Effect of Downhole Pressure Conditions on High-Power Laser Perforation

Abstract Researchers at Gas Technology Institute (GTI) have been exploring the use of high power laser energy as a non-damaging alternative to conventional explosive perforation methods. 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. Clad 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 prototype tool. 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 with a 5.34 kW Ytterbium-doped multiclad fiber laser exposed to 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 paper will discuss 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 will provide the resulting effect of downhole pressure conditions on the laser/rock interaction process.