Abstract
Production of natural gas from unconventional gas-hydrate reservoirs faces several challenges. One of them is the well control issue due to the natural gas released from gas hydrates during well drilling. It is very important for drilling engineers to know if the temperature of drilling fluid in the borehole is lower than the critical temperature that causes hydrate dissociation. However, there is no method to predict the fluid temperature with consideration of the effects of Joule-Thomson cooling and drilling cuttings entrained at the bottom hole. This paper fills the gap. An analytical model was developed in this study for predicting temperature profile in drilling gas-hydrate deposits. Result from the analytical model was verified by a numerical model developed using finite difference method. A case study indicates a good consistency between model-implications and field observations. Sensitivity analyses with the model show that the bottom-hole temperature in gas-hydrate drilling is dominated by the temperature and flow rate of the injected drilling fluid. The temperature of drilling fluid in the annulus can become greater than the geo-temperature at the same depth at high fluid flow rate. The Joule-Thomson cooling effect below the drill bit nozzles rapidly diminishes in a short interval above the bottom hole due to the heating effect of geo-thermal gradient. The rate of penetration of drill bit has negligible effect on the fluid temperature profile due to the low percentage of heat flow contributed by the entrained drill cuttings. This paper provides drilling engineers a rigorous method for predicting wellbore temperature profile during drilling gas-hydrates reservoirs.
