气液两相流循环温度和压力预测耦合模型

为保证欠平衡钻井安全钻进，需要给欠平衡钻井设计提供井筒温度和压力分布等基础数据。基于气液两相流钻井液循环时的流动特征和井筒与地层的传热机理，建立了适用于欠平衡钻井预测气液两相流钻井液循环温度和压力的耦合模型，给出了模型的离散方法和求解方法。在模型的求解过程中，考虑了温度和压力对气相（空气、氮气）的密度、比热、比焓、动力黏度、热导率等热物性参数的影响及热源对气液两相流钻井液温度场的影响，保证了气液两相流循环温度和压力的计算精度。基于大庆油田升深2-17井充氮气欠平衡钻井试验数据，利用气液两相流钻井液循环温度和压力预测耦合模型对欠平衡钻井时的井底温度和压力进行了计算，计算结果与实测结果吻合程度高，验证了模型的有效性。对比分析了以地温、地面温度作为气液两相钻井液温度和考虑井筒换热3种情况下的环空压力剖面特征，为欠平衡钻井设计及控压钻井设计和施工提供了理论基础和技术支持。

A coupled model for wellbore temperature and pressure prediction of gas-liquid drilling fluid

Wellbore temperature and pressure profiles created by circulating gas-liquid two phase drilling fluid are significant to well program and safety drilling for underbalanced drilling operations. On the basis of gas-liquid flow patterns and heat transfer mechanisms among wellbore and formation, a coupled model for the predication of wellbore temperature and pressure of gas-liquid two phase drilling fluid circulation, which is suitable for underbalanced drilling, is developed, and the discretization method and solving method of the model are presented. In order to ensure the calculation accuracy of temperature and pressure of gas-liquid two phase drilling fluid circulation, the effect temperature and pressure on physical parameters including density,specific heat, enthalpy, viscosity and thermal conductivity, and the effect of heat source on the temperature field of gas-liquid two phase drilling fluid were considered during the solving process of the model. Based on the test data of nitrogen underbalanced drilling from the well Shengshen 2-17 in the Daqing Oilfield, bottom hole temperature and presure are calculated according to the coupled model. The calculation results are matched well with measured, which verify the validity of the model. Characterustucs of annulus pressure under three conditions（gas- liquid two phase drilling fluid of formation tempreture and surface temperature, and heat exchange of wellbore）have been analyzed to provide theoretical basis and technical support for the design and construction of underbalanced pressure drilling.