Temperature transient analysis of a very high-permeability geothermal well: A numerical modelling approach

Abstract

Geothermal well tests usually analyse the pressure response throughout a series of injection or production steps assuming isothermal conditions. However, the downhole tool also records the temperature response of the well. In recent years, temperature transient analysis (TTA) has attracted attention because of the improvement of sensors and computational tools, providing additional information about the reservoir and wellbore. This work examines a unique geothermal reservoir characterised by a highly fractured permeable zone, presenting a minimal pressure response during well (completion) testing. However, the temperature response shows a noticeable falloff and buildup throughout the injection-falloff test. We attempted to analyse the pressure response and its derivative using the numerical pressure transient analysis (PTA), but this did not yield reasonable results due to the small change in the transient pressure. Then, we included the analysis of temperature response utilising geothermal TTA through an updated numerical modelling framework. Employing this new approach made it possible to calculate the reservoir parameters by including temperature analysis through a series of time steps to examine the well-test data. Geothermal TTA showed the potential to complement PTA when insufficient. The examination of wells with very high permeability should include TTA to obtain reliable reservoir parameters.