Li Shutong, Liu Xianyang, Deng Xiuqin, Hui Xiao, Guo Ruiliang, Chen Junlin, Zhang Jiaqiang
Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730030, China.
Key Laboratory of Petroleum Resources, Lanzhou 730000, Gansu, China.
ACS Omega. 2021 Jul 1;6(27):17584-17598. doi: 10.1021/acsomega.1c02103. eCollection 2021 Jul 13.
Exploring the tightness mechanism through a quantitative analysis of the pore evolution process is the research hotspot of tight oil reservoirs. The physical characteristics of Chang 6 (Ch-6) sandstones in the western Jiyuan area have the typical features of a tight oil reservoir. Based on the reservoir physical property, lithological characteristics, diagenetic types and sequence, and burial and thermal evolution history, this study analyzes the factors leading to reservoir tightness and establishes the model of the pore evolution process. The results show that the sedimentary microfacies type controls the reservoir detrital material and further affects its physical properties. The high content of feldspar and rock fragments and the fine grain size are the material cause for the reservoir tightness. The sandstones of the main underwater distributary channel are the dominant sedimentary bodies for the development of a high-quality reservoir. In terms of diagenesis, compaction is the primary cause for reservoir tightness, and the porosity reduction by cementation is weaker than that by compaction. Meanwhile, the quantitative calculation results indicate that the porosity losses by compaction, carbonate cementation, kaolinite cementation, chlorite coatings, and siliceous cementation are 23.5, 3.1, 3.8, 3.0, and 0.8%, respectively. In addition, dissolution is significant to improve the reservoir physical property, and the increase of dissolved porosity is around 3.2%. More significantly, this study uses a detailed and systematic method for analyzing the tightness mechanism and the pore evolution process of the Ch-6 sandstones in the western Jiyuan area, Ordos Basin, China.
通过对孔隙演化过程进行定量分析来探究致密油储层的致密化机制是致密油储层研究的热点。鄂尔多斯盆地姬塬西部地区长6砂岩的物性特征具有致密油储层的典型特点。基于储层物性、岩性特征、成岩类型及序列以及埋藏与热演化史，本研究分析了导致储层致密化的因素，并建立了孔隙演化过程模型。结果表明，沉积微相类型控制着储层碎屑物质，进而影响其物性。长石和岩屑含量高以及粒度细是储层致密化的物质成因。主要水下分流河道砂岩是优质储层发育的主导沉积体。在成岩作用方面，压实作用是储层致密化的主要原因，胶结作用导致的孔隙度降低弱于压实作用。同时，定量计算结果表明，压实、碳酸盐胶结、高岭石胶结、绿泥石包膜和硅质胶结导致的孔隙度损失分别为23.5%、3.1%、3.8%、3.0%和0.8%。此外，溶蚀作用对改善储层物性具有重要意义，溶蚀孔隙度增加约3.2%。更重要的是，本研究采用详细系统的方法分析了中国鄂尔多斯盆地姬塬西部地区长6砂岩的致密化机制和孔隙演化过程。
