东营凹陷陡坡带盐18-永921地区砂砾岩沉积与储层特征

Sedimentary and reservoir characteristics of glutenite in Yan 18-Yong 921area, steep slope of Dongying Sag

断陷盆地陡坡带断裂活动强烈,常表现为深水重力流砂砾质沉积和烃源岩同层的特征,储层物性评价成为该区域油气勘探的关键.针对东营凹陷盐18-永921地区沙三下亚段和沙四上亚段,通过地层细分、沉积相厘定和储层特征分析,探索了优质储层发育规律.地质-地震综合的沉积相研究表明,该区沉积充填过程和相类型受控于边界断裂的演化,自下而上经历了扇三角洲沉积、近岸水下扇—洪水型湖底扇沉积和近岸水下扇—滑塌型湖底扇沉积3个演化阶段.砂砾岩储层储集空间以孔隙为主,裂缝不发育,孔隙中原生孔隙明显占优势.当埋深小于2 600 m时,沉积作用是该区砂砾岩储层物性的主控因素;当埋深大于2 600 m时,储层进入晚成岩阶段,溶蚀作用增强,除沉积作用外,溶蚀作用开始对储层物性产生重要影响.根据储层物性主控因素分析结果,提出沙三下亚段和沙四上亚段Ⅰ～Ⅳ砂组中近岸水下扇中扇的辫状水道、沙四上亚段Ⅴ,Ⅵ砂组中洪水湖底扇和Ⅶ,Ⅷ砂组中扇三角洲前缘控制了各时期优质储层的分布.

Steep slope of rift basins with strong faults activities is characterized by deepwater 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 （E2s3X） and the upper fourth member of Shahejie Formation （E2s4s） 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, deepwater near shore subaqueous fan to tlooding lacustrine basin fan and deepwater 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, flooding lacustrine basin fan in sandgroup V and VI of E2s2 and fan delta front in sand group VII and VII of E2s2.