鄂尔多斯盆地西峰油田延长组长8_1低渗透储层成岩作用

Diagenesis of Chang 8_(1) reservoir with low permeability in Xifeng oilfield,Ordos basin

鄂尔多斯盆地西峰油田延长组长81砂岩储集层主要由岩屑质长石砂岩和长石质岩屑砂岩组成,平均孔隙度8.32%,平均渗透率1.33×10-3μm2,属低孔低渗型储集层。储集层经历了成岩作用及交代作用、溶解作用、破裂作用的改造,目前处于晚成岩A期—B期。其中,早成岩阶段的机械压实作用和晚成岩阶段含铁碳酸盐的胶结作用是造成储集层物性差的主要原因。根据成岩作用特点,在研究区辫状河三角洲前缘砂体中划分出压实压溶成岩相、弱压实-碳酸盐胶结相、弱压实-绿泥石膜胶结相和绿泥石膜胶结-长石溶蚀相4个成岩相带。其中,主砂体核部的弱压实-绿泥石膜胶结相和绿泥石膜胶结-长石溶蚀相的砂岩物性好、含油性好,是油气富集的有利相带。

The Chang 81 sandstone reservoir in Xifeng oilfield, Ordos basin, is mainly composed of lithic arkose and feldspathic lithic sandstone, and is of typical low porosity and low permeability reservoir with an average porosity of 8.32% and average permeability of 1.33×10^-3μm^2. The reservoir has experienced diagenesis, metasomasis, dissolution and cataclasis, and is now in the late diagenetic phase A to B. The mechanical compaction in the early diagenetic phase and the ferruginous carbonate cementation in the late diagenetic phase are the main contributors to the poor poroperm characteristics. According to the characteristics of diagenesis, the braided river delta front sandbody in the study area can be divided into 4 diagenetic facies belts, including compaction and pressolution, weak compaction-carbonate cementation, weak compaction-chlorite-film cementation, and chlorite-film cementation-feldspar corrosion. Sandstones in the latter two facies belts in the core of the main sandbody have good poroperm characteristics and oil-bearing accumulation. properties, thus they are favorable for hydrocarbon