Abstract:

In the process of exploration and development of shale gas, we find some areas as Development Zone, with high gas content and high resource abundance. The EUR of a single well is also high, and the economy is good. Since shale gas content equals to the adsorbed gas and free gas, in addition to dissolved gas, free gas, adsorbed gas and dissolved gas are closely correlated with pressure coefficient. In the United States, due to stable geological conditions, it is easy to carry out shale gas geological screening. The overpressure is not so important for shale gas field, normal pressure, even underpressure can be achieved commercially. So, In the United States shale gas geological screening index has no concept of pressure coefficient, or it is not a key indicator. However, due to the different geological formations in China and North America, the North American shale gas is mainly located in the basin of central Canada, and the background is very stable. In contrast, China consists of many blocks with complex structure and long time. Because of the high maturity of marine shale, the porosity is low and decreases. The tectonic movement is active with developed faults, and the preservation condition is relatively poor. For the shale with high maturity and low porosity, it is necessary to reach the same pressure coefficient of gasbearing formation, so that the ultimate recoverable reserves of single well can reach the economic limits, and the commercial development can be realized. South China has abundant marine shale gas, which is characterized by large thickness and stable distribution. The formation of low water saturation often occurs in the process of hydrocarbon generation. Pressure mechanism of the overpressure shale gas field in the Yangtze region mainly consists of uplifting construction, water pressure, the type of clay mineral dehydration, and hydrocarbon generation. The marine shale gas field is mainly resulting from the formation of super pressure. Changning shale gas field is a main hydrocarbongenerating pressurization field. Screening index of favorable area should include core area/enrichment area optimization index. Index value based on the geological characteristics of the super pressure gas field must match the significance of the parameters. Geological areas of North American shale gas need to consider the burial depth, shale thickness, TOC content, and the content of silica. Due to the simple geological conditions and moderate maturity of the North American shale, it can be realized under the condition of low pressure and under pressure, but in the background of high maturity and fault development, the formation pressure coefficient is especially important. Therefore, this paper considers that the basic parameters, such as depth (15004500 m), thickness (>30 m), total organic carbon content (>2%), and silica mineral content (>30%), should be considered as an important index to reflect the characteristics of marine shale gas in southern China.

Key words: South China marine shale, overpressure core area, ultralow saturation, strata pressure coefficient