Evaluation Of Tight Sandstone Reservoir Properties Of Delta Front Subfacies In Ordos Basin, China

The Triassic Yanchang Formation in the Ordos Basin has developed large-scale delta front subfacies tight sandstone oil reservoirs. This type of reservoir has the characteristics of superimposing multiple oil layers in the vertical direction, and compound contiguous distribution in the horizontal direction. Therefore, the exploration of tight oil is difficult. In this paper, taking the Yanchang Formation in Block A in the southern Ordos Basin as an example, we comprehensively evaluate the characteristics of tight sandstone reservoirs in the delta front subfacies, combining a large amount of sedimentary, lithological, oil-bearing, physical properties and logging data. The research results show that the lithology of the target layer Chang 4+5 oil layer group is represented by light gray fine sandstone and dark gray mudstone interbedded with gray argillaceous siltstone and silty mudstone. The main sedimentary structures of the Yanchang Formation are horizontal bedding and cross bedding. The delta front subfacies are mainly divided into three microfacies: underwater distributary channel, distributary channel flanks, and distributary bay. The main rock types of Chang 4+5 reservoir are feldspar sandstone and lithic feldspar sandstone, and the pore types mainly include residual intergranular pores, dissolved pores and intercrystalline pores. The distribution range of sandstone porosity is mainly between 5% and 15%, and the distribution range of sandstone permeability is mainly between 0.1 and 1x10(-3) mu m(2). We determined that the lower limit of lithology of the industrial oil layer in the target layer is fine sandstone, the lower limit of oil grade is oil trace grade, and the lower limit of permeability is 0.10x10(-3) mu m(2), by the cumulative oil storage capacity loss curve.