Abstract: To address the challenges in quantitatively evaluating rock fracture evolution and fracture development intensity within the strongly compressed strata of the Kuqa Depression in the Tarim Basin, this study introduces a method for assessing fracture development intensity. This method is grounded in stress state analysis and is realized through a series of rigorous steps, including geological data analysis, rock mechanical testing, formulation of failure criteria, and development of computational software. The research reveals that deep-seated rocks in the Kuqa Depression exhibit high uniaxial compressive strength, low Poisson’s ratio, and brittle-dominated mechanical properties under intense compression. The failure criterion must account for the intermediate principal stress effect and confining pressure dependency. Building on octahedral energy theory, a generalized failure criterion is established, integrating tensile microcrack initiation and frictional slip coupling mechanisms. A four-level index system for fracture development intensity, centered on the relative fracture surface tensor distance, is proposed, along with supporting computational software. Validation using logging and core data from the Jurassic Ahe Formation in Wells DB5 and DT2 in the Kuqa Depression demonstrates a predictive accuracy exceeding 80% for fracture development intensity, which aligns well with imaging logging results. This method surmounts the constraints of conventional logging techniques confined to localized wellbore detection, enabling dynamic fracture evaluation across entire well sections and throughout their lifecycle. It provides a quantitative basis for optimizing stimulation strategies in ultra-deep hydrocarbon reservoirs under intense compression and for controlling wellbore stability.

Key words: rock mechanics, strongly compressed formation, stress state, failure criterion, fracture development intensity