近岸水下扇扇体沉积新认识与油气勘探再实践——以济阳坳陷陡坡带为例

New Sedimentary Understandings of Nearshore Subaqueous Fan and Its Re-practice on Oil-gas Exploration:Take the steep slope zone of Jiyang Sag as a case

在济阳坳陷砂砾岩体油气勘探中,砂体复杂分布和油水差异聚集等问题引发了对现有近岸水下扇沉积充填样式的思考、探索和补充。为完善断陷湖盆陡坡带砂砾岩体发育模式提供实验素材和地质实例,在系统梳理前人研究硕果的基础上,通过开展水槽沉积模拟实验、解析沉积充填过程,并结合油气勘探实践论证。可将断陷湖盆陡坡带近岸水下扇分为扇根、扇中、扇间和扇端4种沉积亚相,并包括9种沉积微相;较之以往,补充建立了扇中坡积朵叶体微相和扇间侧向迁移朵叶体微相,前者多超覆在早期扇主体斜坡之上,纵向呈独特的前积式反旋回并表现为“底凹上凸”的外部形态,后者则以发育正粒序中—细砂岩为主,沉积充填特征显著;二者均与半深湖—深湖泥岩、扇端和扇间泥岩紧密接触,利于形成岩性圈闭;济阳坳陷陡坡带以坡积朵叶体和侧向迁移朵叶为勘探目标的多口井接连获得高产、稳产工业油气流,在勘探实践中验证了近岸水下扇扇体沉积新认识,拓宽了断陷湖盆砂砾岩体的勘探新空间。科学发展的动力之一来源于理论与实验的矛盾,油气地质学更是着重表现出“问题由实践中来,认识到实践中去”的特点,基于水槽模拟实验的沉积充填模式探讨是促进沉积学繁荣发展的有效手段。

In the oil⁃gas exploration of glutenite bodies in the Jiyang Depression,the complex sand distribution and differential accumulation of oil and water have led us to ponder,explore and supplement the evident deposition filling pattern of nearshore subaqueous fans,which provides experimental materials and geological examples for perfecting the glutenite development patterns in the steep slope of faulted lacustrine basin.Based on systematically sorting out the previous research results,by conducting the flume simulation experiments,analyzing the sedimentation filling process,and combining with the oil and gas exploration practice,it is considered that nearshore subaqueous fans in the steep slope zone of a fault-depressed lacustrine basin is divided into four sedimentary subfacies:fan-root,fanmiddle,fan-inter and fan-terminal,including nine sedimentary microfacies.Compared with previous studies,the mi⁃crofacies of slope accumulation lobes in fan-middle and lateral migrating lobes in fan-inter are established.The slope accumulation lobes mostly overlie the early fan body with an external form of“concave bottom and convex top”having a longitudinal cycle presenting a unique reverse rhythm.Lateral migrating lobes are characterized by positive-rhythm medium and fine sandstones,with notable sedimentary filling characteristics.Both of these are in close contact with semi-and deep-lake mudstones,fan-terminal mudstones and fan-inter mudstones,which is conducive to the forma⁃tion of lithological traps.In the steep slope zone of the Jiyang Depression,many exploration wells targeting slope ac⁃cumulation lobes and lateral migrating lobes have successfully established high,stable industrial oil⁃gas flows.This verifies the new sedimentary understandings of nearshore subaqueous fans in oil⁃gas exploration practice,and sug⁃gests a new exploration space for glutenite bodies in fault-depressed lacustrine basins.One of the driving forces of sci⁃entific development stems from the contradiction between theory and experiment.Petroleum geology especially shows the discipline characteristics of"problems come from practice,and knowledge goes into practice".The study of sedi⁃mentary filling model based on flume simulation experiment is an effective means to promote the development of sedi⁃mentology.