鄂尔多斯盆地东缘A区块盒8段储层特征

Reservoir Characteristics of Shihezi 8 Member in A Block, Eastern Margin of Ordos Basin

鄂尔多斯盆地东缘二叠系下石盒子组盒8段储层为A区块较为有利的致密砂岩气储层,该储层以辫状河三角洲亚相沉积为主。纵向上该段储层具多期砂体叠置、横向连片发育的特点。结合构造、沉积、储层特征以及成岩作用分析结果发现：①该段沉积环境稳定,构造倾角近水平,最大主应力方向近东西向。②古水流方向指示为南东及南向,推测物源方向为盆地北部。③以岩屑石英砂与岩屑砂岩为主,磨圆以次圆为主,分选中等,以颗粒式胶结为主,为典型的致密型储层。④孔隙度介于4%-10%,平均值为9.32%,渗透率值73%小于0.5 m D,主要介于0.01-0.5 m D,同时实验表明砂岩粒度大小与孔渗性成正比,其中盒8段底部发育含砾粗砂岩,物性相对较好。⑤储集空间类型以残余粒间孔、粒间溶孔及粒内溶孔为主。⑥溶蚀作用对于储层发育起到建设性作用,而压实作用及胶结作用往往使储层物性变差。⑦盒8段试气效果显著,综合分析认为盒8段为该区较为有利的勘探层系。

The Permian Shihezi 8 Member, eastern margin of Ordos Basin, is the more favorable tight sandstone gas reservoir in A block, and is well developed with braided-deltaic subfacies deposits. This reservoir represents some features of vertically-superimposed and laterally connected well-developed sandbodies. In addition, some studies on its tectonic, deposition, reservoir characteristics, and diagnesis show that for this reservoir,(1)the depositional environment is stable, the structural dip approximates to zero,and the maximum principal stress is near E-W-trending;(2)the deposits might be originated from northern part of Basin according to palaeocurrent direction;(3)it is mainly composed of lithicquartzose sandstone and debris sandstone which is mainly featured by subangular roundness, medium sorting, rock cementation, further resulting in a typical tight reservoir;(4)the porosity ranges from 4 % to 10 %, 9.32 % on average, permeability less than 0.5 m D accounts for 73 %, mostly between 0.01 m D to 0.5 m D. Meanwhile,our experiments also illustrate that grain size is in proportion to porosity and permeability. At the base of Shihezi 8 Member, coarse sandstone with conglomerate is developed and has better petrophysical property; and(5)reservoir space chiefly contains residual intergranular pore, dissolution intergranular pore, and dissolution intragranular pore; and dissolution is constructive to reservoir development whereas both compaction and cementation often make petrophysical property poorer. Finally, results from gas testing also show that the Shihezi 8 Member is a favorable exploration target in this area.