RESEARCH OF SHALE GAS RESERVOIR HETEROGENEITY: A CASE OF THE LOWER CAMBRIAN QIONGZHUSI FORMATION OF THE SICHUAN BASIN

Along with the development of shale gas in favorable areas in China,the research of shale gas reservoir heterogeneity has become the key to improving shale gas recovery. Based on the detailed investigation of research programs on shale gas reservoir heterogeneity at home and abroad,taking the Lower Cambrian Qiongzhusi Formation in Sichuan Basin as a case, we studied the shale gas reservoir heterogeneity in three aspects: plane heterogeneity,interlayer heterogeneity and micro-anisotropy. The plane heterogeneity is mainly affected by regional depositional framework and organic geochemistry. The western part of the basin is dominated by argillaceous sandstone and sandy mudstone with low organic matter and low maturity, while the northeastern part of the basin dominated by argillaceous limestone with high organic matter and high maturity. The southern part of the basin, however, is dominated by carbonaceous mudstone with rich organic matter and highest maturity. The vitrinite reflectance Ro can reach 4%. Well correlation and mineralogy of a single mudstone layer shows that the reservoir interlayer heterogeneity is strong,the total thickness of the Formation,thickness of single shale layer,number of shale layers and intercalations vary strongly in lateral direction. The lithology of the roof and floor changes quickly along the horizontal section,and the mineral composition and rock brittleness change quickly along the vertical profile. The micro-heterogeneity is mainly affected by the pore types and matrix microcracks. The clay interlayer porosity and organic matter porosity are well developed. Matrix microcracks play an important role in pore connection. Through the comprehensive analysis of the Lower Cambrian Qiongzhusi Formation,it is concluded that the heterogeneity characteristics of a shale gas reservoir renders important effect on shale gas productivity and recovery rate.