Borehole Televiewer Research Articles

Assessing the geometry of defect waviness from borehole data

Within the large, open cut, iron ore mines of the Pilbara region of Western Australia, defect shear strengths often control the slope design where bedding dips shallowly to moderately out of the pit slope. The presence of metre to decametre scale open folding or waviness in these units can contribute to the friction angle of bedding shear strengths, potentially allowing for steeper slope angles and improved economics for the deposit. Traditionally, waviness affecting defect shear strength is assessed from surface mapping, bench mapping or qualitatively from observations in core. Surface mapping of bedrock is often not possible due to detrital cover or a lack of suitable outcrop, while bench mapping is inherently conducted perpendicular to the direction of sliding risk. The use of downhole data from boreholes drilled into the slopes circumvents these issues. The method presented here involves assessing characteristic downhole wavelength, inter-limb angle and amplitude of folding from defect orientation data interpreted from borehole televiewer imaging. The downhole wavelength and defect orientations are transformed to a true down-dip wavelength, dilation angle, and estimated amplitude in the direction of sliding risk. The calculation of down-dip wavelength is critical for assessing the applicability of the associated dilation angle to the scale of the slope and failure mechanism in question. The adoption of defect shear strengths that include a waviness contribution to the friction angle allows for implementation of steeper slope angles in structurally controlled slopes.

Modelling and inferring fracture curvature from borehole GPR data: A case study from the Bedretto Laboratory, Switzerland

AbstractFracture curvature has been observed from the millimetre to the kilometre scales. Nevertheless, characterizing curvature remains challenging due to data sparsity and geometric ambiguities. As a result, most numerical models often assume planar fractures to ease computations. To address this limitation, we present a novel approach for inferring fracture geometry from travel‐time data of electromagnetic or seismic waves. Our model utilizes co‐kriging interpolation of control points in a three‐dimensional surface mesh to simulate fracture curvature effectively, resulting in an unstructured triangular grid. We then refine the fracture surface into a structured grid with equidistant elements so that both small‐scale heterogeneities and large‐scale curvature can be modelled. To constrain the fracture geometry, we perform a deterministic travel‐time inversion to optimally place these control points. We validate our methodology with synthetic data and address its limitations. Finally, we infer the geometry of a large (more than 200 m) fracture observed in single‐hole ground‐penetrating radar field data. The fracture surface closely agrees with borehole televiewer observations and is also constrained far from the boreholes. Our modelling approach can be trivially adapted to multi‐offset ground‐penetrating radar or active seismic data.

Uranium anomaly in groundwater of the hard rock aquifer system in southeast Brazil

This study presents a hydrogeological characterization that fills knowledge gaps in an area where a complex geological scenario connects two fractured (granite/metamorphic rocks and diabase) and one porous (sedimentary rocks) aquifer systems. Previous groundwater studies from the four local deep supply wells suggested the sedimentary aquifer as the source of uranium (∼60 μg/L) in one of the wells. Despite the water extraction interruption from this well, this finding needed to be supported by evidence provided by the geological and structural characteristics of the aquifers. Data collected through video inspection, caliper, optical (OPTV), and acoustic borehole televiewers (ATV) revealed the predominance of the crystalline aquifer in the area. As recorded by video inspection, the well's borehole with high U intersects the crystalline rocks at several open fractures and presents the highest gamma radiation values. Therefore, we infer that the origin of dissolved U is the weathering of primary minerals locally occurring in those rocks. The U leaching and complexation as calcium-uranyl-carbonates favors its solubility in that specific aqueous medium, as shown by hydrogeochemical modeling using PHREEQC. Additionally, the major ions and trace elements concentrations allow the division of the wells into two groups: a) two with higher U concentrations, influenced by the granite/metamorphic aquifer and possibly longer residence times, and b) the other two wells with lower U concentrations, higher nitrate concentrations, influenced by the diabase aquifer, possibly have younger residence times.

Evaluation of EDZ characterization technology for URL based on field investigation at BET

Detailed characterization of the Excavation Damage Zone (EDZ) is an important issue for the high-level radioactive waste (HLW) geological disposal engineering, which is closely related to the long-term safety of the HLW repository. With drill-blast experiment in Beishan Exploration Tunnel (BET, a platform for the field experiment and validation of potential technologies used for China’s HLW disposal engineering in crystalline rock), systematic field tests were carried out to evaluate the suitability of techniques in characterizing EDZ, and to study EDZ characteristic in crystalline tunnel. A series of investigation technologies were used to delineate EDZ and to examine the process of its formation, which includes: p-wave velocity measurement, ground penetrating radar (GPR), acoustic emission (AE) monitoring and borehole televiewer. P-wave velocity measurement along borehole reveal that wave velocity decreased significantly (more than 10%) in 30 cm to 50 cm from the excavation surface, and this zone is defined as EDZ. Clear images of borehole televiewer were obtained, which is helpful for EDZ delineation. GPR and borehole radar were also used for EDZ delineation. Strong reflection signals were detected in the range of 10 cm to 25 cm by GPR with high frequency antenna, indicating significant changes of physical properties of rock-mass in the zone, which is defined as Highly Damaged Zone (HDZ). Moreover, the formation process of EDZ induced by blast in crystalline rock tunnel was analyzed using AE monitoring. Damage process of surrounding rock was divided into blasting damage stage and progressive damage stage. AE events location show the induced cracking activities were clustering within 30 cm to 100 cm from excavation surface. With the experience from field investigation and result analysis, the feasibility and suitability of the techniques for EDZ characterization is evaluated. Finally a specialized EDZ characterization technique system is proposed for underground research laboratory construction in crystalline host rock in Beishan area.

Evaluating the structure and mechanical properties of deep rock masses based on drilling process monitoring and borehole televiewer

Evaluating the structure and mechanical properties of deep rock masses based on drilling process monitoring and borehole televiewer

Application of Ground-Penetrating Radar with the Logging Data Constraint in the Detection of Fractured Rock Mass in Dazu Rock Carvings, Chongqing, China

Geologic interpretation results from conventional ground-penetrating radar (GPR) detection methods tend to have a certain degree of uncertainty. In order to improve the reliability of ground-penetrating radars in the detection of rock mass fissures in grottoes, this study proposes a ground-penetrating radar detection method with the logging data constraint, which is applied to detect the fractured rock mass in the Baodingshan Scenic Area of Dazu Rock Carvings, Chongqing, China. First, conventional logging and borehole televiewer data were compared and verified, yielding detailed lithological and wellbore fissure information. Next, electromagnetic wave velocity was calibrated using GPR profile and the depth of the stratigraphic interface determined by borehole data. Utilizing this calibrated velocity, we are able to accurately calculate the depth values of anomalies in GPR interpretation profiles. Subsequently, we compared the preliminary GPR interpretation profile with the borehole televiewer images. After eliminating false anomalies caused by interference, we obtained more reliable location information for detection targets such as fissures, fracture zones, and weak interlayers. The results of fissure detection in the Dazu Rock Carvings indicate that the detection results of ground-penetrating radar are verified and supplemented under the constraints of stratigraphic and well-wall fissure information obtained by logging. This effectively mitigates the influence of multiplicity and false anomalies of GPR detection on interpretation results. GPR with the logging data constraint enhances the accuracy of the fissure detection results, providing novel technical means for the protection and restoration of grotto relics.

Borehole deformation based in situ stress estimation using televiewer data

The knowledge of in situ stress is critical in safe and optimised extraction of minerals and energy resources. In situ stresses are either measured directly (e.g. overcoring) or estimated indirectly (e.g. borehole breakouts). Borehole breakout analysis for in situ stress estimation is considered as a relatively simple and cost-efficient technique. This technique, however, poses certain limitations such as progressive formation of breakouts and requires inputs such as rock failure parameters that are not often available. As a result, significant effort has been made to develop new indirect methods for in situ stress estimation. Borehole deformation analysis using four-arm caliper has been recently proposed for in situ stress estimation and has shown promising results. In this study, we demonstrate a new methodology that analyses the borehole televiewer data with the technique of borehole deformation analysis to estimate the in situ stresses through a field case study. The advantages and challenges of using borehole televiewer data for stress estimation based on borehole deformation analysis are discussed and the best practice to obtain the reliable results is explained. The limitations of using four-arm caliper and borehole deformation analysis for in situ stress estimation are also discussed and it is shown how televiewer data can overcome such limitations. Finally, the in situ stress results obtained from televiewer data and borehole deformation analysis are compared with independent in situ stress measurements to show the robustness and reliability of the proposed methodology.

Blasting damage control of slit charge structure

This study investigates the control mechanism of blasting damage to surrounding rock and conducts a quantitative evaluation of the damage using laboratory experimentation and field test. A comprehensive evaluation system of blasting damage for roadway contour quality and internal damage of surrounding rock is established using digital image processing, multifractal spectrum calculation, CT scanning, borehole televiewer, and acoustic testing. The results show that the evolution of blasting damage conforms with fractal law, and the relationship between blasting damage area and fractal dimension follows a power function. Slit charge blasting causes the initiation and propagation of two straight main cracks along the slit. The peak velocity measured at the center of the slit charge is found to be 1.74 times that of the ordinary charge. The slit charge can effectively reduce the blasting damage.

Deep ensemble learning for quantitative geological fracture analysis using borehole televiewer images

In the geological survey of hydraulic engineering projects, the Borehole televiewer (BHTV) technique is applied widely. The BHTV images are usually interpreted by engineers. To improve the automatic level of geological images analysis and decrease the subjective influence of the engineers, a fracture quantitative approach based on deep ensemble learning is proposed. In the research, the BHTV images' segmentation using the ensemble model is the basis of the fracture quantitative analysis. Therefore, the accuracy of segmentation can not be ignored. In the experimental study, the different deep learning architectures, UNet, SegNet, and FRRN based on VGG and ResNet, are employed. The evaluation result shows that the IoU values of the single models are in the range of 83.96%–84.36%, while the ensemble model outperforms all of them with a mean IoU of 86.36% and ranks top-3 for the all testing images. Through comparison of the segmentation for the single image, it is evident that the ensemble model is effective for noises removal, which improves the accuracy and efficiency of fracture parameter quantitative analysis. Finally, the thinning method and sine function based on Hough Transform (HT) and the generalized least squares (GLS) are adopted to fit the fracture curve. The calculation result of the dip azimuth, dip angle, and mean thickness also validates the effectiveness of the ensemble model.

Using geophysical log data to predict the fracture density in a claystone host rock for storing high-level nuclear waste

Previously drilled boreholes of a host rock for a potential nuclear waste repository in Hungary revealed a highly fractured claystone rock body. A crucial step for characterizing the hydrodynamic behavior of such a fractured reservoir is fracture identification and accurate calculation of the fracture density. Although acoustic borehole televiewers provide a reliable base for determining the fracture density, older boreholes usually lack such data. However, conventional borehole geophysical measurements are often accessible in such cases. The aim of this study was to identify any correlations between well log data and fracture density. Multiple linear regression analysis was performed on data from two boreholes penetrating the Boda Claystone Formation in southwest Hungary. The upper section of the BAF-4 borehole was used for training, where the fracture density was estimated with a fit of R2 = 0.767. The computed regression function predicted the fracture density with high accuracy in both boreholes for all intervals with typical lithological features. However, in some sections where anomalous well log data indicated changes in the lithology, the prediction accuracy decreased. For example, the function underestimated the fracture density in sandy intervals.

Metre-scale damage zone characterization usingS-coda waves from active ultrasonic transmission measurements in the STIMTEC project, URL Reiche Zeche, Germany

SUMMARYStudies of controlled hydraulic stimulation experiments with active and passive seismic monitoring conducted in Underground Research Laboratories (URLs) benefit from specific knowledge of hydraulic parameters, close by microseismic monitoring revealing structural details of the rock mass, and detailed evolution of seismicity in response to injection operations. Microseismic monitoring is commonly used to characterize a stimulated reservoir volume, for example, in terms of damage evolution of the rock mass. Since seismic attenuation is affected by damage of the rock volume, active seismic sources covering sizes from the centimetre to decimetre scale may help us to investigate space–time varying attenuation properties in a reservoir. This may allow us to monitor damage evolution of the stimulated rock volume in more detail, also since active seismic sources produce stronger signals leading to a broader frequency range that can be analysed compared to passive seismic signals. Within the STIMTEC project in the URL Reiche Zeche (URL-RZ) in Freiberg (Germany), more than 300 active Ultrasonic Transmission (UT) measurements were performed before and after hydraulic stimulations in two boreholes in the targeted rock volume, an anisotropic metamorphic gneiss. The signal-frequency content ranges between 1 and 60 kHz. Assuming scattering attenuation to dominate over intrinsic attenuation, we here apply the single isotropic scattering model. S-coda waves of 88 spatially representative UT measurements are used to estimate the coda quality factor (QC). We obtain stable QC estimates for centre frequencies of octave-width frequency bands between 3 and 21 kHz. We group neighbouring UT measurements to stabilize the observations and form eight UT groups in total, covering different depth intervals in three boreholes and four different time periods to investigate scattering attenuation changes in a spatiotemporal manner. Our final mean QC ($\overline {{Q}_C} $) estimates show characteristic frequency-dependence as observed at the field scale in geological reservoirs. We find temporal variations of QC are strongly connected to hydraulic stimulation, and these variations are more significant than those resolved from velocity changes. $\overline {{Q}_C} $ estimates at frequencies above 15 kHz indicate healing of injection-induced small-scale fractures during a two-months post-stimulation phase. Larger fractures, mostly sampled by lower frequencies (<15 kHz), seem to be more persistent with time (over 15 months). We observe spatial differences of $\overline {{Q}_C} $ values near the mine galleries (driftway and vein drift) and relate these observations to different extents and characteristics of the galleries’ excavation damage zones. Our results further support previous assumptions based on borehole televiewer logs and mapped structures of an existing fault with larger damage zone that crosses the stimulated rock volume NW-SE between the galleries. We conclude that the coda analysis of active UT measurements complements established imaging methods used during experiments in URLs. In particular, coda analysis is a powerful tool for the detection of damage zones and for monitoring local fracture networks with immediate application for imaging georeservoirs considered for exploitation or underground storage of gases and liquids.

Water flux profiling in fractured rock boreholes with an In-Well Point Velocity Probe (IWPVP)

• First field measurements with the fracture adapted IWPVP reached 38 m below ground surface. • Depth profile of water fluxes compares well with PFM, ORP, and FLUTe liner profiles. • Demonstrated calibration of probe measurements with acoustic borehole televiewer data. • IWPVP shown to be a simple, cost-effective tool for measuring flow in fractures. Flow in a fractured rock aquifer beneath the Edwards Air Force Base in California was characterized by depth profiling two wells with In-Well Point Velocity Probes (IWPVPs). The probes, which were originally designed for use in porous media wells, were optimized for use in fractured rock wells and to meet several challenges including: sampling depths up to 38 m; high background site-water salinity; and variable well construction (screened vs open borehole, and well diameters of 7.62 cm and 15.8 cm). The IWPVP measures water flux inside the probe (internal flux), which is converted to fluxes in the aquifer through calibration. At this site, the internal fluxes ranged from 3 to 53 m/d. The channeled internal design of the probe inherently provides information about general flow directions and allows further interpretation of specific flow direction within ±15°, which at this site was generally consistent with the expected regional flow direction. Notably, a significant shift in the flow system was observed following a rain event (up to 180° shift in the flow direction). The IWPVP identified highly transmissive zones in the fractured rock, which were independently confirmed by passive flux meters and oxidation-reduction potential sensors. Transmissivity profiles determined during a FLUTe (Flexible Liner Underground Technologies™) liner deployment also showed similarities in the depths of potentially high flow rates, particularly in the shallower portion of the well (<20 m). With additional information on fracture apertures provided by an acoustic televiewer, the internal fluxes were converted to water fluxes in the observed fractures, indicating seepage velocities in the rock aquifer between 3.7 m/d and 22.4 m/d.

Investigating fault zone hydraulic properties and groundwater potential in a fault-dominated aquifer system: A case study of the Dili fault in Central Taiwan

Discovering groundwater resources in a fault-controlled aquifer system appears to be a viable solution to water scarcity in the mountainous areas of Taiwan. Regoliths, fractured bedrock, and faults commonly exist in such aquifer systems. To investigate the groundwater behavior in the three subsurface media, a 3-D hybrid model (equivalent porous media/discrete fracture network) involving various in situ investigation techniques (borehole drilling, outcrop investigation, borehole televiewer logging, sonic logging, and downhole hydraulic tests) was proposed to assess the hydraulic properties and groundwater storage of the Dili fault zone of Central Taiwan and its surrounding formations. Subsequently, the model was verified through a case study of a simple fracture network. Based on the validated model, flow path analysis was successfully performed to reveal the hydrogeological role of the fault zone, which acts as a conduit for groundwater flow. To ensure the simulated result regarding the hydraulic properties of the fault zone, this study proposes three additional cross-checking techniques, namely stable water isotopes, derivative plots of pumping test data, and identification of hydraulic gradients. The results of the investigation show that the hydraulic properties of the fault zone obtained by the three approaches are consistent with those determined by the numerical method, and the use of the three cross-checking techniques has been confirmed to be suitable for effectively exploring the hydraulic properties of a fault because the site characterization data are insufficient. Finally, the developed hybrid model was used to calculate the groundwater storage of each geological zone, indicating its great potential for the development of groundwater resources in the study area. Therefore, this study integrates in situ investigation techniques, numerical models, and three evaluation approaches of fault zone hydrogeology to construct a systematic, feasible, and applicable exploration methodology that can be employed for groundwater resource exploration in a fault-dominated aquifer system.

“Detection and characterization of fractures in the Eocene Thebes formation using conventional well logs in October field, Gulf of Suez, Egypt”

Fractures are one of the most prevalent and important geological features in petroleum exploration and production, as they have a substantial impact as conduits for hydrocarbon flow and improve the overall permeability of the formation. Despite their necessity, detecting and characterizing natural fractures still represents a difficult challenge. This study provides a technique for detecting and characterizing naturally fractured reservoirs using conventional well logs in the Eocene Thebes Formation, October Field, Gulf of Suez. Especially as this technique is not applied widely in October Field or even in the Gulf of Suez. Most carbonate reservoirs are complex and heterogeneous; one of the reasons is their naturally fractured characteristics. These fractures can significantly affect reservoir behavior, performance, and production. Despite being the most commonly available data source, logs are rarely employed in a systematic way to have a complete quantitative analysis of naturally fractured reservoirs. Since the presence of fractures affects all well logs in one way or another. This study presents an integrated workflow for determining fracture presence potentiality by combining conventional well logs, thin sections, and other available data in absence of directly advanced logging technologies such as Formation MicroImager (FMI), Dipole Shear Image (DSI), and Borehole Televiewer (BHTV). This integrated workflow was very effective and useful in the evaluation of potential fractures' existence, reservoir characterization, and development. Finally, the results of this integrated workflow suggest a high probability of fracture existence and identification in Thebes Formation, confirming that integration between conventional logging and other available data is very precious, and has a good potential to be used in absence of direct advanced methods for fractured reservoir characterization. For further studies, core data and advanced logs would be beneficial for correlation, since they would provide a more accurate picture of the fracture parameters.

Floor Failure Characteristics in Deep Island Longwall Panel: Theoretical Analysis and Field Verification

Floor failure in deep coal mining above confined aquifers with high-water pressure may induce floor water inrush disasters. Considering the effects of mining stress and nonuniformly distributed water pressure, a mechanical calculation model of the island longwall panel in up-dip mining was established, and the stress distribution and floor failure characteristics were analyzed. The failure characteristics of the floor at NO. 2129 panel in Xingdong coal mine were detected by the borehole televiewer and microseismic monitoring system to validate the theoretical model. The results indicated that the floor failure characteristics along the strike and inclination of the island longwall panel in up-dip mining were “asymmetric inverted saddle-shaped” and “spoon-shaped,” respectively. The maximum floor failure depths before and after roof hydraulic fracturing (RHF) were 45.7 m and 29.1 m, respectively. The theoretical calculation results of the maximum depths of floor failure were 45.1 m and 29.9 m, respectively. The theoretical failure characteristics were consistent with those measured on site. The stress concentration magnitude and floor failure depth on the side of the isolated coal pillar were greater than those of other areas, and the water-inrush-prone zones were concentrated on the side of the isolated coal pillar near the intersection of the working face and the roadway. The research results could provide a certain reference for floor failure and water inrush mechanisms under complex geological conditions in deep mining.

Segmentation and quantitative analysis of geological fracture: a deep transfer learning approach based on borehole televiewer image

Segmentation and quantitative analysis of geological fracture: a deep transfer learning approach based on borehole televiewer image

3D Seismic Anatomy of a Watershed Reveals Climate‐Topography Coupling That Drives Water Flowpaths and Bedrock Weathering

AbstractTo investigate how bedrock transforms to soil, we mapped the topography of the interface demarcating onset of weathering under an east‐west trending shale watershed in the Valley and Ridge province in the USA Using wave equation travel‐time tomography from a seismic array of &gt;4,000 geophones, we obtained a 3D P‐wave velocity (Vp) model that resolves structures ∼20 m below land surface (mbls). The depth of mobile soil and the onset of dissolution of chlorite roughly match Vp = 600 m/s and Vp = 2,700 m/s, respectively. Chlorite dissolution initiates porosity growth in the shale matrix. Depth to the 2,700 m/s contour is greater under the N‐ as compared to S‐facing hillslopes and under sub‐planar as compared to concave‐up land surfaces. Broadly, the geometries of the ‘soil’ and ‘chlorite’ Vp contours are consistent with the calculated potential for shear fracture opening under weak regional compression. However, this calculated fracture potential does not consistently explain observations related to N‐ versus S‐facing aspect nor fracture density observed by borehole televiewer. Apparently, regional compression is only a secondary influence on Vp: the primary driver of P‐wave slowing in the upper layers of this catchment is topographic control of reactive water flowpaths and their integrated effects on weathering. The Vp result is best explained as the long‐term integrated effect of groundwater flow‐induced geochemical weathering of shale in response to climate‐driven patterns of micro‐ and macro‐topography.

Regional tectonic stress field evolution based on multi-source stress data—a case study in the Jinzhou area, North China Craton

Regional tectonic stress fields are key crustal stress elements that drive tectonic movements and associated with the evolution of regional tectonics, as well as the formation, preservation, and development of geological resources. The evolution of the regional tectonic stress field of the Jinzhou area, which is located in the eastern block of the North China Craton (NCC), may provide a deeper understanding of the tectonics of western Liaoning and the NCC. In this work, borehole image logging technology and focal mechanism solutions were used to invert the paleo and present regional tectonic stress fields. Four groups of tensile fractures in the southern Jinzhou area were identified via the borehole televiewer, and the azimuths of these fractions were NNW-SSE, NWW-SEE, nearly W-E, and NE-SW in sequence. Focal mechanism solutions showed that the stress states of the area were normal fault and strike-slip, thereby revealing that the southern Jinzhou area is undergoing NEE-SWW-oriented compression and nearly N-S-oriented extension in accordance with the strike-slip mechanism. From the Early Cretaceous to the present, the direction of the regional extensional stress in the southern Jinzhou area has evolved in a counterclockwise and sequential manner from NNW-SSE to NWW-SEE, W-E, NE-SW, and near-N-S; moreover, the regional tectonic mechanism has transitioned from extension to extension-strike-slip to strike-slip.

Grouting effect evaluation of fractured rock mass based on borehole televiewer observation

Grouting is a common means to improve the strength and anti-seepage performance of fractured rock mass. Due to crack concealment, evaluating the grouting effect is a critical problem. An evaluation method of the grouting effect based on borehole televiewer observation is proposed. The optical image of the borehole wall is obtained using a borehole televiewer observation, and the fracture-filling characteristics in the measured image are recognized. The evaluation index is established based on the number of filled and unfilled cracks, defined as the borehole fracture-filling index (BFFI). By analyzing the relationship between BFFI and packer permeability test results, the evaluation standard based on BFFI is established. The evaluation method is applied to a grouting test of a hydropower station’s fractured rock mass. The results show that (1) the grouting effect evaluation results of the packer permeability test and BFFI methods correlate well. (2) The grouting effect evaluation method not only visually shows the filling characteristics of grouting but also quantifies the grouting effect.

Multiscale Hydraulic Conductivity Characterization in a Fractured Granitic Aquifer: The Evaluation of Scale Effect

AbstractWe characterized horizontal hydraulic conductivity (K) of a fractured granitic aquifer using single‐ and cross‐hole hydraulic tests to evaluate “scale effect.” For selected boreholes, K estimates were obtained using single‐hole FLUTe liner and slug tests. Several cross‐hole pumping tests were carried out at various durations. Drawdown responses were first interpreted using analytical well‐test solutions to obtain an effective horizontal conductivity (Keff) assuming a homogeneous and infinite aquifer. The same drawdowns were then numerically inverted using transient hydraulic tomography (THT) to delineate spatial distributions of K and storativity in the area encompassing the boreholes. Papadopulos (1965) and a nonlinear least squares minimization method produced a similar principal Keff direction that is consistent with the dominant fracture strike observed from outcrop and borehole televiewer data. However, principal direction and magnitude of this Keff depend on the pumping test duration and the number of monitoring boreholes used in the interpretation. As a group, K obtained from cross‐hole tests is larger than that obtained from single‐hole tests. However, because cross‐hole tests stressed the aquifer at both interwell and larger scales, Keff obtained from interpreting cross‐hole data is observed to decrease with pumping time, likely due to the dominance of less permeable fractures at larger scale. This lateral reduction of mean K is also revealed by THT as low K zones surrounding the test boreholes. Overall, K is found to increase from single‐hole to the interwell scale and then decrease at larger scale, exhibiting a non‐monotonic scale effect.