Whole petroleum system and ordered distribution pattern of conventional and unconventional oil and gas reservoirs.

The classical source-to-trap petroleum system concept only considers the migration and accumulation of conventional oil and gas in traps driven dominantly by buoyance in a basin, although revised and improved, even some new concepts as composite petroleum system, total petroleum system, total composite petroleum system, were proposed, but they do not account for the vast unconventional oil and gas reservoirs within the system, which is not formed and distributed in traps dominantly by buoyancedriven. Therefore, the petroleum system concept is no longer adequate in dealing with all the oil and gas accumulations in a basin where significant amount of the unconventional oil and gas resources are present in addition to the conventional oil and gas accumulations. This paper looked into and analyzed the distribution characteristics of conventional and unconventional oil/gas reservoirs and their differences and correlations in petroliferous basins in China and North America, and then proposed whole petroleum system (WPS) concept, the WPS is defined as a natural system that encompasses all the conventional and unconventional oil and gas, reservoirs and resources originated from organic matter in source rocks, the geological elements and processes involving the formation, evolution, and distribution of these oil and gas, reservoirs and resources. It is found in the WPS that there are three kinds of hydrocarbons dynamic fields, three kinds of original hydrocarbons, three kinds of reservoir rocks, and the coupling of these three essential elements lead to the basic ordered distribution model of shale oil/gas reservoirs contacting or interbeded with tight oil/gas reservoirs and separated conventional oil/gas reservoirs from source rocks upward, which is expressed as "S\T-C". Abnormal conditions lead to other three special ordered distribution models: The first is that with shale oil/gas reservoirs separated from tight oil/gas reservoirs. The second is that with two direction ordered distributions from source upward and downward. The third is with lateral distribution from source outside. [ABSTRACT FROM AUTHOR]