鄂尔多斯盆地东缘临兴区块致密砂岩优质储层形成的主控因素

Research on the main factors of high quality tight sandstone reservoir in Linxing block,Ordos Basin

寻找储层甜点区是致密气勘探的重点。以粒度、X-射线衍射、铸体薄片、压汞等各种实验分析为基础,结合成像测井,对临兴区块上古生界致密砂岩储层岩石学特征、孔喉与物性特征进行了研究,详细总结了优质储层形成的主要控制因素。研究表明,研究区储层孔喉以极细—细微孔喉为主,粒间溶孔和溶蚀颗粒孔是其主要储集空间,孔隙度主要集中在4%~10%之间,渗透率主要集中在(0.1~1)×10^(-3)μm^2之间,属于特低孔特低渗储层;优质储层平面上受沉积微相、微裂缝控制,纵向上受成岩作用影响,溶蚀作用是改善储层物性的关键因素。主要表现在:不同相带砂体,物性差异较大,潮坪相的砂坪、三角洲相的分流河道及曲流河相砂岩中边滩等微相砂体物性最好。粒度较粗的砂岩原始粒间孔隙发育,可形成良好储层。构造运动和紫金山岩浆侵入、冷却隆起衍生的微裂缝发育区可能是优质储层发育的场所。成岩过程中长石颗粒溶蚀形成的次生孔隙及溶蚀发育带,是致密砂岩优质储层发育的基础;部分矿物和岩石成分对储层物性影响具双重性:在成岩作用下加剧了储层致密化的同时,适量的脆性矿物、自生黏土矿物及碳酸盐岩、火山碎屑对优质储层的形成起建设性作用。该认识对致密砂岩储层甜点区预测具有借鉴意义。

It is the key point to find the sweet point in the process of exploration.Based on the experimental analyses on particle size,X-ray diffraction,casting thin sections and mercury injection,combined with ima- ging logging,we performed a series of research on tight sand petro-physical characteristics, and concluded the main controlling factors of high quality reservoirs in Linxing area, Ordos Basin. The reservoir pore throat size consists of fine-small pore throat,intergranular dissolved pore and dissolution particles are the main reservoir space,and porosity and permeability mainly concentrates in 4%-10 % and （0.1～1）×10^-3μm2 , respectively,belonging to low porosity, low permeability reservoir. High quality reservoir surface is con trolled by sedimentary micro-facies and micro-cracks,and is also influenced by diagenesis in the longitudi- nal direction.Dissolution is also one key factor to improve the reservoir property.As facies variation,corre sponding physical property also changes.The sand flat of tidal flat, distributary channel of delta facies and edge beach of meandering river facies are of best quality.Good reservoir can be formed by the development of pore of the coarse-grained sandstone.The site micro-fractures derived from tectonic movement and Zijin- shan magma intrusion and cooling may be the site where high quality reservoir develops. The secondary pores and dissolution development which are formed by the dissolution of feldspar in the diagenetic process are the basis for the development of the quality reservoir of tight sandstone.Part of mineral and rock com- position have dual influence on reservoir property： diagenesis exacerbated the densification of the reservoir at the same time,and the amount of brittle mineral,authigenic clay minerals and carbonate rocks,pyro- clastic construction play an important role in the formation of high quality reservoirs.