EGS Sistemi Geotermici Potenziati Univ.-Prof. Dr. Gioia Falcone Clausthal University of Technology Institute of Petroleum Engineering Rome, June 20 th, 2014
Summary What is EGS? Deep Geothermal = EGS? Cataloguing Deep Geothermal by Depth, Temperature, Flow Rate, Rock Type, Stimulation Methods and more Nomenclature Misunderstandings Lessons Learnt / Conclusions Institute of Petroleum Engineering TU Clausthal 2
Deep Geothermal = EGS? MIT definition (2006) Engineered reservoirs that have been created to extract economical amounts of heat from low permeability and/or porosity geothermal resources. For this assessment, we have adapted this definition to include all geothermal resources that are currently not in commercial production and require stimulation or enhancement. EGS would exclude high-grade hydrothermal but include conduction dominated, low-permeability resources in sedimentary and basement formations, as well as geopressured, magma, and low-grade, unproductive hydrothermal resources. In addition, we have added coproduced hot water from oil and gas production as an unconventional EGS resource type that could be developed in the short term and possibly provide a first step to more classical EGS exploitation Institute of Petroleum Engineering TU Clausthal 3
Deep Geothermal = EGS? EGEC definition (2012) An EGS is an underground reservoir that has been created or improved artificially Institute of Petroleum Engineering TU Clausthal 4
Deep Geothermal Enhanced (or Engineered) Geothermal Systems Institute of Petroleum Engineering TU Clausthal 5
What is Deep Geothermal? Jules Verne, Voyage au centre de la Terre, 1864 Institute of Petroleum Engineering TU Clausthal 6
What is Deep Geothermal? There is no precise definition! Minimum depth of 400 m is usually accepted. 400 m is the boundary set in the German Association of Engineers (VDI) Guideline 4640. Is there a maximum depth? Deepest bottomhole temperature (BHT) measurements to date are 180 o C at 12,261 m in the Kola super-deep borehole SG-3, Russia, and 265 o C at 9,101 m in the deep KTB borehole, Germany. Institute of Petroleum Engineering TU Clausthal 7
How Deep? What BHT? (Breede et al., 2013) Institute of Petroleum Engineering TU Clausthal 8
So if T is the target, it seems that depth cannot be used as a universal cut-off value....and T alone does not ensure project s feasibility. End use defines min flow rate (Q) & T required at surface, vis-à-vis project s life span heat flux vs. time e.g., for an EGS doublet system to be of commercial size, assuming a depth > 3 km and T > 150 C, the system should operate at flow rates between 50 and 100 L/s and produce an electric power of 3-10 MW e over a life of at least 25 years (Jung, 2013). Institute of Petroleum Engineering TU Clausthal 9
What Flow Rate? (Breede et al., 2013) Institute of Petroleum Engineering TU Clausthal 10
Assuming Q & T are proven in the short-term, how is long-term heat recharge ensured?.is fluid the recuperator, or rock? Conductive vs. convective/advective Hydrothermal vs. petrothermal Crystalline vs. sedimentary Dry vs. wet Competent vs. naturally fractured Institute of Petroleum Engineering TU Clausthal 11
Rock Type & Reservoir Stimulation Method Original Hot Dry Rock concept based on multi-zone hydraulic fracturing in competent crystalline formations. Original EGS concept based on open-hole massive injection in naturally fractured crystalline formations. More recent EGS concept based on multi-zone massive injection (with the objective of generating multiple wing cracks) in naturally fractured crystalline formations. (Jung., 2013) (Breede et al., 2013) Institute of Petroleum Engineering TU Clausthal 12
Induced Seismicity (Breede et al., 2013) Institute of Petroleum Engineering TU Clausthal 13
Nomenclature Misunderstandings? -1 Tiefe Geothermie (Bohrtiefe > 400 m) No EGS Institute of Petroleum Engineering TU Clausthal 14
Nomenclature Misunderstandings? -2 December 2013 (EGEC, 2013) Institute of Petroleum Engineering TU Clausthal 15
Nomenclature Misunderstandings? -3 November 2013 (Breede et al., 2013) Institute of Petroleum Engineering TU Clausthal 16
Key Lesson Learnt Lack of a clear, universal EGS definition! And perhaps one cannot exist, considering the variety of reservoir environments. Yet, we expect to secure tailored subsidies for EGS or Deep Geothermal projects Better to discontinue the use of EGS Need to re-focus on petrothermal, hydrothermal, geopressured, HSA.
Conclusions EGS conveys multiple meanings. The typical EGS system does not exist. The geothermal community does not have a universally accepted and unambiguous definition of deep geothermal or EGS. This lack of clarity may constitute a potential obstacle to the implementation of tailored subsidies. Recommendation to discontinue the use of EGS and re-focus on petrothermal, hydrothermal, geopressured, HSA. Institute of Petroleum Engineering TU Clausthal 18
EGS Sistemi Geotermici Potenziati Univ.-Prof. Dr. Gioia Falcone Clausthal University of Technology Institute of Petroleum Engineering Rome, June 20 th, 2014