Integrated Geothermal System Combines Deep Geothermal Storage And Energy Production Management, What Are The Risks?

Abstract

Today, the development of the low-carbon energy mix is implemented in a context of growing environmental constraints and, most importantly, climate urgency. Hybrid energy systems are presently the most efficient and available integrated systems. For electricity production in remote areas, they combine wind, photovoltaics, generators and batteries and are optimized systems capable to ensure energy service quality. The design of hybrid energy systems is fundamentally built around an energy buffer storage solution whose power capacity is used to dimension the extension of the system. In countries with large enough water stocks, hydroelectricity is used mainly as an energy buffer storage solution. This usage allows to stabilize the power distribution and to integrate all sources of power production. By offering a geological solution for energy storage and buffering, geothermal energy can become a high capacity storage solution that could enable an efficient hybridization at a large power grid scale. This solution is potentially achievable in almost all of the world’s sedimentary basins, and unlike hydroelectricity deep underground storage would not be dependent on local water stocks availability. A risk analysis for two underground energy storage and buffering examples, will illustrate the principles of a new application for geothermal energy called IGS (Integrated Geothermal Systems). Like a natural geological trap for hydrocarbons, IGS system requires deep, warm and sealed structure, with: • an interesting storage capacity (reservoir), • reservoir characteristics allowing a good productivity, • an effective energy carrier and phase change fluid, fit for large underground storage. Unlike conventional geothermal exploitation, IGS systems will extract the energy and return it as a cooled fluid into a closed subsurface structure. This production and reinjection is performed into a sealed and constrained geological structure and will obviously require additional energy inputs to counterbalance the frequent and local energy outputs. IGS process draw up rules for the dynamic management of an energy buffer storage, where the natural weakness of the geothermal heat flow is compensated at surface by the thermal storage of natural and free energies (e.g. solar thermal) and power generation surplus (e.g. ENR or nuclear electricity). This dynamic energy management based on determined withdrawals and modelled surface preheating of the energy carrier, is the process, integrated to the geothermal storage of the fluid. Known and discussed heat carrier fluids are LPG and super critical CO2. According to the sum of the challenges represented by the energy transition, clean and balanced energy choices would have to be made preferably, having a system-based and sustainable vision. To date, most energy solutions have been put side by side and have been mainly based on the extraction (and the net degradation) of energy (whether fossil, mineral or poorly renewable, like biomass or conventional geothermal energy), as well as on the random capture of wind or solar energy. Based on well-operated deep geological structures, this paper presents a new possibility for a clean and truly renewable energy solution, thanks to its integrated energy surface/subsurface management. We will also point out that IGS projects can offer a guarantee for clean, economic and sustainable energy services, for the very long term.

AAPG Datapages/Search and Discovery Article #90346 ©2019 AAPG European Region, 3rd Hydrocarbon Geothermal Cross Over Technology Workshop, Geneva, Switzerland, April 9-10, 2019