Gas accumulation conditions and exploration orientation of coal measure gas in Shahezi Formation in Xujiaweizi Fault Depression
In order to identify the favorable exploration area for coal measure gas in Xujiaweizi Fault Depression,seismic data,coal samples and geochemical data are used to systematically study the favorable gas accumulation conditions,including genesis of coal measure gas,source rock type,reservoir characteristics and reservoir-cap rock combination.The study results show that:(1)No.l and No.2 coal seams in Shahezi Formation are two sets of consistent coal rocks deposited in delta-front and shallow lake swamp environments,with a thickness of 3-10 m,average TOC of 29.65％,and high to over-high maturity;(2)The coal measure gas is dominated by methane,showing a self-generation and self-storage type highly-over matured coal-generated gas;(3)There are diverse reservoir space types,which are dominated by tensile micro-fissures,primary plant tissue pores,vesicles and mineral pores,with the porosity and permeability of 4.74％and 4.42 mD,showing a favorable reservoir for coal measure gas in deep formations;(4)There are two types of cap rocks at the top Shahezi Formation,i.e.,mudstone and argillaceous siltstone,and three types of reservoir-cap rock combinations,among which the mudstone roof and floor type and mudstone roof and sandstone floor type have good sealing capacity,providing favorable preservation conditions for coal measure gas together with the widespread overpressure sealing box in the coal seam;(5)Based on the study of geological characteristics of coal measure gas reservoir,gas resources in all hydrocarbon generation sub-sags are estimated by using hydrocarbon generation simulation method,and two favorable exploration areas are optimally selected,i.e.,No.l coal seam in Songzhan sub-sag,and No.2 coal seam in Xuxi sub-sag by integrating multiple parameters such as coal thickness,burial depth,and maturity.The area with mudstone cap rock thickness of greater than 5 m is exploration orientation in the near future for achieving breakthroughs of coal measure gas.
万方数据
维普
