SELECTION OF CANDIDATE GEOTHERMAL WELLS FOR DEFLAGRATION

Abstract

Deflagration uses the energy created by the expanding gas generated from the slow burning of propellant to enhance the near wellbore permeability of an inherently tight or skin-damaged well through the creation and propagation of fractures. Deflagration is an established stimulation method for oil and gas wells but the application of deflagration on geothermal wells is limited. One of the difficulties of the application of the deflagration technology to a geothermal well is the lack of definitive criteria for determining what makes a good candidate well for deflagration.
A matrix for selecting candidate wells for deflagration was developed based on published geothermal case studies and consultation with subject matter experts on deflagration. The matrix included resource potential and well suitability for deflagration as main factors. The resource potential considered both reservoir and well characteristics. Reservoir properties, e.g. well location, number of offset producing wells, and average power output or injection capacity were used for determining the potential of the well to produce steam or accept brine injectate. Well characteristics, e.g. shut-in temperature, permeability, skin, injectivity ratio and potential gain in output were included for estimating well potential. The suitability of a well for deflagration was determined based on its primary feedzone characteristics and structural geology.
The matrix was used to evaluate each deflagration target depth based on rock properties, geological and drilling indicators, presence of geological structure and permeability, and capacity of the feedzone. The evaluation method, however, was limited by the absence of a geomechanical model hence book values for rock properties and regional stress regime were used for the assessment.