In order to clarify the sequence stratigraphy and sedimentary facies distribution of Donghe Sandstone Member-Breccia Member of Bachu Formation in the eastern Lunnan ancient buried hill-Caohu Sag of Tabei Uplift, Tarim Basin, the sequence stratigraphy and sedimentary environment in the study area were studied based on drilling, logging and seismic data by applying the principles of sedimentology, sequence stratigraphy and seismic sedimentology. The results show that the Donghe Sandstone Member can be divided into three parasequences, the Breccia Member can be divided into one parasequence, and these four parasequences are named DH-1, DH-2, DH-3 and DH-4 from bottom to top. These four parasequences all developed in marine transgressive sendimentary environment. A fan-delta-shore sedimentary system are mainly developed during the deposition period of Donghe Sandstone Member-Breccia Member in the study area, in which the first and fourth parasequences are dominated by fan-delta deposits, and the second and third parasequences are dominated by marine shore sandstone deposits. The above understanding has an important reference role for the exploration of structural-lithologic oil and gas traps in the eastern Lunnan ancient buried hill-Caohu Sag of the Tabei Uplift.

In early Hercynian period, epigenic karst, semi open confined karst, and buried confined karst are developed in the Middle-Lower Ordovician of Tahe Oilfield, Tarim Basin, of which the semi open confined karst is developed in the shallow coverage zone. There are giant oil and gas resources in karst fracture-cave reservoirs of Middle-Lower Ordovician in the shallow coverage area of Tahe Oilfield. Confined by the Upper Ordovician Lianglitage Formation and deep insoluble beds, the fracture-cave reservoirs of Middle-Lower Ordovician in the shallow coverage area show typical strata-bound distribution characteristics. Karst conditions and karst fracture-cave structure in shallow coverage area are different from those of exposed karst controlled by drainage base level and buried karst with deep-circulating. In order to clarify the karst genetic mechanism and fracture-cave structure of Middle-Lower Ordovician of T738 well block in the Upper Ordovician shallow coverage zone of Tahe Oilfield, the "residual thickness trend combination method" which takes advantage of both the "residual thickness method" and the "construction trend surface method", was used to restore the ancient landform and ancient water system of the Early Hercynian, and the insoluble beds and cave beds were identified by logging and seismic methods. Further more, combined with the dynamic production characteristics of the reservoir, the transverse-rising fracture-cave structure model under the confined karst conditions in shallow coverage area is constructed. The results show that: (1) The Early Hercynian paleogeomorphology is generally high in the northeast and low in the southwest, with shallow-cutting dendritic surface water system developed in NE-SW direction, and the northern exposed area provides high hydraulic gradient and high-flow karst water supply. (2) T738 well block is in semi open confined karst conditions, and three sets of insoluble beds (the Chalbach Formation-Lianglitage Formation, the bottom dense section of the Yijianfang Formation, the lower section of the Yingshan Formation) and two sets of cave maze beds (the Yijianfang Formation and the upper section of the Yingshan Formation) are developed in Middle-Lower Ordovician. (3) Influenced by factors such as insoluble beds, hydrodynamic gradients and faults, the cave beds in Yijianfang Formation and the upper section of Yingshan Formation have longitudinal hydrodynamic relations, and four types of confined karst fracture-cave structures, including transverse-rising type, isolated type, transverse type and blind end type, are developed. The research results have important geological guiding significance for the development of fracture-cave reservoirs of T738 well block in shallow coverage zone of Tahe Oilfield.

There are abundant oil and gas resources and geothermal resources in microbial dolomite reservoirs of Wumishan Formation in Renqiu buried hill, Jizhong Depression, but the characteristics and main controlling factors of the high-quality reservoirs are not clear, which constrained the exploration and development process. Based on the outcrop, drilling core, petrographic thin section, logging data and experimental analysis data, the characteristics as well as types of microbial dolomite reservoirs in Wumishan Formation are investigated, and the controlling factors and evolution of high quality reservoirs are generalized. The reservoirs in Wumishan Formation dominated by microbial dolomite, which associated with the microbial mound and shoal. The microbial dolomites consists of stromatolite dolomite, thrombolite dolomite, laminite dolomite, oncolite dolomite, while the microbial related granular dolomites are mainly dolarenite and dolorudite. The storage space of microbial dolomite can be divided into three types(pores, fractures, vugs), and the reservoirs overall have poor physical properties with average porosity of 3.55% and average permeability of 0.89×10-3 μm2, which belongs to the pore-vug-fracture composite type with the characteristics of low porosity and low permeability. The microbial dolomite reservoir can be divided into type I, type II, and type III, different types of reservoirs have big differences in lithology and physical property. Depositional environment are the basis of reservoir formation and evolution, which controls the facies distribution and the porosity development. Dissolution are the key to the formation of multiple types of reservoir space, which determine the modification and distribution of the reservoirs. Tectonic disruption is an important complement to form effective storage space, for the structural fractures generated by tectonic disruption are constructive for the reservoir properties in increasing the reservoir physical property and the seepage ability. Analysis shows that the evolution of the microbial dolomite reservoirs of Wumishan Formation in the study area can be mainly divided into five stages: sedimentation-penecontemporaneous pore formation stage, phaseⅠsupergene pore increasement stage, shallow burial pore reduction stage, fold and fault transformation phaseⅡsupergene pore increasement stage, deep burial pore reduction stage. The combined effects of multiple factors ultimately formed a porosity of 2% to 5% today. Key words：microbial dolomite; buried hill; reservoir characteristics; controlling factor; reservoir evolution; Wumishan Formation; Jizhong Depression

Through the analysis of drilling, logging and three-dimensional seismic data, the sequence stratigraphic composition, source-to-sink system difference, sedimentary evolution, sand control mechanism and lithologic-stratigraphic trap model in hanging wall of Pinghu fault in PH slope overlap belt of Xihu Sag are comprehensively studied. The results indicate that: (1) The Pinghu Formation in the PH slope overlap belt is controlled by different genetic slope breaks such as erosion and flexural, and is divided into three third-order sequences (SQ1 to SQ3) from bottom to top. Among them, SQ1 is limited in distribution, and development of the lowstand system tract is controlled by the steep slope break of deflection, forming the fan delta system coupled with ancient valley and slope break, which is dominated by the nearby basement provenance of Mesozoic magmatic rock. SQ2 and SQ3 are widely distributed, and development of the transgression and highstand system tracts are controlled by gentle slope break of erosion, forming the delta system dominated by the distant basement provenance of Proterozoic metamorphic rock. (2) The slope break controls the sand body distribution, and the slope break trough under the flexural slope break is a restrictive landform, which controls the layer by layer accretion and overlap of fan delta sand body vertically overlaied in lowstand tract. The low-lying area under the erosion slope break is the place where the highstand tract delta sand bodies are distributed, and the sand bodies of delta front are superimposed and dsitributed contiguously on plane. (3) Under the control of system tract and slope break, three types of lithologicstratigraphic trap models are developed. During the low stand stage, the fan delta front sand body overlaping stratigraphic traps blocked by the physical properties of bedrock and fan root are mainly developed under the flexural slope break. During the transgressive stage, the tidal sand bar and tidal channel lateral pinchout lithologic traps blocked by the mudstone in the flooding period are mainly developed. During the highstand stage, lithologic traps in distributary channels of delta plain controlled by erosion slope break, updip pinch out and lateral pinch out, are mainly developed.

The Central Canyon-Channel Gasfield in Qiongdongnan Basin is the first deep-water large-scale gas field discovered by self operated exploration in China sea area, which is an important support for the production of oil and gas fields in the western South China Sea. Influenced by the large-scale decline of global sea level, the basin had sufficient sediment sources during the deposition of the upper Miocene Huangliu Formation, and incised turbidity channels called the Central Canyon-Channel (CCC) developed through the whole basin. In order to reasonably formulate the gas field development plan, based on the core analysis data and engineering test data, the petrology, physical property, and pore structure of the CCC sandstone of Huangliu Formation in Ledong Sag-Lingshui Sag were revealed, and the reservoir types were classified and the control factors for the difference of reservoir characteristics were explored. The results show that: (1) The lithology of the CCC is dominated by siltstone and fine sandstone. The pore space is dominated by intergranular pores, followed by intergranular and intragranular dissolution pores. The pore throat size varies from medium to micro, being different among different development blocks. (2) Based on the physical property, fluidity, petrology, productivity, lithology and pore structure, the CCC reservoir can be divided into four types: good, medium, poor and tight. The quality of the CCC reservoir gradually improves from west to east: the good reservoir is distributed in the Lingshui X, ZX blocks, the medium reservoir is distributed in the Lingshui Z block, the poor reservoir is distributed in the Yacheng A, B blocks, and tight reservoir is distributed commonly in a small amount in all blocks. (3) Hydrodynamic conditions primarily control the CCC reservoir quality. Compaction and carbonate cementation reduce pore throat. Abnormal overpressure inhibit the compaction process and retain intergranular pores. These factors together determine the distinct variation in the pore structures among different development blocks. This research will provide a new visual angle that is beneficial for the optimization of exploration targets and development plans of the CCC Gasfield.

After more than 40 years of oil and gas exploration, it has not yet made a industrial breakthrough in Ulungu Depression, northern Junggar Basin. In 2016, the first natural gas reservoir was found in the Triassic system of Shibei Sag. Therefore, it is of great significance to clarify the origin of natural gas and gas source rocks for evaluating the potential and scale of oil and gas exploration. The geochemical data of natural gas in Ulungu Depression and its surrounding areas are systematically collected. The characteristics and types of natural gas in Well Zhunbei-1 are recognized based on the analysis of compositions of natural gas, carbon isotope and light hydrocarbon. Based on the results of closed system hydrocarbon generation simulation experiment of three Carboniferous and one Permian source rock samples, the gassource rocks correlation in Well Zhunbei-1 is carried out with the carbon isotope compositions of methane, ethane and propane, and the genetic mechanism of natural gas is analyzed in combination with seismic profile, regional magnetic anomaly and other data. The results show that: (1) The natural gas of Well Zhunbei-1 is characterized with low methane content (54.5%- 73.9%), low drying coefficient (＜0.95), high nitrogen content (11.1% - 32.7%), heavy ethane carbon isotope (-26‰), and high content of methyl cyclohexane (MCC6) in light hydrocarbons (63.6%), belonging to humic pyrolysis gas. (2) Several regional large faults are developed in the north of Shibei Sag. Influenced by the diorite intrusions, organic matter was thermally catalyzed, and nitrogen-rich natural gas was formed by magmatic degassing. Combined with regional analysis, it is considered that the magmatic degassing caused by diorite intrusions developed along the faults is the main reason for high nitrogen content in natural gas of Well Zhunbei-1. (3) The carbon isotope characteristics of the natural gas in Well Zhunbei-1 are similar to those of the hydrocarbon generation simulation products of the source rocks of the Lower Carboniferous Dishuiquan Formation (with δ13C2 of - 27.6‰ to - 24.0‰), indicating that they have certain affinity. It is inferred that the natural gas mainly comes from the marine terrestrial transitional mature source rocks of the Dishuiquan Formation. The traps adjacent to the source rock of Dishuiquan Formation are important plays for the exploration of natural gas reservoirs in Ulungu Depression.

Halahatang Oilfield in the northern Tarim Basin was discovered in 2009, and obtained proven oil geological reserves of 2.47×108 t in the Ordovician carbonates by 2015. It is an important field for increasing reserves and production of crude oil from carbonate rocks in Tarim Basin. However, the geological conditions of the oilfield are so extremely complex that geological understanding and exploration guidance have undergone many changes, and Halahatang Oilfield has experienced many types of hydrocarbon reservoir exploration stages, such as siliciclastic rock trap, reef-shoal reservoir, interlayer karstic reservoir and fault-related karstic reservoir. Based on comprehensive analysis of the exploration history and exploration and development production data of the oilfield, it is recognized that the fracture-cave reservoir controlled by multiple factors such as faults, karstification and unconformity is the major place for oil and gas occurrence. Further, the distribution and enrichment of oil and gas controlled by the strike-slip faults have complex rules, and the strike-slip faults could connect the Cambrian source rocks to form large-scale petroleum accumulation and preservation. The exploration example of Halahatang Oilfield shows that the superior petroleum geological conditions are the basis for the formation of large oil fields, the breakthrough of geological understanding is the key to the discovery of complex large oil and gas fields, the progress of geophysical prospecting technology is the guarantee for the exploration and development of complex oil and gas fields, and the integration of exploration and development is an effective way to rapidly increase the reserves and production of carbonate rocks. It is suggested that the discovery and exploitation of deep complicated oilfield is depended on the favorable petroleum accumulation condition and geological understanding of the explorer, and appropriate seismic technology and the integrated organization of exploration and development. This case study has important reference significance for the exploration and development of complicate fracture-cave reservoirs.

Kuqa Depression is an important oil and gas exploration area in Tarim Basin, but the understanding of Mesozoic petroleum geological conditions of Yangxia Sag in the east is insufficient, which in turn affects the determination of exploration direction. Based on outcrop, drilling and seismic data, this paper analyzes the petroleum geological conditions of Yangxia Sag from the aspects of tectonic evolution, stratigraphic distribution, hydrocarbon source rock conditions and sedimentary reservoir characteristics, etc. It is believed that Triassic and Jurassic coal measure and lacustrine source rocks are developed in the Middle-Lower Jurassic in Kuqa Depression, and Yangxia Sag is in the relatively developed area of Jurassic-Triassic source rocks. The organic carbon content of hydrocarbon source rocks is between 2.1% and 6%, which belongs to high-quality hydrocarbon source rocks. The CPI value ranges from 1.00 to 1.02, indicating that the hydrocarbon source rock is in the mature-high mature stage. The Middle Jurassic Kizilenur Formation in Yangxia Sag developed braided river delta downstream plain facies and front facies sandstone reservoirs, with the main provenance from the southern Tianshan Mountains in the north and the secondary provenance from Luntai fault uplift in the south. The distributary channel, subaqueous distributary channel and estuarine bar sand bodies in the downstream plain faces-front facies of braided river delta form high-quality reservoirs with porosity of 4%-10% and permeability mainly of (1-30)×10-3 μm2, which belong to classⅡ-Ⅲ reservoirs. The sandstone reservoirs and the coal measure source rocks of the Kizilenur and Yangxia Formations are superimposed on each other vertically, forming a hydrocarbon-reservoir "sandwich" structure. The sand body pinch out upward to form a lithological trap in the middle and southern slopes of Yangxia Sag, being overlied by the Cretaceous and Paleogene mudstone cover, forming a self-generating and self-storing oil and gas reservoir model. The southern boundary of Yangxia Sag developed a sag-controlled fault during the Jurassic deposition period. Still, since the Cretaceous to the present, the tectonic activity is weak, which is favorable for oil and gas preservation and reservoir formation. The rich hydrocarbon shows in the actual wells indicate that the Yangxia Sag has good oil and gas prospect. A series of lithologic traps formed by southward pinching-out lens-shaped sand bodies in the Kizilenur and Yangxia Formations were found in the south-central slope zone of the Yangxia Sag, and the comprehensive analysis suggests that this area is the next key exploration field of the Yangxia Sag.

The geological conditions of shale gas accumulation, gas-bearing characteristics and shale gas preservational conditions of Doushantuo Formation in western Hubei Province was studied based on comprehensive analysis of drilling, outcrops, and testing data. The Doushantuo Formation in the study area can be divided into four members, and the black carbonaceous dolomite developed in the second Member of Doushantuo Formation (Z1d2) is the main shale gas reservoir. From west to east, the shallow shelf, basin and platform facies are developed in turn, and two isolated platform are developed among the basin. On the plane, the depocenter is mainly developed in Zigui-Wufeng region, with the thickness of organic-rich strata more than 100 m; the areas with the TOC values greater than 1.0% are distributed in the Shengnongjialinqu-Zigui-Wufeng area. Overall, the TOC values are at the range of 0.5%-2.0% belonging to low to medium level, and Ro is mainly high maturity of 2.0%-3.5%. The Z1d2 is characterized by the dominated dolomite mineral, the calcareous shale, the ultralow-low porosity, and ultra-low permeability reservoir. The dolomite intergranular pores and clay mineral stratified pores are the most important pore types, and pyrite intercrystalline pores and organic matter pores are much more developed in the samples with high TOC value. The areas with the high gas content are limited only to the north of the Tianyangping fault and southern of the Huangling anticline with the gas content over 1.0 m3/t. It is believed that the shale gas accumulation in Doushantuo Formation is mainly influenced by the superposition of sedimentary facies and structural types. Basin and platform basin facies, stable structural belt, the footwall of reverse fault, and the area far away from regional normal faults with a buried depth of more than 2,000 m are conducive for shale gas accumulation. This paper also provide a scientific basis for further shale gas exploration and development of the Doushantuo Formation in western Hubei Province. It is proposed that favorable areas are mainly distributed in the Yangye-1 well block and Yiye-1 to Yidi-3 well block in the southeast margin of Huangling anticline.

China’s oil companies have several oil and gas cooperation projects in the east of Lekhwair Uplift of the foreland basin on the west side of Oman Mountain, Middle East. Due to the lower degree of regional exploration, the analysis of structure-faults and hydrocarbon accumulation was not deep enough, which restricts the regional exploration process. Based on the new well and seismic data, this paper carried out system structural interpretation and analysis of hydrocarbon accumulation. The results show that: (1) Once being in a regional tensile environment during Triassic-Jurassic, the Lekhwair Uplift is a reverse anticline developed in Late Cretaceous mainly under the control of the rapid uplift and compression of the Oman Mountain, and the overlying Paleogene is directly draped over the Middle Cretaceous in angular unconformity contact in the uplift area. (2) Two sets of high-angle normal faults developed in the uplift area, the different scale faults appear as Y-shape or composite Y-shape forming graben-horst structure on section, and as X-shape distribution in the plane. In Late Cretaceous, these faults are in a closed state due to the orogenic compression. (3) This region was in the passive continental margin for a long time in the Mesozoic era, and the temporal -spatial configuration of source, reservoir and cap is good. The study area has three typical reservoir forming models, namely, the Lower Cretaceous Shuaiba reef-shoal lithologic reservoir, the Upper Cretaceous Natih fault-block reservoir and stratigraphic unconformity reservoir, and the Paleogene Umm er Radhuma bioclastic limestone reservoir. The two sets of main source rock, Diyab Formation of Upper Jurassic and Bab Formation of Lower Cretaceous, have entered a mature stage since Late Cretaceous, then unconformity and vertical faults constitute an important oil and gas conducting system in the region, promoting regional oil and gas accumulation. It is believed that the top and west slope of Lekhwair Uplift have similar geological conditions with those in the east, so they have larger exploration potential and are important exploration directions in the future.

Focusing on the passive continental margin basins with similar structural and sedimentary characteristics in Morocco and Western Sahara offshore areas, this paper conduct research on basin evolution, petroleum geological characteristics, and resource potential, and point out the direction of oil and gas exploration. Morocco-Western Sahara passive continental margin basins are composed of Aaium Tarfaya Basin, Souss Trough, Essaouira Basin and Doukkala Basin. These basins experienced three stages of tectonic evolution, including pre-rift stage, rift stage and post-rift subsidence stage. The pre-rift stage is characterized by the passive continental margin evolution from Cambrian to Early Carboniferous and uplift from Late Carboniferous to Permian. Rifting commenced in Triassic and continued to Early Jurassic. The Triassic and Lower Jurassic terrestrial-marginal marine strata are separated from Paleozoic strata by the Hercynian unconformity. The post-rift stage prevailed from Middle Jurassic to present day, which can be divided into thermal subsidence period of Middle Jurassic to Cretaceous and uplift period of Paleogene to Neogene . Multiple sets of source rocks, reservoirs and a variety of trap types are developed due to the basin structural evolution and sea level change. The most important source rock is post-rift Jurassic-Cretaceous marine mudstone, and the main reservoir is Jurassic-Cretaceous carbonate rock and clastic rock reservoirs. The trap types are mainly structural traps and structurallithologic traps formed under the salt tectonics mechanism. Three main reservoir forming assemblages are divided in the Moroccan -Western Sahara passive continental margin basins, with the Jurassic and Cretaceous-Neogene reservoir forming assemblages being the most important. Jurassic carbonate rock and Cretaceous Albian-Cenomanian turbidite sandstone are the current key exploration fields in this area. Stratigraphic lithologic traps formed by Cretaceous salt tectonics and slope fan in deep water area may be the future exploration potential area.