Effects of Different Downhole Fluid Media on Laser-Induced Rock-Breaking Characteristics

Abstract

As conventional oil and gas resources continue to decline, laser rock-breaking has attracted increasing attention as a high-energy-density drilling technology. However, the influence of complex downhole fluid environments on its performance and underlying energy coupling mechanisms remains insufficiently understood. In this study, realistic downhole conditions were simulated to systematically investigate the effects of fluid types, ionic species, and concentrations on laser-induced rock breaking under dry, pure-water, and complex fluid environments. The results demonstrate that fracturing fluids significantly suppress rock-breaking performance, with the maximum penetration depth decreasing from 2.786 cm (dry) to 1.848 cm, and the rate of penetration reduced by up to 65%. Meanwhile, the specific energy in fracturing fluids increases to 4.39 times that of the dry condition, indicating severe deterioration in energy utilization efficiency. The introduction of saline ions partially alleviates this inhibition, as NaCl and KCl increase the penetration depth by 0.182 and 0.090 cm, respectively, compared to the pure-water condition. Notably, ion-specific effects are observed: the specific energy of the KCl solution is consistently lower than that of the NaCl solution, and the average specific energy of the former is approximately 76.4% of the latter, suggesting more efficient laser–rock energy coupling. Furthermore, the 15% concentration delivers the most favorable performance within the tested range for the KCl system, whereas the NaCl system shows a continuous improvement in energy efficiency with increasing concentration. These findings highlight the critical role of fluid–ion interactions in governing laser energy coupling and provide a theoretical basis for optimizing laser rock-breaking performance in complex downhole environments.