Structural diagenesis and high-quality reservoir prediction of tight sandstones: A case study of the Jurassic Ahe Formation of the Dibei gas reservoir, Kuqa depression, Tarim basin, NW China

Abstract

• The paleo-tectonic stress was verified to be an important factor for porosity reduction in tight sandstones . • The structural diagenesis of tight sandstone of Ahe Formation was quantitatively characterized. • The favorable reservoir areas were predicted based on structural diagenesis and stress field simulation. Structural diagenesis is an important factor controlling the reservoir characteristics of the Jurassic Ahe Formation (J 1 a) of the Dibei gas reservoir in the northern structural belt of the Kuqa depression, which is mainly manifested as the compaction-attributed porosity reduction by the paleo-tectonic stress and structural fracture formation. Based on the analysis of the reservoir and tectonic stress characteristics, the control effects of the paleo-tectonic stress on porosity reduction and structural fracture characteristics of the Ahe Formation reservoir are quantitatively investigated. With numerical simulation based on the finite element method, the high-quality reservoir area of the Jurassic Ahe Formation of the Dibei gas reservoir is predicted. The results show that paleo-tectonic stress is an important element affecting reservoir physical properties and structural fracture characteristics of the Ahe Formation. The maximum paleo effective compressive stress is negatively linearly correlated with the average reservoir porosity, while it is positively exponentially correlated with the porosity reduction attributed to tectonic compaction. The direction of the maximum paleo effective compressive stress controls the dominant striking direction of structural fractures, and the stress magnitude determines the development degree of structural fractures. A clear positive exponential correlation is found between the maximum paleo effective compressive stress and both the areal density and plane porosity of fractures. The Well DX1-YN2-DB104 district and Well TZ4 district present high gas production, and the circular zone in the central-southern part of the study area has paleo-tectonic stress and reservoir characteristics similar to those of the above two districts. Thus, it is a potential favorable area for high gas production and should be considered a key exploration orientation of the Dibei gas reservoir.