Reservoirs Characteristics And Main Factors Controlling Natural Gas Accumulation In Lingshui Sag,Qiongdongnan Basin

Lingshui sag in Qiongdongnan Basin is rich in petroleum and has great exploration potential.Several reservoirs such as LS17-2 have been found in recent years,but several unsuccessful explorations in study area indicates that the law and main factors controlling natural gas accumulation remain to be resolved.In order to have an overall analysis of the gas reservoir differences between the north and south slopes of the study area and the key factors controlling natural gas accumulation which could help future exploration a lot,based on seismic data,well geological data and analytical tests,the anatomy and comparison of typical reservoirs and unsuccessful structure in the study area are carried out according to analysis of regional reservoir conditions.Through the study of reservoiring mechanisms,accumulation model of natural gas is determined and the key factors controlling accumulation are summarized.The study suggests that the reservoir conditions in Lingshui Sag are fine,source rock is of medium-quality,the reservoir rock quality is medium-good,and lithologic traps dominate the study area;Reservoirs can be divided into two types including the northern slope area and southern slope area of the Lingshui Sag respectively by differences in characteristics of reservoir rock physical properties,temperature and pressure characteristics,natural gas maturity and so on;LS33-1 structural failure is due to poor reservoir rock quality and migration path blocked by reversing faults;Overpressure is the driving force for natural gas migration in deep strata,buoyancy is the main force of migration in shallow strata;Faults and mud diapirs are the main vertical migration channels for natural gas in the north and south of Lingshui sag,respectively,while the lateral migration channels are mainly sand bodies;Natural gas accumulation time is late,natural gas accumulated in northern slope area of Lingshui Sag before overpressure arrival;Reservoiring model of northern slope area of Lingshui sag is “overpressure driving-migration through faults-periodically charging”;Reservoiring model of southern slope area of Lingshui Sag is “overpressure and buoyancy driving–migration through mud diapirs and sand bodies-periodically charging”;Key factors controlling natural gas distribution include: reservoir rock quality limits natural gas distribution zone,conduits system control the reservoirs distribution and scale,vertically stacked sand bodies affects the degree of accumulation of natural gas in traps.