2017 Vol. 35, No. 2
Display Method:
2017, 35(2): 203-216.
doi: 10.14027/j.cnki.cjxb.2017.02.001
Abstract:
The Neoproterozoic Era witnessed a series of geological and biological events which may have significantly changed the Earth's surface environment. These events are suspected to be linked and their temporal relationships have long been a focus of multidisciplinary studies. Superplume activity and true polar wander through the early Neoproterozoic led to the break-up of Rodinia supercontinent. Indeed, such a large perturbation of deep mantle dynamics exerted a crucial impact on the global cycles of O2 and CO2, thus further inducing the extraordinarily dramatic climate. Biological consequences of tectonic re-configuration are mainly reflected in nutrient availability and living conditions. The elevated upwelling and surface runoff could sustain persistent blooms of marine organisms. A Snowball Earth hypothesis has been proposed to explain the tropical glaciation. During times of widespread ice, there must be an intense environmental filter on the evolution of early life. Moreover, the subsequent rapid melting of glaciers may result in the explosion of productivity as well as the formation of major sedimentary minerals. Besides these geological and biological events, this period is also characterized by prominent fluctuations of geochemical proxies, which indicate great changes of atmosphere and ocean at this critical interval.
The Neoproterozoic Era witnessed a series of geological and biological events which may have significantly changed the Earth's surface environment. These events are suspected to be linked and their temporal relationships have long been a focus of multidisciplinary studies. Superplume activity and true polar wander through the early Neoproterozoic led to the break-up of Rodinia supercontinent. Indeed, such a large perturbation of deep mantle dynamics exerted a crucial impact on the global cycles of O2 and CO2, thus further inducing the extraordinarily dramatic climate. Biological consequences of tectonic re-configuration are mainly reflected in nutrient availability and living conditions. The elevated upwelling and surface runoff could sustain persistent blooms of marine organisms. A Snowball Earth hypothesis has been proposed to explain the tropical glaciation. During times of widespread ice, there must be an intense environmental filter on the evolution of early life. Moreover, the subsequent rapid melting of glaciers may result in the explosion of productivity as well as the formation of major sedimentary minerals. Besides these geological and biological events, this period is also characterized by prominent fluctuations of geochemical proxies, which indicate great changes of atmosphere and ocean at this critical interval.
2017, 35(2): 217-227.
doi: 10.14027/j.cnki.cjxb.2017.02.002
Abstract:
Two types of carbonate sedimentary facies, two types of subfacies, and five types of carbonate microfacies are identified based on rock thin section identification and fossil identification from the Permian-Triassic boundary at Zhijin profile of Guizhou province. The values of δ13Corg turn negative from -27.7‰ to -28.3‰ from the later Permian to the early Triassic period, reflecting the change of organic matter types from higher plant to lower microbes. The values of δ13Crock present increasing from -24.2‰ to -20.9‰ in the late Permian period and into the early Triassic period, reflecting a mass extinction event in the late Permian. This resulted in the disappearance of marine organisms and the intensive enrichment of 12C in the ocean. Mixed organic matter is not neglected in the testing process. The values of Fe-HR/Fe-T, Fepy/Fe-HR, V/(V+Ni) and V/(V+Cr) distributed at the boundary of the Permian and Triassic indicate that the paleooceanographic chemistry condition at the end of the Permian was oxidation and weak reduction environment. These values also reveal that the paleooceanographic chemistry condition at the early of Triassic was reduction and iron environment, and there was no sulfide environment within the basin. The ratio of V/Ni increases from 0.97~1.97 (in the upper of Permian) to 1.67~7.33 (in the lower of Triassic), which shows a deeper process of seawater. This conclusion coincides with the result of carbonate microfacies evolution. From the view of biogenic evolution, biotic assemblages change from the type of foraminifera-algal-trilobite in the Late Permian to the type of small scale of shelly and microbial assemblage zones in the Early Triassic, which indicate two ceremonies of extinction and organic evolution model in the late of Permian and early of Triassic in the southern China.
Two types of carbonate sedimentary facies, two types of subfacies, and five types of carbonate microfacies are identified based on rock thin section identification and fossil identification from the Permian-Triassic boundary at Zhijin profile of Guizhou province. The values of δ13Corg turn negative from -27.7‰ to -28.3‰ from the later Permian to the early Triassic period, reflecting the change of organic matter types from higher plant to lower microbes. The values of δ13Crock present increasing from -24.2‰ to -20.9‰ in the late Permian period and into the early Triassic period, reflecting a mass extinction event in the late Permian. This resulted in the disappearance of marine organisms and the intensive enrichment of 12C in the ocean. Mixed organic matter is not neglected in the testing process. The values of Fe-HR/Fe-T, Fepy/Fe-HR, V/(V+Ni) and V/(V+Cr) distributed at the boundary of the Permian and Triassic indicate that the paleooceanographic chemistry condition at the end of the Permian was oxidation and weak reduction environment. These values also reveal that the paleooceanographic chemistry condition at the early of Triassic was reduction and iron environment, and there was no sulfide environment within the basin. The ratio of V/Ni increases from 0.97~1.97 (in the upper of Permian) to 1.67~7.33 (in the lower of Triassic), which shows a deeper process of seawater. This conclusion coincides with the result of carbonate microfacies evolution. From the view of biogenic evolution, biotic assemblages change from the type of foraminifera-algal-trilobite in the Late Permian to the type of small scale of shelly and microbial assemblage zones in the Early Triassic, which indicate two ceremonies of extinction and organic evolution model in the late of Permian and early of Triassic in the southern China.
2017, 35(2): 228-240.
doi: 10.14027/j.cnki.cjxb.2017.02.003
Abstract:
There have been abundant research fruits on contourites for about 50 years. The work on the contourite are developed rapidly with technique and ocean awareness improving in recent 10 years, and hence, lots of new achievements have been emerged. Based on reviewing the research history of contourites in brief, combing the latest research results, the advance and achievement has been summarized. Contourites showing fine-coarse-fine cyclicity is usually fine, whose sedimentary structures and bioturbations are abundant. Based on morphology and sedimentary process, the contourites could be divided into elongated, mounded drifts, channel-related drifts, patch drifts and so on. The sedimentary model includes simple current pathway, multiple current pathway and down-slope and along-slope interaction. Furthermore, interaction between down-slope and along-slope is one of the hot spots of deepwater deposits research. At last, the facing problem and direction of work on contourites in the future were proposed as follows:1) Perfecting identification marks and popularizing research results. 2) Integrating various measures and theories, discussing the coupling relationship between sedimentary processes and tectonic evolution, paleoceanography, climate changing. 3) Reinforce to work potential of hydrocarbon exploration.
There have been abundant research fruits on contourites for about 50 years. The work on the contourite are developed rapidly with technique and ocean awareness improving in recent 10 years, and hence, lots of new achievements have been emerged. Based on reviewing the research history of contourites in brief, combing the latest research results, the advance and achievement has been summarized. Contourites showing fine-coarse-fine cyclicity is usually fine, whose sedimentary structures and bioturbations are abundant. Based on morphology and sedimentary process, the contourites could be divided into elongated, mounded drifts, channel-related drifts, patch drifts and so on. The sedimentary model includes simple current pathway, multiple current pathway and down-slope and along-slope interaction. Furthermore, interaction between down-slope and along-slope is one of the hot spots of deepwater deposits research. At last, the facing problem and direction of work on contourites in the future were proposed as follows:1) Perfecting identification marks and popularizing research results. 2) Integrating various measures and theories, discussing the coupling relationship between sedimentary processes and tectonic evolution, paleoceanography, climate changing. 3) Reinforce to work potential of hydrocarbon exploration.
2017, 35(2): 241-252.
doi: 10.14027/j.cnki.cjxb.2017.02.004
Abstract:
Pagoda limestone, which is widely distributed in Yangtze area, refers to a set of micritic limestone or bioclastic micritic limestone in Ordovician Pagoda Formation. The unique network structure is developed pervasively throughout the entire Pagoda Formation in bedding-plan view, and these networks are similar to turtle shell or horseshoe, so it is also known as "turtle-shell cracks" or "horseshoe cracks". In this study, combining with the field survey in Tangjiahe section of Wangcang in Sichuan province, we systematically reviewed the literature on the issue of the unique network structure, and summarized the main views about the explanations. Up to now, agreements have been achieved that the cracks should not be considered as an evidence of desiccation during surface exposure; biogliph, hardground and other origins are lack of evidence; while syneresis, diagenesis and other causes are still in heated discussion. In addition, some new phenomena were observed on Tangjiahe section, for example, we found the black fine lines on the bedding surface of gray Pagoda limestone. Both the existing problems and the new findings may boost the study on the origin of the special network structure in Pagoda Formation. They can also help improve our understanding of the mechanisms of the special networks.
Pagoda limestone, which is widely distributed in Yangtze area, refers to a set of micritic limestone or bioclastic micritic limestone in Ordovician Pagoda Formation. The unique network structure is developed pervasively throughout the entire Pagoda Formation in bedding-plan view, and these networks are similar to turtle shell or horseshoe, so it is also known as "turtle-shell cracks" or "horseshoe cracks". In this study, combining with the field survey in Tangjiahe section of Wangcang in Sichuan province, we systematically reviewed the literature on the issue of the unique network structure, and summarized the main views about the explanations. Up to now, agreements have been achieved that the cracks should not be considered as an evidence of desiccation during surface exposure; biogliph, hardground and other origins are lack of evidence; while syneresis, diagenesis and other causes are still in heated discussion. In addition, some new phenomena were observed on Tangjiahe section, for example, we found the black fine lines on the bedding surface of gray Pagoda limestone. Both the existing problems and the new findings may boost the study on the origin of the special network structure in Pagoda Formation. They can also help improve our understanding of the mechanisms of the special networks.
2017, 35(2): 253-263.
doi: 10.14027/j.cnki.cjxb.2017.02.005
Abstract:
As we know, soft sediment deformation structures in the geological history can be found in different space-time sedimentary rocks, however, its deformation process, active force and trigger mechanism are still in dispute in academia. Through the observation on the field outcrops in the front of Micangshan, there develop multiple sets of soft sediment deformation structures in the sandstone, siltstone and shale strata in Early Silurian. The distribution of the layer is stable, and each stratum has different morphological characters. According to its morphological characteristics and stratigraphic distribution, it can be divided into wavy deformation structure, convolute bedding, pillow structure and flamy structure. What's more, they always accompany with hummocky cross-beddings. On the basis of the lithologic character and profile structure combination of the soft sediment deformation structures, they can be divided into three types, which all belong to the continental shelf sedimentary environments. Based on the characteristics of the soft sediment deformation structures and combined with the paleoclimate and paleo-plate materials, carbon isotope data, and modern hurricane research results, the study area is located in the north of the equator. There is hot and arid, and the storm occurs frequently. The soft sediment deformation structures of the research area are mainly the consequence of the storm. Unconsolidated sediments are oscillated and liquefied when the strong storm hit the bottom of the sea. The discovery and the trigger mechanism of the soft sediment deformation structures in the front of Micangshan has a great significance for studying the recovery of the paleoclimate and paleo-plate, and the evolution of ancient Yangtze plate.
As we know, soft sediment deformation structures in the geological history can be found in different space-time sedimentary rocks, however, its deformation process, active force and trigger mechanism are still in dispute in academia. Through the observation on the field outcrops in the front of Micangshan, there develop multiple sets of soft sediment deformation structures in the sandstone, siltstone and shale strata in Early Silurian. The distribution of the layer is stable, and each stratum has different morphological characters. According to its morphological characteristics and stratigraphic distribution, it can be divided into wavy deformation structure, convolute bedding, pillow structure and flamy structure. What's more, they always accompany with hummocky cross-beddings. On the basis of the lithologic character and profile structure combination of the soft sediment deformation structures, they can be divided into three types, which all belong to the continental shelf sedimentary environments. Based on the characteristics of the soft sediment deformation structures and combined with the paleoclimate and paleo-plate materials, carbon isotope data, and modern hurricane research results, the study area is located in the north of the equator. There is hot and arid, and the storm occurs frequently. The soft sediment deformation structures of the research area are mainly the consequence of the storm. Unconsolidated sediments are oscillated and liquefied when the strong storm hit the bottom of the sea. The discovery and the trigger mechanism of the soft sediment deformation structures in the front of Micangshan has a great significance for studying the recovery of the paleoclimate and paleo-plate, and the evolution of ancient Yangtze plate.
2017, 35(2): 264-278.
doi: 10.14027/j.cnki.cjxb.2017.02.006
Abstract:
The Nanhua System in Quruqtagh area could record a synchronous volcanic-sedimentary events along the northern margin of the Tarim craton. The characteristics of the detrital components of Nanhua System sandstones from various sections indicate that sandstones from Bayisi Formation in different section have different detrital components. In Xishankou section, litharenites are the key components, in which the rock fragments are volcanic rocks and sedimentary rocks, obviously, indicating a recycled sedimentary provenance. Whereas, in Yigezitage section, the key components are arkoses and lithic arkoses, and the rock fragments are metamorphic rocks while there are lots of mineral inclusions in quartz, which all indicate a metamorphic provenance. Vertical variation of sandstone's detrital components recorded a transform event between the boundary of Bayisi Formation and Zhaobishan Formation(725 Ma±), which causes Zhaobihsan, Altungol and Tereeken Formation have a uniform sandstone component. Converted to a typical arkose composition those represent a basement uplift-transitional continental provenance. The detrital component of Nanhua System sandstones and temporal-spatial variation demonstrates a continental rift setting of Nanhua System at Quruqtagh area. Meanwhile, it also shows a successive provenance evolution from pre-rift sedimentary successions to transitional rift-shoulder to dissected rift-shoulder to transitional continental and craton interior. Consequently, the petrography of sandstones in Quruqtagh area records the early breakup of Quruqtagh-Mangar aulacogen.
The Nanhua System in Quruqtagh area could record a synchronous volcanic-sedimentary events along the northern margin of the Tarim craton. The characteristics of the detrital components of Nanhua System sandstones from various sections indicate that sandstones from Bayisi Formation in different section have different detrital components. In Xishankou section, litharenites are the key components, in which the rock fragments are volcanic rocks and sedimentary rocks, obviously, indicating a recycled sedimentary provenance. Whereas, in Yigezitage section, the key components are arkoses and lithic arkoses, and the rock fragments are metamorphic rocks while there are lots of mineral inclusions in quartz, which all indicate a metamorphic provenance. Vertical variation of sandstone's detrital components recorded a transform event between the boundary of Bayisi Formation and Zhaobishan Formation(725 Ma±), which causes Zhaobihsan, Altungol and Tereeken Formation have a uniform sandstone component. Converted to a typical arkose composition those represent a basement uplift-transitional continental provenance. The detrital component of Nanhua System sandstones and temporal-spatial variation demonstrates a continental rift setting of Nanhua System at Quruqtagh area. Meanwhile, it also shows a successive provenance evolution from pre-rift sedimentary successions to transitional rift-shoulder to dissected rift-shoulder to transitional continental and craton interior. Consequently, the petrography of sandstones in Quruqtagh area records the early breakup of Quruqtagh-Mangar aulacogen.
2017, 35(2): 279-289.
doi: 10.14027/j.cnki.cjxb.2017.02.007
Abstract:
The meandering river sand body reservoir is important continental clastic reservoir type. Based on a series of basic data of modern high sinuosity meandering river, and the idea "past is the key to the present", the hierarchical quantitative knowledge base was established, and underground sand body scale was characterized quantitatively. Feasibility analysis of the quantitative characterization was carried out. The study shows that the meandering river forms when the bank is mainly composed of fine material and the channel gradient ratio reduces by increasing the channel sinuosity and extending the flow path to achieve sediment transport equilibrium and the least energy consumption and. The plane geometry of meandering river channel is derivative sine curve, and the geometry and sand body scale maintain good regularity during the evolution process. Based on uncertainty of sand body scale, combining the hierarchical characterization idea of reservoir architecture theory, multiple sets of empirical formula were built hierarchically and quantitative knowledge base of high sinuosity meandering river was established by fitting the modern sedimentary data with proper confidential level. The compaction of sediment is the main factor of volume decrease of sediment after burial. Quantitative relation between modern sediment and underground sand body was built by decompaction correction. Based on these cognitions, the underground meandering river sand body scale with primary sedimentary state was characterized quantitatively. The results are objective and accurate to be proved by real data.
The meandering river sand body reservoir is important continental clastic reservoir type. Based on a series of basic data of modern high sinuosity meandering river, and the idea "past is the key to the present", the hierarchical quantitative knowledge base was established, and underground sand body scale was characterized quantitatively. Feasibility analysis of the quantitative characterization was carried out. The study shows that the meandering river forms when the bank is mainly composed of fine material and the channel gradient ratio reduces by increasing the channel sinuosity and extending the flow path to achieve sediment transport equilibrium and the least energy consumption and. The plane geometry of meandering river channel is derivative sine curve, and the geometry and sand body scale maintain good regularity during the evolution process. Based on uncertainty of sand body scale, combining the hierarchical characterization idea of reservoir architecture theory, multiple sets of empirical formula were built hierarchically and quantitative knowledge base of high sinuosity meandering river was established by fitting the modern sedimentary data with proper confidential level. The compaction of sediment is the main factor of volume decrease of sediment after burial. Quantitative relation between modern sediment and underground sand body was built by decompaction correction. Based on these cognitions, the underground meandering river sand body scale with primary sedimentary state was characterized quantitatively. The results are objective and accurate to be proved by real data.
2017, 35(2): 290-298.
doi: 10.14027/j.cnki.cjxb.2017.02.008
Abstract:
In marine methane seepage areas, sedimentary magnetic susceptibility was characterized by abnormally low values, which was related to the formation of authigenic minerals resulted from the anaerobic methane oxidation (AOM) within the sulfate-methane transition zone (SMTZ). In this study, 400 sedimentary core samples from Site DH-CL11, Site973-2 and Site973-4 drilled in the northern South China Sea were measured. In connection with the relative content and the sulfur isotopic values of the authigenic pyrites handpicked from the aforementioned 3 sites, the variation characteristics of sedimentary magnetic susceptibility and its indication for methane seep events at the potential gas hydrate areas in the northern South China Sea were discussed. At Site DH-CL11, sedimentary magnetic susceptibility first significantly decreased and then abnormally increased within the paleo-SMTZ (705.5~765.5 cmbsf), which is probably related to the depth change of the SMTZ. At Site 973-2, sedimentary magnetic susceptibility showed a decreasing trend within the paleo-SMTZ (453~492.5 cmbsf). Greigites were discovered under the SMTZ, which may be related to frequent changes of the SMTZ or the anaerobic oxidation of authigenic pyrites. At Site 973-4, sedimentary magnetic susceptibility significantly decreased within the paleo-SMTZ (584.5~878 cmbsf), which was considered to be resulted from methane seep events. In general, these results show that under the methane seepage environments, HS- produced by AOM reacts with magnetic minerals in sediments, resulting in the dissolution of magnetic minerals coupled with precipitation of paramagnetic pyrite, both of which will make an anomalously low MS value in the SMTZ; However, with low HS- concentration, insufficient supply of HS- will lead to partial pyritization, which will result in the preferential formation of greigites followed by secondary magnetic susceptibility signals. Therefore, in gas hydrate prospecting areas, abnormal characteristics of the sedimentary magnetic susceptibility are feasible to indicate deep methane flux variation, thus to show a further indication for the evolution of the underlying gas hydrate occurrence. The abnormal characteristic of sedimentary magnetic susceptibility becomes an indirect but available method to explore gas hydrate occurrence, which is helpful for gas hydrate exploration in the northern South China Sea.
In marine methane seepage areas, sedimentary magnetic susceptibility was characterized by abnormally low values, which was related to the formation of authigenic minerals resulted from the anaerobic methane oxidation (AOM) within the sulfate-methane transition zone (SMTZ). In this study, 400 sedimentary core samples from Site DH-CL11, Site973-2 and Site973-4 drilled in the northern South China Sea were measured. In connection with the relative content and the sulfur isotopic values of the authigenic pyrites handpicked from the aforementioned 3 sites, the variation characteristics of sedimentary magnetic susceptibility and its indication for methane seep events at the potential gas hydrate areas in the northern South China Sea were discussed. At Site DH-CL11, sedimentary magnetic susceptibility first significantly decreased and then abnormally increased within the paleo-SMTZ (705.5~765.5 cmbsf), which is probably related to the depth change of the SMTZ. At Site 973-2, sedimentary magnetic susceptibility showed a decreasing trend within the paleo-SMTZ (453~492.5 cmbsf). Greigites were discovered under the SMTZ, which may be related to frequent changes of the SMTZ or the anaerobic oxidation of authigenic pyrites. At Site 973-4, sedimentary magnetic susceptibility significantly decreased within the paleo-SMTZ (584.5~878 cmbsf), which was considered to be resulted from methane seep events. In general, these results show that under the methane seepage environments, HS- produced by AOM reacts with magnetic minerals in sediments, resulting in the dissolution of magnetic minerals coupled with precipitation of paramagnetic pyrite, both of which will make an anomalously low MS value in the SMTZ; However, with low HS- concentration, insufficient supply of HS- will lead to partial pyritization, which will result in the preferential formation of greigites followed by secondary magnetic susceptibility signals. Therefore, in gas hydrate prospecting areas, abnormal characteristics of the sedimentary magnetic susceptibility are feasible to indicate deep methane flux variation, thus to show a further indication for the evolution of the underlying gas hydrate occurrence. The abnormal characteristic of sedimentary magnetic susceptibility becomes an indirect but available method to explore gas hydrate occurrence, which is helpful for gas hydrate exploration in the northern South China Sea.
2017, 35(2): 299-314.
doi: 10.14027/j.cnki.cjxb.2017.02.009
Abstract:
The East China Sea Shelf Basin (ECSSB) is the largest sedimentary basin in offshore China, which contains the largest hydrocarbon bearing unit of Xihu Depression. However, after years of exploration practices, the Huagang Formation in Oligocene has been proven as a major gas reservoir, which has undergone controversy on subdivision of sequence stratigraphy and types of sedimentary systems for a long time. Combining with basin structure and tectonic context, this study subdivides the Oligocene into 5 third-order sequences and 12 system tracts in the Xihu Sag on the basis of base level cycle analysis, core calibration, and seismic reflection features.Furthermore, sedimentary environments were identified by core description, sedimentary structures, trace fossils, and geochemical analysis. Typical sedimentary sequences were established including fluvial, delta, tidal estuary, and beach-bar systems.Sedimentary system types and distribution have been clarified of the Huagang Formation in the Xihu Sag. In the Oligocene, the Xihu Sag was in a transitional environment (mainly in lacustrine environment), which experienced two major times of marine transgressions (around 29.5 Ma and 24.3 Ma). Depositional systems were diverse from south to north, mainly consisting of deltas in the short axis from east to west, tidal estuaries in the south, and beach-bars in the northeast gentle slope. Finally, tectonic-sedimentary genetic model has been established in the ECSSB, showing basin tectonic setting and depositional response under the context of rifting-depression transition and marine-continental alternation.
The East China Sea Shelf Basin (ECSSB) is the largest sedimentary basin in offshore China, which contains the largest hydrocarbon bearing unit of Xihu Depression. However, after years of exploration practices, the Huagang Formation in Oligocene has been proven as a major gas reservoir, which has undergone controversy on subdivision of sequence stratigraphy and types of sedimentary systems for a long time. Combining with basin structure and tectonic context, this study subdivides the Oligocene into 5 third-order sequences and 12 system tracts in the Xihu Sag on the basis of base level cycle analysis, core calibration, and seismic reflection features.Furthermore, sedimentary environments were identified by core description, sedimentary structures, trace fossils, and geochemical analysis. Typical sedimentary sequences were established including fluvial, delta, tidal estuary, and beach-bar systems.Sedimentary system types and distribution have been clarified of the Huagang Formation in the Xihu Sag. In the Oligocene, the Xihu Sag was in a transitional environment (mainly in lacustrine environment), which experienced two major times of marine transgressions (around 29.5 Ma and 24.3 Ma). Depositional systems were diverse from south to north, mainly consisting of deltas in the short axis from east to west, tidal estuaries in the south, and beach-bars in the northeast gentle slope. Finally, tectonic-sedimentary genetic model has been established in the ECSSB, showing basin tectonic setting and depositional response under the context of rifting-depression transition and marine-continental alternation.
2017, 35(2): 315-329.
doi: 10.14027/j.cnki.cjxb.2017.02.010
Abstract:
Taking the Yanchang Formation Shale for Well YK-1 in Tongchuan Area of the south of Ordos Basin as the target, pore characteristics and controlling factors were investigated by using Argon-ion Polishing Scanning Electron Microscope(SEM)and low-temperature nitrogen adsorption experiments. The results show that pores of Yanchang Formation shale can be classified into inter-granular pore, intra-granular pore, intra-crystalline pore in pyrite, dissolved pore and micro-cracks, of which inter-granular pore in clay mineral is most developed, but organic pore is basically not developed. The pore characteristics of Yanchang Formation in different members have obvious differences. Chang 9 has larger proportion of micropores along with larger specific surface area, while the pore volume of Chang 8 is occupied by largest mesopores and pore morphology of Chang 8 and Chang 9 is mainly in the shape of column and slit parallel to the wall. Chang 7 has the largest proportion of macropores, smallest proportion of micropores and corresponding smallest specific surface area, of which there are many close pores and wedge-shaped pores with one or both ends open. The proportion of pore volume and specific surface area of Chang 6 are between other members, the pore morphology of which is mainly parallel-plate shaped silt pores. The content of clay is the main controlling factor of pore development, but TOC content shows a negative correlation with the pore volume and the specific surface area, mainly due to residual hydrocarbon which block the pore space. The pore volume, the specific surface area will increase after extraction.
Taking the Yanchang Formation Shale for Well YK-1 in Tongchuan Area of the south of Ordos Basin as the target, pore characteristics and controlling factors were investigated by using Argon-ion Polishing Scanning Electron Microscope(SEM)and low-temperature nitrogen adsorption experiments. The results show that pores of Yanchang Formation shale can be classified into inter-granular pore, intra-granular pore, intra-crystalline pore in pyrite, dissolved pore and micro-cracks, of which inter-granular pore in clay mineral is most developed, but organic pore is basically not developed. The pore characteristics of Yanchang Formation in different members have obvious differences. Chang 9 has larger proportion of micropores along with larger specific surface area, while the pore volume of Chang 8 is occupied by largest mesopores and pore morphology of Chang 8 and Chang 9 is mainly in the shape of column and slit parallel to the wall. Chang 7 has the largest proportion of macropores, smallest proportion of micropores and corresponding smallest specific surface area, of which there are many close pores and wedge-shaped pores with one or both ends open. The proportion of pore volume and specific surface area of Chang 6 are between other members, the pore morphology of which is mainly parallel-plate shaped silt pores. The content of clay is the main controlling factor of pore development, but TOC content shows a negative correlation with the pore volume and the specific surface area, mainly due to residual hydrocarbon which block the pore space. The pore volume, the specific surface area will increase after extraction.
2017, 35(2): 330-342.
doi: 10.14027/j.cnki.cjxb.2017.02.011
Abstract:
Permian clastic reservoir is an important exploration horizon in the northwest margin of Junggar Basin, with the burial depth more than 3 600 meters. And it is very important to study Permian clastic reservoir secondary pore developement and its controlling factors. Based on the thin section analysis of 1 400 pieces in more than 120 wells, core observation, fluorescent thin-section, scanning electron microscopy, clay mineral, and in combination with sedimentary facies, tectonic evolution and organic evolution characteristics, Permian clastic reservoir secondary porosity developed law and controlling factors are studied. Casting thin section show that Permian clastic reservoir has development not only primary intergranular pore, but also grain dissolved pore, cement dissolution pore and fracture of secondary porosity. It is concluded that primary intergranular pore is mainly controlled by sedimentary facies belt, compaction and cementation. The primary intergranular pore developed in coarse, well-sorted, high maturity of structure and composition. The corresponding microfacies are braided channel of fan delta plain and underwater channel of fan delta front. The primary intergranular pore are developed in basin edge, and decreased to basin center. The dissolved pore of grains, carbonate cements and zeolite cements are controlled by the scale and scope of inorganic acid and organic acids. The inorganic acid dissolution pore is developed regionally in basin edge where the unconformity surface and faults are developed. The organic acid dissolution pore is developed in near hydrocarbon of source rock, mainly distributed in basin center. Fractures are generated under the action of tectonic compression, and it is controlled by tectonic stress strength, grade size and matrix content. Fractures are mainly distributed in low matrix content sandy conglomerate in fault zone of northwest margin. Horizontally in the basin edge, the mainly Permian reservoir pore type is primary intergranular pore, followed by the inorganic acid dissolution pore and fracture. In basin center, the major pore type is organic acid dissolution pore, secondly is primary intergranular pore. Integrating with distribution characteristics of sedimentary facies and zeolite cements, structural feature and the evolution history of organic matter, it is considered that middle-belt of basin is the favorable zone to form lawnontite dissolution pore because it is the fan delta front sub-facies and laumontite cement development area, meanwhile it is near hydrocarbon source rocks and located in the updip direction of three periods organic acid migration. It points out that central basin is laumonite dissolution pore development area, and it's the favorable Permian clastic reservoir for Permian petroleum exploration.
Permian clastic reservoir is an important exploration horizon in the northwest margin of Junggar Basin, with the burial depth more than 3 600 meters. And it is very important to study Permian clastic reservoir secondary pore developement and its controlling factors. Based on the thin section analysis of 1 400 pieces in more than 120 wells, core observation, fluorescent thin-section, scanning electron microscopy, clay mineral, and in combination with sedimentary facies, tectonic evolution and organic evolution characteristics, Permian clastic reservoir secondary porosity developed law and controlling factors are studied. Casting thin section show that Permian clastic reservoir has development not only primary intergranular pore, but also grain dissolved pore, cement dissolution pore and fracture of secondary porosity. It is concluded that primary intergranular pore is mainly controlled by sedimentary facies belt, compaction and cementation. The primary intergranular pore developed in coarse, well-sorted, high maturity of structure and composition. The corresponding microfacies are braided channel of fan delta plain and underwater channel of fan delta front. The primary intergranular pore are developed in basin edge, and decreased to basin center. The dissolved pore of grains, carbonate cements and zeolite cements are controlled by the scale and scope of inorganic acid and organic acids. The inorganic acid dissolution pore is developed regionally in basin edge where the unconformity surface and faults are developed. The organic acid dissolution pore is developed in near hydrocarbon of source rock, mainly distributed in basin center. Fractures are generated under the action of tectonic compression, and it is controlled by tectonic stress strength, grade size and matrix content. Fractures are mainly distributed in low matrix content sandy conglomerate in fault zone of northwest margin. Horizontally in the basin edge, the mainly Permian reservoir pore type is primary intergranular pore, followed by the inorganic acid dissolution pore and fracture. In basin center, the major pore type is organic acid dissolution pore, secondly is primary intergranular pore. Integrating with distribution characteristics of sedimentary facies and zeolite cements, structural feature and the evolution history of organic matter, it is considered that middle-belt of basin is the favorable zone to form lawnontite dissolution pore because it is the fan delta front sub-facies and laumontite cement development area, meanwhile it is near hydrocarbon source rocks and located in the updip direction of three periods organic acid migration. It points out that central basin is laumonite dissolution pore development area, and it's the favorable Permian clastic reservoir for Permian petroleum exploration.
2017, 35(2): 343-357.
doi: 10.14027/j.cnki.cjxb.2017.02.012
Abstract:
Focusing on the complex characteristics and controlling factors of buried-hill inner volcanic reservoir, this paper takes the Cretaceous volcanic rocks in Qinhuangdao 30A area of Bohai Sea for example. The space type, filling stage, diagenetic evolution and controlling factors of buried-hill inner volcanic reservoirs were studied based on core observation, thin section identification and scanning electron microscope analysis. The lithology of volcanic reservoirs in the study area is mainly explosive facies andesitic volcanic breccia. The reservoir space can being classified as primary pore, secondary pore and fissure. As main primary pores, the gas pores experienced early filling stage and late filling stage, leading to primary pores being sharply reduced. According to the filling minerals and interaction cutting relation, the fractures are categorized as four periods while the late fractures were more weakly filled than early ones. The reservoirs experienced three diagenetic stages:syndiagenetic stage, epidiagenetic stage and burial diagenetic stage. The volcanic hydrothermal activity during syndiagenetic stage influenced the reservoirs most and is the primary cause for the reservoir physical properties becoming worse, while the weathering and leaching in epidiagenestc stage and the dissolution in burial diagenestic stage improved the reservoir physical properties to a limited extent. The development of unfilled effective fractures in reservoir is the main controlling factor, resulting in the differences of volcanic reservoir physical properties and oil-gas production capacity in the study area. The structurally high part close to volcanic conduit contains more fractures than slope zone, but the fractures were more affected by hydrothermal activity and filled by minerals, leading to less effective fractures, poorer reservoir permeability and much lower oil-gas production capacity than that in slope zone. Structure position, formation period and size of fractures controlled the development of effective fractures. The fractures are mostly distributed within a certain range nearby major faults and those developed in area far away from volcanic conduit and formed late with small width were less filled and are effective fractures. The area with those fractures developed is the favorable region of high-quality reservoirs and target for oil-gas exploration.
Focusing on the complex characteristics and controlling factors of buried-hill inner volcanic reservoir, this paper takes the Cretaceous volcanic rocks in Qinhuangdao 30A area of Bohai Sea for example. The space type, filling stage, diagenetic evolution and controlling factors of buried-hill inner volcanic reservoirs were studied based on core observation, thin section identification and scanning electron microscope analysis. The lithology of volcanic reservoirs in the study area is mainly explosive facies andesitic volcanic breccia. The reservoir space can being classified as primary pore, secondary pore and fissure. As main primary pores, the gas pores experienced early filling stage and late filling stage, leading to primary pores being sharply reduced. According to the filling minerals and interaction cutting relation, the fractures are categorized as four periods while the late fractures were more weakly filled than early ones. The reservoirs experienced three diagenetic stages:syndiagenetic stage, epidiagenetic stage and burial diagenetic stage. The volcanic hydrothermal activity during syndiagenetic stage influenced the reservoirs most and is the primary cause for the reservoir physical properties becoming worse, while the weathering and leaching in epidiagenestc stage and the dissolution in burial diagenestic stage improved the reservoir physical properties to a limited extent. The development of unfilled effective fractures in reservoir is the main controlling factor, resulting in the differences of volcanic reservoir physical properties and oil-gas production capacity in the study area. The structurally high part close to volcanic conduit contains more fractures than slope zone, but the fractures were more affected by hydrothermal activity and filled by minerals, leading to less effective fractures, poorer reservoir permeability and much lower oil-gas production capacity than that in slope zone. Structure position, formation period and size of fractures controlled the development of effective fractures. The fractures are mostly distributed within a certain range nearby major faults and those developed in area far away from volcanic conduit and formed late with small width were less filled and are effective fractures. The area with those fractures developed is the favorable region of high-quality reservoirs and target for oil-gas exploration.
2017, 35(2): 358-370.
doi: 10.14027/j.cnki.cjxb.2017.02.013
Abstract:
Using cores, thin section, log and well log data, based on the identification of every base types and characteristics of the cycle interface, the Permian Lucaogou Formation strata in Jimsar sag are divided into 1 long-term cycles, 6 medium-term cycles and 44 short-term cycles, the high resolution sequence stratigraphy correlation framework is established. On the basis of summarizing the geochemistry, lithology, sedimentary structure and electrical characteristics, comprehensive analysis of fossils and logging data to identify the sedimentary facies marks, single well, well connected and plane sedimentary facies analysis, the Permian Lucaogou Formation strata are mainly salified-lake facies, locally delta facies deposit, with the complex lithology formed by mechanical deposition, chemical deposition, and the deposition of fine clastic rocks, mud and carbonate rocks which are deposited under the influence of the deposition. Lucaogou Formation developed two tight oil body sweet spot, the upper body is a kind of salty lacustrine carbonate rocks, the types of micro facies in shallow lake dam; The inferior dessert is mainly based on the delta front to the former delta subfacies. Micro facies type is sheet sand and far sand dam. At the same time, the advantage of horizontal continuous change of reservoir in the area of the study area and the level of the well is to be revealed by the reservoir, control of planar micro facies boundary in tight oil reservoir, thus more accurately reflect the plane distribution characteristics of tight oil reservoir. Research shows that the quality of Lucaogou Formation near to the sweet spot is beach bar microfacies mainly developed in the center of the sag at low uplift.
Using cores, thin section, log and well log data, based on the identification of every base types and characteristics of the cycle interface, the Permian Lucaogou Formation strata in Jimsar sag are divided into 1 long-term cycles, 6 medium-term cycles and 44 short-term cycles, the high resolution sequence stratigraphy correlation framework is established. On the basis of summarizing the geochemistry, lithology, sedimentary structure and electrical characteristics, comprehensive analysis of fossils and logging data to identify the sedimentary facies marks, single well, well connected and plane sedimentary facies analysis, the Permian Lucaogou Formation strata are mainly salified-lake facies, locally delta facies deposit, with the complex lithology formed by mechanical deposition, chemical deposition, and the deposition of fine clastic rocks, mud and carbonate rocks which are deposited under the influence of the deposition. Lucaogou Formation developed two tight oil body sweet spot, the upper body is a kind of salty lacustrine carbonate rocks, the types of micro facies in shallow lake dam; The inferior dessert is mainly based on the delta front to the former delta subfacies. Micro facies type is sheet sand and far sand dam. At the same time, the advantage of horizontal continuous change of reservoir in the area of the study area and the level of the well is to be revealed by the reservoir, control of planar micro facies boundary in tight oil reservoir, thus more accurately reflect the plane distribution characteristics of tight oil reservoir. Research shows that the quality of Lucaogou Formation near to the sweet spot is beach bar microfacies mainly developed in the center of the sag at low uplift.
2017, 35(2): 371-382.
doi: 10.14027/j.cnki.cjxb.2017.02.014
Abstract:
Due to the multiple types of conglomerate rock, strong reservoir heterogeneity, it is difficult to establish a relationship between seismic attributes and reservoir. Application of seismic attributes often leads to uncertainty and multiple solutions. In order to surmount the one sideness of single attribute reflecting the distribution of coarse-grain sediments, mutual interference between similar attributes-related information and blindness of seismic facies predicting the distribution of the fan body, a method based on seismic multi-attributes matching technology is proposed:1) established lithology identification scheme; 2) sandy conglomerate ratio was matched based on an attribute optimization and linear regression; 3) RMS attribute to constraining sand boundary; 4) the coarse-grain fan sedimentary facies was mapped according to matching sand ratio contour, lithofacies and logging facies. And application of this method to Baikouquan Formation Member 2 in Ma 131 area shows that it is not only probiding a new way to study coarse-grain deposition, but also providing a reliable basis for rolling exploration and demonstration wells in Mahu sag.
Due to the multiple types of conglomerate rock, strong reservoir heterogeneity, it is difficult to establish a relationship between seismic attributes and reservoir. Application of seismic attributes often leads to uncertainty and multiple solutions. In order to surmount the one sideness of single attribute reflecting the distribution of coarse-grain sediments, mutual interference between similar attributes-related information and blindness of seismic facies predicting the distribution of the fan body, a method based on seismic multi-attributes matching technology is proposed:1) established lithology identification scheme; 2) sandy conglomerate ratio was matched based on an attribute optimization and linear regression; 3) RMS attribute to constraining sand boundary; 4) the coarse-grain fan sedimentary facies was mapped according to matching sand ratio contour, lithofacies and logging facies. And application of this method to Baikouquan Formation Member 2 in Ma 131 area shows that it is not only probiding a new way to study coarse-grain deposition, but also providing a reliable basis for rolling exploration and demonstration wells in Mahu sag.
2017, 35(2): 383-392.
doi: 10.14027/j.cnki.cjxb.2017.02.015
Abstract:
Oil reservoirs in Chang 6 and Chang 8 members of Yanchang Formation in Gufengzhuang-Mahuangshan area of Ordos Basin are typical ultra-low permeability reservoirs. Comprehensive analysis of homogenous temperatures of fluid inclusions and geothermal and burial history shows that oil accumulation of Chang 6 and Chang 8 members happened in early Cretaceous. During the oil accumulation petroleum generating from Chang 7 source rock only charged into Chang 8 reservoir at the early stage, then charged up and down into Chang 6 and Chang 8 at the middle stage, and only filled into Chang 6 reservoir at the late stage. The difference of accumulation process was controlled by the relationship between source and reservoir, and the peak time of hydrocarbon generation, and the reservoir tightness prior to the accumulation.
Oil reservoirs in Chang 6 and Chang 8 members of Yanchang Formation in Gufengzhuang-Mahuangshan area of Ordos Basin are typical ultra-low permeability reservoirs. Comprehensive analysis of homogenous temperatures of fluid inclusions and geothermal and burial history shows that oil accumulation of Chang 6 and Chang 8 members happened in early Cretaceous. During the oil accumulation petroleum generating from Chang 7 source rock only charged into Chang 8 reservoir at the early stage, then charged up and down into Chang 6 and Chang 8 at the middle stage, and only filled into Chang 6 reservoir at the late stage. The difference of accumulation process was controlled by the relationship between source and reservoir, and the peak time of hydrocarbon generation, and the reservoir tightness prior to the accumulation.
2017, 35(2): 393-404.
doi: 10.14027/j.cnki.cjxb.2017.02.016
Abstract:
Geochemistry characteristics of the source rock and oil from Dongdaohaizi Sag are studied, such as carbon isotope, Pr/Ph and sterane relative composition, to analyse the hydrocarbon origin and accumulation.The oil-source correlation revealed that:The oil comes mainly from Permian source rock of Pingdiquan Formation, but in the western and central area of Dinan Uplift, the oil is mixed by materials from carboniferous source rock. The maturity of oil is studied through biomarker parameters and alkylphenanthrene index (MPI), as well as the source rock evolution, which indicated that the oil was generated in different stages of source rock evolution. The source rock of Pingdiquan Formation is mature, but oil generated in the peak period of hydrocarbon generation has not migrated into the structural high, which still lies in the slope region of the sag possibly. As a conclusion, low-amplitude structures or the lithology traps in the slope region of Dongdaohaizi Sag is probably a good choice for exploring the oil generated in the peak period of hydrocarbon generation.
Geochemistry characteristics of the source rock and oil from Dongdaohaizi Sag are studied, such as carbon isotope, Pr/Ph and sterane relative composition, to analyse the hydrocarbon origin and accumulation.The oil-source correlation revealed that:The oil comes mainly from Permian source rock of Pingdiquan Formation, but in the western and central area of Dinan Uplift, the oil is mixed by materials from carboniferous source rock. The maturity of oil is studied through biomarker parameters and alkylphenanthrene index (MPI), as well as the source rock evolution, which indicated that the oil was generated in different stages of source rock evolution. The source rock of Pingdiquan Formation is mature, but oil generated in the peak period of hydrocarbon generation has not migrated into the structural high, which still lies in the slope region of the sag possibly. As a conclusion, low-amplitude structures or the lithology traps in the slope region of Dongdaohaizi Sag is probably a good choice for exploring the oil generated in the peak period of hydrocarbon generation.
2017, 35(2): 405-412.
doi: 10.14027/j.cnki.cjxb.2017.02.017
Abstract:
The Hala'alat Mountain structural belt is controlled by the multi-period structural superposition during the long geohistory, which caused stratum repetition, absence or reversion, the geological structure is complicated, and the rule of hydrocarbon accumulation is not clear, which restricts the efficient hydrocarbon exploration. Through typical reservoirs and wells dissecting, the geological structure of anatomy and the combination of organic geochemical analysis, based on the geological chromatographic effect principle of molecular compounds in crude oil in the process of migration, the study is performed in the characteristics of hydrocarbon transport in different tectonic units. The style of hydrocarbon migration in different tectonic units is cleared, and four models of hydrocarbon migration and accumulation are established. The geochemical fingerprint parameter characteristics of source rocks are contrasted and analyzed in detail, the sedimentary water salinity, oxidative indicators are different in Mahu Depression and the Hala'alat Mountain structural belt of the source rocks of Fengcheng Formation. Hydrocarbon migration is studied through geochemical tracing based on biomarker compounds and nitrogen compounds of crude oil (oil sand). The results showed that the shallow slop zone and the middle-deep nappe-thrust zone had different source rocks, and belonged to different hydrocarbon transporting systems. Through the "fault-carpet" highly efficient transportation framework for hydrocarbon accumulation, the reservoir-formation characteristics of the slop zone which was mainly derived from the Fengcheng Formation source rocks in Mahu Depression generally showed distal lateral transportation and carpet-edge enrichment. The reservoir-formation characteristics of the nappe-thrust zone which was mainly derived from the Fengcheng Formation source rock in Hashan area generally showed proximal vertical and "multi-fault" transportation. Furthermore, the style of "multi-fault" model can be further subdivided into three types, which are fault micro-fracture net-shaped model in the western nappe superimposed region, the fault-sand ladder model in the middle thrust superimposed region, the fault dominant and sand body assisted model in the eastern faulted fold region. The results have important guidance for the exploration of hydrocarbon in Hala'alat Mountain structural belt.
The Hala'alat Mountain structural belt is controlled by the multi-period structural superposition during the long geohistory, which caused stratum repetition, absence or reversion, the geological structure is complicated, and the rule of hydrocarbon accumulation is not clear, which restricts the efficient hydrocarbon exploration. Through typical reservoirs and wells dissecting, the geological structure of anatomy and the combination of organic geochemical analysis, based on the geological chromatographic effect principle of molecular compounds in crude oil in the process of migration, the study is performed in the characteristics of hydrocarbon transport in different tectonic units. The style of hydrocarbon migration in different tectonic units is cleared, and four models of hydrocarbon migration and accumulation are established. The geochemical fingerprint parameter characteristics of source rocks are contrasted and analyzed in detail, the sedimentary water salinity, oxidative indicators are different in Mahu Depression and the Hala'alat Mountain structural belt of the source rocks of Fengcheng Formation. Hydrocarbon migration is studied through geochemical tracing based on biomarker compounds and nitrogen compounds of crude oil (oil sand). The results showed that the shallow slop zone and the middle-deep nappe-thrust zone had different source rocks, and belonged to different hydrocarbon transporting systems. Through the "fault-carpet" highly efficient transportation framework for hydrocarbon accumulation, the reservoir-formation characteristics of the slop zone which was mainly derived from the Fengcheng Formation source rocks in Mahu Depression generally showed distal lateral transportation and carpet-edge enrichment. The reservoir-formation characteristics of the nappe-thrust zone which was mainly derived from the Fengcheng Formation source rock in Hashan area generally showed proximal vertical and "multi-fault" transportation. Furthermore, the style of "multi-fault" model can be further subdivided into three types, which are fault micro-fracture net-shaped model in the western nappe superimposed region, the fault-sand ladder model in the middle thrust superimposed region, the fault dominant and sand body assisted model in the eastern faulted fold region. The results have important guidance for the exploration of hydrocarbon in Hala'alat Mountain structural belt.
2017, 35(2): 413-424.
doi: 10.14027/j.cnki.cjxb.2017.02.018
Abstract:
The development of Ordovician carbonate reservoir in Ordos Basin was obviously controlled by burial dissolution, while the condition and environment of fluid-rock interaction in the deep stratum were much more complicated than the epigenic karstification, which increased the difficulty of burial dissolution study, reservoir evaluation and prediction. This contribution aimed to study the dissolution effects on carbonate rocks with different mineralogical compositions and petrofabric in acetic acid and CO2 solution, under burial environment with simultaneously changing temperature (30℃~180℃) and pressure (5~50 MPa) by equipment of water-rock interaction. For this simulation experiment, the typical six carbonates samples were collected from the Kelimoli and Majiagou Formation of Ordovician in Ordos Basin. The results showed that:1) The dissolution rates of carbonate rocks all increased in acetic acid, while tended to increase firstly when the temperature reached from 30℃ to 120℃ and pressure reached from 5 MPa to 30 MPa, then decreased gradually in CO2 solution with increasing temperature and pressure. The dissolution peak scope were between 110℃ to 130℃ under the condition where CO2 solution acted as dissolution fluid. However, when exceeded the peak, the differentiation of corrosion rates gradually decreased and kept the same in the deep burial settings. 2) Burial dissolution was not only controlled by petrofabric and mineralogical composition, the size and connectivity of pre-existing pores also palyed an important role, except for the condition of temperature, pressure and fluids, the occurrence of crystal could also have significant impact on the dissolution of post diagenesis. As the selective solution of petrofabric, the rocks with lower content of insoluble mineral such as clay mineral and quartz, high grain micrite ratio and complex components were likely more easier to dissolve.With the increase of the calcite content, dissolution rates of carbonate rocks increased as well, but mineral composition content differences contributed little in the deep buried digenetic environments.Anhydrite was prior to dissolution and further developped as gypsum mould pores, at the same time promoted dolomite to dissolve and improve reservoir, when it developed along with dolomite.In terms of different lithology, limestones were more likely to occur burial dissolution than dolomite and transitional rock types.The burial dissolution rates and intensity of calcarenite and gypsodolomite were superior compared with other rock, thus when they inherited the pre-existing pores conducted by the early selective corrosion pore and modulated, superposed with late burial karstification, they were able to become high quality reservoirs based on the analysis in combination with the actual geological conditions.
The development of Ordovician carbonate reservoir in Ordos Basin was obviously controlled by burial dissolution, while the condition and environment of fluid-rock interaction in the deep stratum were much more complicated than the epigenic karstification, which increased the difficulty of burial dissolution study, reservoir evaluation and prediction. This contribution aimed to study the dissolution effects on carbonate rocks with different mineralogical compositions and petrofabric in acetic acid and CO2 solution, under burial environment with simultaneously changing temperature (30℃~180℃) and pressure (5~50 MPa) by equipment of water-rock interaction. For this simulation experiment, the typical six carbonates samples were collected from the Kelimoli and Majiagou Formation of Ordovician in Ordos Basin. The results showed that:1) The dissolution rates of carbonate rocks all increased in acetic acid, while tended to increase firstly when the temperature reached from 30℃ to 120℃ and pressure reached from 5 MPa to 30 MPa, then decreased gradually in CO2 solution with increasing temperature and pressure. The dissolution peak scope were between 110℃ to 130℃ under the condition where CO2 solution acted as dissolution fluid. However, when exceeded the peak, the differentiation of corrosion rates gradually decreased and kept the same in the deep burial settings. 2) Burial dissolution was not only controlled by petrofabric and mineralogical composition, the size and connectivity of pre-existing pores also palyed an important role, except for the condition of temperature, pressure and fluids, the occurrence of crystal could also have significant impact on the dissolution of post diagenesis. As the selective solution of petrofabric, the rocks with lower content of insoluble mineral such as clay mineral and quartz, high grain micrite ratio and complex components were likely more easier to dissolve.With the increase of the calcite content, dissolution rates of carbonate rocks increased as well, but mineral composition content differences contributed little in the deep buried digenetic environments.Anhydrite was prior to dissolution and further developped as gypsum mould pores, at the same time promoted dolomite to dissolve and improve reservoir, when it developed along with dolomite.In terms of different lithology, limestones were more likely to occur burial dissolution than dolomite and transitional rock types.The burial dissolution rates and intensity of calcarenite and gypsodolomite were superior compared with other rock, thus when they inherited the pre-existing pores conducted by the early selective corrosion pore and modulated, superposed with late burial karstification, they were able to become high quality reservoirs based on the analysis in combination with the actual geological conditions.
