The deep, ultra-deep and unconventional resources have grown to be the major exploration and development fields for increasing reserves and production in China. Since the 13^th Five-Year Plan period, the engineering technology has continuously been researched by focusing on the key exploration and development targets in six basins (including five oil basins and three gas basins) and drilling speed acceleration difficulties, such as high temperature and high pressure formations and narrow fluid density window, and a large number of technical achievements have been obtained. For example, the key drilling and completion technologies for deep, ultra-deep and unconventional horizontal wells have been developed rapidly, forming key technologies with the core of unconventional well structure optimization, safe, highefficiency,optimal and fast drilling, high-temperature resistant drilling fluid, finely pressure-controlling drilling and completion, and expansion pipe, and a number of landmark ultra-deep wells have successfully been drilled; The equipment has been developed such as high-power top drive, integrated geo-steering system, and green economic reservoir reconstruction tool, as well as core additives such as temperature resistance high-performance drilling fluid and high-efficiency leak-proof and plugging materials have been researched, which have accelerated the lowcost,large-scale and cost-effective development of unconventional oil and gas resources. The drilling depth of deep wells exceeds 9000 m, the horizontal section length of horizontal wells is up to 5000 m, and the maximum footage of one trip drilling is 3700 m, with some indicators comparable to those in North America. The research achievements have boosted the discovery and development of large oil and gas fields such as Tarim Fuman, Sichuan Shuangyushi and Daqing Gulong, and provided powerful engineering and technical supports for improving the utilization rate and benefits of resource exploration and development. Associated with the continuous progress of petroleum exploration and development, the engineering geological risks and new challenges faced by drilling operations occur frequently. Therefore, further research is still necessary, including accurate prediction of formation pressure, optimization and expansion of wellbore structure, well trajectory control,high-temperature resistant working fluid system, high-efficiency rock breaking and speed-up tools, as well as integration of geology and engineering, so as to realize the continuous iteration and upgrading of key drilling technologies and equipment, and support the high-efficiency exploration and development of deep, ultra-deep, and unconventional oil and gas resources.

In recent years, the continuous exploration progress in mature areas in continental fault basins in eastern China enables to achieve the benefit reserve increase and obtain discoveries and expansion in new exploration zones, new resource types and new series, and shale oil is growing to be the strategic replacement resources. However, the high-quality exploration also faces some challenges, such as few discoveries with leading significance, great difficulty in large-scale development after obtaining discovery, significant increase in dependence on key exploration support technologies, deterioration in resource quality, and decrease in exploration benefits. By systematically analyzing the exploration situation and potential in mature areas in eastern fault basins of Sinopec, the main direction and countermeasures of exploration transformation and development are clarified. The mature exploration areas in eastern fault basins of Sinopec have resource, theoretical and technological advantages, which is a “ballast stone” for continuous reserve increase. In the exploration work, the objective characteristics of multi-stage and long-term exploration, and coexistence of multi-type resources should be emphasized, and the concept of “no forbidden exploration field” in oil and gas rich basins should be establish to liberate the mind and innovate ideas, so as to achieve the high-quality development. The main direction of exploration transformation and development should be followed to coordinate the relationship between conventional and unconventional resources, fine exploration and large-scale expansion, seismic deployment and high-efficiency exploration,technological breakthrough and achievements transformation; The main countermeasures include the continuous optimization of differentiated deployment in conventional and unconventional resources, improvement in high-precision and high-density seismic exploration, emphasis on the evaluation of remaining oil and gas resources, deployment optimization in “three new” fields, and integrated evaluation; Strengthening the basic exploration work, iterative upgrading of exploration technology, and exploration and development integrated organization and operation are the main means to achieve the high-quality exploration.

Shale oil is an important strategic resource to ensure the long-term steady oil production and production growth in China.PetroChina has made significant exploration breakthroughs in Ordos, Junggar, and Songliao basins, and has discovered shale oil with various lithofacies association types. In order to ensure the steady oil production of 2×10⁸ ton/a and improve the security of national energy supply,PetroChina strengthened its efforts in shale oil exploration and development in 2021 and achieved progress in four aspects: (1) The large-scale shale oil development has been conducted in Longdong area, and an integral shale oil demonstration zone has been established with a capacity of one million tons; (2) The construction of Xinjiang Jimsar and Daqing Gulong National Continental Shale Oil Demonstration Zones has been promoted, obtaining shale oil production capacity of up to one million tons in Jimsar area and opening a new chapter in pure type shale oil development in Gulong area; (3) Great efforts have continuously been made in new areas, and historic exploration breakthroughs have been achieved in several basins; (4) The theory, technology, and management have continuously been innovated, obtaining significant results in quality and efficiency improvement. On the whole, the exploration and development different types of shale oil are still in different stages, but there is still a gap to achieve the large-scale benefit development.

In recent years, fruitful achievements have been obtained in petroleum exploration in Ordos Basin by innovating geological understanding,highlighting risk exploration, strengthening large-scale exploration, and focusing on benefit exploration, with annual output exceeding 60 million tons of oil equivalent during the 2020-2022, in which risk exploration has played an important role in the exploration of “four new” fields. Based on the previous research results and the deep analysis of hydrocarbon accumulation conditions of the Ordovician subsalt, limestone in the Permian Taiyuan Formation, and shale oil in the seventh member of the Triassic Yanchang Formation (Chang 7 member), the innovative understanding of hydrocarbon accumulation and technical achievements have been formed, including the “new gas-bearing system in the subsalt dolomite mound beach body within source rock”, “sandwiched hydrocarbon accumulation pattern of Taiyuan Formation limestone”, and “sweet spot evaluation standard and special reservoir reconstruction technology for the laminated shale oil in Chang 7₃ sub member”, which have grown to be the replacement fields during the 15^th Five-Year Plan period and in the medium-long term. Meanwhile, by highlighting the exploration concept of “marching towards source rocks,new fields, and deep formations”, the characteristics of hydrocarbon accumulation and exploration potential in zones with low exploration degree are re-recognized according to two levels of key research orientation and zone preparation, and the prospects and orientation of risk exploration fields in the future are proposed. Among them, the key research orientation refers to the zones that have promising signs and great resource potential, mainly including the Ordovician marine shale gas, lower combination of Yanchang Formation, tight gas in coal measures and the Proterozoic Great Wall System; While the zone preparation aims at zones with basic hydrocarbon accumulation conditions, but low research degree and high exploration difficulty, such as the Cambrian in the peripheral of the central paleo uplift, complex structural areas in the western basin margin, and new series of the third-second members of the subsalt Majiagou Formation (Ma 3-Ma 2 members) in the eastern basin. The new geological understanding, achievement summary, and potential analysis of the risk exploration fields will support to achieve the orderly replacement of exploration zones in the basin and play an important guiding role in accelerating the further strategic development of Changqing Oilfield.

In order to identify the differential development mechanism and distribution law of reservoirs in the Middle Permian Maokou Formation in Zigong area in Sichuan Basin, reservoir types and main controlling factors are comprehensively analyzed by using abundant wireline logging, mud logging, core samples and well testing data. The study results show that there are two main reservoir types in the study area, i.e., limestone and dolomite. The dolomite reservoirs were mainly developed in the second member (Mao 2) and the fourth member (Mao 4) of Maokou Formation, with a single layer thickness of over ten to tens of centimeters, and generally developed at the top of upward shallowing sedimentary sequence. Laterally, the dolomite reservoir in Mao 2 member is mainly distributed in Weiyuan-Zigong-Fushun area and that in Mao 4 member mainly in Guanyinchang-Qinggangping area. The limestone reservoirs show a large variation in thickness and strong heterogeneity, which are distributed in Mao 2-Mao 4 members vertically, and the paleo highland or slope zone of the depositional or weathering crust karst geomorphology laterally. The further analysis shows that the formation of dolomite reservoirs was related to evaporation concentration-reflux infiltration dolomitization and short-term karst exposure driven by high-frequency sea level drop, and the limited evaporative seawater environment was intensified in the study area by the relative slope break during the depositional period and overlapping migration of beach bodies; The genesis of limestone reservoirs was classified into types, i.e., beach controlled early diagenetic karst, weathering crust karst and fault dissolution reconstruction, which were controlled by slope break, highland or slope of karst landform and fault, respectively. It is concluded that the highly heterogeneous and multi-genetic reservoirs in Maokou Formation were jointly controlled by “four-paleo” factors, namely, paleo geomorphology during the depositional period, paleo environment, paleo weathering crust karst geomorphology, and paleo faults. The favorable reservoirs are distributed along the “circum-slope highland”. The exploration orientation in the near future includes the stereoscopic exploration of multi-layer and multi-type reservoirs in Zigong-Fushun area in the northeast and the large-scale dolomite reservoirs in Guanyinchang-Qinggangping area in the southwest.

As the major exploration and evaluation target of lithologic type oil and gas reservoirs of continental shallow shore lake facies, the beach bar sand body shows more and more important position in increasing reserves in recent years. The formation mechanism and spatial distribution law of beach bar sand body in the second member of Shahejie Formation (Sha 2 member) in Qibei slope in Qikou Sag are analyzed to guide the exploration in the oilfield. The analysis of paleo sedimentary settings indicates that beach bar sand body was mainly developed in the early stage of base-level rising half cycle, with the largest scale in Bin Ⅳ^U and Bin Ⅲ^L oil groups; The distribution of thick bar sand body was controlled by underwater paleo uplift and influenced by the sufficient material supply by the adjacent provenance, repeatedly turbulent hydrodynamic force, and the shape of lake basin floor. The forward seismic modeling technique enables to define the seismic response characteristics of thick bar sand body. The threshold value of low frequency-strong amplitude of thick bar sand is determined by spectrum analysis, and the favorable zone for the development of thick bar sand is predicted by using low frequency-strong amplitude attribute fusion technology. Based on the exploration practice, the exploration and evaluation method of beach bar sand body is established, namely,delineating the range of beach bar in shallow water area with wide and gentle structure, searching for thick bar sand in underwater paleo uplift, and determining the favorable zone for the development of thick bar sand by low frequency-strong amplitude attribute fusion method.The research results guided the selection of three favorable zones with bar sand developed in Sha 2 member in Qibei slope, and commercial oil flows were obtained in all four wells, with a drilling success rate of 100%. The exploration practice shows that the beach bar sand body is well developed in Qibei slope, and the thick bar sand is characterized by oil enrichment and high-yield production, which shows an important replacement field and orientation for increasing reserve and production in mature oil area.

In recent years, exploration breakthroughs have continuously been obtained in deepwater fields by major international oil companies. Among them, the joint venture company led by ExxonMobil has discovered 31 deepwater oil and gas fields in Stabroek block in Guyana, making it a rising star in the petroleum industry in South America and driving the exploration boom in the peripheral offshore areas. Guyana Basin spans Guyana and Suriname offshore areas. ExxonMobil’s petroleum exploration in Guyana Basin mainly experienced three stages, namely, the advanced layout in Suriname offshore area during the 1957-1982, re-exploration in Guyana Basin and long-term research in Guyana offshore area during the 1999-2015, and a series of discoveries by applying new geological understanding and seismic technologies since 2015. The exploration practice of major international oil companies in Guyana, especially the joint venture company led by ExxonMobil, shows that it is a feasible and typical way to implement risk exploration by conducting comprehensive regional geological study and applying new data to strengthen exploration confidence and introducing partners to share risks and benefits, which provides reference for Chinese oil companies in promoting overseas petroleum exploration business from “going global” to “going better”.

The central African strike-slip rift basin group was composed of the Mesozoic-Cenozoic continental rift basins influenced by the Central African Shear Zone (CASZ), showing complex and diverse structures, as well as low exploration degree. The unclear understanding of hydrocarbon accumulation rules restricted the exploration and discovery in the region. Based on the analysis of basin structure, sedimentary system, hydrocarbon accumulation assemblage characteristics, as well as the discovered oil and gas fields, the hydrocarbon enrichment rules and main controlling factors are summarized, and the exploration potential and orientation are analyzed. The study results show that the central African strike-slip rift basin group experienced multi-stage extensional, strike-slip and reversed tectonic activities after the Early Cretaceous, which significantly controlled the sedimentary strata, structural features and hydrocarbon accumulation; Influenced by reservoir-cap rock assemblages and tectonic evolution, there are great differences in oil discoveries and plays in various basins in the central African strike-slip rift basin group, showing hydrocarbon distribution characteristics of “rich in the west and poor in the east, and light in the lower part and heavy in the upper part”; The main controlling factors for hydrocarbon enrichment include the effective hydrocarbon kitchen, tectonic activity and fault; Doba Basin in the west has the most abundant oil and gas resources, with several sets of hydrocarbon accumulation assemblages developed and large-scale oil and gas resources discovered in the Upper and Lower Cretaceous, and the Lower Cretaceous lithologic and buried-hill traps are the main exploration orientation in the future; For Doseo Basin in the central part, there is a lack of the regional cap rocks in the Upper Cretaceous, and the main exploration targets include the Lower Cretaceous sandmudstone association, and fault anticline and fault block traps formed by strike-slip activities, as well as the potential bedrock buried hill; Salamat Basin in the east has no proved effective hydrocarbon accumulation assemblage, which shows a limited exploration potential.

Huanghua Depression in Bohai Bay Basin has favorable conditions for the formation of laminated shale oil. The three sets of lacustrine laminated shales in the second member of Kongdian Formation (Kong 2 member), third member of Shahejie Formation (Sha 3 member) and the first member of Shahejie Formation (Sha 1 member) have a superimposed area of about 2400km², the maximum cumulative thickness of about 1200m,and the calculated shale oil resource volume of 1.2 times that of conventional oil resources, showing great exploration and development potential.However, the benefit development still faces a series of difficulties. By conducting 52 items of joint experiments and tests on 22640 shale samples (701m core) collected from five wells, and analyzing mud logging and wireline logging data in 116 vertical wells, the distribution of the laminated shale oil is identified, which is enriched in (fan) predelta to semi-deep lake subfacies laterally and in the transition zone of the base level T/R cycle vertically in the form of retained oil generated by source rocks in the medium thermal evolution stage. In addition, the quantitative evaluation standard for three types of shale oil favorable areas and enrichment layers is established by eight factors, which effectively guides the “sweet spots” evaluation and selection of the laminated shale oil. Moreover, the field tests of different development schemes, different types of fracturing methods, and different production regimes are conducted in 37 shale oil horizontal wells, which indicate that the optimal horizontal well placement mode can be achieved by using horizontal well spacing of 300m and horizontal section length of 2000m, single-point densely-cutting network volume fracturing enables to greatly improve the production and EUR of single well, as well as the optimally formed “four steps” shale oil well production method, namely,pressure control and water production by small choke, liquid lift/production and blockage prevention by large choke, steady natural flow by medium choke, and long-term production by deeply-set small pump, supports to achieve the high and steady shale oil production. Guided by understanding of enrichment law and key technologies for production and efficiency enhancement of the laminated shale oil, major breakthrough has been made with the highest cumulative oil production of 1×10⁴ ton in the first year and EUR of over 3.5×10⁴ ton of a single well, achieving the benefit development at an oil price of USD 50 $/barrel, which shows promising development prospect of shale oil in fault basins in eastern China.

The exploration of tight gas in the Upper Triassic Xujiahe Formation in Sichuan Basin has always focused in western, central and northern Sichuan Basin, while that in eastern Sichuan Basin has not been attached emphasis due to its complex structural location in ejective fold structural belt, resulting in a low exploration level. In recent years, new breakthroughs have successively been made in the exploration of tight gas in Xujiahe Formation in northeastern Sichuan Basin, and high-yield commercial gas flows have been tested in two wells, which show tight gas potential in Xujiahe Formation in the syncline area in eastern Sichuan Basin. From the perspective of source rock, reservoir and structural conditions, the geological characteristics of tight gas reservoir in Xujiahe Formation in northeastern Sichuan Basin are analyzed,so as to open a new prelude to the tight gas exploration in eastern Sichuan Basin. The study results show that: (1) The hydrocarbon source of Xujiahe Formation gas reservoir in northeastern Sichuan Basin was mainly supplied by source rocks in the Upper Triassic Xujiahe Formation and the Upper Permian Wujiaping Formation, with high intensity of hydrocarbon generation and characteristics of “hydrocarbon supply by dual sources”, which had the material basis for tight gas accumulation; (2) The matrix pores were underdeveloped in Xujiahe Formation reservoir in northeastern Sichuan Basin, and the “fracture-sand body” served as high-quality reservoir. The large-area sand bodies and quasi-continuous fractures in the fifth member of Xujiahe Formation (Xu 5 member) delivered favorable conditions for the formation of large-scale superior “fracture-sand body” reservoir; (3) The gas reservoir in the fifth member of Xujiahe Formation in northeastern Sichuan Basin is characterized by “hydrocarbon supply by dual sources, two-stage gas accumulation and quasi-continuous distribution”, showing superior conditions for gas accumulation. To sum up, Xujiahe Formation in northeastern Sichuan Basin has the conditions for forming large-area and “quasi-continuous” gas reservoir, which has great exploration potential and is of great significance for promoting the exploration of tight gas in the syncline area in the ejective fold structural belt in eastern Sichuan Basin.

How to objectively evaluate the pore fluid in shale oil reservoir and accurately measure and quantitatively characterize parameters such as oil saturation and mobile oil content in shale oil and tight oil reservoirs are key technical problems that need to be solved urgently.The vehicle-mounted mobile full diameter core NMR measurement instrument is firstly introduced in domestic to conduct on-site core testing analysis and shale oil evaluation, which supports to realize the continuous, high-precision, non-destructive and rapid NMR scanning of drilled core on well site, make up for the shortcomings of NMR logging and indoor core experiments, and fill the blank of on-site measurement technology of full diameter shale oil core in China. Based on field core description, other supporting experimental data and well testing verification, the characteristics of 2D NMR T₁-T₂ spectrum of various fluid components are systematically summarized, the change rule of T₁/T₂ ratio of oil and water fluid signals in pores with different diameters is identified, and the pore fluid component analysis method and identification standard are established by using 2D NMR spectrum characteristics of full diameter core, which support to realize the accurate identification of pore fluid components and quantitative interpretation of fluid saturation of shale oil, tight oil and complex clastic rock reservoirs. The technology of vehicle-mounted mobile full diameter core NMR measurement has played an important role in the exploration and evaluation of Gulong shale oil in Songliao Basin, Chang 7₃ shale oil in Ordos Basin, as well as in Hetao Basin, and has widely been applied in tight oil and gas oilfields in Daqing, Changqing, Xinan, Huabei, and Xinjiang oilfields, in which good results have been achieved.

Reservoir heterogeneity has a significant impact on the development results of well pair by using steam assisted gravity drainage technology (SAGD). Given the complex reservoir conditions, it is difficult to ensure the uniform development of steam chambers, restricting the development result of a single well pair. In view of the low peak production and low recovery factor of a single well during the development process of oil sand project in Mackay River block in Canada due to the strong reservoir heterogeneity,complex geological conditions, as well as limited and uneven development of steam chambers blocked by mud drape layer, an updip multi-lateral well technology is proposed for various pattern types. The well numerical simulation and dynamic analysis are conducted to explore the methods of steam chamber passing through the mud drape layer and condensate oil passing through the mud drape barrier and flowing into the production wellbore after heating, and accurately recognize the development of steam chambers in multi-lateral wells of various well patterns and evaluate their development results. By constructing a mechanism model, four combination schemes of steam injection wells and production wells are designed and the well simulation is conducted based on the field operating parameters to analyze the production performance, remaining oil distribution, steam chamber development, and recovery rate of horizontal section,and summarize the production law of multi-lateral horizontal wells given the complex reservoir conditions; By conducting analysis of well production performance, the SAGD development results of multi-lateral wells are evaluated, and the differences in development results among various well types are compared. The study results show that a multi-lateral well design enables to significantly increase the effective footage, facilitate the dominant pathway for steam injection and oil drainage, improve the steam injection capacity of well pair, increase the swept volume of the steam chamber, and increase the peak oil rate of the well pair, which solves the problem of barrier by mud drape layer to some extent; In actual field production, multi-lateral production well enables to increase the recovery degree of horizontal sections and improve the development results of single well. However, to some extent, it will increase frac-hit and difficulty in well adjustment, leading to an increase in remaining oil in the lower part of the reservoir.

The lower limit of porosity (L_φ) is one of the essential parameters determining the effective reservoir thickness and further estimating geological reserves of oil and gas reservoirs by using volumetric method. Effective reservoir refers to that has the ability to produce commercial oil and gas flows. The reservoir permeability has a better correlation with production capacity than porosity, and the lower limit of permeability (L_k) enables to more accurately classify the effective reservoir than L_φ. However, due to the technological limitations in current,L_φ is often used to classify effective reservoirs in practice instead of L_k. The carbonate reservoirs in Sichuan Basin show characteristics of high heterogeneity with diverse pore types, complex pore throat structure and uneven fracture development. In order to identify the determination method of L_φ of highly heterogeneous reservoir, the characteristics of reservoirs in the Sinian Dengying Formation in Aanyue Gasfield are analyzed by using core samples, thin sections, SEM, and mercury injection experiments, and the reservoir is divided into matrix pore type and fractured type. Furthermore, the production capacity simulation comparison experiments on these two types of reservoirs are conducted given the same conditions, which enable to determine L_k to be 0.008 mD. On the other hand, L_φ is a variable, that is, regardless of L_φ value taken in classifying effective reservoirs, a part of effective reservoir with low porosity and high permeability will be ignored, while a part of ineffective reservoir with high porosity and low permeability will be added. If an L_φ value is determined that makes these two parts of reservoir space consistent in volume, the real total volume of reservoir space can be reached by applying the current technologies. Guided by the equivalent substitution concept, and combined with production capacity simulation, as well as physical property results of 200 rock samples, L_φ of Dengying Formation reservoir in Anyue Gasfield is determined to be 1.56%.

In terms of the traditional reserve prediction methods, such as Hubbert model and Weng's model, univariate polynomials are generally used to fit the reserve growth trend, which are unable to determine the influence of multiple variables on reserve prediction,resulting in a significant gap between the predicted results and objective reality. Based on the random forest machine learning model,a new method for predicting the growth trend of cumulative proven reserves is established, with the details as follows: Identify the quantifiable indicators that affect the growth of proven reserves through correlation analysis to determine the input attributes in the training model; Establish a random forest machine learning sample data set by taking the annual cumulative proven reserves of oilfields in the same basin as the evaluation unit; Optimize and train the model by adjusting the number of decision trees and the maximum characteristic number of a single decision tree, thus establishing a prediction model for the cumulative proven reserves, which supports to predict the nonlinear reserve growth affected by multiple factors. As a result, remarkable results have been achieved in predicting the annual cumulative proven reserves of oil fields in the eastern fault basin by applying this method, with a fitting accuracy of up to 88.19%, showing great promotion and application value.