Study On Rheological Properties Of Drilling Fluid At High Temperature And High Pressure

As oil and gas exploration and development gradually develop into deep formation and deep water,the number of high temperature and high pressure wells is constantly increasing,which poses new challenges for drilling operations.In the calculation of hydraulic parameters of conventional well drilling engineering,the traditional calculation model often ignores the influence of temperature and pressure on the rheology of drilling fluid,but in the high temperature and high pressure wellbore,the span of temperature and pressure at the bottom of the well is large,and the influence of temperature and pressure on the rheological properties of drilling fluid is large,which can not be ignored.With the development of computer application technology,the improved hydraulic parameter calculation model begins to consider the effect of temperature and pressure on the actual rheology of drilling fluid,but the range of temperature and pressure used is limited,and the drilling fluid system used in high temperature and high pressure wells is more complicated,which makes the calculation error of hydraulic parameters large and causes frequent well blowout and leakage in some formations whose safety drilling pressure window is narrow.In this paper,the OFITE high temperature and high pressure rotary viscometer was used to conduct high temperature and high pressure rheological experiments on 4 water-based drilling fluids and 3 oil-based drilling fluids used in the field.The relationship between rheological properties of each drilling fluid and temperature and pressure in the experimental temperature and pressure range is analyzed.Multivariate nonlinear regression analysis was carried out on the experimental data,and based on this,a rheological model of drilling fluid suitable for high temperature and high pressure range is proposed.The model agrees well with the experimental data,with the determination coefficients(R²)reaching 0.99 except for individual points.Compared with the existing rheological models,the rheological model proposed in this paper has a smaller relative error in the shear rate less than 200 s^-1.Combining the widely accepted Arrhenius equation describing the relationship between rheological parameters and temperature of drilling fluids,this paper proposes an improved prediction model of apparent viscosity?_a,plastic viscosity?_p and yield point?₀ of drilling fluid on the basis of experiments and the rheological parameters prediction model proposed by predecessors.The model is in good agreement with the rheological parameters of drilling fluids obtained in this paper,and its determination coefficient(R²)was greater than 0.95.Under the high temperature and high pressure experimental conditions,the maximum relative error of apparent viscosity and plastic viscosity prediction does not exceed±11%.It can accurately predict the rheological parameters of each drilling fluid according to the temperature and pressure conditions.At the same time,using the experimental data of two oil-based drilling fluids published in the literature,the prediction accuracy of the proposed model is compared and analyzed,which proves that the proposed model is reliable for predicting the rheological parameters of drilling fluids.