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.