The Ordos basin is the second largest sedimentary basin in China with abundant oil and gas resources and broad exploration prospects. Typical low-permeability-tight oil reservoirs are develpoed in the Triassic Yanchang formation in the basin,which are difficult to explore. Through continously geological researches on the Mesozoic oil reservoirs in the Ordos basin over the past 50 years,some theories about hydrocarbon accumulation in Jurassic reservoir groups,in large-scale lithologic reservoirs in inland depression lake basins and in continental shales have been formed. By virtue of three strategic shifts,four conventional hydrocarbon provinces with reserves exceeding 10×108 t and a successive zone with shale oil reserves of 20×108 t have been discovered. The proven oil reserves have increased by an average of over 3×108 t per year for 10 consecutive years. Thus,Changqing oilfield in Ordos basin has become an oil and gas province with the fastest increase in reserves and production in China and contributed 12.5% of China's annual oil production,which provides a reference for the petroleum exploration in other similar basins.
Bauxite gas reservoir is a kind of very rare unconventional gas reservoir recently discovered in the Ordos basin, and well logging evaluation plays an important role in its exploration and development. In the early well logging evaluation, bauxite was considered as the weathering crust caprock, but not as a reservoir, and there was no systematic well logging evaluation method suitable for the exploration and development of bauxite gas reservoirs. Based on the aluminous rocks in Taiyuan formation in the Longdong area, southwestern Ordos basin, the well logging evaluation method for bauxite gas reservoirs was studied from five aspects, that is, qualitative lithology identification, mineral composition, reservoir physical properties, quantitative calculation of gas-bearing properties and systematic summary of imaging model-pore structure characteristics. The well logging response for identifying aluminous rock formations was clarified and the aluminous rock identification chart by acoustic time-gamma ray was established. The porosity-permeability-saturation evaluation model for bauxite gas reservoirs was constructed through petrophysical experiments, and the criteria for identifying bauxite reservoir was proposed by combining micro-resistivity scanning imaging and nuclear magnetic resonance logging data. Finally, a well logging evaluation method for bauxite gas reservoirs was formed.
As an important reservoir for storing oil and gas,the sand bodies in delta front are found with enormous petroleum exploration potential. However,there are few studies on architecture of sand bodies in shallow delta front through field outcrops. Guided by sedimentology and reservoir architecture theories,the outcrop observation and sampling was combined with the results of laboratory experiments and statistical analysis to clarify the sedimentary characteristics and sand body architecture of Chang 9 member in the Shiwanghe section in Yichuan,Ordos basin. The results show that during the deposition,the Chang 9 member in Shiwanghe section lied in a warm and humid environment,especially an oxidation to weak-reduction transitional freshwater environment that was not obviously stratified,and shallow delta front subfacies was mainly developed,including microfacies such as underwater distributary channel,estuary bar,sheet sand and interdistributary bay. The single sand bodies of shallow delta front in Chang 9 member in the study area can be divided into two vertical stacking styles such as non-connected and connected,and two lateral contact styles such as butted and cut-stacked. The accommodation growth rate and sediment supply rate jointly controlled by terrain slope and lake level rise/fall are important factors affecting the spatial development style of the composite sand bodies. The gentle slope allows the channels to incise weakly and present the characteristics of plane intersection. The rise of lake level and the decrease of source supply increase the ratio of accommodation growth rate to sediment supply rate,which may lead to the weakening of sand body connectivity. The architecture models of sand bodies like river-river cut stacking and river-bar cut stacking are favorable for hydrocarbon accumulation.
The Fengcheng formation in the Mahu sag is an alkaline lake sediment，and is divided into Feng 1 member，Feng 2 member and Feng 3 member from bottom to top. In the Fengcheng formation，the lithology vertically changes rapidly，the mineral composition is complex，and the organic-rich shale source is integrated with the shale reservoir. The formation bears oil universally，but the sweet spots are scattered. The results of formation testing for single layers are not satisfied，showing an unclear production potential. According to core slices and geochemical analyses，the Fengcheng formation in the Mahu sag is dominated by lamellar silty shale intercalated with dolomite，which are mainly composed of terrigenous clastic minerals and carbonate minerals. With the variation of burial depth，the pore volume changes consistently with the variation of surface area of pores，and the pore volume is mainly contributed by macropores (pore diameter > 50 nm). The source rock is dominated by Type Ⅱ organic matter，and the vitrinite reflectance ranges from 0.85% to 1.40%，indicating a peak oil generation period. There are many shear fractures with middle to high angles in the Feng 2 member，and shear fractures with middle to high angles and structural fractures with low angles in the Feng 3 member，whose formation and development degree are controlled by lithology，mineral composition，rock mechanical properties，etc. Based on the characteristics of lithologic assemblage，reservoir property and oil-bearing property，four relatively concentrated sweet spots have been identified. When performing multi-interval formation testing and production testing in vertical wells，it is necessary to select sweet spots with good oil content and more fractures to conduct geological research and geology-engineering integration technology research，and to perform production improvement tests in horizontal wells，so as to realize comprehensive breakthrough for shale oil exploration and development in the Fengcheng formation in the study area
To realize the shift of oil and gas exploration from shallow-middle to deep strata, and from conventional to unconventional resources, and then to promote the exploration of deep oil and gas resources in the Turpan-Hami exploration area, the tectonic-lithofacies palaeogeographical evolution of Turpan-Hami basin, Santanghu basin, and Zhundong block of Junggar basin were analyzed, the characteristics and exploration potential of the petroleum systems in these basins were evaluated, the main exploration targets were determined, and the fields for strategic breakthrough were selected. In the Carboniferous-Permian period, the Turpan-Hami exploration area was a unified sedimentary basin with similar sedimentary environments and structures. In the Triassic-Jurassic period, the study area was separated into several independent foreland basins. With the tectonic-lithofacies palaeogeographical evolution, three sets of source rocks (marine-transitional facies of Carboniferous, lacustrine facies of Permian, and lacustrine-coal measure of Jurassic) were formed, contributing to three major petroleum systems. The change in exploration ideas has promoted significant progress in petroleum exploration in deep strata. Significant breakthroughs have been made in the exploration of Shiqiantan formation marine clastic oil and gas reservoirs, Permian shale oil reservoirs and conventional sandstone oil reservoirs in the Zhundong block, and the Middle-Lower Jurassic large-scale tight sandstone gas reservoirs in the Turpan-Hami basin, which enables the discovery of large-scale high-quality reserves and the orderly succession of strategic resources. Future exploration should be carried out at three levels: strategic preparation, strategic breakthrough, and strategic implementation, with a focus on 10 favorable directions.
The Shunbei No. 4 strike-slip fault zone which is located in the Shuntuoguole low uplift of the Tarim basin and extends northward to the Shaya uplift is characterized by deep burial，horizontal segmentation，vertical stratification，multi-stage activities，and complex structure. Through the interpretation of high-quality 3D seismic data from the Shunbei No. 4 strike-slip fault zone，the stratification，segmentation，staging，activity and favorable area evaluation of the fault zone were carried out. The results show that the Shunbei No. 4 strike-slip fault zone has a 4-layer structure in the Paleozoic，roughly bounded by the top of the Middle Ordovician，above which echelon faults are found and below which high-steep strike-slip faults are developed. The strike-slip fault zone is visibly segmented into the northern segment，the middle segment，and the southern segment according to the strike，showing an overall characteristic of compressed in south and extended in north. In the Paleozoic，the strike-slip fault zone successively experienced four periods of activity，namely，EpisodeⅠof the middle Caledonian，Episode Ⅲ of the middle Caledonian，late Caledonian，and Hercynian. By combining the main controlling factors (e.g. source-reservoir connectivity，reservoir size，and late adjustment) for hydrocarbon enrichment and accumulation in the Shunbei area，the favorable areas in the Shunbei No. 4 strike-slip fault zone were evaluated. Multiple favorable areas have been identified and then verified by actual drilling.
The origins of X-shaped conjugate strike-slip faults are complex. Considering the geological conditions of large X-shaped conjugate strike-slip faults in the Tabei area of the Tarim basin，7 sets of sandbox experiments with different parameters were designed to explore the controlling factors and evolution process of the X-shaped conjugate strike-slip faults. The experimental results show that conjugate strike-slip faults tends to be formed in the model with large thickness，large width and high clay content under the rapid compression on both sides. In the experiment，the fault tail propagation and the dominant development of a group of faults are obvious，while the fault linkage growth and the localization of overlapping area are weak. The formation of conjugate strike-slip faults requires three conditions: certain caprock thickness，and lack of pre-existing faults; good physical homogeneity of rocks，certain viscoplasticity，and high movement rate; and two-way compression. In the natural world and experiments，symmetrical pure shear conjugate strike-slip faults can hardly be formed，but most faults are single-shear strike-slip faults that develop as a group in dominant direction. In the Tarim basin，the conjugate strike-slip faults are also asymmetric，and they are dominantly single-shear faults in NW-SE direction; the inherited development with small displacements is the main controlling factor for the formation of large-scale conjugate strike-slip faults.
The Fengcheng formation in the Hashan area in the northwestern margin of Junggar basin experienced strong tectonic deformation and structural displacement. There are few studies on the sedimentary system of the Fengcheng formation, which restricts the oil and gas exploration in this area. The 3D seismic, drilling, logging and core data in the Hashan area were systematically analyzed, and the structural evolution of the Fengcheng formation in different parts of the Hashan area was investigated, so that the original stratigraphic position of the Fengcheng formation was restored, the sedimentary facies types were analyzed and compared, and finally the original sedimentary system of the Fengcheng formation in this area was restored. The results show that in the Hashan area the tectonic compression strength gradually weakens from west to east, and the shortened distances of the Lower Permian from the Early Permian to the present in the western, central and eastern parts due to the compression are 33.0-40.0 km, 25.0-30.0 km and 15.0-20.0 km, respectively. Three types of sedimentary facies such as fan delta, beach bar and lake are developed and volcanic rocks of a certain scale are found in the Fengcheng formation. During the deposition of Feng 1 member, large-scale fan deltas and shore-shallow lakes were developed in the northern part of the Hashan area, semi-deep to deep lakes and beach bars in a small range in the central-western part, and volcanic rocks in the central-eastern part. During the deposition of Feng 2 member, the sedimentary range of semi-deep to deep lakes expanded significantly, thick layers of dolomitic mudstone was developed, and the distribution range of fan-delta sandy conglomerate and volcanic rocks decreased. During the deposition of Feng 3 member, the provenance supply capacity was enhanced, large-scale contiguous fan-delta sandy conglomerate was developed in the northern and western parts and semi-deep to deep lakes and beach bars were found locally.
The Turpan-Hami basin has great potential of oil and gas resources in the Lower Jurassic strata, with a large quantity of remaining resources. The discovered oil and gas reservoirs are mainly distributed in the positive structural belts around the Shengbei and Qiudong subsags in the Taibei sag, and they are primarily structural reservoirs. Less researches on the oil and gas resources in the hinterland of the subsags have been performed. Based on the dissection of known reservoirs, a systematic study was carried out on the depositional system, source rock, reservoir rock and accumulation conditions of three major hydrocarbon-rich subsags in the Taibei sag. The results show that the coal-measure source rocks are widely developed in the Shuixigou group in the Taibei sag and are in broad contact with the braided river delta sandstones, which is conducive to the formation of near-source tight sandstone gas reservoirs. There are two types of tight sandstone gas reservoirs in the Lower Jurassic, namely, trap-type and continuous-type. The hinterlands of the subsags are favorable areas for the formation of continuous-type tight sandstone gas reservoirs. Therefore, the exploration should be switched from the source-edge positive structure to the hydrocarbon-rich subsag, and from the above-source conventional oil reservoirs to the in/near-source tight sandstone gas reservoirs. The hinterlands of the Shengbei and Qiudong subsags have the conditions to form large gas reservoirs, so they are favorable areas for exploring near-source tight sandstone gas reservoirs in the lower Jurassic.
In the condensate gas reservoirs of the Lower Jurassic Lianggaoshan formation in the Fuling area, southeastern Sichuan basin, the fluid properties are complex and the gas-oil ratios from multi-well testing differ greatly. In this paper, the basic characteristics of oil and gas were clarified by using the data such as crude oil chromatography-mass spectrometry, gas composition, carbon isotopes and fluid inclusions. The gas reservoir properties and phase states were determined with the empirical calculation method for gas compositions and through the experiments simulating PVT fluid phase state. On this basis, the genesis and forming process of condensate gas reservoirs were discussed. The results show that the gas reservoirs in the Lianggaoshan formation are mainly condensate gas reservoirs without oil rings, where hydrocarbons are mainly primary condensate oil and gas generated from Type Ⅱ2 kerogens in the mature stage, and cracking gas is found locally. The thermal evolution degree of source rocks and the differences in the present temperature and pressure conditions of formation are the main contributors to different reservoir properties. The superimposed areas of the relatively deep-burial areas during the hydrocarbon accumulation period on the areas with relatively high pressure at present are favorable targets for future exploration.
In order to improve the drilling rate of pay zones in the Ma55 gas reservoir in eastern Sulige gas field, Ordos basin, using the drilling, logging, core and gas production testing data, and analyzing the main factors controlling pay zones such as sedimentary microfacies, diagenesis and paleotopography, the distribution law of dolomite in the Ma55 gas reservoir was clarified. Moreover, the reservoirs were comprehensively classified and evaluated, and the favorable gas enrichment areas in the Ma55 gas reservoir were selected. The research results show that the pay zones in the Ma55 reservoir are distributed as “lens” in local areas, with poor continuity. The most favorable reservoir rocks are granular dolomite and coarse powder crystalline dolomite, and the main storage space consists of intergranular pores, intergranular dissolved pores and structural fractures. Sedimentary facies and diagenesis are the main controlling factors of the Ma55 reservoir, and the grain beach is the most favorable sedimentary microfacies of the Ma55 dolomite. The pay zones are mainly controlled by quasi-contemporaneous dolomitization and buried dolomite diagenesis. The paleoslope on the relatively high position is a favorable area for the development of the Ma55 gas reservoir.
In the Qingyang gas field, Ordos basin, which is a typical tight sandstone gas field, the major pay zone is the first member of the Permian Shanxi formation. Its sedimentary sand bodies change rapidly with small thickness, making the prediction of reservoir distribution difficult, which restricts the productivity construction of the gas field. In this paper, sedimentary sand body characterization and thin layer prediction were carried out using logging-seismic combination, the main factors controlling reservoir development were discussed, and favorable reservoir distribution areas were identified. The results show that the paleogeomorphology and paleo-flow direction jointly controlled the distribution of delta sand bodies, the underwater distributary channel sand bodies with developed dissolution facies are the most favorable reservoirs, and the local micro-amplitude nose uplift structure is the natural gas enrichment area. Based on the factors such as sand body distribution, reservoir physical properties, diagenesis and structural characteristics, a set of standards for classifying reservoirs in the study area was established, by which two Type I reservoir enrichment areas were defined in the southern and central parts of the study area.
In order to determine the influence of natural rheology of shale on microscopic pore structure, taking the marine shale of the Lower Cambrian Qiongzhusi formation in the Chengkou area, northeastern Sichuan basin as an example, the types and characteristics of rheological structure and microscopic pore structure in the shale and their relationship were studied by using rock thin sections, focused ion beam scanning electron microscope and low temperature liquid nitrogen adsorption experiment. The microstructures of shale rheology mainly include porphyroclast system, cataclastic flow, pressolutional stylolites, microscopic fold, S-C fabric and crenulation cleavage, and the micro-nano structures include mylonite zone, micro-hybrid zone, and rotating porphyroclast. Rheological shale is dominated by nanoscale intergranular pores, and most of the primary pore structure is difficult to preserve under rheological action. Ductile rheology leads to a decrease in the number of pores, pore diameter, pore volume and pore specific surface area of shale, which reduces the storage performance of shale.
In order to evaluate the petroleum exploration prospects of the Fengcheng formation in the western Central depression of the Junggar basin, the lithology assemblage and sedimentary facies of the Fengcheng formation were studied by means of analyzing the trace element, core, rock thin section, paleomorphology, logging facies and seismic facies of the formation. The results show that the Fengcheng formation in the study area is fan delta-alkaline lake deposition which formed in an arid-semi-arid climate, foreland tectonic setting and geological environment with periodic changes in water salinity and water depth. From the edge to the center of the Central depression, basin-marginal fan-delta clastic rocks, outer-slope front dolomites, slope-highland volcanic rocks, low-uplift dolomitic calcareous beach-bar peperites, and the central lake-basin alkali rocks are found in sequence. According to the sedimentary characteristics, an evolution model for the fan delta-alkali lake deposition was established for the Fengcheng formation. Based on the sedimentary facies, lithofacies and petroleum exploration status, the Fengcheng formation in the study area can be divided into 5 areas such as conventional hydrocarbon area in basin-margin ultra-denudation belt, tight hydrocarbon area in outer-slope front, shale oil/gas area in lake basin, conventional hydrocarbon area in low-uplift dolomitic calcareous beach-bar and conventional hydrocarbon area in highland volcanic rocks. The favorable exploration area with the depth less than 7 000 m reaches 1.2×104 km2, with hydrocarbon reserves of more than one billion tons, which demonstrates huge exploration potential of the total petroleum system of the Fengcheng formation in the study area
A number of favorable oil-bearing areas have been discovered in the lower assemblage adjacent to the Chang 9 source rocks on Yishaan slope, Ordos basin. In order to promote the petroleum exploration of the lower assemblage in this area, it is urgent to deepen the research on the characteristics and hydrocarbon generation potential of the Chang 9 source rocks. The distribution of the Chang 9 source rocks were analyzed using well logging, mud logging and core data. The geochemical characteristics and hydrocarbon generation potential of the Chang 9 source rocks were studied by various methods such as rock pyrolysis analysis, total organic carbon analysis, kerogen maceral analysis, and biomarker analysis by saturated hydrocarbon gas chromatography-mass spectrometry. The results show that the Chang 91 source rocks are distributed in Wuqi, Jingbian, Zhidan, Ansai and other areas, with the maximum thickness of over 20 m, and the Chang 92 source rocks are mainly developed in Ganquan-Luochuan area, with the maximum thickness of over 12 m. The Chang 9 source rocks hold a high abundance of organic matters that were originated from lower aquatic organisms and terrestrial higher plants. With Type Ⅰ and Ⅱ1 organic matters in dominance, which are in the mature stage, the Chang 9 source rocks exhibit high hydrocarbon conversion rate and especially strong hydrocarbon generation capability in Zhidan-Ansai area. The Chang 9 source rocks are mostly good and locally high-quality rocks with strong hydrocarbon generation and expulsion capacities, which provides a material basis for hydrocarbon accumulation in the lower assemblage of Yanchang formation on Yishaan slope.
The exploration practice in the Fengcheng formation in the Mahu sag，western Junggar basin，has revealed the orderly coexistence of conventional and unconventional hydrocarbons. By finely dissecting the characteristics of the total petroleum system in the Fengcheng formation in the Mahu sag，and combining with the macro-and micro-analysis and production data of the reservoirs，the hydrocarbon accumulation mechanism of the total petroleum system was analyzed. The results show that conventional oil，tight oil and shale oil accumulate in an orderly pattern in the total petroleum system，which essentially complies with the hydrocarbon accumulation pattern of “source-reservoir coupling” and “dynamic sealing” of oil and gas. In the early diagenesis stage，the present tight reservoirs and shale reservoirs were conventional reservoirs with medium-large pore throats，where hydrocarbons accumulated because of buoyancy. In the middle-later diagenesis stage，the medium-large pore throats gradually evolved to micro-to nano-pore throats，the buoyancy was weakened，and the capillary force was strengthened. The hydrocarbon in the reservoir adjacent to or integrated with the source rocks underwent primary or micro migration continuously until the source-reservoir pressure difference resulted from hydrocarbon generation and expulsion and the capillary force originated from micro-to nano-pore throats reached a dynamic equilibrium，forming a “self-sealing” continuous unconventional oil and gas accumulation. The capillary force in the present conventional reservoirs is far less than the buoyancy，so “external sealing”is needed for hydrocarbon accumulation in traps. Generally，the hydrocarbon accumulation in the Fengcheng formation is represented by the space-time evolution of the pore throat structure in the reservoir and the dynamic coupling of source rock and reservoir on hydrocarbon generation-expulsion-migration-accumulation.
Zeolite is found in the tight sandy conglomerate reservoirs of the Permian Wuerhe formation in the Mahu sag, Junggar basin, leading to great difficulties in oil-bearing property evaluation and productivity estimation for the tight sandy conglomerate reservoirs due to their abnormal reservoir physical properties. The experiments by using casting thin sections and scanning electron microscope were carried out to analyze the geological characteristics of zeolite, including the occurrence, symbiotic relationship with other minerals, and diagenetic sequence of zeolite cement. Through the analysis of core and logging data, it is clear that the zeolite-bearing tight sandy conglomerate reservoirs show the logging responses featured with low density, high neutron porosity and high acoustic slowness. By intersecting the difference between neutron logging porosity and density logging porosity with the difference between neutron logging porosity and acoustic slowness porosity, the chart for identifying the sandy conglomerate reservoirs containing zeolites was established. Based on the normalized tri-porosity logging parameters, a model for quantitatively predicting zeolite content was built. By comparing the zeolite content from core analysis with the content predicted by the model, it is confirmed that the prediction accuracy of the model is high. Based on the identification results of the zeolite-bearing tight sandy conglomerate reservoirs in 132 wells, the development zones of tight sandy conglomerate reservoirs containing zeolites in the Wuerhe formation in the study area were determined. The dissolution of zeolites can create a lot of accommodations for hydrocarbon accumulation. The study results provide reliable guidance for predicting favorable areas of tight sandy conglomerate reservoirs in the study area.
By means of thin section observation，scanning electron microscope (SEM) analysis，X-ray diffraction (XRD) analysis of clay minerals，and cathodoluminescence experiment，the diagenesis of the Upper Permian upper Wuerhe formation in the Mahu and Shawan sags in the Junggar basin were analyzed and compared，and the types of diagenetic products and pore evolution process were clarified. Compaction，carbonate mineral cementation and zeolite cementation are the main factors controlling the differences in reservoir physical properties in the study area. The compaction in the Mahu sag is relatively weak，while the dissolution in the Shawan sag is relatively strong. There are differences in diagenesis and pore evolution of sand bodies in the two sags. The reservoirs in the Mahu sag are dominated by feldspar particles and dissolved tuff debris pores，and the reservoirs in the Shawan sag are dominated by feldspar particles，dissolved tuff debris pores，and dissolved zeolite pores. There are a few primary pores developed in the reservoirs in both Mahu sag and Shawan sag. The differences between the reservoirs in the two sags are mainly caused by the different properties of diagenetic fluids and rock components. Specifically，the rock components represent the main cause for the differences in pore structure characteristics in the sandy conglomerate reservoirs in the Mahu sag and the Shawan sag.
In order to further investigate the diagenetic environment, formation mechanism of carbonate cements and its influences on the physical properties of the sandy conglomerate reservoirs in the Lower Triassic Baikouquan formation on the northern slope of the Mahu sag, Junggar basin, the types, forming periods, and genesis of the carbonate cements in the study area and their effects on the reservoirs were studied through combining core observation, rock thin section identification and measurement of carbon and oxygen isotopes in carbonate cements. The results show that there are three periods of carbonate cements in the Baikouquan formation on the northern slope of the Mahu sag, that is, from early to late, micritic calcite in Period Ⅰ, ferrocalcite in Period Ⅱ, and ankerite in Period Ⅲ. δ13CPDB ranges from -47.23‰ to 3.88‰, while δ18OPDB ranges from -23.64‰ to -17.98‰. The bigger range of δ13CPDB reveals the presence of various carbon sources and the complex interaction between water and rock. The paleosalinity and paleotemperature restored from the carbon and oxygen isotope calculations show that the carbonate cements were mainly formed in freshwater environments, and partly influenced by seawater. The Baikouquan formation in Well Ma-19 is a low-porosity and low-permeability reservoir as a whole. The physical properties of the Bai 2 member are slightly better than those of the Bai 3 member, presumably indicating the presence of secondary pores. Post-drilling analysis finds that oil layers are developed in both Bai 2 member and Bai 3 member, which is basically consistent with the conclusion obtained from carbon and oxygen isotope analysis.
In order to further expand the petroleum exploration and enrich the basic theory and understanding on petroleum geology in Junggar basin，based on the exploration practices in recent years，the characteristics of present petroleum exploration and its trend are summarized，and the total petroleum system in Permian strata and the conditions for large-scale accumulation of unconventional natural gas in inner-source deep strata are described. The results show that the middle and lower reservoir assemblages have become the major exploration targets，deep strata have the conditions for oil and gas accumulation，the source rock controls the distribution of oil and gas，and a distribution pattern with orderly coexistence of conventional and unconventional reservoirs is established. The continuous hydrocarbon supply from high-quality Permian source rocks is the premise for the formation of the total petroleum system，and two sets of oil and gas accumulation systems are found inside source and outside source. Various inner-source reservoirs are developed in the Permian strata，which have great potential for natural gas exploration，especially unconventional natural gas. The understanding not only broadens the petroleum exploration area in Junggar basin，but provides theoretical and practical support for construction of a large oil and gas field. Moreover，it is of great significance for further improving the theory of total petroleum system. Deep inner-source unconventional oil and gas are becoming an important frontier for future exploration in hydrocarbon-rich sags.
