The PetroChina has continuously made a number of major oil and gas discoveries and implemented a number of large-scale reserves in the field of deep-ultradeep clastic rocks, demonstrating the huge exploration potential in this field. Based on the exploration progress and geological cognition obtained, combined with the characteristics of onshore oil and gas basins in China, the deep-ultradeep clastic rock domain could be divided into three types: foreland basin, graben basin and depression basin, and the scale distribution of deep effective source rocks and the characteristics of riching in oil especially gas are revealed. The new recognitions that four formation mechanisms control the development of deep high-quality clastic reservoirs and deep reservoir-forming factors are well configured are also proposed from the research. Combining the basic geological understanding of deep clastic rocks, source rock and resource potential, effective reservoir distribution and reservoir-controlling factors of deep clastic rocks, four major directions for future research are proposed: (1)Strengthen research on deep geological structure, sedimentary filling and tectonic evolution, determine favorable reservoir combination and their plane distribution. (2)Strengthen the evaluation of main hydrocarbon source rock distribution, and objectively estimate the deep resource potential, then determine the favorable resource enrichment area. (3)Strengthen researches on the formation, preservation mechanism and distribution law of different types of reservoirs, and implement the vertical layer distribution and plane distribution of large-scale effective reservoirs. (4) Strengthen analysis of the control factors, preservation mechanism, and trap evaluation of oil and gas reservoirs, implement favorable zones from priority areas, and determine drilling targets. Based on the distribution characteristics of the remaining resources and exploration understanding, ten zones in the deep-ultradeep clastic rock field of the three types of basins are selected as the next key exploration targets. The estimated resource potential is nearly 3 billion tons of oil and over 7 trillion cubic meters of natural gas.

Pores are widely developed in the dolomite of the Lower Ordovician Penglaiba Formation-Yingshan Formation in the Gucheng area, Tarim Basin, which are characterized by needle-like dissolution pores, ultra-grain pores, intercrystalline micropores, etc., and are generally considered to be related to dolomitization. Based on data of core, thin section, cathodoluminescence, inclusions, rare earth elements, carbon and oxygen isotopes, etc., the genesis, pore types and genesis, pore evolution model of dolomite in the Lower Ordovician Penglaiba Formation-Yingshan Formation in Gucheng area are analyzed. The results show that:(1) The dolomite is dominated by penecontemporaneous dolomitization, partially superimposed by deep thermal fluid, and the dolomite filling in the fracture-vug is of hydrothermal origin. (2) The super grain pores are macroscopically needle-like dissolution pores, which are developed in fine-medium crystalline dolomite with original fabric as particles, mainly being medium-big pores, and are mostly developed in the middle and upper parts of a single grain shoals cycle. They are intragranular dissolution pores, mold pores and intergranular dissolution pores formed by selective dissolution of atmospheric fresh water in the penecontemporaneous period before dolomitization. The intercrystalline micropores are isolated with poor connectivity and are formed by penecontemporaneous dolomitization. Although the penecontemporaneous dolomitization did not directly produce a large number of pores, it provided a framework that resisted compaction and hindered the later fluid precipitation, which was the key to the preservation of pores. (3) The porous-type dolomite reservoir of Penglaiba Formation-the lower member of Yingshan Formation in Gucheng area of Tarim Basin is characterized by multiple sets of thin layers. Its thickness and scale are affected by the superposition of multi-stage granular shoals and their exposure degree. Exploration for this type of reservoir should be focus on the high areas of paleogeomorphology where are conducive places to the development of dolomitization granular shoals.

The mound-shoal complex is the most important sedimentary facies for natural gas in the Dengying Formation of the Sichuan Basin, and microbial mound is an important component of the mound-shoal complex. Based on a comprehensive analysis of the cores, thin sections, and logging of 11 wells in the fourth member of the Penglai gas field, three types of microbial mounds are classified according to spatial morphology, and the internal structure and evolution rule are clarified respectively. The rock types of microbial mounds are divided into microbial dolomite, residual granular dolomite, breccia dolomite and crystalline dolomite. The microfacies such as mound base, mound core, mound cover, and mound flank are identified. Three types of microbial mound developed as follows: Vertical accretion microbial mound was formed in an environment where the construction rate of microbial mounds was close to the rate of sea level rise, with a growth sequence of "mound base → mound core → mound cover". The cumulative thickness of this type developed at the platform margin is generally 64-93 m. Lateral migration of the microbial mound was formed in environments where the construction rate of microbial mounds was greater than the rate of sea level rise, with a growth sequences of "mound base → mound core → mound flank" and "mound core → mound flank". The cumulative thickness of this type developed at the platform margin is generally 25-49 m. Small isolated microbial mound was distributed between mounds, with a thickness of generally decimeters and a small scale. The microbial mounds of vertical accretion and lateral migration concentrated at the platform margin in the second to third sub-members of the fourth member, with large total thickness and continuous horizontal distribution, which are the most favorable facies for the Dengying Formation in the Penglai gas field.

In 2021, high production gas flow was obtained in tight limestone of Lower Permian Taiyuan Formation in Well A, a risk exploration well. Through integrated exploration and development, Hengshan gas field, the first limestone gas field in Ordos Basin, was discovered with a submitted reserve of over 200 billion cubic meters. It is a replacement field of reality for increasing reserves and production in the Changqing Oilfield. Based on data of cores, casting thin sections, scanning electron microscopy, physical properties, logging, and gas testing, comprehensive research on reservoir characteristics such as sedimentary facies, petrology, reservoir space and diagenesis is conducted to analyze the formation mechanism and the distribution pattern of favorable reservoirs. The results show that: (1) The lithology of limestone reservoir is mainly composed of bioclastic very finely crystalline limestone, algal bound limestone and bioclastic micritic limestone. The storage space is mainly composed of dissolution pores, residual organism cavities, intergranular pores and microcracks. Dissolution pores, nano-submicron scale intergranular micropores and fractures form a three-dimensional network storage space, which is the key to form a tight limestone gas reservoir in the Taiyuan Formation. (2) The limestone reservoir is mainly formed in the intermittent exposure of bioclastic shoals under the influence of karst during the quasi contemporaneous period. The bioclastic shoal are the material basis for reservoir formation, determining the type and planar distribution of reservoir space. Quasi syngenetic karstification is conducive to the formation of dissolution pores and can effectively improve the reservoir storage performance. Cracks play a crucial role in improving the permeability of tight limestone reservoirs. (3) Controlled by sea level cycles and paleogeomorphology, the favorable limestone reservoirs of Taiyuan Formation are vertically developed in Xiedao Member, and horizontally developed with a pattern of "around depression and along highland", especially with larger reservoir thickness at the slope due to lateral stacking under the background of regression. This study will help to promote a further understanding of biogenic limestone of Taiyuan Formation in North China, and have important implications for the exploration and development of ancient carbonate rock in China.

The hydrocarbon reservoirs, which formed with the sediment supply of Altun mountain, have overall poor physical properties and strong anisotropy in the western margin of Qaidam Basin. For the purpose of predicting favorable reservoir distribution, it is urgent to carry out detailed division of the source-sink system. Using field outcrop and drilling core samples, comprehensive methods such as detrital zircon U-Pb isotopic dating, heavy mineral assemblages and sand body distribution are employed to conduct source-sink system analysis of the Upper Member of Lower Ganchaigou Formation of Paleogene in western margin of Qaidam Basin. As a result, five source-sink systems named as Qigequan, Shibei, Ganchaigou, Xianshuiquan, and Xiandong, respectively, are identified. They are different in heavy mineral assemblages and symbolic heavy mineral contents, and present different peak ages, peak age combinations and age spectrum patterns from each other. The age of sediment sources is mainly from 200 to 520 Ma, and the parent rocks is mainly composed of magmatic and metamorphic rocks. Affected by the supply of these sources, fan delta-sublacustrine fan systems are developed with greatly-varied scales in the study area correspondingly. It is shown that a single analytical method may lead to uncertainty in the division of source-sink systems. To achieve a more accurate understanding, multiple analytical methods should be combined and mutually validated.

The deep-water submarine fans of the Miocene Meishan Formation in Ledong-Lingshui sags in the west area of Qiongdongnan Basin，are the main gas exploration area. A comprehensive analysis is conducted to study the diagenesis and its influence on the porosity evolution of deep-water submarine fan reservoir under the background of high temperature and overpressure，by means of thin section, X diffraction, scanning electron microscopy(SEM), cathodoluminescence, stable isotope, and fluid inclusion analysis. The results show that:(1) The rock types of deep-water submarine fan reservoir in Meishan Formation are mainly lithic quartz sandstone and feldspar lithic sandstone. The reservoir properties are mainly characterized by low-medium porosity and low to ultra-low permeability, with strong heterogeneity. (2) The reservoirs evolved as follows: early compaction and clay mineral cementation→the first phase of low mature oil filling→feldspar dissolution, secondary enlargement of quartz, ferrocalcite cementation→the second phase of higher mature oil-gas filling→（ferrodolomite）dolomite cementation, quartz and its secondary enlargement dissolution， overpressure formation→the third phase of high mature natural gas accumulation→late CO2 charging, hydrothermal action. (3) The reservoir pore evolution is controlled by the compaction-cementation with overpressure protection and dissolution. Early compaction and cementation are the main destructive factors. The pore preservation of overpressure and dissolution are the main constructive factors. The influence degree of diagenesis on the deep-water submarine fan reservoir is different in the different tectonic zones, resulting in the current differential pore characteristics.

Based on the analysis of sedimentary background, high-resolution sequence stratigraphic framework and sedimentary microfacies distribution, by using the method of stratigraphic forward simulation and comprehensive use of seismic, well logging, core and other data, the three-dimensional sedimentary spatiotemporal evolution simulation is carried out, and the sedimentary evolution process of wave-dominated delta of the Miocene Zhujiang Formation in the north-central Pearl River Mouth Basin is quantitatively restored, and the influences of sedimentary environment and wave parameters on the distribution of sand bodies are discussed. The results indicate that: (1) Being located at the coastal area of a shallow continental shelf, the study area was subject to strong wave action during the Miocene, developing a typical wave-dominated delta sequence, and the sedimentary microfacies of the Zhujiang Formation evolved regularly with the change of the base level, and the shoreline moved first to the land and then to the sea. (2) The wave action during the Zhujiang Formation sedimentation period is strong, and the wave angle is near the southeast direction. The wave action has a significant impact on the distribution of the delta sand body. With the increase of wave height, the effect of impeding the accumulation of fine sediment in the delta estuary increases, and it is transported to the deep water area; muddy sediments are deposited in the area below the wave base, while sandy sediments in the area above the wave base have a higher content. The inclination of the incident angle in wave action can lead to asymmetric sedimentation and morphology in the evolution of delta. (3) The evolution characteristics of basin filling in the time domain indicate that favorable reservoir sand bodies are mainly developed near the shoreline, and source rocks are concentrated on slopes. Sedimentary forward simulation provides a more intuitive method for quantitatively restoring sedimentary evolution processes and has predictive value in determining the potential morphology of wave-dominated deltas.

The Permian Qixia and Moukou formations in Sichuan Basin have been the key targets for natural gas exploration since 1950s. With the continuous deepening of the exploration and development, it has been different of the exploration ideas and directions. In order to clarify the next direction of natural gas exploration, based on a combination of drilling, outcrop, logging, seismic and geochemical data, this paper systematically analyses the geological questions and explorational domains of Qixia and Moukou formations. The results indicate that: (1) The Qixia Formation-Maokou Formation in the Sichuan Basin is mainly a platform depositional system, which can be divided into three stratigraphic sequences (SQ1, SQ2, and SQ3 from bottom to top). In addition to the western Sichuan platform margin, the Qixia Formation-Maukou Formation in the central and eastern Sichuan Basin developed a number of high-energy shoals in the highstand system, encompassing an area of over 40,000 km². This has laid a solid foundation for the development of shoal reservoirs. (2) The primary reservoirs of the Qixia Formation-Maukou Formation are pore-cavity dolomite, karst fractured-vuggy limestone, and microporous-microfractured marlite of which, pore-cavity dolomite is the main reservoir of recently explored. The dolomite of the Qixia Formation is primarily developed in the Guanyuan-Beichuan-Ya’an E’mei area in the west of the Sichuan Basin, while the main deposits of the Maokou Formation are distributed in Xuanhan-Wanzhou, Guanyuan-Jiange, and Jiange-Guangan-Fengdu area. Karst fractured-vuggy limestone reservoirs are mainly developed in the central Sichuan to southern Sichuan region. Microporous-microfractured marlite reservoirs are mainly distributed in local areas of northern and eastern Sichuan, and the research level is relatively low. (3) Four realistic fields and two potential fields can be distinguished in the Qixia-Maokou formations natural gas exploration in the Sichuan Basin. The dolomitized shoal zone of the Maokou Member 2 in the northern-central-eastern Sichuan Basin is the most significant realistic exploration field for the Middle Permian natural gas storage and production. We need to accelerate the comprehensive evaluation of reservoirs and submit or upgrade natural gas reserves. The isolated dolomited shoal in the lower sub-member of the Maokou Member 2 in the eastern Sichuan Basin is anticipated to be one of the most significant potential exploration field in the future. We need to deepen the research and finely characterize the distribution range of reservoirs, striving to achieve a breakthrough in this field as soon as possible and promote it becoming a replacement field for natural gas exploration.

Due to the relatively limited drilling and other relevant data during the exploration stage, the resource and favorable area evaluation of shale gas have certain specificity. Suitable evaluation ideas and methods should be sorted out based on the characteristics of the stage. According to the practice of marine shale gas exploration, the content and ideas of shale gas resource and favorable area evaluation in the exploration stage are systematically sorted out, and the corresponding resource and favorable area evaluation methods for this stage are clarified. The shale gas exploration stage is divided into three secondary evaluation stages: play evaluation, target evaluation, and gas reservoir evaluation. It is believed that the main methods for resource evaluation in the play evaluation stage are gas content analogy, resource abundance analogy, genesis method, and comprehensive method. The main methods for target evaluation stage are gas content volume method, gas content analogy method, resource abundance analogy method, and comprehensive method. The main methods for gas reservoir evaluation stage are gas content volume method, gas content volume method+gas saturation volume method and comprehensive method. Taking the Wufeng Formation-Longmaxi Formation in the Jiaoshiba area as an example, a system of analogy parameters for the total gas content and resource abundance of marine shale gas is established. This system can further improve the important aspects of analogy that still have shortcomings. The methods for shale gas favorable area in the exploration stage can be summarized into two main methods: comprehensive parameter superposition analysis method (stacking map method) and parameter normalization quantitative evaluation method. The two favorable area evaluation methods are applicable for both play evaluation and target evaluation, with the main difference of the differences in parameter types and quantities in the evaluation parameter system. In view of the emphasis on the evaluation of shale gas formation and enrichment conditions (geological conditions) and fracturing high production conditions (engineering conditions) in the play evaluation stage, a dual factor play evaluation parameter system of “geological conditions-engineering conditions” has been established. In the stage of target evaluation, it is necessary to consider the evaluation of economic benefits and further enrich the parameters. A three factor target evaluation parameter system of “geological conditions-engineering conditions-economic conditions” has been established. At the same time, the evaluation parameters in terms of hydrocarbon generation, preservation, resources, and geostress have also been further deepened. The established play evaluation and target evaluation parameter system can better reflect the characteristics of the evaluation stage and meet the corresponding evaluation needs.

The Laoyemiao area of Nanpu Sag has developed slope-controlled sand-type reservoirs. The middle and deep strata in this area are rich in oil and gas resources and have broad exploration prospects, where is an important replacement area for exploration and development. At present, there are some problems in this field, such as deep burial depth, weak effective seismic signal, rapid lateral change of sand body and unclear description of sand body shape, which restrict the deployment of high-efficiency wells and the tapping of remaining oil in reservoirs. Based on the analysis of core, logging and seismic data in the study area, a new seismic sedimentary interpretation method for “three domains and three elements” has been explored, which includes three seismic sedimentary interpretation methods, such as stratigraphic structure identification at energy half-life, sequence stratigraphic tracking by minimum cost function method and lithology identification by relative Poisson's ratio. It is shown that : (1) The sedimentary body of upper submember of the Dongying Member 3 in the study area has the sedimentary characteristics of “bottom gravel and top sand” in the longitudinal direction, that is, nearshore subaqueous fan deposition is developed at the bottom and braided river delta deposition is developed at the top. (2) The upper submember of the Dongying Member 3 in the Laoyemiao area is bounded by the Laoyemiao strike-slip fault conversion zone, and multiple point dams are developed to the north of the boundary, showing sand island deposition; the fan delta sedimentary system is developed in the south of the boundary. From the early deposition to the late deposition, the scale of the fan body first expands and then shrinks, and the shape gradually evolves from the skirt shape to the narrow strip underwater distributary channel deposit, and the fan body is closed to the oil source fault, so it is the replacement area of exploration and development. (3) The method of “three domains and three elements” seismic sedimentary reservoir characterization has good applicability for sedimentary microfacies characterization and favorable reservoir distribution prediction in complex structural areas, and the coincidence rate of sand body thickness prediction reaches 90%.