鄂尔多斯盆地姬塬地区延长组长3油组成岩作用分析

Diagenesis of Chang 3 reservoir of Yanchang Formation in Jiyuan area,Ordos Basin

姬塬地区延长组长3油组是陆相三角洲背景下的岩性油藏,骨架砂体是三角洲前缘水下分流河道。储层岩性为长石砂岩和岩屑质长石砂岩,岩石成分成熟度偏低,结构成熟度较好。孔隙度均值为12.62%,渗透率均值为0.8×10-3μm2,是典型的低孔、低渗油藏。根据扫描电镜、铸体薄片、阴极发光及X衍射等资料,对研究区的成岩作用进行了研究,认为长3油组现处于早成岩期B亚期向晚成岩期A亚期过渡时期。研究区成岩各阶段均为酸性(pH<6.5)环境,在早成岩期为开启型弱酸性水循环环境,在晚成岩期为封闭型弱酸性水循环环境,这都为溶蚀作用提供了良好的条件。机械压实作用、胶结作用和交代作用是造成长3油组储层物性变差的主要原因。溶蚀作用在一定程度上改善了储层物性。

The Chang 3 sandstone reservoir of Yanchang Formation in Jiyuan area is lithologic reservoir,which belongs to continental delta deposits.The framework sand body is delta front subsea distributary channel.The reservoir lithology is arkose and syrosem arkose,with the low maturity of lithologic composition and good texture maturity.The reservoir is typical low porosity and low permeability reservoir with average porosity of 12.62% and average permeability of 0.8×10-3μm2.Based on the data of SEM,cast slice cathodeluminescence and X diffraction etc.,the diagenesis of the study area was analyzed.The result showed that the third member of Yanchang Formation is now in the transition period from the early diagenetic stage B to late diagenetic stage A.In the early diagenetic stage,the stratum water circulating environment is a relative opened type of weak acid,and in the late diagenetic stage,it is a relative closed type of weak acid,which provide good conditions for denudation.The mechanical compaction,cementation and displacement result in the poor physical property of Chang 3 reservoir,and the denudation is in favor of the reservoir