Controlling Factors of Hydraulic Fractures Based on a Post-Fracturing Cored Well in Glutenite Reservoirs: A Case Study from Mahu Depression, Junggar Basin

Summary

A test site was established for hydraulic fracturing testing, and a horizontal well was drilled for coring to study hydraulic fracture (HF) in the Baikouquan Formation (Fm) on the northern slope of Mahu Depression, Junggar Basin, western China. A total of 345 fractures were obtained over 323.19-m cores, and HFs were identified by integrating the core, imaging logs, and computed tomography (CT) scans. Shear and tensional fractures, both forms of HFs, were found in the glutenite reservoir, with shear fractures being nearly twice as common as tensional fractures. This result contradicts the hypothesis of HF propagation in the glutenite reservoir during petroleum exploration, which suggests that the HF is prone to bypass the gravels, mainly forming tensional fractures. The condition of building an HF network was evaluated based on the present in-situ stress, rock brittleness, and natural fracture. Fracturing treatments are examined to understand the roots of the varying distribution of HFs. The fracture geometry was further studied based on post-fracturing cores. The HFs consist of a principal fracture subperpendicular to the wellbore with a considerable width and branch fractures that intersect the wellbore obliquely at a smaller angle with a lower width. Controlling factors for the propagation of HFs were investigated from both geological and fracturing treatment perspectives. The findings are as follows: (1) HFs prefer to penetrate gravels in the glutenite reservoir when the gravel is large in size, poorly sorted, and high in content; (2) two parameters control the fracture density and mode of fracture propagation, which are the minimum distance between the cored well and the fractured well’s cluster of perforation (SC) and distance density (DS); higher fracture densities and more shear fractures can occur when SC is lower and DS is higher.