东营凹陷北部陡坡带砂砾岩体成岩圈闭成因及主控因素

东营凹陷北部陡坡带砂砾岩体发育扇根封堵的成岩圈闭。通过岩心观察、粒度分析、薄片鉴定和粘土矿物分析等方法,对研究区扇根和扇中的岩相组构与差异成岩演化进行研究,以揭示成岩圈闭的成因机理,并探讨其形成的主控因素。结果表明,扇根以杂基支撑的砾岩相为主,杂基含量高,抗压实能力弱,机械压实作用阶段,其原生孔隙不易保存,在碱性为主的成岩环境下,以重结晶作用为主,孔隙度、渗透率持续降低;扇中以砂质杂基支撑或颗粒支撑的砾质砂岩相和含砾砂岩相为主,杂基含量较少,抗压实能力较强,在酸性和碱性交替的成岩环境下,成岩作用多样,形成多个次生孔隙发育带。因此,岩相组构是形成成岩圈闭的物质基础,而扇中和扇根的差异成岩演化控制下的物性差异是形成扇根封堵成岩圈闭的内在机制。成岩圈闭的形成主要受到沉积层序、岩相组构和成岩流体的影响。

Study on genetic mechanism and controlling factors of conglomerate diagenesis trap in northern Dongying sag

There is a new type of diagenesis trap of conglomerate body which is sealed by root fan in northern Dongying sag. Based on core observation, grain size analysis, thin sections identification and clay mineral analysis, the lithofacies architecture and different diagenetic evolution of root fan and middle fan are studied, the genetic mechanism and controlling factors are proposed. The root fan lithology is conglomerate with complex matrix, the content of matrix is high, which disfavors the preservation of primary pores with the depth of burial. The main diagenetic types include the compaction and the recrystallization, and the porosity and permeability are persistently declined. The middle fan lithology is grain-supported pebbled sandstone or conglomeratic sandstone, the content of matrix is lower, which favors the preservation of primary pores. The main diagenetic types include the compaction, cementation,dissolution and replacement in acid environment, which formed several secondary pore zones. So, the lithofacies architecture is the foundation for the diagenesis trap, and the difference of diagenesis between root fan and middle fan is determinant for the diagenesis trap. The influences of diagenesis trap include sedimentary sequence, lithofacies architecture and diagenesis fluid.