Numerical Approach for Temperature Estimation in Geothermal Drilling Operation

Abstract

Temperature affects various drilling parameters and considerations such as drilling mud properties, wellbore stability, and bottom-hole assembly design. Most of the recent publications emphasize analytical solution for temperature profile in the wellbore. Despite providing the simplest approach, the analytical solution is not always doable in complex wellbore system with temperature-dependent fluid properties. Numerical approach taken in this work enables temperature profiling in wellbore that involves a complex trajectory, multiple tubular strings, multiple formations, temperature-dependent fluid properties, and Herschel-Buckley (YPL) fluid rheology. The wellbore is discretized into grids in which piece-wise YPL hydrodynamics and heat transfer calculations are performed, thus enable calculation of downstream grid temperatures with known upstream grid temperatures. This process is repeated until the wellbore bottom is reached. With fluid properties dependent on temperature, both annular and drill pipe fluid temperature have to be solved simultaneously from top to bottom. Both drill pipe and annular fluid surface temperatures have to be specified initially. This approach may lead to difference between drill pipe and annular fluid bottom temperatures if the surface temperature inputs are completely arbitrary. Iterative method is applied on annular surface temperature to match drill pipe and annular fluid bottom temperature values. This iteration is not required if both surface temperature inputs are taken from field data. The program has been tested against arbitrary wellbore trajectories and data from referred publications. The tests show reasonable results or good agreement with referred data.