Abstract

For the past nine years, a team of scientists has been examining the possibility of applying high-powered laser technology as a non-explosive alternative to current well construction and completion methods. With an application emphasis on wellbore perforation, experiments have demonstrated that high-powered fiber lasers are capable of cutting and perforating through rocks while improving porosity and permeability.

Fiber lasers are a leading candidate for downhole laser applications. They exhibit several key advantages over other industrial and military lasers, including high efficiencies in energy conversion; rugged, transportable dimensions; and the only ones that can deliver laser power at a long distance from the surface to downhole targets via fiber optics with minimum energy loss.

This experiment simulated rock perforations at surface and downhole pressure conditions using a 5.34 kiloWatt (kW) Ytterbium-doped multiclad fiber laser and a specially designed high-pressure triaxial cell that allowed the beam to strike a pressure-charged core.

At downhole conditions (with under-balanced pressure at 2000 psi), the fiber laser perforated sandstone and limestone with 87 % and 35 % more efficiency, respectively, than at zero-pressure conditions. When at-balanced (with triaxial conditions at 2000 psi and no pore pressure), the fiber laser perforated sandstone and limestone with 61 % and 17 % more efficiency, respectively, than at zero-pressure conditions. This increased efficiency for rocks perforated at downhole conditions affirms high-powered laser as a highly promising alternative to convention wellbore perforation.

Background

Since 1997, the Gas Technology Institute (GTI) and its research partners have investigated the application of high-power laser energy to well perforation and completion. In this research, various types of lasers (CO2, Nd:YAG, COIL, MIRACL, and fiber laser) with output power ranging from 1 to 1200 kiloWatts (kW) were evaluated for perforation applications. Advances in fiber laser technology make the fiber laser the leading laser for perforation and downhole application. Its advantages over other commercially available lasers are its high output efficiency of 20% (Figure 1), electric efficiency (wall plug) 20 to 25%, small footprint of 0.5 m2 (Figure 2), no maintenance, and ease of deliverability to downhole through fiber optics cable. With the small footprint and high efficiency, the laser can be transported to the field at any location.

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