The effect of spatial aperture variations on the thermal performance of discretely fractured geothermal reservoirs

Fox, Don B.; Koch, Donald L.; Tester, Jefferson W.

doi:10.1186/s40517-015-0039-z

Cited by 39 publications

(27 citation statements)

References 59 publications

(69 reference statements)

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“…As anticipated, a fracture aperture of 0.1, 1, or 10 mm produces identical production well temperature curves. This result is consistent with the conclusions in Hawkins et al () and Fox et al ().…”

Section: Motivationsupporting

confidence: 94%

“…For most mathematical models of heat transport in fractures, hydrodynamic dispersion is treated as negligible (e.g., Axelsson et al, 2001;Bodvarsson, 1972;Doe et al, 2014;Fox et al, 2015Fox et al, , 2016Gringarten et al, 1975). This assumption can be justified based on an analysis of Taylor dispersion, D taylor , in rock fractures.…”

Section: Production Well Temperature Predictionsmentioning

confidence: 99%

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Inert and Adsorptive Tracer Tests for Field Measurement of Flow‐Wetted Surface Area

Hawkins

Becker

Tester

2018

Water Resources Research

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Field tests in a discrete rock fracture validated a combined inert/adsorbing tracer test method to estimate the contact area between fluids circulating through a fracture and the bulk rock matrix (i.e., flow‐wetted surface area, A). Tracer tests and heat injections occurred at a mesoscale well field in Altona, NY. A subhorizontal bedding plane fracture ∼7.6 m below ground surface connects two wells separated by 14.1 m. Recovery of the adsorbing tracer cesium was roughly 72% less than the inert tracer iodide. Using an advection‐dispersion‐reaction model in one‐dimension, the adsorbing/inert tracer method identified substantial flow channelization. These results are consistent with Ground Penetrating Radar (GPR) and thermal sensors. All characterization methods suggest circulating fluids were concentrated in a narrow, 1–2 m wide channel directly connecting the injection and production well. The inert/adsorbing tracer method identified two flow channels with areas of 28 and 80 m2. A one‐dimensional heat transport model predicted production well temperature rises 20.5°C in 6 days, whereas measured temperature rise was 17.6°C. For comparison, two‐dimensional heat transport through a fracture of uniform aperture (i.e., homogeneous permeability) predicted roughly 670 days until production well temperature would rise 17.6°C. This suggests that the use of a fracture of uniform aperture to predict heat transport may drastically overpredict the thermal performance of a geothermal system. In the context of commercial geothermal reservoirs, the results of this study suggest that combined inert/adsorbing tracer tests could predict production well thermal drawdown, leading to improved reservoir monitoring and management.

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Section: Motivationsupporting

confidence: 94%

Section: Production Well Temperature Predictionsmentioning

confidence: 99%

Inert and Adsorptive Tracer Tests for Field Measurement of Flow‐Wetted Surface Area

Hawkins

Becker

Tester

2018

Water Resources Research

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“…The horizontal length axis, x , and vertical length axis, y , are normalized to the radius of the circular fracture, R. Figure is reproduced from Fox et al . [].…”

Section: Introductionmentioning

confidence: 99%

Measurement and simulation of heat exchange in fractured bedrock using inert and thermally degrading tracers

Hawkins

Fox

Becker

et al. 2017

Water Resources Research

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Multicomponent groundwater tracer tests were conducted in a well‐characterized field site in Altona, NY using inert carbon‐cored nanoparticles and a thermally degrading phenolic compound. Experiments were conducted in a mesoscale reservoir consisting of a single subhorizontal bedding plane fracture located 7.6 m below ground surface contained between two wells separated by 14.1 m. The reservoir rock, initially at 11.7°C, was heated using 74°C water. During the heating process, a series of tracer tests using thermally degrading tracers were used to characterize the progressive in situ heating of the fracture. Fiber‐Optic Distributed Temperature Sensing (FODTS) was used to measure temperature rise orthogonal to the fracture surface at 10 locations. Recovery of the thermally degrading tracer's product was increased as the reservoir was progressively heated indicating that the advancement of the thermal front was proportional to the mass fraction of the thermally degrading tracer recovered. Both GPR imaging and FODTS measurements reveal that flow was reduced to a narrow channel which directly connected the two wells and led to rapid thermal breakthrough. Computational modeling of inert tracer and heat transport in a two‐dimensional discrete fracture demonstrate that subsurface characterization using inert tracers alone could not uniquely characterize the Altona field site. However, the inclusion of a thermally degrading tracer may permit accurate subsurface temperature monitoring. At the Altona field site, however, fluid‐rock interactions appear to have increased reaction rates relative to laboratory‐based measurements made in the absence of rock surfaces.

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“…The storage and transport of fluids in fault zones is generally assumed to be highly partitioned owing to the structural complexity of fault‐related fracture systems (Bonnet et al, ; Kim et al, ; Sibson, ; Tchalenko, ) and sharp contrasts in hydraulic properties (Bense et al, ; Brace, , ; Caine et al, ; Evans & Goddard, ; Roques et al, ). This affects processes in the Earth's crust operating on a broad range of scales, from the emergence of flow pathways (Tsang & Neretnieks, , and references therein) channeling solute (Kang et al, ) and heat transport (De La Bernardie et al, ; Fox et al, ; Geiger & Emmanuel, ; Klepikova et al, ) to convecting instabilities (Murphy, ; Patterson et al, ), frictional heating (Mase & Smith, ; Rice, ; Vredevoogd et al, ), dynamic fault weakening (Byerlee, ), and earthquake sequences (Jansen et al, ; Miller et al, ; Noir et al, ; Nur & Booker, ; Ross et al, ; Shapiro et al, ; Wang et al, ). Tracking how fluids migrate in faults in situ can therefore provide insights on key geological and physical processes.…”

Section: Introductionmentioning

confidence: 99%

Tracking Fluid Flow in Shallow Crustal Fault Zones: 2. Insights From Cross‐Hole Forced Flow Experiments in Damage Zones

et al. 2020

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Cross-hole fluid injection tests were performed on shallow (0.5 km depth) crustal fault zones to characterize their internal flow structures on scales of 3-30 m. The data were acquired at the Grimsel Rock Laboratory, Switzerland, after the zonal isolation of damage zones in boreholes equipped with multipacker systems. We show that 80% of the pressure responses detected evolved as a power function of time due to fracture-controlled flow and were best described by a fractional model with a flow dimension (n) in the range of [1.3,1.5]. The scaling of characteristic times (t c ) and intermediate transitions in the flow dimension is shown to be inconsistent with the trend expected for normal diffusion, indicating a diffusion slowdown process caused by the spatial integration of structurally different damage zones. An analysis of the entire data set points to a subdiffusive regime where the mean squared displacement of pressure fronts, ⟨r 2 (t)⟩, scales as ⟨r 2 (t)⟩ ∝ t 0.59 , similar to an anomalous diffusion process on synthetic fractal systems. We characterize this diffusion slowdown by calculating a network connectivity exponent ( ) of 1.4, from which we estimate a fractal dimension of d f = 2.23 for the tested fault zones. Such a value close to 2.0 supports the view of fault damage zones as hierarchical systems promoting flow channeling. Our results provide further support to theoretical models of fractional flow and their application to fractured media in nature.

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The effect of spatial aperture variations on the thermal performance of discretely fractured geothermal reservoirs

Cited by 39 publications

References 59 publications

Inert and Adsorptive Tracer Tests for Field Measurement of Flow‐Wetted Surface Area

Inert and Adsorptive Tracer Tests for Field Measurement of Flow‐Wetted Surface Area

Measurement and simulation of heat exchange in fractured bedrock using inert and thermally degrading tracers

Tracking Fluid Flow in Shallow Crustal Fault Zones: 2. Insights From Cross‐Hole Forced Flow Experiments in Damage Zones

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