Pore evolution characteristics of beach facies reservoir of Feixianguan Ⅱ Member in Yuanba area, Sichuan Basin

Key words:  Sichuan Basin  Yuanba area  Feixianguan Formation  carbonate rock  marginal platform beach  reservoir  pore structure

Abstract:

Using analyses of rock thin sections, cathodoluminescence, electron microprobe and fluid inclusion, the reservoir characteristics and the diagenesis that affected on reservoir pore formation and preservation of the Feixianguan Ⅱ Member in Yuanba area were studied. The pore evolution model was discussed combined with hydrocarbon infill injection period times. The results show that the oolitic limestone with intergranular and intragranular dissolved pores is the main reservoir in the study area. Reservoir pores are mainly formed by micritization, dissolution, cement filling, compaction, pressure solution and tectonic rupture. Meteoric dissolution is the key for secondary porosity formation. The first buried dissolution provides a good channel and gathering place for hydrocarbon filling, but meteoric calcite cement plays a significant role in the destruction of the secondary porosity preservation. There are three stages of reservoir pore evolution in the study area, namely, dissolution pore forming and the alternative variation of pore fluctuating before oil charging; pore decreasing in the transformation period from oil to gas; and fracture and dissolution pore forming and slow pore increasing after transformation from oil to gas.