Observations of hydraulic stimulations in seven enhanced geothermal system projects

Xie, Linmao; Min, Kyoung-Bok; Song, Yoonho

doi:10.1016/j.renene.2014.07.044

Cited by 40 publications

(21 citation statements)

References 15 publications

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“…Based on the study conducted by Brown and Hoek (1978) on the relationship between the measured in situ stresses and depth, 0.5-2.0 is a suggested range for the horizontal-to-vertical stress ratio at depths below 1000 m (3280 ft). Field stress states for seven EGS sites collected by Xie et al (2015) confirm this range. The polygonal stress plot in Fig.…”

Section: Fracture Opening Versus Fracture Slip In Forgementioning

confidence: 55%

Effect of natural fractures on determining closure pressure

Nadimi

Forbes

Moore

et al. 2019

J Petrol Explor Prod Technol

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In Utah FORGE reservoir, eight pressure transient tests (microhydraulic fracturing and DFIT™) show natural fracture/ pressure-dependent leakoff. This behavior may lead to misinterpretation of the closure pressure (proxy for minimum principal stress). The closure pressures obtained from DFIT™ (or microhydraulic fracturing) testing may reflect shear failure along natural fractures or discontinuities rather than tensile failure and lead to inaccurate estimates of the minimum principal stress. In pressure tests conducted at the Utah FORGE site showed that reactivation or opening of natural fractures intersecting the wellbore and were suggested by multiple closure events in DFIT™ tests. In addition, comparisons between the pre-and postwell-tests FMI logs show that there are populations of induced fracture and reactivated natural fractures which are mostly vertical and sub-vertical. In this study, DFIT™ (or microhydraulic fracturing) test analysis and numerical simulations were used to suggest that hydraulic shearing of critically stressed natural fractures can contribute to multiple closure signatures and possibly lead to incorrect determination of the minimum principal stress. As other authors have previously advocated, the DFIT™ test analyses and numerical simulations suggest that better estimations of minimum principal stress may be derived by injecting at relatively high rate and pressure and insuring that tensile breakdown is reached. In addition, extended shut-in period is required to determine accurate reservoir characteristics and fluid flow regime. Keywords Utah FORGE • Microhydraulic fracturing and DFIT™ • Natural fracture/pressure-dependent leakoff • Minimum principal stress • Closure pressure • XSite™ 1 , 2 and 3 Maximum, intermediate and minimum principle stresses, respectively (psi) q Flow rate (bpm) P wf Well flowing bottomhole pressure (psi) P i Reservoir pore pressure (psi) II Injectivity index (bpm/psi)

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Section: Fracture Opening Versus Fracture Slip In Forgementioning

confidence: 55%

Effect of natural fractures on determining closure pressure

Nadimi

Forbes

Moore

et al. 2019

J Petrol Explor Prod Technol

View full text Add to dashboard Cite

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“…This shows that fracture surface roughness can be considered as a key source of uncertainty that needs further attention in future stimulation studies. It is also noteworthy that during the fluid injection, especially over longer term, appropriate strategies have to be utilized to identify the controlling factors to reduce the seismic risks—especially large magnitude events, which can occur during both injection and shut‐in—as well as uncertainties associated with the induced seismicity in geothermal reservoirs (Xie et al ).…”

Section: Resultsmentioning

confidence: 99%

A Study of Permeability Changes Due to Cold Fluid Circulation in Fractured Geothermal Reservoirs

Doonechaly

Azim

Rahman³

2015

Groundwater

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Reservoir behavior due to injection and circulation of cold fluid is studied with a shear displacement model based on the distributed dislocation technique, in a poro-thermoelastic environment. The approach is applied to a selected volume of Soultz geothermal reservoir at a depth range of 3600 to 3700 m. Permeability enhancement and geothermal potential of Soultz geothermal reservoir are assessed over a stimulation period of 3 months and a fluid circulation period of 14 years. This study-by shedding light onto another source of uncertainty-points toward a special role for the fracture surface asperities in predicting the shear dilation of fractures. It was also observed that thermal stress has a significant impact on changing the reservoir stress field. The effect of thermal stresses on reservoir behavior is more evident over longer circulation term as the rock matrix temperature is significantly lowered. Change in the fracture permeability due to the thermal stresses can also lead to the short circuiting between the injection and production wells which in turn decreases the produced fluid temperature significantly. The effect of thermal stress persists during the whole circulation period as it has significant impact on the continuous increase in the flow rate due to improved permeability over the circulation period. In the current study, taking into account the thermal stress resulted in a decrease of about 7 °C in predicted produced fluid temperature after 14 years of cold fluid circulation; a difference which notably influences the potential prediction of an enhanced geothermal system.

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“…The flow rates applied to the numerical models also considered the values targeted and observed in the commercial projects of Soultz and Rittershoffen [68]. The effective stimulation pressure required to induce shear slip in the pre-existing natural fractures is also found to be comparable to the values found at those four geothermal sites [37]. The potential heat and power output from an EGS developed in Kuujjuaq is also similar to the power generated and heat produced at Soultz and Rittershoffen [68].…”

Section: Comparison With Other Deep Geothermal Energy Projectsmentioning

confidence: 87%

“…Since the 1970s, several projects have been started worldwide, applying different stimulation techniques and in geological contexts ranging from crystalline to sedimentary rocks. A review of these projects is given by, for instance, Tester et al [35], Breede et al [36], Xie et al [37], Olasolo et al [38], Lu [39] and Kumari and Ranjith [40]. This research increased knowledge of the behavior of rock masses and joints subjected to hydraulic stimulation.…”

Section: Background Information 21 Engineered/enhanced Geothermal Sys...mentioning

confidence: 99%

Are Engineered Geothermal Energy Systems a Viable Solution for Arctic Off-Grid Communities? A Techno-Economic Study

Miranda

Raymond

Willis-Richards

et al. 2021

Water

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Deep geothermal energy sources harvested by circulating fluids in engineered geothermal energy systems can be a solution for diesel-based northern Canadian communities. However, poor knowledge of relevant geology and thermo-hydro-mechanical data introduces significant uncertainty in numerical simulations. Here, a first-order assessment was undertaken following a “what-if” approach to help design an engineered geothermal energy system for each of the uncertain scenarios. Each possibility meets the thermal energy needs of the community, keeping the water losses, the reservoir flow impedance and the thermal drawdown within predefined targets. Additionally, the levelized cost of energy was evaluated using the Monte Carlo method to deal with the uncertainty of the inputs and assess their influence on the output response. Hydraulically stimulated geothermal reservoirs of potential commercial interest were simulated in this work. In fact, the probability of providing heating energy at a lower cost than the business-as-usual scenario with oil furnaces ranges between 8 and 92%. Although the results of this work are speculative and subject to uncertainty, geothermal energy seems a potentially viable alternative solution to help in the energy transition of remote northern communities.

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Observations of hydraulic stimulations in seven enhanced geothermal system projects

Cited by 40 publications

References 15 publications

Effect of natural fractures on determining closure pressure

Effect of natural fractures on determining closure pressure

A Study of Permeability Changes Due to Cold Fluid Circulation in Fractured Geothermal Reservoirs

Are Engineered Geothermal Energy Systems a Viable Solution for Arctic Off-Grid Communities? A Techno-Economic Study

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