The study of Carboniferous-Permian marine continental transitional facies shale gas in Ordos Basin mainly focuses on the second member of Shanxi Formation， and Shan23 sub-member is the most abundant layer of organic matter in the second member of Shanxi Formation. Based on the observation and sampling analysis of Chengjiazhuang section in Liulin County， through the organic carbon content， whole rock mineral composition， combined with the analysis and test data of major and trace elements， the paleoclimate， water environment， paleoproductivity and their relationships with the development of organic-rich shale in Shan23 sub-member of Shanxi Formation in the eastern margin of Ordos Basin were studied. The results show that quartz and clay minerals are absolutely dominant in Shan23 shale， and the average TOC is 2.04%. The analytical results of Sr， Sr/Ba and δ18O content show that the sedimentary environment of Shan23 shale experienced the change from saline water to brackish water and then to freshwater from bottom to top. The discrimination of Ceanom， Ni/Co and V/（V+Ni） shows that Shan23 shale was deposited under an oxygen deficient anoxic reduction environment； CaO/Al2O3*MgO and CIA indexes show that the temperature gradually decreases from bottom to top and the weathering degree weakens during the deposition period； The contents of V/Ni， Mn/Ti and δ13C isotopes indicate that the depth of the sedimentary water in the Shan23 sub-member increases first and then gradually becomes shallow. The change trend of P/Al and biological Ba in Shan23 sub-member is consistent， which shows that it increases first and then decreases from bottom to top. The enrichment of organic matter in Shan23 sub-member is mainly affected by water redox conditions and terrestrial debris input.
The major elements， trace elements and rare earth elements of the sandstones of Yanchang Formation in the Xunyi area from the southern Ordos Basin were analyzed to research the sedimentary environment， the weathering intensity of the source area and the paleoclimate， as well as to decipher the source rock type and tectonic setting of these sandstones. Trace element ratios and the related diagrams suggest that the depositional environment for the Yanchang Formation in the Xunyi area of the southern Ordos Basin belong to oxygenation environment. The important indicators that can reflect the paleoclimatic conditions show that during the Yanchang Formation in Xunyi area it belonged to a typical arid climate. The chemical alteration index （CIA） value of the sandstone ranges from 10.93 to 86.17 with an average of 45.38， and the chemical Index of Weathering （CIW） value of the samples ranges from 0.42 to 56.42， with a mean value of 10.52， which reflect that the sandstones experienced weak weathering since it was carried from source area to the sedimentary basin， which is consistent with the conclusion of A-CN-K triangle diagram. The diagrams of Th-U and Sm-Ce show that the studied sandstones are first-cycle deposits. The chondrite-normalized REE patterns of the studied sandstones show a slight LREE enrichment， smooth HREE slopes， a negative Eu anomaly in a “V” shape and Ce is normal. The REE patterns are characterized by obvious “right” and are comparable to UCC and PAAS， these indicate that the sandstones being derived from the upper continental crust mainly composed of felsic igneous source rocks. This conclusion is consistent with the conclusions obtained from the diagrams of F1-F2， Cr/V-Y/Ni， Th/Co-La/Sc， Th/Sc-Zr/Sc and La/Yb-∑REEs. Ternary diagrams of La-Th-Sc and Th-Sc-Zr/10 of the sandstone demonstrate the depositional tectonic setting of their parent rocks evolved in a continental island arc or an active continental margin setting. The significantly high content of Fe， P and other elements and the high loss on ignition indicate that the sediments was rich in nutrients during Yanchang Formation. Moreover， the arid and hot climate conditions and the acid igneous rocks with low weathering degree are conducive to the preservation and transformation of organic matter in the hydrocarbon source rocks in this area. The favorable reservoir conditions and dominant reservoir cap assemblages provide good conditions for the development of large oil and gas fields in this area.
The shale oil of shale type for the seventh member of Yanchang Formation is poor in mobility， difficult to exploit， and weak in relevant research. Based on the full coring well data of Chang 73 sub-member of Well N228 in the Ningxian area of Ordos Basin， through the observation of the fluorescent thin slice scanning map， combined with the indicators of single step rock pyrolysis， analysis of soluble organic matter， TOC content， biomarkers and other parameters， the maturity， sedimentary environment， parent material type and oil-bearing characteristics of shale oil in Chang 73 sub-member of the study area are comprehensively analyzed， and their guiding significance for unconventional oil and gas exploration is discussed. The results show that the shale organic matter type is II1， which is an oil dipping parent material. Saturated hydrocarbons have obvious light carbon advantages. The hydrocarbon generating parent material is mainly composed of lower aquatic organisms mixed with a small amount of higher plants. The organic matter is in the low to medium mature evolutionary stage as a whole， Pr/Ph<1， the average value of γ-Ga/C30H is 0.04， and the average value of C30*D H/C30H is 0.11， indicating that the mud shale of Chang 73 sub-member was formed in the oxygen poor reducing freshwater deep lake sedimentary environment.In mud shale series， the OSI value of oil saturation index is low（<70 mg/g）， and the proportion of free oil content is low， indicating that free hydrocarbons have not reached their own retention status， and there is no transcendental effect and poor mobility. These results provide a new reference for further understanding the geochemical characteristics and oil-bearing evaluation of shale oil in Chang 73 sub-member of Ningxian area， Ordos Basin.
The organic phases of source rocks are the comprehensive embodiment of organic matter mass fraction， organic matter type， organic geochemical characteristics and sedimentary environment. Using organic phases to evaluate the characteristics of source rocks is an effective tool in petroleum exploration nowadays. The study on organic phases of source rocks in Miaoxi area （East sag of Huanghekou Depression and South sag of Miaoxi Depression） of Bohai Sea is relatively weak， which restricts the exploration of high-quality source rocks of this area. Therefore， it is necessary to investigate the characteristics of the longitudinal distribution of organic phases， the characteristics of plane spreading and source rock formation in this area. This article based on the evaluation of hydrocarbon source rocks of Dongying Formation， Shahejie Formation and Kongdian Formation in Miaoxi area， the organic phase comprehensive evaluation and prediction of high quality hydrocarbon source rock development area are carried out by combining the microscopic components of cheese roots and the composition characteristics of biomarkers， taking into account the organic matter generation source of hydrocarbon source rocks， sedimentary phase and sedimentary environment characteristics. The results show that Es3 in the middle of South sag of Miaoxi Depression and the middle of East sag of Huanghekou Depression and Es1+2 in the middle and south of South sag of Miaoxi Depression are the high-quality source rocks. Their organic phases types are semi-deep lake mixed source parent material facies （AB facies） to shore-shallow lake terrestrial parent material facies （B facies）. Paleo-water depth and paleo-climate are the main environmental factors controlling the development of lacustrine hydrocarbon source rocks of the Shahejie Formation in the Miaoxi area. Paleo-water depth affects the type of organic matter-generating parent material and the preservation conditions of organic matter in the input lake， and paleo-climate changes control the sediment content and the reproduction degree of plankton in the input lake.
In order to clarify the development rules and main origins of deep conglomerate reservoir in Mahu area of Junggar Basin， the basic characteristics and effective reservoir origins of the reservoir are determined by systematic research with various materials and data of deep wells. The results show that： The reservoir is mainly fine and medium fine conglomerate， belonging to fan delta distributary channel conglomerate； The reservoir belongs to typical deep tight conglomerate reservoir with low to ultra-low porosity and permeability； The gravel is mainly composed of volcanic rock that is composed of tuff and intermediate acid volcanic lava， and the cement is mainly laumontite and calcite； It has experienced three types of diagenesis： Compaction， cementation and dissolution. The first two has dual effects of destruction and construction， and the result of dissolution is the widespread development of secondary pore enrichment zones that are composed of intergranular solution pores formed by the dissolution of zeolite， carbonate cements and argillaceous matrix， as well as intragranular solution pores formed by the dissolution of feldspar and dark minerals. Different from the middle and shallow layers， the reservoir space is composed of secondary pores and fractures： The effective reservoir is mainly caused by rock composition， dissolution， fracture system and abnormal high pressure； The rock composition is the internal cause and provides sufficient material basis， while the dissolution， fracture system and abnormal high pressure are the external cause； The dissolution forms a secondary pore enrichment zone， the fracture system improves seepage capacity of the reservoir， and abnormal high pressure can effectively maintain and increase pores. Four factors control the formation and distribution of relatively high-quality deep tight conglomerate reservoirs.
The tight conglomerate reservoir of the first sand group of the second member of Jiamuhe Formation in the Zhongjia area of the northwest margin of the Junggar Basin had a large thickness and wide distribution. The test results of oil and gas were not satisfactory，and the distribution pattern of reservoir “sweet spot”area was unclear. Based on logging，analysis and assay，and pre-stack 3D seismic data， the discriminatory parameters of geological“sweet spot”and engineering“sweet spot” were established. The relationship between “sweet spot” characteristics and gas recovery capacity was revealed，and the“sweet spot”characterization parameters were selected for reservoir “sweet spot” prediction and evaluation.The results showed that the reservoir was a tight conglomerate reservoir with low porosity and exceptionally low permeability of the first sand group of the second member of Jiamuhe Formation in the Zhongjia area，and the seepage conditions were deviated overall. The reservoir brittleness characteristic index was generally greater than 60%，“sweet spots” were identified by combining longitudinal and transverse wave velocity reflecting better reservoir compressibility and more likely to obtain high production.The “sweet spot” reservoir had low gamma，high resistivity，low density，low neutron porosity， high acoustic time difference，high pore permeability，high gas saturation，low longitudinal to transverse velocity ratio， low wave impedance， and high brittleness index value. Based on the comprehensive evaluation of reservoir classification characteristics combined with the inversion results of longitudinal and transverse wave velocity ratio， porosity and brittleness index parameters， the distribution range of the two types of “sweet spot” areas were identified and characterized.The Type I “sweet spot” was located in the Zhongjia 7-Xinguang 1 well area in the fan delta's inner frontal phase zone，with a total area of 50 km2；the Type II “sweet spot”was mainly located in the peripheral area of the Zhongjia 7-Xinguang 1 well area，with an area of 48 km2.The Well ZJHW201， deployed in the Class I “sweet spot” area， obtained 700 000 m3 of high production gas flow， which promoted the exploration and development of thick Permian tight conglomerate gas reservoirs in the Junggar Basin， and was of great significance to further promote the accelerated development of natural gas business in Xinjiang Oilfield Company.
In order to clarify the natural fracture distribution of fault anticlines in the ultra-deep reservoirs， this paper takes the Cretaceous Bashijiqike Formation in the Keshen area of the Kelasu tectonic belt in the Kuqa Depression of Tarim Basin as an example. Combined with geological data， seismic data， FMI image logs， in-situ stress and rock mechanics parameters， the distribution characteristics of natural fractures in the typical faulted anticlines in the Keshen area are clarified by reservoir geomechanics， and the results provide a geological basis for the favorable zone exploration of tight gas in the study area. Different fault anticlines have the general characteristics of natural fracture intensity of “high-low-high” from the top， middle to bottom of the faulted anticlines. The larger the angle between wings， the more limited the distribution of fractures at the top and in the middle of the faulted anticlines， and the wider the distribution of fractures at the bottom of the faulted anticlines. The farther away from the fracture anticline axis， the more limited the fracture distribution at the top and bottom of the faulted anticlines， and the more extensive the fracture distribution in the middle of the faulted anticlines. The natural fractures at the hinge zone at the top of the fault anticlines are more developed than those in the middle and at the bottom of the fault anticlines， which improves the physical properties of the reservoirs and provides reservoir space and seepage channels for tight gas.
In order to clarify the influence of quasi-contemporaneous dolomitization on the reservoir， based on the laboratory simulation of synthetic dolomite experiments， the order degree and simulation time obtained by the experiment were used to determine the burial history of the Tabei area of the Tarim Basin and the comprehensive Cambrian histogram. It is concluded that the Cambrian dolomite in the northern Tabei area has undergone a high degree of dolomitization at a depth of about 521 Ma and 480 m. Through the calculation of dolomite unit cell parameters in different regions， it is found that dolomite with large unit cell volume has low degree of order， while dolomite with small unit cell volume has high degree of order， which reflects that the adjustment of dolomite order will lead to the reduction of the overall mineral volume in the process of dolomitization. It is concluded that the dolomite order is negatively related to the unit cell volume. According to the calculated value of the unit cell volume， the average value of the unit cell volume reduction during the calcite dolomitization process is 12.6%， that is， 12.6% of the intercrystalline pores are generated in this process. Through the observation of limestone dolomite compaction curve and thin section， it is found that the physical and chemical properties of the rocks have changed after dolomitization. Its compression resistance has preserved the intergranular voids generated in the quasicontemporaneous period， which is conducive to the dissolution and recrystallization of the hydrothermal fluid in the later deep burial environment on the basis of the original Sabha dolomite intergranular voids， thus expanding the storage space to form high-quality dolomite reservoirs.
Two sets of source rocks， Wenchang Formation and Enping Formation， were developed in Baiyun Sag of the Pearl River Mouth Basin during the rifting period. Through 3D seismic data and deep drilling analysis， it is believed that axial braided river delta system， fault controlled fan delta system， braided river delta system in the north gentle slope zone and shore shallow lake medium deep lake system in the basin are developed during the rifting period of Baiyun Main Depression. In the early stage of rifting， many groups of NE trending fault terraces are developed and the landform is characterized by many ups and depressions. The provenance mainly enters the depression from the east to the west， forming multi-point source water systems and developing multi depressions to generate hydrocarbons； In the middle of rifting， due to the extension of detachment faults， the lake basin expanded， and the Panyu low uplift in the north was strongly uplifted， forming a large delta system and a large lake basin with gentle slopes； In the late rifting period， the lake basin was dominated by depression， and coal type and transgressive source rocks were developed under the influence of South China provenance and transgression from south to north. According to sedimentary facies and geochemical indicators， the source rocks in Baiyun Sag can be divided into three types： Type I-II1 source rocks of middle-deep lacustrine facies in Wenchang Formation， Type II2 source rocks of shallow lacustrine facies in Wenchang Formation and Types II2-III source rocks of shallow lacustrine facies in Enping Formation. The hydrocarbon generation potential of different types of source rocks is different， and the middle-deep lacustrine facies source rocks in Wenchang Formation are the best. The element geochemical indicators reveal that the overall hydrocarbon generating environment of the lake basin belongs to freshwater to brackish water， reducing to strong reducing water environment， while the paleontology reveals that the oil generating parent material of the lake basin is Huxiang planktonic algae and terrestrial plants， and the organic matter of high-quality hydrocarbon source rocks mainly comes from planktonic algae. In a word， the detachment fault activity and sedimentary system of Baiyun Sag control the development thickness and scale of hydrocarbon source rock， and the high-quality water environment controls the formation of high-quality hydrocarbon source rock. Therefore， the source rocks in Baiyun Sag have geological conditions of large thickness and wide distribution， and have great resources and exploration potential.
The third member of Weizhou Formation of Oligocene is the most important reservoir in Haizhong Sag， Beibuwan Basin， so it is very important to study the distribution regulation of depositional systems for oil and gas exploration in the area. Based on the fine description of drilling cores in the study area， combined with the characteristics of logging facies， seismic facies and seismic attributes， the depositional facies were determined and the sedimentary models in faulted lacustrine basins is established. The results show that the discal-sheeted reflection， progradational reflection and channel filling reflection are the most sand-rich seismic facies in the third member of Weizhou Formation； There are four types of depositional facies： Shore-shallow lacustrine facies， braided river delta， fan delta and alluvial fan in the third member of Weizhou Formation； Under the background of shore-shallow lake and controlled by the half-graben lake basin structure with gentle southern and steep northern slope， the Haizhong Sag as a whole shows the sedimentary characteristics of north-south differentiation， which is manifested by the development of braided river delta in the gentle slope zone in the south， braided river deltas and fan deltas was developed in the north； At the same time， factors such as slope break zone， fault style and gully ancient landform control the deltas from three different directions， and the provenances of Qixi uplift in the south mainly develop braided river deltas. The plain and front are divided on the plane by the slope break zone， and the source of the Weixinan low uplift in the middle of the Beibuwan Basin is controlled by the fault to develop braided river deltas and fan deltas in the west， the sediments from Wanshan uplift in northwest formed a braided river delta by long-distance transport in the edge of Lake basin in the northwest of the study area.
Confirmation of shale gas resources is the most realistic field for the future growth of natural gas production in China. The quantity of shale gas resources/reserves， fundamental in shale gas development， is one of the important bases for making development plans and strategies. In current shale gas resource/reserve calculation method， the volume method is used to calculate the adsorbed gas reserves and the free gas reserves. This method， however， does not take into account the co-existence of adsorbed gas and free gas in shale pores， in which case the free gas reserves should be estimated by deducting the pore volume occupied by the adsorbed gas. For evaluating the shale gas resources/reserves， the new model of shale pore and shale gas occurrence and the new petrophysical model of shale gas reservoir have been established. Based on the new models， a new method of shale gas resources/reserves estimation in line with the characteristics of shale gas reservoir was established. Taking the appraisal wells of marine shale gas reservoirs in Luzhou and marine-continental transitional shale gas reservoirs in the eastern Ordos Basin as examples， the calculation results of the new proposed method and the existing method were compared. It is found that the methods in the current practice overestimate the geological reserves of shale gas by more than 20%. Compared with marine shale， marine-continental transitional shale has a relatively low porosity， where the content of free gas is only 12% if the pore space occupied by adsorbed gas is deducted. Such a low content of free gas is one of the causes for low well productivity in marine-continental transitional shale.
In recent years， deep shale gas exploration breakthroughs have been achieved in the Wufeng -Longmaxi formations in the complex tectonic region of the Sichuan Basin and southeastern margin， showing good prospects for deep shale gas exploration and development. Based on the data from drilling wells and experimental analysis tests， the study of deep shale gas enrichment characteristics is carried out in the Nanchuan area of the complex tectonic region of the southeastern Sichuan Basin margin， focusing on the role of changes in the formation environment such as formation temperature and pressure on deep shale gas enrichment. The study concludes that： （1） The dominant sedimentary phase zone is the basis for hydrocarbon formation in shale gas reservoirs. The Wufeng Formation - the first member of Longmaxi Formation in the study area was formed in a deep-water shelf sedimentary environment with high-quality shale development， which has good material conditions for the formation of shale gas reservoirs. （2） Organic carbon content controls the degree of development of nanoscale organic matter pores， and the high-pressure-ultra-high-pressure environment is conducive to the maintenance of pores and it plays a positive role in improving the physical properties of deep shale. （3） Deep shale gas has the typical geological characteristics of high temperature， high ground stress， and exceptionally low permeability. The influence of temperature on the adsorption capacity of shale is more obvious than that of pressure， and the deep shale gas is mainly free gas. High pressure can slow down or inhibit the gas flow， which is beneficial to shale gas preservation. （4）The changes of temperature and pressure have complex effects on gas diffusion. High temperature will increase the diffusion coefficient of gas， aggravate the migration and escape of gas， while high pressure can slow down or inhibit the flow of gas， which is beneficial to the preservation of shale gas. （5） The burial depth and pressure coefficient show a certain positive correlation， and the burial depth has a more significant effect on the pressure coefficient of syncline shale gas， indicating that the preservation conditions of deep syncline shale gas reservoirs have a tendency to become better. The residual syncline core with larger depths， inner-sag uplift， and slopes with reverse faults can be favorable targets for shale gas exploration in complex tectonic zones.
The shale of the Qigequan Formation of Quaternary in the Sanhu area， Qaidam Basin is in the early stage of diagenesis and has high water saturation， which greatly affects the adsorption and flow capacity of natural gas， and then affects the gas content of the shale interval and the productivity of gas wells. For this purpose， shale samples of the Quaternary Qiquan Formation in the Sanhu Tainan area and the Chaerhan area were selected to carry out scanning electron microscopy and gas adsorption-mercury intrusion combined measurement to clarify the pore development characteristics of the Qigequan Formation. Isothermal adsorption and overburden permeability experiments under water saturation conditions were performed to reveal the influence of water saturation on methane adsorption and gas flow capacity of shale. The research results show that the mud shale of Qigequan Formation has a relatively high content of clay minerals， with an average of 33.0%； the reservoir space includes two types of mineral intergranular pores and intragranular pores. The pore size distribution is unimodal， and the main peak pore size is 50-150 nm. The contribution of macropores to the pore volume is the largest， with an average proportion of up to 66.8%. Qigequan group mud shale gradually decreases with the increase of water saturation， when the water saturation exceeds the critical value of 10%-20%， the decline in the amount of adsorbed gas slowed down. The amount of adsorbed gas has a good positive correlation with clay minerals， among which illite has the largest contribution to the amount of adsorbed gas； the Qigequan Formation mud shale gas flow mode is mainly slip flow. Water content makes the gas flow capacity weaker. Under the condition of 2 MPa， when the water saturation increases from 10% to 50%， the shale permeability decreases by 52.93% on average. In the gentle area surrounding the syn-sedimentary anticline structure， shale gas can be retained and accumulate. The shale gas well has good gas abundance and strong development potential， making it a favorable area for exploration.
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