Fluid circulating temperature model for workover operations
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abstract
An accurate fluid temperature profile in both tubing and annulus during circulation is desirable to allow prediction of circulation rate. However, because the circulating fluid exchanges heat with the formation, fluid temperature changes both with time and depth. Consequently, the fluid's intrinsic properties of density and viscosity change as circulation time is increased, thereby impacting the optimal pumping rate. In this work, we present generalized analytical models for computing circulating fluid temperature in conduits, for both forward- and reverse-circulation cases, as a function of circulation time and well depth. In the first approach, we use an energy balance for fluid in a tank to express its temperature as a function of time. This model assumes unsteady-state heat transport in the formation and steady-state heat flow in the tubulars. In the second approach, the changing heat flux at the wellbore/formation interface is accounted for by the principle of superposition in time. The heat flux schedule is represented by adding constant heat sources at successive times. The model represents a fully transient coupled wellbore/reservoir heat transfer formulation. Results indicate that fluid temperatures estimated using the new approach can differ significantly from those estimated with models which neglect tank temperature variations or formation heat flux. The difference grows with increasing temperature difference between the bottomhole and the wellhead. Thus, for estimating circulating fluid temperature in a cold environment, varying tank fluid temperature and formation heat flux need to be accounted for.
