Integral equation solution of heat extraction‐induced thermal stress in enhanced geothermal reservoirs

Ghassemi, Ahmad; Tarasovs, S.; Cheng, Alexander H.‐D.

doi:10.1002/nag.440

Cited by 55 publications

(27 citation statements)

References 12 publications

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“…It is also assumed that the poro-and thermoelastic properties of the rock are constant. Other assumptions are similar to those postulated in Ghassemi et al [11,12]. In particular, we assume that all properties such as fracture thickness, permeability, and reservoir heat capacity are constant; the injection rate of cold water is steady, the reservoir is permeable to water but the fracture has no storage capacity, the production rate of hot water is not equal to the injection rate but it is assumed not to influence the heat transport; and the heat storage and dispersion effects in the fracture fluid flow are negligible.…”

Section: Governing Equationsmentioning

confidence: 71%

“…The temperature of the extracted fluid T ext is unknown and a part of the solution. The solution to the thermoelasticity system using the integral equation formulation is similar to that of the poroelasticity; it has been treated in detail by Ghassemi et al [11,12] using the Laplace domain boundary element method.…”

Section: Heat Transport In the Fracture And The Rock Matrixmentioning

confidence: 99%

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A three‐dimensional integral equation model for calculating poro‐ and thermoelastic stresses induced by cold water injection into a geothermal reservoir

Zhou

Ghassemi

Cheng

2009

Num Anal Meth Geomechanics

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SUMMARYPoro-mechanical and thermo-mechanical processes change the fracture aperture and thus affect the water flow pattern in the fracture during the cold water injection into enhanced geothermal systems (EGS). In addition, the stresses generated by these processes contribute to the phenomenon of reservoir seismicity. In this paper, we present a three-dimensional (3D) partially coupled poro-thermoelastic model to investigate the poroelastic and thermoelastic effects of cold water injection in EGS. In the model, the lubrication fluid flow and the convective heat transfer in the fracture are modeled by the finite element method, while the pore fluid diffusion and heat conductive transfer in the reservoir matrix are assumed to be 3D and modeled by the boundary integral equation method without the need to discretize the reservoir. The stresses at the fracture surface and in the reservoir matrix are obtained from the numerical model and can be used to assess the variation of in situ stress and induced seismicty with injection/extraction. Application of the model shows that rock cooling induces large tensile stresses and increases fracture conductivity, whereas the rock dilation caused by fluid leakoff decreases fracture aperture and increases compressive total stresses around the injection zone. However, increases in pore pressure reduce the effective stresses and can contribute to rock failure, fracture slip, and microseismic activity.

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Section: Governing Equationsmentioning

confidence: 71%

Section: Heat Transport In the Fracture And The Rock Matrixmentioning

confidence: 99%

A three‐dimensional integral equation model for calculating poro‐ and thermoelastic stresses induced by cold water injection into a geothermal reservoir

Zhou

Ghassemi

Cheng

2009

Num Anal Meth Geomechanics

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“…Using (8), the Mass Breakthrough Time (MBT) is calculated against velocity for a given RC value. This RC specific MBT is calculated at the outlet D, that is, the time to travel 1 mm in distance.…”

Section: Mass Transport (Isothermal Coupling)mentioning

confidence: 99%

“…Perkins and Gonzalez [6] as well as Kocabas [7] proposed analytical models to investigate the state of stresses induced by cold fluid injection. Ghassemi et al [8] developed an integral equation to calculate thermally induced stresses associated with the cooling of a planar fracture in a hot rock. The findings from these studies are relevant to the induced tensile stresses present in the cooled region of the EGS reservoir that stimulate thermal fractures.…”

Section: Introductionmentioning

confidence: 99%

On Heat and Mass Transfer within Thermally Shocked Region of Enhanced Geothermal System

et al. 2017

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An Enhanced Geothermal System (EGS) is an artificially created geothermal reservoir formed by hydrofracturing hot dry rock. Thermal shock occurs when the cold water contacts the hot rock near the injection borehole, creating a network of small, disorganized, closely spaced micro cracks. As the cold-water injection continues, the hot rock cools down and the micro cracks coalesce, becoming a better-defined network of thermal fractures. Thermal fractures in an EGS reservoir are believed to improve reservoir performance by increasing the surface area for heat exchange and lowering flow impedance; however, it is difficult to precisely predict how they grow and affect the permeability of the reservoir. The goal of this paper is to provide an insight into the transport mechanisms within the thin, permeable, thermally shocked region of an EGS reservoir. COMSOL Multiphysics5 is used to set up an indealized porous region with identical geometrical features at different domain scales to show the scale dependence of heat and mass transport in the initial microscale crack network and in the later coalesced thermal fractures. This research shows the importance of EGS maturity in determining how heat and mass are transferred and how to select appropriate analytical tools for different stages of development.

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“…In these more complicated cases, numerical schemes, such as finite element [7], Markerand-Cell method [17] and finite difference approaches [18,19], have to be used to obtain the thermal behavior of the fluid and reservoir. Normally, finding the solution is computationally demanding.…”

Section: Introductionmentioning

confidence: 99%

An Efficient and Accurate Approach for Studying the Heat Extraction from Multiple Recharge and Discharge Wells

Wu¹,

Zhang²,

Bunger

et al. 2013

Effective and Sustainable Hydraulic Fracturing

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In order to understand the thermal recovery Behavior of an engineered geothermal system (EGS), this paper develops a model in which fluid circulates in a single, planar hydraulic fracture with a constant hydraulic aperture via multiple recharging and discharging wells. The coupled equations for heat convection in the fracture plane and heat transfer into the rock are provided for steady and irrotational fluid flow conditions. By using velocity potentials and streamline functions, the temperature along a streamline is found to be only a function of the potential. By utilizing the Laplace transformation, the analytical solutions in the Laplace space for the temperature field are found, which are numerically inverted for timedomain results. Several examples with different arrangements of injection and production wells are investigated and the comparison with other published results is provided. The semi-analytical results demonstrate that the proposed model provides an efficient and accurate approach for predicting the temperatures of a multi-well reservoir system.

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Integral equation solution of heat extraction‐induced thermal stress in enhanced geothermal reservoirs

Cited by 55 publications

References 12 publications

A three‐dimensional integral equation model for calculating poro‐ and thermoelastic stresses induced by cold water injection into a geothermal reservoir

A three‐dimensional integral equation model for calculating poro‐ and thermoelastic stresses induced by cold water injection into a geothermal reservoir

On Heat and Mass Transfer within Thermally Shocked Region of Enhanced Geothermal System

An Efficient and Accurate Approach for Studying the Heat Extraction from Multiple Recharge and Discharge Wells

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