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上白垩统嫩江组三段时期,松辽盆地进入坳陷晚期演化阶段,浅水三角洲广泛发育.在新立地区,与III、II、I3个砂组对应,嫩三段由3个浅湖-三角洲前缘的沉积旋回组成,指示了湖盆水体逐渐变浅的过程.基于研究区密井网资料,通过对3个砂组沉积相平面展布和水下分流河道砂体结构解剖表明,随着盆地坡度逐渐变缓和水体变浅,三角洲规模迅速增大,水下分流河道稳定性增强,单支水道延伸距离增加,分叉-合并频率降低,决口-漫溢作用增强,水下分支间湾面积比例增加,由此导致水下分流河道砂体连通性依次减弱,分别呈中厚席状、窄薄条带-斑块状、宽厚条带状,并控制了油藏类型由构造型向岩性油藏的转变.最终,归结出网状、枝状、似曲流河3种浅水三角洲沉积模式.
During the three periods of Upper Cretaceous Nenjiang Formation, the Songliao Basin entered the late evolution stage of depression and developed extensively in shallow water delta. In Xinli area, corresponding to III, II and I3 sand groups, Based on the data of the Wells well network in the study area, the sedimentary facies distribution of the three sand bodies and the structural dissection of the underwater distributary channel sand body show that with the The gradient of the basin slopes gradually and the water body becomes shallow, the size of the delta increases rapidly, the stability of the underwater distributary channel increases, the extension distance of single water channel increases, the bifurcation-mergence frequency decreases, the burst-overflow effect increases, Which leads to the weakened connectivity of subaqueous distributary channel sand bodies, which are in the shape of medium-thick sheet, thin strip-plaque and generous strip, and control the type of reservoir from structural to lithological oil Finally, three kinds of shallow delta depositional patterns, such as reticulate, dendritic and meandering rivers, are summarized.