Accurate Prediction Model for Rheological Properties of Drilling Fluids at High Temperature and High Pressure Conditions

Abstract

Abstract Tremendous amounts of hydrocarbons are located in deeper formations, such as in Tarim basin of China, some reservoirs buried so deeply (>7600m) that we experience higher temperature (>180°C) and pressure (>180MPa). And the drilling fluids rheological properties are often affected by HTHP, the careful research on the drilling fluids rheological properties at HTHP is very important for precisely predicting ECD as well as controlling the bottomhole pressure. An accurate prediction methodology of HTHP drilling fluids rheological properties was formulated, which can accurately predict the HTHP rheological parameters. First, the rheological properties of a high density (2.04sg) oil-based drilling fluid at high temperature and pressure were measured. The experimental results indicate that the pressure effect on the rheological properties at ambient temperature was considerable, and this effect could be gradually reduced with the increase of temperature. Second, based on the experimental results, a comprehensive prediction model of HTHP rheological parameters was established, a novel mathematical model for calculating the HTHP shear stress of different shear rate was formulated, the influence of high temperature was taken into account first and then the comprehensive influence of high temperature and high pressure was taken into account too. Based on the mathematical model, we can obtain the HTHP shear stress of different shear rate easily. Based on the HTHP shear stress, a utility HTHP rheological model optimization method and parameters calculation model was proposed. Because of this model related the HTHP shear stress to the influence of HTHP directly, and then calculated the rheological parameters, rather than relating the specific rheological parameters to HTHP as the traditional models, therefore the prediction model is applicable for all rheological model (Bingham, Power-Law, Herschel-Bulkely, Robertson-Stiff et al.). Finally, a novel HTHP rheological properties analyzing system was developed, through which the HTHP rheological parameters can be obtained easily, a series predictions of this model have been compared with the experimental data about different type drilling fluids (oil-based, synthetic-based fluids), and the results show very good agreements with the experimental data. Therefore it can be used to accurately predict the rheological parameters and calculate the hydraulic parameters in the HTHP conditions while drilling.