Search

The new century has witnessed a strategic breakthrough in unconventional oil & gas. Hydrocarbon accumulated in micro-/nano-scale pore throat shale systems has become an important domain that could replace current oil & gas resources. Unconventional oil & gas plays an increasingly important role in our energy demand. Tight gas, CBM, heavy oil and asphaltic sand have served as a key domain of exploration & development, with tight oil becoming a 'bright spot' domain and shale gas becoming a 'hotspot' domain. China has made great breakthroughs in unconventional oil & gas resources, such as tight gas, shale gas, tight oil and CBM, and great progress in oil shale, gas hydrate, heavy oil and oil sand. China has an estimated (223-263)×108t of unconventional oil resources and (890-1260)×1012 m3 of gas resources. China has made a breakthrough for progress in unconventional oil & gas study. New progress achieved in fine-grained sedimentary studies related to continental open lacustrine basin large-scale shallow-water delta sand bodies, lacustrine basin central sandy clastic flow sediments and marine-continental fine-grained sediments provide a theoretical basis for the formation and distribution of basin central reservoir bodies. Great breakthroughs have been made in unconventional reservoir geology in respect of research methodology & technology, multi-scale data merging and physical simulation of formation conditions. Overall characterization of unconventional reservoirs via multi-method and multi-scale becomes increasingly popular and facilitates the rapid development of unconventional oil & gas geological theory, method and technology. The formation of innovative, continuous hydrocarbon accumulation theory, the establishment of the framework of the unconventional oil & gas geological theory system, and the determination of the implications, geological feature, formation mechanism, distribution rule and core technology of unconventional oil & gas geological study lays a theoretical foundation for extensive unconventional oil & gas exploration and development. Theories and technologies of unconventional oil & gas exploration and development developed rapidly, including some key evaluation techniques such as 'sweet spot zone' integrated evaluation and a six-property evaluation technique that uses hydrocarbon source, lithology, physical property, brittleness, hydrocarbon potential and stress anisotropy, and some key development & engineering technologies including micro-seismic monitoring, horizontal drilling & completion and 'factory-like' operation pattern, 'man-made reservoir' development, which have facilitated the innovative development of unconventional oil & gas. These breakthroughs define a new understanding in four aspects: ① theoretical innovation; ② key technologies; ③ complete market mechanism and national policy support; and ④ well-developed ground infrastructure, which are significant for prolonging the life cycle of petroleum industry, accelerating the upgrade and development of theories and technologies and altering the global traditional energy structure. [ABSTRACT FROM AUTHOR]

The petroleum systems of Chinese nonmarine rifted and depression basins, dominated by lacustrine strata, have distinctive source rocks, reservoir types and trap characteristics. The rifted basins are characterized by numerous faults and multiple structural salients and sags (half grabens). Sags include many subdivisions and smaller isolated sags. Most sags constitute relatively independent petroleum systems that have efficiently generated and expelled hydrocarbons, have excellent reservoir properties in a variety of sand-body types, and have multiple traps. These attributes impart a petroliferous character to the entire sag. Depression basins (intracratonic flexural basins) developed on large cratons and hosted large lacustrine systems. They feature very gentle structure, large deltaic sand-bodies, source rocks in extensive contact with sand-bodies, heterogeneous low-porosity-low-permeability reservoirs and large, widespread lithology-controlled pools. In recent years, large oil and gas reserves have been discovered in these two types of lacustrine-dominated basins, contributing significantly to the growth of reserves in onshore China, and stratigraphic oil and gas pools have become the major type of accumulation in nonmarine lacustrine basins. [ABSTRACT FROM AUTHOR]

Volcanic rocks are distributed widely in China, which are important exploration targets. By analyzing many discovered volcanic hydrocarbon reservoirs all over the world, the authors summarized the geologic characteristics of the formation of volcanic hydrocarbon reservoirs in China, and gave further exploration directions and advices. (1) There are mainly Carboniferous-Permian, Jurassic-Cretaceous, Paleogene-Neogene volcanic rocks in oil- and gas-bearing basins in China, which are mainly distributed in the Junggar Basin, Songliao Basin, Bohai Bay Basin, etc. There are mainly intermediate rocks and acidic rocks in east China, and intermediate rocks and basic rocks in west China. They primarily develop in intracontinental rift settings and island are environments. (2) Porefissure reservoirs are distributed widely in basins, which are volcanic rocks mainly in explosive and effusive facies. (3) Volcanic hydrocarbon reservoirs are chiefly near-source lithostratigraphic hydrocarbon reservoirs, and the oil and gas accumulation is predominantly controlled by lithotypes, faults and structural positions. (4) Deep-seated oil and gas reservoirs in the Songliao Basin and Carboniferous volcanic hydrocarbon reservoirs in the Junggar Basin are potential giant volcanic gas provinces, the volcanic hydrocarbon reservoirs in the Bohai Bay Basin and Santanghu Basin are favorable for oil and gas reserves increase, and volcanic rocks in the Turpan Basin, Sichuan Basin, Tarim Basin have exploration potentiality. (5) The technology series of oil and gas exploration in volcanic rocks have been preliminarily formed. [ABSTRACT FROM AUTHOR]

Abstract: The comprehensive analysis of geological setting, accumulation condition, trapping mechanism and distribution regularity of oil-gas of the Upper Triassic in Sichuan Basin reveals that the gas accumulation in Xujiahe Formation is a layered lithologic giant gas province. Coal source rocks in layers expelled hydrocarbon evaporatively. Under the setting of the episodic fold-thrusting and compression in the boundary orogen, multi-sources charged quickly and formed a coarse deltaic environment with a large-scale delta plain and a small-scale delta front. In gentle structures, Darcy and non-Darcy flow mechanisms coexist because of the limited buoyancy of low permeability sandstone, thus forming the coexisting oil-gas-water system. This paper classifies the diagenetic facies quantitatively using compaction percentage, cementation percentage and corrosion percentage, and defines eight diagenetic subfacies and twenty diagenetic microfacies. Besides, the origin of diagenetic facies is analyzed by using Ro and formation water parameter. This kind of giant gas province originated mainly from stable large-scale continental depressions, gentle foreland slopes and paralic facies in central China. It is characterized by large-area layered distribution, no obvious trap and cap formation, large-scale resource, low-abundance reserves, and difficult to exploit. [Copyright &y& Elsevier]

Large-scale shallow-water deltas in lacustrine basins have recently been identified as important reservoir plays worldwide. The Poyang Lake, the largest fresh water lake in China, develops a series of modern shallow-water deltas, hence provides an excellent modern analogue for understanding various key depositional processes that control deltaic development and evolution. This paper uses SEDSIM, a three-dimensional stratigraphic forward modelling programme, to simulate the development and evolution of the shallow-water deltas in the Poyang Lake by considering a number of key processes and parameters affecting the deltaic deposition over 1200 years. The simulations show that the shallow water deltas have some unique characteristics. The delta plain is dominated by distributary channel sandbodies and thins towards the lake centre, whereas the delta front thickens lake-centre-wards. The major delta has very gentle delta slope less than 0.06°. The frequency of lake level oscillations appears to be a significant controlling factor in determining the deltaic architecture within the deltaic systems. The simulation indicates that the "Gilbert-type" deltas would not commonly develop in shallow-water basins even if the basin margin may be steeply sloped. The study has demonstrated that the process-based modelling approach can be effectively used to simulate complex geological processes and environments and quantify key controlling factors that otherwise cannot be easily acquired due to physical constraints. [ABSTRACT FROM AUTHOR]