鄂尔多斯盆地环县-华池地区长8砂岩储层成岩作用及孔隙演化

来源期刊:中南大学学报(自然科学版)2014年第9期

论文作者:廖朋 王琪 唐俊 郝乐伟 田兵 韩元红

文章页码:3200 - 3211

关键词:成岩作用;孔隙演化;低渗致密储层;长8;环县-华池地区;鄂尔多斯盆地

Key words:diagenesis; porosity evolution; low permeability tight reservoir; Chang 8; Huanxian-Huachi region; Ordos Basin

摘    要:通过薄片观察、扫描电镜、X线衍射和常规物性等分析测试手段对鄂尔多斯盆地环县-华池地区长8低渗-致密砂岩储层岩石学特征和成岩作用展开研究,同时结合埋藏史分析,恢复了储层孔隙演化过程。研究结果表明:长8储层目前处于中成岩阶段A2亚期,主要经历压实作用、胶结作用、烃类侵位和溶蚀作用,压实作用和胶结作用是导致储层低孔低渗的根本原因,它们分别使平均孔隙度损失17.2%和14.7%。在孔隙演化过程中,早成岩阶段A期的压实作用和中成岩阶段A2亚期的自生黏土矿物和碳酸盐胶结作用是造成孔隙度大幅降低的2期成岩作用;早成岩阶段B期因持续时间较短而损失较少的孔隙度;早成岩阶段A期产生的次生孔隙基本上都被微晶方解石充填,而中成岩阶段A1亚期的有机酸溶蚀作用有限,仅产生约0.6%的孔隙度。定量孔隙演化过程与油气充注史的结合显示出研究区长8“先成藏后致密”的特点,为进一步的油气勘探奠定基础。

Abstract: The petrography and diagenesis of low permeability tight reservoir sandstones from the 8th member of Yanchang formation in Huanxian-Huachi region of Ordos basin were investigated by analyses of thin section, SEM, X-ray diffraction and physical property, with which the study of buried history was combined and applied to the restoration of process of porosity evolution. The results show that the reservoir sandstones from the 8th member of Yanchang formation are in A2 sub-stage of mesodiagenesis stage, which have mainly experienced compaction, cementation, hydrocarbon emplacement and dissolution. Compaction and cementation are the dominant factors that lead to a reservoir with low-porosity and low-permeability. The average primary porosity of the reservoir is reduced by 17.2% by compaction and 14.7% by cementation respectively. In the process of porosity evolution, a significant decrease of porosity is caused by compaction in eodiagenesis stage A and carbonate cementation, authigenic clay minerals cementation in A2 sub-stage of mesodiagenesis stage while the prosity is less reduced in eodiagenesis stage B as to the shorter duration. The secondary pores formed in eodiagenesis stage A are basically full-filled with microcrystal calcite, and the dissolution evoked by organic acids in A1 sub-stage of mesodiagenesis stage results in an approximate increase of porosity by 0.6%, which improves the reservoir physical property scarcely. The combination of process of porosity evolution and hydrocarbon filling history displays characteristics of “accumulation prior to densification” in the 8th member of Yanchang formation in the research region, which lays a foundation for further exploration of oil and gas.

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