High-pressure fluid jet-assisted drilling is attractive for drilling horizontal holes because of the potential for high penetration rate in hard formations using low-cost, small-diameter tools. Unfortunately, the threshold pressure for water-jet erosion of most sedimentary rocks is much higher than the pressure capacity of conventional coiled tubing. Recent experiments have demonstrated that supercritical carbon dioxide (SC-CO2) jets will cut hard shale, marble and granite at much lower pressure than water. SC-CO2 was also shown to enhance mechanical drilling rates. The use of SC-CO2 to drill ultra-short-radius lateral well completions is evaluated here. SC-CO2 is a dense, low-viscosity fluid with excellent hole cleaning capabilities. Conventional under-balanced drilling equipment can be used to control formation pressures while drilling with SC-CO2. SC-CO2 is a non-damaging fluid that should provide enhanced production from completions relative to holes drilled with water-based fluids. The use of SC-CO2 for jet assisted drilling would allow fast drilling of small-diameter, ultra-short radius laterals using low-cost, small diameter coiled tubing equipment.

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