A major breakthrough has been obtained in the glutenite reservoir in the lower member of the Cretaceous Yagelem Formation in Well Ketan 1 located in Kela 2 trap of Kelasu Structural Belt in Tarim Basin, realizing the idea of “discovering another Kela gas field below Kela Gas Field”, which is of great significance to the exploration of the deep Cretaceous. The in-depth study of hydrocarbon accumulation conditions, reservoir physical properties and structural model in Well Ketan 1 is conducted, which supports to identify the hydrocarbon accumulation assemblage of “hydrocarbon supply by source rock in the Jurassic-Triassic, fractured type sandstone reservoir in Yagelem Formation,and mudstone cap rock in Shushanhe Formation” and establish a new hydrocarbon accumulation pattern of “lower generation and upper storage,vertical transport and stereoscopic accumulation” in Kelasu Structural Belt. The successful drilling of Well Ketan1 confirms that there is superior reservoir-cap rock assemblage below the Cretaceous Bashijiqik Formation in Kelasu Structural Belt, and the hydrocarbon accumulation conditions are more favorable when approaching to the deep source rock. In addition, the fault-anticline traps in Yagelem Formation are developed in rows and belts, which show great resource potential and can form a new strategic replacement area for gas exploration.

The early exploration in Baoding Sag in Bohai Bay Basin mainly targeted at the buried hill and deep Paleogene, but no substantial discovery was achieved in nearly 60 years. Based on 3D seismic acquisition and 2D seismic re-processing, the geological structure was reunderstood as a whole, and the following results were obtained: (1) In the Early-Middle Paleogene (during the deposition period of Kongdian Formation-Second member of Shahejie Formation), the fault rift activity was strong in the west and weak in the east, and the lake basin was shallow and small in sedimentary range; In the Late Paleogene (during the deposition period of the first member of Shahejie Formation-Dongying Formation), the fault rift activity was strong in the east and weak in the west, and it was a large lake basin in the maximum flooding period. (2) The organic-rich algal source rock in the saline lake basin in the lower part of the first member of Shahejie Formation experienced early and multi-stage hydrocarbon generation, forming early and low mature oil. (3) The reservoir-cap rock combination in shallow Dongying Formation is good, which is the main target layer. In addition, hydrocarbon accumulation pattern of “two-way hydrocarbon supply, hydrocarbon transport by sand and fault, and hydrocarbon enrichment in shallow formation” is constructed. As a result, several exploratory wells such as G77X and BQ1X were drilled in the optimally selected Qingyuan structural belt, and high-yield oil flows were tested in Dongying Formation,marking an exploration breakthrough in Baoding Sag, and confirming the oil and gas enrichment in shallow formation in the first row of sags in Taihang piedmont, which had reference significance for the exploration of mature oilfields in Bohai Bay Basin.

With the increasing degree of exploration and development, “whether breakthroughs can be achieved in deep to ultra-deep formation” has become an important scientific issue affecting the stable development of mature oil fields in eastern China. It is particularly prominent in Liaohe Oilfield due to the small mining rights area, and extremely difficult in Liaohe Depression because of its narrow lake basin and poor data quality. The regional tectonic evolution is analyzed and hydrocarbon-generating kinetics and hydrocarbon accumulation dynamics are researched to identify the mechanisms of basin formation, hydrocarbon generation and accumulation in eastern tidal zone of Liaohe Depression. The study results show that: (1) Controlled by the dustpan structure of the protype lake basin, the main source rocks were characterized by “great burial depth, large thickness and wide distribution area”; (2) Two genetic types of mature-highly mature gas, i.e.,kerogen pyrolysis type and crude oil cracking type, were developed in deep formation, showing great resource potential; (3) An independent “fluid sealing box” was developed in deep to ultra-deep formation by the coupling of two factors of multi-set argillaceous rocks in the sedimentary filling sequence and the early strike-slip shear faults, forming two types of hydrocarbon accumulation modes, namely selfgeneration and self-storage type and side-generation and side-storage type, which had favorable geological conditions for the formation of medium to large-scale gas reservoir. A major breakthrough has been achieved in risk exploration well Kuitan 1, which provide significant practical and hydrocarbon accumulation theory guidance to further deepen the exploration of deep to ultra-deep formation in Liaohe Depression and even fault basins.

Prospect evaluation and management are a key link to improve the efficiency of exploration decision-making and the success rate of exploration wells. The high-efficiency and standardized management serves as a bridge connecting prospect evaluation and exploration deployment. By investigating prospect classification, evaluation and management practices of major oil companies worldwide, and combining with the overseas exploration practice of Chinese oil companies, a set of prospect classification, evaluation and full-cycle management mode in line with the international practice is proposed. (1) Based on the data coverage, geological understanding, engineering conditions, and economic value of the prospect, four levels of prospects are classified, including Concept, Lead, Prospect, and Drill Ready Prospect, and the definition, conception, evaluation content and management requirements of each level are specified; (2) The classification system of undiscovered resources of the four levels of prospects is established, achieving the classified management of the undiscovered resources, which enriches and develops SPE-PRMS resource classification system; (3) The purpose, meaning, and connotation of full-cycle prospect management are clarified, and the key links in the full-cycle closed-loop management from Concept to post-drilling evaluation are determined, which have a significant guiding role in formulating annual exploration plans or medium and long-term plans. The application of this system clearly shows the requirements of prospect portfolio of various levels and the work objectives at different exploration stages to achieve the annual reserve increase target and maintain the sustainable development of the company, realizing the dynamic management of various levels of prospects and high-efficiency decision-making, which has good promotion and application value.

The benefit development of Sulige Gasfield faced great challenges after its discovery. In order to learn from international advanced technologies and management thoughts, an international cooperative development mode has been established between Total and PetroChina (operator) to achieve development breakthroughs. More than 10 years’ international cooperative practice shows that, the production performance of a single well in international cooperation zone is significantly better than that in self-operated development zone given the same reservoir geological conditions. Therefore, it is of great significance to systematically summarize the development technologies to improve the development effect in self-operated development zones. Different from the development concept of pursuing large-scale benefits and cost control in self-operated development zones, the economic benefits and positive cash flow are targeted and risk control is centered in international cooperation zone. In addition, six main development technologies have been formed by research and practical tests for several years, including 3D seismic-geological fusion reservoir evaluation, grid partition and checkerboard cluster well pattern deployment, well factory drilling and completion operation, TAP Lite layered fracturing reservoir reconstruction, moderate pressure relief and intermittent gas production well management, and speed string measures for production increase. By comparing development technologies applied in self-operated zones, five key development technologies are determined to be referred and three important enlightenments are concluded: (1) Continuously deepen geological study to support high-quality deployment; (2) Strengthen the top-level optimization design to support scientific and orderly implementation; (3) Strengthen the whole process management and quality control to boost the development results. The absorption and reference of key development technologies and important experience in international cooperation zone provide strong support for the improvement of development effect in new tight gas zones.

Bozhong 34-9 Oilfield is characterized by the first Cenozoic sandstone oil reservoir discovered in Bohai Sea by 2022 that affected by igneous rocks the most, as well as the first in offshore oilfield development in China. Therefore, the fine identification of igneous rocks and its lateral sealing capacity for sandstone reservoir are very crucial to the high-efficiency oilfield development.By fully using core, thin section, well drilling, logging, and forward modeling data, igneous rock facies are finely characterized and identification chart is established in Bohai Sea area. The sealing capacity of igneous rocks is evaluated from aspects of petrology and logging physical property characterization, which indicates that the lithologic-structural oil reservoir is dominated in the study area,and igneous rocks mainly segment and seal oil traps. Specially, the lateral sealing capacity of igneous rocks is evaluated, the pattern of igneous rocks laterally sealing sandstone trap is summarized, and potential area is proposed. The study results show that volcanic conduit facies, intrusive facies and overflow facies igneous rocks were mainly developed in the study area, and three patterns of igneous rocks laterally sealing sandstone trap are identified, i.e., lateral sealing by dike, lateral sealing by stratified igneous rock mass or lateral non-sealing by stratified igneous rock mass. The first two types of igneous rocks lateral sealing patterns have favorable conditions for further evaluation. A total of 78 development wells have successfully been implemented in the oilfield, which enriches the exploration and development technical means of sandstone oil reservoirs in the igneous area in Bohai Sea area, and has important guiding significance for the exploration and development of similar oilfields at home and abroad.

Since the large-scale development of Taiyang Shallow Shale Gas Field in Zhaotong demonstration block, there has been always problems such as low reserve production rate and low recovery factor caused by the development mode of large well spacing and single target layer, which also bring severe engineering risks for the later well pattern infill or adjustment. Therefore, pilot well group with small well spacing is deployed and implemented in Platform TYH11 for stereoscopic development of Taiyang Shallow Shale Gas Field. Based on hydraulic fracture simulation and production numerical simulation methods, the whole process evaluation of “pilot well deployment-drillingfracturing-production-production capacity” is conducted by applying geological, drilling, fracturing and production test data. The study results indicate that : (1) ClassⅠ+Ⅱ reservoir in first sub member of the first member of Longmaxi Formation (Long 11 sub member) in the Upper Ordovician Wufeng- Lower Silurian has conditions for high-yield production and basis for multi-target production in vertical; (2) The engineering technology series have been developed for the whole process of drilling, fracturing and well testing, which enable the successful implementation of stereoscopic development well groups with small well spacing; (3) The stereoscopic development mode with small well spacing supports to effectively increase the reserve production rate by 23.0% and the recovery factor by 11.0%; (4) The communication of natural fractures causes pressure channeling interference within the well group and with adjacent wells, which greatly impacts on the production of old wells; (5) The frac-hit is aggravated by the change of in-situ stress field around the adjacent old producing wells, so it is recommended to keep a well spacing of at least 380-500 m between the new well and the old well. The study results lay a foundation for the promotion and application, overall development plan design, development policy formulation, and large-scale and beneficial stereoscopic development of Taiyang Shallow Shale Gas Field in Zhaotong demonstration block.

With the deepening of petroleum exploration, new discoveries have been made in tight reservoirs in the eighth member of the Triassic Yanchang Formation (Chang 8 member) in Pengyang area in the southwestern margin of Ordos Basin, indicating a great exploration potential. However, the overall research level is low, such as the extremely complex oil-water contact and the unclear law of hydrocarbon charging. The fluid inclusions provide a basis for analyzing the process of hydrocarbon charging. By using fluid inclusion testing methods such as microscopic observation, homogenization temperature measurement and PVT simulation, as well as the quantitative grain fluorescence (QGF) experimental technology, the process of hydrocarbon accumulation and adjustment in Chang 8 member is discussed and the difference of hydrocarbon accumulation in the interior of the basin and basin margin is analyzed. The study results show that oil and gas inclusions are relatively developed in the study area, the maturity of crude oil is low, the oil display grade and modern/paleo oil saturation are lower than those in the interior of the lake basin, showing an overall low intensity of hydrocarbon charging. The large-scale hydrocarbon charging events mainly occurred at the end of Early Cretaceous and the early stage of Late Cretaceous. The limited pressure difference between source rock and reservoir provided driving force for the short-distance hydrocarbon migration, but it was lower in the study area than that in blocks in the main basin, which led to a low oil saturation in the basin marginal area. The relationship between quantitative grain fluorescence (QGF) and quantitative grain extract fluorescence (QGF-E) indexes shows an inconsistent trend, indicating the change of the paleo oil-water contact or the adjustment of oil reservoir in the study area. The later tectonic movements greatly adjusted/destroyed oil reservoir near the faults in the southwestern basin margin, which further decreased the scale of oil charging in Chang 8 member. The deep research on oil charging and accumulation laws and evolution process of oil reservoir in the basin margin has a great guiding significance for identifying the exploration potential of low-permeability tight oil and gas sandstone reservoir in various tectonic settings.

In Dongying Sag, a typical “red bed” is developed in the deep formation, lower sub member of the fourth member of Shahejie Formation-Kongdian Formation (Es₄^x-Ek₂), which has a large thickness but few discovered reserves, showing a great exploration potential.Based on the comprehensive evaluation of deep source rocks, high mature source rock-oil correlation and systematic analysis of self-source type hydrocarbon accumulation pattern, characteristics of two sets of source rocks in Es₄^x-Ek₂ are determined, and resource potential in the deep formation is identified. In addition, the self-sourced differential hydrocarbon accumulation pattern is established by deeply analyzing the key elements of hydrocarbon accumulation. The study results show that Ek₂ source rock is dominated by Type Ⅱ₁ -Ⅲ organic matter, which is over-mature medium source rock, and Es4x source rock is Type Ⅰ-Ⅱ₁ organic matter, which is a set of mature high-quality source rock. The wellseismic tracking of the prototype basin is used to identify the lateral distribution of source rocks, and the estimated resources are 11.35×10⁸t in deep formations. In addition, two types of differential hydrocarbon accumulation patterns are established. One is a vertically ordered condensate gas-conventional oil reservoir formed by direct connection between Es₄^x source rock and deep glutenite reservoir in the steep slope zone. The other is the “source rock-fault-reservoir-trap” differential hydrocarbon migration and accumulation pattern within Ek₂ source rock in the southern slope zone. Based on the deepening understanding of the quality and scale of deep source rocks in Dongying Sag, as well as the two self-sourced hydrocarbon accumulation patterns, the exploration target can be extended down at least 1500m, and the preliminarily estimated new addition trap resources are nearly 2×10⁸t. A major breakthrough is expected in the deep self-sourced oil reservoir in Dongying Sag during the 14^th Five-Year Plan period.

The organic geochemical characteristics of crude oil and source rocks in the Cretaceous Albian, Cenomanian, and Turonian from wells Z-1 and X-1 in the southern continental margin of MSGBC Basin are systematically analyzed. In Well Z-1, the average values of TOC,I_H, and R_o of the Albian source rock are 1.9%, 283 mg/g, and 0.88%, those of the Cenomanian source rock are 2.1%, 456 mg/g, and 0.81%,and those of the Turonian source rock are 3.4%, 538 mg/g, and 0.66%, respecitvely. In Well X-1, the average values of TOC, I_H, and R_o of the Albian source rock are 1.3%, 246 mg/g, and 0.67%, respectively. Based on the organic geochemical and sedimentary characteristics of oil and source rock samples, six organofacies are classified, i.e., predelta dysoxic humic organofacies, delta front dysoxic humic organofacies, shallow marine dysoxic sapropelic-humic organofacies, bathyal anoxic sapropelic organofacies, bathyal dysoxic sapropelic organofacies, and pelagic dysoxic sapropelic-humic organofacies. By analyzing the organofacies characteristics, source rock deposition patterns during the Albian and Cenomanian-Turonian are constructed, and influence factors are discussed, including organic matter source, marine paleo-productivity, redox condition, and depositional process, among which the oceanic anoxic event was the key controlling factor for the deposition of high-quality source rocks. From Albian to Turonian, the organic matter source changed from a mixture of terrestrial higher plants and marine algae to marine algae, showing an increasing abundance of marine algae, increasing marine paleo-productivity, and enhancing bacteria modification on organic matter. From Albian to Turonian, the depositional environment changed tremendously, and the reductive water environment was enhanced. In the transition period during Cenomanian-Turonian, the water oxygen content decreased rapidly, while the salinity increased rapidly, which might be related to the Oceanic Anoxic Event. The study results enable to determine the organofacies characteristics and the key controlling factor of the Cretaceous marine source rocks in MSGBC Basin, which have great significance to identify source rock series, delineate the distribution of source rocks, and guide the petroleum exploration in the basin.

Associated with the continuous implementation of exploration and development of volcanic oil and gas reservoirs, the “inner reservoir” with a large distance below the weathering crust volcanic rocks has been proved to have potential to form large-scale oil and gas reservoirs. However, the study on the characteristics, main controlling factors and distribution law of inner volcanic reservoir is still in the initial stage due to the significantly different reservoir formation mechanism from that of the weathering crust reservoir. By taking the footwall of West Dishuiquan Fault in Dinan Bulge as an example, core samples, thin section, physical properties, logging and seismic data are used to conduct the identification and depth division of inner volcanic reservoir, analyze the lithology, lithofacies and physical properties, and determine the main controlling factors for the development of inner volcanic reservoir. The results show that: (1) The inner reservoir is mainly distributed in the range of 250-600 m below the unconformity surface; (2) The favorable lithofacies (lithology) of the inner reservoir are thermal base wave subfacies (breccia tuff) of explosive facies and the caved subfacies (tuffaceous breccia) of explosive facies; (3) The reservoir space is dominated by dissolution pores, followed by tectonic fissures; (4) The main controlling factors of the favorable reservoir include paleogeomorphology, fault distribution, crater distribution, and volcanic eruption stages. The low-lying trough near the crater is favorable area for the development of inner reservoir. The inner volcanic reservoir is relatively developed near the crater and fault. The vertical distribution of inner reservoir is affected by volcanic cycles, and the inner volcanic rocks overlaid by source rocks are more easily transformed into inner reservoir.

Given the complex geological characteristics of Sulige Gasfield, such as multi-layer gas bearing in vertical and strong reservoir heterogeneity in lateral, technology research and field practice of sidetrack horizontal well have been conducted in Sulige Gasfield since 2011, so as to tap the remaining reserves in mature areas and ensure the high-efficiency and stable production of gas field. As a result, a series of supporting technologies, including remaining gas characterization, well location selection, drilling and completion, reservoir reconstruction, and drainage gas recovery, have gradually been improved, and a set of mature sidetrack horizontal well development technologies has been researched for tight sandstone gas reservoir in Sulige Gasfield. By the end of June 2022, 57 wells had been drilled, with the average horizontal section increased from 614.2 m to 753 m, drilling cycle decreased from 63.7 days in the initial stage to 35 days, a decrease of 45.1%, and well completion period decreased from 91.5 days to 52.6 days, a decrease of 42.5%. The cased-hole completion and bridge plug staged fracturing by using φ88.9 mm casing were achieved for the first time in 2021, with a success rate of 100%. Till now, 42 wells have been put into production, with the average wellhead pressure increased from 9.4 MPa to 13.3 MPa, average gas rate increased from 2.0×10⁴m³/d to 4.0×10⁴m³/d of a single well in the first month, and the internal rate of return remained higher than 8%, showing significant economic benefits. Targeting at the goal of cost reduction and production increase, further technology research will be conducted focusing on the diversified design, intelligent development, integrated collaboration, and full-life cycle management. The technology of slim-hole sidetrack horizontal well drilling provides technical support for the beneficial development of Sulige tight sandstone gas reservoir in the late stage and technical reference and solutions for the high-efficiency production of remaining oil and gas in other oilfields.

Buried hill type oil and gas reservoir is a continuous growth point of reserves in fossil energy exploration in China. However, the extremely strong reservoir heterogeneity brings great difficulties to the study of spatial distribution of dominant reservoirs. From the perspective of petrophysics, the buried hill type reservoir is classified into strong transformation zone, transformation zone and non-transformation zone in vertical direction based on the degree of reservoir transformation, so as to characterize the vertical zoning of different types of buried hills and predict the dominant reservoir. Furthermore, it is subdivided into five sub-zones based on the buried hill development pattern and sedimentary evolution process, i.e., weathering fractured zone, vertical connecting zone, transition zone, horizontal connecting zone and primary zone. The differences of reservoir electrical properties and pore characteristics are summarized and the logging characterization method of vertical zonation of buried hill type reservoir is constructed by using porosity spectrum, acoustic fracture and comprehensive characterization coefficients calculated by logging information. The above method is used to establish the classification standard for vertical zonation of buried hill type reservoirs in Xinjiang, South China Sea and other regions. The application results show that the weathering fractured zone, vertical connecting zone and horizontal connecting zone are favorable for the development of dominant reservoir. The plane distribution law of the dominant reservoir in Tabei area shows that, from northeast to southwest, the thickness in the weathering fractured zone increases first and then decreases, that in the vertical connecting zone decreases gradually, and that in the horizontal connecting zone increases gradually.