Abstract
Deep well drilling in high-salinity geological formations presents significant challenges, including recurrent loss of drilling fluids and repeated plugging failures. These issues necessitate a reevaluation of conventional lost circulation materials (LCMs) and their performance metrics. Here, we investigate the behavior of commonly used bridging LCMs under high-salinity conditions characteristic of the Kuqa foreland in China's Tarim Basin. Our comprehensive experimental study reveals that high-salinity environments substantially impact the stability of LCM formed plugging zones. We demonstrate that after exposure to formation water with 200,000 mg/L salinity at 150 °C for 24 h, millimeter-sized calcium carbonate LCMs exhibit significant physical and mechanical changes. These include color darkening, 4.79% mass loss, and a 13.75% reduction in friction coefficient. The compressive strength degradation rates at D90 for pre- and post-high-salinity treatment were 17.58% and 5.48%, respectively. Walnut shell LCMs showed more pronounced alterations, with color change from dark brown to black, 32.51% mass loss, and a 28.57% decrease in friction coefficient. Their compressive strength degradation rates at D90 were 3.53% and 28.76% for pre- and post treatment, respectively. Synthetic polymer LCMs, while maintaining color stability, experienced a 9.51% mass loss and a 20.86% reduction in friction coefficient, with compressive strength degradation rates of 2.40% and 22.96% for pre- and post-treatment, respectively. Our findings indicate that the frictional performance and compressive strength of LCMs are compromised in deep, high-salinity geological formations. This deterioration leads to shearing instability and particle size degradation, ultimately resulting in plug failure. This study provides crucial insights for the selection of LCMs capable of maintaining long-term pressure stability in challenging deep, high-salinity formations, potentially revolutionizing drilling practices in such environments.