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^{- 3} μm² ,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(p H < 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^{- 3} μm² . 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 t he denudation is infavor of the reservoir.