四川盆地寒武系洗象池组岩相古地理及储层特征

Lithofacies palaeogeography and reservoir characteristics of the Cambrian Xixiangchi Formation in Sichuan Basin

在典型野外露头、岩心以及岩石薄片观察的基础上,结合实验分析数据,对四川盆地寒武系洗象池组岩相古地理、储层特征及其主控因素进行了研究。结果表明:①洗象池组沉积期为镶边碳酸盐台地沉积环境,盆地整体位于局限台地内部,在梁平-重庆台洼两侧发育高能滩相;②储层多发育在洗象池组中上段,岩性以颗粒白云岩、晶粒白云岩、藻白云岩为主,主要储集空间为溶蚀孔洞、粒间孔、晶间孔与裂缝,孔隙度集中分布在2%~5%之间,平均为3.46%;③储层的形成与分布受沉积相、准同生溶蚀作用与表生岩溶作用共同控制,储层主要发育在古地貌较高部位、海水向上变浅旋回的上部及奥陶系尖灭线附近。预测位于台洼两侧的合川-广安与南川-石柱一带古地貌高部位为有利滩相储层发育区,西充-广安-潼南地区为有利岩溶储层发育区;指出西充-广安一带为有利勘探靶区。

Based on the observation of typical outcrops,cores and petrographic thin sections,combined with the experimental analysis data,the lithofacies palaeogeography,reservoir characteristics and their main controlling factors of the Cambrian Xixiangchi Formation in Sichuan Basin were studied.The results show that:(1)The Xixiangchi Formation is developed in the rimmed carbonate platform,and the Sichuan Basin is located in the interior of the limited platform as a whole,with the high-energy shoal facies developing on both sides of the Liangping-Chongqing platform depression;(2)The effective reservoirs are mainly developed in the middle and upper part of Xixiangchi Formation,dominated by grain dolomite,crystalline dolomite and algae dolomite.The reservoir spaces are consisted of dissolution pore,intergranular pore,intercrystalline pore and fracture,with porosity mostly at the range of 2%~5%and the average of 3.46%.(3)The formation and distribution of reservoirs are controlled by sedimentary facies,penecontemporaneous dissolution and supergene karstification.Reservoirs are mainly developed in the higher part of paleogeomorphology,and in the upper part of upward-shallowing cycle of sea water,and near the pinchout line of Ordovician.It is predicted that the areas of Hechuan-Guang’an and Nanchuan-Shizhu,as the high parts of palaeogeomorphology at the both sides of Liangping-Chongqing platform depression,are the favorable shoal reservoir zones,and Xichong-Guang’an-Tongnan area is the favorable karst reservoir zone.It is concluded that the Xichong-Guang’an area is the main target zone of natural gas exploration in the future.