川中雷口坡组膏盐岩成因及对储层的影响

通过岩心观察、薄片鉴定、成岩孔隙演化与埋藏史关系研究等手段,分析了川中雷口坡组膏盐岩微相的成因及其演化,并从沉积相、成岩过程、构造作用三个方面论述了膏盐岩对川中雷口坡组储层的控制与影响。研究表明,川中雷口坡组膏盐岩形成于受限陆表海的潮坪环境,其微相分为潮上带的膏盐池、潮间带的膏盐湖和局限潮下带的膏盐盆;其成因可分为潮上带浓卤水在低洼处汇聚成因或潮间潮下带表层浓卤水下沉置换成因;其分布与海平面升降导致的膏盐岩沉积中心迁移有关,同时与点滩的分布也有一定联系。膏盐岩的形成以及同生—准同生期溶蚀、表生期溶蚀垮塌、中—深埋藏期的硫酸盐热化学还原反应产生的埋藏溶蚀等作用对川中雷口坡组中上部储层的形成控制有重要贡献。此外,膏盐岩的底辟作用和构造运动产生的裂缝、断层,对烃源的运移、气藏的重新分布起着一定的促进作用。

The origin of gypsum-salt rock of Leikoupo Formation and its influence on the gas reservoir in central Sichuan basin

Based on core observation, thin section identification, diagenetic porosity evolution and studies of burial history relationship, the authors analyzed the origin and evolution of gypsum- salt rock microfacies of Leikoupo Formation in central Sichuan basin and investigated the controlling role and influence of gypsum-salt rocks on the reservoir of Leikoupo Formation in the aspects of sedimentary facies, diagenetic process, and tectonization. It is shown that the gypsum- salt rocks in central Sichuan basin were formed in a limited tidal flat environment of epicontinental sea, which included gypsum-halite pond of supratidal zone, gypsum- halite lake of intertidal zone and gypsum- halite basin microfacies of limited subtidal zone. Its origin included the concentration of the supratidal zone shallow dense brine in low areas, and the sinking and replacement of superficial dense brine produced in the intertidal-subtidal zone. The distribution of gypsum-salt rocks was related to the deposit center migration resulting from rising and falling of the sea level, and also had something to do with the distribution of the point beach. The formation of gypsum- salt rocks, the dissolution effects in the contemporaneous-penecontemporary period, the supergene period karst collapse and the medium-deep burial period dissolution generated by thermochemical sulfate reduction (TSR) all had important contribution to the formation and control of the upper reservoir in Leikoupo Formation in central Sichuan basin. In addition, gypsum-salt rock diapir as cracks and fractures generated by tectonic movements played a certain role in promoting the migration of hydrocarbon source and the redistribution of the gas reservoir.