成岩作用对深水致密砂岩储层微观非均质性的影响

鄂尔多斯盆地上三叠统延长组长7深水砂岩储集体发育，但受成岩作用影响导致储层孔渗低、物性差，微观非均质性强。通过铸体薄片、扫描电镜、黏土矿物XRD分析、高压压汞等资料，结合前人研究成果及孔隙演化规律，对盆内合水地区长7深水致密砂岩储层成岩作用进行研究，旨在找出影响储层微观非均质性的主要成岩作用类型，并以此为基础定量表征储层微观非均质性，更好地预测有利储层分布。结果表明:1）胶结作用与溶蚀作用分别控制了储层原生及次生孔隙的大小，是影响储层微观非均质性的两类主要成岩作用，从120 Ma之后，储层开始受其影响，微观非均质性变强；2）胶结—溶蚀指数影响着储层微观孔喉结构，胶结—溶蚀指数越小，储层孔隙含量越高、渗流能力越强。提出以胶结—溶蚀指数为标准，定量表征储层微观非均质性；3）根据胶结—溶蚀指数，将研究区储层分为三类:Ⅰ类为弱胶结—强溶蚀区，胶结—溶蚀指数在小于0.55，微观非均质性最弱，是有利储层分布的主要区域；Ⅱ类为中等胶结—溶蚀区，胶结—溶蚀指数在0.55~0.80之间，微观非均质性中等；Ⅲ类为强胶结—弱溶蚀区，胶结—溶蚀指数大于0.80，微观非均质性最强。平面上，有利储层主要分布在研究区马岭—固城—盘客—九岘一带，以条带状、片状分布。

Effect of Diagenesis on Microheterogeneity of Deepwater Tight Sandstone Reservoirs: A case study from the Triassic Chang 7 oil-bearing formation in Heshui area,Ordos Basin,NW China

Chang 7 deepwater sandstone reservoirs are developed in the Upper Triassic Yanchang Formation of the Ordos Basin； however， diagenetic effects have led to reservoirs with some cases of low porosity and low permeability， poor physical properties and strong microheterogeneity. In order to determine the main diagenesis types causing the microheterogeneity， the diagenesis of the Chang 7 deepwater tight sandstone reservoirs in the Heshui area of the Ordos Basin was studied by techniques including casting thin sections， scanning electron microscope， clay mineral XRD analysis， high?pressure mercury injection， among others — and also by studying the reported findings from previous research， using the pore evolution law. The microheterogeneity of reservoirs was quantitatively characterized in this way， allowing better prediction of the location of major reservoirs. The results show that: 1） Cementation and dissolution respectively control the size of primary pores and secondary pores， which play an important role in the microheterogeneity of reservoirs， and which began to be more marked after 120 Ma. 2） The micropore throat structure of reservoirs is indicated by the cementaton?dissolution index （CDI）: a smaller CDI indicates a higher porosity content and greater permeability. This index was adopted as the standard measure for quantitative characterization of the microheterogeneity of Chang 7 reservoirs. 3） The CDI suggests that the reservoirs in the study area may be divided into three types: Category I areas （CDI < 0.55） exhibit weak cementation and strong dissolution； they are the least heterogeneous and therefore contain the dominant reservoirs. Category II areas （CDI = 0.55?0.80） exhibit medium cementation and medium dissolution， with moderate microheterogeneity. Category III areas （CDI > 0.80） display strong cementation and weak dissolution， and therefore the strongest microheterogeneity. In plan， the dominant reservoirs are mainly located in the Maling?Gucheng?Panke?Jiuxian banded schistose zone where the matter?source intersection is located in the middle of the study area.