考虑材料非线性的环空增压预测模型

A prediction model of annular pressure build-up considering material nonlinearity

为了准确预测深水油气井钻采过程中的环空增压,建立了改进的环空增压计算模型。该模型考虑了材料的非线性性质和套管变形的影响,其中材料的非线性性质包括了流体热膨胀系数和压缩系数随温度、压力变化的性质以及套管弹性模量、热膨胀系数随温度变化的性质。模型中的非线性函数由插值方法获得,并进行了实验验证和误差分析。计算中,将各个环空沿轴向进行分段,并将变温以增量的方式进行加载。通过算例,将该模型与忽略材料非线性性质和套管变形的简化模型进行了对比,讨论了各非线性参数及井筒变温对环空增压预测结果的影响。结果表明,与改进模型相比,简化模型的误差范围为2.51%~26.11%;在变温较小的深水井中,同时忽略材料非线性和套管变形对环空增压影响较小;而井筒变温较大时,忽略材料非线性后造成的环空增压预测误差非常显著;流体膨胀系数对环空增压的预测结果影响最大,若将流体膨胀系数取为常数,则误差达到70%。

To accurately predict the annulus pressure build-up(APB)during the drilling and production of deepwater oil and gas wells,the paper establishes an improved APB calculation model.The model considers the impacts of nonlinear properties of the material and casing deformation.The nonlinear properties of the material include the variations of thermal expansion coefficient and compression coefficient of fluid with temperature and pressure,and the variations of elastic modulus and thermal expansion coefficient of casing with temperature.The nonlinear function in the model is obtained by interpolation method,and this study also performs experimental verification and error analysis.During calculation,each annulus is segmented in the axial direction,and the variable temperature is loaded in an incremental manner.Through an example,this model is compared with a simplified model that ignores material nonlinearity and casing deformation;additionally,the effects of various nonlinear parameters and variable temperature of wellbore on the prediction results of APB is explored.The results show that compared with the improved model,the error range of the simplified model is 2.51%-26.11%;in deepwater wells with a small range of variable temperature,ignoring material nonlinearity and casing deformation has a small influence on APB;within a large range of variable temperature,the prediction error of APB caused by neglecting material nonlinearity is very significant;the expansion coefficient of fluid has the greatest influence on the prediction result of APB.If the expansion coefficient of fluid is taken as a constant,the error may reach 70%.