海上高温高压井环空ECD精细预测模型

为了准确预测高温高压井环空ECD，基于高温高压下钻井液流变性测试数据，利用多元非线性回归得到了钻井液密度和流变参数计算模型。通过将钻井液密度和流变参数计算模型与井筒传热模型耦合，建立高温高压井环空ECD精细预测模型。相比Drillbench软件计算结果，该模型更接近于实测PWD数据，误差更小。实例井计算结果表明，循环钻进过程中，下部环空温度不断降低，钻井液密度和稠度系数受温度影响不断增加，导致环空ECD不断增加；钻井液排量与地温梯度是影响环空ECD分布的关键因素，排量越大，环空压耗越大，进而环空ECD也越大；地温梯度直接影响环空温度分布，地温梯度的增加将导致环空ECD的不断降低。 

A Precise Model for Prediction of Annular ECD in Offshore HTHP Wells

To accurately predict the annular ECD of high temperature high pressure (HTHP) wells, a model for calculating the density and rheology of drilling fluids was established through multielement nonlinear regression based on the rheological data of drilling fluids obtained under HTHP conditions. By coupling this model with the heat transfer model of wellbore, a precise prediction model for calculating the annular ECD of drilling fluids under HTHP conditions was established. Compared with the results obtained using the Drillbench software, this model gives results that are closer to the measured PWD data. Results from the model using actual operation data showed that during drilling operation, as the temperatures in the lower part of the annulus are continuously decreasing, the density and consistency index of the drilling fluid are continuously increasing, resulting in continuous increase in the annulus ECD. The flow rate of drilling fluid and the geothermal gradient are two key factors affecting annular ECD; the higher the flow rate, the higher the annular pressure losses, and hence the higher the annular ECD. Geothermal gradient directly affects the distribution of temperatures in the annulus, and increase in the geothermal gradient results in continuous decrease in annular ECD.