Rheological properties of oil-based drilling fluids at high temperature and high pressure

The rheological properties of two kinds of oil-based drilling fluids with typically composition were studied at pressures up to 138 MPa and temperatures up to 204. using the RheoChan 7400 Rheometer. The experimental results show that the apparent viscosity, plastic viscosity and yield point decrease with the increase of temperature, and increase with the increase of pressure. The effect of pressure on the apparent viscosity, plastic viscosity and yield point is considerable at ambient temperature. However, this effect gradually reduces with the increase of temperature. The major factor influencing the rheological properties of oil-based drilling fluids is temperature instead of pressure in the deep sections of oil wells. On the basis of numerous experiments, the model for predict the apparent viscosity, plastic viscosity and yield point of oil-based drilling fluids at high temperature and pressure was established using the method of regressive analysis. It is confirmed that the calculated data are in good agreement with the measured data, and the correlation coefficients are more than 0.98. The model is convenient for use and suitable for the application in drilling operations.