An Energy Based Comparison of Alternative Drilling Methods

Abstract

During the last decades, non-conventional solutions for more economical well bore drilling have been investigated. Big research efforts and budgets have been spent on alternative drilling methods; such as laser drilling or jet assisted drilling. Simplified assumptions predicted a big future for such technologies. However, to get a better and more realistic picture of the feasibility of such unconventional ways to drill rock, the ability to apply them in field scale applications needs to be questioned. In this paper a holistic energy approach to evaluate drilling alternatives is proposed. To evaluate the energy balance of the drilling system the amount of energy generated, e.g by the rig at surface, needs to be put in comparison with all system energy consumption to lead to an effective energy available to destroy rock at the bottom of the hole. To test this concept a small scale laboratory setup is used to compare different drilling methods under similar conditions. This paper presents a systematic approach using an energy concept to compare alternative drilling methods on a laboratory scale. In this first approach laser assisted spallation and conventional drilling were compared. As a by-product, also the optimum mode for spallation drilling, continuous versus pulse wave, will be presented.

Laser Drilling Using Nd:YAG on Limestone, Sandstone and Shale Samples: ROP Estimation and the Development of a Constant ROP Drilling System

“…Elahifar et al (2011) has demonstrated that granite can withstand higher laser power intensities while remaining in the spallation zone than sandstone which began to exhibit lower ROP, indicating a shift from spallation to melting, after increasing laser power intensity past 4.8 kW. Granite, on the other hand, continued to have a higher ROP as laser power increased past 4.8 kW, indicating that it remained in the spallation zone.…”

“…When energy is absorbed by the rock, it can spall, melt, or vaporize (Elahifar et al 2011). As radiation is absorbed, the grains in contact with the beam quickly increase in temperature and expand by a small yet significant amount.…”

“…If the energy being absorbed is greater than the energy dissipated by the rock, the local temperature will quickly rise to the melting point (Gahan et al 2001). The ultimate product is a smooth glass-like melt that coats the walls of the hole (Elahifar et al 2011). If temperature continues to increase rapidly, the rock will begin to vaporize.…”

“…Elahifar et al (2011) showed that a continuous beam yields higher ROP than a pulsed beam, keeping all other parameters constant. However, it was noticed that a continuous laser beam caused a shift to the melting zone much sooner than a pulsed beam.…”

“…Instead, a gas purging system is used to remove the cuttings. Elahifar et al (2011) has demonstrated that the purging gas used to lift cuttings to the surface had an effect on the ROP, even though this effect was small. He also observed that COIL performs better within a nitrogen environment than an argon environment.…”