关键词: 低孔、低渗储层, 储层特征, 成因机理, 文昌组, 惠州凹陷

Abstract: Steep slope of rift basins with strong faults activities is characterized by deep water gravity flow sandstone and conglomerate and high-quality source rocks in the same layer. As a result, reservoir properties became the key factor for hydrocarbon exploration in this area. In this paper, strata division, sedimentary facies and reservoir characteristics were studied to well understand the forming rules of high-quality reservoir of the lower third member of Shahejie Formation（E₂ s₃^x）and the upper fourth member of Shahejie Formation （E₂ s₄^s ）in steep slope in Yan 18-Yong 921 area, Dongying Sag. Geological-seismic integrated sedimentary facies study shows that basin filling processes and sedimentary facies composition were mainly controlled by the evolution of boundary faults, and sedimentary system evolution from bottom to top included three stages as follows: fan delta with shallow water, deep water near shore subaqueous fan to flooding lacustrine basin fan and deep water near shore subaqueous fan to slump lacustrine basin fan. The reservoir spaces mainly come from pore, with less fractures. Sedimentation is the key controlling factor of reservoir properties when the buried depth is less than 2 600 m. However, dissolution increased when the buried depth is more than 2 600 m and the reservoir entered into the late diagenetic stage. According to the analyses of reservoir controlling factors, we proposed that high quality reservoirs come from mid-fan of near shore subaqueous fan in E2 s3x and sand group Ⅰ-Ⅳ of E₂ s₄^s ,flooding lacustrine basin fan in sand group Ⅴ and Ⅵ of E₂ s₄^s and fan delta front in sand group Ⅶ and Ⅷ of E₂ s₄^s .

Key words: low porosity and low permeability reservoir, reservoir characteristics, origin mechanism, Wenchang Formation, Huizhou Depression