Jia-2 Member doloarenite reservoir in the Moxi gas field, middle Sichuan Basin

Abstract

Based on analysis on the macroscopic and microcosmic features of doloarenite in C layer, sub-member 2, Jia-2 Member of the Jialingjiang Formation in the Moxi gas field, the genetic mechanism of favorable reservoirs in beach facies carbonate rock is established. Primary inter-granular pores are the main reservoir spaces in the beach facies carbonates, and have the following key characteristics and identification signs: reservoir development was strictly controlled by the depositional microfacies; main pore types are residual inter-granular pores and dissolved-enlarged residual inter-granular pores; only submarine cement existed in grain contacts; initial compaction led to grains under framework support in line-concave-convex contact; and the burial cement in some separate inter-granular pores being not dissolved. The conservation mechanism of primary inter-granular pores is described as follows: after submarine cementation, the initial compaction created grains with early rim cement under framework support and the throats decreased accordingly; the compaction fluid cementation compressed the beach body's margin, the limited shallow burial cementation in inter-granular pores plugged the throats, and the cementation terminated after the diagenetic fluid reached dissolution-cementation balance. Late burial-dissolution adjusted and optimized early porous strata, which played a secondary role in increasing the reservoir space of each permeable reservoir bodies and did not change the spatiotemporal distribution of this kind of reservoir. Key words: beach facies carbonate, doloarenite, reservoir space, primary inter-granular pore, genetic mechanism, Jialingjiang Formation, Moxi gas field