塔河油田阿克亚苏三叠系下油组沉积演化与油气关系

塔河油田阿克亚苏三叠系下油组为厚层的上泥下砂的良好储盖组合,主要发育缓斜坡浅水辫状河三角洲和滨浅湖沉积,三角洲平原亚相上的辫状河道、心滩和前缘亚相的河口坝构成了下油组的主砂体。实际勘探表明,厚层块状的河道砂体、河口坝往往是地下水层的主要载体,油气主要产于顶部的薄层心滩砂体内,形成上油下水的局部低幅度次生油气藏。究其原因,首先是沿断裂运移来的油气主要聚集在上部的上油组和中油组的河道砂体中,下油组充注程度不高;其次是下油组连通性很强的河道砂体网络发育,造成油气容易运移输送,而不易聚集成藏,只有在低幅构造上发育的心滩尖灭砂体内才能形成油气聚集,加之运移距离远,形成零星发育的低幅构造—岩性油气藏。因此,确定心滩砂体的分布范围和低幅构造的叠合关系,弄清连通河道砂与断裂的时空匹配关系等因素,才是阿克亚苏三叠系下油组进一步勘探的关键。

Sedimentary Evolution of Triassic Lower Oil Formation in Akeyasu of Tahe Oilfield and Its Relation to Oil and Gas

The Triassic Lower Oil Formation in Akeyasu of Tahe Oilfield is a nice thick reservoir-cap combination featuring in upper mud and lower sand,where shallow braided river delta and shore-shallow lacustrine sediments developed.The braided channel and mid channel of the delta plain intrafacies and the debouch bar of the front intrafacies constitute the main sand body of the Formation.Practical exploration indicated that thick massive channel sand body and debouch bar were main carriers of underground aquifer,oil and gas was mainly generated from the thin mid-channel sand body on the top and constituted local low-amplitude secondary oil and gas reservoirs characterized by upper oil and lower water.Investigating the cause showed that firstly oil and gas that migrated along the fault mainly accumulated in the channel sand body of Upper and Lower Oil Formations on the top,and the Lower Oil Formation had lower filling degree.Secondly,oil and gas was easily migrated and transported and difficult to be accumulated,due to the development of channel sand bodies of strong connectivity in Lower Oil Formation.Oil and gas could only be accumulated in mid-channel pinchout sand body that developed in low-amplitude structures,in addition,the distance of migration and transportation was so long that only low-amplitude structural-lithologic oil and gas reservoirs developed.Therefore,to determine the distribution range of mid-channel sand body and its superimposition relations to low-amplitude structures,and to make clear the time-space matching relation between channel sand and faults were critical to further exploration in Triassic Lower Oil Formation of Akeyasu.