3-D visualization and application of tectonic stress fields: a case study of shale reservoirs in northern Guizhou, South China

Abstract:

The tectonic stress field usually guides the in situ stress field resulting from or caused by tectonic movement. At a large scale, the Earth's crustal stress field controls crustal deformation, earthquakes, and volcanoes and drives plate motion; at a small scale, the tectonic stress field controls the generation of natural fractures, oil and gas migration and accumulation, and rock porosity evolution. Therefore, studying the three-dimensional visualization of tectonic stress has theoretical and practical value. Here, we take the shale reservoir of the lower Cambrian Longmaxi Formation in the complex structural area of northern Guizhou as an example to realize the three-dimensional visualization of the tectonic stress field in the area. The spatial distributions of Poisson's ratio and Young's modulus in the Niutangtang shale are established through the distribution of total organic carbon (TOC) and rock mineral content. The principal stress directions during the fracture development period are determined by the strikes of natural fractures, faults, and folds; the magnitude of the paleostress is determined by acoustic emission experiments. Based on the establishment of the Yanshanian geological model, the visualization of the paleostress field in the late Yanshanian period is realized by using reservoir geomechanical heterogeneity modeling technology, and the three-dimensional distribution of structural fractures is predicted by using the paleostress and strain data. The results show that the paleostress field was mainly controlled by the mechanical parameters and faults. Different faults have different effects on the development degree of fractures; in different positions along a fault, the development degrees of fractures differ significantly. N-S-trending faults exert weak control on fracture density; faults in the central part exert stronger control on fracture density. Fracture distribution in the northern Guizhou area is helpful for optimizing well deployment and provides a basis for the exploration of shale gas.