Enhanced Water⁃Drive Recovery Based on Microscopic Seepage Mechanism for Low Permeability Glutenite Reservoir with Ternary Pore⁃Throat Structure Characteristics of WS Field
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摘要: 针对低渗砂砾岩与砂岩储层产能测试结果差异大的问题,以北部湾盆地乌石凹陷流沙港组低渗砂砾岩储层为主要研究对象,通过设计室内岩心实验开展了微观孔隙结构、微观渗流能力、微观渗流特征和改善水驱提高采收率策略研究. 研究发现,乌石凹陷流沙港组低渗砂砾岩储层具有三元孔隙结构特征,大孔喉和微小孔喉更加发育,导致“高气测渗透率、低液测渗透率、低驱油效率”的渗流特征和“大孔喉富含注入水、中吼喉富含剩余油、微小孔喉富含原始束缚水”的剩余油微观分布特征,提高微观波及系数、增加中孔喉动用率是提高采收率的关键,建议采用注低价高矿化水转变润湿性和不稳定注水发挥渗吸作用的策略改善水驱效果、提高最终采收率.Abstract: In view of the large difference in productivity test results between low⁃permeability glutenite pay zone and sandstone pay zones, taking the low⁃permeability glutenite reservoir of Liushagang Formation in Wushi Sag of Beibu Gulf Basin as the main research object, the research on microscopic pore structure, microscopic seepage capacity, microscopic seepage characteristics and strategies for improving water flooding effect to enhance oil recovery was carried out through the indoor core experiments. The results show that the low⁃permeability glutenite reservoir has the characteristics of ternary pore structure, and the large pore throat and micro pore throat are more developed, resulting in the seepage characteristics of "high gas permeability, low liquid permeability, and low oil displacement efficiency" and the post⁃displacement fluid microscopic distribution characteristics of "large pore throat is rich in injection water, medium throat is rich in remaining oil, and micro pore throat is rich in original bound water". The key to improve the recovery factor of low permeability glutenite reservoir is to improve the microscopic sweep coefficient to increase the utilization rate of medium pore throat crude oil. It is suggested to change wettability by injecting low valent and high salinity water and utilize imbibition role by unsteady water injection to improve water flooding effect and enhance oil recovery.
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图 7 砂砾岩岩心CT扫描和Qemscan矿物扫描图像
a. 2.5 cm直径柱塞岩心CT扫描切片,WS17⁃9井2 774.35 m;据张恒荣等(2020);b. Qemscan矿物扫描图,WS17⁃9井,2 779.35 m
Fig. 7. CT and Qemscan images of glutenite core
图 19 真实岩心的微观渗流可视化实验电子显微镜照片数字图像识别图
a.砂岩岩心饱和模拟油完成时,模拟油在砂岩岩心薄片均匀蔓延,基本填充了整个岩心孔隙;b. 砂岩岩心地层水驱完成时,砂岩岩心基本被水饱和,剩余油主要为滞留在孔喉中非连续相的油滴残余油;c.砂砾岩岩心饱和模拟油完成时,由于非均质性影响,模拟油只填充了整个砂砾岩岩心的连通孔隙;d.砂砾岩岩心地层水驱完成时,砾岩岩心被水部分饱和,剩余油由主要为滞留在孔喉中的呈连续相的柱状残余油
Fig. 19. Digital recognition image of electron microscope photos in microscopic seepage visualization experiment of real core
表 1 研究区储层特征对比
Table 1. Comparison of formation characteristics
研究区 沉积环境 岩石类型 成岩相 物性 乌石17油田流三段 扇三角洲沉积 岩屑砂砾岩、含砾中粗砂岩 强压实、极弱胶结、强溶蚀 中孔中低渗 乌石16油田流二段 滨浅湖沉积 长石石英中、细砂岩 中等压实、中等胶结、中等溶蚀 中孔中低渗和低孔特低渗 涠洲7油田流三段 浅水扇三角洲沉积 长石石英含砾中粗砂岩、细砂岩 强压实、弱胶结、中等溶蚀 特低孔特低渗 表 2 非粘土矿物含量对比表
Table 2. Comparison table of non clay mineral content
井区 岩性 非粘土矿物含量(%) 石英 钾长石 斜长石 方解石 白云石 铁白云石 黄铁矿 菱铁矿 重晶石 乌石17油田流三段 砂砾岩 88.3 3.3 0.2 0.6 0.0 0.3 0.0 0.2 0.0 乌石16油田流二段 砂岩 78.2 1.3 4.4 1.6 0.0 0.0 0.0 0.0 0.0 涠洲7油田流三段 砂岩 73.3 7.4 0.0 3.1 0.0 0.1 0.3 0.5 0.2 表 3 粘土矿物含量和类型对比表
Table 3. Comparison of clay mineral contents and types
井区 岩性 粘土矿物含量(%) 伊/蒙混层比(%) 粘土矿物总含量(%) 伊利石 高岭石 绿泥石 伊/蒙混层 蒙皂石层 伊利石层 乌石17油田流三段 砂砾岩 45.4 10.7 6.5 37.5 20.9 79.1 7.1 乌石16油田流二段 砂岩 27.6 46.2 8.9 17.3 - - 14.6 涠洲7油田流三段 砂岩 69.7 8.4 9.8 12.1 9.7 90.3 15.2 表 4 不同水驱倍数下岩心水驱油核磁驱替结果对比
Table 4. Comparison of NMR displacement results of water flooding in different PV
岩性 渗透率(10-3 μm2) 孔隙度(%) 核磁驱油效率(%) 10PV 15PV 20PV 25PV 砂岩 5.19 18.62 50.01 50.21 50.31 50.36 砂砾岩 23.97 17.89 30.51 30.86 30.93 31.07 砂砾岩 13.30 18.58 39.74 40.04 40.10 40.16 -
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