The distribution and main controlling factors of organic matter carbonization points （zones） of over-mature marine shale are important issues for shale gas exploration. This paper focuses on the Lower Cambrian and Lower Silurian shale in the Sichuan Basin and its periphery. Based on the detailed anatomy of key carbonization areas， predictions of shale organic matter carbonization areas and regional mapping of thermal maturity are carried out to explore and reveal the distribution and main controlling factors of the carbonization zones of organic matter in the two sets of shales.Four preliminary conclusions were obtained：（1）In the Lower Silurian shale distribution area，there are four organic matter carbonization zones，namely，eastern Sichuan-western Hubei， nor-thwestern Hubei，southern Sichuan and Renhuai-southwestern Chongqing，covering an area of nearly 40 000 km2，of which the main part of the western carbonization zone in southern Sichuan is located in the Emei basalt distribution area. （2）In the Lower Cambrian shale distribution area， the organic carbonization area accounts for more than 80%. The non-carbonization area is only distributed in Weiyuan-Ziyang， Moxi-Gaoshiti， Changyang and Weng'an-Zhenyuan with an area of about 62 600 km2. （3）The Emei igneous rock event was an extreme heat event in the Late Permian， which increased the thermal maturity RO value of the Lower Silurian and Lower Cambrian shale in the western part of southern Sichuan by 0.2%-0.4% and 0.2%-1.0%， respectively. Mabian-Ebian is located in the high-value area of the Emei basalt thickness， and is also the area with the highest degree of carbonization of organic matter in the Lower Cambrian and Lower Silurian shale. （4）The main controlling factors of organic matter carbonization of the Lower Cambrian and Lower Silurian shale have similarities and differences. The main controlling factor of the former is the long-term deep burial background， and the extremely thermal event in the Late Permian only made the degree of carbonization in some areas more serious.The latter’s main controlling factors are relatively complex， and are controlled by deep burial background in the three regions of Renhuai-southwestern Chongqing， eastern Sichuan-western Hubei， and northwestern Hubei. In western Sichuan， it was controlled by deep burial background and high ground temperature in Late Permian.
Taking Well W， a typical coring well of Wufeng-Longmaxi formations in Weirong area， south Sichuan as the research object， based on core observation， thin section， argon ion polishing， scanning electron microscope， X-diffraction， organic geochemistry， tight physical properties and pore structure， the development characteristics and controlling factors of shale reservoir in the study area are discussed. The research shows that： （1） The shale of Wufeng-Longmaxi formations in Weirong area is mainly calcareous silicon rich carbonaceous shale， calciferous siliceous shale and calcium containing silicon rich carbonaceous shale. The organic matter type is type I， which is in the over mature stage. The black shale is characterized by medium to high organic carbon content， with an average clay mineral content of 40.0%， an average quartz content of 34.7% and an average carbonate mineral content of 18.2%. The mineral content of carbonate rock is relatively high. （2） The shale of Wufeng-Longmaxi formations in the study area is generally a low porosity and low permeability reservoir， mainly developing organic pores， interlayer pores （fractures） of clay minerals， inter-granular pores of pyrite， feldspar alteration pores （fractures） and grain edge fractures （pore） equal reservoir space. （3） The average value of micropores in Wufeng-Longmaxi formations is 0.009 73 mL/g， the average value of mesopores is 0.018 00 mL/g， and the average value of macropores is 0.003 77 mL/g. The reservoir space is mainly composed of micropores and mesopores. Organic matter is the main contributor to micropores， mesopores and specific surface area， and quartz minerals are the main contributor to macropores. Micropores and mesopores develop together， and they are specific surface area. Macropores are different from micropores and mesopores on the basis of development materials， and the contribution of macropore to relative surface area is limited. （4） From top to bottom， the proportion of organic pores increases gradually. At the bottom of Wufeng-Longmaxi formations， the proportion of organic pores can reach 76.73%， with an average of 55.73%. In the upper part of the sampling section， inorganic pores are relatively developed， accounting for an average of more than 80%. The main contributor of organic pores is organic matter， and the main contributor of inorganic pores is clay minerals. （5）Under the deep high temperature and high pressure conditions of Wufeng-Longmaxi formations in South Sichuan， it can develop and maintain organic rich shale reservoir and high-quality shale reservoir. The contribution of carbonate minerals to shale reservoir space is limited. Finding thick organic rich shale will still be the key to shale gas dessert.
The special mineral composition and complex pore structure of shale reservoir make the occurrence mechanism of shale gas in pore fracture system diverse. An in-depth understanding of the occurrence state of shale gas in the micro pore fracture system is helpful to reveal the occurrence mechanism of shale gas， enrich the enrichment theory of shale gas and optimize the development process of shale gas. Focusing on the micro pore structure and shale gas storage mechanism of L11 sublayer shale reservoir in western Chongqing， this paper carried out argon ion polishing scanning electron microscope， nuclear magnetic resonance， nuclear magnetic freeze-thaw and methane adsorption nuclear magnetic resonance experiments of plunger like shale samples under different water （oil） states， focusing on the characteristics of micro pore structure and its influence on shale gas storage. It is concluded that the adsorbed gas is mainly controlled by oil wetted pores less than 5 nm， and the analytical ratio is about 45.81%； Free gas is mainly controlled by pores and microcracks with pore diameter greater than 110 nm， and the analytical ratio is about 89.60%； 5-110 nm organic pores and inorganic pores are important storage spaces for adsorbed gas and free gas， which can realize the effective transformation of adsorbed gas and free gas， and the resolution ratio is about 78.81%. They are the main source of formation energy during mining. For shale gas wells with more developed organic pores at 5-110 nm， the initial production is not high， but it is longer than stable production， and the cumulative production in the same time is higher， which effectively explains the reasons for the production difference between shale gas wells.
On the basis of characteristics of shale reservoir formation， such as lithology and mineral composition， organic geochemistry， reservoir characteristics， gas-bearing characteristics， combined with structural style and burial depth， faults and fractures， top and floor cap rocks， reservoir pressure， a comprehensive characterization of the Niutitang shale is performed. The results indicate the Niutitang shale has high TOC， high RO， brittle mineral contents and methane sorption capacity. The main pores of shale minerals include mud particle pores， bedding cracks， interlayer cracks， which are large in number and mainly primary， and have a significant impact on the porosity and permeability of the reservoir. The total gas content of shale has a significant positive correlation with porosity， specific surface area and TOC， and is inversely proportional to clay mineral content. So the contribution of porosity and specific surface area to gas content of shale is greater than that of clay mineral content. From the perspective of preservation conditions， the gentle anticline and saddle structural strata sandwiched by the anticline in the study area is relatively slow， the burial depth of Niutitang Formation is moderate， and it has good roof and floor caprock， which is conducive to the preservation of shale gas. But poor sealing， strike slip and high angle fracture fault are not conducive to preservation， which will destroy the preservation of shale. In addition， reservoir pressure does not play a decisive role in preservation conditions， and there is also industrial value of shale gas accumulation in low-pressure and atmospheric pressure formations. Finally， a valuation index system of preservation conditions is put forward and the comprehensive favorable areas for shale accumulation in the study area are optimized.
As an important reservoir type in Southwest Sichuan， Permian volcanic rocks have become one of the research hotspots in recent years. Through the analysis of the porosity and permeability from Permian volcanic rocks in Southwest Sichuan， it is found that the trachyte andesitic pyroclastic rock reservoir of explosive facies pyroclastic flow subfacies is the best， followed by the self broken breccia of the upper subfacies in overflow facies and the trachyte basaltic fused pyroclastic rock of explosive facies. The porosity and permeability of lava reservoirs are poor. Through core， outcrops and microscopic observation， the reservoir space of volcanic rock is mainly dissolution holes and fractures， and the intergranular micropores of albite make a great contribution to the reservoir of trachy and esitic fused tuff. Volcanic rock facies are the basis of reservoir development. The upper subfacies of overflow facies and explosive facies are similar. Pyroclastic flow sub-middle source accumulation is a favorable facies belt for reservoir development. The reservoir heterogeneity of pyroclastic flow sub-middle source accumulation is strong， and the reservoir physical properties in the upper and lower parts of each eruption unit are better than those in the middle. Through condensation consolidation diagenesis and hydrothermal process， the porosity of trachytic basaltic fusion breccia and self broken breccia in the upper subfacies of overflow facies decreases rapidly from 25%-30% to 5%-10%； Due to the formation of a large number of intergranular micropores of albite offsetting part of the pores lost in this diagenetic process， the porosity of trachytic andesitic fused tuff lost about 10% during this diagenesis. Low temperature and low salinity inclusions reveal that the first stage calcite and quartz cements in the reservoir pores were formed in shallow to medium burial after the volcanic eruption stopped， the organic matter was immature to low mature， there was no large-scale hydrocarbon expulsion， and the dissolution of organic acids to the reservoir was limited； It shows that weathering and leaching in the early epigenetic rock stage is the key to reservoir improvement and preservation. The burial stage is the stage of continuous hole filling， and the improvement of reservoir by organic acid dissolution is limited.
The central Sichuan Basin and the Tarim Basin have a similar tectonic background for the development of strike-slip faults， and there are a large number of strike-slip faults. Therefore， it is important to clarify the controlling effect of strike-slip faults on reservoirs and gas enrichment， which is of great significance for the efficient production in Anyue Gas Field. However， the Anyue Gas Field is also faced with the complicated accumulation model （mound beach + karst + fault）， and it is difficult to analyze the single factor of the fault. Therefore， based on the comprehensive study of sedimentation and karst， this paper identifies three different types of similar sedimentary and karst backgrounds. In the block， single-factor analysis is carried out for the controlling effect of strike-slip faults on reservoirs and gas enrichment， so that the analysis results are more reasonable and reliable. The research results show that： （1）Dengying Formation reservoir development is jointly controlled by sedimentation and karst paleo-geomorphology， and is the main controlling factor； （2）Strike-slip faults have a certain improvement effect on reservoir development， and their improvement effects have the characteristics of zoning and zoning， that is， the improvement degree of the intra-platform area is stronger than that of the platform margin area； （3）Under the same sedimentary and karst background， strike-slip faults have a normal distribution controlling effect on the permeability of the reservoir， and the permeability increased rapidly within the range of 0-2 km， and the permeability can increase locally by 2-3 orders of magnitude； （4）Strike-slip faults have obvious controlling effect on gas enrichment， and the relationship between production and fault distance is in a normal distribution pattern. Its controlling effect is mainly manifested by faults transforming the reservoir permeability， and at the same time， the secondary structures are formed by fault activities. It is a favorable area for oil and gas migration. It is concluded that the sedimentation and karst paleomorphology in the Anyue gas field are the basis for the development of the reservoir， and strike-slip faults have a significant effect on the improvement of permeability and productivity. Therefore， strike-slip faults are one of the key factors for the development， evaluation， deployment and efficient production in the Anyue Gas Field.
Comprehensive analysis of reservoir bitumen， fluid inclusion composition， sulfur distribution and sulfur isotope characteristics in Sinian system， Gaoshiti-Moxi area of Sichuan Basin， shows that thermochemical sulfate reduction （TSR） occurred in the Gaoshiti-Moxi area， but the TSR is weak and it is mainly controlled by hydrothermal fluid flow related to strike-slip faults. Main evidences are as follows： （1） Sulfide and sulfate minerals such as galena， sphalerite， pyrite and barite are developed in many Sinian reservoirs in outcrops of the peripheral area of Sichuan Basin and Gaoshiti-Moxi area. The sulfur isotope is characterized by high δ34S values， which are generally greater than 12‰， indicating that the source of sulfur is seawater and related to TSR. （2） The S/C range of Sinian solid bitumen in Gaoshiti-Moxi area is 0.031-0.059， which has typical characteristics of TSR bitumen. （3） The content of H2S in some fluid inclusions is high， and the fluid inclusions containing elemental sulfur， bitumen and calcite daughter crystals are direct evidence of TSR. （4） The content of H2S in Sinian gas reservoir is 0.24%-6.8%， with an average of 1.22%. It is a micro-high H2S gas reservoir. The absence of gypsum deposits in the formation and SO42- in the formation water is quite low， which is completely different from the global high sulfur gas reservoir where TSR occurs， indicating that the effect intensity of TSR in Sinian gas reservoir is weak. （5） Wells， which have found sulfide in the Sinian system in Gaoshiti-Moxi area， are mainly located near the NW and NWW strike-slip faults， and the distribution is obviously controlled by faults. TSR may be derived from deep hydrothermal fluids communicated by faults， and TSR is mainly developed near faults， which is fault-controlled TSR. H2S generated by TSR of hydrocarbons in Sinian reservoirs in Sichuan Basin promotes the formation of lead-zinc deposits and other sulfide deposits， that is， hydrocarbon accumulation， cracking and fracture fluid activity， TSR and the formation of MVT type lead-zinc deposits are closely linked， which is an ideal area for the study of deep organic-inorganic interaction.
In order to find out the genesis of low-amplitude structure in Ma51+2 sub-member in western Yan'an and its relationship with oil and gas enrichment， based on the fine identification of current low amplitude structure by trend surface analysis， this study carried out the comparison between paleogeomorphology and current structure， and preliminarily discussed the genesis and petroleum geological significance of positive low-amplitude structures in combination with drilling， logging， gas testing and cast thin section data. The results show that： （1） A total of 10 positive low-amplitude structures are developed on the top of Ma51+2 sub-member in this area， mainly in the form of nose uplift， and the structural axis has three trends： Near east-west， near northeast-southwest and near northwest-southeast； （2） The positive low-amplitude structure under the current west dipping monocline background is mainly inherited and evolved from the high parts of pre-Carboniferous karst paleogeomorphology； （3） There is a certain coupling between the positive low-amplitude structure and the distribution of high-quality reservoirs in the limestone deficient area of Ma6 Member； （4） The development of positive low-amplitude structures is conducive to the formation of structural-lithologic traps and has an obvious control over the enrichment of natural gas.
The lower limit of physical property and distribution of tight reservoir in the 8th Member of Permian Shihezi Formation （He 8 Member ） of Yanchang Gas Field in Ordos Basin are clarified， which can provide theoretical basis for tight gas exploration and development in Yanchang Gas Field. The lower limit of physical properties of tight reservoir in He 8 Member of Y113-Y133 gas well area in Yanchang Gas Field， Ordos Basin was studied by comprehensive application of core， logging and gas test data. The results show that He 8 Member in the study area is mainly lithic sandstone， the interstitial materials are mainly hydromica and siliceous， and the types of pores are primary pores and secondary pores， with the latter predominating. Comprehensive use of empirical statistics， mercury injection method and gas test method， and through the establishment of physical property model， maximum pore-throat radius and physical property fitting and production dynamic data inspection， the lower limit of physical property of He 8 tight reservoir is determined as follows： The porosity is 5% and the permeability is 0.06×10-3 μm2， corresponding displacement pressure is 1.7 MPa， median pressure is 20 MPa， and maximum pore throat radius is 300 nm. On this basis， the effective reservoir can be divided into three types： Type Ⅰ reservoir with the best physical and gas-bearing properties is the most favorable reservoir located in the center of the channel， Type Ⅱ reservoir is the best reservoir， and Type Ⅲ reservoir is the worst reservoir located at the edge of the channel.
Based on the 3D seismic interpretation of Bodong Sag， Bohai Bay Basin the structural characteristics of secondary depressions and the differential evolution of depression-controlled faults are discussed by using the methods of structural section restoration. The study shows that there are six sub-depressions in the Bodong Sag， and the sag structure from north to south shows the differential deformation law of single fault and half graben area， half graben-graben transition area and asymmetric double fault graben area. There are three types （extensional， strike-slip and superimposed） and three groups （NNE， NE and NW-trending） faults in Bodong Sag. The NNE-NE extensional faults are mainly dry-controlled depression faults， while the NW-trending extensional faults are small in scale and cut into depressions. In the early stage of strike-slip faults， the extensional nature of controlled deposition is localized， and the distribution pattern of strike-slip reformed strata is strong in the late stage. The evolution process of paleogene sub-depressions can be divided into four stages： the sedimentary period of the 4th Member of Shahejie Formation-Kongdian Formation is the initial fault depression stage， the NE extending fault is the main control， and the NW fault cuts the depression， showing the characteristics of “north and south zone”， and the depositional center is located in the northeast. The sedimentary period of the third Member of Shahejie Formation was a stage of strong fault depression. The NNE extensional fault became the main control and the NW fault weakened. The sedimentary stage of the 1st and 2nd Members of Shahejie Formation is thermal subsidence stage， and the NNE extension fault is still the main control. The sedimentary period of the third Member of Dongying Formation is the strengthening period of fault depression， and the NNE main control faults are actively active， showing the characteristics of “east-west zonation”， and the depositional center has moved to the southwest.
The hydrochemical parameter distribution of Fuyang payzone in the north of Fuxin uplift of Songliao Basin is very complicated， and the relationship with oil and gas accumulation is also quite different from other basins or other payzones in Songliao Basin. Through the statistics and correlation analyses of the hydrochemical parameters in different formations， different depth intervals， five genetic hydrochemical zones of the formation water are determined. Furthermore， the main controls of the formation water properties and distribution are determined based on the petroleum geology background analysis. The study shows that the properties of the formation water in north Fuxin uplift are mainly affected by the rock types of the sediment provenance， the thermal evolution of source rocks， the water-rock interaction in diagenesis and so on. Composition of the parent rocks dominated by acid magmatic and volcanic rocks is the prerequisite for the origination of NaHCO3 type formation water. Large quantity of organic acids expelled before the peak of hydrocarbon generation and the companying CO2 are the key factors affecting the origin of NaHCO3 type formation water. Production of the high salinity formation water of NaHCO3 type is closely related to the perfect condition for CO2 capturing and sealing in local anticline traps and the dissolution of the albite. The Na/Cl coefficient is a good indicator of the secondary pores caused by the dissolution of acid feldspar under the condition of enriched CO2 in formation water， and so it is an index of oil richness.
To further understand the genetic types and gas sources of newfound natural gas in Xiaohelong area of Dehui Depression， Songliao Basin， the source rock evaluation of Yingcheng， Shahezi and Huoshiling formations， as well as the genetic and gas source analysis of Denglouku and Quantou formations are carried out by using source rock organic carbon， pyrolysis data， natural gas composition and carbon isotope data. The results show that the source rocks in Xiaohelong area are medium-good source rocks with TOC content of 0.42%-58.11%， mainly of types II2 and III kerogen， which are in mature-high mature stage. The natural gas in Denglouku-Quantou formations is organic coal gas， and some samples have the characteristics of mixed gas. The equivalent maturity of natural gas is 0.97%， which is similar to the type and maturity of source rocks in Yingcheng Formation. Different from the gas bearing horizons that mainly contributed by the source rocks of Huoshiling and Shahezi formations in previous exploration， the source rocks of Yingcheng Formation are the main source of natural gas of Denglouku and Quantou formations in Xiaohelong area， which are a set of newly discovered exploration strata.
The Carboniferous Benxi Formation shale is an important target interval for shale gas exploration in the Upper Paleozoic in the central and eastern Ordos Basin. On the basis of its representative field profile， drilling core system observation and sampling analysis， using the analyticaldata of major and trace elements， combined with the test data of the whole rock mineral composition， organic carbon content， organic microscopic composition， and so on， the palaeoclimate， water environment and the relationship with the development of organic-rich mud shale during the sedimentary period of the First Member of Benxi Formation in the eastern Ordos Basin are studied. The results show that the shale in the First Member of Benxi Formation of the study area is mainly clayey shale and siliceous shale， and quartz and clay minerals are absolutely dominant in the mineral composition； the CIA， Sr/Cu， and C value parameters indicate that the sedimentary period of the first member is mainly hot characteristics of wet paleoclimate； Sr content， Sr/Ba， Ba/Ga and other parameters indicate that the salinity of the sedimentary water in the upper and lower sub-members of the member is saline water， saline water-brass water， respectively，indicating that the water body salt in the late depositional period of this member was at relatively high degree；V/（V+Ni），Ceanom，Th/U and other parameters indicate that the water body in this sedimentary period was dominated by anoxic-poor oxygen environment. The hot and humid paleo-climate， the saline anoxic-poor sedimentary water environment and other good organic matter preservation conditions are favorable factors for the development of organic-rich shale in this section， especially the upper subsection. The development of high-quality shale provides a good foundation for shale gas exploration in the study area.
In order to reveal the oil and gas resource potential of Upper Paleozoic coal measure source rocks in Huanghua Depression， Bohai Bay Basin， based on experiments such as rock pyrolysis， maceral identification， thermal simulation and previous research data， the geochemical characteristics， macerals and hydrocarbon generation of C-P coal seam in Dagang exploration area in Huanghua Depression are studied in detail. The results show that the macerals of C-P coal measure source rocks in Huanghua Depression are mainly vitrinite， followed by inertinite. The content of vitrinite is 60.35%， inertinite is 28.6%， and crustite + sapropel group is 11.05%. The organic matter types of the source rock are mainly type Ⅱ2 and type Ⅲ， with high abundance of organic matter. The organic matter is mainly in the mature stage. Some areas are in the high mature stage due to magmatism. Moreover， the source rock has the characteristics of gas generation and oil generation， and has good hydrocarbon generation potential.
甘公网安备 62010202000678号
