Quantitative prediction of the 3D permeability tensor for a fractured reservoir in the Dingbian oilfield, Ordos basin, Central China

Abstract

Understanding existing fractures is critical to achieving high and stable yields in low‐permeability reservoirs, tight sandstones, and shale reservoirs. When multiple fracture sets are present in a reservoir, accurately determining the seepage direction of fluids is critical for the deployment of the well network, fracture reformation, and the design of horizontal wells. In this paper, based on conventional logging data calculations and rock triaxial mechanical experiments, a heterogeneous finite element model was established using the finite element software. The densities and the occurrence of the natural fractures were calculated by numerical simulation of the paleostress field; the fracture apertures were calculated numerically by a current in situ stress simulation. Using a combined static coordinate system and dynamic coordinate system approach, a model suitable for determining the 3D permeability tensor of multiple fractures is established, and the formula of the permeability tensor is given. In addition, by adjusting the rotation angle and flip angle in the dynamic coordinate system, the permeability of elements is predicted for different directions. The results show that fractures mainly trend in the NE (45°) and ESE (120°) directions. Additionally, the results of differential strain, microseismic monitoring, stress relief, and regional borehole collapse observations indicate that the dominant direction of the in situ stress field is ENE (70°). The principal values of maximum permeability in the reservoirs in the Chang 71 layer mainly range from 0.05 to 2 × 10−3 μm2, and in the horizontal plane, the direction of maximum principal permeability ranges from 56 to 124°.

Numerical simulation of the stress field and fault sealing of complex fault combinations in Changning area, Southern Sichuan Basin, China

“…The numerical simulation of tectonic stress field based on finite-element analysis can better solve this problem, and can inverse the stress field of different tectonic elements in different periods. [30][31][32][33][34][35][36][37][38][39][40] By using the results of structural interpretation, establishing the corresponding geological model, and carrying out numerical simulation calculations of the tectonic stress field, the tectonic stress field of specific structures and the normal and shear stresses on the fault plane can be obtained, and the characteristics of stress on a section in different periods can be reproduced. [41][42][43][44] On this basis, through the comparison of section normal and shear stresses and section rock compressive and shear strengths, the quantitative study of fault sealing has the advantages of simplicity, effectiveness, and easy visualization.…”

Tectonic Fracture Formation and Distribution in Ultradeep Marine Carbonate Gas Reservoirs: A Case Study of the Maokou Formation in the Jiulongshan Gas Field, Sichuan Basin, Southwest China

“…The prediction methods mainly include the curvature method, fractal dimension method, seismic attribute method, and numerical simulation method based on the tectonic stress field. Among them, the numerical simulation method is developed from the tectonic fracture mechanism and has certain advantages over other methods. − It establishes the finite element geological model of the study area, determines the boundary constraints and stress loads in combination with the regional tectonic background, and performs numerical simulation of the tectonic stress field. Then, on the basis of the measured data from a single well, the relationship between the tectonic fracture parameters and tectonic stress is established, and then, the spatial distribution of the tectonic fractures is predicted.…”