Study On Law Of Gas-liquid Two-phase Flow Heat Transfer In Deep-Water Wellbore

In deepwater drilling, the low temperature of deepwater will effect the density and rheological properties of drilling fluid. The natural gas entering the wellbore will form hydrate in some high pressure and low temperature conditions, which block in the choke line, and et al. These problems are all in connection with temperature in wellbore, the key scientific problem is the heat transfer of wellbore gas-liquid two phase flow in deepwater low temperature condition. The laws of heat transfer of seawater with the fluid in the riser above the mud line is different from that below the mud line, it is significant to be studied technically. Although some researches on the calculation of deepwater wellbore temperature field have made some progress, but the existent wellbore temperature field models all exclude the influence of flow pattern and low temperature of deepwater. So studing the laws of heat transfer of gas-liquid two phases flow in deep water is very important for amending the theoretical model and explorating oil and gas in deepwater.The heat transfer models of bubbly flow, slug flow, churn flow and annular flow are built by considering the feature of each flow pattern and the distribution of gas and liquid. According to the flow fingerprint of slug flow, the structure of slug flow is demarcated, that contains three parts of transition segmen, Taylor bubbly segmen and steady segmen. And the void fraction distribution of slug flow and the length change of transition segmen in radial direction are studied.The laws of gas-liquid two-phase flow heat transfer in low temprature of deepwater conditions are studied on the“deepwater in-tube gas & liquid two-phase flow heat transfer simulated system”. The results are as follows: in bubbly flow, the heat transfer coefficient rised up with the liquid flow velocity. In slug flow, the heat transfer coefficient rises up with the liquid flow velocity, the gas flow velocity affected the heat transfer little, and the heat transfer coefficient decrease with the average void fraction. For the inherent behaviour of gas core and liquid film near the wall in churn flow, the influence of gas velocity, liquid velocity and average void fraction on the heat transfer is small. In annular flow the heat transfer coefficient rises unlinearly with the liquid velocity, decreases unlinraly with the gas velocity, and decrease quickly with average void fraction.The experiment of single phase fluid heat transfer is done in simulating deepwater conditon, the result is: in low temperature of deepwater condition the influence of velocity on heat transfer is almost same with that in ordianry temperature in turbulence, but in the laminarer the influnce enhances notably.According to the feature of dual-gradient drilling technology by injecting gas, the influence of ocean temperature and formation temperature, heat transfer fingerprint of each flow pattern, the heat transfer fingerprint of low temperature sea flow, the distribution of sea flow speed and some other factors are taken into account, the multiphase flow governing equations of dual-gradient drilling technology by injecting gas are established, they are continuity equations, momentum equations and energy equations, and the solution is provided.On basis of the calculation model above, a software has been made, which contains the influence of low temperature of deepwater and the laws of heat transfer in each flow pattern. By changing the well depth, water depth, mud discharge, gas discharge, geothermal gradient, inlet temperature and some other parameters, the temperature in wellbore is computed, the influence of these factors on the wellbore temperature are studied, the results are as follows:The temperature in annulus is mainly affected by the water depth, and well depth mainly affects the temperature in annulus below the seabed. The mud discharge exerts great influence on the temperature in annulus, as the mud discharge increases, the temperature in annulus changes more gently. Gas discharge has little influence on the temperature in annulus. As the inject temperature increases, the temperature in annulus rises. The geothermal gradient only exertes influence on the temperature in annulus below the seabed and has no influence on the flow regime. The range of temperature in the riser annulus decreases remarkably when the risers are covered by insulating layer.