Laser Drilling - Drilling with the Power of Light (2007)

Gas Technology Institute (GTI) has been the leading investigator in the field of high power laser applications research for well construction and completion applications. Since 1997, GTI (then as Gas Research Institute- GRI) has investigated several military and industrial laser systems and their ability to cut and drill into reservoir type rocks. In this report, GTI continues its investigation with a 5.34 kW ytterbium-doped multi-clad high power fiber laser (HPFL). When compared to its competitors; the HPFL represents a technology that is more cost effective to operate, capable of remote operations, and requires considerably less maintenance and repair. Work performed under this contract included design and implementation of laboratory experiments to investigate the effects of high power laser energy on a variety of rock types. All previous laser/rock interaction tests were performed on samples in the lab at atmospheric pressure. To determine the effect of downhole pressure conditions, a sophisticated tri-axial cell was designed and tested. For the first time, Berea sandstone, limestone and clad core samples were lased under various combinations of confining, axial and pore pressures. Composite core samples consisted of steel cemented to rock in an effort to represent material penetrated in a cased hole. The results of this experiment will assist in the development of a downhole laser perforation or side tracking prototype tool. To determine how this promising laser would perform under high pressure in-situ conditions, GTI performed a number of experiments with results directly comparable to previous data. Experiments were designed to investigate the effect of laser input parameters on representative reservoir rock types of sandstone and limestone. The focus of the experiments was on laser/rock interaction under confining pressure as would be the case for all drilling and completion operations. As such, the results would be applicable to drilling, perforation, and side tracking applications. In the past, several combinations of laser and rock variables were investigated at standard conditions and reported in the literature. More recent experiments determined the technical feasibility of laser perforation on multiple samples of rock, cement and steel. The fiber laser was capable of penetrating these materials under a variety of conditions, to an appropriate depth, and with reasonable energy requirements. It was determined that fiber lasers are capable of cutting rock without causing damage to flow properties. Furthermore, the laser perforation resulted in permeability improvements on the exposed rock surface. This report has been prepared in two parts and each part may be treated as a stand-alone document. Part 1 (High Energy Laser Drilling) includes the general description of the concept and focuses on results from experiments under the ambient lab conditions. Part 2 (High Energy Laser Perforation and Completion Techniques) discusses the design and development of a customized laser pressure cell; experimental design and procedures, and the resulting data on pressure-charged samples exposed to the laser beam. An analysis provides the resulting effect of downhole pressure conditions on the laser/rock interaction process.