6 - Energy Extraction from abandoned wells

Abstract

The costs associated with the development of geothermal wells is a major barrier toward the exploitation of geothermal resources, hence energy extraction from abandoned wells is emerging as one of the most promising circular economy approaches in the sector. Globally, the cost of drilling geothermal wells can range from tens of thousands of dollars in the case of small projects for direct use to millions of dollars per well in cases where the wells need to access high-temperature geothermal resources for electricity generation. In Kenya, the cost of drilling a single well is about half a billion Kenyan shillings (USD 5 million), and when wells are abandoned as a result of not being productive after drilling, it is a major economic loss. Important reservoir parameters that determine the productivity of a geothermal well include porosity, permeability, transmissivity, temperature, and fluid saturation. This chapter presents and analyzes the techniques that have been used to stimulate the productivity of abandoned geothermal wells. Although stimulation of abandoned geothermal wells is one of the most promising reclamation approaches, it is hindered by the fact that most of the stimulation techniques that have been explored are still in the infancy stages of development and will need more research in order to be ready to be implemented on a wider scale. Well-established geothermal well-stimulation techniques, including overpressurizing (hydraulic fracturing), thermal fracturing, and matrix acidizing are discussed. The application of other techniques for reclaiming abandoned geothermal wells including casing perforation, high-energy gas fracturing/explosive stimulation, and other techniques with potential for geothermal well stimulation such as acoustic stimulation and electric stimulation are presented. The use of enhanced geothermal systems (EGS) that operate with supercritical CO2 instead of water as heat transmission fluid is introduced. Important questions that should inform the further discourse on abandoned geothermal wells are provided. Based on the current work, future research can focus on (1) exploring the mechanism of novel stimulation techniques including ultrasonic and cavitation techniques on abandoned geothermal wells, (2) establishing unified evaluation criteria for selecting geothermal well stimulation techniques, and (3) developing the basis for identification of potential and determination of geothermal well reclamation.