Research On HTHP ECD Calculation Method Of Oil-based Drilling Fluids Used In Xinjiang Oilfield

The density and rheological properties of oil-based drilling fluids are significantly affected by temperature and pressure,and ignoring the influence of temperature and pressure will lead to a big error in bottom hole ECD calculation results.At present,there are few researches on the variation law of the density and rheological properties of oilbased drilling fluids commonly used in Xinjiang oilfield with temperature and pressure.In order to clarify the variation law of the density and rheological properties of oil-based drilling fluids commonly used in Xinjiang oilfield with temperature and pressure,and to establish an accurate bottom hole ECD calculation model,the following research work is carried out in this paper:(1)Through the high temperature and high pressure density experiment,the compound density model of oil base drilling fluids commonly used in Xinjiang oil field is established,the calculation error of the model is analyzed,and the model is modified.The calculation accuracy of the modified model is high,and the relative error is less than1.9%.(2)The experiment of high temperature and high pressure rheological properties of oil-based drilling fluids commonly used in Xinjiang oil field is carried out,the shear stress prediction model of oil-based drilling fluids is established by multiple linear regression analysis of the experimental data,and the rheological properties of oil-based drilling fluids at high temperature and high pressure were analyzed.(3)The deficiency of traditional circulating pressure loss calculation method is analyzed,and a circulating pressure loss calculation method based on generalized flow index is introduced,which unifies the research method of non-Newtonian fluid circulating pressure loss of different rheological modes with the research method of Newtonian fluid circulating pressure loss.This method is not simplified in the process of derivation,and the calculated result of circulating pressure loss is more accurate than the traditional method.(4)The ECD calculation model of oil-based drilling fluids considering the influence of temperature and pressure is established by combining the compound density model of oil-based drilling fluid,the shear stress prediction model and the circulating pressure loss calculation method based on generalized flow index.Using this model,an example calculation is carried out according to the field drilling data of Xinjiang oil field and the accuracy of the model is analyzed.The calculation results show that the ECD calculation model established in this paper has high accuracy.