In view of the unclear distribution pattern of in deep high-quality K₁g₃ sandstone reservoirs in Jiudong Oilfield, Jiuquan Basin, the diagenetic characteristics, diagenetic evolution, diagenetic facies and high-quality reservoir distribution of sandstone were studied according to casting slice, scanning electron microscope, physical properties and other data. The results showed that the deep K₁g₃ sandstone in Jiudong Oilfield had three types of diagenetic characteristics, and the sandstone with Type Ⅱ and Ⅲ diagenetic characteristics was developed from Type Ⅰ iron-bearing dolomite cemented tight sandstone under the differential action of acidic dissolution fluid. There were three stages of acid dissolution fluid. The fluid was atmospheric freshwater in the first two stages, and was organic acid fluid in the third stage. The atmospheric freshwater then became a acidic fluid that contributed the most to sandstone dissolution. K₁g₃ sandstone could be divided into 4 types of diagenetic facies and 2 diagenetic facies belts. Type B diagenetic facies were high-quality reservoirs with high porosity and permeability, Type D diagenetic facies were reservoirs with medium porosity and low permeability, and Types A and C diagenetic facies were ankerite-bearing cemented tight and heterogeneous reservoirs. The main oil-producing area to the west of Chang2 Fault was a Type B diagenetic facies band, the expanded-margin area to the east was a Type D diagenetic facies band, and Types A and C diagenetic facies were not developed in general. The study results are of providing important reasons for the development plan adjustment and expanded-margin exploration and deployment of Jiudong Oilfield.

Low-permeability reservoirs are rich in reserves, with great commercial value, but they are defective in poor porosity and permeability, high reservoir heterogeneity, poor water absorption capacity, etc., increasing the technical difficulties in development. To address these defects, the technology of enhancing oil recovery in low-permeability reservoirs was discussed based on extensive reference. The study results show that low-permeability reservoirs (10.0-50.0 mD) were principally developed by polymer flooding, polymer-surfactant binary flooding, microbial flooding and in-depth profile control and surfactant flooding, extra-low-permeability reservoirs (1.0-10.0 mD) chiefly developed by surfactant flooding, foam flooding and nano-material flooding, and ultra-low-permeability reservoirs (0.1-1.0 mD) primarily developed by imbibition, CO₂ flooding, N₂ flooding and air flooding, etc. It is the development trend of low-permeability reservoir development in China to gradually improve the oil-displacement mechanism of the replacement medium, develop economical and efficient environment-friendly oil displacement system and promote its application in the field practice. This study provides technical support for efficient development of low-permeability reservoirs.

Carbon capture, utilization and storage (CCUS) is an effective carbon treatment technology. In the context of carbon neutrality, the CCUS technology in China will usher in a trillion-dollar industrial trend. At present, a significant progress has been made in all aspects of CCUS technology, but large-scale applications still face many challenges. By investigating the domestic and international CCUS technology literature and the CCUS projects in operation and planned to be built worldwide, the current development status and research progress of CCUS technology at home and abroad are summarized, and the challenges and future development prospects of CCUS are further clarified. The study shows that the current carbon capture efficiency is less than 90%, and the cost of carbon capture accounts for 60%-85% of the total cost of CCUS projects. The research and development of carbon capture technology should focus on pre-combustion capture (such as ethanol, ammonia and natural gas processing industries) and post-combustion capture to improve carbon capture efficiency and reduce carbon capture costs; the CO₂ utilization technology is currently at the industrial demonstration stage, and breaking the high-temperature and high-pressure environmental bottleneck and finding suitable catalysts to improve carbon utilization efficiency are the key research directions for the next stage of CO₂ utilization technology; the CO₂ storage in oil and gas fields and saline aquifer shall be further researched and promoted on a large scale in terms of an improvement of CO₂ enhanced oil and gas recovery and an increase of CO₂ storage potential; In CCUS projects, challenges such as achieving economic profitability, technological innovation, cost reduction and efficiency, and policy subsidy incentives need to be overcome; new energy sources coupled with CCUS, such as hydrogen and geothermal energy from oil and gas fields, will become a new model for CCUS promotion in the future. This study has implications for accurately grasping the research direction of CCUS technology, promoting the progress and innovation of CCUS technology, and accelerating the leapfrog development of CCUS technology.

In order to better understand the remaining oil research methods, a comprehensive summary of remaining oil research methods and applications in the world was conducted by means of investigation and research. The result shows that the analysis methods of sedimentary micro-phase, micro structure and reservoir flow unit take the basic geological research as the starting point and are the basis for remaining oil research; the core analysis method, micro-seepage simulation, physical simulation and nuclear magnetic imaging technology are important tools for micro-remaining oil research and describe the characteristics of remaining oil distribution from the micro perspective; the material balance method and numerical simulation technology are important tools for macro-remaining oil research and are also the basic data for oilfield development adjustment; the logging technology, chemical tracer monitoring method, four-dimensional seismic method and other methods are useful supplements to remaining oil research methods; for the dynamic analysis method, the data obtained from multiple disciplines need to be synthesized and applied, debunked, and verified against each other to obtain accurate remaining oil research results. This result provides reference for the study of the remaining oil in the middle and late stages of development.

In order to clarify the distribution law of overlying oil and gas reservoirs formed by fault conduit in hydrocarbon-bearing basins, based on the study of the conditions required for the formation of overlying oil and gas reservoirs by fault conduit, a set of prediction methods for the favorable site of overlying oil and gas reservoirs formed by fault conduit were established by determining and overlapping the distribution area of underlying oil and gas reservoirs, the area not sealed by the fault-caprock matching of underlying oil and gas reservoirs, the area sealed by the fault-caprock matching of overlying oil and gas reservoirs and the favorable site for oil-gas migration through faults, and applied to the prediction of the favorable site for the formation of hydrocarbon reservoirs from the fault-conducted Nantun Formation to the Damoguaihe Formation in the Hodomol Area of the Beier Sag in the Hailar Basin. The result shows that the favorable site for the formation of hydrocarbon reservoirs from the fault-conducted Nantun Formation to the Damoguaihe Formation in the Hodomol area of the Beier Sag in the Hailar Basin is mainly located within the 3 local areas of the nucleus of the Hodomol nasal structure, which is conducive to the formation of overlying oil and gas reservoirs from the fault-conducted Nantun Formation to the Damoguaihe Formation in the Hodomol Area of the Beier Sag, which coincides with the current distribution of discovered oil and gas in the Damoguaihe Formation in the Hodomol Area of the Beier Sag, indicating that the method is feasible for predicting favorable sites of overlying oil and gas reservoirs formed by fault conduit. The research method has important guiding significance for the exploration and development of overlying oil and gas reservoirs formed by fault conduit in hydrocarbon-bearing basins.

A great breakthrough was made in the field of Permian volcanic rock exploration in Jingyan Area, southwest Sichuan Basin, but there are various volcanic rock types, obvious differences in seismic reflection characteristics, little coring data, thin reservoirs and unclear distribution patterns; therefore, it is important to further identify the distribution of volcanic facies and high-quality reservoirs in Jingyan Area for volcanic oil and gas exploration in the area. A forward model of volcanic reservoir was established based on the real drilling data to simulate the factors affecting the variation of seismic reflection characteristics of volcanic rock, and an identification model was established for volcanic rock facies and reservoirs. On the basis of the analysis on single well cycle, lithology, lithofacies and seismic waveforms, the types and distribution of volcanic facies were determined by seismic facies, stratigraphic thickness, coherence cube, three-dimensional visualization and other methods. After fine calibration of volcanic reservoirs, the distribution of upper and lower volcanic reservoirs was determined by wave impedance, neural network inversion and other method. Finally, the areas developed with high-quality reservoirs were delineated in combination with the favorable lithofacies, reservoir thickness, fault, and fracture distribution of volcanic rocks. The study results show that there are three types of lithofacies developed in Jingyan Area, namely, eruptive facies, volcanic channel facies and overflow facies. The distribution of volcanic rocks is relatively stable, and two reservoirs are developed in this area. The development of reservoir under the eruptive facies has an obvious effect on the seismic reflection at volcanic rock bottom. As predicted by various methods, the high-quality reservoirs of volcanic rocks are mainly distributed in the west and southwest of the work area, and the superimposed area of basement rift and fractures is the next target of favorable area exploration. There is much guiding significance of the study results for the exploration of volcanic oil and gas in Jinyan Area.

In view of the great difficulty in classifying Carboniferous volcanic rock reservoirs in Kebai Fault Area 1 and the inconsistent classification standards, eight important parameters affecting the classification of volcanic rock reservoirs in this zone are analyzed according to the drilling, logging, testing and other data. The parameters such as lithology, lithofacies, matrix porosity, fracture porosity, permeability, reservoir space type, lithofacies thickness and volcanic mechanism facies zone are assigned according to the reservoir characteristics of the research area and related reservoir classification data are calculated. Combined with the reservoir classification results of each single well, the classification method and classification standard of Carboniferous volcanic rock reservoirs in the research area are obtained. The study results show that according to the classification indicators of volcanic rock reservoirs, the Carboniferous volcanic rock reservoirs in Area 1 can be divided into three types: Type I (0.6≤RCI<1.0), Type II (0.4≤RCI＜0.6), Type (III 0.0≤RCI<0.4), among which Type I reservoirs are the best, Type II reservoirs are the better and Type III reservoirs are the worst. The research results are applied to the reservoir classification of 16 wells that are not involved in the formulation of the standard, and the accuracy rate reaches 93.8%, indicating that the classification standard is suitable for the research area. The research results have important guiding significance for the classification and prediction of Carboniferous volcanic reservoirs in this zone.

In view of great difficulties in the exploration of Permian shale gas under complex geological conditions in Xuancheng Area, Lower Yangtze Block, an effective shale gas exploration method under complex geological conditions is explored by applying a joint exploration with high-accuracy gravity prospecting, high-precision magnetic method and complex resistivity method (CR method) based on rock property testing. The study shows that The shale of Gufeng Formation in Xuancheng Area is characterized by "low magnetic intensity, low density, medium low resistivity and high polarization", the carbonaceous siliceous shale characterized by low resistivity and high polarization, and the intrusive rock (granite porphyry) that mainly affects Gufeng Formation characterized by "low magnetic intensity, low density, low resistivity and low polarization". In the shale gas exploration at Gufeng Formation, Weidun Belt, Xuancheng Area, high-accuracy gravity prospecting and high-precision magnetic method are applied to identify the areas with low magnetic intensity and low gravity and to deduce the distribution of rock mass. Then, CR profile is arranged in the area where magmatic rock is not developed, and wells are drilled for verification at the locations with low resistivity (less than 1 000.00 Ω·m) and high polarisation (more than 4.00%). A total of 50.89 m thick carbonaceous siliceous shale and siliceous mudstone of Gufeng Formation are drilled, achieving excellent application effect. This study provides an important guide to the identification of organic-rich shale formations and the selection of shale gas "sweet spot" in Xuancheng Area and even in the area with complex geological conditions in Lower Yangtze Block.

To address the problem that there are many kinds of calculation methods for the thickness of irreducible water film in tight reservoirs, and the method cannot be accurately selected in the actual research, the calculation methods and influencing factors of irreducible water film thickness in tight reservoirs are summarized in recent years. The study shows that the calculation methods for irreducible water film thickness in tight reservoirs are divided into macroscopic calculation methods based on the ratio of irreducible water film volume to pore throat surface area and microscopic derivation methods that simplify the matrix into capillary model or from the perspective of microelements; the irreducible water film is divided into initial water film, post-displacement water film and post-imbibition water film, and the thickness of the initial water film is influenced by the relative humidity, reservoir depth and permeability of the reservoir, and the thickness of the post-displacement water film is influenced by the displacement pressure, permeability and porosity, and the post-imbibition water film thickness is influenced by the water saturation, ion mass concentration and matrix composition. This study has implications for the selection of calculation methods for the irreducible water film thickness in tight reservoirs and the study of recovery enhancement.

In view of the unclear genesis of calcite veins in 8# Coal Bed of Benxi Formation on Eastern Margin of Ordos Basin, the calcite vein development stages were analyzed to determine the source and formation time of vein-forming fluids by micro petrography, isotope geochemistry, fluid inclusion and other methods. The study results indicated that calcite veins (C1 and C2) in Stage 2 were developed in 8# coalbed in the study area, the diagenetic fluids of C1 calcite veins were mainly stratigraphic brine and biogas-rich organic fluids from surrounding rock and parent rock, the diagenetic fluids of C2 calcite veins were mainly liquid hydrocarbon fluids formed by the decarboxylation of organic matter, and meanwhile the formation of C1 and C2 calcite veins was affected by deep hydrothermal fluid formed by Early Cretaceous tectonic thermal events. Combined with the analysis of the hydrocarbon formation and burial history in the study area, it was clear that C1 calcite veins were formed from Late Triassic to Early Jurassic and C2 veins were formed from Late Jurassic to Early Cretaceous. Production of 8# coalbed in the study area, the calcite vein development area had a high degree of CBM enrichment, indicating bright prospects for exploration and development. The study results provide an important reference for the exploration of CBM-rich areas.

Upper Paleozoic Benxi Formation, Shanxi Formation and Shihezi Formation in Yichuan-Huanglong Area are the chief target formations for exploration and development, and the natural gas enrichment and accumulation are principally controlled by the sedimentary facies and reservoir physical properties. After the evolution of marine-marine-continental transition facies-continental sedimentary system in the Late Paleozoic, the sedimentary facies types are different and the change law of reservoir physical properties is not clear yet. Therefore, the characteristics of Upper Paleozoic reservoirs in Yichuan-Huanglong Area were comprehensively studied with sedimentary evolution analysis, field outcrops, drilling cores, micro reservoir analysis, logging curves and other data. The result shows: Benxi Formation is mainly developed with tidal-flat facies, Shanxi Formation and He₈ Member of Shihezi Formation mostly developed with meandering river-braided delta facies. Tidal channel of Benxi Formation and underwater distributary channel of Shanxi Formation and He₈ Member are the most favorable reservoir facies zones. The sand bodies of the tidal channel of Benxi Formation are lenticular in shape and limited in distribution; the sand bodies of the underwater distributary channel at the front edge of the meandering river delta in Shanxi Formation are migrated and superimposed in multiple periods, with a certain scale; the sand bodies of the underwater distributary channel at the front edge of the braided river delta in He₈ Member are superimposed vertically and connected horizontally, with a blanket-shaped distribution. The reservoir of Benxi Formation is dominated by quartz sandstone, with main pore types of primary intergranular pores and secondary dissolution pores; the reservoirs of Shanxi Formation and He₈ Member are mainly composed of lithic quartz sandstone, with main pore type of lithic dissolution pore. The lithology and pore structure of the Upper Paleozoic sandstone reservoir are the main factors affecting the hydrocarbon showing. The reservoir as a whole is characterized by extra-low porosity and ultra-low permeability, but the content of quartz in the rock gradually decreases from bottom to top, the content of rock chip and fillings gradually increases, and the lithology and pore structure of the reservoirs gradually become worse from Benxi Formation to Shanxi Formation and He₈ Member. The sand bodies of the thick tidal channel of Benxi Formation and the continuously superimposed distributary channel of Shanxi Formation and He₈ Member are lithologically pure and coarse-grained, with good physical properties and high gas abundance, and they are the dominant reservoirs, will the high-quality pores developed in Benxi Formation, which is easy to accumulate natural gas. There is much for reference of the study results to the exploration, development and reserve enhancement of Yichuan-Huanglong Area.

SW Beier Sag is currently a key exploration block with high oil reserves in Hailar Basin. In order to identify the influence of hydrocarbon migration on hydrocarbon accumulation, a "four-in-one” comprehensive determination method of hydrocarbon migration path, which was based on hydrocarbon source analysis, with hydrocarbon distribution characteristics as an indicator, migration numerical simulation as a constraint and geochemical tracing as a supporting evidence, was adopted to study the hydrocarbon migration paths and patterns of Nantun Formation in the study area. The results indicated that there were three hydrocarbon migration paths in Nantun Formation. One path was to migrate laterally from NW Beier Sub-sag to West Beier Slope along its short axis; the second path was to migrate from SW Beier Sub-sag to Huhenuoren Tectonic Belt along its short axis; and the third path was to accumulate hydrocarbon from NW and SW Beier Sub-sags to Huhenuoren Tectonic Belt and migrate to the southwest along the strike of tectonic ridge and fault. On the basis of the identification of migration paths, three types of lateral hydrocarbon migration patterns were summarized, including the migration along the strike of tectonic ridge and fault, the "stepped" migration along synclinal fault and the "toothbrush-like” migration along reverse fault. There were significant differences in the hydrocarbon accumulation sites and reservoir types controlled by the various migration patterns. The results of the study are of some significance for the next selection of favorable zones in the study area and for oil and gas exploration in similar areas.

Nearly 20 passive continental margin basins developed on both sides of the South Atlantic Ocean, and a number of major oil and gas discoveries obtained in deep-water areas, however, a lack of understanding of the geological characteristics of the passive continental margin basins resulted in the low level of exploration in deep-water areas, and the amount of oil and gas resources to be discovered was enormous. For this reason, on the basis of comprehensive analysis of a large amount of data and cases, and fully combining the study results and understanding in recent years, the key geological characteristics of the passive continental margin basins in the middle and southern part of both sides of the South Atlantic Ocean were systematically summarized, and the impact of the geological features on the exploration of oil and gas was deeply analyzed. The study shows that igneous rocks of 3 orogenic types and 3 active phases are widely developed throughout the rifting period in the basin complex on both sides of the South Atlantic Ocean; in the southern section, the thick, seaward-tilted reflective wedges are widely developed in the volcanic passive continental margin basin; in the middle section, the salt rock planar distribution and thickness change rule of the salt rock development type basin complex has both similarity and difference between the two banks, and the salt cementation of the subsalt sandstone reservoir may occur; dirty salts are developed in the Gabon Basin, Santos Basin, Campos Basin, and Lower Congo Basin; the Kwanza Basin in the middle section of West Africa has become the only saltstone-hard gypsum-carbonate interbedded sedimentary basin on both sides of the South Atlantic Ocean due to the cyclonic evaporation pattern, and the thinner inter-salt carbonate layer is both a hydrocarbon source rock and a reservoir. The above geologic characteristics have a great impact on the prediction of the subsalt seismic imaging, subsalt reservoirs, hydrocarbon source rocs and inter-salt carbonate rocks, and increase the multiplicity of solutions for seismic exploration. This study provide a basis for the precise positioning of the future technical attack direction of the passive continental margin basin.

Horizontal wells have obvious advantages in increasing the productioncapacity of oil and gas wells, but influenced by the non-homogeneity of the reservoir, the water breakthrough from horizontal wells is more common during the development of edge and bottom water reservoirs or water drive reservoirs, which brings great challenges to the efficient development of oil fields. Therefore, effective water detection and water plugging technology is one of the important means to improve the development effect of horizontal wells. To address the problem of difficult water breakthrough identification in horizontal wells, the characteristics and field applications of horizontal well water detection methods such as dynamic verification, mechanical water detection, water detection by logging and water detection with tracers were comprehensively summarized, and the problems and development directions of horizontal well water detection and water plugging methods were analyzed. This study can provide a reference for water detection and water plugging in high water-bearing inefficient horizontal wells.

To explore the mechanism of enhancing the oil recovery of tight oil reservoirs by surfactant combined with low-salinity water flooding, in a study case of a tight sandstone reservoir in Xinjiang Oilfield, the effects of low-salinity water flooding, surfactant flooding and their combination on the recovery efficiency at different injection rates and solvent ratios are studied with self-made test equipment. The result shows: The surfactant combined with low-salinity water flooding can effectively play the synergistic advantages to improve the recovery efficiency of tight oil reservoirs. When the injection rate is too low, the surfactant can effectively modify the pore throat interface, but the energy of water flooding is insufficient. When the injection rate is too high, it is easy to induce the coning of oil-water interface, and the effect of surfactant on modifying the pore throat interface is limited, leading to oil displacement efficiency increasing first and then decreasing with the increase of injection rate. At the injection rate of 0.3 mL/min, the highest oil displacement efficiency of 89.79% is achieved with a 7∶3 mass ratio of low-salinity water (0.1% NaCl mass fraction) to sodium dodecyl-benzene sulfonate anionic surfactant (0.4% mass fraction), which is at least 29.83% higher than that of single-fluid flooding. The field application shows that the surfactant combined with low-salinity water flooding can effectively enhance oil recovery and increase monthly production by about 47% in tight reservoirs where the production is severely depleted per well. The study results can be referred for efficient development of similar tight oil reservoirs.

In order to clarify the characteristics and exploration and development potential of shale reservoirs in Longyi₁⁴ Sub-bed, Longmaxi Formation, Luzhou Block and to realize the longitudinal three-dimensional development of the shale reservoirs in Longmaxi Formation, Southern Sichuan, Longyi₁⁴ Sub-bed is divided into three single horizons: a, b and c, and their characteristics are analyzed, including shale thickness, organic matter abundance, mineral composition, physical characteristics, reservoir pace type and hydrocarbon showing. The result shows: Class I reservoir of Longyi₁⁴ Sub-bed in Luzhou Block is featured by an average thickness of 35.6 m, a distribution area of about 1 900 km² and geological resources of more than 8 000×10⁸m³, indicating bright prospects for exploration and development. The shale reservoir at Horizon b is of a thickness of greater than 20 m, an average TOC is greater than 2.5%, a content of brittle minerals of greater than 55%, an average porosity of 4.9%, and an average gas content of 4.5 m³/t, which demonstrates superior reservoir conditions. Compared with the current main pay - Longyi₁¹ Sub-bed, the shale reservoir at Horizon b of Longyi₁⁴ Sub-bed has higher clay content and inorganic pore proportion, which requires scientific fracturing technology and shut-in and drainage measures in the exploitation process to achieve better development results. The results of the study will provide technical support for expanding shale gas exploration and development horizons and improving the production degree of shale gas resources in Longmaxi Formation, Luzhou Block.

The authigenic acid acidizing technology is one of the main measures for stimulation high temperature (ultra-high temperature) and low permeability tight oil and gas reservoirs. The research progress of authigenic acid acidizing technology was comprehensively analyzed, and the acid-rock reaction characteristics of authigenic acid, the main acid-generating mechanism of authigenic acid, and the research progress of authigenic organic acid, authigenic hydrochloric acid, authigenic hydrofluoric acid and composite authigenic acids were introduced, the influence of the type of authigenic acid, hydrogen supply capacity, cost, retardation capability, corrosion inhibition capability and other factors on the field application of acidizing work fluid was analyzed, and the application of authigenic acid in acidizing operation was prospected. This study can provide a reference for the development, popularization and application of autogenic acid acidizing technology.

To further improve the evaluation accuracy of CO₂ storage potential in saline layer, a new method for calculating the theoretical tectonic CO₂ storage volume was proposed based on the material balance equation of CO₂ tectonic storage process and the accurate calculation of underground volume of CO₂ storage. As found in the results, the error of theoretical tectonic CO₂ storage volume calculated by the new method was smaller than that of area method and volume method, which was only about 10%; the new method can predict the theoretical tectonic storage volume under both CO₂ pressurized and pressure-retaining underground storage conditions; both theoretical tectonic CO₂ storage volume and formation pressure showed a trend of increasing with the increase of injection time or injection-production ratio. The new method is of great significance to the study of CO₂ tectonic storage and real-time dynamic control.

In order to further clarify the detailed description of the distribution characteristics of the micro remaining oil in the reservoir in the middle and high water-cut stage, CT nondestructive analysis was combined with conventional displacement test to analyze the distribution characteristics and influencing factors of micro remaining oil in different displacement stages by means of in-situ comparison technology. The results show that the production effect of micro remaining oil is affected by the size of micro pore throat, the connectivity of pore throat and the spatial distribution of pore throat, etc. The characteristics of remaining oil distribution and occurrence are affected jointly by the main driving force formed by various micro forces and the micro pore throat structure. In the water flooding stage, the production effect is mainly affected by the micro-pore structure, the micro remaining oil in the large pore channel with good connectivity can be migrated for a long distance, with high production effect, while the oil droplets in the small channels with poor connectivity will only be thinned slightly along the edge, with poor production effect. Polymer-surfactant composite flooding is followed by water flooding is conducted, the heterogeneity of micro-pore throat distribution is the most important factor affecting the production effect, and the production effect of low-permeability and high-permeability cores with high micro-heterogeneity is more obvious. Different injection and production strategies should be applied in different development stages of the oilfield. Homogeneous intervals with large pores should be selected for development in water flooding stage, while heterogeneous intervals with poor water flooding sweep effect should be preferentially selected for development in the polymer-surfactant composite flooding stage. The results of the study are of guiding significance for the occurrence and enhanced oil recovery of micro remaining oil in the reservoirs.

In response to the problems of low water flooding control degree in conglomerate reservoirs and extremely imperfect well networks in Wellblock Bai 21, Baikouquan Oilfield in the Junggar Basin, the reservoir engineering method and reservoir geology are used as guidance to conduct fine research on reservoir architecture by applying dynamic and static data, analyze reservoir structure, sedimentation, reservoir in-homogeneous characteristics and oil and water distribution law, and improve the injection-production well patterns. The study results show that The idea of water injection optimization and adjustment “different strategies for different layer systems, adjustment and control by zone, classification by single well, and optimization of method” proposed in the article is very effective for the Baikouquan Oilfield. By carrying out the study on the distribution characteristics of the remaining oil and the reservoir injection and production well patterns in the Triassic system of Wellblock Bai 21, 56 dominant seepage channels were identified through comprehensive analysis by applying flowline simulation technology, and the submitted producing petroleum geological reserves were 975.00×10⁴t, and the accumulated oil increase was 16.60×10⁴t. This study has a reference effect for the improvement of injection and production well patterns and efficient tapping of similar reservoirs.

Deep HPHT wells have the characteristics of complex wellbore temperature field changes and large changes in the physical properties of drilling fluids, multiplying the difficulties in accurate prediction of the equivalent circulating density (ECD) of drilling fluid. To this end, based on the drilling data of deep HPHT wells in a study area in the South China Sea, the characteristics of response between the equivalent static density and rheological parameters of deep water-based drilling fluids and the temperature and pressure were investigated by means of PVT meter and rotary viscometer. The parameters of empirical model were fitted based on experimental data, while the ECD calculation model of deep HPHT wells was improved with consideration of the influence of temperature and pressure on the physical parameters of drilling fluid and the influence of subsea pressurization on the flow field and temperature field of wellbore. The study showed that, the physical properties of the water-based drilling fluid were greatly affected by high temperature and pressure, and the higher the displacement of the subsea booster pump, the higher the ECD in the wellbore. The model was used in the calculation of Well ST362-1d well in the South China Sea, and the average error was only 0.249% between the predicted value of ECD model and the measured value. The results of the study can serve as references for the optimal design of hydraulic parameters and wellbore pressure control in deep HPHT wells.

The Liaohe Depression has already entered the high maturity stage of exploration. The deepening exploration in mature exploration area cannot be limited to the scope of geophysical technology progress, drilling level improvement and revolution of oil and gas reservior stimulation technology, but should be reflected in the accurate grasping and innovative understanding of the objective existence of subsurface geological conditions. To address the problems that the conventional oil and gas exploration is difficult to achieve oil and gas discovery on a large scale and conventional exploration ideas are difficult to adapt to new unconventional oil and gas targets, the ideas of deepening geological understanding and reconstructing reservoir formation model were applied to innovate reservoir accumulation model in the Qingshui Depression of Western Sag to newly discover oil reserves of 2 800×10⁴t in rocky oil and gas reservoirs; a new "two-element“ evaluation model was created in Leijia area, which realized the surface-to-body transformation of unconventional oil and gas target evaluation; the exploration unit was reconstructed in the Member 3, Shahejie Formation of the Eastern Sag, and a new exploration unit was discovered and the Well X47 was deployed and implemented to obtain high production gas flow. A number of achievements were made during the exploration of oil and gas in mature exploration area of Liaohe Depression, which provided ideas and methodological reference for the exploration of similar type of mature area.

The stratigraphic space stacking pattern and sedimentary characteristics of alluvial fan controlled by paleo gully geomorphology are more complicated, making it difficult to conduct the study of sedimentary characteristics with existing model. Guided by the research results of the modern Baiyanghe alluvial fan and combined with seismic, core, well logging, physical properties, oil-bearing characteristics and other data, the fluvial alluvial fan controlled by paleo gully geomorphology in Shawan Formation, Chunguang Oilfield was systematically studied in terms of palaeogeomorphology, lithofacies characteristics, microfacies distribution and other sedimentary characteristics, and a dynamic sedimentary evolution model was established. The results of the study show that this area was featured by two-channel paleo gully geomorphology, and the formation went through the filling process of gully-filling-progradation-retrogradation, with unbalanced deposition. Limited by the regional location, sedimentary subfacies were developed only at the middle and rear of the fan. The early stage was a flood period, and the fan was dominated by sedimentation. Controlled by the paleo gully geomorphology, the restricted channelized fan deposits were also developed. From the middle to the end of the fan, gravity current deposition was converted to traction current deposition. The late stage was a flood regression period, and with the filling and consolidation of the strata, the unrestricted fan deposits were developed and dominated by sheet flow deposit. On the basis of fine identification of sedimentary microfacies, the classification and evaluation criteria for reservoirs were established, the study results were applied to the northwest of Chunguang Oilfield, and three favorable areas were selected, and new wells were deployed to achieve breakthrough in the paleo-gully alluvial fan reservoirs. The study results have deepened the understanding of sedimentary evolution characteristics of alluvial fans controlled by different landforms and have important significance for the study of sedimentary characteristics of paleo-gully alluvial fan reservoirs.

To address the problems of low recovery rate and poor water injection huff-n-puff effect in the depleted development of Jimsar shale oil. A study on the applicability of CO₂ huff-n-puff technology in shale oil reservoirs was carried out by means of hydrocarbon phase experiments and numerical simulation methods for reservoirs to guide the implementation of CO₂ huff-n-puff technology in the field. The results show that Compared with CH₄, CO₂ interacts better with Jimsar shale oil. Under the conditions of formation pressure and formation temperature, the solution gas-oil ratio of CO₂ in crude oil is 497.83 m³/m³, the crude oil viscosity is reduced by 70.65%, and the crude oil volume is expanded by 2.05 times; for typical shale oil wells, multi-cycle CO₂ huff-n-puff can improve the recovery rate by 9.43 percentage points and crude oil production by 31 472.40 t. With the shortening of fracture spacing and the increase of reservoir porosity, the effect of CO₂ huff-n-puff on oil enhancement gradually becomes better, and the influence of permeability and oil saturation on the effect of CO₂ huff-n-puff is relatively small. The results of the field test show that CO₂ huff-n-puff can effectively enhance the recovery rate of shale oil, and the oil enhancement effect is better under the condition of no fracture disturbance. The research results have some implications for the efficient development of shale oil.

The gas storages converted from deep carbonate gas reservoirs are characterized by large high and low pressure variations, stress sensitivity, and strong heterogereity. Using conventional methods to calculate its injection-production capacity will lead to large errors in production capacity. In response to the above problems, stress sensitivity is considered. The binomial productivity equation was revised in view of the influence of stress sensitivity and gas physical property changes, and on this basis, a calculation method of injection-production capacity suitable for the gas storage converted from deep carbonate gas reservoirs was established. Example calculations are carried out in conjunction with the Shapingchang Carboniferous Gas Reservoir in the Sichuan Basin, the influencing factors are analyzed, and the results show that: for type Ⅰ and Ⅱ pore-fracture collocation model reservoirs, the reasonable gas production rate of gas wells is controlled by outflow dynamics under low pressure and limited by erosion flow under high pressure, while the reasonable gas injection rate is controlled by outflow dynamics under high pressure and limited by erosion flow under low pressure; for type Ⅲ pore-fracture collocation model reservoirs, the reasonable gas injection and production rates of gas wells are mainly controlled by the outflow dynamics. The influence of stress sensitivity on the maximum gas injection rate of the gas well is 0.81%~9.69%, and the influence of the change of gas physical parameters is 5.15%~35.29%; under the existing wellbore structure conditions, when the gas injection rate is 55×10⁴ to 70×10⁴ m³/d, the frictional pressure loss can reaches to 10 MPa; when the inner diameter of the tubing increases from 62.0 mm to 112.0 mm, the maximum gas injection volume increases to 2.6 times. The research results can provide technical support for the calculation of the injection-production capacity of deep carbonate gas storages, and have guiding significance for the construction and operation of such gas storages.

The conventional acid fracturing working fluid system has problems such as too fast acid-rock reaction and short effective distance, the microencapsulated solid acid is one of the effective means to solve this problem, and it is commonly used for deep acid fracturing of unconventional oil and gas reservoirs. This study describes the mechanism of action, structure and performance characteristics of microencapsulated solid acids, summarizes the research progress of acid fracturing technology with microencapsulated solid acid, and indicates the main research directions of acid fracturing technology with microencapsulated solid acid in the future. This study can provide technical support for the stimulation of ultra-high temperature carbonate reservoirs, and provide theoretical guidance for the research and application promotion of acid fracturing technology with microencapsulated solid acid.

In view of the strong heterogeneity of the glutenite oil reservoir, an in situ emulsification enhanced oil recovery technology was proposed. The emulsification performance, interfacial tension reduction performance and oil displacement performance of the new W/O emulsification system (DMS) were studied, and at the same time the results were compared with the polymer/surfactant binary system used in the oil field. The experimental result shows that under different water contents, DMS can emulsify with crude oil to form W/O emulsion. With the increase of water content, the viscosity of emulsion increases. When the water content is 70%, the viscosity reaches the maximum value, which is 9 times of the viscosity of crude oil, much higher than the viscosity of binary system, and the fluidity control ability is stronger. DMS can be directionally adsorbed on the oil-water interface and reduce the oil-water interfacial tension to 0.12mN/m. Under the influence of DMS, oil and water are emulsified in situ to form W/O emulsion with a particle size of 0.5-6.0μm. In the glutenite core, DMS flooding and subsequent water flooding can improve the recovery by 18.6%. Under the permeability max-min ratio of 10, dual flooding and subsequent water flooding can improve the recovery by 24.0%, while DMS flooding and subsequent water flooding can improve the recovery by 35.3%, showing better fluidity control and the ability to improve the water absorption profile. The research result will provide theoretical support for enhanced oil recovery of glutenite oil reservoir

A microfracturing-based expansion technology for horizontal wells was proposed to improve the seepage conditions around the horizontal wellbore, because the infill horizontal wells were not connected to the original wells in composite well pattern under steam flooding and gravity drainage in the heterogeneous reservoirs, Qigu Formation, F Oilfield, Xinjiang Oilfield. The feasibility of microfracturing-based expansion technology and the change characteristics of expanded reservoir were analyzed by laboratory core test, geomechanical finite element simulation and thermal numerical simulation. The results show that he reservoir was high in high quartz while low in clay mineral content, and well developed with pores, which was favorable for water flooding for expansion; in the process of stable pressurization, the spread range of the injection fluid was expanded to reduce the effective confining pressure of the surrounding reservoir and significantly improve the expansion effect; the displacement and porosity of the expanded reservoir in longitudinal direction were obviously better than that in transverse direction, which is conducive to the connection of upper and lower injection-production wells. After five rounds of steam stimulation for preheating after microfracturing-based expansion, the oil wells were connected quickly. In the preheating period, the periodic oil production and oil-steam ratio were significantly improved, and the productivity of horizontal section was greatly enhanced. The study results provide a reference for improving the connectivity among injection and production wells in composite well pattern under steam flooding and gravity drainage.

It is difficult to exploit the crude oil with conventional technology due to high viscosity, high flow resistance and poor flow capacity of crude oil in heavy oil reservoirs. A conclusion was made in this paper to summarize the study of heavy oil modification additives (catalysts and hydrogen donor), point out the existing problems, and outline the future study directions. The study shows that the existing heavy oil modification catalysts are disadvantaged by unclear catalytic mechanism, poor universality, high cost, regeneration difficulties, easy deactivation and environmental pollution. In addition, the uneven mass transfer and severe reaction conditions of hydrogen donor in heavy oil modification reaction will lead to limited hydrogen supply. Therefore, the future study of heavy oil modification additives is to further explore the modification mechanism of heavy oil at the molecular level, and develop modification additives with wide application scope, high activity and controllable cost in combination with complex formation conditions. The study provides a reference for studying and developing heavy oil modification additives and applying the EOR technology in oil fields.

In response to unclear sources of associated gas during thermal stimulation by steam injection, laboratory experiments were conducted on crude oil, core and formation water samples from Block Qi 40, Liaohe Oilfield with high-temperature and high-pressure reaction still to explore the generation mechanism and influencing factors of associated gas. The study results showed that, crude oil was the main source of associated gas in thermal recovery and mainly took place in aquathermolysis, and reservoir minerals played a catalytic role in the aquathermolysis; the starting temperature of associated gas production was 150 ℃, and its production increased with the increase of temperature, when the temperature reached 300 ℃, the joint action of aquathermolysis and heavy oil pyrolysis led to a sharp increase of associated gas production; at 250 ℃, the aquathermolysis of crude oil was basically completed after 9 days, after which there was no significant increase in associated gas production. The study is of guiding significance for the full utilization of associated gas in thermal recovery of Liaohe Oilfield by steam injection.

Since the PVT test consistency test method is inapplicable to high-temperature reservoirs, a systematic test method was proposed for the consistency of phase state test results in high-temperature hydrocarbon reservoirs, in which the equilibrium constant calculation method at high temperature was used to modify the material balance method, Hoffman method and equilibrium constant method, and to test the consistency between the component data of the phase state test and the constant-volume depletion test data with such two methods and the component verification method, so as to judge the test results more accurately. A consistency test was conducted between the component data and the constant-volume depletion test data of two fluid samples taken from high-temperature hydrocarbon reservoir, namely Condensate Gas Sample A from Well Bozi 104 and Volatile Oil Sample B from Well Bozi 7 in Tarim Oilfield. The results verified the validity and reliability of the method in this paper. This study is important to clarify the phase characteristics of formation oil and gas, especially volatile oil and condensate gas at high temperature.

In view of the problems of high condensate oil reservoir, cold damage caused by wax precipitation and low recovery efficiency by water flooding, were the microbial high throughput sequencing analysis and experimental evaluation method for chemical flooding and used the core physical simulation and CT scanning and other means to propose the enhanced high pour-point oil recovery technology through microbial + chemical compound flooding combination and research the microbial-chemical compound flooding formula. The system has the advantages of chemical flooding greatly improving the oil displacement efficiency and microbe reducing the waxy composition of crude oil. Finally, the slug combination of microbial and chemical flooding formula is optimized by physical model experiment. The experimental result shows that: The microbial + chemical compound flooding can improve the oil displacement efficiency by 35.19% than the water flooding, and if compared with the single chemical compound flooding, it can improve the oil displacement efficiency by 7.27%, and the oil increment increases by1.16 t/t. This research provides an effective replacement technology for the mode conversion and enhanced oil recovery in the late development stage of high condensate oil reservoir.

Fractured reservoirs are developed with pores, fractures and caves in reservoir bed, and it is difficult to accurately characterize the reservoir. In order to accurately describe the spatial distribution characteristics of fractured reservoirs, the geological and petrophysical models of embedded multi-scale fractured reservoirs of key wells were established according to logging and drilling data and petrophysical test data; a study was made on the multi-medium connectivity and conductivity and the geological modeling technology of embedded fractures, and the model was used to numerically simulate the fractured reservoirs in the lost oil field. The study results show that the geological modeling based on the multi-scale embedded fracture model can be used for detailed description and numerical simulation of large-scale fractures such as structure and fault, as well as small-scale fractures based on the equivalent principle, and the fitting rate of single-well dynamic indicators was more than 90%. The numerical simulation study of Liuhua Oilfield proves that the reservoir will maintain the current fluid recovery rate of each well for continuous development, most of the wells will not experience serious water flooding, and the wells with higher risk are mainly located near the fault on the northeast edge of the work area. This study provides a reference for geological modeling, numerical simulation and development for similar reservoirs.

To address the problem that the main controlling factors of single shale gas well production in Weiyuan Block, Sichuan Basin are unknown, based on the geological and engineering data and production data of 132 gas wells which have been put in production for more than a year in the area, an analytical study was conducted by the gray correlation method. The study shows that, the main controlling factors affecting the first-year cumulative production of a single shale gas well are proppant dose, number of fracturing stages, median vertical depth of horizontal wells, fracturing section length, fracturing fluid volume, porosity, pressure coefficient and sanding intensity. It was clear that the machine learning method was higher in accuracy after comparison of the machine learning method and the traditional empirical formula method to predict the first year's cumulative output and initial output. Meanwhile, based on the analysis of the main controlling factors, the machine learning method applicable to the study area was preferably selected as the support vector machine method, and its prediction accuracy was higher than 90%. The study has an important implication to the productivity evaluation of similar shale gas blocks.

Shallow gas resources are widely distributed and have a broad prospect for exploration and development. In view of unclear understanding of shallow gas distribution in the Changchunling South Block, by taking the shallow-buried reservoir at the fourth member of Quantou Formation as the target formation, main controlling factor is specified by analyzing the reservoir forming conditions so as to obtain the controlling effect of sedimentary microfacies and fault on gas reservoir formation. The study results show that the gas source in the research area is mainly derived from the associated gas of crude oil generated by the hydrocarbon source rock at the first member of Qingshankou Formation. The reservoir is the fluvial facies deposition with thick channel sand body and good physical property, which is conducive to shallow gas enrichment. The reservoir sand bodies in fault structure and incline provide good vertical and lateral migration channels for shallow gas. The research area has an anticlinal shape, which is cut by three groups of faults in North-South, NW and a few NE strikes, and the structural trap conditions are good. Meanwhile, the hydrocarbon source rock at the first member of Qingshankou Formation is the regional cap rock with large thickness. The fault stops its activity at the late period of the Mingshui Formation and the preservation condition is good. Sedimentary microfacies and faults are the main controlling factors of shallow gas accumulation in the research area, so fault-lithologic gas reservoirs should be mainly sought, and the anticline uplift zone in the eastern part of the research area is a favorable exploration area. The research results point out a favorable direction for further exploration of this block.

Block J-XC is a common heavy oil reservoir with high porosity and permeability, shallow reservoir burial, and thin thickness. Due to high viscous resistance in the water flooding process, small effect range of water flooding, low reservoir productivity and low recovery rate by water flooding, it is necessary to change the development method and employ polymer flooding method to enhance the oil recovery. On the basis of polymer injectivity evaluation, the injection parameters and injection-production relationship of polymer flooding were optimized by core flow test and numerical simulation, including the mass concentration of polymer injection, injection volume, injection rate, well pattern, well spacing, injection-production ratio, so as to obtain the best injection parameters and injection-production relationship. The result shows that the injectivity and high utilization efficiency of the polymer were actualized under the conditions of 2 100×10⁴ relative molecular mass of the polymer, 1 500 mg/L injection mass concentration and 0.400 times of pore volume; the optimal reservoir engineering parameters were a five-spot pattern, a reasonable injection-production well spacing of 150 m, an injection rate of 0.070 times the pore volume per year, and an injection ratio of 1.1 to 1.2 for different thicknesses of oil reservoirs according to their optimal single-well daily injection volumes. The pilot test in the field proves the significant effect of increasing oil and decreasing water cut in the target well cluster. As of June 2021, the cumulative injection rate of polymer is 0.228 times the pore volume, and the cumulative oil increase is 5.06×10⁴t, the recovery factor is enhanced by 6.75 percentage points and the water cut is decreased by 15.8 percentage points. There is much for reference of the results to the optimization of polymer flooding parameters and reservoir engineering design in shallow ordinary heavy oil reservoirs.

To understand the sedimentary characteristics and sedimentary patterns of the Triassic Shaofanggou Formation in the North Santai High area of the eastern Junggar Basin and clarify the constraints on reservoir development, a study on the sedimentary patterns of the Shaofanggou Formation and its control on reservoir development was carried out on the basis of sedimentology and in combination with the data such as core, thin section, grain size and conventional physical properties. The study shows that there are nine typical petrographic types developed in the Shaofanggou Formation, namely channeled interlaminated conglomerate phase, platy interlaminated conglomerate phase, massive laminated conglomerate phase, channeled interlaminated sandstone phase, platy interlaminated sandstone phase, massive laminated sandstone phase, wave-formed sand laminated sandstone phase, parallel laminated siltstone phase and massive laminated mudstone phase; the Shaofanggou Formation is mainly dominated by braided river delta phase, and the sedimentary microphases include 10 types such as floodplain, abovewater braided river channel, channel bar, natural dike, underwater braided river channel, interdistributary area, underwater natural dike, estuary bar, prodelta mud and beach bar, among which, underwater braided river channel, estuary bar and beach bar reservoirs have the best physical properties, with average porosity of 17.31%, 20.66% and 21.81%, and average permeability of 6.89, 7.05 and 12.98 mD, respectively. The reservoir properties in this area are mainly controlled by sedimentation, and the high-quality reservoirs are mainly developed in underwater braided channels, estuary bar and beach bar microphase. The study can provide a theoretical basis for further fine exploration and development of oil and gas within the study area.

To address the problem that conventional reservoir numerical simulation software cannot accurately simulate the fracture propagation during the development of pressure drive water injection of tight oil; based on the dynamic fracture propagation law during the development of pressure drive, the fracture propagation model is organically coupled with the oil-water two-phase seepage model of tight oil reservoir, a pressure drive water injection model was established, and the problem was solved by the finite difference method. The model was applied to the five-point injection and recovery well network of Well Cluster X8 in an oilfield to study the production dynamic characteristics of pressure drive development under high-speed constant displacement and step increasing displacement. The result shows that the injection displacement is positively correlated with the fracture propagation velocity; under the same injection displacement, the fracture propagation speed in the near-wellbore zone of the water injection well is faster; dynamic fracture made the pressure and injected water propagate along the fracture propagation direction; in a five-spot pattern well network with a cumulative injection volume of 3×10⁴m³, compared with the step increasing displacement with high-speed constant displacement method, the fracture propagation length is increased by 11.9 m, and the oil-water front edge migration lags by 4.2 m; corresponding to corner wells, the effective time was 5 days later, the water breakthrough time was 31 days later, and the staged recovery degree was 0.45 percentage points higher; the step increasing displacement pressure drive method improved the affecting area of the injected water, delayed the water breakthrough time of the production well, and improved the development effects of the reservoir. The research results can provide technical support for pressure drive development water injection design of tight reservoirs.

To address the problem of unclear distribution of high-quality reservoirs in He8 Member in Daning-Jixian Area, the reservoir development characteristics and influencing factors were analyzed from petrology and mineralogy, diagenesis and other aspects by using cast thin section, X-ray diffraction, cathodoluminescence and scanning electron microscope. The results show that the rock type of the He8 member reservoir is mainly lithic quartz sandstone, and the lithology is mainly of medium and coarse sandstone; the type of reservoir space includes intergranular dissolution pore, feldspar dissolution pore, lithic dissolution pore and clay mineral intercrystalline pore, etc. The reservoir has low-porosity and low-permeability physical properties, but it is a dense reservoir with good porosity-permeability correlation; the compaction is the main factor for the dense reservoir in the study area, the average compaction reduction rate is 80.16%, the average cementation reduction rate is 17.00%, the dissolution can improve the reservoir properties, the average dissolution increase pore rate is 7.34%; the high-quality reservoir does not exist in the middle or at the top or bottom of the sand body, its development in the sand unit follows the distribution pattern “Upper and lower sides of the sand body center”; under the influence of factors such as compaction resistance, dissolution conditions and various types of cementation properties, the high-quality reservoirs are mostly developed in quartz sandstone and medium and coarse sandstone. The research results can provide reference for the accurate prediction of high-quality reservoirs in the study area.

To reveal the macro heterogeneity of shale oil reservoirs in the Chang 7 oil reservoir formation, Ganquan area in the southeastern part of the Yishan Slope, Ordos Basin and its control on oil distribution, the macro heterogeneity of the Chang 7₁ and Chang 7₂ oil reservoir sub-formations was quantitatively characterized and compared by means of barrier bed and interbed identification statistics, permeability statistics and Lorenz curve construction, and the influence of macro heterogeneity on oil distribution was analyzed by the method of correlation analysis and multifactor overlay. The results of the study show that the average number of interbeds developed in the Chang 7₁ and Chang 7₂ shale oil reservoirs in the study area is 3.8 and 5.1 respectively, and the permeability of the sand body is dominated by composite rhyme and is strongly heterogeneous; the average number of barrier beds developed is 3.4 and 2.8 respectively, and the average thickness of single barrier bed is 6.0 and 4.9 m respectively; Chang 7₁ exhibits slightly weaker intra-layer heterogeneity and stronger inter-layer heterogeneity than Chang 7₂. The rhythmicity of the shale oil sandstone reservoir has obvious influence on the oil saturation, and the barrier bed with thickness greater than 10.0 m have obvious capping effect on oil and gas, while the "physical" barrier beds and interbeds constitute lateral shielding for oil and gas accumulation. The barrier bed is more developed in Chang 7₁ than Chang 7₂, and the oil and gas are more abundant in Chang 7₂. In the plane, the distribution of oil-gas accumulation area is strip-like, mostly located in the area with large sand thickness, good continuity and permeability of greater than 0.2 mD.The thickness of oil layer varies slightly in the direction of sand body extension along the river, but varies more in the direction of vertical river extension. The conclusion of the study can provide theoretical reference for the evaluation of the favorable area and the selection of development parameters for the Chang 7 sandwich type shale oil in the southeastern part of the Yishan slope of Ordos Basin.