Research On Carbonate Reservoirs Of The Changxing Formation In Northeastern Sichuan Basin

Puguang Gas Field as the largest gas field of Sichuan Basin is also the biggest marine carbonate formational gas reservoir. More prospecting and investigating work should be done in order to achieve an even bigger breakthrough.Based on reservoir sedimentology, reservoir geology and diagenesis theory with the combination of thin-section observation, XRD and electronic probe micro-analysis, the paper has made deep research on problems of sedimentary facies, microfacies, diagenesis, reservoir characteristics and the dominating factors controlling hydrocarbon accumulation which has great guidance significance on analyzing favorable exploration potential, evaluating exploration targets, effective guidance to further oil and gas exploration.Firstly, according to the outcrops, cores, thin section and well loggings data et al, the sedimentary mode and the sedimentary characteristics are established on the basis of considering the macrocosmic depositional setting and the microcosmic sedimentary characteristics. Platform margin organic reefs, platform margin shoals, open carbonate platform and limited carbonate platform, carbonate slope facies, basin facies and platform evaporate are developed in the study area. The main microfacies are subordinate organisms, sparry grain dolomite microfacies, breccia dolomite, dolomite mudstone microfacies, organism bindstone limestone, limestone mudstone microfacies, spar grain limestones and litter limestone. Wherein the most favorable facies is breccia dolomite, organism bindstone dolomite and spar grain limestones.Secondly, based on the above research, the paper also studies the diagenesis, diagenesis phase, diagenetic environment and diagenetic sequence and discusses the relationship between diagenesis and the pore evolution of the reservoir. It comes to the conclusion that the most favorable diagenesis includes dolomitization, dissolution and recrystallization. The favorable diagenesis phases are syngenetic and late diagenetic stage. The favorable diagenetic environment is exposure-burial dissolution environment.Besides, the porosity evolution study shows platform margin shoals had the largest porosity with complex types of pores and good reservoir property. The platform margin reefs are secondary with medium reservoir property. The porosity in open-platform limestone is not derdeveloped with any reservoir capability.Lastly, by analyzing the cores, logs, seismic data and the reservoir physical properties, it comes to conclusion that sedimentary facies and diagebesis are the main factors controlling the researvior distribution. Generation and evolution of carbonate reservoirs. Sedimentary processes are the bases, which control the researvior distribution. Diagenesis is the key, which not only influence the reservoir space revolution process but also determines the specific distribution of the current reservior. Therefore, the reef shoal dolostones from the Changxing Formation have best potentials for oil and gas reservoirs. The most favorable microfacies are organism bindstone dolomite and spar grain limestones.