鄂尔多斯盆地苏里格气田北部苏75区块盒8段成岩作用及其对储层的影响

Diagenesis and its influence on reservoir in He 8 Member of Su 75 block in northern Sulige Gas Field,Ordos Basin

二叠系石盒子组8段是鄂尔多斯盆地致密砂岩气勘探的重要目标层之一,目前对影响储层储集性能的成岩作用研究较薄弱。基于苏里格气田北部苏75区块盒8段的岩心、薄片、扫描电镜、岩屑录井及物性测试等资料,对盒8段致密砂岩的成岩作用及其对储层的影响进行了综合分析。结果表明:盒8段储层岩性以长石石英砂岩为主,总体为低孔低渗的孔隙型储层。储层的储集空间以各类溶蚀孔隙为主,其占比超过了90%,原生孔隙孔、晶间孔和裂缝的占比较少。盒8段处于中成岩A期—中成岩B期,其成岩演化序列为早期机械压实—石英I期—绿泥石膜—粒间高岭石、伊利石胶结—岩屑及长石溶蚀I—少量自生石英、伊利石胶结—少量石英II期加大—少量长石、方解石溶蚀—石英III期加大。储层发育主要受压实作用、胶结作用及溶蚀作用的影响。压实作用使储层孔隙平均减小了22.36%,降至0%~28.6%,平均为12.65%。胶结作用使得孔隙度减少了9.12%,降至0%~9.45%,平均为2.22%。溶蚀作用使储层的孔隙度增加0%~22.4%,平均增加15.8%。其中岩屑、杂基、方解石和长石的溶蚀增加缝孔隙度分别为18.65%、12.3%、17.5%和14.3%。

As one of the important target layers for tight sandstone gas exploration in the Ordos Basin,the study of diagenesis affecting reservoir performance is relatively weak in the eighth member of Shihezi Formation(He 8 Member,P_(1)x_(8))of Permian.Based on the core,thin section,scanning electron microscopy,cuttings logging and physical properties of P_(1)x_(8),Su 75 block,the diagenesis of tight sandstone and its influence on reservoir genesis are comprehensively analyzed.The results show that the reservoir lithology of P_(1)x_(8) is mainly feldspar quartz sandstone,which is generally a porous reservoir with low porosity and low permeability.The reservoir space of the reservoir is dominated by various dissolution pores,which account for more than 90%,while the primary pore,intergranular pore and fracture account for relatively little.P_(1)x_(8) is in the middle diagenetic stage A-middle diagenetic stage B,and its diagenetic evolution sequence is early mechanical compaction-quartz I-chlorite filmintergranular kaolinite,illite cementation-debris and feldspar dissolution I-a small amount of authigenic quartz,illite cementation-a small amount of quartz II-a small amount of feldspar,calcite dissolution-quartz III.Reservoir development is mainly influenced by compaction,cementation and dissolution.Compaction reduces the porosity of reservoir by 22.36%,dropping to 0%-28.6%,with an average value of 12.65%.Cementation reduces the porosity by 9.12%to 0%-9.45%,with an average of 2.22%.The porosity of the reservoir increased by 0.0%-22.4%,with an average increase of 15.8%.The dissolution of cuttings,matrix,calcite and feldspar increased the fracture porosity by 18.65%,12.3%,17.5%and 14.3%,respectively.