Comparison of Specific Energy Between Drilling With High Power Lasers and Other Drilling Methods

Abstract

Abstract

Specific energy is often used as a measure of a drilling methods performance. Specific energy as defined in this paper is the amount of energy required to remove a given volume of rock (energy/volume). This is a normalization method used to compare the efficiency of one rock destruction technique to another. This paper compares specific energy between drilling with high power lasers and other drilling techniques such as traditional rotary and other novel methods such as water jets.

Specific energy calculations made from laboratory measurements taken using four high power lasers, are compared to specific energy calculations reported in the literature. Although many other rock types were lased in this research, all comparisons are made on Berea sandstone, as it is the most commonly tested rock. A discussion of how the sample type, shape of test sample, and experimental conditions effect the calculations and results is included.

It was found that there could be, and probably is, confusion caused by the way that specific energy is defined and calculated. The definition of specific energy, as used in this paper, is often compared to specific kerfing energy that is defined as power per kerf depth multiplied by the speed the cutting mechanism is moving across a rock surface. It was also found, by reviewing published work, that there have been many comparisons made in the literature that did not take into consideration such things as rock type and shape. Experimental conditions such as the atmosphere where the "cutting" tool and the rock interact have not been accounted for when many of the previous comparisons were made. Sample size in relationship to power density has also not been accounted for.

Introduction

In 1997, a research project funded by the Gas Research Institute (now Gas Technology Institute) revitalized the interest in revolutionizing well drilling using lasers1,2,3. This research demonstrated the feasibility of laser/rock destruction using three U.S. military lasers; MIRCAL, COIL, and CO2 and two Russian lasers; CO and CO2. Tests were conducted on 11 different rock types under varying conditions of sample size and shape, saturation, stress, purge gas, lasing time, pulsing, etc. Details of the study are explained in the above references.

The second phase of the research used what was learned in the first phase and focused on three rock types; Berea sandstones, limestone, and shale, two saturations; air and water and one laser; the Nd:YAG which is located at the Argonne National Laboratory in Argonne, IL. The project was funded by the U.S. Department of Energy (DOE), GTI, PDVSA, and Halliburton. Preliminary work was also done using a Direct Diode Laser located at Native American Technologies in Golden, CO.

During the many technical presentations made over the last five years, many questions regarding topics such as economics, efficiency, beam deliverability, environmental issues, and comparison to other novel drilling methods, as well as traditional rotary methods, arose. These questions have been or are currently being addressed in on-going projects. This paper gives some answers regarding the comparisons to other methods using specific energy as the benchmark. The confusion and varying ways to calculate specific energy are demonstrated and "true" comparisons are made.