Experimental and numerical study of the rheological characteristics and flow law of water-based drilling fluids in high-temperature and high-pressure wellbores

The local distributions of both the temperature and pressure have a great influence on the rheological characteristics of the drilling fluid, thereby affecting its flow law in a wellbore. Along these lines, in this work, the rheology of water-based drilling fluid samples under high-temperature (30°C–210°C) and high-pressure (34.5 MPa–172.4 MPa) (HTHP) conditions was systematically analyzed. The constitutive model of the variation of the apparent viscosity of the drilling fluid with the temperature and pressure was successfully established. The analysis revealed that, among the Bingham model, the Power law model, the Herschel-Bulkley (H-B) model, and the Casson model, the H-B model can accurately describe the rheology of the drilling fluid under HTHP conditions. Therefore, the H-B model was used to perform numerical simulations of the flow law of the water-based drilling fluid in the wellbore. The simulation results demonstrated that the drilling fluid viscosity decreased as the depth of the wellbore increased, and was mainly influenced by the temperature. The maximum viscosity inside the drill pipe was mainly concentrated in the middle region, and that of the fluid when flowing in the annulus was mainly concentrated on the side near the outer wall of the annulus. This work provides valuable insights for setting the key parameters of the drilling fluid and wellbore cleaning in the drilling operation of a 1×10⁴ m deep well.