Geothermal well testing

Abstract

Geothermal wells are fundamental components in geothermal research and utilization and improved understanding of geothermal systems during the last century coincided with geothermal wells becoming the main instruments of geothermal development. Geothermal wells provide access deep into the systems, not otherwise possible, which enables a multitude of direct testing and measurements of conditions at depth. The testing made possible through wells includes well testing, one of the main tools of geothermal reservoir physics/engineering. Through well testing and consequent pressure transient analysis the main reservoir parameters, such as permeability and storativity, can be estimated along with reservoir boundary conditions, if a test is sufficiently long-lasting. Such estimates consequently provide key information for conceptual model development. Pressure transient analysis is performed on the basis of appropriate reservoir models, often the well-known Theis model, and involves in fact model simulation of the pressure transient data collected. Well tests range from very short step-rate injection or production tests, via longer production (discharge or pumping), pressure build-up and interference tests to longterm (months – years) reservoir testing, often involving several wells. Tracer testing, also a kind of well testing, is the most important tool for the purpose of assessing the danger of production well cooling during long-term reinjection, if combined with comprehensive interpretation and cooling predictions (reinjection modelling).