Characteristics and main controlling factors of hydrocarbon accumulation in Jurassic tight reservoirs of Wudun Sag,Dunhuang Basin

The Jurassic tight reservoirs in Wudun Sag of Dunhuang Basin are characterized by fine pores and throats.The unclear key controls on hydrocarbon accumulation seriously hinder the efficient development of tight oil resources.Based on data from drilling,logging,core analysis,geochemical testing,and production tests,this study analyzes the rock mineralogy,reservoir physical properties,and pore structure characteristics of the Jurassic tight reservoirs in the sag,aiming to investigate the main controls on accumulation and propose a tight oil accumulation model. The results indicate that the reservoirs in the study area are well-developed, primarily composed of sandstone and sandy conglomerate. The lithic fragments are dominant in composition,with quartz and feldspar as the main minerals. The porosity ranges from 1.07% to 11.30%,and permeability varies from 0.01×10^-3 μm² to 5.95×10^-3 μm²,classified as tight reservoirs. Three main types of reservoir space are identified:intergranular pores(6 ×10^-3-600 ×10^-3 μm in radius),dissolved pores（0.6-4 μm）,and micro-fractures（greater than 4 μm）. The pore systems are mainly categorized as intergranular-pore dominant and dual-porosity（intergranular and dissolved pores） balanced types. The source rocks in the area are extensive with high organic matter abundance,consisting of mature Type Ⅱ₁and Ⅱ₂kerogen. Although sandstone reservoirs are well-developed,their pore spaces are generally small. Favorable source-reservoir and sourcetrap configurations exist. Following hydrocarbon generation,migration occurred along faults and through near-source charging,forming tight oil accumulations. In later development,applying horizontal drilling combined with multi-stage fracturing technology to engineer these tight reservoirs is expected to yield commercial oil flow.