Drilling a Hole in Granite Submerged in Water By Use of CO2 Laser

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 119914, ’Drilling a 2-inch in Diameter Hole in Granites Submerged in Water by CO2 Lasers,’ by Toshio Kobayashi, SPE, and Masahiro Nakamura, Japan Drilling Company, and Satoshi Kubo and Makoto Ichikawa, SPE, Japan Oil, Gas, and Metals National Corporation, originally prepared for the 2009 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 17-19 March. The paper has not been peer reviewed. As part of a fundamental study of rock drilling by laser irradiation, the full-length paper describes laser drilling of a 5.08-cm-diameter hole in granites submerged in water. The laser beams melted the granite surface locally to form small glassy beads. Repetition of this procedure demonstrated that a high-power laser beam propagating in water can be used to generate a hole in rocks. Experimental A 10.6-µm carbon dioxide (CO2) laser was used. The laser had a 5-kW peak-output power, a 5-ms pulse width, a 10-Hz repetition rate, a 250-J pulsed energy, and a 50% duty ratio. The CO2 laser has a ring mode. A laser-irradiation nozzle with a 20-in. focal length was used for irradiation in air and in water. For irradiation in water, a 300-mm3 acrylics chamber was used. A high-speed video camera was placed at the side of the chamber to photograph the dynamic behavior of the formation of bubbles induced by laser irradiation. A rock specimen was placed in the chamber so that the distance from the water surface to the top surface of the granite was 50 mm. The CO2 laser was intermittently irradiated perpendicularly from a muddy-water surface. The irradiated laser beam was absorbed in the water and formed cone-shaped bubbles that had an irregular interface. Because the induced bubbles kept their shape until a subsequent laser beam reached the rock, the laser beam could drill the rock effectively. Rock Specimens Inada granite was selected as a rock specimen because the Inada granite is representative of quartz-group minerals and quartz-bearing rocks in Japan. Its K-Ar chronology is 60 Ma. Inada granite often is used as construction materials and experimental materials. The Inada granite contains 33.7% quartz, 32.1% potash feldspar, 30.3% plagioclase, and 3.8% biotite. Physical characteristics of Inada granite are as follows: 180-MPa uniaxial compressive strength, 0.75-MPa split-ting tensile strength, 65-GPa Young’s modulus, 2.63 g/cm3, 0.75% porosity, 0.0167- to 0.0377-J/(g-K) specific heat, and 54.4- to 83.7-W/(m.K) thermal conductivity. Results and Discussion In earlier experiments with Inada granite irradiated in air with a CO2 laser, transparent glassy objects crystallized on the walls of the created hole. It was observed that the fused Inada granite could not fully flow out of the hole, solidifying on the bottom to close the bottom of the hole. As a result, a complete hole cannot be created by the laser irradiation in air.