The key geological factors influencing on development of low-permeability sandstone reservoirs: A case study of the Taizhao area in the Songliao Basin, China

Abstract

As a typical low-permeability reservoir in the periphery of the Daqing oilfield, the Putaohua reservoir in the Taizhao area has a development characteristic similar to that of the low-permeability sandstone reservoirs in China. Through a synthetic analysis of its geology, logging and dynamic data, sandbody connectivity, small faults, tiny structures, fractures and present-day stress are the geological factors influencing the developmental effects. The connectivity of single sandbody and its anisotropy influence distribution of oil and water and inhomogenous fluid flow. The early water breakthrough in some oil wells was mostly caused by high permeability sandbobies. Sand bodies together with small faults and tiny structures influence the development effect of lowpermeability reservoirs throuh impacting on fluid flow. Fractures are the main factor for high-water-cut oil-producing wells. Fractures developed in the paleotectonic stress field. The preservation and permeability of every assemblage of fractures are controlled by the present-day stress field, which also influences cracking and injection. There developed four assemblages of tectonic fractures of high dip angle in the Putaohua reservoir. Affected by the presentday stress field, the E-W fractures that have a good connectivity and permeability and big apertures, are the main seepage orientation. At present, the injection pressure has exceeded the unsealing pressure of E-W fractures. Therefore, water content appears early and goes up quickly, causing a serious water flood in the E-W array of oil wells. However, oil wells of other directions show a poor effect.