The influence of argillaceous content in carbonate rocks on the 3D modeling and characterization of tectonic fracture parameters—Example from the Carboniferous and Ordovician formations in the Hetianhe gas field, Tarim Basin, NW China

Abstract This study aims to understand the influences of argillaceous content on carbonate rocks’ mechanical parameters in the Hetianhe gas field. Through core observation, thin section study and log identification, we characterized the argillaceous content and tectonic fractures in the carbonate rock. We then determined the fracture generation mechanism and fracture distribution in an Ordovician bioclastic-limestone section. Through mechanical testing, log interpretation, and rupture quantification, we established the relationships between the mechanical parameters (Young’s modulus, Poisson’s ratio) and the argillaceous content of the carbonate. Increasing argillaceous content correlated with a decrease in the Young’s modulus, exhibiting an inverse relationship. However, where the argillaceous content increased, the Poisson’s ratio slightly increased and the limestone tenacity increased. Conjugated fractures developed in limestone with a low argillaceous content. The fracture dip angle decreased in limestones with medium argillaceous content. The dip of tectonic fractures in limestone with high argillaceous content was very low. Combined with the Mohr–Coulomb and the Griffith criteria, the relationship among the fracture density, aperture, porosity, permeability, and the argillaceous content was deduced. Four categories of limestone argillaceous content were distinguished, 0−10%, 10−20%, 20−40%, and 40−100%. Based on the finite element simulation software, the fracture development and distribution in typical wells was simulated. In the Hetianhe gas field, the gas production was significantly controlled by the fracture porosity and permeability. We show that as the argillaceous content increased, the fracture density decreased and the porosity increased. Our simulated results agreed well with the production data, exhibiting a correlation coefficient greater than 85%.