The Paleozoic marine strata series in the middle Yangtze area is basically similar to that of the upper Yangtze area. However, no substantial results have been achieved over a long and tortuous exploration period. This paper studies and analyzes regional structures, sedimentary development, hydrocarbon source rock, reservoir sedimentation belts and reservoir-cap assemblages in the middle Yangtze area. It concludes that two main potential exploration targets exist in the middle Yangtze area – the lower one composed of Sinian System and Cambrian Systen and the upper one composed of Permian System and Triassic System. This area has the desirable petroleum geological conditions for discovery of conventional natural gas and shale gas with great resources potential. It is supposed to be a key potential area for natural gas exploration. It is proposed that the effective exploration areas of the upper target include Shizhu complex syncline located from West Hubei to East Chongqing, Tuditang and Dangyang synclinorium on Jianghan Plain, and the southern part of Lichuan synclinorium in West Hunan-Hubei area. The effective exploration areas of the lower target include Shizhu complex syncline from West Hubei to East Chongqing and favorable zones in West Hunan-Hubei area. The Cambrian Niutitang Formation in West Hunan-Hubei area is the favorable zone for shale gas exploration while the Jiangzhi-Dangyang block is the favorable zone for shale gas exploration of Ordovician Wufeng Formation – Silurian Longmaxi Formation. The exploration principles should be focused on structural development and accumulation process, highlighting evaluation of reservoirs and preservation, putting the same emphasis on both conventional and unconventional oil and gas, and strengthening technological research to make breakthroughs in marine exploration of the middle Yangtze area.

Carboniferous pinchout belts developed in a large area in the eastern part of Sichuan Basin. The reservoirs of these pinchout belts are strongly heterogeneous, leading to a complex natural gas accumulation law. It is concluded that the stratigraphic pinchout belts of Carboniferous Huanglong Formation in East Sichuan are controlled by a series of factors, such as strata, lithologic characters, structural and fault, with development of lithologic-structural compound gas reservoirs, structural-lithologic-stratigraphic compound gas reservoirs and lithologic gas reservoirs. In the strongly folded areas, natural gas is accumulated mainly in a lithologic-structural compound pattern because these gas reservoirs are influenced by structural characteristics. In the wide and gentle slope areas, natural gas is accumulated mainly in a lithologic-stratigraphic compound pattern. It is also assumed that the lithologic gas reservoirs of stratigraphic pinchout belts are not only small-scale and numerous but also abnormally high and ultra abnormally high in pressure, showing the characteristic of strong regional lithologic closure. Development of compact belts of reservoirs creates the favorable conditions for large-area lithologic closure of the structural enclosing slope zones. It is concluded that four favorable exploration areas exist in East Sichuan – the Guang’an-Chongqing Carboniferous southwestern pinchout belt, the Mingyuexia-Peilingbei Carboniferous southern pinchout belt, the Carboniferous pinchout belt east of Liangping palaeo-uplift, and the Kaixian-Macaoba Carboniferous northeastern pinchout belt. These belts are not only the favorable development areas of Carboniferous lithologic-stratigraphic compound traps in East Sichuan but also the important new types of Carboniferous natural gas exploration in the future.

Fresh breakthrough has been recently made in natural gas exploration of Sinian Dengying Formation and Cambrian Longwangmiao Formation in central Sichuan palaeo-uplift. A giant gas field, with three vertically-distributed producing layers, was found in the eastern segment of the palaeo-uplift. The proven natural gas reserve of Longwangmiao Formation exceeds 4400×108m3 while the controlled gasbearing area of the 4th member of Dengying Formation is 7500 km2. The study indicates that the giant gas field of central Sichuan palaeouplift is characterized in aged production layers, large buried depth, a multiple of gas horizons, a multiple of gas reservoir types and large scale. A number of factors helped development of this gas field, such as superimposition of extensive high-quality source rock and largearea karst reservoirs, existence of large-scale stable palaeo-uplift, and composition of ancient and modern structural traps. The more crucial factor is that successive development of palaeo-uplift matches with various accumulation elements. The high position in the eastern segment of central Sichuan palaeo-uplift is the favorable zone for natural gas abundance, where the marginal area of the south-north ribbon-shaped zone from Gaoshiti to the western part of Moxi is the high-yield natural gas abundance zone of Dengying Formation. The composition area of Moxi-Longnvsi ancient and modern structures is the high-yield natural gas abundance zone of Longwangmiao Formation.

The reserve-production ratio is the ratio between the remaining reserves and production in the same year, reflecting the changes in the oil production situation. Based on the study of the oil and natural gas reserve-production ratio of major oil areas nationwide in the past decade, this paper makes analysis of the oil and gas development momentum. The strategy to put the same emphasis on both oil and natural gas has been basically realized in the efforts for exploration and development in the past three decades, with new oil and gas industrial bases established. The practice indicates that tapping of potential in old oil areas is an important condition for sustainable development. Lowgrade reserves and even unconventional oil and gas reserves have become more and more important strategic areas of oil and gas exploration and development. However, the growth of reserves and production has been obviously slowed down in recent years with the reserveproduction ratio reduced. Since the early-developed oilfields become aging and deteriorating, it is of great urgency to open up new fields and new producing areas while tapping the potential in old oil areas for strategic resources replacement. The development strategy should be focused on the following areas. First, put the same emphasis on both conventional and unconventional oil and gas development. Investment in conventional oil and gas development should follow the order of such priorities: increase of reserves and production in old oil areas, development of unproduced reserves, expansion of new oilfields and oil areas and drilling of adequate risk exploration wells. (2) The efforts should be continued for onshore deep layers and offshore Mesozoic oil and gas areas of marine facies. (3) Energetically promote exploration and development of the new producing areas which are confirmed to have oil and gas prospect, such as the well-preserved Qiangtang block of marine in Tibetan Plateau and the rift belt of continental facies represented by Bangong Lake – Nujiang River area, and the Upper Paleozoic System of marine facies in the north excluding Huabei area and Tarim area as well as the deep to ultra-deep zones outside the continental shelf of South China Sea.

Based on study of the sequential stratigraphy and sedimentary system of Paleogene Liushagang Formation in Fushan Depression of Beibu Bay Basin, this paper focuses on the controlling factors of lithologic reservoirs and analyzes the favorable areas of lithologic oil and gas reservoirs in Fushan Depression on the basis of the research on the discovered lithologic reservoirs, aiming to guide exploration of lithologic oil and gas reservoirs at the next stage. The study indicates that the Paleogene System in Fushan Depression can be divided into three three-level sequences. The types of main sedimentary system are braided delta, fan delta, sublacustrine fan and lake. The lithologic reservoirs are mainly controlled by ancient landform of structure, development background of sedimentary system and matching relations between physical properties of reservoirs and source-reservoir-cap assemblages. In each three-level sequence, lithologic reservoirs are most easily formed in the area of lake-invaded system. On the plane, lithologic reservoirs related to channel mouth bar, slip block and sublacustrine fan are easily formed in delta frontal belts.

Based on the sequential stratigraphic research, this paper is focused on the environment for hydrocarbon source rock of the Paleogene System in the sequential stratigraphic framework of Qikou Depression by means of organic geochemistry, studying the distribution law and controlling factors of high-quality source rock. The Paleogene System in Qikou Depression can be divided into three secondary sequences. A number of sets of effective source rock developed in the strata of different sequences, but source rock is strongly heterogeneous. The different sequences are divided into six types of sedimentary organic facies according to the differences in the palaeoenvironment, palaeoecology and palaeoclimate. Of those types, the high-quality source rock of near source - saline lake - strong reduction atmosphere - plant and algal source facies developed most. Vertically, high-quality source rock developed mainly in the faulted lacustrine basin in the stable lake flooding period, particularly in the upper part of SQEs₃ 2 - SQEs₃ 1, the upper part of SQEs₁ lower - SQEs₁ middle. Horizontally, high-quality source rock development mainly in the southern part of Qikou Depression because it was controlled by the conditions of material sources and the environment of water bodies. The sedimentary and sourcing environments controlled space development of highquality source rock in common.

Sulige gas field is a typical low-permeability, low-pressure and low-abundance gas field in Ordos Basin. The sand bodies of the He-8 Member of the Lower Permian Shihezi Formation are vertically overlaid and horizontally linked up. The effective layers are relatively thin with the water-gas relations complicated. The technological research is focused on multi-wave seismic processing and fluid detection in the light of the above-stated issues. A number of key multi-wave processing technologies are emphasized in the study, such as static correction of conversion wave, velocity analysis, and P and S wave consistency processing, improving imaging precision of multi-wave seismic data. Meanwhile, multi-wave joint pre-stack simultaneous inversion, multi-wave AVO analysis, and rock elastic parameter crossplot are applied in a creative way to acquire more accurate elastic parameters and reduce the multi-description of reservoir prediction by use of only P wave. Based on crossplot of two independent elastic parameters to identify abnormal response, the resolution of reservoir is improved as compared to the prediction by using a single seismic parameter. As a result, the accuracy of lothologic and fluid detection is improved, enabling the coincidence rate of predicting effective reservoirs (referring to gas-bearing layers and accumulated thickness of gas-bearing layers) to exceed 80 percent. Remarkable achievements have been made in application of this technology for deployment of well location in exploration and development of Sulige Gas Field. It also provides a technological support for large-scale and effective development of the gas field.

This paper tries to make a quantitative evaluation of the 3D seismic geometry attributes and particularly takes into account the vertical and horizontal uniformity. From an angle of creation, it comes up with the concepts of the geometry’s uniform factors, new aspect ratio, effective folds and formula for expression of relations and points out the geophysical significance of these new concepts. The uniform factors, new aspect ratio and effective folds are used, together with the maximum offset, to establish an overall quantitative evaluation method of the geometry attributes on the basis of their contributions to the geometry, and offer a numerical example. The results of the numerical example indicate that the mathematical formula of the overall quantitative evaluation covering uniform factors, azimuth, amount of folds and maximum offset can be used to directly calculate the attributes of different geometries and the assessed values of the attributes in the future design of 3D geometry. This method is simple, fast and effective.

Changqing Oilfield is rich in tight oil resources. Drilling of horizontal well and volume-fracturing process are the main methods for development. Volume-fracturing tools hold the key to development process. Based on the analysis comparison of the pipe string and support tools used for staged renovation of horizontal wells in the previous stage and combined with the requirements on the tools for volume-fracturing process and cluster perforation, this paper briefs about hydro-jetting cluster-perforating volume-fracturing tools, large-bore and fast-drilling bridge plug fracturing tools and switchable fracturing sliding sleeve tools with casing. The results indicate that hydro-jetting cluster-perforating tools are advantageous for their simple use and low operating cost under the conditions that 139.7 casing is used for cementation and completion and the pumping rate is less than 8m3/min. Therefore, hydro-jetting cluster-perforating tools become the main volume-fracturing tools for volume-fracturing of horizontal wells in Changqing Oilfield. a total of 505 horizontal wells have been fractured by means of these tools. When the pumping rate exceeds 8m3/min, large-bore and fast-drilling bridge plug fracturing tools are used because no drilling is needed after fractured and the wells can be directly put into production. A total of 42 horizontal wells have been fractured by means of such tools. Switchable fracturing sliding sleeve tool with casing, the most potential for development, can not only meet the need for large-rate fracturing renovation but also the need for later-on layered testing, water plugging and repeated renovations, indicating the development orientation for volume-fracturing tools.

North Gabon Sub-basin experienced the rift period, transition period and passive continental marginal depositing period since the Cretaceous era. Salsich Block is located in North Gabon Sub-basin off the coast of Gabon. Hydrocarbon is accumulated mainly in the postsalt strata series of the Cretaceous System. Hydrocarbon distribution comes under influence of regional structural development. Hydrocarbon accumulation belts are in line with the regional structural strike. The black mudstone of the Upper Cretaceous Azile Formation is the main hydrocarbon source rock of oil and gas reservoirs in Salsich Block. The organic carbon content of source rock is 3-5 percent on average while the organic matter is mainly composed of kerogen type I and II. The reservoirs are subsea turbidite fan sandstone of the Upper Cretaceous Anguille Formation and shallow sea delta sandstone of the Upper Cretaceous Point Clairette Formation. There are two hydrocarbon accumulation models – primary and secondary accumulation patterns with sourcing in lower part and accumulated in the upper part. The characteristics of reservoirs under the two accumulation patterns are quite different from each other. Five structural belts developed in Salsich Block, namely WZ structural belt, OZ structural belt, IE structural belt, NT structural belt and GG structural belt. One structural belt is different from another in terms of oil and gas resources potential. Of those, WZ structural belt is the most favorable one for oil and gas accumulations with unique conditions for oil and gas abundance and a considerable potential for exploration. The oil and gas exploration potential of other structural belts become less desirable owing to influence of comprehensive geological conditions.