Feasibility analysis of coiled tubing drilling with supercritical carbon dioxide

摘要

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 CO2fluid 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 CO2fluid 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 CO2jet 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 CO2takes 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-CO2will bring an innovation in the drilling technology, and will become an efficient drilling technique for special reservoir development.