Numerical investigation on the effects of the fracture network pattern on the heat extraction capacity for dual horizontal wells in enhanced geothermal systems

Hydraulic stimulation is the process of initiating fractures in a target reservoir for subsurface energy resource management with applications in unconventional oil/gas and enhanced geothermal systems. The fracture characteristics (i.e., number, size and orientation with respect to the wellbore) determines the modified permeability field of the host rock and thus, numerical simulations of flow in fractured media are essential for estimating the anticipated change in reservoir productivity. However, numerical modeling of fluid flow in highly fractured media is challenging due to the explosive computational cost imposed by the explicit discretization of fractures at multiple length scales. A common strategy for mitigating this extreme cost is to crudely simplify the geometry of fracture network, thereby neglecting the important contributions made by all elements of the complex fracture system.The proposed &#8220;Hierarchical Finite Element Method&#8221; (Hi-FEM; Weiss, Geophysics, 2017) reduces the comparatively insignificant dimensions of planar- and curvilinear-like features by translating them into integrated hydraulic conductivities, thus enabling cost-effective simulations with requisite solutions at material discontinuities without defining ad-hoc, heuristic, or empirically-estimated boundary conditions between fractures and the surrounding formation. By representing geometrical and geostatistical features of a given fracture network through the Hi-FEM computational framework, geometrically- and geomechanically-dependent fluid flow properly can now be modeled economically both within fractures as well as the surrounding medium, with a natural &#8220;physics-informed&#8221; coupling between the two.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

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Simulation of heat extraction from CO2-based enhanced geothermal systems considering CO2 sequestration

Energy ◽

10.1016/j.energy.2017.09.139 ◽

2018 ◽

Vol 142 ◽

pp. 157-167 ◽

Cited By ~ 31

Author(s):

Chang-Long Wang ◽

Wen-Long Cheng ◽

Yong-Le Nian ◽

Lei Yang ◽

Bing-Bing Han ◽

...

Keyword(s):

Co2 Sequestration ◽

Heat Extraction ◽

Enhanced Geothermal Systems ◽

Geothermal Systems

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Design, modeling, and evaluation of a doublet heat extraction model in enhanced geothermal systems

Renewable Energy ◽

10.1016/j.renene.2016.12.064 ◽

2017 ◽

Vol 105 ◽

pp. 232-247 ◽

Cited By ~ 34

Author(s):

Yidong Xia ◽

Mitchell Plummer ◽

Earl Mattson ◽

Robert Podgorney ◽

Ahmad Ghassemi

Keyword(s):

Heat Extraction ◽

Enhanced Geothermal Systems ◽

Geothermal Systems ◽

Extraction Model

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Thermo-hydro-mechanical modelling study of heat extraction and flow processes in enhanced geothermal systems

Advances in Geosciences ◽

10.5194/adgeo-54-229-2021 ◽

2021 ◽

Vol 54 ◽

pp. 229-240

Author(s):

Dejian Zhou ◽

Alexandru Tatomir ◽

Martin Sauter

Keyword(s):

Production Rate ◽

Flow Rate ◽

Heat Production ◽

Analytical Solutions ◽

Pressure Difference ◽

Heat Extraction ◽

Enhanced Geothermal Systems ◽

Geothermal Systems ◽

Fracture Zones ◽

Heat Production Rate

Abstract. Enhanced Geothermal Systems (EGS) are widely used in the development and application of geothermal energy production. They usually consist of two deep boreholes (well doublet) circulation systems, with hot water being abstracted, passed through a heat exchanger, and reinjected into the geothermal reservoir. Recently, simple analytical solutions have been proposed to estimate water pressure at the abstraction borehole. Nevertheless, these methods do not consider the influence of complex geometrical fracture patterns and the effects of the coupled thermal and mechanical processes. In this study, we implemented a coupled thermo-hydro-mechanical (THM) model to simulate the processes of heat extraction, reservoir deformation, and groundwater flow in the fractured rock reservoir. The THM model is validated with analytical solutions and existing published results. The results from the systems of single fracture zone and multi-fracture zones are investigated and compared. It shows that the growth of the number and spacing of fracture zones can effectively decrease the pore pressure difference between injection and abstraction wells; it also increases the production temperature at the abstraction, the service life-spans, and heat production rate of the geothermal reservoirs. Furthermore, the sensitivity analysis on the flow rate is also implemented. It is observed that a larger flow rate leads to a higher abstraction temperature and heat production rate at the end of the simulation, but the pressure difference may become lower.

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Longevity of Enhanced Geothermal Systems with Brine Circulation in Hydraulically Fractured Hydrocarbon Wells

Fluids ◽

10.3390/fluids4020063 ◽

2019 ◽

Vol 4 (2) ◽

pp. 63

Author(s):

Zuo ◽

Weijermars

Keyword(s):

Limit State ◽

Extraction Process ◽

Heat Extraction ◽

Working Fluid ◽

Heat Equations ◽

Enhanced Geothermal Systems ◽

Geothermal Systems ◽

Geothermal Heat ◽

Horizontal Fracture ◽

Rock Temperature

A simple, semi-analytical heat extraction model is presented for hydraulically fractured dry reservoirs containing two subparallel horizontal wells, connected by a horizontal fracture channel, using injected brine as the working fluid. Heat equations are used to quantify the heat conduction between fracture walls and circulating brine. The brine temperature profiles are calculated for different combinations of fracture widths, working fluid circulation rates, and initial fracture wall temperatures. The longevity of the geothermal heat extraction process is assessed for a range of working fluid injection rates. Importantly, dry geothermal reservoirs will not recharge heat by the geothermal flux on the time scale of any commercial heat extraction project. A production plan is proposed, with periodic brine circulation maintained in a diurnal schedule with 8 h active production alternating with 16 h of pump switched off. A quasi-steady state is achieved after both the brine temperature and rock temperature converge to a limit state allowing fracture-wall reheating by conduction from the rock interior in the diurnal production schedule. The results of this study could serve as a fast tool for assisting the planning phase of geothermal reservoir design as well as for operational monitoring and management.

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Study of heat extraction and flow process by fully coupled thermal- hydro- mechanical model

10.5194/egusphere-egu2020-5998 ◽

2020 ◽

Author(s):

Dejian Zhou ◽

Alexandru Tatomir ◽

Martin Sauter

Keyword(s):

Mechanical Model ◽

Cold Water ◽

Fractured Rock ◽

Water Pressure ◽

Initial Permeability ◽

Heat Extraction ◽

Enhanced Geothermal Systems ◽

Geothermal Systems ◽

Flow Process ◽

Fully Coupled

Enhanced Geothermal Systems (EGS) are widely used in the development and application of geothermal energy. They usually consist of two parallel deep boreholes, where cold water is injected into one borehole and abstracted at the second one after being heated when passing through the fractured network system. Recently, simple analytical solutions have been proposed to estimate the water pressure at the output. Nevertheless, these methods do not take into account the influences of the coupled thermal and mechanical processes. In this research study we build a fully coupled Thermal &#8211; Hydro-mechanical model (THM model) to simulate the processes of heat extraction, deformation and water flow in the nearby fractured rock formations. The influences of single thermal &#8211; hydraulic and mechanical &#8211; hydraulic effects were compared with the fully coupled and decoupled results, showing that temperature influences mostly the water pressure in the second borehole, compared with temperature. The mechanical effect alone has little influences on the water pressure. A sensitive analysis was also conducted to study which parameters affect the simulation results the most. It was shown that the initial permeability and temperature are playing the main roles in this simulation.

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Hydraulic Fracturing in Enhanced Geothermal Systems—Field, Tectonic and Rock Mechanics Conditions—A Review

Energies ◽

10.3390/en14185725 ◽

2021 ◽

Vol 14 (18) ◽

pp. 5725

Author(s):

Rafał Moska ◽

Krzysztof Labus ◽

Piotr Kasza

Keyword(s):

Hydraulic Fracturing ◽

Fracture Network ◽

Hydraulic Fractures ◽

Enhanced Geothermal Systems ◽

Seismic Velocities ◽

Geothermal Systems ◽

Principal Stresses ◽

Pumping Rate ◽

Work Related ◽

Stimulation Method

Hydraulic fracturing (HF) is a well-known stimulation method used to increase production from conventional and unconventional hydrocarbon reservoirs. In recent years, HF has been widely used in Enhanced Geothermal Systems (EGS). HF in EGS is used to create a geothermal collector in impermeable or poor-permeable hot rocks (HDR) at a depth formation. Artificially created fracture network in the collector allows for force the flow of technological fluid in a loop between at least two wells (injector and producer). Fluid heats up in the collector, then is pumped to the surface. Thermal energy is used to drive turbines generating electricity. This paper is a compilation of selected data from 10 major world’s EGS projects and provides an overview of the basic elements needed to design HF. Authors were focused on two types of data: geological, i.e., stratigraphy, lithology, target zone deposition depth and temperature; geophysical, i.e., the tectonic regime at the site, magnitudes of the principal stresses, elastic parameters of rocks and the seismic velocities. For each of the EGS areas, the scope of work related to HF processes was briefly presented. The most important HF parameters are cited, i.e., fracturing pressure, pumping rate and used fracking fluids and proppants. In a few cases, the dimensions of the modeled or created hydraulic fractures are also provided. Additionally, the current state of the conceptual work of EGS projects in Poland is also briefly presented.

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