The purpose of this research is to develop Underwater Laser Drilling Technology in drilling and completing oil and natural gas wells. Recent challenges in oil fields are caused by: the geometry of oil or gas wells is becoming more complicated in profile; drilling in hard formations like granite requires more tripping times for changing rotary bits made of steel; as the water depth at which floater rigs can operate increases, tripping has to take longer than ever. Underwater Laser Drilling is a key to solution of these challenges since the laser may allow for non-contact / non-rotating drilling method. Granite is one of the most difficult rocks to be drilled by lasers. Consequently, no successful report has been found on underwater granites drilled by lasers. This paper describes experimental tests of irradiating carbon dioxide (CO2) laser to granite submerged in water/ bentonite solutions. Sample granite was submerged at 50mm from the water-surface and then a CO2 laser with a wavelength of 10.6µm which has a high absorption coefficient in water was intermittently irradiated into the 4wt% bentonite solutions. A laser induced underwater shock waves, cavitation bubble formations, and micro-water jet formations upon bubble collapse. The high power laser beam locally melted the granite into molten glass, which successively turned to a molten glass bead. The generated glass beads were small enough to be removed out of the created hole. A high-speed video camera was employed to record the laser beam in the water. We observed the generation of initial cone shaped water bubbles through which the laser beams reached bottom rock surface with a minimum absorption energy loss. The laser beam indeed drilled the granite specimen submerged in the solution. The research will continue to collect data for designing a prototype.
Melting Rocks. Relatively low-power continuous wave CO2 lasers with output powers?1 kW had been used for most of the experimental results on laser-rock interaction before 2000. It was reported by Mukhamedgalieva et al (1975, 1976, 1978, 1981. 1982) that CW CO2 laser radiation on various rocks forms a laser plume. They concluded that the laser-plume absorbs laser radiation. This absorption leads both to a temperature rise of the plume and a further increase in absorption of laser radiation by the plume, causing the rock destruction process to completely cease (Mukhamedgalieva et al (1976)).