Thermal Manipulation of Magma Boundary: Advancing Controls on Fluid Flow Via the Krafla Magma Testbed (KMT)
Yan LAVALLÉE, Anthony H. LAMUR, Jackie E. KENDRICK, Gudjon H. EGGERTSSON, Joshua WEAVER, John C. EICHELBERGER, Paolo PAPALE, Freysteinn SIGMUNDSSON, Donald B. DINGWELL, Sigurdur H. MARKUSSON, Anette K. MORTENSEN, Guðmundur O. FRIÐLEIFSSON, Charles CARRIGAN, John LUDDEN, Hjalti P. INGOLFSSON, and The KMT Consortium
[University of Liverpool, United Kingdom]
Magmatism generates the strongest heat fluxes in the Earth’s crust and powers geothermal resources. There is, however, a long-standing paradox as to the occurrence and extent of fracturing in magma and superhot rocks deemed ductile, which would prevent efficient fluid exchange. Drilling of IDDP-1 (at Krafla caldera, Iceland) was associated with complete fluid loss as reservoir rock temperature rose from ca. 400 to 850 °C in a 30-meter thick rock-magma boundary. Tripping out and back of the drill string allowed upwelling of magma, hot enough to flow in and clog the bottom of the borehole. This behavior provides evidence for the importance of thermal controls to open or maintain pathways for extracting fluids along magma boundaries. What is envisioned here is cooling-induced contraction fracturing of a hot rock/ magma, rather than fracturing by increasing fluid pressure above the least principal stress in cold rocks, as practiced in EGS. Laboratory measurements provide accurate constraints for the modeling of thermal stimulation, showing that the magnitude of cooling and the thermo-mechanical properties of rocks and magmas are primary controls on the width of fractures and the magnitude of reservoir permeability. The resultant width of thermal fractures in this high-temperature boundary region is greater than those developed in conventional geothermal reservoirs, and thus access to this resource may require a new generation of proppants and/ or thermal stimulation practices. Laboratory tests on hot rocks show that damage accumulation from successive rupture cycles may contribute to the ingression and/ or displacement of fragments along fracture intersections, acting as natural proppants. Tests on magma show that fracture healing may be prevented by lowering the temperature and injecting proppants with slow diffusive properties. Whilst material properties suggest that cooling is the solution to maintaining fluid pathways, field surveys and mineralogical investigations of the eroded vestiges of hydrothermal systems show the important role of secondary mineral precipitation in clogging fluid pathways as a result of pressure and temperature changes (mostly cooling). Thus field constraints, drilling information and laboratory descriptions must be combined to determine the optimum temperature window in which fluid exchange may be maximized for prolonged timescales. This framework will be developed in this study and tested in the Krafla Magma Testbed (KMT), with the aim to shift the current paradox to a paradigm whereby temperature regulation of magma body boundaries will enable use of this new magma energy resource.
|        Topic: Advanced Technology (Magma, Geopressure, etc.)||Paper Number: 37023|