Wellbore pressure model for drilling fluid in ultra-deep rock salt formations at high temperatures and pressures

The Kuqa Mountain front area of Tarim is rich in oil and gas resources, but the development of ultra-deep rock salt formation is common, leading to a narrow safety density window and significant impacts on engineering operation safety and wellbore quality, such as overflow and leakage. Managed pressure drilling (MPD) is an effective solution to the problem of drilling in narrow density windows, and a precise wellbore pressure calculation method is essential to ensure the reasonable determination of MPD parameters. Conventional wellbore pressure models treat fluid properties as constant and do not consider the impact of ultra-deep rock salt formation on wellbore pressure calculation, leading to incomplete calculation accuracy that cannot fully meet engineering requirements. In this paper, an improved wellbore temperature field model coupled with the rock salt formation is established. Additionally, rheological experiments on drilling fluids used in the field are conducted and a prediction model for shear stress and density is established based on the varying degrees of temperature and pressure influences. Based on the temperature field of the wellbore and the rheological experimental, a wellbore pressure prediction model is established, and field application is conducted in Keshen Well X. By comparing the measured values, the overall error does not exceed 5%. Compared with neighboring blocks, the rate of penetration has been increased by 73.8%, and the drilling efficiency has been significantly improved. The use of wellbore pressure calculation method, which is studied in this paper, has facilitated efficient operations in drilling ultra-deep rock salt formation.