Competition between cooling contraction and fluid overpressure on aperture evolution in a geothermal system

Kang, Fangchao; Li, Yingchun; Tang, Chun’an; Huang, Xin; Li, Tianjiao

doi:10.1016/j.renene.2022.01.033

Cited by 13 publications

(4 citation statements)

References 41 publications

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“…Figure 3(e1,e2,e3) shows that porosity increment with respect to the initial value which represents that it may double in the region close to the injection wellbore. It should be noted that porosity variation inside the faulted zone is mainly controlled by the fracture aperture variation, which has the possibility to be doubled [16][17][18][19][20][21][22][23][24][25][26]. Figure 3(f1,f2,f3) shows the permeability development based on the Equation (10).…”

Section: Resultsmentioning

confidence: 99%

“…Their simulation results show an up to 10 times increase in the fracture permeability for the different spacing in the multi-lateral fracture system after 30 years of operation. In a recent study, Kang et al [26] reported that, of the fracture aperture changes due to the thermoelasticity, around 22% result from poroelasticity after one year of the numerical simulation. However, the contribution of the thermal stress on the fracture aperture increases with time and, after 30 years, its impact increases to 161% in comparison to the hydraulic effects.…”

Section: Parametermentioning

confidence: 99%

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Numerical Simulation of Thermo-Hydro-Mechanical Processes at Soultz-sous-Forêts

Mahmoodpour¹,

Singh

Mahyapour

et al. 2022

Energies

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Porosity and permeability alteration due to the thermo-poro-elastic stress field disturbance from the cold fluid injection is a deciding factor for longer, more economic, and safer heat extraction from an enhanced geothermal system (EGS). In the Soultz-sous-Forêts geothermal system, faulted zones are the main flow paths, and the resulting porosity–permeability development over time due to stress reorientation is more sensitive in comparison with the regions without faulted zones. Available operational and field data are combined through a validated numerical simulation model to examine the mechanical impact on the pressure and temperature evolution. Results shows that near the injection wellbore zones, permeability and porosity values are strongly affected by stress field changes, and that permeability changes will affect the overall temperature and pressure of the system, demonstrating a fully coupled phenomenon. In some regions inside the faulted zones and close to injection wellbores, porosity doubles, whereas permeability may be enhanced up to 30 times. A sensitivity analysis is performed using two parameters which are not well discussed in the literature the for mechanical aspect, but the results in this study show that one of them impacts significantly on the porosity–permeability changes. Further experimental and field works on this parameter will help to model the heat extraction more precisely than before.

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Section: Resultsmentioning

confidence: 99%

Section: Parametermentioning

confidence: 99%

Numerical Simulation of Thermo-Hydro-Mechanical Processes at Soultz-sous-Forêts

Mahmoodpour¹,

Singh

Mahyapour

et al. 2022

Energies

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show abstract

“…As such, non-linear flow around the injection well might cause higher flow velocities and therefore intensify heterogeneous heat transfer. Further, many thermally triggered effects such as the increase in fracture apertures due to thermal compaction during cooling 26 , 27 , fines mobilization 28 , 29 , or biofilm generation 30 , 31 might strongly affect a reservoir’s longtime behavior. The prediction of these effects can possibly be improved with heterogeneous heat transfer models because they might occur more locally along individual fractures than previously thought.…”

Section: Discussionmentioning

confidence: 99%

Velocity-dependent heat transfer controls temperature in fracture networks

Heinze

Pastore

2023

Nat Commun

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Heat transfer between a fluid and the surrounding rock in the subsurface is a crucial process not only, but most obviously, in geothermal systems. Heat transfer is described by Newton’s law of cooling, relating the heat transferred to a coefficient, the specific surface area, and the temperature difference between rock and fluid. However, parameterizing the heat transfer coefficient in fracture networks poses a major challenge. Here we show that within a fracture network the heat transfer coefficient is strongly heterogeneous but that laboratory single fracture experiments can provide a reasonable estimate in dependence of flow rate. We investigate the distribution of the heat transfer coefficient experimentally as well as numerically and analyze the heat transfer at individual fractures. Our results improve the prediction of temperatures in engineered and natural geothermal systems and allow sustainable management and design of reservoirs considering the role of individual fractures.

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“…Additionally, a numerical study showed that a high-permeability flow path would be formed in a fracture network, owing to cooling-induced fracture opening during exploiting geothermal energy in EGS at conventional geothermal conditions (Sun et al 2017). Other numerical studies on conventional geothermal environments reported that the thermal contraction may lead to permeability enhancement of existing fractures (Kang et al 2022). Additionally, it was also showed numerically that permeability enhancement will occur when the induced tensile thermal stress reduces normal stress on a fracture to near-zero (Kaneta et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Cooling-induced permeability enhancement for networks of microfractures in superhot geothermal environments

et al. 2023

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Recent researches have proposed the use of enhanced geothermal system reservoirs consisting of dense networks of microfractures, created by hydraulic and/or thermal fracturing in superhot/supercritical geothermal environments, because of their suitability for thermal energy harvesting. During fracturing and energy extraction, the fracture networks are exposed to cooling due to the injection of cold fluid into the reservoirs. Previous studies showed such cooling enhanced reservoir permeability in conventional geothermal environments. However, the cooling may result in a higher risk of seismicity, owing to decreased normal stress on the fractures. Nevertheless, it is unclear whether cooling-induced permeability enhancement and a higher risk of seismicity occurs within networks of microfractures which consist of numerous interconnected microfractures at various orientations to the in situ triaxial stress. Thus, no dominant fractures have the possibility to cause permeability enhancement/induced seismicity. In this study, results are presented for borehole cooling experiments on a dense network of microfractures in granite, at 400 °C, under true triaxial stress. Permeability and acoustic emissions were measured with decreases in borehole temperature (up to ~ 90 °C). Results showed that permeability increased with increasing temperature drop at relatively low stress levels (15 and 20 MPa). The permeability enhancement occurred without intensive failure, and was reversible. However, permeability was almost constant at a higher stress level (65 MPa). Results showed that permeability enhancement required a thermal stress equivalent to the mean stress, so that the normal stress was reduced to near-zero, for a considerable amount of the microfractures. Additionally, the permeability of dense microfracture networks can be increased by cooling primarily through thermo-elastic deformation (without intensive failure), which may be useful to compensate for the reduction in injectivity due to cooling-induced fluid property changes.

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Competition between cooling contraction and fluid overpressure on aperture evolution in a geothermal system

Cited by 13 publications

References 41 publications

Numerical Simulation of Thermo-Hydro-Mechanical Processes at Soultz-sous-Forêts

Numerical Simulation of Thermo-Hydro-Mechanical Processes at Soultz-sous-Forêts

Velocity-dependent heat transfer controls temperature in fracture networks

Cooling-induced permeability enhancement for networks of microfractures in superhot geothermal environments

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