Geomechanical simulation of low-order fracture of tight sandstone

Abstract

Abstract The core factors in the study of fractures within tight sandstone reservoirs are tectonics, geomechanics and fluid mobility, which are not independent but are coupled to each other. In this paper, taking the upper Paleozoic gas reservoir within the low-amplitude tectonic zone in the Sulige gas field of the Ordos Basin as an example, the developmental characteristics and geomechanical model of fractures and their relationships with the productivity of tight gas sandstone reservoirs were systematically studied. The results show that this low-amplitude structural zone develops mainly low-order ruptures. The paleotectonic stress field of the target layer in the Yanshanian period was restored using a 3D finite element method. The horizontal principal stresses exhibited stress diffusion and were affected by local low-amplitude structures. There was a positive correlation between σH and σh, and σH/σh was distributed primarily between 1.35 and 1.95 with an average of 1.62. The strain energy density (U) was calculated to quantitatively characterize the microfracture distribution of the target layer based on the principle of energy conservation. There are certain positive correlations between U and the horizontal principal stresses. The geostresses of high-U regions underwent a certain degree of stress torsion, which manifested as a stress deflection reaching up to 30° during stress propagation. Finally, we proposed the concept of U-value geomechanical sweet spots in a tight gas sandstone. Based on this criterion, commercial gas wells can be effectively identified.