Laser Drilling Using Nd:YAG on Limestone, Sandstone and Shale Samples: ROP Estimation and the Development of a Constant ROP Drilling System

Abstract

Abstract Background/Scope: Mechanical drilling, the gold standard to reach oil and gas reservoirs, is associated with drilling risks and increased time and costs. Laser drilling has emerged as a potential new drilling tool. However, studies about its practical applications are limited. This study investigates the feasibility and performance of laser technology in drilling oil wells. Methods: Core samples from the three lithologies were irradiated with Nd:YAG laser at different power intensities and exposure times while holding other parameters constant. Some core samples were saturated with brine to investigate the effect of fluid saturation. We developed a novel laser drilling system that enables users to input the lithology of encountered formations and output the power intensity needed to be drawn from the electric source to maintain the constant ROP. Results: The Nd:YAG laser beam fully penetrated the cores in all the study trials conducted in shale. In limestone, the laser beam fully penetrated the cores in 5/13 trials and partially penetrated them in 7 trials. The experiments could not be performed in sandstone due to rough surfaces and high porosity. The ROP values ranged between 58 and 66 ft/hr (mean 62.4 ±5.3 ft/hr) in shale and between 221.7 and 460.6 ft/hr (mean 328.5±71.5 ft/hr ft/hr) in limestone. The specific energy values ranged between 650 and 5433 KJ/cm3 (mean 2885.1±1525.8 KJ/cm3) for the limestone samples. A statistically significant inverse correlation was observed between laser energy and ROP (r=-0.952, P<0.001). The developed software was tested and validated. Added value: The study provides further evidence that laser drilling technology is a promising new technology for oil well drilling. The current study utilized high specific power laser which has not been previously used and developed a novel computer based constant ROP laser system. The rock removal mechanism should be shifted away from melting to spallation to achieve an efficient laser drilling mechanism through the optimization of the laser specific power and decreasing the specific energy during rock removal. Laser beam reflection, sample thickness and fluid saturation were identified as potential factors that influence the efficiency and performance of the laser drilling operation.