2007 Vol. 25, No. 6
Display Method:
2007, 25(6): 815-824.
Abstract:
Sulfate reduction has been recognized recently as a process of geologic significance, and is common and widespread in the Feixianguan of Triassic, NE Sichuan Basin of China. The widespread distribution of calcite cements with extremely high strontium concentrations (more than 3 000×10-6) indicate that the digenesis of Feixianguan carbonate have been strongly influenced by an unconventional strontium-rich pore fluids. The interstitial fluid with strontium concentration much higher than normally encountered is resulted by bacterial and (or) thermochemical sulfate reduction which removed the SO42- from the system and therefore, changed the solubility of celestite (SrSO4). The strontium in diagenetic pore fluids is original from the recrystallization of metastable aragonite and highMg calcite to diagenetic lowmagnesium calcite and dolomite. This mechanism must be related to the large and superlarge scale celestite deposits of Triassic, NE Sichuan Basin of China. Both H2S and CO2 are the common products of bacterial and thermochemical sulfate reduction. The increment of Gibbs free energy (ΔG) and equilibrium constants (K) for the reactions of
H2S(aq)H2S(g) and CO2(aq)CO2(g) were calculated here. The results indicate that, in the temperature interval of 25℃ to 220℃, the equilibrium constants (K) for the two reactions increase from about 10 to 240 and from about 20 to 500, respectively, and always more than 1. Both H2S and CO2 are more preferable to gas than aqueous solution, and the solubility of H2S and CO2 drop down with the increase of temperature, so the lower ability of dissolution for carbonate of H2S and CO2 in the deeper burial environment should be expected. The lower temperature diagenetic setting, hydrothermal migration upward, the mixing of oxygenated groundwater and aqueous solution of H2S to form sulfuric acid，and metal sulfide precipitation are the four ways to enhance the ability of dissolution of CO2 and (or) H2S for carbonate. The carbonate dissolution by H2S and CO2 during earlier diagenesis is closer relation to bacterial sulfate reduction rather than thermochemical sulfate reduction. The presence of faults is an important condition for the path of H2S and CO2 fluidflow upward. The facies such as bankmargin lime grainstones or reef limestones with more primary porosity and permeability are the preferential sites for lateral fluid flow and carbonate leaching. The uplift of the crust and karstification can provide a geologic setting for the oxidation of H2S in order to enhance the leaching ability. We hope that the research conclusion here is helpful for the prediction of good quality reservoir in the Feixianguan carbonate of Triassic, NE Sichuan Basin of China.
Sulfate reduction has been recognized recently as a process of geologic significance, and is common and widespread in the Feixianguan of Triassic, NE Sichuan Basin of China. The widespread distribution of calcite cements with extremely high strontium concentrations (more than 3 000×10-6) indicate that the digenesis of Feixianguan carbonate have been strongly influenced by an unconventional strontium-rich pore fluids. The interstitial fluid with strontium concentration much higher than normally encountered is resulted by bacterial and (or) thermochemical sulfate reduction which removed the SO42- from the system and therefore, changed the solubility of celestite (SrSO4). The strontium in diagenetic pore fluids is original from the recrystallization of metastable aragonite and highMg calcite to diagenetic lowmagnesium calcite and dolomite. This mechanism must be related to the large and superlarge scale celestite deposits of Triassic, NE Sichuan Basin of China. Both H2S and CO2 are the common products of bacterial and thermochemical sulfate reduction. The increment of Gibbs free energy (ΔG) and equilibrium constants (K) for the reactions of
H2S(aq)H2S(g) and CO2(aq)CO2(g) were calculated here. The results indicate that, in the temperature interval of 25℃ to 220℃, the equilibrium constants (K) for the two reactions increase from about 10 to 240 and from about 20 to 500, respectively, and always more than 1. Both H2S and CO2 are more preferable to gas than aqueous solution, and the solubility of H2S and CO2 drop down with the increase of temperature, so the lower ability of dissolution for carbonate of H2S and CO2 in the deeper burial environment should be expected. The lower temperature diagenetic setting, hydrothermal migration upward, the mixing of oxygenated groundwater and aqueous solution of H2S to form sulfuric acid，and metal sulfide precipitation are the four ways to enhance the ability of dissolution of CO2 and (or) H2S for carbonate. The carbonate dissolution by H2S and CO2 during earlier diagenesis is closer relation to bacterial sulfate reduction rather than thermochemical sulfate reduction. The presence of faults is an important condition for the path of H2S and CO2 fluidflow upward. The facies such as bankmargin lime grainstones or reef limestones with more primary porosity and permeability are the preferential sites for lateral fluid flow and carbonate leaching. The uplift of the crust and karstification can provide a geologic setting for the oxidation of H2S in order to enhance the leaching ability. We hope that the research conclusion here is helpful for the prediction of good quality reservoir in the Feixianguan carbonate of Triassic, NE Sichuan Basin of China.
2007, 25(6): 831-839.
Abstract:
The proved reserves of sour gas pools were up to 1×1012 m3 from oolitic dolostone reservoirs of Feixianguan Formation in northeast Sichuan Basin，that are mainly distributed in the sedimentary sequence with evaporites. Remnant gypsum and anhydrite , their moidic pores or molds in the reservoirs indicate that the dolomitization was related to the evaporated seawater. Furthermore, in some diagenesis sequence of the reservoirs, the dolomitization extent increases with depth from ancient subaerial exposure surface downwards. This implies that the dolomitization of the oolitic limestone took place in the early stage of diagenesis，and was possibly influenced by mixing rain water and evaporated seawater.
For δ13C and δ18O values between structural constituents of the oolitic dolomite in the reservoirs, the difference is great, so the values of intermix sample of reservoir rock are not suited for dolomitization research.
In the reservoirs , the most oolitic dolostone preserved the remainder of oolitic fabric or original rock framework , the various pores of the dolostone are almost secondary dissolved pores and not shrinkage pores due to dolomite crystals shrink. The replacement process of dolomitization is a volume replacement for volume, not a mole for mole. The relationship between bitumen and secondary dissolved pores indicates that late burial dissolution pores are dominant in the reservoirs .
The ionization constant of H2CO3 is much higher than that of H2S in the solution ,whereas the mole of CO2 is much lower than that of H2S in the sour gas of Feixianguan Formation. The late period calcite cement ，filled in the dissolved pores and fractures of the oolitic dolomite reservoirs， is characterized by low δ13C (-18‰) and high homogenization temperature (130~180℃), so the CO2,related to thermochemical sulfate reduction in the reservoirs , causes mainly late burial dissolution.
The proved reserves of sour gas pools were up to 1×1012 m3 from oolitic dolostone reservoirs of Feixianguan Formation in northeast Sichuan Basin，that are mainly distributed in the sedimentary sequence with evaporites. Remnant gypsum and anhydrite , their moidic pores or molds in the reservoirs indicate that the dolomitization was related to the evaporated seawater. Furthermore, in some diagenesis sequence of the reservoirs, the dolomitization extent increases with depth from ancient subaerial exposure surface downwards. This implies that the dolomitization of the oolitic limestone took place in the early stage of diagenesis，and was possibly influenced by mixing rain water and evaporated seawater.
For δ13C and δ18O values between structural constituents of the oolitic dolomite in the reservoirs, the difference is great, so the values of intermix sample of reservoir rock are not suited for dolomitization research.
In the reservoirs , the most oolitic dolostone preserved the remainder of oolitic fabric or original rock framework , the various pores of the dolostone are almost secondary dissolved pores and not shrinkage pores due to dolomite crystals shrink. The replacement process of dolomitization is a volume replacement for volume, not a mole for mole. The relationship between bitumen and secondary dissolved pores indicates that late burial dissolution pores are dominant in the reservoirs .
The ionization constant of H2CO3 is much higher than that of H2S in the solution ,whereas the mole of CO2 is much lower than that of H2S in the sour gas of Feixianguan Formation. The late period calcite cement ，filled in the dissolved pores and fractures of the oolitic dolomite reservoirs， is characterized by low δ13C (-18‰) and high homogenization temperature (130~180℃), so the CO2,related to thermochemical sulfate reduction in the reservoirs , causes mainly late burial dissolution.
2007, 25(6): 847-851.
Abstract:
The experimental results of formation watersource rock interaction in different temperature suggest the following results:(1) organic acid is generated in the experimental temperatures（60～300℃）,the total contents of organic acids is between 35.4 mg/l and 153.9 mg/l. The contents of organic acids are higher in the temperatures of 100℃ and 140℃ than that other temperatures; (2) the source rocks with high maturity （Ro）and high total organic carbon content（TOC）are favorable to the generation of organic acids in the low temperature（60℃）,but the generation of organic acids are commonly controlled by the maturity （Ro）, total organic carbon content（TOC）and carbonate content of source rocks in the middle（140℃）and high temperature（180℃,220℃ and 300℃）;(3)the contents of organic acids gradually decrease with the increase of carbonate content in source rocks in the low and middle temperature（60℃ and 140℃）,it suggests that the dissolution and precipitation of carbonate are mainly controlled by organic acids in the range of 60℃ to 140℃,but the dissolution and precipitation of carbonate are commonly controlled by organic acids and CO2 in the high temperature（180℃,220℃ and 300℃）,it makes the correlation between organic acids and carbonate complicated.
The experimental results of formation watersource rock interaction in different temperature suggest the following results:(1) organic acid is generated in the experimental temperatures（60～300℃）,the total contents of organic acids is between 35.4 mg/l and 153.9 mg/l. The contents of organic acids are higher in the temperatures of 100℃ and 140℃ than that other temperatures; (2) the source rocks with high maturity （Ro）and high total organic carbon content（TOC）are favorable to the generation of organic acids in the low temperature（60℃）,but the generation of organic acids are commonly controlled by the maturity （Ro）, total organic carbon content（TOC）and carbonate content of source rocks in the middle（140℃）and high temperature（180℃,220℃ and 300℃）;(3)the contents of organic acids gradually decrease with the increase of carbonate content in source rocks in the low and middle temperature（60℃ and 140℃）,it suggests that the dissolution and precipitation of carbonate are mainly controlled by organic acids in the range of 60℃ to 140℃,but the dissolution and precipitation of carbonate are commonly controlled by organic acids and CO2 in the high temperature（180℃,220℃ and 300℃）,it makes the correlation between organic acids and carbonate complicated.
2007, 25(6): 852-857.
Abstract:
Layer E13 in north area of west Qaidam Basin develops good clastic rock. Reservoir properties and diagenesis have a big relevance. To recognize favorable reservoir in E13 in North area of west Qaidam Basin, we divide diagenesis sequence of this area on the basis of core observation, microscope research and analyses experiments, and research the controlling factors of diagenesis further through thermodynamic analyses. In this area, there are four times of widescale diagenesis mainly. The first is dolomite cementation and replacement. The second is calcite cementation and alternation. The third is dissolution and the fourth is anhydrite cementation and alternation. The oil flow happens between dissolution and anhydrite cementation. In addition, compaction and pressolution run through the whole diagenesis. Each diagenesis proceeds in thermodynamic system. Through carefully deduction, we draw five component phase diagram including calcite, dolomite and anhydrite, etc, and get the geochemistry characteristics of diagenesis environment.
Layer E13 in north area of west Qaidam Basin develops good clastic rock. Reservoir properties and diagenesis have a big relevance. To recognize favorable reservoir in E13 in North area of west Qaidam Basin, we divide diagenesis sequence of this area on the basis of core observation, microscope research and analyses experiments, and research the controlling factors of diagenesis further through thermodynamic analyses. In this area, there are four times of widescale diagenesis mainly. The first is dolomite cementation and replacement. The second is calcite cementation and alternation. The third is dissolution and the fourth is anhydrite cementation and alternation. The oil flow happens between dissolution and anhydrite cementation. In addition, compaction and pressolution run through the whole diagenesis. Each diagenesis proceeds in thermodynamic system. Through carefully deduction, we draw five component phase diagram including calcite, dolomite and anhydrite, etc, and get the geochemistry characteristics of diagenesis environment.
2007, 25(6): 858-868.
Abstract:
Three types of paleokarstification, including syndepositional, weatheringcrust, and buried ones, are distinguished in Ordovician marine carbonate within Tarim basin. It is synthetically considered that the paleokarstification is a key factor of the formation of Ordovician carbonate reservoirs. Intragranular and intergranular solution spaces and moldic pores formed by syndepositional meteoric freshwater selective dissolution, are provided matrix porosity for the carbonate reservoir. These reservoirs are controlled by meteoric diagenetic lens in the distribution and are generally developed along the highenergy platform margin facies in the shape of discontinuous lenticle. The carbonate reservoirs related to weathering karstification are regionally distributed within ancient buried hills of exposed Ordovician carbonate, and are vertically limited within 200 meters below erosional unconformity interface of Ordovician carbonate. Based on vertical and lateral development characteristics of weathering karstification, it is directed that karst-type reservoirs are largely distributed within cap rubblerock of surface karst, vertical vadose and horizontal phreatic zones in the vertical direction, and generally developed at karst upland margin, karst slope, upstream karst valley, and karst hammock in the region. Burial karstification is generally related to the dissolution of carbonate minerals resulted from organic acid by which the thermal evolution of organic matter accompanied, is commonly proceeded along previous pore and fissure system, is characterized by more stages and various scales, and is a key factor for the optimized reworking of carbonate reservoir.
Three types of paleokarstification, including syndepositional, weatheringcrust, and buried ones, are distinguished in Ordovician marine carbonate within Tarim basin. It is synthetically considered that the paleokarstification is a key factor of the formation of Ordovician carbonate reservoirs. Intragranular and intergranular solution spaces and moldic pores formed by syndepositional meteoric freshwater selective dissolution, are provided matrix porosity for the carbonate reservoir. These reservoirs are controlled by meteoric diagenetic lens in the distribution and are generally developed along the highenergy platform margin facies in the shape of discontinuous lenticle. The carbonate reservoirs related to weathering karstification are regionally distributed within ancient buried hills of exposed Ordovician carbonate, and are vertically limited within 200 meters below erosional unconformity interface of Ordovician carbonate. Based on vertical and lateral development characteristics of weathering karstification, it is directed that karst-type reservoirs are largely distributed within cap rubblerock of surface karst, vertical vadose and horizontal phreatic zones in the vertical direction, and generally developed at karst upland margin, karst slope, upstream karst valley, and karst hammock in the region. Burial karstification is generally related to the dissolution of carbonate minerals resulted from organic acid by which the thermal evolution of organic matter accompanied, is commonly proceeded along previous pore and fissure system, is characterized by more stages and various scales, and is a key factor for the optimized reworking of carbonate reservoir.
2007, 25(6): 876-884.
Abstract:
The main gasbearing layers at Panyu gas field was belong to delta deposits of marine facies. The main bearing gas layer, SB13.8 layer was as main sediments of deltaic plain, but MFS18.5 layer was the depositing product of deltaic front. Based on the data of core, thin section; scan microscope, Xdiffraction, etc., the reservoir characteristics and diagenesis of Panyu gas field had been studied in detail. According to the latest classified criterion on diagenetic stage of clastic reservoirs, SB13.8 layer, one of the two main gas bearing layers, its stratum water circulating environment was an open type of alkalescence (pH>7.5), which was belong to stage B in early diagenesis with weak cementation and feeble diagenesis. MFS18.5 Layer, an other gas bearing layer, its stratum water circulating environment was an relative closed type of feeble acid(pH<6.5), which was belong to stage A in middle diagenesis. So, the augment of temperature had been catalyzed the dissolution course of organic acid water solution for silicate minerals, which had provided sufficient and indispensable conditions for the development of the secondary porous zones. Hereby, the diagenetic pattern of mavine quartzite sandstone reservoir has been established. As the view of reservoir characteristics, the texture and mineral component mature of MFS18.5 layer was higher than that of SB13.8 layer and it descended from lower to upper. Meanwhile, MFS18.5 layer had been reconstructed by waves and transported with long distance that was much more than those of SB13.8 layer. According to the results on cathode luminescence and scan microscope, the secondary enlargement of quartzs was to be the third degree and autogenetic kaolinite was well developed. This is the reason why the sandstone of MFS18.5 layer has the lower permeability and poor porosity contrasting with other reservoirs in Peal River Mouth basin. On the other hand, using specify basin simulating method of single well, the vertical change of porosity and permeability on the basis of burial history have been simulated, which can intuitively and more accurately analyze one another difference and characteristics of vertical multiply.
The main gasbearing layers at Panyu gas field was belong to delta deposits of marine facies. The main bearing gas layer, SB13.8 layer was as main sediments of deltaic plain, but MFS18.5 layer was the depositing product of deltaic front. Based on the data of core, thin section; scan microscope, Xdiffraction, etc., the reservoir characteristics and diagenesis of Panyu gas field had been studied in detail. According to the latest classified criterion on diagenetic stage of clastic reservoirs, SB13.8 layer, one of the two main gas bearing layers, its stratum water circulating environment was an open type of alkalescence (pH>7.5), which was belong to stage B in early diagenesis with weak cementation and feeble diagenesis. MFS18.5 Layer, an other gas bearing layer, its stratum water circulating environment was an relative closed type of feeble acid(pH<6.5), which was belong to stage A in middle diagenesis. So, the augment of temperature had been catalyzed the dissolution course of organic acid water solution for silicate minerals, which had provided sufficient and indispensable conditions for the development of the secondary porous zones. Hereby, the diagenetic pattern of mavine quartzite sandstone reservoir has been established. As the view of reservoir characteristics, the texture and mineral component mature of MFS18.5 layer was higher than that of SB13.8 layer and it descended from lower to upper. Meanwhile, MFS18.5 layer had been reconstructed by waves and transported with long distance that was much more than those of SB13.8 layer. According to the results on cathode luminescence and scan microscope, the secondary enlargement of quartzs was to be the third degree and autogenetic kaolinite was well developed. This is the reason why the sandstone of MFS18.5 layer has the lower permeability and poor porosity contrasting with other reservoirs in Peal River Mouth basin. On the other hand, using specify basin simulating method of single well, the vertical change of porosity and permeability on the basis of burial history have been simulated, which can intuitively and more accurately analyze one another difference and characteristics of vertical multiply.
2007, 25(6): 915-922.
Abstract:
According to a research on oilgas reservoir diagenetic characteristic and spreading block frame of sequence stratigraphy, the highdegree association was found between diagenetic facies charactertic which was decided by the process of diagenetic evolution and spreading of sequence stratigraphy. The ordinary rule of diagenasis near the boundaries and in the internal of a sequence was introduced in this article. It can be distinguished that the reservoir characteristic was controlled by diagenetic facies and diagenetic sequence. It was thought that some of success of exploration in Lower Tertiary in Dongying Sag was connected with differences of diagenesis. The reasons of oilgas richness was reasonably explained by the study on reservoir characteristic and diagenetic sequence. The results are that oil exploration must provide with specific aim, which was discovered by scientific way. So the best effectiveness would be acquired for exploration.
According to a research on oilgas reservoir diagenetic characteristic and spreading block frame of sequence stratigraphy, the highdegree association was found between diagenetic facies charactertic which was decided by the process of diagenetic evolution and spreading of sequence stratigraphy. The ordinary rule of diagenasis near the boundaries and in the internal of a sequence was introduced in this article. It can be distinguished that the reservoir characteristic was controlled by diagenetic facies and diagenetic sequence. It was thought that some of success of exploration in Lower Tertiary in Dongying Sag was connected with differences of diagenesis. The reasons of oilgas richness was reasonably explained by the study on reservoir characteristic and diagenetic sequence. The results are that oil exploration must provide with specific aim, which was discovered by scientific way. So the best effectiveness would be acquired for exploration.
2007, 25(6): 934-941.
Abstract:
There is a close relation between the sequence framework and reservoir quality, the different lithologic assemblage exists in different systems tracts which go through the different diageneisis, therefore, the reservoir quality in different systems tract is different. The relation among the sequence framework, diageneisis process, and reservoir quality has been paid much attention in this paper by the comprehensive study of geological and geophysical data. The Sha 1 Member of Tertiary in Qikou Sag could be divided into three sequences in the third class, which are consisted of LST, TST and HST. The sandstone and conglormarate from delta and subaqeous fan were developed in HST and has been in middle stage of diagenisis evolution with relative shallow depth, therefore, the reservoir quality of the sandstone and conglormarate is better than sandstone of LST. The reservoir quality in different systems tract is obvious different. Lastly, favorable and high quality reservoir has been forecasted according to the results of sequence framework, sedimentary facies and diagenesis of Sha1 member, that is, reservoir quality of Sha1 member in Qibei sub depression could be better than the quality in Qinan sub depression, and the reservoir quality of Sha 11 member could be better than the quality of Sha 12 member and Sha 13 member.
There is a close relation between the sequence framework and reservoir quality, the different lithologic assemblage exists in different systems tracts which go through the different diageneisis, therefore, the reservoir quality in different systems tract is different. The relation among the sequence framework, diageneisis process, and reservoir quality has been paid much attention in this paper by the comprehensive study of geological and geophysical data. The Sha 1 Member of Tertiary in Qikou Sag could be divided into three sequences in the third class, which are consisted of LST, TST and HST. The sandstone and conglormarate from delta and subaqeous fan were developed in HST and has been in middle stage of diagenisis evolution with relative shallow depth, therefore, the reservoir quality of the sandstone and conglormarate is better than sandstone of LST. The reservoir quality in different systems tract is obvious different. Lastly, favorable and high quality reservoir has been forecasted according to the results of sequence framework, sedimentary facies and diagenesis of Sha1 member, that is, reservoir quality of Sha1 member in Qibei sub depression could be better than the quality in Qinan sub depression, and the reservoir quality of Sha 11 member could be better than the quality of Sha 12 member and Sha 13 member.
2007, 25(6): 942-948.
Abstract:
Based on the published depositional models of lateral accretion bars formed in different environment, this paper studied the spatial assemblage patterns of the lateral accretion bodies and established architectures of lateral accretion bars through model prediction method. It is revealed that lateral accretion bars are formed by small-size river in the Ng52+3 of 7th block west, Gudong oil field. The spatial assemblage model of the lateral accretion bodies is horizontal echelon pattern, the width of the lateral accretion bodies is 80～240 m, and the dip angle is 5°～12°. By thin slice and SEM (Scanning Electronic Microscope) analysis, it is concluded that diagenesis is weak and the primary intergranular pores are in good conservation in the Ng52+3 of 7th block west, Gudong oil field. The average porosity and permeability of the reservoir are 32.3% and 3 500×10-3 μm2, respectively. There are several types of clay minerals in the lateral accretion bars, such as kaolinite, montmorillonite and illite, which weaken the quality of the reservoir.
Based on the published depositional models of lateral accretion bars formed in different environment, this paper studied the spatial assemblage patterns of the lateral accretion bodies and established architectures of lateral accretion bars through model prediction method. It is revealed that lateral accretion bars are formed by small-size river in the Ng52+3 of 7th block west, Gudong oil field. The spatial assemblage model of the lateral accretion bodies is horizontal echelon pattern, the width of the lateral accretion bodies is 80～240 m, and the dip angle is 5°～12°. By thin slice and SEM (Scanning Electronic Microscope) analysis, it is concluded that diagenesis is weak and the primary intergranular pores are in good conservation in the Ng52+3 of 7th block west, Gudong oil field. The average porosity and permeability of the reservoir are 32.3% and 3 500×10-3 μm2, respectively. There are several types of clay minerals in the lateral accretion bars, such as kaolinite, montmorillonite and illite, which weaken the quality of the reservoir.
2007, 25(6): 954-960.
Abstract:
Taken Chang 81 reservoir of Baimanan area, Xifeng Oilfield, Ordos Basin as an example, established the geologic models of Chang 81 reservoir by using the stochastic methods of Sequence Guass Simulation and Sequence Indicator Simulation, and then discussed the controlling factors of relative high permeable layer that formed in very low permeable lighological reservoir. The research results indicated that the sedimentary process was the most important reason why Chang 81 reservoir was made. The diagenesis and the fractures had also great influence on improving the reservoir properties and the migration of petroleum. The 3D model of sandstone distribution revealed that the main sandbody which lied in the west of the region of interest appeared to be a band with the direction from southwest to northeast. The results of stochastic modeling of the reservoir property indicated that the distribution of highquality reservoir which was matched with the regions of feldspar dissolution diagenetic facies and chlorite film cementation diagenetic facies in the main sandbody was mainly controlled by the sedimentation and the diagenesis of the research area.
Taken Chang 81 reservoir of Baimanan area, Xifeng Oilfield, Ordos Basin as an example, established the geologic models of Chang 81 reservoir by using the stochastic methods of Sequence Guass Simulation and Sequence Indicator Simulation, and then discussed the controlling factors of relative high permeable layer that formed in very low permeable lighological reservoir. The research results indicated that the sedimentary process was the most important reason why Chang 81 reservoir was made. The diagenesis and the fractures had also great influence on improving the reservoir properties and the migration of petroleum. The 3D model of sandstone distribution revealed that the main sandbody which lied in the west of the region of interest appeared to be a band with the direction from southwest to northeast. The results of stochastic modeling of the reservoir property indicated that the distribution of highquality reservoir which was matched with the regions of feldspar dissolution diagenetic facies and chlorite film cementation diagenetic facies in the main sandbody was mainly controlled by the sedimentation and the diagenesis of the research area.
2007, 25(6): 825-830.
Abstract:
It is thought generally that dissolution of acidic fluids is an important controlling factor for forming carbonate reservoir. This study focuses on the ability of dissolution of different type carbonate rocks in CO2 solution using a new simulating experiment way. The results show that the ability of dissolution of different carbonate rocks changes from low to high and again to lower with the simulating temperature from 25℃ to 200℃,and the maximum ability of dissolution is at 60～90℃; the ability of dissolution of dolomite is lower compared with the ability of dissolution of calcite, and the ability of dissolution of transitional type carbonate rocks is between calcite’s and dolomite’s, and the ability of dissolution is very lower and their different is very small for all type carbonate rocks in CO2 solution when the simulating temperature is higher than 150℃.This indicates that CO2 solution has important effect on dissolution of limestone and less effect on dissolution of dolomite during late stage of early diagenetic to early stage of middle diagenetic and the forming of good dolomite reservoir is related to dolomitization.
It is thought generally that dissolution of acidic fluids is an important controlling factor for forming carbonate reservoir. This study focuses on the ability of dissolution of different type carbonate rocks in CO2 solution using a new simulating experiment way. The results show that the ability of dissolution of different carbonate rocks changes from low to high and again to lower with the simulating temperature from 25℃ to 200℃,and the maximum ability of dissolution is at 60～90℃; the ability of dissolution of dolomite is lower compared with the ability of dissolution of calcite, and the ability of dissolution of transitional type carbonate rocks is between calcite’s and dolomite’s, and the ability of dissolution is very lower and their different is very small for all type carbonate rocks in CO2 solution when the simulating temperature is higher than 150℃.This indicates that CO2 solution has important effect on dissolution of limestone and less effect on dissolution of dolomite during late stage of early diagenetic to early stage of middle diagenetic and the forming of good dolomite reservoir is related to dolomitization.
2007, 25(6): 840-846.
Abstract:
The cause of formation and dynamical mechanisms in multiply medium of dissolved pores in deep formation of Dongying sag were revealed by those means such as core observation, thinsection analysis, scan electricity microscope observation, inclusion analysis and Ro test, etc and combining histories of stratum pressure, tectonic development and organic maturation. It was recognized that the reservoir in deep formation has multiply dissolving mechanisms. They are acidity medium dissolving mechanism and alkalescence medium dissolving mechanism. The former includes organic acid dissolution, abioacid dissolution and dissolution caused by sulfate thermochemistry oxidationreductive reaction and oil field fluid. The later gives priority to quartz dissolution. 6 kinds of methods to recognize quartz dissolution are put forward. The dynamical mechanisms of dissolution include cyclic thermal convection, atmosphere water infiltrating through active faults and exceed pressure leak near the faults.
The cause of formation and dynamical mechanisms in multiply medium of dissolved pores in deep formation of Dongying sag were revealed by those means such as core observation, thinsection analysis, scan electricity microscope observation, inclusion analysis and Ro test, etc and combining histories of stratum pressure, tectonic development and organic maturation. It was recognized that the reservoir in deep formation has multiply dissolving mechanisms. They are acidity medium dissolving mechanism and alkalescence medium dissolving mechanism. The former includes organic acid dissolution, abioacid dissolution and dissolution caused by sulfate thermochemistry oxidationreductive reaction and oil field fluid. The later gives priority to quartz dissolution. 6 kinds of methods to recognize quartz dissolution are put forward. The dynamical mechanisms of dissolution include cyclic thermal convection, atmosphere water infiltrating through active faults and exceed pressure leak near the faults.
2007, 25(6): 869-875.
Abstract:
The article studies on controlling factors of lower Juarassic sandstone diagenesis and porosity preservation in Tugerming Anticline of Kuqa foreland basin from the geological backgrounds of deposit, structure and themal current,and suggests that sandstone granular diameter, themal maturation and structure stress are three main controlling factors of sandstone diagengsis and porosity preservation.But the front two controlling factors are not important ones which resulted in the smaller sandstone compaction and more pore preservation in the southern wing of Tugerming anticline,and stronger sandstone compaction and smaller pore preservation in northern wing of Tugerming anticline. Further research shows that it was the Paleostructure stress that produced the most important effect on sandstone compaction and pore preservation because there was 72.2 MPa Paleotectonic stress differential tested by AE acoustic emission which could decreased 7.6 % of sandstone porosity between the northern and southern wing.
The article studies on controlling factors of lower Juarassic sandstone diagenesis and porosity preservation in Tugerming Anticline of Kuqa foreland basin from the geological backgrounds of deposit, structure and themal current,and suggests that sandstone granular diameter, themal maturation and structure stress are three main controlling factors of sandstone diagengsis and porosity preservation.But the front two controlling factors are not important ones which resulted in the smaller sandstone compaction and more pore preservation in the southern wing of Tugerming anticline,and stronger sandstone compaction and smaller pore preservation in northern wing of Tugerming anticline. Further research shows that it was the Paleostructure stress that produced the most important effect on sandstone compaction and pore preservation because there was 72.2 MPa Paleotectonic stress differential tested by AE acoustic emission which could decreased 7.6 % of sandstone porosity between the northern and southern wing.
2007, 25(6): 885-890.
Abstract:
Silurian sandstones of Manjiaer depression, Tarim basin deposited in the tidal, beach and braided delta environment, which are litharenite and quartzarenite. The study on the diagenesis, especially carbonate cementation history, sandstone porosity between northern Manjiaer and EasternSouthern Manjiaer indicates that the carbonate cementation time in sandstones has important influence on the porosity of sandstones. An abundant carbonate cements developed in sandstones in northern Manjiaer. These cements were formed before the thorough compaction of sandstones by the microscopical study because the sandstone grains are isolated in the carbonate cements. These cementations restrained the late compaction of sandstones. Although the buried depth of Silurian sandstones in northern Manjiaer only is 5 000～6 500 m, the compaction of sandstones is feeble, a great deal of carbonate cements exist in the sandstones around or between the grains of sandstones. The carbonate cements were dissolved lately and generated an abundant porosity. However, in the eastern and southern Manjiaer area, the cementation of carbonate took place after the thorough compaction of sandstones and carbonate cements were distributed in the limited space between sandstone grains. Thus late dissolution only generated less porosity compared with northern Manjiaer area although they were with shallow buried denpth（3 700～5 000 m）. This is related mainly to the time of carbonate cementation. Early carbonate cementation saved the intergranular space and provide the late dissolution, thus controles on the evolution of porosity of sandstone.
Silurian sandstones of Manjiaer depression, Tarim basin deposited in the tidal, beach and braided delta environment, which are litharenite and quartzarenite. The study on the diagenesis, especially carbonate cementation history, sandstone porosity between northern Manjiaer and EasternSouthern Manjiaer indicates that the carbonate cementation time in sandstones has important influence on the porosity of sandstones. An abundant carbonate cements developed in sandstones in northern Manjiaer. These cements were formed before the thorough compaction of sandstones by the microscopical study because the sandstone grains are isolated in the carbonate cements. These cementations restrained the late compaction of sandstones. Although the buried depth of Silurian sandstones in northern Manjiaer only is 5 000～6 500 m, the compaction of sandstones is feeble, a great deal of carbonate cements exist in the sandstones around or between the grains of sandstones. The carbonate cements were dissolved lately and generated an abundant porosity. However, in the eastern and southern Manjiaer area, the cementation of carbonate took place after the thorough compaction of sandstones and carbonate cements were distributed in the limited space between sandstone grains. Thus late dissolution only generated less porosity compared with northern Manjiaer area although they were with shallow buried denpth（3 700～5 000 m）. This is related mainly to the time of carbonate cementation. Early carbonate cementation saved the intergranular space and provide the late dissolution, thus controles on the evolution of porosity of sandstone.
2007, 25(6): 896-902.
Abstract:
Calcarenaceous sandstone is widely distributed in the fourth member of Xujiahe formation(T3x4) in West Sichuan Depression, and it can be seen in every structure and well.Most of the rocks are tight. Presently, welldeveloped pore that can be effective reservoir can be seen in local place.On the basis of thin sections identification and data statistics, the lithology, diagenesis, petrophysical properties and pore development properties for calcarenaceous sandstone in Fenggu area are analyzed in detail. It is indicated from the research that calcarenaceous sandstone layers in Fenggu are characterized by large thickness of single sand body, high content of carbonate debris, low content of calcite and welldeveloped secondary pores. Major pore type is dissolved intergrnular pores; and natural gas is mainly produced from source rock of lower Triassic Maantang formation, the third member of Xujiahe formation (T3x3) and the forth member of T3x4.Gas layers of calcarenaceous sandstone are closely related to its diagenesis,which belong to diagenetic trap.The form process of calcarenaceous sandstone gas layers in Fenggu area offers guidance for exploration of similar lithologic gas reservoirs.
Calcarenaceous sandstone is widely distributed in the fourth member of Xujiahe formation(T3x4) in West Sichuan Depression, and it can be seen in every structure and well.Most of the rocks are tight. Presently, welldeveloped pore that can be effective reservoir can be seen in local place.On the basis of thin sections identification and data statistics, the lithology, diagenesis, petrophysical properties and pore development properties for calcarenaceous sandstone in Fenggu area are analyzed in detail. It is indicated from the research that calcarenaceous sandstone layers in Fenggu are characterized by large thickness of single sand body, high content of carbonate debris, low content of calcite and welldeveloped secondary pores. Major pore type is dissolved intergrnular pores; and natural gas is mainly produced from source rock of lower Triassic Maantang formation, the third member of Xujiahe formation (T3x3) and the forth member of T3x4.Gas layers of calcarenaceous sandstone are closely related to its diagenesis,which belong to diagenetic trap.The form process of calcarenaceous sandstone gas layers in Fenggu area offers guidance for exploration of similar lithologic gas reservoirs.
2007, 25(6): 903-914.
Abstract:
Diagenesis and reservoir quality in sandstones are important research scopes for petroleum exploration. Taking the delta front to delta plain facies from upper Chang 7 to middle Chang 4+5 member of Yanchang Formation, Yanhe River outcrop, eastern Ordos Basin as an example, this paper addresses the differences of authigenetic minerals, porosity types, petrophysical attributes and oilshowing in sandstones between baselevel semirising and semidowning cycles, and their origins. Both of abundant laumontite and early calcite cement in concretion prevent the formation of authigenetic minerals including chlorite, chlorite/smectite, quartzovergrowth and albiteovergrowth in baselevel semidowning cycle under the 3rd sequence stratigraphic boundary surface, whereas authigenetic chlorite, chlorite/smectite, quartzovergrowth and albiteovergrowth are relatively well developed resulting from poor development of laumontite cement owing to lack of tuffaceous deposites and lower formation temperature, and lack of early calcite cement due to little influence of lake in baselevel semirising cycle above the 3rd sequence stratigraphic boundary sequence. The 3rd sequence boundary surface together with well developed Chang16sandbodies immediately above the sequence boundary surface was the predominant fluid conduits through which acidic fluid, which dissolved laumontite and calcite cement and feldspar grains, and oil migrated originated from the mature source rocks.
Diagenesis and reservoir quality in sandstones are important research scopes for petroleum exploration. Taking the delta front to delta plain facies from upper Chang 7 to middle Chang 4+5 member of Yanchang Formation, Yanhe River outcrop, eastern Ordos Basin as an example, this paper addresses the differences of authigenetic minerals, porosity types, petrophysical attributes and oilshowing in sandstones between baselevel semirising and semidowning cycles, and their origins. Both of abundant laumontite and early calcite cement in concretion prevent the formation of authigenetic minerals including chlorite, chlorite/smectite, quartzovergrowth and albiteovergrowth in baselevel semidowning cycle under the 3rd sequence stratigraphic boundary surface, whereas authigenetic chlorite, chlorite/smectite, quartzovergrowth and albiteovergrowth are relatively well developed resulting from poor development of laumontite cement owing to lack of tuffaceous deposites and lower formation temperature, and lack of early calcite cement due to little influence of lake in baselevel semirising cycle above the 3rd sequence stratigraphic boundary sequence. The 3rd sequence boundary surface together with well developed Chang16sandbodies immediately above the sequence boundary surface was the predominant fluid conduits through which acidic fluid, which dissolved laumontite and calcite cement and feldspar grains, and oil migrated originated from the mature source rocks.
2007, 25(6): 923-933.
Abstract:
In the Ordos Basin, the Upper Paleozoic could be divided 5 types of sandstone, mainly including quartz sandstone, lithic sandstone, graywacke, "felty" sandstone, black quartz sandstone, etc. These types of sandstone have some characteristics as that the compositional maturity of the sandstone are relatively high; the textural of the sandstone are relatively medium to low; normal grading; grain size is Coarse and Medium Grains, tuff fillings in the reservoir have multitype, and their concentrations vary greatly. The reservoir experienced three important diagenesis phases that early compaction phaseseriously damaged and losing primary pore phase, intermediate diagenetic A phaseoganic acids corrosionSecondary Porosity development phase, intermediate diagenetic B phaseburial, pressolution and secondary cementation diagenesis phases. The main diagenesis of SQ8 are pressure solution,kaolinite corrosion and quartz overgrouth, et al.The ones of SQ11 are siliceous cementation and carbonate cementation. The diagenetic facies are divided into three grades and five types: the first is strong pressure solutionquartz overgrouth facies;the second is pressure solutioncarbonate corrosionkaolinite metasomatic facies and corrosionweak matrix filledkaolinite metasomatic facies;the third is strong compactionclay cemented facies and strong compaction-carbonate cemented ,metasomatic facies. The main reservoir of studying region is low porosity, low peremeability sandstone,and mostly develops secondary pores,which include intergranular corrosion pores, and kaolinite intercrystal pores. few primary pores were preserved. Through multidisciplinary analysis of sand body distribution, reservoir diagenetic facies types and reservoir property, to predict the favorable reservoir distribution zone.
In the Ordos Basin, the Upper Paleozoic could be divided 5 types of sandstone, mainly including quartz sandstone, lithic sandstone, graywacke, "felty" sandstone, black quartz sandstone, etc. These types of sandstone have some characteristics as that the compositional maturity of the sandstone are relatively high; the textural of the sandstone are relatively medium to low; normal grading; grain size is Coarse and Medium Grains, tuff fillings in the reservoir have multitype, and their concentrations vary greatly. The reservoir experienced three important diagenesis phases that early compaction phaseseriously damaged and losing primary pore phase, intermediate diagenetic A phaseoganic acids corrosionSecondary Porosity development phase, intermediate diagenetic B phaseburial, pressolution and secondary cementation diagenesis phases. The main diagenesis of SQ8 are pressure solution,kaolinite corrosion and quartz overgrouth, et al.The ones of SQ11 are siliceous cementation and carbonate cementation. The diagenetic facies are divided into three grades and five types: the first is strong pressure solutionquartz overgrouth facies;the second is pressure solutioncarbonate corrosionkaolinite metasomatic facies and corrosionweak matrix filledkaolinite metasomatic facies;the third is strong compactionclay cemented facies and strong compaction-carbonate cemented ,metasomatic facies. The main reservoir of studying region is low porosity, low peremeability sandstone,and mostly develops secondary pores,which include intergranular corrosion pores, and kaolinite intercrystal pores. few primary pores were preserved. Through multidisciplinary analysis of sand body distribution, reservoir diagenetic facies types and reservoir property, to predict the favorable reservoir distribution zone.
2007, 25(6): 949-953.
Abstract:
Dina 2 Gas Field, which is one of major gas field of Xiqidongshu, with the FMP of more than 106 MPa and the pressure coefficience of more than 2.0, belongs to a low porosity, low particular permeability and abnormal pressure gas reservoir with crack. Dina 2 Gas Field has carried through stress sensitivity experimentation research of reservoir to evaluate rightly elasticplastic deformation with the FMP dropping among developing the gas field. by mean of testing porosity and permeability of drillcore sample under vary effective stress, the paper reserves representative reservoir complete stress strain curve of Dina 2 Gas Field, and depicts quantitatively forever plastic deformation character of rock with the FMP dropping. This job settles basement for confirming flow potential of single well and drawing up development planning of Dian 2 Gas Field, also offers valid method and measure for fundamental research of analogous gas reservoir development.
Dina 2 Gas Field, which is one of major gas field of Xiqidongshu, with the FMP of more than 106 MPa and the pressure coefficience of more than 2.0, belongs to a low porosity, low particular permeability and abnormal pressure gas reservoir with crack. Dina 2 Gas Field has carried through stress sensitivity experimentation research of reservoir to evaluate rightly elasticplastic deformation with the FMP dropping among developing the gas field. by mean of testing porosity and permeability of drillcore sample under vary effective stress, the paper reserves representative reservoir complete stress strain curve of Dina 2 Gas Field, and depicts quantitatively forever plastic deformation character of rock with the FMP dropping. This job settles basement for confirming flow potential of single well and drawing up development planning of Dian 2 Gas Field, also offers valid method and measure for fundamental research of analogous gas reservoir development.
