Characteristics of Stress Zonation in the Bashijiqike Formation and Control Factors on Reservoir Development (Kelasu Structural Belt, Kuqa Depression, North-Western China)

Abstract

The deep to ultra-deep sandstone reservoirs of the Cretaceous Bashijiqike Formation in the Kelasu structural belt of the Kuqa Depression exhibit strong heterogeneity. This study integrates single-well stress calculation, image log fracture interpretation, thin-section petrographic analysis, and porosity–permeability testing to compare stress, fracture, and reservoir characteristics across the Dabei–Bozi cross-section. The results show that the northern stress release zone is characterized by low SH (98 to 148 MPa) and E (9220 to 23,420 MPa), indicating weak cumulative stress, low effective fracture density (0.09 fractures/m), and primary-pore dominated reservoirs. The central stress transition zone has progressively increasing SH (136 to 187 MPa) and E (27,450 to 33,210 MPa) from north to south, indicating strong cumulative stress, high effective fracture density (0.31 fractures/m), and mixed primary–secondary pore-fracture reservoirs. The southern stress accumulation zone shows increasing SH but decreasing E to the south, indicating that the late-stage high stress results in low effective fracture density (0.08 fractures/m) and preserving primary pores. These results demonstrate that reservoir quality is governed by the cumulative effect of the stress field, rather than by present-day stress or peak paleo-stress alone. This reservoir distribution model could provide a theoretical basis for reservoir prediction in the foreland basin.