城口—鄂西海槽周缘长兴组储层特征及主控因素分析

Reservoir Characteristics and Main Control Factors of Upper Permian Changxing Formation in the Focus Exploration Area around Chengkou——Western Hubei Oceanic Trough,Sichuan,China

城口—鄂西海槽周缘长兴组发育了海相碳盐岩生物礁相沉积,但钻井少,总体勘探程度较低。针对奉节地区长兴组地层,以露头、岩心、薄片的详细观察为基础,结合扫描电镜、物性测试等分析手段,对研究区储层发育特征及主控因素进行分析。研究区长兴组储层岩性以礁白云岩、颗粒白云岩和晶粒白云岩为主;储集空间类型主要以晶间孔、晶间溶孔、超大溶孔以及各种裂缝所组成的以次生孔隙为主的裂缝-孔隙型储层;总体物性较差,属低孔特低渗型储层。该区储层发育受多方面的影响,主要是岩性、沉积相带、相对海平面变化以及成岩作用对储层发育起到主要作用;其中,礁滩相为研究区储层的有利相带,相对海平面下降有利于礁滩储层的发育;同生期大气淡水溶蚀作用为储层形成的首要机制,埋藏期溶蚀作用和白云石化作用对储层的改善起到了重要作用。在储层特征及主控因素分析的基础上,对研究区有利储集区带进行了预测。

Marine carbonate platform—edge reef facies is deposited of Changxing Formation around Chengkou—Western Hubei Oceanic Trough, but the number of drilling is small and the degree of exploration is low. Based on the observation of outcrop, core and thin section, with the SEM and physical property analysis, the characteristics of the Upper Permian Changxing Formation reservoir in Fengjie area, eastern Sichuan Basin was studied. The main reservoir rock types of Changxing Formation are bioherm dolomites, grain dolomites and crystalline grain dolomites in the study area. The main reservoir space are the intercrystal pore, intergranular bore hole and dissolved pore and the type of reservoir is fracture-pore with low-porosity and low-permeability. The growth of high-quality reservoir is affected by lithology, sedimentary facies, sea level and diagenesis. The reef and flat facies are favorable for the de-velopment of reservoir space. The falling sea-level is good for the reservoir forming. The first mechanism of reser-voir forming is atmospheric fresh water dissolution. Moreover, dolomitization and solution promotes the property of reservoir. Based on the reservoir characteristics and main controlling factors, we predictes the favorable zones.