Influence of sedimentary microfacies on the rock mechanics of ultra-deep reservoirs and its application: a case study of the Cretaceous formation in the BZ gas field of Kuqa Depression, Tarim Basin

Abstract

To optimize the identification of sweet spots with natural fracture development in ultra-deep tight sandstone reservoirs of Cretaceous in the Kuqa Depression, Tarim Basin, this study systematically analyzed the differences in rock mechanical properties across various sedimentary microfacies in the BZ gas field. Utilizing data from outcrops, rock slices, imaging logging, and other sources, a method for optimizing the rock mechanics parameter model of reservoirs was proposed, which enhanced the prediction accuracy of natural fractures within 200 m around the wellbore. Key findings of the research include: (1) In the third member of the Cretaceous Bashijiqike Formation in the BZ gas field, different sedimentary microfacies and the same microfacies at different positions had differences in rock composition and rock assemblages (including debris content, matrix content, grain size sorting, sand-to-mud ratio, and sand-mudstone combinations). These variations affected the reservoir's Poisson's ratio and Young's modulus, and different microfacies had different rock mechanical parameters. (2) The extent of fracture development differed across various sedimentary microfacies of sand bodies. Fractures were most developed in the underwater distributary channel sandstones at the fan delta front, making them more prone to fracturing compared to the interdistributary bay microfacies and distributary channel microfacies on the delta plain. (3) By further establishing three-dimensional models of different microfacies based on geometric parameters derived from outcrops, it would be feasible to optimize sedimentary microfacies models and rock mechanical parameter models around the wellbore, thereby facilitating more accurate fracture prediction.

Keywords

• fracture prediction
• reservoir geomechanics
• sedimentary microfacies
• tight sandstone
• ultra-deep reservoir
• tarim basin