Simulation of tectonic stress field and prediction of tectonic fracture distribution in Longmaxi Formation in Lintanchang area of eastern Sichuan Basin

Abstract

Shale is a low-porosity and low-permeability reservoir, and structural fractures are the main controlling factor for the migration and accumulation of shale gas. Moreover, tectonic fractures are controlled by the paleo-tectonic stress field. In this paper, taking the Longmaxi Formation of the Lintanchang area as an example, the finite element numerical simulation technology is used to analyze the distribution law of the paleo-tectonic stress field, and further, the fracture development areas under the superposition of two periods of tectonic stress are predicted using seismic, rock mechanics, and field data. The results show that the tectonic fractures developed in the Lintanchang area are mainly EW- and NNW-striking conjugate shear fractures formed in the Mid-Yanshanian period, followed by the NWW- and SWW-striking conjugate shear fractures formed in the late Yanshanian period. The distribution of tectonic fractures is affected by faults, folds, rock physical parameters and tectonic stresses. It is found that the comprehensive fracture coefficients of the anticline core and fault areas are both greater than 1.1, which are the areas with the most developed structural fractures, and these areas have poor shale gas preservation conditions. However, the comprehensive fracture coefficients of the western flanks of the anticline and the eastern and western dipping ends are between 1.0 and 1.1, which are areas with better shale gas preservation conditions. In addition, the development degree of tectonic fractures in the east and northwest areas of the Lintanchang anticline is lower than that in other areas. The comprehensive fracture coefficients of shale in these areas are between 0.9 and 1.0. The shale is in a state of “breaking without cracking”, and shale gas can be well preserved.

Characterization of fractures in low‐permeability thin tight sandstones: A case study of Chang 6 Member, Yanchang Formation, western Ordos Basin

“…As can be seen, vertical and horizontal fractures are well developed (Figure 8a). Fractures that occur in groups and have several stable strikes are regionally distributed fractures (Chen et al, 2021; Zeng & Liu, 2010; Zhang et al, 2022; Zoback, 2007). The fractures in the target layer have a straight pattern, long extension and small opening, and appear as multiple parallel groups of fractures.…”

Seawater composition variation in the eastern Sichuan evaporite formation basin: Constraint from 87 Sr/ 86 Sr and major ion compositional evidence of halite

“…During this period, the value of 87 Sr/ 86 Sr and its change rate uctuated several times, and the environment experienced many rapid changes. The 87 Sr/ 86 Sr ratios of 18 halite samples from Well CP3 range from 0.708151 to 0.708286, with an average value of 0.708202 37…”

Seawater composition variation in the eastern Sichuan evaporite formation basin

“…During this period, the value of 87 Sr/ 86 Sr and its change rate fluctuated several times, and the environment experienced many rapid changes. The 87 Sr/ 86 Sr ratios of 18 halite samples from Well CP3 range from 0.708151 to 0.708286, with an average value of 0.708202 37 . Compared with conodont Sr and carbonate Sr in the same period, the comparative stratigraphic chronology is between the Smithian and Spathian periods, which constrains the evaporite age of the Jialingjiang Formation to 251.2-252 Ma.…”