Need for the Development of a Facility to Study the Behavior of Rocks, Proppants, Diverters, Cements, Instrumentation and Equipment at Greater Than Supercritical Conditions



Key Words:

SuperHot, EGS, very high temperature, supercritical, testing


Stanford Geothermal Workshop




Emerging Technology



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566 KB

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SuperHot rock ( greater than 374°C) is much more energy dense than conventional hot dry rock ( less than 225°C), and production of supercritical steam through Enhanced Geothermal Systems (EGS) would represent an energy breakthrough. Recovery of just 1–2% of the thermal energy stored in hot rock at 3 to 10 km depths would be sufficient to meet world energy consumption for many centuries. Recovery of this energy can be achieved through creation of Enhanced Geothermal Systems (EGS), which involves injection of high-pressure water into a well to enhance or create fracture permeability and connect two or more wells separated by several hundred meters of hot rock, effectively creating an underground heat exchanger. Despite significant worldwide investment in the last two decades, EGS development has been limited, and the goal of economic EGS may not be achieved unless power production per well can be greatly improved. Typically, EGS developers target rock temperatures between 150 and 225°C, but super-hot rock (SHR) ( greater than 374°C) is much more energy dense, and a SHR EGS well would produce 5 to 10 times as much electricity as other well types. The most geothermal savvy countries in the world, Iceland, Italy, Japan, Mexico, and New Zealand, are pursuing projects to produce supercritical geothermal fluids. Geothermal wells have been drilled to 400°C or hotter in the USA, Japan, Iceland, and Italy. Given the enormous potential economic benefits of supercritical geothermal wells, what is holding back the research, technology development, and testing needed to make super-hot geothermal energy viable? Several scientific and technical gaps and barriers need to be filled to make that happen and among them the in-situ physical, geochemical, and mechanical characteristics and behavior of rock and produced fluids at temperatures up to 500°C and pressure greater than 22 Mpa are not well understood. At these pressure and temperature the mechanical behavior of rocks change from brittle to ductile and the extent of fracturing and the associated changes in the permeability of the formation remain big unknowns. The role of thermal fracturing is also important since low temperature fluids are used during the drilling inducing thermal shock in the immediate proximity of the well. This fracturing mechanism is also poorly studied in the range of SHR temperatures. The knowledge and modeling of all these phenomena constitute important factors of development for supercritical steam geothermal energy and here are some important questions that need to be addressed: - How can fractures develop in the brittle to ductile transition zone? Can an EGS reservoir be created and sustained in these conditions? - What are the corresponding porosity and permeability changes? - What the main mechanisms at stake? - What are the main parameters of the host rock and fluids controlling these changes? - What is the importance of chemical reactions between the fluids and the reservoir rocks? In order to bring some answers, we propose to realize a series of laboratory fracturing experiments using water, CO2 and other fluids on various rocks representative of the most common geological settings for this kind of geothermal reservoirs and at SHR pressure and temperature (T greater than 374°C, P greater than 22 MPa). To complete these experiments, two different HP/HT cells will be constructed: 1. One pseudo tri-axial compression apparatus to study fracture creation on cores. 2. One polyaxial frame to study fracture propagation on cubic-foot or larger rock samples. 3. Very high temperature flow reactor system to study the changes in permeability in rock with high temperature fluid flow over time. 4. System for testing casing components and cements at very high temperatures under stresses produced with thermal cycling

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