On the Practical Aspects of Determination of the True Reservoir Temperature under Spherical Heat Flow Conditions

This paper presents additional unpublished aspects related to a recenty published method to calculate equilibrium formation temperatures, under spherical flow conditions in geothermal reservoirs. This method considers that the evolution of equilibrium bottom-hole temperatures following a cold fluid circulation time during drilling, follows a radialspherical pattern. F'rom the mathematical solution to this heat transfer boundaryvalue problem, it can be concluded that formation temperature recovery after a cold fluid circulation period, follows a straight line relationship on a T vs. l/& plot. The interception of this plot provides the formation equilibrium temperature. An advantage of this method compared to similar methods previously published, is that no explicil knowledge of fluid circulation lime previous to shut-in is required. On the other hand, it usually estimates equilibrium formation temperatures somehow higher than those obtained from the standard Horner-type of analysis. This is due to the fact that the proposed method takes into account the additional vertical heat transfer component at bottom-hole, while the Horner type of anlysis neglects any vertical heat transfer contribution, since it assumes a purely radial-cilindrical heat flow in the formation. Field data are used to illustrate the proposed technique.