ALBERT

Description: The discovery and large-scale exploration of deep basin oil/gas resources since 1980s have been considered as the most important advancement in the history of petroleum geology. It has not only changed the balance of supply and demand in the global energy market, but also improved our understanding of the formation mechanisms and distribution characteristics of oil/gas reservoirs. However, misconceptions widely exist in studies of different types of petroleum accumulations because of the lack of a unified genetic classification. Unconventional reservoir has been used in the literature as a general name for various oil/gas reservoirs that are formed under complex dynamic mechanisms as long as buoyancy is not the major controlling factor. On the other hand, different terms have been given to the reservoirs even with the same formation mechanism. This paper studies the progress of unconventional oil/gas exploration in North America in the past 30 years, analyzes the drilling results of 80762 reservoir layers from 12237 exploration wells in six representative basins in China and the discovered 52,926 oil/gas reservoirs in 1,186 basins around the world, and reviews the classification schemes about oil/gas reservoirs by different scholars. It is found that there are five differences between conventional and unconventional reservoirs, including hydrocarbon composition, spatial relation with source rocks, reservoir lithology and quality, distribution in geological settings, and reservoir formation mechanism. Meanwhile，it is also found that there are five aspects of relevance among them, including petroleum source, distribution in strata within the same geological age, coexisting in sedimentary basins, in petroleum systems, and in target reservoir layers. A unified genetic classification scheme about conventional and unconventional oil/gas reservoirs was introduced based on clarifying their differences, correlations and formation mechanisms. All petroleum reservoirs are classified into 3 categories and 6 subcategories according to dynamic mechanisms of formation, reclassified into 15 types based on main controlling factors, and further divided into 49 styles considering their underground occurrences. The application results show that all different oil/gas reservoirs can find their corresponding positions in the classification scheme, and all the oil/gas reservoirs with the same genetic mechanism, major controlling factor and occurrence can find their particular position in this classification scheme.