Investigation Of Flow Law Of Cuttings Carrying By Foam Fluid In Vertical Annular Of Geothermal Drilling

Geothermal resource is a kind of clean and efficient unconventional energy with huge reserves.At present,the exploitation of geothermal resource has entered a rapid development stage.In geothermal drilling,foam drilling is a very important technical means,and the efficiency of cuttings carrying has always been a very important issue in the drilling process,because it's an important basis for safe drilling and designing reasonable hydraulic parameters.Referencing the previous research results and methods,knowledge about multiphase dynamics,computational fluid dynamics and heat transfer is used for the study of unsteady flow and heat transfer of foam in vertical geothermal well,as well efficiency of cuttings carrying of foam in annular.The phase transition model of air foam was deduced based on phase transition and thermodynamic theory and obtained the phase change judgment criterion.The rheological properties of air foam under high temperature and high pressure were studied by HTHP rheometer and obtained the rheological pattern of the foam as well as the relationship between foam quality,temperature and pressure and rheological parameters.A one-dimensional transient foam flow and heat transfer mathematical model was established based on the theory of fluid flow and heat transfer,in which the frictional heat of foam flow and the phase transition were considered.The influence of various factors on the temperature and pressure distribution of foam in annular was studied,such as gas and liquid injection rate.And the influence of rheology on wellbore flow and heat transfer was also studied.On the basis of solid-liquid two-phase flow model and heat transfer theory,a one-dimensional transient foam carrying cuttings mathematical model was established,and the modified SIMPLEC algorithm and Gauss-Seidel method were used to discrete and solve the model.The distribution of cuttings concentration in annular was studied,and obtained the influence of drilling parameters on the distribution of cuttings concentration in annular.Meanwhile,the parameter sensitivity analysis of pressure and cuttings concentration in bottom hole was carried out.And the effect of phase transition on cuttings-carrying efficiency rocks was also studied.