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Generally, the temperature and pressure of drilling fluid increase with the increase in depth. By the increase in pressure, viscosity of the drilling fluid increases due to compression whereas high temperature decreases its viscosity due to thermal expansion. Under these extreme conditions, well control problems become more complicated. Current logging tools even at their best are unreliable because the provided temperature of the bottom-hole is often well beyond their operational limits. This literature shows the limited experimental data on the properties of the drilling fluid over 350°F and 20,000psig. The way of extrapolation of the properties of fluids at extreme-HT/HP (XHT/HP) conditions could result in significant inaccuracies in the well hydraulic calculations. This study is focused on developing a methodology of testing the drilling fluids at HT/HP conditions using viscometer, which is capable of accurately measuring the drilling fluids properties up to 600°F and 40,000psig. A series of experiments were performed on typical XHT/HP oil-based drilling fluids to investigate the effects on rheological properties at these extreme conditions (200 to 600°F and 15,000 to 40,000 psig). The results of experiments demonstrated that various drilling fluids disintegrate at different temperatures depending upon their composition. In short, the combined effect of the temperature - pressure on the rheology of the drilling fluid is complex. This research is important because correct design of drilling fluid is a first important step to control the rate of incidents often associated with operation of the HT/HP. According to Minerals Management Service (MMS), more than 50% of the reserves of oil and gas in the U.S. are under 14,000ft subsea. So the drilling in HT/HP is quickly becoming commonly faced phenomenon particularly in the Gulf of Mexico, where HT/HP resistant drilling fluid is commonly used to ensure safe and successful operation.
