鄂尔多斯盆地延长组深水块状砂岩形成机理及沉积模式研究

The massive sandstones are the main object of the global deep-water (deep-marine and deep-lacustrine) oil and gas exploration in recent years, the large oil and gas fields formed by which were also found in the deep lake of the Triassic , Ordos Basin, however, the transport process,mechanism and discrimination criteria of this kind of massive sands still lack in-depth study.Applicants observed the individual outcrops in deep lake of Yanchang Formation, considered that the part of the massive sands originating from sandy debris flow ,and put forward mud-coated structures,which are discriminant mark of the massive sands. Combining the outcrops, logging and seismic data,this project will analyse sedimentary structure features of massive sands in deep lake of central basin, divide their origin types,and make clear the relationship within origin,channel and intersection.At the same time, through the geochemical analysis and experimental simulation, this project will show the possible transport mechanism of sandy debris flow in Yanchang Formation, and further confirm formation and evolution process of mud-coated structures, expect to propose a kind of recognized identification marks .which can distinguish the transport process of sandy debris flow. Eventually,this project would establish the entire process and pattern from initiation to transport and deposition of deep-water sandstone in Yanchang Formation . These researches have significance in deep-water oil and gas exploration and development of all continental basin in China including Ordos Basin,meanwhile, which have a certain scientific value in enriching and perfecting the current deep-water deposition theory.

块状砂岩是近年来全球深海沉积环境油气勘探的重要对象，在鄂尔多斯盆地上三叠统延长组深湖区也发现了由其形成的大型油气田。然而，目前国内外对这种块状砂岩的形成搬运过程、搬运机理及判别标志还缺乏深入了解。申请者前期通过对延长组深湖区砂岩露头的观察研究，认为部分块状砂岩属于砂质碎屑流成因，并初步提出了其判别标志-“泥包砾”结构。本课题将综合利用露头、岩心、测井与地震资料，深入解剖湖盆中央深水区块状砂岩的沉积构造特征，划分成因类型，明确源-渠-汇关系；同时，通过地球化学分析与实验模拟，揭示延长组砂质碎屑流搬运的可能机理，进一步确认“泥包砾”结构形成与演变过程，预期提出一种能够判别湖盆砂质碎屑流搬运-沉积过程的公认鉴别标志，并由此建立延长组深水砂岩从启动到搬运、再到沉积的过程模式。该项研究不仅对我国鄂尔多斯与其它陆相盆地深水（深湖）油气勘探具有指导意义,而且对丰富和完善当前的深水沉积理论有一定科学价值。

内陆湖盆深水区广泛发育沉积物重力流砂体并拥有丰富的页岩油与致密油等非常规油气资源，正确认识深水砂岩成因对提高勘探成功率和拓展勘探领域意义重大。本项目以鄂尔多斯盆地中上三叠统延长组为例，紧密围绕申请书中的提出的2个科学问题（①目前缺失砂质碎屑流与浊流搬运过程的可靠判别标志，②砂质碎屑流或砂质块体搬运沉积（SMTD）的搬运机理尚不清楚），经过深入研究，取得3方面成果认识：一是提出延长组湖盆中央至少存在浊流、异重流与砂质碎屑流3种类型重力流砂体，并建立了其综合判识标志，尤其在延长组块状砂岩中首次发现并命名了一种新沉积现象：泥包砾（mud-coated intraclast），沉积学家Shanmugam 认为该研究为深水砂质碎屑流搬运沉积（SMDT）建立了判别标准。二是认为由等厚黏土膜形成的颗粒间粘附力（adhesion）主导了晚三叠世延长组大规模含油砂体的形成与搬运，由此揭示了延长组砂质碎屑流能够在水下环境长距离搬运的机理奥秘。三是建立了延长组深水砂岩从开始启动到搬运、再到沉积的3种过程模式，即“粒粒模式”、“层层模式”及“块块模式”。其中“粒粒模式”以浊流为代表，“层层模式”以高密度浊流或异重流为代表，“块块模式”以砂质块体搬运沉积为代表。提出低位域+坡脚带是规模有利砂体集中发育区，为深水砂体精准预测提供了科学依据。. 上述研究创新发展了内陆坳陷湖盆深水重力流理论认识，同时支撑了庆城十亿吨页岩油大油田发现及陇东百万吨国家页岩油开发示范区建设，其中以“深水沉积模式”指导部署的风险井城页1、城页2分别获得121.38t/d和108.38t/d的高产油流，实现了盆地页岩油勘探的重大突破。该研究对我国其它陆相盆地深水沉积研究起到了引领与示范作用，带动了松辽盆地、准噶尔盆地、渤海湾盆地及酒泉盆地等诸多大中小内陆湖盆深水重力流勘探开发。