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Understanding the micro-mechanisms underlying the localized–ductile transition (LDT) as well as the brittle–plastic transition (BPT) has become crucial for our wider understanding of crustal processes and seismicity. Given how difficult in situ observations of these transitions are to perform, laboratory experiments might be our only way to investi...
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... can be found on the website put together by Mark Zimmerman. All original blueprints were personally shared by Paterson to A. Schubnel. The TARGET apparatus is based on the combination of a high-pressure, internally heated pressure chamber that is commonly used in experimental petrology (Edgar and Edgar, 1973) with an axial deformation system (Fig. 1). The confining pressure is applied with an inert gas, argon, and can reach 400 MPa. The high-pressure confining vessel houses an internal Kanthal furnace allowing it to reach temperatures of up to 800 ○ C (Fig. 1). The large inner diameter of the confining vessel also allows for the use of large samples up to 48 mm in length and 24 mm ...
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... heated pressure chamber that is commonly used in experimental petrology (Edgar and Edgar, 1973) with an axial deformation system (Fig. 1). The confining pressure is applied with an inert gas, argon, and can reach 400 MPa. The high-pressure confining vessel houses an internal Kanthal furnace allowing it to reach temperatures of up to 800 ○ C (Fig. 1). The large inner diameter of the confining vessel also allows for the use of large samples up to 48 mm in length and 24 mm in diameter. Moreover, TARGET is equipped with an internal straingauge based force sensor located inside the high-pressure vessel. This design allows for force readings free from the contribution of the frictional ...
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... piston past the high pressure seals. The axial load is applied externally using a servohydraulic actuator. The piston is compensated, i.e., the confining pressure does not exert a force on it (Griggs, 1936), and the maximum achievable axial force is 1000 kN, representing an axial stress of 2.2 GPa on 24 mm samples and 3.2 GPa on 20 mm samples (Fig. 1). Similarly, the design of the compensation chamber (based on that described in Paterson, 1990) allows for piston displacement without changes in pressure vessel volume (i.e., constant confining pressure). Two piezo-electrical sensors for active and passive seismic measurements are located at either end of the loading column. Two high ...
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... (i.e., constant confining pressure). Two piezo-electrical sensors for active and passive seismic measurements are located at either end of the loading column. Two high precision syringe pumps for controlling gas or water pore-fluid pressure are installed and allow continuous pore-volume changes and permeability measurements during experiments (Fig. ...
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... sample assembly is composed of a rock core wrapped in an inner copper foil jacket (0.025 mm thickness) to improve contact with the outer copper jacket (0.2 mm thickness) with an internal diameter of 24 ± 0.1 mm, isolating the sample from the confining medium (see Fig. 1). The jacket is a tube cut to 285 mm and then swaged in its middle section onto a former with the diameter of the sample (i.e., between 20 and 24 mm). The Mg-stabilized zirconia pistons are conical at their ends to accommodate the change in diameter between the ample and loading columns. Sample compression is accompanied by an intense ...
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... total confining system is about 1400 × 730 × 2470 mm 3 in size and weighs ∼690 kg. The chamber (1.4542 X5 CrNiCuNb17-4 P1070 steel) is closed at the top by two screw caps and at its base by the main deformation piston (Fig. 1). The vessel is encased in a cooling sleeve (3.2315 AlMgSi1 steel) that comprises a water-cooled copper coil (2.0060 E-Cu 57) with an internal diameter of 12 mm. Sealing of the high-pressure chamber (also referred to as "vessel") is ensured by lip seals supported by anti-extrusion polyether ether ketone (PEEK) rings. The vessel contains ...
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... the confining pressure due to a high-pressure compensation chamber that maintains the gas volume constant in the confining vessel (Fig. 1). The confining gas is drawn and pressurized from argon commercial bottles to the pressure vessel in two stages. A primary pneumatic pump (gas booster from Haskel) draws argon from the bottle and brings the pressure in the vessel up to 100 Mpa (Fig. 2). For higher confining pressure, the primary system is isolated by a valve before ...
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... axial piston (1.4112 X90CrMoV18 steel) is located under the high-pressure vessel and connected to the internal load cell (Fig. 1). Two pumps can drive the axial piston: a hydraulic one (for large displacements) and a syringe-pump volume/pressure controller (for very low strain rates and constant force experiments). The hydraulic unit generates the hydraulic oil pressure required for FIG. 2. Synoptic diagram of the confining pressure system (orange) and the pore ...
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... controllers (VPC, maximum pressure 300 Mpa). The whole pore pressure system is about 400 × 700 × 2455 mm 3 and weighs about 380 kg. The pore pressure system connects to the sample through the top of the pressure vessel, and the upper sealing piston is designed to accommodate a high-pressure fluid feed tube with an internal diameter of 1 mm (Fig. 1). The thermocouple is slid into this supply tube. A junction T-fitting is used between the thermocouple tube and the fluid pressure piping. The thermocouple is silver-soldered to a cone fitting, which is then screwed onto the T-fitting. The bottom pore fluid line is attached to the bottom anvil within the confining pressure chamber. The ...
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... conducted experiments to estimate the permeability range in which TARGET can be used, i.e., the maximum and minimum recordable values for rock permeability. In our setup, maximum recordable permeability is controlled by the permeability of the piping used in the pore pressure system (see "pore pressure line" in Fig. 1) as well as by the permeability measurement method. The piping used here is standard high-pressure piping with an internal diameter of 1 mm. To record its permeability, we conducted an experiment with a hollow alumina sample with extremely high permeability at an effective confining pressure of 50 MPa and an argon pore pressure of 15 ...
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... In nature, rock is heterogeneous, with variations in properties, stress states, strain rates and pre-existing fractures and fault zones. Direct in situ measurements of permeability are rare at depths > 2-3 km (Ingebritsen and Manning 1999) and non-existent below 12 km depth, and even laboratory measurements of permeability are rare at temperatures representative of NDR-EGS (Meyer et al. 2023). Our models illustrate the need for additional research addressing (i) the dominant mechanisms of permeability creation and destruction, and (ii) fluid flow dynamics at fine spatial scales and protracted temporal scales. ...
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Continental crust at temperatures > 400 °C and depths > 10–20 km normally deforms in a ductile manner, but can become brittle and permeable in response to changes in temperature or stress state induced by fluid injection. In this study, we quantify the theoretical power generation potential of an enhanced geothermal system (EGS) at 15–17 km depth using a numerical model considering the dynamic response of the rock to injection-induced pressurization and cooling. Our simulations suggest that an EGS circulating 80 kg s ⁻¹ of water through initially 425 ℃ hot rock can produce thermal energy at a rate of ~ 120 MWth (~ 20 MWe) for up to two decades. As the fluid temperature decreases (less than 400 ℃), the corresponding thermal energy output decreases to around 40 MWth after a century of fluid circulation. However, exploiting these resources requires that temporal embrittlement of nominally ductile rock achieves bulk permeability values of ~ 10 –15 –10 –14 m ² in a volume of rock with dimensions ~ 0.1 km ³ , as lower permeabilities result in unreasonably high injection pressures and higher permeabilities accelerate thermal drawdown. After cooling of the reservoir, the model assumes that the rock behaves in a brittle manner, which may lead to decreased fluid pressures due to a lowering of thresholds for failure in a critically stressed crust. However, such an evolution may also increase the risk for short-circuiting of fluid pathways, as in regular EGS systems. Although our theoretical investigation sheds light on the roles of geologic and operational parameters, realizing the potential of the ductile crust as an energy source requires cost-effective deep drilling technology as well as further research describing rock behavior at elevated temperatures and pressures.
