Feasibility analysis of coiled tubing drilling with supercritical carbon dioxide

Supercritical CO2 (SC-CO2) fluid has the properties of low viscosity and high diffusion capacity near to gas, and higher density near to liquid. Compared with nitrogen, air, liquid, aerated fluid, foam and other drilling fluids, the supercritical CO2 fluid has a wide range of density which can not only allow it to generate enough torque to run a downhole motor, but also ensure the downhole condition is in an underbalanced state while drilling. Even if the supercritical CO2 fluid invades into reservoir, the reservoir will not be damaged, on the contrary, it can increase the reservoir porosity and permeability further more, reduce flow resistance, and enhance production and recovery. Meanwhile, the velocity of a supercritical CO2 jet is faster than that of water jet and the threshold pressure is lower also resulting in improved rock breaking. When the coiled tubing drilling with supercritical CO2 takes place, it can significantly decrease the coiled tubing drilling system pressure and expand the coiled tubing operating range, it is more suitable for slim hole, microhole, short radius horizontal wells, and complex structures wells. The coiled tubing drilling with SC-CO2 will bring an innovation in the drilling technology, and will become an efficient drilling technique for special reservoir development.