Aperture Distribution Research Articles

Anomalous transport and upscaling in critically-connected fracture networks under stress conditions

Anomalous transport in fractured rocks is of high importance for numerous research fields and applications in hydrogeology and has been widely studied in the last decades. This phenomenon is due to the structural heterogeneities of fractured rocks and the high contrast between the fractures and matrix properties. At the same time, the fracture properties in terms of fracture density and geometrical characteristics are related to in-situ stress conditions that impact the connectivity of the system and the distributions of fracture aperture and length, including the creation of new cracks when the differential stress conditions are strong enough. In order to understand how all these features impact the observed anomalous transport, we study the role of in-situ stress in mass transport through a two-dimensional fractured rock. The fracture network is based on a real outcrop with a connectivity state around the percolation threshold, over which we simulate stress-dependent fracture deformation and propagation, and perform hydrodynamic transport through the deformed rock mass. The impact of the changes in aperture and the creation of new cracks on transport behavior is evaluated for various stress scenarios and reproduced with upscaled representations of transport processes. We also consider matrix diffusion as a source of anomalous transport and demonstrate that this process can be incorporated into the proposed upscaled models. Results showed that traditional upscaling methods with space-Lagrangian velocities description capture well the Gaussian-like breakthrough curves (BTCs) under low-stress ratio conditions, but fail under high-stress ratio conditions with multiple-peak early-times BTCs. To characterize the emergence of strong anomalous transport, we extend the Random Walk model Directed by a Markov Process with space-Lagrangian velocity sampling by incorporating multiple transition matrices conditioned by different initial velocity states. This new transport upscaling model shows high accuracy in predicting complex transport behaviors in critically connected fracture networks.

On the tensorial nature of the hydraulic aperture of rough fractures

Current fractured porous media models may account for the roughness and geometry of the fractures to upscale hydraulic apertures that represent the local aperture distributions. Still, such approaches do not discuss the tensorial nature of the hydraulic aperture, and by employing scalar representations, these models may fail to capture the anisotropy of the fluid flow in rough fractures. By mimicking natural fractures with walls of varying roughness and contact area, we derive hydraulic aperture tensors that preserve the anisotropic flow patterns enforced by local aperture distributions. This work underscores the critical need to represent hydraulic apertures as tensors to model anisotropic fluid flow in rough fractures and proposes a method for upscaling such tensors.

Hierarchically Porous Covalent Organic Frameworks: Synthesis Methods and Applications.

Covalent organic frameworks (COFs) with high porosity have garnered considerable interest for various applications owing to their robust and customizable structure. However, conventional COFs are hindered by their narrow pore size, which poses limitations for applications such as heterogeneous catalysis and guest delivery that typically involve large molecules. The development of hierarchically porous COF (HP-COF), featuring a multi-scale aperture distribution, offers a promising solution by significantly enhancing the diffusion capacity and mass transfer for larger molecules. This review focuses on the recent advances in the synthesis strategies of HP-COF materials, including topological structure design, in-situ templating, monolithic COF synthesis, defect engineering, and crystalline self-transformation. The specific operational principles and affecting factors in the synthesis process are summarized and discussed, along with the applications of HP-COFs in heterogeneous catalysis, toxic component treatment, optoelectronics, and the biomedical field. Overall, this review builds a bridge to understand HP-COFs and provides guidance for further development of them on synthesis strategies and applications.

Fracture aperture anisotropic effects on field scale enhanced geothermal system thermal performance

The thermal performance of a field-scale Enhanced Geothermal System was investigated, considering anisotropy in fracture aperture distributions. The fracture aperture distribution was treated as an autocorrelated random field with different ranges in the x- and y-directions, defined by geometric anisotropic ratios between 1.5 and 4. To model realistic aperture distributions, constraints were applied to ensure the aperture distributions had Hurst exponents that are typical of fractures observed in nature.The thermal drawdown between the perpendicular and parallel flow configurations was compared, revealing a 60 % likelihood of improved heat transfer in the perpendicular flow configuration. When exploring the impact of geometric anisotropy ratios on thermal performance, aperture distributions with a geometric anisotropy ratio of 2 demonstrated about 70 % better thermal performance in favor of the perpendicular flow direction. This ratio also exhibited aperture distributions with Hurst exponents within the range found in natural faults and fractures, suggesting a 70 % likelihood of improved thermal performance in the perpendicular flow configuration for actual fracture behavior.The perpendicular flow configuration mainly exhibited tortuous flow paths, while the parallel flow direction mostly had near-horizontal flow paths. The tortuous flow paths increased contact between the fluid and fracture surface area, resulting in improved thermal performance.The findings suggest the importance of considering shear direction at the field scale when placing wells. Placing a well perpendicular to the direction of slip or shear may yield enhanced thermal performance compared to placing a well parallel to the direction of slip or shear.

Anisotropic flow characteristics in single-fractured tensile and shear fractures in granite subjected to various confining stress

Anisotropic flow characteristics in single-fractured tensile and shear fractures in granite subjected to various confining stresses were investigated by experiments and experimental results-based flow simulations. Anisotropic characteristics in aspects such as the permeability reduction rate, stress dependency of permeability, and flow paths in fracture and fracture aperture distribution were analysed and compared between tensile and shear fractures. The main conclusions are as follows: (1) for tensile fractures, the permeability in the X direction, k X , is slightly lower than the permeability in the Y direction, k Y , and the average permeability anisotropic coefficient, α k ( α k = k X / k Y ), is in the range 0.236–0.779. For shear fractures, k X is obviously lower than k Y , and α k is in the range 0.038–0.163; therefore, the permeability anisotropy in shear fractures is stronger than in tensile fractures. (2) Strong channelling effects exist in both shear and tensile fractures. The stress-dependence coefficient of permeability is 0.731 MPa −1 in the X direction and 0.365 MPa −1 in the Y direction for tensile fractures, and 0.034 and 0.010 MPa −1 , respectively, for shear fractures, indicating that the dependency of permeability on stress also shows anisotropy. (3) An empirical model for α k based on stress and fracture aperture variograms is proposed. Based on α k , permeability along both the X and Y directions can be well predicted, especially under relatively high confining stress.

Ultra-low SLL slotted waveguide antenna array using Chebyshev aperture distribution function for MM-wave tracking radar applications

A non-uniform aperture distribution slotted waveguide antenna is presented. The slotted waveguide antenna array is chosen for its ease for aperture distribution control and the flexibility of gain adjustment. Multiple aperture distribution functions, including uniform, binominal, Chebyshev, and Blackman, have been extensively investigated to achieve the best possible side lobe suppression. These distribution functions have been converted to slot displacement from the center line of the antenna. Number of slots in the proposed array is chosen to be eight to satisfy the required gain for mm-wave radar tracking application. The proposed antenna is simulated and optimized using the full wave simulator package (CSTMWS). Rounded edge slots are adapted instead of the sharp ones, as they are more applicable for the CNC fabrication process. An eight-slot waveguide antenna is fabricated and gold-plated, considering the Chebyshev distribution approach. The proposed design achieves very stable radiation characteristics and performance over the operating bandwidth, which extends from 33.6 GHz up to 35.9 GHz. At 35 GHz, the total realized gain of the overall antenna is found to be 13.4 dBi, with an overall radiation efficiency of 95.21 %. An obvious low SLL of −30 dB is obtained at the frequency of 35 GHz. The low side lobe level parameter is very crucial for radar applications as it enhances the overall target SNR and reduces false target observations. The pre-stated antenna characteristics make it a good candidate for mm-wave radar applications and point-to-point communications (P2P).

Apparent activation energy of mineral in open pit mine based upon the evolution of active functional groups

This study aimed to investigate the mechanism of mineral spontaneous combustion in an open pit. On the study of coal and mineral mixture in open pit mines, as well as through the specific surface area and Search Engine Marketing (SEM) experiments, the specific surface area and aperture characteristics of distribution of open pit coal sample and pit mineral mixture samples were analyzed. Thermal analysis experiments were used to divide the oxidation process was divided into three stages, and the thermal behavior characteristics of experimental samples were characterized. On the basis of the stage division, we explored the transfer law of the key active functional groups of the experimental samples. The apparent activation energy calculation of the key active groups, performed by combining the Achar differential method with the Coats–Redfern integral method, microstructural and oxidation kinetic properties were revealed. The resulted showed that the mixed sample had high ash, the fixed carbon content was reduced, the specific surface area was far lower than the raw coal, the large aperture distribution was slightly higher than the medium hole, the micropore was exceptionally low, the gas adsorption capacity was weaker than the raw coal, the pit coal sample had the exceedingly more active functional groups, easy to react with oxygen, more likely to occur naturally, and its harm was relatively large. The mixed sample contained the highest C–O–C functional group absorbance. The functional groups were mainly influenced by the self-OH content, alkyl side chain, and fatty hydrocarbon in the sample. The main functional groups of the four-like mixture had the highest apparent activation energy, and the two reactions were higher in the low-temperature oxidation phase.

Effects of Topological Properties with Local Variable Apertures on Solute Transport through Three-Dimensional Discrete Fracture Networks

In this study, the effects of topological properties with local variable apertures on fluid flow and solute transport through three-dimensional (3D) discrete fracture networks (DFNs) were investigated. A series of 3D DFNs with different fracture density, length, and aperture distribution were generated. The fluid flow and solute transport through the models were simulated by combining the MATLAB code and COMSOL Multiphysics. The effects of network topology and aperture heterogeneity on fluid flow and transport process were analyzed. The results show that the fluid flow and solute transport exhibit a strong channeling effect even in the DFNs with identical aperture, in which the areas of fast and slow migration fit well with the high- and low-flow regions, respectively. More obvious preferential paths of flow and migration are observed in individual fractures for the DFN with heterogeneous aperture than the model with identical aperture. Increasing the fracture length exponent reduces the available flow and transport paths for sparse fracture networks but does not significantly change the flow and transport channels for dense fracture networks. The breakthrough curves (BTCs) shift towards the right and slightly lag behind as the fracture density decreases or the aperture heterogeneity increases. The advection–diffusion equation (ADE) model cannot properly capture the evolution of BTCs for 3D DFNs, especially the long tails of BTCs. Compared to the ADE model, the mobile-immobile model (MIM) model separating the liquid phase into flowing and stagnate regions is proven to better fit the BTCs of 3D DFNs with heterogeneous aperture.

Characterizing fractured reservoirs by integrating outcrop analogue studies with flow simulations

This research focuses on how ‘static’ properties of fracture networks can be studied by considering ‘dynamic’ flow simulation, while static properties such as clustering, connectivity, variation in aperture and, of course, anisotropy of fracture networks can be quantified using different geostatistical/data analysis techniques. The flow responses through such networks can be simulated to check if flow simulation can be used as a tool for evaluating its geometry. In order to achieve this, outcrop analogues of fractured reservoirs are converted into permeability structured grids implementing the fracture continuum (FC) concept. These FC models are flow simulated in a streamline simulator, TRACE3D. Results of the first experiment show that rather than the ‘fractal dimension’, the ‘lacunarity parameter’, which quantifies scale-dependent clustering of fractures, is a unique identifier of network geometry and acts as a proxy for fracture connectivity and an indicator of flow behaviour. The FC model further accommodates variability in fracture apertures and, thus, in a second experiment a set of models with a hierarchical aperture distribution was built and tested for their time-of-flight (TOF) and recovery curves, which showed that smaller fractures with narrow apertures do not significantly contribute to flow. In a third experiment considering anisotropy, it was observed that tightly clustered fractures along preferential directions can be identified from anisotropy in flow patterns. The results from these three experiments show that flow patterns in fracture networks can indicate the overall scale-dependent clustering, the anisotropy that arises from such clustering and that narrower fractures do not significantly alter the overall flow behaviour. Thematic collection: This article is part of the Digitally enabled geoscience workflows: unlocking the power of our data collection available at: https://www.lyellcollection.org/topic/collections/digitally-enabled-geoscience-workflows

Study on the microstructural evolution and photocatalytic mechanism of (Au)/PCN photocatalyst

In this paper, the microstructure evolution of polymeric carbon nitride was investigated and Au ions was used to improve its photocatalytic efficiency. Their structures were investigated by FT-IR, XPS, XRD, SEM and TEM. Their specific surface area and aperture distribution were measured by BET. Meanwhile, the energy band structure and electron-hole separation efficiency were analyzed by UV–Vis and PL spectroscopy. In addition, the photocatalytic performance of the photocatalysts was assessed by photocatalytic degradation of RhB and photocatalytic hydrogen evolution. The results showed that 600-PCN possessed the best photocatalytic performance, with a degradation rate of 46.92 % in 150 min. What's more, the degradation rate of RhB solution by 2 % Au/PCN reached 47.88 %, which was 2.17 times higher than that of 550-PCN (22.01 %). During the degradation process, h+ oxidatively degrade RhB. The hydrogen production rate of 2 % Au/PCN was about 11.658 μmol/g/h, which was 41.23 times higher than that of 550-PCN (0.282 μmol/g/h).

Existence analysis of hydraulic conductivity representative elementary volume in fractured rocks based on three-dimensional discrete fracture network method

The complexity of fractures in rocks results in heterogeneity and anisotropy of their hydraulic properties. The existence of hydraulic conductivity representative elementary volume (KREV) is a fundamental question in comprehending the hydraulic behavior of fractured rock masses. This article introduces an analytical procedure for determining the existence of KREV in fractured rock masses, which considers the distribution of underground apertures using a discrete fracture network (DFN) model. The procedure follows four basic steps: inverse modeling to generate a 3D DFN; calibration of the effective aperture by combining the results of packer tests and flow simulation using finite difference methods; calculation of the equivalent conductivities in 10 domains and 31 different flow directions; analysis of the fit error between the conductivity ellipsoid to determine the existence of KREV. The proposed approach is applied to the fractured rocks surrounding the 3013 exploration adit near the underground powerhouse of the Three Gorges Project as a case study. The results show that most fractures in the study area have apertures ranging from 0.06 to 0.25 mm and follow a lognormal distribution. The KREV size is 14–16 times the fracture spacing. Investigation of this model has significant implications for understanding flow through fracture networks in related fields.

A method to interpret fracture aperture of rock slope using adaptive shape and unmanned aerial vehicle multi-angle nap-of-the-object photogrammetry

The aperture of natural rock fractures significantly affects the deformation and strength properties of rock masses, as well as the hydrodynamic properties of fractured rock masses. The conventional measurement methods are inadequate for collecting data on high-steep rock slopes in complex mountainous regions. This study establishes a high-resolution three-dimensional model of a rock slope using unmanned aerial vehicle (UAV) multi-angle nap-of-the-object photogrammetry to obtain edge feature points of fractures. Fracture opening morphology is characterized using coordinate projection and transformation. Fracture central axis is determined using vertical measuring lines, allowing for the interpretation of aperture of adaptive fracture shape. The feasibility and reliability of the new method are verified at a construction site of a railway in southeast Tibet, China. The study shows that the fracture aperture has a significant interval effect and size effect. The optimal sampling length for fractures is approximately 0.5–1 m, and the optimal aperture interpretation results can be achieved when the measuring line spacing is 1% of the sampling length. Tensile fractures in the study area generally have larger apertures than shear fractures, and their tendency to increase with slope height is also greater than that of shear fractures. The aperture of tensile fractures is generally positively correlated with their trace length, while the correlation between the aperture of shear fractures and their trace length appears to be weak. Fractures of different orientations exhibit certain differences in their distribution of aperture, but generally follow the forms of normal, log-normal, and gamma distributions. This study provides essential data support for rock and slope stability evaluation, which is of significant practical importance.

Characterising a rock fracture rough surface using spatial continuity and kriging: a new approach to meshing coupled thermo–hydraulic–mechanical–chemical (THMC) models

Abstract. Fluid flow through low permeability rocks is mainly accomplished through fractures. In order to model fluid flow, coupled thermo–hydraulic–mechanical–chemical (THMC) numerical models are used, which rely on fracture surface representations to construct a distribution model of the empty space (aperture) between the two fracture faces. The traditionally used statistical representations of fracture surfaces often overlook spatial continuity (SC), i.e. how well correlated points are in direction and distance. Examples are the fractures' aperture distribution random sampling to the joint roughness coefficient. This may result in a poor representation of the aperture distribution and thus a poor model. The first aim of this study is to investigate the possibility of characterising a fracture surface roughness using its SC parameters, an upscaled fracture surface and ordinary kriging (OK) interpolation algorithm. This method provides better control over the aperture model creation, which will have implications for its complexity and computation times. The second aim is to utilise the SC information and the distribution of a fracture in order to extrapolate (i.e. blind predict) the distribution of the fracture where no observations exist. A statistical analysis was performed in a greywacke in order to acquire the parameters necessary to describe the SC of the fracture surface topography. The surface was then interpolated using the OK algorithm. These parameters and the surface distribution will be used to inform the OK algorithm to extrapolate the fracture to where no data has yet been acquired. A reasonable match between the kriged and original surfaces has been achieved and the fit quantified by analysing the error between the two and by R2, which offer positive measurements of methodological quality. The aperture can easily be calculated from the difference between both complementary surfaces. The aperture between the two original fracture surfaces versus the two kriged fracture surfaces was also quantified and compared, yielding good results. This method may provide a new alternative to current storing and computing solutions for fracture representation, especially in aperture distribution calculation for coupled THMC numerical models and simulations. To verify advances in accuracy and computing times for this method, results between models derived from the original versus kriging aperture data will have to be compared. Another potential applicability of the SC information is to know a priori from any modelling which directions are those of Darcy's flow and which are the directions of the highest and lowest dilation rates with shearing, which will have to be confirmed with future planned modelling work.

An Improved Model for Evaluating the Hydraulic Behaviour of a Single Rock Joint Considering Contact Area Evolution During Shearing

The contact of rock joints during shearing induced by underground excavation significantly impacts the hydro-mechanical behaviour of fractured rock mass, since fluid tends to flow through a rough-walled fracture along connected channels while bypassing the contact areas with tortuosity. However, previous research mostly considered joint roughness or aperture changes based on 2D joint profiles, while the contact and tortuosity using 3D surfaces were often overlooked. This paper considers the evolution of contact area and aperture distribution during shearing. The concept of the critical inclination angle is introduced and correlated with the contact area during shearing based on Grasselli’s criterion. The standard deviation of the mean mechanical aperture is calculated using the modified algorithm. An improved model for estimating the hydraulic aperture with the mechanical aperture is then developed, applying an aperture correction term and a contact correction term. A number of shear-flow tests on artificial joint samples under constant normal loads are conducted. The accuracy and reliability of the proposed model are verified by comparing it against the experimental results and by comparing the prediction performance with other published models. Results show that the proposed model can improve the prediction of the hydraulic aperture and hydraulic conductivity of a single rock joint during shearing.

Near-Field Gain Expression for Tapered Circular Aperture Antennas

Near-field electromagnetic wave, which is radiated by tapered circular aperture antennas, has found more engineering applications in many diverse fields. Through the simulation of a reflector antenna whose efficiency is up to 51.4%, it can be found that the aperture distribution cannot be regarded as uniform distribution but as tapered distribution. Thus, expressions for near fields of uniform circular apertures cannot be applied to tapered circular aperture antennas in practical engineering. To alleviate such problem, near-field calculation formulas are proposed based on the Sommerfeld integrals with steepest descents technique, which ensures the accurate and efficient analysis of the near field of the tapered circular aperture antenna. And near-field characteristics of tapered circular aperture antennas are displayed. The maximum difference of normalized near-field amplitudes between tapered and uniform distribution is 0.35V/m. Three-dimensional near-field gain of circular aperture antennas is developed from the near-field radiation pattern. The proposed expression extends the range of calculation from the axial to more directions compared with the previous expression. Also, this expression is valid in both the near field and the far field. Using full-wave simulations, results obtained from the proposed expression are compared with the simulated results. And the deviation in near-field gain is less than 0.3dB, which indicates the convenience and effectiveness of our expression. The proposed near-field gain expression can be applicable to the near-field measurement and design of millimeter or terahertz radar systems that work in the near-field region.

Investigation and evaluation methods of shallow geothermal energy considering the influences of fracture water flow

The energy replenishment and heat convection induced by fracture water flowing through the rock mass impact the shallow geothermal energy occurrence, transfer and storage mechanisms in it. In this article, a suitability evaluation and categorization system is proposed by including judgement indexes that are more closely aligned with the actual hydrogeological conditions in fracture developed regions; an assessment approach of regional shallow geothermal energy is proposed by coupling the influences of fracture water into the calculation methods of geothermal capacity, thermal balance and heat transfer rate. Finally, by taking two typical fracture aperture distributions as examples, the impacts of fracture water on the investigation and evaluation of shallow geothermal energy are quantitatively analyzed. Although the fracture apertures only share 1.68% and 0.98% of the total length of a borehole, respectively, in the two examples, the fracture water convection contributes up to 11.01% and 6.81% of the total heat transfer rate; and the energy replenishment potential brought by the fracture water is equivalent to the total heat extraction of 262 boreholes. A single wide aperture fracture can dominate the aforementioned impacts. The research results can support more accurate evaluation and efficient recovery of shallow geothermal energy in fracture developed regions.

Rock aperture image acquisition and processing based on Mehanics moment, Steger theory and Fractal analysis

In the realm of rock engineering, the distribution of apertures plays a crucial role in predicting the stability of dams, slopes, and others, and it affects the energy transportation in rock mass. In this study, the rock slice samples were obtained using a fluorescent dyesoluble in field. They were examined under a microscope with ultraviolet light, yielding rock aperture image resolutions up to 3.9 μm/pixel. For image binarization, a novel image segmentation technique, grounded in mechanics moments, is investigated to extract the aperture networks from each slice image. For aperture extraction, an algorithm based on Steger's theory is put forth for irregularly-shaped apertures. For aperture analyses, various aperture parameters are assessed and scrutinized, employing 1D Fractal analysis. It is new that the 1D Fractal analysis is utilized for the entire aperture network instead of a single line-like aperture within an image. Ultimately, each aperture is measured and analyzed through continuous aperture images. Experimental results demonstrate that this innovative approach provides the comprehensive aperture information by processing multiple images and is suitable for other analogous applications.

Effects of fracture aperture distribution on the performances of the enhanced geothermal system using supercritical CO2 as working fluid

Enhanced Geothermal Systems (EGS) technology has the potential to be a significant source of clean, renewable energy worldwide. A promising alternative to water as the working fluid in EGS is the supercritical carbon dioxide (scCO2), which simultaneously contributes to reducing the atmospheric greenhouse gas emissions. The existing thermal-hydraulic coupled numerical models for non-isothermal two-phase flow in fractured porous media overlook the fracture aperture distributions, which significantly affects EGS performance. This study employs a discrete fracture model with a normal distribution of fracture apertures to investigate the EGS energy performance and carbon sequestration ability. The Monte Carlo method is applied to ensure the simulation results reach a statistical equilibrium from multiple realizations. Results show that the aperture distribution significantly affects EGS performances. The cumulative energy output and total sequestered scCO2 mass can be roughly divided into three stages based on fracture aperture distributions. On the other hand, the effects of aperture distribution become more important as the increase of mean fracture aperture and the reduction of injection pressures. Furthermore, comparing the performances of the EGS using scCO2 and H2O as working fluid, the study found that scCO2-EGS performs better with larger injection pressure, but it is more sensitive to aperture distribution.

Enhanced Effective Aperture Distribution Function for Characterizing Large-Scale Antenna Arrays

Accurate characterization of large-scale antenna arrays is growing in importance and complexity for the fifth-generation (5G) and beyond systems, as they feature more antenna elements and require increased overall performance. The full 3D patterns of all antenna elements in the array need to be characterized because they are in general different due to construction inaccuracy, coupling, antenna array's asymmetry, etc. The effective aperture distribution function (EADF) can provide an analytic description of an antenna array based on a full-sphere measurement of the array in an anechoic chamber. However, as the array aperture increases, denser spatial samples are needed for EADF due to large distance offsets of array elements from the reference point in the anechoic chamber, leading to a prohibitive measurement time and increased complexity of EADF. In this paper, we present the EADF applied to large-scale arrays and highlight issues caused by the large array aperture. To overcome the issues, an enhanced EADF is proposed with a low complexity that is intrinsically determined by the characteristic of each array element rather than the array aperture. The enhanced EADF is validated using experimental measurements conducted at 27-30 GHz frequency band with a relatively large planar array.

Influence of extreme fracture flow channels on the thermal performance of open-loop geothermal systems at commercial scale

Adequate stewardship of geothermal resources requires accurate forecasting of long-term thermal performance. In enhanced geothermal systems and other fracture-dominated reservoirs, predictive models commonly assume constant-aperture fractures, although spatial variations in aperture can greatly affect reservoir permeability, fluid flow distribution, and heat transport. Whereas previous authors have investigated the effects of theoretical random aperture distributions on thermal performance, here we further explore the influence of permeability heterogeneity considering field-constrained aperture distributions from a meso-scale field site in northern New York, USA. Using numerical models of coupled fluid flow and heat transport, we conduct thermal–hydraulic simulations for a hypothetical reservoir consisting of a relatively impervious porous matrix and a single, horizontal fracture. Our results indicate that in highly channelized fields, most well design configurations and operating conditions result in extreme rates of thermal drawdown (e.g., 50% drop in production well temperatures in under 2 years). However, some other scenarios that account for the risks of short-circuiting can potentially enhance heat extraction when mass flow rate is not excessively high, and the direction of geothermal extraction is not aligned with the most permeable features in the reservoir. Through a parametric approach, we illustrate that well separation distance and relative positioning play a major role in the long-term performance of highly channelized fields, and both can be used to help mitigate premature thermal breakthrough.