Well Perforation Using High-Power Lasers

Abstract

Abstract Conventional wellbore perforation techniques are designed to establish flow from the hydrocarbon-bearing reservoir through the cemented casing into the wellbore. The explosive force of shaped charges is focused and intensified into a small-diameter jet that penetrates the casing and cement into the reservoir rock. This process reduces reservoir rock porosity and permeability as metal and carbon debris are forced into the perforation tunnel, while very fine grain particles plug or reduce the pore throat size. As a result, it is necessary to perform time-consuming and costly post-perforation operations to minimize flow restrictions into the wellbore. Developing alternative perforation methods that reduce or eliminate formation damage could significantly boost production rates, cumulative production and overall economic returns. The research team led by Gas Technology Institute (GTI) has demonstrated, through the application of high-energy lasers to rock samples, that damage to permeability and porosity of the adjacent zones cannot only be reduced, but that near-hole permeability in a reservoir sandstone can be increased up to 171%. By applying this technique downhole, perforations and other directionally controlled completion and stimulation methods could be employed without damaging the reservoir. This paper presents the experimental methods and results of exposing sandstone, limestone, and shale rock samples to high-power laser beams. A grid pattern was applied to the rock samples from which acoustic velocity and permeability measurements in and near the perforated tunnel where taken. In addition, rock mineralogy and rock properties were analyzed before and after the test. Introduction Lined shaped charges were first introduced as a cased hole perforation technique following their successful use as an anti-tank device in World War II, and their use in perforators have since set the standard in the industry.1 This method, however, can result in lower than optimal production, due to the physical damage caused in the wall of the perforation tunnel and the adjacent formation zone. When a high velocity jet is released into the formation from a shaped charge, the explosive force causes high shock pressure, ranging from 15 million to 150,000 psi at the tunnel entrance and tunnel tip2. This process results in crushing the rock matrix, fracturing sand grains and pulverizing cement, producing very fine grain particles that plug or reduce the pore throat size and, therefore, reducing permeability. The perforated tunnel is lined with rock fragments, melted casing metal and explosive by-products (mostly carbon). In general, problems inherent in using lined shaped charge for perforating cased holes include:Production of debrisCompaction of rock formation adjacent to tunnelReduction of permeability due to reduction of pore throat size from migrating fines and debrisHealth and safety concerns in handling explosives. Remedial technologies have been continuously developed and applied to reduce the impact of these problems, including stimulation techniques to reduce the effects of resulting flow restrictions. The effects of the damage may be reduced, but not eliminated. This study presents a novel well perforation method using high-power lasers as alternative to high-velocity line shaped charges and the formation damage they create. Photonic energy can create fluid communication channels from the reservoir to the wellbore while enhancing the permeability and porosity in the tunnel and adjacent zones. To accomplish the research goals, several rocks, including sandstone, limestone and shale have been analyzed and lased using two laser types, the Mid-Infrared Advanced Chemical Laser (MIRACL) at the U.S. Army HELSTAF facility, White Sand, NM; and the Chemical Oxygen Iodine Laser (COIL) at the U.S Air Force Directed Energy facility. Albuquerque, NM.