments have the reguIatory variety in the Laojunmiao section of Jiuxi basin since 13 MaBP；detaiIed study of the heavy mineraI has reveaIed four heavy mineraI stages of sedimentary evoIution. they are： ①stabIe heavy mineraI associations before 12.18 Ma BP, ②reIativeIy stabIe heavy mineraI associations between 12.18 and 8.26 Ma BP, ③ unstabIe heavy mineraI associations between 8.26 and 4. 9 Ma BP,and ④ the very unstabIe heavy mineraI associations since 3.66 Ma BP. The associated mountain erosion and u-pIift are suggested having experienced three phases on the upIifting process of the northern Tibetan PIateau,that is,tec-tonic stabIe （13 ~ 8.26 Ma BP） ,graduaI staggered upIift （8.26 ~ < 4.96 Ma BP） ,and rapid intense intermittent mass upIift（ > 3.66 ~ 0 Ma BP）.
Sediments in basins couId record the ascending and descending difference of the earth crust. The sediments of the Late Cenozoic in the Jiuxi basin,Iocated in the northern margin of the Tibetan pIateau,have sensitiveIy and com-pIeteIy recorded the upIifting process of northern pIateau. The heavy mineraIs of sediments have the reguIatory variety in the Laojunmiao section of Jiuxi basin since 13 MaBP；detaiIed study of the heavy mineraI has reveaIed four heavy mineraI stages of sedimentary evoIution. they are： ①stabIe heavy mineraI associations before 12.18 Ma BP, ②reIativeIy stabIe heavy mineraI associations between 12.18 and 8.26 Ma BP, ③ unstabIe heavy mineraI associations between 8.26 and 4. 9 Ma BP,and ④ the very unstabIe heavy mineraI associations since 3.66 Ma BP. The associated mountain erosion and u-pIift are suggested having experienced three phases on the upIifting process of the northern Tibetan PIateau,that is,tec-tonic stabIe （13 ~ 8.26 Ma BP） ,graduaI staggered upIift （8.26 ~ < 4.96 Ma BP） ,and rapid intense intermittent mass upIift（ > 3.66 ~ 0 Ma BP）.
2002, 20(4): 568-573.
Abstract:
In Gansu province, Jiuxi Cretaceous Basin is a monotype basin,in which grows sedimentary system of fan-shaped aIIuviaI fan deIta,subgravity fIow,Iacustrine and fIuviaI facies. It was made up of some patterns combined by sedimentary system of fan-shaped aIIuvium-fan deIta-shaIIow Iakeshore-graveIIy braided stream,subgravity fIow-mid-deep Iacustrine fan deIta and fan deIta-mid-shaIIow fIuviaI facies. According to isochronic surface,fiIIed seguences in Iacus- trine basin can be divided into three tectonic seguences corresponding respectiveIy to three evoIutionary stages of embryon-ic rift,spread rift-thermaI attenuationary subsidence and basin shrinkage cIosure. On the basis of these evidences,it can be seen that either formation and attenuation of mantIe' s thermaI coIumn or remote stress , such as Yanshan movement,etc., controIIed the evoIution of the Jiuxi Cretaceous Basin.
In Gansu province, Jiuxi Cretaceous Basin is a monotype basin,in which grows sedimentary system of fan-shaped aIIuviaI fan deIta,subgravity fIow,Iacustrine and fIuviaI facies. It was made up of some patterns combined by sedimentary system of fan-shaped aIIuvium-fan deIta-shaIIow Iakeshore-graveIIy braided stream,subgravity fIow-mid-deep Iacustrine fan deIta and fan deIta-mid-shaIIow fIuviaI facies. According to isochronic surface,fiIIed seguences in Iacus- trine basin can be divided into three tectonic seguences corresponding respectiveIy to three evoIutionary stages of embryon-ic rift,spread rift-thermaI attenuationary subsidence and basin shrinkage cIosure. On the basis of these evidences,it can be seen that either formation and attenuation of mantIe' s thermaI coIumn or remote stress , such as Yanshan movement,etc., controIIed the evoIution of the Jiuxi Cretaceous Basin.
2002, 20(4): 588-594.
Abstract:
The sedimentary facies of Neogene in Bohai sea area used to be considered as fIuviaI facies over a Iong time because of the Iimitation of the expIoration degree. Therefore,the risks of the seaI rock in the Neogene expIoration were beIieved to be great. The standpoint has restrained the Neogene expIoration in Bohai sea area. With the increasing of the expIoration degree,it is recognized that Bozhong depression of Bohai sea area is one of the main catchment area for Bohai bay basin in Neogene. The Iacustrine and deItaic depositionaI systems were discovered in Neogene in Bozhong depression in the recent years. This paper focuses on eIaborating the evidences of the existence of the Iacustrine and deItaic depositionaI systems and the characteristic of the deIta depositionaI system（incIuding normaI Iacustrine deIta and braided deIta）.The discovery of Iacustrine and deItaic depositionaI systems in Bozhong depression have a very important significance in the oiI and gas expIoration. The deveIopment area of the deItaic systems wiII be the major fieId of the expIoration in Bohai sea area in the future.
The sedimentary facies of Neogene in Bohai sea area used to be considered as fIuviaI facies over a Iong time because of the Iimitation of the expIoration degree. Therefore,the risks of the seaI rock in the Neogene expIoration were beIieved to be great. The standpoint has restrained the Neogene expIoration in Bohai sea area. With the increasing of the expIoration degree,it is recognized that Bozhong depression of Bohai sea area is one of the main catchment area for Bohai bay basin in Neogene. The Iacustrine and deItaic depositionaI systems were discovered in Neogene in Bozhong depression in the recent years. This paper focuses on eIaborating the evidences of the existence of the Iacustrine and deItaic depositionaI systems and the characteristic of the deIta depositionaI system（incIuding normaI Iacustrine deIta and braided deIta）.The discovery of Iacustrine and deItaic depositionaI systems in Bozhong depression have a very important significance in the oiI and gas expIoration. The deveIopment area of the deItaic systems wiII be the major fieId of the expIoration in Bohai sea area in the future.
2002, 20(4): 608-613.
Abstract:
The sequence stratigraphy feature of intersalt sediments is the special rock in Qianjiang saline lake basin, which isn' t simple sediments and has major changes in component and texture with basin area and geologic age. It is very difficult to name it on the basis of their petroleum characteristic. This paper discusses its compo-nent, petrology characteristic and petroleum geologic significance.Its rhythmics on petrochemical element and grain component has an important significance in lake-level relative change. So the comparison and study of the in tersalt nonsandstone rhythm and sequence stratigraphic units was done.By the way, the intersalt nonsandstone is a very eminent assemblage of hydrocarbon reservoir and source rocks, which is a potential good reservoir because of its more secondary porosity. Recently, a very good commercial well was drilled in the rock. sequence.
The sequence stratigraphy feature of intersalt sediments is the special rock in Qianjiang saline lake basin, which isn' t simple sediments and has major changes in component and texture with basin area and geologic age. It is very difficult to name it on the basis of their petroleum characteristic. This paper discusses its compo-nent, petrology characteristic and petroleum geologic significance.Its rhythmics on petrochemical element and grain component has an important significance in lake-level relative change. So the comparison and study of the in tersalt nonsandstone rhythm and sequence stratigraphic units was done.By the way, the intersalt nonsandstone is a very eminent assemblage of hydrocarbon reservoir and source rocks, which is a potential good reservoir because of its more secondary porosity. Recently, a very good commercial well was drilled in the rock. sequence.
2002, 20(4): 621-627.
Abstract:
As one of the most stable petrogenetic minerals in clastic reservoir, quartz isgenerally considered to be indissoluble to directly form secondary porosity during diagenesis, and the dissolved rim of quartz in reservoir has been thought to be the result of dissolution of cements that substituted quartz formerly. In this study, quartz was found to have been dissolved directly in the reservoir of Hetaoyuan formation in Biyang depression, and form a new genetic type of porosity, i. e. quartz dissolution porosity, which is one of the most important porosity types in reservoir in the studied area. The dissolution of quartz reaches 2%～ 7%, and sometimes up to more than 8 %of microscopic porosity in the reservoir rock,, which accounts for 10%～ 35 %of total porosity.Several lines of microscopic evidence for quartz dissolution are listed as follows:( 1)Partial dissolution of clastic quartz. Quartz was dissolved partially to form irregularly rim, isolated grains, intercrystalline pores, sometimes quartz grains can be dissolved partly, and even completely, and result in the for-mation of stretched pores. ( 2)Dissolution of quartz develops along contact seam, the opening of contact seams can form irregular pore throat, which couldnot be the result of dissolution of quartz substituting cements. ( 3)Partial dissolution of quartzose detritus, the erosion of the detritusis obvious, and sometimesit can form honeycombed mi-cropores. ( 4)Shape of carbonate components, both carbonate cements and debritus do not show much dissolution in reservoir rocks of the studied area, however, adjacent quartz grains were dissolved obviously, this further reveals that quartz was dissolved directly.Quartz dissolution in the studied area is the result of sedimentary environment, diagenesis, and evolution of formation water. Biyang depression was an arid to semi-arid subtropical enclosed fault-trough lake during deposi-tion, and the depositional environment of which was an alkaline lake. The original formation water of the reservoir was alkaline to strong alkaline. As a result, together with the influence of alkaline strata, formation water remains its alkalinity mostly during the stages of burial diagenesis. Under such environment, quartz was unstable and easily dissolved. However, early diagenetic stage B is the most important formation period of quartz dissolution and such genetic type of porosity.The existence of aboundant quartz dissolution pores provides new possibility for the interpretation of quartz dissolution itself, SiO 2 cement, secondary porosity formation, as well as for reservoir prediction and evaluation in clastic reservoir.
As one of the most stable petrogenetic minerals in clastic reservoir, quartz isgenerally considered to be indissoluble to directly form secondary porosity during diagenesis, and the dissolved rim of quartz in reservoir has been thought to be the result of dissolution of cements that substituted quartz formerly. In this study, quartz was found to have been dissolved directly in the reservoir of Hetaoyuan formation in Biyang depression, and form a new genetic type of porosity, i. e. quartz dissolution porosity, which is one of the most important porosity types in reservoir in the studied area. The dissolution of quartz reaches 2%～ 7%, and sometimes up to more than 8 %of microscopic porosity in the reservoir rock,, which accounts for 10%～ 35 %of total porosity.Several lines of microscopic evidence for quartz dissolution are listed as follows:( 1)Partial dissolution of clastic quartz. Quartz was dissolved partially to form irregularly rim, isolated grains, intercrystalline pores, sometimes quartz grains can be dissolved partly, and even completely, and result in the for-mation of stretched pores. ( 2)Dissolution of quartz develops along contact seam, the opening of contact seams can form irregular pore throat, which couldnot be the result of dissolution of quartz substituting cements. ( 3)Partial dissolution of quartzose detritus, the erosion of the detritusis obvious, and sometimesit can form honeycombed mi-cropores. ( 4)Shape of carbonate components, both carbonate cements and debritus do not show much dissolution in reservoir rocks of the studied area, however, adjacent quartz grains were dissolved obviously, this further reveals that quartz was dissolved directly.Quartz dissolution in the studied area is the result of sedimentary environment, diagenesis, and evolution of formation water. Biyang depression was an arid to semi-arid subtropical enclosed fault-trough lake during deposi-tion, and the depositional environment of which was an alkaline lake. The original formation water of the reservoir was alkaline to strong alkaline. As a result, together with the influence of alkaline strata, formation water remains its alkalinity mostly during the stages of burial diagenesis. Under such environment, quartz was unstable and easily dissolved. However, early diagenetic stage B is the most important formation period of quartz dissolution and such genetic type of porosity.The existence of aboundant quartz dissolution pores provides new possibility for the interpretation of quartz dissolution itself, SiO 2 cement, secondary porosity formation, as well as for reservoir prediction and evaluation in clastic reservoir.
2002, 20(4): 633-637.
Abstract:
The thick carbonate was deposited on the foreland of western Kunrin mountain in northwest margin of Tarim basin in Yigeziya Formation of the upper Cretaceous. The distribution of carbonate is from Kashi in the west to Keliyang of Yecheng county in the east. The bioclast limestone is one of the most important lithofacies of eight lithofacies. Oosparite and bioclast sparite are the main compositions of carbonate. The main sedimentary facies are carbonate plateform edge,open carbonate platform and limited carbonate platform. From the west to the east,the evolution of sedimentary environment is from carbonate plateform edge,open carbonate platform to limited car-bonate platform. From the west to the east, the thickness of Yigeziya Formation changes from 125 meters to 20 me-ters. Seven meter scale sychles were recognized in thick carbonate deposition. They are new sequence of oil and gas survey in Cretaceous in Tarim basin. The rich fossils of oyster mactra and spiral shell, carbonate plateform and reef shore show that the north-western Tarim basin was sea with the mouth open to the northwest,and the palaeocli-mate was warm, the palaeosalinity was salt to semisalt. The palaeosea graphic shape was long narrow band from Tajike in the west to Keliyang of Yecheng county in the east.
The thick carbonate was deposited on the foreland of western Kunrin mountain in northwest margin of Tarim basin in Yigeziya Formation of the upper Cretaceous. The distribution of carbonate is from Kashi in the west to Keliyang of Yecheng county in the east. The bioclast limestone is one of the most important lithofacies of eight lithofacies. Oosparite and bioclast sparite are the main compositions of carbonate. The main sedimentary facies are carbonate plateform edge,open carbonate platform and limited carbonate platform. From the west to the east,the evolution of sedimentary environment is from carbonate plateform edge,open carbonate platform to limited car-bonate platform. From the west to the east, the thickness of Yigeziya Formation changes from 125 meters to 20 me-ters. Seven meter scale sychles were recognized in thick carbonate deposition. They are new sequence of oil and gas survey in Cretaceous in Tarim basin. The rich fossils of oyster mactra and spiral shell, carbonate plateform and reef shore show that the north-western Tarim basin was sea with the mouth open to the northwest,and the palaeocli-mate was warm, the palaeosalinity was salt to semisalt. The palaeosea graphic shape was long narrow band from Tajike in the west to Keliyang of Yecheng county in the east.
2002, 20(4): 644-649.
Abstract:
The discovery of the mature crude oil of low-sulfur and high quality show s prospecting value for oil-gas in Chagan Depression.The clastic rock reservoirs are characterized by low maturities of composition and texture,high contents of rock debris and filling materials, multi-composition of filling materials and multi-ty pe cementation.The selective solution of carbonate cement and the deceleration of layered volcanic rock for the compaction in clastic rock resulted in the development of secondary po res in low-porosi ty and permeability clastic rock.The dist ribution of oil layers in the reservoirs is controlled by the adv antageous sand-body dist ribution in the favorable sedimentary facies zones, the sections where secondary po re developed and the structural type.
The discovery of the mature crude oil of low-sulfur and high quality show s prospecting value for oil-gas in Chagan Depression.The clastic rock reservoirs are characterized by low maturities of composition and texture,high contents of rock debris and filling materials, multi-composition of filling materials and multi-ty pe cementation.The selective solution of carbonate cement and the deceleration of layered volcanic rock for the compaction in clastic rock resulted in the development of secondary po res in low-porosi ty and permeability clastic rock.The dist ribution of oil layers in the reservoirs is controlled by the adv antageous sand-body dist ribution in the favorable sedimentary facies zones, the sections where secondary po re developed and the structural type.
2002, 20(4): 656-662.
Abstract:
The characteristics of grain size parameters of modern coastal aeolian sands are the basic problems of coastal aeolian sand research. This paper, taking the temperate coastal zone in China as an example, makes use of the grain size parameter such as component of grain size, mean size, standard deviation, skewnss and kurtosis to study the characteristics of grain size parameters of modern coastal aeolian sands on the basis of data of 136 grain size samples. The research results can be concluded that the modern coastal aeolian sands in the temperate coastal zone in China are not all composed of fine sands with high sorting degree which were thought as before. Most are positively skewed. The parameters of grain size clearly change in different coastal zones and change with different sand dune type and dune size as well as distance from coastal line. Compared with beach sands, dune sands have the characteristics of contenting silt, thinner, more positive skewness and sharper kurtosis, but the beach sands and the dune sands in the temperate coastal zone in China can not be distinguished by use of the parameter plot of grain size and component analysis method. These characteristics of modern dune sands in the temperate coastal zone in China are connected with the special physical conditions and evolution process of the temperate coastal zone in China, in which the clear monsoon climate and short formation time as well as narrow space for aeolian activities play leading role in the formation of characteristics above.
The characteristics of grain size parameters of modern coastal aeolian sands are the basic problems of coastal aeolian sand research. This paper, taking the temperate coastal zone in China as an example, makes use of the grain size parameter such as component of grain size, mean size, standard deviation, skewnss and kurtosis to study the characteristics of grain size parameters of modern coastal aeolian sands on the basis of data of 136 grain size samples. The research results can be concluded that the modern coastal aeolian sands in the temperate coastal zone in China are not all composed of fine sands with high sorting degree which were thought as before. Most are positively skewed. The parameters of grain size clearly change in different coastal zones and change with different sand dune type and dune size as well as distance from coastal line. Compared with beach sands, dune sands have the characteristics of contenting silt, thinner, more positive skewness and sharper kurtosis, but the beach sands and the dune sands in the temperate coastal zone in China can not be distinguished by use of the parameter plot of grain size and component analysis method. These characteristics of modern dune sands in the temperate coastal zone in China are connected with the special physical conditions and evolution process of the temperate coastal zone in China, in which the clear monsoon climate and short formation time as well as narrow space for aeolian activities play leading role in the formation of characteristics above.
2002, 20(4): 668-674.
Abstract:
Based on the integrated study of sediment cores in the South China Sea, the sedimentation rates fea-ture during the Late Pleistocene has been shown. ( 1)On the whole, the rates of glacial stages is 1. 3 ～ 1. 6 timesfor the interglacials. ( 2) T rend analysis on the sedimentation rate is performed, which indicates that the rates of cores during δ18 O Stage 1 were high in the northeastern and south western continental slope. The features resulted from trend analysis were the main controlling factorsof the river distribution, monsoon and ocean current etc. The sedimentation rates of cores during δ18 O Stage 2 and 3 were similar, which were different from that of during δ 18 O Stage 1, only that were high on the northeastern continental slope. So the sediment environment in the South Chi-na Sea was significantly modified after the δ18 O Stage 2.Based on the study of sediment cores in the Eastern South China Sea, the constituents of the main matter and sedimentation fluxes feature were obtained. ( 1) From the last glacial stage, the sedimentation fluxes on the north- ern continental slope were higher than that of the deep basin. ( 2)The sedimentation fluxes of silicon -organic-sub-stances during the glacial stage were higher than that of the interglacials. ( 3) From the last glacial stage, the ter-rigenous constituents were 44 %above in the abyssal plains sediments.
Based on the integrated study of sediment cores in the South China Sea, the sedimentation rates fea-ture during the Late Pleistocene has been shown. ( 1)On the whole, the rates of glacial stages is 1. 3 ～ 1. 6 timesfor the interglacials. ( 2) T rend analysis on the sedimentation rate is performed, which indicates that the rates of cores during δ18 O Stage 1 were high in the northeastern and south western continental slope. The features resulted from trend analysis were the main controlling factorsof the river distribution, monsoon and ocean current etc. The sedimentation rates of cores during δ18 O Stage 2 and 3 were similar, which were different from that of during δ 18 O Stage 1, only that were high on the northeastern continental slope. So the sediment environment in the South Chi-na Sea was significantly modified after the δ18 O Stage 2.Based on the study of sediment cores in the Eastern South China Sea, the constituents of the main matter and sedimentation fluxes feature were obtained. ( 1) From the last glacial stage, the sedimentation fluxes on the north- ern continental slope were higher than that of the deep basin. ( 2)The sedimentation fluxes of silicon -organic-sub-stances during the glacial stage were higher than that of the interglacials. ( 3) From the last glacial stage, the ter-rigenous constituents were 44 %above in the abyssal plains sediments.
2002, 20(4): 680-686.
Abstract:
Chemical compositions of 33 surface sediment samples were measured.The samples were collected from the continental shelf, slope and the south Okinaw a Trough, respectively.The major chemical compositionsare dominantly composed of SiO2, CaO and Al2O3, w hich account for about 68 percent weig ht of the sediments.Most of the elements change w ith a w ide range in the shelf and slope sediments, but keep stable in the trough sediments.From shelf to trough, the g rain size of the sediment becomes finer, at the same time, the content of SiO2 and CaO decrease, and the content of Al2O3 and most of other elements increase.Based on the dist ributions of the major elements/ Al2O3 ratio, it can be concluded that the sediments are transported from the provenance area to the trough.The sediments mainly composed of terrigenous, biogenic and autogenetic deposits in the study area.Comparing the enrichment factors (EF )of some element s of the shelf sediment swith the Yang tse River and Yellow River sediment s, It can be concluded that the sediments in the study area are similar to the Yang tse River sediments.The high enrichment factors of Cu, Zn, Pb, Co, Ni and Cr in the slope are caused by the biogenic enrichment.The enrichment of Mn is caused by autogenetic deposit.Based on the R -mode factor analy sis of the chemical compositions, combined w ith analysis of the distributions of the elements, four major facto rs indicate four sedimentary environments respectively.Every sedimentary area has its own typical elements group.They are, 1)Shelf-type elements group :SiO2, TiO2, Zr,CaO and Sr;2)Slope-type elements group :Fe2O3,MgO and P2O5;3)Trough-type elements group :Al2O3, K2O, Cu, Zn, Co, Ni, Cr and Ba, and 4)Redox elements group :MnO and FeO respectively.
Chemical compositions of 33 surface sediment samples were measured.The samples were collected from the continental shelf, slope and the south Okinaw a Trough, respectively.The major chemical compositionsare dominantly composed of SiO2, CaO and Al2O3, w hich account for about 68 percent weig ht of the sediments.Most of the elements change w ith a w ide range in the shelf and slope sediments, but keep stable in the trough sediments.From shelf to trough, the g rain size of the sediment becomes finer, at the same time, the content of SiO2 and CaO decrease, and the content of Al2O3 and most of other elements increase.Based on the dist ributions of the major elements/ Al2O3 ratio, it can be concluded that the sediments are transported from the provenance area to the trough.The sediments mainly composed of terrigenous, biogenic and autogenetic deposits in the study area.Comparing the enrichment factors (EF )of some element s of the shelf sediment swith the Yang tse River and Yellow River sediment s, It can be concluded that the sediments in the study area are similar to the Yang tse River sediments.The high enrichment factors of Cu, Zn, Pb, Co, Ni and Cr in the slope are caused by the biogenic enrichment.The enrichment of Mn is caused by autogenetic deposit.Based on the R -mode factor analy sis of the chemical compositions, combined w ith analysis of the distributions of the elements, four major facto rs indicate four sedimentary environments respectively.Every sedimentary area has its own typical elements group.They are, 1)Shelf-type elements group :SiO2, TiO2, Zr,CaO and Sr;2)Slope-type elements group :Fe2O3,MgO and P2O5;3)Trough-type elements group :Al2O3, K2O, Cu, Zn, Co, Ni, Cr and Ba, and 4)Redox elements group :MnO and FeO respectively.
2002, 20(4): 695-704.
Abstract:
On the base of research on diagenesis of Ordovivian carbonati te and quartzose sandstone in Ordos basin, preliminary S tudy on inclusio ns in these rocks have been done.There are three sections of homgogenization temperature of inclusio ns in Ordovician carbonate rock :60 ℃～ 100 ℃, 100 ℃～ 160 ℃, 160 ℃～ 220 ℃;and there are three sections of homogenization temperature of inclusions in Permocarboniferous quartzose;90 ℃～ 110 ℃, 120 ℃～140 ℃, 160 ℃～ 220℃.Making use of temperature data of inclusions combined w ith the recently research result of vitrinite reflectivity and apatite fission track, the paper discussed the application of fluid inclusions to formation and evolution of oil-gas reservoirs in Ordos basin.
On the base of research on diagenesis of Ordovivian carbonati te and quartzose sandstone in Ordos basin, preliminary S tudy on inclusio ns in these rocks have been done.There are three sections of homgogenization temperature of inclusio ns in Ordovician carbonate rock :60 ℃～ 100 ℃, 100 ℃～ 160 ℃, 160 ℃～ 220 ℃;and there are three sections of homogenization temperature of inclusions in Permocarboniferous quartzose;90 ℃～ 110 ℃, 120 ℃～140 ℃, 160 ℃～ 220℃.Making use of temperature data of inclusions combined w ith the recently research result of vitrinite reflectivity and apatite fission track, the paper discussed the application of fluid inclusions to formation and evolution of oil-gas reservoirs in Ordos basin.
2002, 20(4): 716-720.
Abstract:
The origin of Kekey a crude oil is very complex.The author emphatically analyzes the biological marker features of tw o sets of hydrocarbon source rocks, i.e.Jurassic and Permian, in the Southwest of Tarim, and defines the standard that could differentiate the tw o sets of hydrocarbon source rocks.On this foundation, we have comprehensively scan the biological marker of Kekey a crude oil, and the result indicates that Kekeya crude oil mainly derived from Permian hydrocarbon source rock.Moreover, we measure tiny diterpenoid in crude oil, indicating that the Jurassic hydrocarbon source rock has important contribution.
The origin of Kekey a crude oil is very complex.The author emphatically analyzes the biological marker features of tw o sets of hydrocarbon source rocks, i.e.Jurassic and Permian, in the Southwest of Tarim, and defines the standard that could differentiate the tw o sets of hydrocarbon source rocks.On this foundation, we have comprehensively scan the biological marker of Kekey a crude oil, and the result indicates that Kekeya crude oil mainly derived from Permian hydrocarbon source rock.Moreover, we measure tiny diterpenoid in crude oil, indicating that the Jurassic hydrocarbon source rock has important contribution.
