四川盆地开江—梁平海槽两侧台地边缘形态及其对储层发育的影响

晚二叠世长兴期,受勉略洋扩张和区域拉张应力的影响,四川盆地北部发育了开江—梁平海槽。为弄清该海槽两侧台地边缘的形态及其上礁滩体发育的主控因素,在区域构造和沉积背景分析的基础上,基于二维、三维地震资料中礁滩体的反射特征和钻井资料,利用地质—地震解释技术,刻画出长兴期海槽两侧台地边缘的形态变化,建立了不同类型台地边缘之上礁滩体发育的地震反射模式和沉积模式,分析了其储层分布的主控因素和分布规律。结论认为:①长兴期,开江—梁平海槽两侧台地边缘形态可划分为断控陡坡型和缓坡型2大类,包含断层—陡坡型、陡坡型、缓坡—坡折型和缓坡型4种类型;②长兴期,海槽两侧台地边缘的形态是控制礁滩体规模、沉积模式的关键地质因素,也是造成礁滩体储层特征差异性的根本原因;③白云石化、多期溶蚀和裂缝作用是改善长兴组礁滩体储层质量的关键作用,有利储层主要位于每期礁滩体的顶部,分布于台缘带陡坡或基底断裂一侧。

Morphological characteristics of platform margins along the Kaijiang Liangping Trough and their influences on reservoir development in the Sichuan Basin

During the Late Permian Changxingian period, the depositional pattern of the Sichuan Basin was influenced by the spreading of Mianlüe Ocean and regional extensional stress, and the Kaijiang Liangping Trough was developed in the north of the basin. The morphological characteristics of platform margins and the major controlling factors of reef shoal complexes development on both sides of the Trough need to be defined. Based on the analysis of regional tectonic and depositional background, the reflectance signatures of reef shoal complexes in 2D and 3D seismic and drilling data were integrated to describe the variations of platform margins morphology along the Trough during the Changxingian period. Seismic reflection patterns and geological models were built for reef shoal complexes on platform margins of different types, and the major controlling factors and distribution patterns of the reservoirs were analyzed. Three conclusions were obtained as follows: (1) The profile of platform margins on the east and west sides of Kaijiang Liangping Trough during the Changxingian period can be divided into two major categories, i.e. fault controlled steep slope type and ramp type. Four sub types of platform margins are defined, including fault steep slope type, steep slope type, ramp slope break type, and ramp type. (2) The morphological characteristics of platform margins on the east and west sides of Kaijiang Liangping Trough are the key factors controlling the scale of reef shoal complexes, depositional patterns, and reservoir properties. (3) Dolomitization, multi stage dissolution, and fracturing are the key factors for improving reservoir qualities in reef shoal complexes. Favorable reservoirs are mainly located on the top of reef shoal complexes along the steep slope on platform margins, or along basement faults.