Subsurface Located Geothermal Well – Case Study

Abstract The recovery of geothermal energy has become very attractive in the last decades. Advantages like the small footprint, the waste-free and CO2 neutral energy production and the continuous geothermal resource, will highly promote geothermal energy usage soon. This paper presents a case study of a subsurface located geothermal well. The overall approach is to use existing subsurface facilities and construct the geothermal energy recovery system within them.Currently, the generated power, produced by geothermal energy systems, is more expensive than energy produced from competitive sources, because of the costs associated with the construction of the wellbore. To extend the use of geothermal energy, its recovery costs have to be reduced. The primary wellbore cost driver is the depth. The drilling costs rise exponentially with depth. When situating a geothermal power plant in an underground structure, the temperature at the start point of such a geothermal well is already at an elevated temperature level, and the total amount of meters to be drilled is substantially reduced, thus saving drilling costs. A primary focus of this paper is, on the one hand, the amount of energy to be recovered and, on the other hand, the technical realization of such a project. The results have shown that the efficiency of subsurface located geothermal wells is higher than for surface located ones. Technical equipment and technology for drilling subsurface are already available today. A case study for investigating the influence of parameters like depth and number of wells is performed. Depending on geology, simulations have indicated that it is from the technical point of view more efficient to drill a deeper well in comparison to drill several shallow subsurface wells. Nevertheless, from the economic point of view, currently, surface drilled wells are more economical.So far, a drilling rig has never been positioned below ground, and the legal framework is just partially defined so far. This paper presents a case study of a subsurface located geothermal well positioned in existing underground infrastructure. This case study shows the vast potential but indicates the risks and limitations as well.