Quantitative Study on the Porosity Evolution History of Deep-buried Tight Clastic Reservoirs

It is fundamental to study the development and preservation of porosity in the clastic reservoirs in the field of reservoir geology. Specifically, porosity evolution history of deep-buried tight clastic reservoirs has been... [ view full abstract ]

It is fundamental to study the development and preservation of porosity in the clastic reservoirs in the field of reservoir geology. Specifically, porosity evolution history of deep-buried tight clastic reservoirs has been paid much attention to, such as that in the Tarim basin. Based on characteristics of actual geological data, functional relationship models correlating porosity and geological parameters (including buried depth, temperature, vitrinite reflectance, and so on) have been established, which can be further employed to estimate the present porosity of reservoirs. Therefore, a quantitative study method concerning the porosity evolution history of the deep-buried tight clastic reservoirs has been proposed in this study: (1) comprehensive analyses are primarily conducted in the study of diagenetic types, reservoir features, and evolution sequences; (2) the influence degree of diagenesis on the reservoir space is calculated based on the pore structure characteristics by thin section observation and computer imaging techniques, in which contents of authigenic minerals, cements, and dissolution pores are counted quantitively by using microscope; (3) constrained by the burial-diagenetic evolution history, the control degree on physical property changes of reservoirs by various diagenetic processes at each stage were reconstructed and adjusted, which is employed to renovate the factual reservoir porosity evolvements. By quantitatively restored the porosity evolution history, the influence of various diagenesis on the reservoir physical property was clarified. Combining with accumulation history matching analysis, this method represents great practical and guiding significance for exploring effective reservoirs in the deep, tight part of the basins during hydrocarbon exploration and development. Application of the method in deep tight reservoirs in Bashijiqike Formation has been seen good results in Kelasu structure zone, Kuqa Depression, China. The major gas reservoirs are more than 8000m deeper. The findings indicate that the reservoirs undergo densification with gas accumulation synchronously and tight gas accumulation occurred in late stage efficiently.