基于地震沉积学理论,根据基准面旋回变化,利用沿层地层切片的高分辨率纵向演化特征与高精度地震成像技术,研究川东北地区通南巴背斜中下侏罗统的古河道展布、古河道定量化特征与演变过程.结果表明:研究区中下侏罗统沉积时期发育4期古河道(湖侵体系域两期曲流河河道、高位体系域早期顺直型河道与晚期辫状河河道),古河道为厚层砂岩沉积,测井响应为幅度较大的箱型特征,地震响应为同向轴强振幅不连续,河道内部(沿河道)地震响应为强振幅连续反射.基准面上升旋回时期(自流井组),发育2套曲流河沉积体系,可容空间增大,以垂向加积为主,河网密度小(0.050～0.060 km/km2),河道弯曲因数高(1.31～1.48).基准面下降旋回早期(千佛崖组),物源供给速率增加缓慢,可容纳空间快速减小,沉积动力响应以河道垂向加积为主、侧向迁移为辅,河网密度增加(平均为0.247 km/km2),河道弯曲因数减小(平均为1.07),形成高位体系域早期多河道体系的顺直型河道.随基准面的持续下降,沉积物供给快速增加,可容空间持续减小,河道侧向加积与迁移加强,河网密度增加(平均为0.263 km/km2),河道弯曲因数增加(平均为1.32),河道由顺直河网体系演变为曲流河网体系.该结果为定量研究基准面旋回变化对古河道演变的影响提供技术方法与范例.

By the observation of the drilling core, it is found that a new type of reservoir, named gravel-sized grain carbonate rocks, is mainly distributed in the Feixianguan Formation of Puguang Gas Field in the foreslope of platform. Based on the analysis of gravel composition, development scale, grain size and degree of roundness, it could be divided into calcirudyte and dolorudite. It is shown that small scale calcirudyte is mainly formed by long distance transportation and with relationship to the turbidity current; and large scale dolorudite is mainly formed by no moving or by short distance transportation and with relationship to the collapsing sediment. In the sedimentary model of gravel-sized grain carbonates in slope belt in Feixianguan Formation of Puguang Gas Field, the source of calcirudyte is from the carbonate platform, and the big scale dolorudite is usually distributed in the upper slope belt where the favorable reservoir is well developed, but the thin calcirudyte is distributed in the lower slope where the reservoir is not developed.