四川盆地洗象池组储集层的主控因素与有利区分布

寒武系洗象池组是四川盆地天然气的后备勘探领域和接替层系,目前其整体勘探程度较低,沉积相带展布规律尚不清楚,还有待深入的研究工作。为此,通过典型野外露头剖面、岩心以及岩石薄片观察,结合实验分析数据,研究了该盆地洗象池组的沉积相展布特征和储集层的岩性、储集空间及物性等特征,进而探讨了储集层形成的主控因素,预测了有利储集区带的分布范围。结果认为:①有效储集层多发育在洗象池组中上段,岩性以颗粒白云岩、晶粒白云岩为主,次为藻白云岩和膏溶角砾岩;②储集层厚度介于43.75~136 m(平均约为87 m),孔隙度多介于1.27%~11.95%,其主要储集空间为溶蚀孔洞、粒间孔与晶间孔;③颗粒滩亚相是储集层发育的基础,而准同生溶蚀作用则是形成主要储集空间的关键因素;④该储集层受古地理格局约束,在盆地内具双颗粒滩带特征。结论认为:宜宾—合川—广安、永安—三汇—石柱一带古地貌高部位为有利的洗象池组储集层发育区,可作为该区下一步天然气勘探的主攻方向。

Main controlling factors and favorable zone distribution of Xixiangchi Formation reservoirs in the Sichuan Basin

The Cambrian Xixiangchi Formation is the gas exploration backup and replacement reservoirs in the Sichuan Basin. However, it is just less explored, and its distribution rules of sedimentary facies belts are not clear. It is necessary to carry out further studies in this area. First, based on observation of typical field outcrop section, cores and rock thin sections, and experimental analysis data, the distribution characteristics of Xixiangchi Formation sedimentary facies and the lithology, reservoir space and physical properties of the reservoirs were analyzed. Furthermore, main factors controlling the formation of reservoirs were discussed, and the distribution range of favorable reservoir zones was predicted. Results show that effective reservoirs are mostly distributed in the middle and upper members of Xixiangchi Formation, and primarily dominated by grain dolomite and crystalline dolomite and secondarily by algae dolomite and gypsum breccia. Besides, the reservoirs are generally 43.75-136 m thick and 87 m averagely, and the main types of reservoir spaces are dissolution pores, intergranular pores and intercrystalline pores, with porosity between 1.27%-1.95%. Also, the development of the reservoirs is based on grain shoal subfacies, and the formation of reservoir spaces is controlled by penecontemporaneous dissolution. Finally, due to the restriction of paleogeographic patterns, the reservoirs present the characteristics of double grain shoal belts within this basin. It is concluded that the palaeogeomorphic highs in the areas of Yibin-Hechuan-Guang'an and Yong'an-Sanhui-Shizhu are the favorable reservoir zones of Xixiangchi Formation and they are the main targets of natural gas exploration in this area in the future.