深井井筒油基钻井液密度与液柱压力解析模型

Analytic Model of Oil-Based Drilling Fluid Density and Wellbore Liquid Column Pressure in Deep Wells

高温高压深井在钻井和完井时,由于钻井液在井筒内受到温度和压力的双重作用,使得地面测量的钻井液密度与井筒内实际密度存在差异,导致井筒液柱压力难以准确计算。分析国内外有关油基钻井液密度的预测模型,前人的模型均为特定配方条件下少数实验数据回归的经验模型,不具有通用性,且计算精度难以满足深井(尤其是超深井)的需求。为此,采用数学解析法建立精确的钻井液密度和液柱压力预测模型。与多位学者的经验模型对比,认为多数经验模型为新建解析模型的简化,该解析模型能更全面准确地反映温度和压力对钻井液密度的影响。在实际应用时,将油基钻井液视为基础油、盐水及固体材料的混合物,通过室内实验数据确定基础油的密度函数,可实现多种配方及油水比的油基钻井液密度及井筒液柱压力的预测。

During the drilling and completion in high-temperature and high-pressure deep wells,there are differences between the mea-sured drilling fluid density on the ground and actual drilling fluid density in wellbore because the drilling fluid is affected by both tempera-ture and pressure,which will lead to the difficulties in accurate calculation of the drilling fluid pressure in the wellbore.Based on the inves-tigation on the prediction models of oil-base drilling fluid density at home and abroad,it is considered that all the previous models are not general and the calculation accuracy can’t meet the demands of deep wells,especially ultra-deep wells because they are empirical models using a few experimental data under the condition of specific formulas.Therefore,the paper uses a mathematical analytical method to estab-lish a precise model to predict drilling fluid density and drilling fluid column pressure.Compared with the empirical models of many schol-ars,it is concluded that most empirical models are the simplified forms of the newly-established analytical model which can reflect the in-fluences of temperature and pressure on drilling fluid density more fully and accurately.In the actual application,regarding the oil-based drilling fluid as the mixture of base oil,salt water and solid material,the prediction for oil-based drilling fluid density and wellbore liquid column pressure with different formula and oil-water ratio can be performed.