Current explosive shaped charge perforating methods causes formation damage that results in reducing the permeability and imposing the costly post-perforation operations. One of the newest technologies recommended as a suitable alternative for the conventional perforating methods is laser perforation which is gone along with micro and macro fractures initiation. In this paper, the results of experimental studies on implementation of high power lasers in perforation and fracture initiation in oil and gas wells is presented.
1. INTRODUCTION
In petroleum industry, perforation is a process of creating tunnels through the cemented steel casing and rock formation to let the formation fluid flow into the well. For decades the petroleum industry has been applying the wellbore perforation method introduced in the 1940s which is using explosive shaped charges that originally were antitank devices in World War II [1]. In this method, a perforating gun is lowered through the casing by a wire line. When it is in the proper position, explosive shaped charges are blown up and create the path between the formation and the well. This process imposes around 1.5*106 psi pressure at the tunnel entrance [2] that crushes the rock matrix and produces fine grain particles which plug or reduce the pore throat size that leads to formation damage and hence remarkable permeability reduction in the rock formation adjacent to the created tunnel [3]. Thus, for many years the petroleum industry has been looking for a non-explosive and non-damage alternative that not only create holes effectively but also minimize the formation damage. Recent advances in high power lasers technology provide a new tool to replace the current perforation methods in oil and gas wells. Since 1997, Gas Technology Institute (GTI) and its associated partners have paved the way for applying high power lasers in drilling and completion of oil and gas wells. The results of their experimental studies have proven that high power fiber laser represents a technology that remarkably decreases the shortcomings of the current explosive shaped charge perforation methods and operates more effective. The significant permeability increase even as high as 500 –1000% [4] is the most important priority of laser perforation over the conventional perforation methods while increasing the permeability can result in the higher rate of production. Also, experimental studies have shown that laser perforation leads to fracture the adjacent rock formation due to generation of thermal stresses in laser-rock interaction which results in improving permeability and facilitating fracture initiation [5]. The main objective of this paper was to show the efficiency of laser energy for perforation and fracture initiation in oil and gas wells.
2. LASER-ROCK INTERACTION
Transferred laser energy into the rock will be mainly reflected, scattered and absorbed. The ratio of energy reflected by a surface is due to the composition of the rock while the scattering of radiation is due to wavelength [6]. When a rock surface is exposed to a high power laser, the local temperature will rise instantaneously and spallation, melting, or vaporization may take place.
