Abstract

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Title:: Accumulation Mechanism and Model of Natural Gas Compartment in Qinshui Basin of Shanxi, China

Author(s):: LIN Yu-xiang; WU Yu-chen; ZHAO Cheng-jin; ZHU Chuan-zhen; LI Jia; College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, Shandong, China

Keywords:: salinity; compartment; accumulation mechanism; formation water; hydrodynamic condition; “discus” box; tight sandstone gas; Qinshui Basin

Abstract:: Based on the existing exploration data and research findings in Qinshui Basin, the accumulation model of natural gas compartment was set up by comprehensive analysis of structure characteristics, formation water composition and natural gas distribution. The hydrodynamic conditions are very complex, and the formation water can be divided into five zones in turn, including water supply zone, strong runoff zone, weak runoff zone, alternating block zone and discharge zone. According to the relationship between hydrodynamic and salinity of formation water, the change rules of formation water salinity and distribution of formation gas content were studied. Then, it is proposed that the roof and floor combined by tight formations (coal, mudstone, etc.) form the model of widely distributed and nearly concentric “discus” box. Meantime, the accumulation mechanism and sealing mechanism of tight sandstone gas in Qinshui Basin were analyzed. It is found that the “discus” box can be divided into the upper and lower layers. The upper layer is tight sandstone of Shanxi Formation above No.3 coal bed; the lower layer is tight sandstone between No.3 and No.15 coal beds. Although the sealing mechanism of upper and lower layers is different, the distribution of “discus” box is stable from the edge to the interior, then to the edge of Qinshui Basin.