川西北部飞三段鲕粒灰岩孔隙演化及储层特征

PORE EVOLUTION AND RESERVOIR CHARACTERISTICS OF T_1f^3 OOLITIC LIMESTONES IN THE NORTH PART OF WEST SICHUAN

川西地区北部飞三段鲕粒灰岩是在消亡后的晚二叠世广旺海槽之上的鲕粒滩沉积。在海底、浅埋藏、中埋藏、深埋藏和构造期五种成岩环境中 ,经历了三期胶结、两期溶蚀 ,最后保留的粒内、粒间、晶间溶孔和粒间孔及裂缝主要发生在深埋藏至构造期。在沉积、构造演化中 ,由于成岩早期多数地区暴露不充分 ,淋滤作用不强 ,白云化作用弱 ,导致储层总体上具小喉道、细歪度、高中值压力的特征 ,并形成孔隙—裂缝和裂缝—孔隙两种不同类型的储渗体 ,前者多分布于构造压力强、靠龙门山推覆体的山前断褶构造带 ,后者主要分布在白云化作用相对较强的江油松花岭和剑阁、广元、旺苍鲕滩发育区。

T 1f 3 (the third member of Feixiaguan Formation,Lower Triassic) oolitic limestones in the north part of West Sichuan are the oolitic beach sediments situated on the vanished Late Permian Guangyuan-Wangcang Trough.Three-period cementations and two-period corrosions were suffered in five (sea bottom,shallow burial,medium burial,deep burial and tectonic phase) diagenetic environments and the finally reserved intragranular,intergranular and intercrystalline solution pores,intergranular pores and fractures mainly occurred from the deep burial to tectonic phase diagenetic environments.Because of the unsufficient exposition,weak leaching and weak dolomitization in most regions during early diagenesis in the process of the sedimentary and tectonic evolutions,the reservoirs are of the characteristics of small throats,fine skewnesses and high median point pressures,thus forming two different storage-permeability bodies of pore-fracture type and fracture-pore type.The former is mainly distributed in the mountain front fault-fold structural belts near the Longmenshan Mountain nappe with strong tectonic pressures and the latter in the Songhua Ridge of Jiangyou with relatively strong dolomitization and the oolitic beach-developed Jiange-Guangyuan-Wangcang region.