The deep-water area in the Qiongdongnan Basin is one of the most important natural gas exploration areas in the north of the South China Sea. It is also the main battlefield for continuous reserve increases of large and medium gas fields. After the discovery of the large L17 gas field in the Upper Miocene central canyon, shallow targets similar to the central canyon gas field have been decreasing, and it is necessary to carry out more researches on deep water exploration for finding new large and medium-sized gas fields. In the past five years, innovations of ideas, theory and technology have focused on regional structure, petroleum geology and understanding of laws of hydrocarbon generation, migration and accumulation in sags, for the purpose of transforming deep water exploration in the Qiongdongnan Basin. The study shows that, in the Songnan low bulge in the eastern ultra-deep-water area, the Mesozoic buried hills and the Paleogene trap group are surrounded by multiple sags, and have a large transport ridge as a lateral migration pathway, and thick deep-water mudstone as a caprock. The favorable transport and accumulation conditions mean a large potential of resources, which makes the Mesozoic buried hills and the Paleogene trap group the preferred direction for exploration transformation and new breakthroughs. The recent breakthrough in natural gas exploration in this area confirmed abundant natural gas resources in the Mesozoic buried hill. It opened the prelude to the discovery of large gas fields at the scale of 100 billion m3 in the deep-water area, and greatly expanded the exploration of the Mesozoic buried hill in the Tethys tectonic domain in the western South China Sea.

Geothermal resources at medium - low temperature are abundant in the Shandong area. They are widely distributed and have various types, good development and utilization conditions. However, there are less studies on the distribution of thermal bedrock karst reservoirs and the development and utilization potential of the geothermal resources. Comprehensive analysis of drilling, logging, and production test data indicates that the Cambrian-Ordovician bedrock karst with thermal resources has an average density of 2.6722 g/cm3 and a specific heat capacity of 0.5857- 0.95856 J/(g·K). The thermal bedrock karst reservoirs are divided into 12 geothermal regions and 51 geothermal subregions, covering an area of about 4.4×104 km2. Based on the geological division of the Cambrian-Ordovician bedrock karst reservoirs, the temperature of the reservoirs and the chemical characteristics of the geothermal fluids of each region and subregion are analyzed and summarized. Thermal volume method estimates that the geothermal resources are 998.74×1018J, and the recoverable geothermal resources are 149.81×1018 J in the Cambrian-Ordovician bedrock karst reservoirs in the Shandong area.

Predecessors have great differences in the understanding of the hydrocarbon accumulation period and time in the Mesozoic in the Yingen-Ejinaqi Basin. Possible causes for these differences are complex geological conditions and different accumulation times in different sags and even in different structural parts of the same sag in the basin. In addition, previous studies are only based on limited samples, so the research conclusions cannot effectively guide exploration. Taking the Hari sag as the research object, samples were taken from the primary oil- bearing intervals (Bayingebi Formation) in different structural parts, and analyzed on ?uid inclusions. All of the samples contain a large number of ?uid inclusions, and the inclusions are hydrocarbon inclusions and brine inclusions. The ?uorescence of the oil inclusions is light blue and light yellow, and the ?uorescence spectral characteristics indicate that there are at least two hydrocarbon ?lling periods with different maturities in the study area. Numerical stimulation to the sedimentary, burial and thermal evolution history of the sampled wells determined the period and time of hydrocarbon accumulation by considering the homogeneous temperature of the brine inclusions coexisting with the hydrocarbon inclusions. In the Bayingebi Formation in Well YHC1drilled in a subsag, two periods of hydrocarbon ?lling occurred at 107104 Ma and 99 Ma, corresponding to the middle deposition of the Suhongtu Formation and the early deposition of the Yingen Formation. In Well H3 in a slope zone, two periods of hydrocarbon ?lling took place at 99 Ma and 7271 Ma, corresponding to the early deposition of the Yingen Formation and the late deposition of the Wulansuhai Formation. In Well H2, in a marginal zone, two periods of hydrocarbon ?lling took place at 85 Ma and 7571 Ma, corresponding to the middle and late deposition of the Wulansuhai Formation. The difference in hydrocarbon accumulation periods in different structural parts of the Hari sag indicates that the secondary migration distance of hydrocarbons generated by the source rocks of the Bayingebi Formation in the study area is extremely limited, and near-source accumulation is dominant.

Taking the north sag in the Melut Basin in South Sudan as a case, researches were carried out based on regional geology, cores, logging data, grain sizes and seismic facies, which showed that the Paleogene Yabus Formation is a shallow-water delta facies developed in the weak rifting period of the northern sag. In?uenced by rifting activities and lake water level, the upper and lower members of the Yabus Formation have different sedimentary characteristics of shallow-water deltas. During the sedimentary period of the lower member, basin tectonic activities were weak, and the lake water was shallow, so distributary channels of the shallow-water delta plain were widely developed. During the sedimentary period of the upper member, rifting activities were intensive, and the lake water became deep, so there developed widely distributed shallow-water delta frontal sediments and local coastal shallow lake sediments. The underwater distributary channels, distributary mouth bars and other sand bodies may form structural-lithologic traps controlled by faults. The research results are of great signi?cance for continuously estimating the potential and ?nely exploring in the mature exploration areas in the northern sag of the Melut Basin.

The Gaoshiti-Moxi area has been a favorable karst landform after the deposition of the Dengying Formation. However, influenced by complex tectonic movement and obvious differential erosion in the study area, it is unable to effectively indicate favorable reservoirs using traditional paleogeomorphology restoration technologies. On the basis of summarizing the advantages and disadvantages and applicability of traditional paleogeomorphology restoration technologies such as the residual thickness method and the impression method, new paleogeomorphology restoration technology, the impression method + residual thickness method, is proposed by taking the Deng 4 karst reservoir as a case. After mapping a new sedimentary paleogeomorphology, and comprehensively analyzing the sedimentary paleogeomorphology, favorable reservoir facies belts are divided in the Deng 4 Member. The results show that the sedimentary paleogeomorphology map obtained from the new method can eliminate the thickness variation caused by denudation to a certain extent, so original sedimentary thickness could be characterized more realistically. The overlaps on the bottom of the Deng 3 Member and the paleogeomorphology of the Deng 2 Member restored by the residual thickness method proved that, in Well MX47, the Deng 4 Member was in deep water when it began to deposit, resulting in poor reservoir physical properties and low tested production. The most favorable reservoir facies belt is the stripped shoal facies on the platform margin in the western part of the study area. In the eastern part of the study area, there are restricted platform facies where the reservoir properties are the worst.

The Carboniferous ancient volcanic edifices are complex, and have an important impact on the formation, distribution, exploration and development of the gas reservoirs in the Dinan bulge of the Junggar Basin. Based on the interpretation results of new drilling, logging and 3D seismic data, the characteristics of the Carboniferous ancient volcanic edifices and their control on the gas reservoirs were studied and analyzed in the Dinan bulge. The study gives the conclusions as follows: a. According to the morphology of the volcanic edifices and the composition of the volcanic rock, the Carboniferous ancient volcanic edifices can be divided into four types including fractured lava volcanic edifice, central single-crater clastic volcanic edifice, central multi-crater composite volcanic edifice and fractured intrusive volcanic edifice. Controlled by volcanic eruption and sedimentary cycles, the Early Carboniferous volcanic edifices are mainly central single-crater clastic volcanic edifices and fractured intrusive volcanic edifices, and the Late Carboniferous are dominated by fractured lava volcanic edifices. b. The ancient volcanic edifices control the type and distribution of high-quality reservoirs: the fractured lava volcanic edifices contain basaltic reservoirs, the central single-crater clastic volcanic edifices have breccia and dacite reservoirs, and the central multi-crater composite volcanic edifices have breccia and basalt reservoirs, and the fractured intrusive volcanic edifices provide granite porphyry reservoirs. c. Controlled by the ancient volcanic edifices, there are inside-volcano gas reservoirs, weathering crust gas reservoirs, and structural-lithologic gas reservoirs; and the ancient volcanic edifices connecting to deep and large faults are favorable targets for hydrocarbon migration.

In order to understand the characteristics of the Middle and Lower Jurassic reservoirs and the distribution law of the favorable sandstone reservoirs of the Mesozoic in the Kongnan area of Huanghua depression, the characteristics and controlling factors of the reservoirs were analyzed. Accumulation models were predicted for the favorable reservoirs using available well logging, mud logging, core data, and laboratory data. The results show that, although the reservoir physical properties are relatively poor, observation of many rock thin sections indicates that the secondary dissolved pores are well developed, which greatly improve the connectivity and physical properties of the reservoirs. Further studies suggest that the secondary dissolved pores are closely related to organic acid dissolution, and the source of organic acids is related to large faults. Finally, it is proposed that the favorable sedimentary microfacies and strong dissolution control the development of good reservoirs. There are two models of organic acid dissolution, “near source - strong relation - direct transport” and “far source - weak relation - relay transport.” The favorable reservoir zones are classified into five classes, I1, I2, II, III, and IV, based on the composite evaluation of “porosity - effective sandstone thickness - burial depth - fault properties;” according to the spatial configuration of source rocks and reservoirs, the Middle and Lower Jurassic accumulations are divided into “above source” and “under source – beside source.” Their controlling factors were also discussed. Multiple wells deployed in the classes I1 and I2 favorable zones have obtained industrial oil flow, and the drilling success rate was more than 70%.

A breakthrough has been made on the tuff reservoir, a new type of tight oil reservoir, in the Permian Tiaohu Formation in Santanghu Basin. In order to clarify the reservoir forming mechanism and enrichment law, the vertical and horizontal distribution of sweet spots, efficient technology for reserve producing, the distribution law of source rocks, microscopic characteristics of reservoirs, brittleness of reservoir rocks, and oil-bearing ability were investigated. The theory and understanding of exploration and development of the tight tuff reservoir in the Santanghu Basin were summarized using drilling, logging, production tests, and analytical test data based on tight oil geological theory, exploration technology, and development technology, etc. The results show that the oil reservoir enrichment is jointly controlled by the effective configuration of source rocks, stable basin structures, shallow lake environment, tuff composition, later devitrification and dissolution, good match of devitrification and oil filling timing. “Self-source wetting, mixed-source filling, fault-fracture transport, and sweet spot enrichment” characterize the tuff oil reservoir. By developing horizontal well volume fracturing technology and scale development experiments, the tight oil in the Santanghu Basin is produced efficiently. The exploration potential of the tight oil in the Santanghu Basin is huge, and the geological resources of tight oil in the Tiaohu Formation are up to 143 million tons. It is an important resource that guarantees a sustainable and stable oil production. To benefit from the development of the tight oil in the Tiaohu Formation, it is necessary to further identify sweet spots, develop technological innovation, improve organization and management, reduce costs, and increase benefits. These are important factors for the sustainable and stable production of the Tuha Oilfield.

To investigate the types and heterogeneity of reservoirs, fracture distribution and hydrocarbon accumulation models inside the metamorphic buried hills in Jizhong depression, taking the Hejian metamorphic buried hills in the Raoyang sag as an example, studies have been carried out on the oil source conditions, rock characteristics, reservoir physical properties, fracture development, reservoir-caprock assemblages and hydrocarbon accumulation models. The results suggest that reservoir physical properties, reservoir-caprock assemblages and accumulation models are the primary factors controlling the hydrocarbon accumulation in the metamorphic buried hills. The granitic gneiss composed of light-colored minerals such as K-feldspar, acid feldspar and quartz has developed fractures and is the dominant lithology for forming favorable reservoirs. Controlled by lithology, tectonic action and weathering leaching, weathering crust fracture zones, tectonic fracture zones and stratiform dissolution zones are developed. As a result, there are hilltop weathering crust reservoirs, fracture reservoirs and stratiform lithologic reservoirs inside the buried hills. The fracture zone inside the buried hill with a good transport system and developed reservoir space is a favorable exploration target.

In view of complex buried-hill reservoir characteristics and unknown controlling factors in the Shulu sag in the Jizhong depression, the controlling factors on the buried hill hydrocarbon accumulation and accumulating models were studied using petroleum geology and sedimentary petrology. After analyzing the buried hill types, reservoirs and transport systems, it is concluded that the sag has the foundation for forming diverse buried hill reservoirs. Then, the characteristics of diverse accumulation mechanisms were discussed in terms of hydrocarbon source rock, reservoir-cap assemblage and reservoir model. Finally, the controlling factors on various buried hill reservoirs were identified. The study shows that the effective floor is the controlling factor on the formation of the top-cut wedge-like buried hill reservoir, the basement oil source fault is the controlling factor on the formation of the buried hill reservoir in the uplifted fault block, and the lateral seal is the controlling factor on the formation of the fault terrace buried hill reservoir. It is proposed that the fault terrace and gully buried hills in the slope area are the most favorable types and zones for future exploration. The study is a useful reference to identification of buried hill targets and well locations in the Shulu sag, and helpful to make a new breakthrough in buried hill exploration.

The basin group on the passive continental margins on both sides of the South Atlantic is one of the regions with the most abundant oil and gas resources in the world and is also a hot spot of oil and gas exploration in the world today. With the advancement of oil and gas exploration, the increasing of seismic, gravity and magnetic data provides a basis for the study on the structural segmentation and the development law of the basins on both sides of the South Atlantic. Study starting from the tectonic settings of the South Atlantic region, then screening the geophysical and geological sections of the basin groups, and combining the crustal-scale sections with the basin-scale sections, four long structural sections across the basins have been mapped along the transform faults, which are located in the northern, central and southern parts of the South Atlantic. The comparison of the sections at different scales in the same basin shows that plate movement and crustal thinning modes determine the structures of continental shelves and continental slopes, control the development of basins and make the development of strata on the background of gravity. The comparison among the four long structural sections shows a segmental difference in the tectonic features of the basins on both sides of the South Atlantic, but they have similar tectonic evolution stages, and the basins on both sides have an obvious conjugate relationship. The South Atlantic was open from south to north, and according to the primary structural features, three segments of passive continental margins and four types of basins are divided, namely the southern magmatic basins, the central salt-structural basins, the central mud-structural basins, and the equatorial transformed basins.

In the Jizhong depression, many types of buried hills are widely distributed, and have abundant reserves; however, both the deep underground structure and the surface conditions are complex, which leads to unsatisfactory exploration results from deep buried hills and their interior structures. With continuous improvements of geological understanding and equipment, technical research on exploring deep buried hills and their interior structures have been conducted. After several stages, exploration targets have changed from conventional buried hills to deep buried hills and their interior structures; seismic data acquisition from 2D to 3D surveys; conventional to ?ne surveys; and ?ne to target surveys. Operation changed from simple to ?ne, and from explosives to vibroseis green exploration. After nearly 20 years of technological research, a series of seismic survey technologies for deep buried hills and their interior structures have been developed, including “the excitation design based on the quality of buried hill data”, “the design of the recording system based on the structural characteristics of buried hills”, “the performance of the recording system based on complex surface conditions” and “the multi-stage acquisition and vertical observation system”. These mature technologies have improved the exploration data of the deep buried hills and their interior structures, and greatly enhanced the understanding of the deep buried hills in the Jizhong depression.

Sandstone in tight gas reservoirs changes rapidly. At present, static seismic, cores, logging and other data are used to investigate sandstone distribution. However, due to insufficient seismic data in initial exploration and development, the prediction accuracy of sandstone distribution is low, and it is risky to guide later fracturing design using the results. According to the 4D microseismic fracture monitoring results recorded in more than 30 tight gas wells in a block in the eastern Ordos Basin, the direction and boundary of sandstone distribution in target layers to be fractured were corrected, the risk of sand plugging was predicted according to the sandstone position, and 20-30m3 sand addition schemes were proposed. The study results show that the scale of sandstone distribution greatly affects the fracturing and extension of induced fractures; first, sandstone distribution can be judged by the fracturing monitored by 4D microseismic survey; then, the understanding of sandstone distribution can be constrained from sedimentary facies study; and finally, fracturing parameters can be optimized for accurately locating sand plugging and supporting fracturing design and development of tight gas reservoirs.

Flow models are established based on gas desorption and gas-water two-phase flow characteristics to optimize fracturing parameters for horizontal wells under different coal seam conditions. The PEBI grid and finite volume method are used to solve the problems. According to the permeability and thickness of coal seams, coal reservoirs are divided into four types and corresponding mechanism models are established. Then, cumulative gas production and pressure fields are simulated with different fracturing parameters. The study shows that coal seam properties greatly affect the productivity of horizontal wells with multiple stages fracturing. By analyzing the relationship between fracturing parameters and cumulative gas production with different coal seam properties, optimal horizontal section lengths, fracture half-lengths, and fracture spacing can be obtained under simulated conditions. For thick coal seams, it is recommended that the length of the horizontal section could be 1300 m, the fracture spacing of 75100 m, and the fracture half-length of 60 m. For thin and permeable coal seams, it is recommended that the length of the horizontal section could be above 1500 m, the fracture spacing of 75 m, and the fracture half-length could be as long as possible. For coal seams with poor properties, multi-stage fracturing stimulation will not be recommended.