安塞油田晚三叠世长7油层组沉积微相及储层非均质性研究

Sedimentary microfacies and heterogeneity of Chang7 formation in Late Triassic of Ansai Oilfield

安塞油田晚三叠世延长组长7油层组发育浅水型三角洲前缘沉积亚相,进一步划分为水下分流河道、分流间湾、河口坝、席状砂等沉积微相,其中以水下分流河道和分流间湾最为发育。安塞油田长7油层组砂岩以长石砂岩及岩屑质长石砂岩为主,砂岩中填隙物含量较高,主要为绿泥石膜、高岭石、铁方解石、发丝状伊利石等,其中铁方解石胶结物含量最高。从层间非均质性、层内非均质性、平面非均质性3个方面来看,安塞油田长7油层组的储层非均质性强,孔隙度、渗透率高值点沿砂体的展布方向呈片状及点状或不规则状展布,在沉积微相的主砂体体部位孔隙度、渗透率值较高,向砂体的侧翼和沉积末端随砂体厚度的减薄,孔隙度、渗透率值变低。

Based on studying the geological background of shallow water front delta, the sedimentary characteristic, development regularity and heterogeneity of reservoir, the shallow water front delta sedimentary system, the development regularity and heterogeneity of reservoir from Chang 7 oil-bearing interval of the Lower Triassic Yanchang formation in Ansai Oilfield were analyzed. The result shows that shallow water front delta sedimentary system was developed, and subdivided into 4 microfacies： subaqueous distributary channel, subaqueous interdistributary bay, mouth bar, and sheet sand, in which subaqueous distributary channel and subaqueous interdistributary bay are the main microfacies. The Chang7 formation is mainly composed of arkoses and lithic arkoses. The fillings content mainly includes chlorite membrane,kaolinite, ferrous calcite, filamentous illite cementation, in which the ferrocalcite cementation is highest. By the analysis of inlayer heterogeneity, interlayer heterogeneity and planar heterogeneity, there is strong reservoir heterogeneity of Chang7 oil-bearing interval of Ansai Oilfield. The high porosity and permeability are controled by the sand body schistose and point-like, or irregular distribution, the value of main sandbodies in microfacies is high,with the thickness of margin and bottom of sandbodies dimin- ished, the porosity and permeability decrease.