The Diagenesis Influence of Feixianguan Formation on Reservoir Pore Evolution in Dawan Area

Diagenesis and pore evolution characteristics of Feixianguan Formation in Dawan gas reservoir were fully studied based on the microscopic-analysis on casting thin sections, scanning electricity mirror and core analyzing materials. The results showed that the mainly diagenesis types of carbonate reservoir in Feixianguan Formation are as follows: dolomitization, compaction, cementation, filling, dissolution, recrystallization diagenesis, etc. According to comprehensive analysis of diagenetic features, reservoir rocks are mainly formed in sedimentary facies belt of Oolitic beach facies at platform margin, which has a strong wave action with following characteristics: Oolitic grain-refining dolomite and sand cutting grain-refining dolomite are the mainly rock types, with large particles diameter, high level of dolomitization and well-medium sorted, but strong diagenesis. In submarine and syngenetic stages, porosity drop rapidly because of compaction and the calcite cementation. During this stage, the primary pores reduce greatly, although mixed water dolomitization and meteoric fresh water dissolution can form secondary pores; in shallow burial stage, the pores are drastically reduced under the compaction and cementation; the later period of dissolution can form secondary dissolution pore, thus there are enormous contributions to the increase of porosity.