Aiming at the thin interbeds of gravity flow sandstone in organic-rich shale layer of the 7th member of Triassic Yanchang Formation （Chang7 Member） in Ordos Basin， PetroChina Changqing Oilfield Company realized the cost-effective development of interbedded shale oil in continental low-pressure freshwater lacustrine basin， discovered and proved the 1 billion ton Qingcheng shale oil field， and presented proven reserves of 10.52×108 t. It took the lead in building China's first one million ton shale oil integrated development zone. With the continuous expansion of production and construction scale， the difference of geological body is obvious， and the problems of low initial production and rapid decline of single well， low recovery efficiency and high development cost become more and more prominent. Through many years of field practice， the key problems in shale oil development are put forward， and reasonable suggestions are put forward according to systematic analysis. The drilling rate of shale oil horizontal wells can be divided into longitudinal drilling rate and transverse drilling rate. Improving the longitudinal drilling rate and transverse drilling rate of high-quality reservoir is an important measure to increase the production of a single well. When deploying horizontal wells， priority can be given to the extension direction of high-quality reservoirs to improve the drilling rate of high-quality reservoirs. The contribution ratio of elastic energy of fracturing fluid to recovery is relatively low， so the reservoir reconstruction should not overemphasize large sand volume， large fluid volume， and large displacement， but should fully consider well spacing， longitudinal interlayer distribution， and fracture development， and optimize fracturing scale， construction displacement and other parameters. The change of source rock quality and the strength of diagenesis are the main reasons for the difference of oil content in sand bodies， which affect the selection of favorable areas and the distribution of high-quality reservoirs. Pre-CO2 volumetric fracturing has obvious energy increase effect， which is an effective means to reduce viscosity and improve oil recovery. It is an important measure to ensure the efficient development of shale oil in Changqing Oilfield Company by deepening the comprehensive geological research， clarifying the main controlling factors of differential shale oil accumulation， elaborating the three-dimensional sweet spot distribution， and exploring more effective development methods.
Multi-layer commingled production is the main feature of gas well development in Sulige tight sandstone gas reservoirs， Ordos Basin. Whether there is interference between layers and how to characterize them are important issues for effective development of gas reservoir. The physical simulation experiment process and scheme of interlayer commingled mining with fracture communication are designed， and the development simulation experiment of different interlayer combination modes is carried out. The results show that in the process of multi-layer commingled production of tight gas and water layers， whether it is only gas layers production or gas and water layers production at the same time， there is a common phenomenon of cross flow of gas and water between layers， resulting in interlayer interference and reducing the recovery of gas reservoirs. Based on this， the concept of interlayer interference index in multi-layer commingled production in tight sandstone gas reservoirs is proposed， and the interference index model is obtained by fitting the multiple linear regression method. The interference index is related to the physical properties of the reservoir. High water saturation and great permeability ratio of water layer to gas layer （greater than the critical value 1） can result in the early occurring of interlayer interference and great interference index. Finally， based on the interference index model， a new method for productivity evaluation of gas wells in tight gas reservoirs is established. The calculation results show that the interference index curve can effectively describe the interlayer interference performance of gas wells. The productivity and production performance of gas wells calculated by the productivity evaluation method based on the interference index model are consistent with the production history， which proves the effectiveness and accuracy of the interference index model. Therefore， the interference index model can effectively predict the productivity and production performance of gas wells in Sulige tight sandstone gas reservoir. The research results have important theoretical guidance and practical significance for the efficient development of Sulige tight sandstone gas reservoir.
The degree of fracture development is the main controlling factor for high production and water invasion of ultra-deep gas reservoir in Tarim Basin， but there are few studies on the division of fracture development model among different gas reservoirs and its effect on static gas-water distribution and dynamic water invasion. Taking Keshen 2，9 and 8 gas reservoirs as examples，the typical ultra-deep gas reservoirs in Tarim Basin，as the main research object，based on the outcrop，core，FMI，mud loss，well test interpretation and production data， combined with water invasion physical simulation experiment and gas reservoir development practice verification， the gas-water distribution and water invasion law of gas reservoirs under different fracture development models are systematically studied.The results show：（1）Three fracture models are developed in Keshen 2，9 and 8 gas reservoirs， namely direction type， transition type and fracture network type， respectively. The fracture occurrence of each gas reservoir is basically the same， and the mean values of static and dynamic parameters of fracture quantitative characterization， such as fracture size， effectiveness， physical property， open flow rate and mud loss amount， as well as the degree of difference between wells increase successively.（2）The gas-water distribution is mainly controlled by fracture development model， and the gas-water differentiation degree increases gradually in Keshen 2， 9 and 8 gas reservoirs， corresponding to three gas-water distribution models of thick gas-water transition zone， thin gas-water transition zone and normal gas-water differentiation respectively.（3）The fracture development model determines the water invasion rate and recovery factor. The non-uniform water invasion rate of Keshen 2 gas reservoir is fast， and the water flooding efficiency of the physical simulation is low， and the ultimate recovery factor of gas reservoir is low. The water invasion law of Keshen 8 gas reservoir is opposite， and Keshen 9 gas reservoir is in the middle. The research results can provide theoretical model and geological guidance for the formation of water control development and EGR technology in gas reservoir life cycle
The objective of this study was to investigate the effects of the development degree of carbonate dissolved pores and gas injection velocity on the gas-water two-phase seepage. An interparticle-dissolved dual-pore network model was proposed using a convolution algorithm by considering the characteristics of carbonate karst pores. The proposed unsteady-state gas-water seepage model took the effects of gas compressibility and pore-scale pressure propagation into account， and it was validated by comparing the simulation results with the core-derived gas-water two-phase seepage through unsteady-state gas flooding experiments， which comprehensively characterizes the pore-scale gas-water seepage flow in pore-scale modeling. The gas flooding procedure at different injection velocity was simulated by assuming different characteristics of dissolved pores in carbonates. The results indicated that the more developed dissolved pores can bring about a wider gas-water two-phase infiltration area and a longer gas-water co-flow period. Further， the competitive balancing between the gas injection pressure and the capillary and viscous forces could also impact gas sweeping efficiency， resulting in different gas-water spatial distributions， gas injection velocity and pressures. The results provided a deep technical and theoretical view of the gas production in carbonate reservoirs， which has important significance for improving the exploitation efficiency of carbonate reservoirs.
The high-yield reservoir test of the second member of the Dengying Formation （Deng 2 Member） in the Zhongjiang-Penglai area shows great exploration potential. Due to the dual effects of sedimentation and dissolution， the reservoir heterogeneity is strong and the gas-water relationship is complex. In addition to the development of dense zones in the horizontal direction， there are also dense area barriers in the vertical direction， forming multiple independent gas reservoirs with different gas-water interfaces. In this regard， based on the seismic geological characteristics of drilled wells， this paper intends to establish the seismic identification model of Dengying reservoir and dense area， and then deeply analyze the sedimentary evolution process of paleogeomorphology in the upper sub-member of Deng 2 Member， finely characterize lithologic traps， and clarify the spatial distribution law of effective reservoirs. The study shows that the high-quality reservoir of the hilly-shoal reservior is developed in the second layer of the upper sub-member of Deng 2 Member， with a thickness of 30-110 m. Laterally， it is developed in the high landform area near the platform margin， showing a continuous distribution characteristics. The dense area develops in the low part of paleogeomorphology， and has a good coupling relationship with rift of Sinian System， which has a shielding effect on gas reservoir. The practice shows that the understanding in this paper is highly consistent with the actual drilling， which can provide technical support for the exploration of Dengying Formation gas reservoir in the northern slope.
Lianggaoshan Formation of Lower Jurassic in Southeast Sichuan is a new field of tight sandstone oil and gas exploration with great potential. However， its strong reservoir heterogeneity and weak basic research on favorable reservoir characteristics and diagenetic evolution laws restrict exploration and development. In this paper， the Lianggaoshan Formation in Liutang area of Southeast Sichuan was taken as the research object. The diagenetic facies were classified and diagenetic evolution model of tight sandstone was established based on the study of petrology， physical properties and diagenetic characteristics combined with integrating core， cast thin section， scanning electron microscope and clay minerals. The results show that the reservoirs of Lianggaoshan Formation in Southeast Sichuan are dominated by feldspathic lithic sandstone， the reservoir properties are tight， and the reservoir space is mainly residual primary intergranular pores and intergranular dissolved pores. Diagenesis such as compaction， cementation and dissolution is developed in the reservoir， and the diagenetic stage is the middle diagenetic stage B. The reservoir in the study area mainly develops four diagenetic facies： strong compaction diagenetic facies， carbonate cementation diagenetic facies， dissolution diagenetic facies and chlorite membrane cementation diagenetic facies. The sandstone with strong compaction diagenetic facies has fine grain size， high content of plastic particles and dense physical properties. The sandstone with carbonate cementation diagenetic facies has fine grain size， high content of carbonate cement and dense physical properties. The sandstone with dissolution diagenetic faces has high feldspar content， strong dissolution and relatively good reservoir physical properties. The sandstone with chlorite film cemented facies has coarse grains， high chlorite film content， medium compaction， primary pores and dissolution pores. In conclusion， the sandstone with chlorite membrane cementation diagenetic facies and dissolution diagenetic facies are favorable reservoirs in the study area.
The exploration and development of volcanic rocks have entered a new stage since YS1 and YT1 wells in Southwest Sichuan have made significant breakthroughs and progress in porous pyroclastic reservoirs. Based on the latest data collected by gravity， magnetic and electric seismic， drilling and field， combined with the respective advantages of geophysical and geological cognitive tools， the characteristics of basement faults and the distribution of volcanic rocks in the western Sichuan-Shunan regions were analyzed， and the relationship between basement faults and volcanic rocks was discussed. The study shows that two groups of basement faults are developed in the western Sichuan-Shunan regions， mainly in the NE direction and supplemented by the NW direction. It is believed that the NE direction faults are formed first and the NW direction is formed later， and the two groups of faults become a cross-intersectional fault system in the Jinyang-Santai and Shunan regions. The thickness of volcanic rocks in the study area is concentrated in the southwestern part of the basin and thinned toward the basin， and the thickness of volcanic clastic rocks is concentrated in the Xinjin-Jenyang area and thinned toward the surrounding area， while thin layers of volcanic clastic rocks are also developed in southern Sichuan； the distribution and development characteristics of volcanic rocks in the region are controlled by the NE-oriented deep faults that break through to the Permian， and the eruption patterns are different due to the different degrees of intersection of fractures， and the areas with high degrees of intersection of fractures have point-like and small craters that are easy to form multi-point compound central eruption patterns along the fractures and develop eruptive phase volcanic clastic rocks.
A set of tight limestone reservoirs has been developed in the Permian Taiyuan Formation of the Ordos Basin. In recent years， the risk exploration has made a substantial breakthrough and has become a key field of natural gas exploration. Through field outcrop， core observation， thin section identification， scanning electron microscope and stable carbon and oxygen isotope analysis and testing， petrology， reservoir space， reservoir physical properties and microscopic characteristics were studied， and the development characteristics of tight limestone reservoirs and controlling factors of favorable reservoirs were systematically analyzed. The research shows that the rock types that can be used as good reservoirs are bioclastic micrite limestone， bioclastic micrite limestone， algal boundstone， and the reservoir space is mainly dissolved pores， residual organism cavity pores， inter-crystalline pores and micro fractures. The average porosity of the reservoir is 2.1%， and the average permeability is 0.22×10-3 μm2， belonging to low porosity and low permeability reservoirs. The formation of favorable reservoirs of Taiyuan Formation limestone in the study area is controlled by many factors， among which favorable sedimentary microfacies of bioclastic beach and biodome are the material basis for the formation of reservoirs， which determine the type of reservoir space and large plane distribution； Quasisyngenetic karstification under the control of high frequency cycle is favorable for the formation of dissolution holes， effectively improving the reservoir performance， and creating conditions for the development of thick limestone reservoirs； Fractures play an important role in improving the permeability of tight limestone reservoirs. The research results point out the direction for the next step of limestone exploration of Taiyuan Formation in Ordos Basin， and also have important reference significance for the research and exploration of bioclastic limestone reservoirs in North China platform.
The hydrocarbon accumulation period of the Lower Paleozoic Ordovician carbonate reservoirs in the western margin of Ordos Basin is not clear. Carbonate rock samples from eight Lower Paleozoic reservoirs in five typical wells in the study area were selected for petrographic analysis of fluid inclusions， microthermometry and laser Raman spectroscopy. Combined with the burial-thermal history recovery of typical wells， the hydrocarbon accumulation periods of the Lower Paleozoic Ordovician in the western margin of Ordos Basin were determined. The results show that the fluid inclusions in the Lower Paleozoic Ordovician carbonate reservoirs in the western margin of the Ordos Basin can be divided into two stages. The first stage of inclusions is mainly composed of liquid hydrocarbon inclusions and a large number of associated aqueous inclusions. The fluorescence is yellow， mainly in the form of beads distributed in the cave-filled calcite and the early fracture-filled calcite. The peak value of the homogenization temperature of the associated aqueous inclusions is between 120 ℃ and 130 ℃. The inclusions in the second stage mainly develop gaseous hydrocarbon inclusions and their associated large amount of aqueous inclusions and a small amount of asphalt inclusions， which are distributed in the late fracture-filled calcite in bands， with no obvious fluorescence， and the peak value of the homogenization temperature of the associated brine inclusions is between 150 ℃ and 170 ℃. The Lower Paleozoic Ordovician reservoir in the study area has undergone two hydrocarbon filling processes. The first stage occurred in the late stage of Early Jurassic， which was a period of large oil and gas filling. The second stage occurred in the early and middle stage of Early Cretaceous， which was a period of large gas filling.
The pore structure of tight sandstone reservoir is an important factor to determine its reservoir physical properties and oil and gas production capacity， and it is also a hot spot in the research of tight reservoir. The pore structure characteristics of tight sandstone of Denglouku Formation in Changling Gas Field， Songliao Basin were characterized by qualitative and quantitative methods based on the experimental data of nuclear magnetic resonance， constant velocity mercury injection， cast thin section and scanning electron microscopy. Based on the T2 spectra measured in saturated and centrifuged states， the heterogeneity and complexity of pore structure were quantitatively characterized， and the relationship between petrophysical parameters， NMR parameters and fractal dimension was discussed. The results show that： The pore types of tight sandstone reservoirs in Denglouku Formation are diverse， including residual intergranular pores， feldspar dissolution pores and intergranular pores of clay minerals. The pore-throat relationship is mainly characterized by large pores and thin throats and small pores and coarse throats. The NMR T2 spectrum shows bimodal or unimodal distribution. The relationship between pore structure characteristics and movable fluid shows that the maximum connected throat radius is the main factor controlling the size of movable fluid. The fractal dimension D （2.355 1-2.803 5） calculated by T2 spectrum in centrifugal state is higher than that in saturation state （2.239 9-2.755 7）， which indicates that the micro pore domain determines the micro complexity of tight sandstone， and the large pore domain controls the macro reservoir quality of tight sandstone. The tight sandstone reservoirs of Denglouku Formation in Changling Gas Field can be divided into three types based on the reservoir capacity and the occurrence characteristics of fluids. The type Ⅰ pore structure is mostly of small pore and coarse throat type， the lower limit of the maximum connected throat radius is 0.8 μm， and the fractal dimension is small， so it is a high-quality reservoir. The results are helpful to reveal the heterogeneous combination of the pore system and quantitatively characterize the complexity of the pore structure， so as to guide the exploration and development of tight gas reservoirs.
The main source rock of the Lishu Fault Depression in the Songliao Basin has not yet been identified. In order to reveal the Cretaceous hydrocarbon accumulation law of the southeast slope of the Lishu Fault Depression in the Songliao Basin， this paper conducted the source rock evaluation and the comparison of oil and gas sources in the shale samples of the Shahezi Formation and Yingcheng Formation of the southeast slope area of the Lishu Fault Depression， and then recovers the hydrocarbon history of the source rock. The result shows that the source rocks of the Cretaceous Shahezi Formation and Yingcheng Formation of the Lishu Fault Depression have relatively good organic carbon content and hydrocarbon production potential， belonging to medium-good source rocks. The identification of kerogen components and biomarker shows that the chalky source rocks of the southeast slope belongs to kerogen type II-Ⅲ， which is a mixed source of aquatic organisms and terrestrial higher plants and forms in a reducing environment， with a medium degree of thermal evolution， and the source rocks still in the oil-producing stage. The results of oil source comparison show that the oil and gas in the southeast slope area are all derived from the source rocks of the Shahezi Formation. The results of the reconstruction of the history of hydrocarbon production show that the source rocks of Shahezi Formation and Yingcheng Formation reached the hydrocarbon production threshold at 97 Ma and 94 Ma， respectively， and entered the peak of hydrocarbon production at 92 Ma and 89 Ma. After 66 Ma， Lishu Fault Depression was raised as a whole， and the ground temperature gradient decreased， and the hydrocarbon production effect is weakened. Geochemical analysis combined with hydrocarbon history reconstruction technology can be well used to determine the characteristics of the main source rocks in the multi-spin superposition basin， and it plays an important role in clarifying the distribution law of oil and gas reservoirs.
At present， there is little research on the hydrogen isotope of individual sedimentary aromatic compounds in geological bodies. The paper carried out anhydrous thermal simulation experiments on herbaceous peat collected from two regions with different latitudes. The results showed that the polycyclic aromatic hydrocarbons （PAHs） in the pyrolyzed liquid hydrocarbons of the two peat samples were mainly composed of phenanthrene and its alkyl compounds， and the PAHs in the high latitude sample contained more pyrene series and benzopyrenes. The methylphenanthrene index （MPI 1 and MPI 2） values between the pyrolysis samples from the two regions were significantly different， but the methylphenanthrene ratio （F1 and F2） was Relatively close. The δD values of the pyrolysis PAHs were distributed between -142 ‰ and -66 ‰ for the high latitude sample， and between -103 ‰ and -62 ‰ for the low latitude sample and the δD values of the pyrolysis PAHs were lower in the high latitude sample than that in the low latitude sample. The average δD difference between the two regions was -29 ‰ at 350 ℃ and -16 ‰ and 400 ℃. The hydrogen isotope composition of PAHs pyrolyzed at 400 ℃ is obviously heavier than that at 350 ℃， which reflects that the δD value of sedimentary PAHs is closely related to the thermal maturity of organic matter. Compared with the hydrogen isotopic composition of methane and n-alkanes in the same pyrolysis sample， the hydrogen isotopic composition of PAHs was the heaviest. The hydrogen isotope composition of polycyclic aromatic hydrocarbons has a certain negative correlation with their molecular weight， carbon number， ring number and double bond number. These research results provide a new basis for the study of the genesis of coal-forming substances formed in herbaceous swamps.
In recent years， a great breakthrough has been made in the natural gas exploration of bauxite deposits in the Longdong area of the Ordos Basin， but there is little research on bauxite deposits of the Benxi Formation in the east of the basin. It is urgent to strengthen basic geological research. Through core observation， thin section， and other experimental methods， combined with major elements， trace elements， and rare earth elements， geochemical analysis was carried out to study the paleosalinity， paleo-redox conditions， paleoclimate， and provenance characteristics of bauxite deposits. The results show that： （1） The Benxi period of the Late Carboniferous experienced multiple transgressions and regressions. The sedimentary environment changed from a marine saline water environment to a continental freshwater environment， and then changed to a marine saline water environment at the end of the Hutian period， with alternate redox conditions. （2） Bauxite deposits are significantly affected by chemical weathering. In the early stage of the Benxi period， due to the influence of the Late Paleozoic Ice Age， the temperature dropped， and then the temperature rose due to the global warming event. （3） Iron minerals in the bottom of bauxite deposits come from the underlying carbonate rocks of Majiagou Formation， and the material of bauxite and mudstone in the middle and upper parts comes from silicate rocks and magmatic rocks， with various material sources.
In recent years， the Permian terrestrial transition shale has attracted much attention due to the discovery of high-quality source rocks. The mechanism of shale fractures produced by different tectonic stresses on the enrichment or modification of shale gas has yet to be in-depth study. By analyzing the geochemical indicators of the diagenetic fluid and hydrocarbon fluid in the oblique high-angle shear fractures and bedding slippage fractures， this article clarifies the influence mechanism of different genetic types of fracture on shale gas. Based on petrography observation of the fluid inclusion in fracture veins， quantitative analysis of microscopic Raman spectroscopy， U-Pb isotope dating of carbonate rocks and analysis of vein forming fluid environment， it is concluded that the low-angle slip fracture veins are mainly formed during the burial and hydrocarbon generation stage， with CH4-C2H6 fluid inclusions under high temperature and high pressure. Fracture veins are derived from hydrothermal or diagenetic fluid， and are mainly in a closed reduction environment. A large number of hydrocarbon gas inclusions are not developed in the calcite veins with high Angle shear fractures. The calcite veins are mainly formed in an open oxidation environment due to the source of atmospheric fresh water. The U-Pb dating results of carbonate rocks show that the formation of high Angle shear fractures was caused by the uplifting of the Himalayan tectonic movement. The low-angle slip fracture vein has constructive significance for shale gas enrichment， and most of the oblique high-angle shear fracture vein plays a role of disruption and adjustment in shale gas preservation.
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