Abstract:
Coiled tubing drilling has become one of the most emerging technological developments and a preferred technique in oilfields. Drilling fluid is required to provide sufficient power to the drilling motor and downhole drill bits and to circulate drill cuttings out of the wellbore. Water is Common used drilling fluid is water. Water is a high density and viscosity fluid, so its pressure loss inside the coiled tubing is high. Additionally, water is an incompressible fluid. Water has no internal energy and can only deliver hydraulic power. This is a big problem when drilling small, deep holes in hard formations.Water cannot supply sufficient power to the drill bit because much of its energy is lost in the tubing due to friction. Therefore, different fluids are being tested and used as an alternative to water. Hydraulic power delivery of compressible fluids to drilling bit is higher than water. Hence, a comparative study of power delivery in coiled tubing drilling by using water, air, supercritical carbon dioxide (SC-CO2), nitrogen, and foam as drilling fluid is proposed. Calculations were performed to evaluate the pressure loss and power delivery by these fluids. It was found that, high injecting pressure of compressible fluids delivered higher enthalpy and power to the drill bit in coiled tubing drilling. Density and viscosity of compressible fluid is lower than water. As a result, frictional pressure loss of compressible fluid is low. Supercritical CO2 delivers higher power than other fluids to drill bit inside the coiled tubing. SC-CO2 density is higher than air but smaller than water, so it can produce enough torque to drive a downhole motor. Frictional pressure loss is lower than water for low viscosity of SC-CO2 fluid. So, SC-CO2 is the most suitable fluid for Coiled tubing drilling.
