Novel chemical stimulation for geothermal reservoirs by chelating agent driven selective mineral dissolution in fractured rocks

AbstractImproving geothermal systems through hydraulic stimulation to create highly permeable fractured rocks can induce seismicity. Therefore, the technique must be applied at a moderate intensity; this has led to concerns of insufficient permeability enhancement. Adding chemical stimulation can mitigate these issues, but traditional methods using strong mineral acids have challenges in terms of achieving mineral dissolution over long distances and highly variable fluid chemistry. Here, we demonstrate a novel chemical stimulation method for improving the permeability of rock fractures using a chelating agent that substantially enhances the dissolution rate of specific minerals to create voids that are sustained under crustal stress without the challenges associated with the traditional methods. Applying this agent to fractured granite samples under confining stress at 200 °C in conjunction with 20 wt% aqueous solutions of sodium salts of environmentally friendly chelating agents (N-(2-hydroxyethyl)ethylenediamine-N, N′, N′-triacetic acid and N, N-bis(carboxymethyl)-l-glutamic acid) at pH 4 was assessed. A significant permeability enhancement of up to approximately sixfold was observed within 2 h, primarily due to the formation of voids based on the selective dissolution of biotite. These results demonstrate a new approach for chemical stimulation.

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Selective mineral dissolution and permeability enhancement of fractured volcanic rocks by chelating agent flooding in geothermal environments

10.5194/egusphere-egu21-13536 ◽

2021 ◽

Author(s):

Luis Salala ◽

Noriaki Watanabe ◽

Kaori Takahashi ◽

Jose Erazo ◽

Noriyoshi Tsuchiya

Keyword(s):

Aqueous Solution ◽

Geothermal Energy ◽

Volcanic Rocks ◽

Chelating Agent ◽

Chemical Stimulation ◽

Mineral Dissolution ◽

High Concentration ◽

Confining Stress ◽

Permeability Enhancement ◽

Geothermal Environments

Chemical stimulation using high-concentration hydrofluoric and hydrochloric acids has been a classic method to enhance the permeability of a geothermal reservoir. Our research group has recently proposed a new chemical stimulation using a weakly acidic (moderate-reactivity) aqueous solution containing an environmentally friendly chelating agent to create voids, which are sustained under crustal stress, by selective mineral dissolution with preventing precipitation by chelation of metal ions. In the present study, we have conducted chelating agent flooding experiments using an aqueous solution of pH 4 containing readily biodegradable chelating agent (GLDA) on various types of fractured volcanic rocks at 200 oC and effective confining stress of 15 MPa. The experiments have revealed fast permeability enhancement of up to approximately four times, from the initial value, in two hours. Further analyses have revealed phenocrysts of Fe-bearing minerals (ex. Hematite) dissolved faster than the groundmass of the rocks to create the voids. These results show the possibility of the new chemical stimulation.Keywords: Chemical stimulation, Chelating agents, Geothermal energy, EGS

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Hydraulic stimulation and fluid circulation experiments in underground laboratories: Stepping up the scale towards engineered geothermal systems

Geomechanics for Energy and the Environment ◽

10.1016/j.gete.2019.100175 ◽

2020 ◽

Vol 24 ◽

pp. 100175 ◽

Cited By ~ 6

Author(s):

Valentin S. Gischig ◽

Domenico Giardini ◽

Florian Amann ◽

Marian Hertrich ◽

Hannes Krietsch ◽

...

Keyword(s):

Geothermal Systems ◽

Fluid Circulation ◽

Hydraulic Stimulation ◽

Engineered Geothermal Systems

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Kinematic dilation during the hydraulic stimulation of pre-fractured rocks

Géotechnique Letters ◽

10.1680/jgele.18.00173 ◽

2019 ◽

Vol 9 (3) ◽

pp. 186-192 ◽

Cited By ~ 2

Author(s):

S. Roshankhah ◽

L. G. Cruz ◽

H. Shin ◽

A. Lizcano ◽

J. C. Santamarina

Keyword(s):

Fractured Rocks ◽

Hydraulic Stimulation ◽

Stimulation Of

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Modeling fluid flow through complex fracture network in geological media by using hierarchical hydraulic properties

10.5194/egusphere-egu2020-5677 ◽

2020 ◽

Author(s):

Kyung Won Chang ◽

Gungor Beskardes ◽

Chester Weiss

Keyword(s):

Fluid Flow ◽

Surrounding Medium ◽

Computational Cost ◽

Energy Resource ◽

Fracture Network ◽

Fractured Media ◽

Enhanced Geothermal Systems ◽

Geothermal Systems ◽

Hydraulic Stimulation ◽

Complex Fracture

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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Evaluation of hydraulic stimulation-induced shear fracture considering inhomogeneous asperity distribution for enhanced geothermal systems

The Proceedings of Mechanical Engineering Congress Japan ◽

10.1299/jsmemecj.2017.g0300605 ◽

2017 ◽

Vol 2017 (0) ◽

pp. G0300605

Author(s):

Noritake TAKAMICHI ◽

Willis-Richards Jonathan ◽

Toshiyuki HASHIDA

Keyword(s):

Shear Fracture ◽

Enhanced Geothermal Systems ◽

Geothermal Systems ◽

Hydraulic Stimulation ◽

Asperity Distribution

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Deep learning for extracting micro-fracture: Pixel-level detection by convolutional neural network

E3S Web of Conferences ◽

10.1051/e3sconf/202020503007 ◽

2020 ◽

Vol 205 ◽

pp. 03007

Author(s):

Yejin Kim ◽

Seong Jun Ha ◽

Tae sup Yun

Keyword(s):

Neural Network ◽

Deep Learning ◽

Convolutional Neural Network ◽

Experimental Studies ◽

Three Dimensional ◽

Frequency Noise ◽

Enhanced Geothermal Systems ◽

Geothermal Systems ◽

Hydraulic Stimulation ◽

Roughness Analysis

Hydraulic stimulation has been a key technique in enhanced geothermal systems (EGS) and the recovery of unconventional hydrocarbon resources to artificially generate fractures in a rock formation. Previous experimental studies present that the pattern and aperture of generated fractures vary as the fracking pressure propagation. The recent development of three-dimensional X-ray computed tomography allows visualizing the fractures for further analysing the morphological features of fractures. However, the generated fracture consists of a few pixels (e.g., 1-3 pixels) so that the accurate and quantitative extract of micro-fracture is highly challenging. Also, the high-frequency noise around the fracture and the weak contrast across the fracture makes the application of conventional segmentation methods limited. In this study, we adopted an encoder-decoder network with a convolutional neural network (CNN) based on deep learning method for the fast and precise detection of micro-fractures. The conventional image processing methods fail to extract the continuous fractures and overestimate the fracture thickness and aperture values while the CNN-based approach successfully detects the barely seen fractures. The reconstruction of the 3D fracture surface and quantitative roughness analysis of fracture surfaces extracted by different methods enables comparison of sensitivity (or robustness) to noise between each method.

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Chemical Stimulation of Engineered Geothermal Systems

10.2172/935668 ◽

2008 ◽

Cited By ~ 1

Author(s):

Peter, E. Rose

Keyword(s):

Chemical Stimulation ◽

Geothermal Systems ◽

Stimulation Of ◽

Engineered Geothermal Systems

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Application of geochemical modelling for hydraulic stimulation in enhanced geothermal systems

Geosystem Engineering ◽

10.1080/12269328.2020.1832923 ◽

2020 ◽

Vol 23 (6) ◽

pp. 342-350

Author(s):

Junbeum Lee ◽

Eunhyea Chung

Keyword(s):

Geochemical Modelling ◽

Enhanced Geothermal Systems ◽

Geothermal Systems ◽

Hydraulic Stimulation

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Influence of reservoir geology on seismic response during decameter-scale hydraulic stimulations in crystalline rock

Solid Earth ◽

10.5194/se-11-627-2020 ◽

2020 ◽

Vol 11 (2) ◽

pp. 627-655 ◽

Cited By ~ 5

Author(s):

Linus Villiger ◽

Valentin Samuel Gischig ◽

Joseph Doetsch ◽

Hannes Krietsch ◽

Nathan Oliver Dutler ◽

...

Keyword(s):

Seismic Response ◽

Fluid Pressure ◽

Shear Zones ◽

Test Site ◽

Fracture Network ◽

Crystalline Rock ◽

Hydraulic Fractures ◽

Geothermal Systems ◽

Hydraulic Stimulation ◽

Shear Dilation

Abstract. We performed a series of 12 hydraulic stimulation experiments in a 20m×20m×20m foliated, crystalline rock volume intersected by two distinct fault sets at the Grimsel Test Site, Switzerland. The goal of these experiments was to improve our understanding of stimulation processes associated with high-pressure fluid injection used for reservoir creation in enhanced or engineered geothermal systems. In the first six experiments, pre-existing fractures were stimulated to induce shear dilation and enhance permeability. Two types of shear zones were targeted for these hydroshearing experiments: (i) ductile ones with intense foliation and (ii) brittle–ductile ones associated with a fractured zone. The second series of six stimulations were performed in borehole intervals without natural fractures to initiate and propagate hydraulic fractures that connect the wellbore to the existing fracture network. The same injection protocol was used for all experiments within each stimulation series so that the differences observed will give insights into the effect of geology on the seismo-hydromechanical response rather than differences due to the injection protocols. Deformations and fluid pressure were monitored using a dense sensor network in boreholes surrounding the injection locations. Seismicity was recorded with sensitive in situ acoustic emission sensors both in boreholes and at the tunnel walls. We observed high variability in the seismic response in terms of seismogenic indices, b values, and spatial and temporal evolution during both hydroshearing and hydrofracturing experiments, which we attribute to local geological heterogeneities. Seismicity was most pronounced for injections into the highly conductive brittle–ductile shear zones, while the injectivity increase on these structures was only marginal. No significant differences between the seismic response of hydroshearing and hydrofracturing was identified, possibly because the hydrofractures interact with the same pre-existing fracture network that is reactivated during the hydroshearing experiments. Fault slip during the hydroshearing experiments was predominantly aseismic. The results of our hydraulic stimulations indicate that stimulation of short borehole intervals with limited fluid volumes (i.e., the concept of zonal insulation) may be an effective approach to limit induced seismic hazard if highly seismogenic structures can be avoided.

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