Application of Supercritical CO_2 to Gas Circulation Drilling

Supercritical CO2 fluid has the characteristics of high density as liquid and low viscosity as gas, and high diffusion coefficient. As a drilling fluid, it is much better than other ordinary ones because it can(:1)increase the rock breaking efficiency of water jetting(;2)raise the drilling rate(;3)protect the oil and gas reservoirs; and(4)reduce some downhole accidents. In addition, gas circulation drilling is one technology which can significantly reduce the drilling cost. By the technology, the cutting-carrying gas from wellhead may be separated and fine filtered using ground gas recycling and processing equipments, and then the gas is reinjected after compressing and pressurizing. In this paper, the property and advantage of supercritical CO2, and the principle and procedure of gas circulation drilling are presented. Moreover, a new conception combining these two is put forward.