Title:

Technology Needs for SuperHot EGS Development

Authors:

Susan PETTY, Trenton CLADOUHOS, Jill WATZ, Geoffrey GARRISON, Carlos ARAQUE

Key Words:

EGS, supercritical, SuperHot, ultra high temperature, well completions, reservoir stimulation, reservoir management

Conference:

Stanford Geothermal Workshop

Year:

2020

Session:

Emerging Technology

Language:

English

Paper Number:

Petty

File Size:

741 KB

View File:

Abstract:

Several countries around the world are investigating the development of very high temperature geothermal resources using Enhanced Geothermal Systems methods to extract this high energy density resource. Japan, Iceland, Mexico, Italy and New Zealand all have projects aimed at developing an EGS resource in rocks in the brittle-ductile transition zone with temperatures above 400C. Wells have been drilled in Iceland, Italy and Mexico into rocks with greater than supercritical temperature. High enthalpy fluids mean better energy conversion efficiency to electricity. Very high temperatures make thermal energy storage more economic for flexible generation to meet demand. There are many areas around the world where temperatures more than 400C can be reached within 5-6 km of the surface making drilling for this resource feasible today. So where is the technology to exploit this resource today and what is needed to make SuperHot EGS development happen in the near future and to extend it to a wider area in the future? Near and long-term technology development needs are broken into three areas: Well drilling and completion, reservoir characterization and creation, and long-term resource management. While we can drill wells into very high temperature rock now, our methods rely on cooling the wellbore drastically as we drill. Our ability to control direction is limited and we don’t have access to the kinds of Measurement While Drilling (MWD) and direction control systems that we have come to rely on for guiding and turning wells at more typical geothermal temperatures. Bits specifically for these very high temperature rocks are in development and in the meantime, we use conventional bits with cooling. Well completions, including casing and cementing, offer the most technical challenges. Cements are available for temperatures up to 350C but not above that. Casing materials and connections as well as casing design are challenged above 350C. Reservoir creation and reservoir management are perhaps the areas where the greatest technical improvements are needed. The behavior of rock in the brittle ductile transition and the long-term behavior of fluids reacting with rock at these temperatures is not well understood. Basic science and testing is needed to gather data and advance existing models to be able to predict behavior of rock during fracturing and reservoir operation. While we assume that thermal stress cracking will dominate the stimulation and reservoir creation process, it isn’t clear whether tectonic differential stresses will play a role in fracturing or if fractures will remain open after creation. Reservoir management depends on rock/fluid interactions and since EGS involves injecting fluids from the surface not in equilibrium with the rock, it isn’t clear how these fluids will evolve as the flow through the reservoir. Steam flood well completions and reservoir management may help to inform our technology development for SuperHot EGS. This paper will review the status of numerical modeling for fracturing, well life cycle analysis and geochemical rock/fluid behavior as well as the technology needed for near and long term development of SuperHot EGS.


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