The results of a study of the effects of the temperature and pressure conditions in high temperature/high pressure wells on drilling fluid equivalent circulating density and consequently bottom-hole pressure are presented in this paper. High temperature conditions cause the fluid in the wellbore to expand, while high pressure conditions in deep wells cause fluid compression. Failure to take these two opposing effects into account can lead to errors in the estimation of bottom- hole pressure. The rheological behavior drilling fluids is also affected by the temperature and pressure conditions. A simulator called DDSimulator was developed to simulate the wellbore during circulation. A Bingham plastic model was employed to express the rheological behavior of the drilling fluids studied, with rheological parameters expressed as functions of temperature and pressure. The Crank-Nicolson numerical discretizing scheme was employed in the DDSimulator for the evaluation of the wellbore temperature profile. The results of the simulation show that higher geothermal gradients lead to lower bottom-hole pressure. The inlet pipe temperature did not have a significant effect on the bottom-hole temperature and pressure, and higher circulation rates result in lower bottom-hole temperature and higher bottom-hole pressure.
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