川中地区震旦系灯影组微生物岩优质储层成因机制OA

The Upper Sinian Dengying Formation in the central Sichuan Basin serves as a strategic core for deep to ultra-deep carbonate gas reservoir exploration in China,where the Anyue super-giant gasfield and the Penglai gas area have been discovered successively.However,influenced by ancient age of strata and complex tectono-diagenetic evolution process,the genetic mechanisms and distribution patterns of high-quality reservoir spaces in deep ancient carbonates are poorly understood,hindering gas exploration breakthroughs in this area.To address the issue,with the Dengying Formation microbialite reservoirs as the research object,the sedimentary characteristics of different sedimentary subfacies were systematically analyzed,and the diagenetic evolution sequences were reconstructed.Moreover,the coupled multiphase reaction-migration numerical simulation was performed by using the TOUGHREACT software.The following results are obtained.(i)The initial porosities of four subfacies,namely microbial mound,grain shoal,platform flat,and intermound/intershoal depression,are 40%,50%,15%,and 30%,respectively,showing significant difference in diagenetic evolution pathway.(ii)Supergene meteoric freshwater dissolution is crucial to the development of high-quality pores.The microbial mound subfacies achieves a peak dissolution intensity of 36.0%,far exceeding those of grain shoal(17.2%),platform flat(18.8%),and depression(11.0%).(iii)Moderate dolomitization(final dolomite content of about 79.6%in microbial mounds)reduces the compaction coefficient by 20%-30%,significantly enhancing the resistance to compaction;whereas excessive dolomitization(dolomite content＞94%in grain shoal,platform flat,and depression subfacies)may make the rock tight due to cemented fillings.(iv)The microbial mound subfacies preserves a final porosity of approximately 6.5%,while grain shoal,platform flat,and intermound/intershoal depression subfacies only have 4.2%,2.0%,and 0.7%,respectively.It is concluded that,the high-energy microbial mound subfacies represents the most favorable reservoir development zone because of its optimal diagenetic evolution pathway of"high initial porosity → intense supergene dissolution→ moderate dolomitization for compaction resistance → limited burial dissolution compensation".Priority exploration deployment is recommended for microbial mound-shoal complexes along the northern slope and platform margin of the Central Sichuan Paleo-uplift.