Experimental study on the influence of drilling fluid salinity on the strength characteristics of Kangcun Formation mudstone in the Kelasu structural belt

This study investigates wellbore instability in Kangcun Formation mudstone (BZ Block, Kelasu Belt, Tarim Basin) through XRD, SEM, CEC, acoustic velocity, and uniaxial compression experiments before/after drilling fluid soak. Results show the mudstone features abundant micropores/microcracks and high clay content (avg. 28.94%), dominated by illite-smectite mixed layers. Drilling fluid soak significantly degraded mechanical properties: acoustic velocity decreased by 17.55% on average, while uniaxial compressive strength (UCS) and Young's modulus dropped by up to 68.85% and 79.74%, respectively. Notably, increasing drilling fluid salinity mitigated strength reduction. These findings demonstrate the critical impact of water-rock interaction on acoustic-mechanical properties and support using KCl-enhanced fluids for improved wellbore stabilization in this formation.