Enhanced Geothermal Systems (EGS): Hydraulic Fracturing in a Thermo-Poroelastic Framework

2018 ◽  
pp. 465-551
Author(s):  
Benjamin Loret
Keyword(s):  
Hydraulic Fracturing ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems

scholarly journals Environmentally friendly, rheoreversible, hydraulic-fracturing fluids for enhanced geothermal systems

Geothermics ◽  
2015 ◽  
Vol 58 ◽  
pp. 22-31 ◽  
Author(s):  
Hongbo Shao ◽  
Senthil Kabilan ◽  
Sean Stephens ◽  
Niraj Suresh ◽  
Anthon N. Beck ◽  
...  
Keyword(s):  
Hydraulic Fracturing ◽  
Environmentally Friendly ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Fracturing Fluids

scholarly journals Experimental and Numerical Evaluation of Hydraulic Fracturing under High Temperature and Embedded Fractures in Large Concrete Samples

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3171
Author(s):  
Liangliang Guo ◽  
Zihong Wang ◽  
Yanjun Zhang ◽  
Zhichao Wang ◽  
Haiyang Jiang
Keyword(s):  
Numerical Simulation ◽  
High Temperature ◽  
Hydraulic Fracturing ◽  
Laboratory Test ◽  
High Temperatures ◽  
Large Scale ◽  
Hydraulic Fractures ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Fracture Density

In order to study the mechanism of hydraulic fracturing in enhanced geothermal systems, we analyzed the influence of high temperatures and embedded fractures on the initiation and propagation of hydraulic fractures using a laboratory test and numerical simulation. The analysis was conducted via large-scale true triaxial hydraulic fracturing tests with acoustic emission monitoring. Moreover, we discussed and established the elastic-plastic criterion of hydraulic fracturing initiation. The corresponding fracturing procedure was designed and embedded into the FLAC3D software. Then, a numerical simulation was conducted and compared with the laboratory test to verify the accuracy of the fracturing procedure. The influence of high temperatures on hydraulic fracturing presented the following features. First, multi-fractures were created, especially in the near-well region. Second, fracturing pressure, extension pressure, and fracture flow resistance became larger than those at room temperature. 3D acoustic fracturing emission results indicated that the influence of the spatial distribution pattern of embedded fractures on hydraulic fracturing direction was larger than that of triaxial stress. Furthermore, the fracturing and extension pressures decreased with the increase of embedded fracture density. For hydraulic fracturing in a high temperature reservoir, a plastic zone was generated near the borehole, and this zone increased as the injection pressure increased until the well wall failed.

scholarly journals Numerical simulation of hydraulic fracturing in enhanced geothermal systems considering thermal stress cracks

2021 ◽  
Author(s):  
Ziyang Zhou ◽  
Hitoshi MIKADA ◽  
Junichi TAKEKAWA ◽  
Shibo Xu
Keyword(s):  
Thermal Stress ◽  
High Temperature ◽  
Hydraulic Fracturing ◽  
Geothermal Energy ◽  
Confining Pressure ◽  
Numerical Results ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Compression Tests ◽  
High Confining Pressure

Abstract With the increasing attention to clean and economical energy resources, geothermal energy and enhanced geothermal systems (EGS) have gained much importance. For the efficient development of deep geothermal reservoirs, it is crucial to understand the mechanical behavior of reservoir rock and its interaction with injected fluid under high temperature and high confining pressure environments. In the present study, we develop a novel numerical scheme based on the distinct element method (DEM) to simulate the failure behavior of rock by considering the influence of thermal stress cracks and high confining pressure for EGS. We validated the proposing method by comparing our numerical results with experimental laboratory results of uniaxial compression tests under various temperatures and biaxial compression tests under different confining pressure regarding failure patterns and stress-strain curves. We then apply the developed scheme to the hydraulic fracturing simulations under various temperatures, confining pressure, and injection fluid conditions. Our numerical results indicate that the number of hydraulic cracks is proportional to the temperature. At a high temperature and low confining pressure environment, a complex crack network with large crack width can be observed, whereas the generation of the micro cracks is suppressed in high confining pressure conditions. In addition, high-viscosity injection fluid tends to induce more hydraulic fractures. Since the fracture network in the geothermal reservoir is an essential factor for the efficient production of geothermal energy, the combination of the above factors should be considered in hydraulic fracturing treatment in EGS.

scholarly journals Analysis of Hydraulic Fracturing and Reservoir Performance in Enhanced Geothermal Systems

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Mengying Li ◽  
Noam Lior
Keyword(s):  
Hydraulic Fracturing ◽  
Flow Direction ◽  
Fractured Reservoirs ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Fracture Width ◽  
Reservoir Performance ◽  
Flow And Heat Transfer ◽  
Engineered Geothermal System

Analyses of fracturing and thermal performance of fractured reservoirs in engineered geothermal system (EGS) are extended from a depth of 5 km to 10 km, and models for flow and heat transfer in EGS are improved. Effects of the geofluid flow direction choice, distance between fractures, fracture width, permeability, radius, and number of fractures, on reservoir heat drawdown time are computed. The number of fractures and fracture radius for desired reservoir thermal drawdown rates are recommended. A simplified model for reservoir hydraulic fracturing energy consumption is developed, indicating it to be 51.8–99.6 MJ per m3 fracture for depths of 5–10 km.

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

Energies ◽  
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.

scholarly journals Diffusivity-dependent fracturing processes and microseismic activity in granite

2020 ◽  
Vol 205 ◽  
pp. 02009
Author(s):  
Catarina Baptista-Pereira ◽  
Bruno Gonçalves da Silva
Keyword(s):  
Hydraulic Fracturing ◽  
Fluid Pressure ◽  
Injection Rate ◽  
Hydraulic Fractures ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Rock Matrix ◽  
Hydraulic Oil ◽  
Permeability Enhancement ◽  
Microseismic Activity

Enhanced Geothermal Systems have relied on hydraulic fracturing to increase the permeability of rock reservoirs. The permeability enhancement depends on the connectivity between new and existing fractures. This, in turn, depends to a large extent on the interaction between the rock and the fracturing fluid, which not only pressurizes existing and new fractures but also diffuses into the rock matrix. In this research, the effect of the diffusivity of hydraulic oil on the fracturing processes and microseismicity of unconfined prismatic granite specimens was experimentally evaluated using visual and acoustic emission monitoring. The tests consisted of injecting hydraulic oil into two pre-fabricated flaws at two rates (2 ml/min and 20 ml/min), kept constant in each test. The fluid pressure inside the flaws was increased until hydraulic fractures propagated and the fluid front growing from the pre-fabricated flaws was visually monitored throughout the tests. It was observed that the fracturing pressures and patterns were injection-rate-dependent, which shows that diffusivity and poro-elastic effects play an important role in the hydraulic fracturing processes of granite. A smaller fluid front was observed for the 20 ml/min injection rate, associated to a lower volume injected and to a higher fracturing pressure when compared to the 2 ml/min injection rate. This was interpreted to be caused by the different pore pressures that developed inside of the rock matrix, which are function of the fluid front size. Microseismic activity was observed throughout the tests, becoming more intense and localized near the flaws as one approached the end of the test (i.e. visible crack propagation). While microseismic events were observed outside the fluid front region, their density was significantly larger within this area, showing that fluid diffusivity may contribute to an intensification of the microseismic activity.

Characterizing Hydraulic Fracturing With a Tendency-for-Shear-Stimulation Test

2014 ◽  
Vol 17 (02) ◽  
pp. 233-243 ◽  
Author(s):  
Mark McClure ◽  
Roland Horne
Keyword(s):  
Hydraulic Fracturing ◽  
Principal Stress ◽  
Fluid Pressure ◽  
Test Fluid ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Natural Fractures ◽  
Permeability Enhancement ◽  
Minimum Principal Stress ◽  
Tensile Fracturing

Summary The classical concept of hydraulic fracturing is that a single, planar, opening mode fracture propagates through the formation. In recent years, there has been a growing consensus that natural fractures play an important role during stimulation in many settings. There is not universal agreement on the mechanisms by which natural fractures affect stimulation, and these mechanisms may vary depending on formation properties. One potentially important mechanism is shear stimulation, in which increased fluid pressure induces slip and permeability enhancement on pre-existing fractures. We propose a tendency-for-shear-stimulation (TSS) test as a direct, relatively unambiguous method for determining the degree to which shear stimulation contributes to stimulation in a formation. In a TSS test, fluid injection is performed while maintaining the bottomhole fluid pressure slightly less than the minimum principal stress. Under these conditions, shear stimulation is the only possible mechanism for permeability enhancement (except, perhaps, thermally induced tensile fracturing). A TSS test is different from a conventional procedure because injection is performed at a specified pressure (rather than a specified rate). With injection at a specified rate, fluid pressure may exceed the minimum principal stress, and it may cause tensile fractures to propagate through the formation. If this occurs, it will be ambiguous whether stimulation was because of shear stimulation or tensile fracturing. Maintaining pressure less than the minimum principal stress ensures that the effect of shear stimulation can be isolated. Low-rate injectivity tests could be performed before and after the TSS test to estimate formation permeability. An increase in formation permeability would indicate that shear stimulation has occurred. The flow-rate transient during injection may also be interpreted to identify shear stimulation. Numerical simulations of shear stimulation were performed with a discrete-fracture-network (DFN) simulator that couples fluid flow with the stresses induced by fracture deformation. These simulations were used to qualitatively investigate how shear stimulation and fracture connectivity affect the results of a TSS test. Two specific field projects are discussed as examples of a TSS test, the Enhanced Geothermal Systems (EGS) projects at Desert Peak, Nevada, and Soultz-sous-Forêts, France.

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