Slug tests generating oscillating (underdamped) responses are common in high-transmissivity (T) z... more Slug tests generating oscillating (underdamped) responses are common in high-transmissivity (T) zones, and the nature of the response depends on the plumbing of the test equipment and the formation properties. The standard approach for obtaining T is to measure pressure shallow in the riser pipe to obtain an accurate estimate of flow and then predict the formation response from this shallow measurement by accounting for friction and acceleration assuming steady flow conditions (parabolic radial velocity profile). In this study a mathematical solution is developed for unsteady oscillatory laminar flow that shows non-parabolic radial velocity profiles resulting in larger frictional losses, which are out of phase with the average flow velocity, indicating that errors are introduced when using the standard approach for underdamped slug test analysis. The unsteady flow model produces correction factors that can be used to improve the standard approach for predicting the formation pressure; however, not all errors are eliminated. Consequently, a new procedure is presented and applied to underdamped slug tests observed in fractured rock that avoids errors associated with quantifying inertial and frictional effects along the test equipment. This is achieved through the use of two transducers, where one is placed shallow in the water column to infer flow, and one is placed inside the test interval to represent the formation pressure. Comparison of T estimated by the new procedure to T derived from constant head step tests show better agreement than T obtained when predicting the formation pressure from a shallow pressure measurement.
The initial step in the analysis of contaminant transport in fractured rock requires the consider... more The initial step in the analysis of contaminant transport in fractured rock requires the consideration of groundwater velocity. Practical methods for estimating the average linear groundwater velocity (v) in fractured rock require determination of hydraulic apertures which are commonly calculated by applying the cubic law using transmissivity (T) values and the number of hydraulically active fractures in the test interval. High-resolution, constant-head step injection testing of cored boreholes in a 100 m thick fractured dolostone aquifer was conducted using inflatable packers to isolate specific test intervals from the rest of the borehole. The steps in each test interval were gradually increased from very low to much higher injection rates. At smaller injection rates, the flow rate vs. applied pressure graph projects through the origin and indicates Darcian flow; non Darcian flow is evident at higher injection rates. Non-Darcian flow results in significantly lower calculated T values, which translates to smaller hydraulic aperture values. Further error in the calculated hydraulic aperture stems from uncertainty in the number of hydraulically active fractures in each test interval. This estimate can be inferred from borehole image and core logs, however, all of the fractures identified are not necessarily hydraulically active. This study proposes a method based on Reynolds number calculations aimed at improving confidence in the selection of the number of active fractures in each test interval.
Estimation of water and contaminant discharges is an important hydrological problem. Fractured ro... more Estimation of water and contaminant discharges is an important hydrological problem. Fractured rock aquifers are recognized as highly complex flow and transport systems, and the fractured rock passive flux meter (FRPFM) is a recently tested device to simultaneously measure cumulative water and contaminant mass fluxes in fractures intersecting an observation well (boring). Furthermore, the FRPFM is capable of indicating orientations and directions of flow in hydraulically active (''flowing'') fractures. The present work develops a discharge estimator for when FRPFM measurements of fracture fluxes in the direction perpendicular to a transect (control plane) along one or more observation wells are available. In addition, estimation uncertainty in terms of a coefficient of variation is assessed based on a Monte Carlo approach under normalized conditions. Sources of uncertainty considered are spatially random fracture trace locations, random trace lengths, and orientations as well as variability of trace average fluxes (including smooth spatial trends), variability of local fluxes within traces, and flux measurement errors. Knowledge about the trace length distribution, which is commonly not available from borehole surveys, is not required for discharge estimation. However, it does affect the uncertainty assessment, and equations for upper uncertainty bounds are given as an alternative. In agreement with general statistical inference, it is found that discharge uncertainty decreases proportionally with the number of fluxes measured. Results are validated, and an example problem illustrates practical application and performance.
Summary A combination of high resolution hydraulic tests using straddle packers and transmissivit... more Summary A combination of high resolution hydraulic tests using straddle packers and transmissivity ( T ) profiling using the FLUTe flexible liner method (liner profiling) in densely fractured rock boreholes is shown to be efficient for the determination of the vertical distribution of T along the entire hole. The liner T profiling method takes a few hours or less to scan the entire borehole length resulting in a T profile. Under favorable conditions this method has good reliability for identifying the highest T zones identified by distinct decreases in liner velocity when these zones are covered by the descending liner. In contrast, for one short test interval (e.g., 1–2 m) the multiple-test, straddle-packer method takes a few hours to measure T with good precision and accuracy using a combination of steady-state and transient tests (e.g., constant head step tests, slug tests, and constant rate pumping tests). Because of the time consuming aspect of this multiple-test method, it is ...
A method is presented for obtaining depth-discrete values of specific storage ( Ss ) from single-... more A method is presented for obtaining depth-discrete values of specific storage ( Ss ) from single-hole hydraulic tests in fractured rock boreholes using straddle packers (1.5–17 m test intervals). Low flow constant head (CH) step tests analyzed using the Thiem method provide transmissivity ( T ) values free from non-Darcian error. Short-term, constant-rate pumping tests (0.5–2 h) analyzed using the Cooper-Jacob approximation of the Theis method provide S from the hydraulic diffusivity using the Darcian T value from the CH step test. This synergistic use of two types of hydraulic tests avoids the common source of error when pumping tests (injection or withdrawal) are conducted at higher flow rates and thereby induce non-Darcian flow resulting in the underestimation of T. Other errors, such as well bore storage and leakage, can also substantially influence S by causing a shift in the time axis of the Cooper-Jacob semi-log plot. In this approach, the Darcian T values from the CH step te...
The initial step in the analysis of contaminant transport in fractured rock requires the consider... more The initial step in the analysis of contaminant transport in fractured rock requires the consideration of groundwater velocity. Practical methods for estimating the average linear groundwater velocity (v) in fractured rock require determination of hydraulic apertures which are commonly calculated by applying the cubic law using transmissivity (T) values and the number of hydraulically active fractures in the test interval. High-resolution, constant-head step injection testing of cored boreholes in a 100 m thick fractured dolostone aquifer was conducted using inflatable packers to isolate specific test intervals from the rest of the borehole. The steps in each test interval were gradually increased from very low to much higher injection rates. At smaller injection rates, the flow rate vs. applied pressure graph projects through the origin and indicates Darcian flow; non Darcian flow is evident at higher injection rates. Non-Darcian flow results in significantly lower calculated T values, which translates to smaller hydraulic aperture values. Further error in the calculated hydraulic aperture stems from uncertainty in the number of hydraulically active fractures in each test interval. This estimate can be inferred from borehole image and core logs, however, all of the fractures identified are not necessarily hydraulically active. This study proposes a method based on Reynolds number calculations aimed at improving confidence in the selection of the number of active fractures in each test interval.
Abstract An evaluation of published laboratory studies of flow through single rough fractures was... more Abstract An evaluation of published laboratory studies of flow through single rough fractures was conducted to establish a relationship between aperture (2b) and critical Reynolds number (Rec) under controlled conditions for physically measured fractures. Of the relevant 47 published laboratory studies, only six reported physically measured apertures along with adequate hydraulic testing information to determine the corresponding Rec value and show that the fractures follow the cubic law reasonably well. Our analysis indicates a logarithmic relationship between 2b and Rec for cubic-law fractures in the reported aperture range (100–500 µm), consistent with theoretical and modeling studies. Discrete fracture network models used for simulating flow and transport in fractured rock aquifers require reliable values for 2b, usually obtained from the cubic law, using T values from straddle-packer hydraulic tests. The cubic law requires specification of the number of permeable fractures (N) in each test interval, but, distinguishing the permeable from the impermeable fractures is problematic. The relationship between 2b and Rec determined from the laboratory tests provides a fluid-mechanics basis for estimating the number of permeable fractures in straddle-packer tests. Constant-head step-tests carefully done with many steps provide precise identification of the flow rate at the onset of nonlinear flow, and numerous tests have shown that flow deviates from linearity at larger flow rates for larger values of transmissivity (T). A procedure was previously developed to relate N, 2b, and Rec using hydraulic test data, but this approach requires knowledge of the relation between 2b and Rec, thereby motivating this work.
Open boreholes in fractured rock often cross-connect fractures with differing hydraulic head and ... more Open boreholes in fractured rock often cross-connect fractures with differing hydraulic head and the head differences between these fractures cause vertical flow in the water column. This cross-connection has potential to bias transmissivity (T) values obtained from straddle packer tests. This study demonstrates how measurements of the blended head in the open-hole segments above and below the straddle-packer test interval can be used to correct packer tests for cross-connection effects. A pressure response observed in the open-hole segment above and/or below the packers isolating a test interval during a hydraulic test indicates short-circuiting of water from the injection interval through the vertically connected fracture network to the open-hole segments, resulting in the overestimation of T. A method is presented using blended head concepts to minimize this error using a trial-and-error procedure to determine the short-circuiting flow rate to account for the head conditions in the open-hole segments during each hydraulic test. Observed differences between the measured head and the calculated blended head in the open-hole segments above and below the test interval are attributed to cross-connection effects around the 1-m-long packers. The head and corrected T values determined from packer tests are used to estimate the flow in and out of the open hole at each of the intervals tested for assessing the cross-connection effects under open borehole conditions. Understanding open-hole flow dynamics gives insight about the potential for vertical cross connection of chemical constituents caused by the open hole.RésuméLes forages en trou nu en roche fracturée connectent souvent entre elles des fractures de différente charge hydraulique, ce qui cause un écoulement vertical entre ces fractures dans la colonne d’eau. Cette connexion peut biaiser potentiellement les valeurs de transmissivité (T) obtenues à partir de tests entre packers. Cette étude démontre comment des mesures de la charge hydraulique composite dans les segments de forage en trou nu situés en dessus et en dessous de l’intervalle testé entre packers peuvent être utilisées pour corriger les essais entre packers des effets de connexion entre fractures. Une variation de pression observée dans le segment en trou nu situé au-dessus et/ou au-dessous des packers isolant un intervalle testé pendant un test hydraulique indique un court-circuit d’eau depuis l’intervalle d’injection vers des segments en trou nu, à travers le réseau de fractures connecté verticalement, ce qui conduit à surestimer T. Une méthode est présentée utilisant les concepts de charge composite pour minimiser cette erreur au moyen d’une procédure par essais et erreur pour déterminer le débit en court-circuit afin de prendre en compte les conditions de charge dans les segments en trou nu pendant chaque test hydraulique. Les différences observées entre les charges mesurées et la charge composite calculée dans les segments en trou nu au-dessus et au-dessous de l’intervalle testé sont attribuées aux effets de connexion autour des packers de 1 m de long. Les valeurs de charge et de T corrigée déterminées à partir des tests entre packers sont utilisées pour estimer les débits entrant et sortant par le trou nu au sein de chacun des intervalles testés afin d’évaluer les effets de connexion en conditions de forage en trou nu. La compréhension de la dynamique des écoulements en trou nu donne un aperçu du potentiel des interconnexions verticales, causé par les forages en trou nu, vis-à-vis des constituants chimiques.ResumenLos pozos abiertos en rocas fracturadas a menudo conectan fracturas con diferentes cargas hidráulicas y las diferencias de carga entre estas fracturas producen un flujo vertical en la columna de agua. Esta conexión cruzada tiene el potencial para sesgar los valores de transmisividad (T) obtenidos a partir de ensayos de straddle-packer. Este estudio demuestra como las medidas combinadas de carga en los segmentos del pozo abierto por encima y por debajo del intervalo de la prueba de straddle-packer pueden ser utilizados para corregir las pruebas de packer en relación con los efectos de la conexión cruzada. Una respuesta de presión observada en el segmento del pozo abierto por encima y/o por debajo del aislamiento de los packers de un intervalo de prueba durante un ensayo hidráulico indica un cortocircuito de agua desde el intervalo de inyección a través de la red de fracturas verticalmente conectadas a los segmentos del pozo abierto, lo cual resulta en la sobrestimación de T. Se presenta un método usando conceptos de carga combinada para minimizar este error utilizando un procedimiento de prueba y error para determinar el caudal del cortocircuito para dar cuenta de las condiciones de carga en los segmentos del pozo abierto durante cada ensayo hidráulico. Las diferencias observadas entre la carga medida y la carga combinada calculada en los segmentos del pozo abierto por encima y por…
Flow deviates from Darcian flow at low flow rates in fractured rockDarcy-Missbach equation is a b... more Flow deviates from Darcian flow at low flow rates in fractured rockDarcy-Missbach equation is a better alternative to the Forchheimer equationRec numbers calculated from field data compare well with laboratory values
ABSTRACT A series of rising and falling head slug tests with different initial applied head diffe... more ABSTRACT A series of rising and falling head slug tests with different initial applied head differentials (DHo) were conducted in open fractured dolostone and sandstone boreholes using straddle packers isolating specific depth intervals (1.5 m length) to examine the influence of non-Darcian flow. The open holes were developed and inspected using video and acoustic televiewing (ATV) to ensure that evidence of skin effects due to drilling were absent. The transmissivity (T) values obtained from both the rising and falling head slug tests were very similar at low initial applied head; however, the T values were progressively smaller at larger DHo, suggesting error due to non-Darcian flow. Non-Darcian flow behavior was confirmed by constant head step tests conducted in the same test intervals where the injection rate (Q) vs. applied head (dH) relationship became non-linear at relatively low injection rates, and the non-Darcian data also resulted in lower T values. For a series of slug tests conducted at different DHo, non-Darcian flow effects gradually increased as DHo increased, consistent with the trends for constant head step tests conducted in the same test intervals. To maintain Darcian flow conditions in the fractured dolostone and sandstone tested in this study, DHo must be kept small, generally less than 0.2 m. This study demonstrates that by conducting both ‘‘stepped’’ slug tests and constant head step tests, the Darcian flow assumption for both types of tests can be rigorously validated. However, when only slug tests are conducted, it is necessary to conduct a series of ‘‘stepped’’ slug tests, including tests with small applied head differentials, to avoid errors due to non-Darcian flow.
Equipment has been developed for straddle packer testing in fractured-rock boreholes to conduct f... more Equipment has been developed for straddle packer testing in fractured-rock boreholes to conduct four types of tests (constant-head step tests, slug tests, constant-rate pumping tests, and recovery tests) without deflating the packers or adjusting equipment in the hole between tests. The goal is to achieve improved accuracy and precision in the determination of transmissivity (T). Water-pressure measurements are recorded using pressure transducers positioned above and below the test interval to identify connections from the test interval to the open borehole. Insights concerning the nature of test conditions are gathered with this equipment to assess errors related to deviations from assumptions inherent in the mathematical models used to determine T, including validation of the Darcian flow assumption, validation of slug test assump-tions, cross-connection to the open borehole, inadequate borehole development, and dual permeability, thereby giving greater confidence in the calculate...
ABSTRACT Estimation of water and contaminant discharges is an important hydrological problem. Fra... more ABSTRACT Estimation of water and contaminant discharges is an important hydrological problem. Fractured rock aquifers are recognized as highly complex flow and transport systems, and the fractured rock passive flux meter (FRPFM) is a recently tested device to simultaneously measure cumulative water and contaminant mass fluxes in fractures intersecting an observation well (boring). Furthermore, the FRPFM is capable of indicating orientations and directions of flow in hydraulically active ("flowing") fractures. The present work develops a discharge estimator for when FRPFM measurements of fracture fluxes in the direction perpendicular to a transect (control plane) along one or more observation wells are available. In addition, estimation uncertainty in terms of a coefficient of variation is assessed based on a Monte Carlo approach under normalized conditions. Sources of uncertainty considered are spatially random fracture trace locations, random trace lengths, and orientations as well as variability of trace average fluxes (including smooth spatial trends), variability of local fluxes within traces, and flux measurement errors. Knowledge about the trace length distribution, which is commonly not available from borehole surveys, is not required for discharge estimation. However, it does affect the uncertainty assessment, and equations for upper uncertainty bounds are given as an alternative. In agreement with general statistical inference, it is found that discharge uncertainty decreases proportionally with the number of fluxes measured. Results are validated, and an example problem illustrates practical application and performance.
Slug tests generating oscillating (underdamped) responses are common in high-transmissivity (T) z... more Slug tests generating oscillating (underdamped) responses are common in high-transmissivity (T) zones, and the nature of the response depends on the plumbing of the test equipment and the formation properties. The standard approach for obtaining T is to measure pressure shallow in the riser pipe to obtain an accurate estimate of flow and then predict the formation response from this shallow measurement by accounting for friction and acceleration assuming steady flow conditions (parabolic radial velocity profile). In this study a mathematical solution is developed for unsteady oscillatory laminar flow that shows non-parabolic radial velocity profiles resulting in larger frictional losses, which are out of phase with the average flow velocity, indicating that errors are introduced when using the standard approach for underdamped slug test analysis. The unsteady flow model produces correction factors that can be used to improve the standard approach for predicting the formation pressure; however, not all errors are eliminated. Consequently, a new procedure is presented and applied to underdamped slug tests observed in fractured rock that avoids errors associated with quantifying inertial and frictional effects along the test equipment. This is achieved through the use of two transducers, where one is placed shallow in the water column to infer flow, and one is placed inside the test interval to represent the formation pressure. Comparison of T estimated by the new procedure to T derived from constant head step tests show better agreement than T obtained when predicting the formation pressure from a shallow pressure measurement.
The initial step in the analysis of contaminant transport in fractured rock requires the consider... more The initial step in the analysis of contaminant transport in fractured rock requires the consideration of groundwater velocity. Practical methods for estimating the average linear groundwater velocity (v) in fractured rock require determination of hydraulic apertures which are commonly calculated by applying the cubic law using transmissivity (T) values and the number of hydraulically active fractures in the test interval. High-resolution, constant-head step injection testing of cored boreholes in a 100 m thick fractured dolostone aquifer was conducted using inflatable packers to isolate specific test intervals from the rest of the borehole. The steps in each test interval were gradually increased from very low to much higher injection rates. At smaller injection rates, the flow rate vs. applied pressure graph projects through the origin and indicates Darcian flow; non Darcian flow is evident at higher injection rates. Non-Darcian flow results in significantly lower calculated T values, which translates to smaller hydraulic aperture values. Further error in the calculated hydraulic aperture stems from uncertainty in the number of hydraulically active fractures in each test interval. This estimate can be inferred from borehole image and core logs, however, all of the fractures identified are not necessarily hydraulically active. This study proposes a method based on Reynolds number calculations aimed at improving confidence in the selection of the number of active fractures in each test interval.
Estimation of water and contaminant discharges is an important hydrological problem. Fractured ro... more Estimation of water and contaminant discharges is an important hydrological problem. Fractured rock aquifers are recognized as highly complex flow and transport systems, and the fractured rock passive flux meter (FRPFM) is a recently tested device to simultaneously measure cumulative water and contaminant mass fluxes in fractures intersecting an observation well (boring). Furthermore, the FRPFM is capable of indicating orientations and directions of flow in hydraulically active (''flowing'') fractures. The present work develops a discharge estimator for when FRPFM measurements of fracture fluxes in the direction perpendicular to a transect (control plane) along one or more observation wells are available. In addition, estimation uncertainty in terms of a coefficient of variation is assessed based on a Monte Carlo approach under normalized conditions. Sources of uncertainty considered are spatially random fracture trace locations, random trace lengths, and orientations as well as variability of trace average fluxes (including smooth spatial trends), variability of local fluxes within traces, and flux measurement errors. Knowledge about the trace length distribution, which is commonly not available from borehole surveys, is not required for discharge estimation. However, it does affect the uncertainty assessment, and equations for upper uncertainty bounds are given as an alternative. In agreement with general statistical inference, it is found that discharge uncertainty decreases proportionally with the number of fluxes measured. Results are validated, and an example problem illustrates practical application and performance.
Summary A combination of high resolution hydraulic tests using straddle packers and transmissivit... more Summary A combination of high resolution hydraulic tests using straddle packers and transmissivity ( T ) profiling using the FLUTe flexible liner method (liner profiling) in densely fractured rock boreholes is shown to be efficient for the determination of the vertical distribution of T along the entire hole. The liner T profiling method takes a few hours or less to scan the entire borehole length resulting in a T profile. Under favorable conditions this method has good reliability for identifying the highest T zones identified by distinct decreases in liner velocity when these zones are covered by the descending liner. In contrast, for one short test interval (e.g., 1–2 m) the multiple-test, straddle-packer method takes a few hours to measure T with good precision and accuracy using a combination of steady-state and transient tests (e.g., constant head step tests, slug tests, and constant rate pumping tests). Because of the time consuming aspect of this multiple-test method, it is ...
A method is presented for obtaining depth-discrete values of specific storage ( Ss ) from single-... more A method is presented for obtaining depth-discrete values of specific storage ( Ss ) from single-hole hydraulic tests in fractured rock boreholes using straddle packers (1.5–17 m test intervals). Low flow constant head (CH) step tests analyzed using the Thiem method provide transmissivity ( T ) values free from non-Darcian error. Short-term, constant-rate pumping tests (0.5–2 h) analyzed using the Cooper-Jacob approximation of the Theis method provide S from the hydraulic diffusivity using the Darcian T value from the CH step test. This synergistic use of two types of hydraulic tests avoids the common source of error when pumping tests (injection or withdrawal) are conducted at higher flow rates and thereby induce non-Darcian flow resulting in the underestimation of T. Other errors, such as well bore storage and leakage, can also substantially influence S by causing a shift in the time axis of the Cooper-Jacob semi-log plot. In this approach, the Darcian T values from the CH step te...
The initial step in the analysis of contaminant transport in fractured rock requires the consider... more The initial step in the analysis of contaminant transport in fractured rock requires the consideration of groundwater velocity. Practical methods for estimating the average linear groundwater velocity (v) in fractured rock require determination of hydraulic apertures which are commonly calculated by applying the cubic law using transmissivity (T) values and the number of hydraulically active fractures in the test interval. High-resolution, constant-head step injection testing of cored boreholes in a 100 m thick fractured dolostone aquifer was conducted using inflatable packers to isolate specific test intervals from the rest of the borehole. The steps in each test interval were gradually increased from very low to much higher injection rates. At smaller injection rates, the flow rate vs. applied pressure graph projects through the origin and indicates Darcian flow; non Darcian flow is evident at higher injection rates. Non-Darcian flow results in significantly lower calculated T values, which translates to smaller hydraulic aperture values. Further error in the calculated hydraulic aperture stems from uncertainty in the number of hydraulically active fractures in each test interval. This estimate can be inferred from borehole image and core logs, however, all of the fractures identified are not necessarily hydraulically active. This study proposes a method based on Reynolds number calculations aimed at improving confidence in the selection of the number of active fractures in each test interval.
Abstract An evaluation of published laboratory studies of flow through single rough fractures was... more Abstract An evaluation of published laboratory studies of flow through single rough fractures was conducted to establish a relationship between aperture (2b) and critical Reynolds number (Rec) under controlled conditions for physically measured fractures. Of the relevant 47 published laboratory studies, only six reported physically measured apertures along with adequate hydraulic testing information to determine the corresponding Rec value and show that the fractures follow the cubic law reasonably well. Our analysis indicates a logarithmic relationship between 2b and Rec for cubic-law fractures in the reported aperture range (100–500 µm), consistent with theoretical and modeling studies. Discrete fracture network models used for simulating flow and transport in fractured rock aquifers require reliable values for 2b, usually obtained from the cubic law, using T values from straddle-packer hydraulic tests. The cubic law requires specification of the number of permeable fractures (N) in each test interval, but, distinguishing the permeable from the impermeable fractures is problematic. The relationship between 2b and Rec determined from the laboratory tests provides a fluid-mechanics basis for estimating the number of permeable fractures in straddle-packer tests. Constant-head step-tests carefully done with many steps provide precise identification of the flow rate at the onset of nonlinear flow, and numerous tests have shown that flow deviates from linearity at larger flow rates for larger values of transmissivity (T). A procedure was previously developed to relate N, 2b, and Rec using hydraulic test data, but this approach requires knowledge of the relation between 2b and Rec, thereby motivating this work.
Open boreholes in fractured rock often cross-connect fractures with differing hydraulic head and ... more Open boreholes in fractured rock often cross-connect fractures with differing hydraulic head and the head differences between these fractures cause vertical flow in the water column. This cross-connection has potential to bias transmissivity (T) values obtained from straddle packer tests. This study demonstrates how measurements of the blended head in the open-hole segments above and below the straddle-packer test interval can be used to correct packer tests for cross-connection effects. A pressure response observed in the open-hole segment above and/or below the packers isolating a test interval during a hydraulic test indicates short-circuiting of water from the injection interval through the vertically connected fracture network to the open-hole segments, resulting in the overestimation of T. A method is presented using blended head concepts to minimize this error using a trial-and-error procedure to determine the short-circuiting flow rate to account for the head conditions in the open-hole segments during each hydraulic test. Observed differences between the measured head and the calculated blended head in the open-hole segments above and below the test interval are attributed to cross-connection effects around the 1-m-long packers. The head and corrected T values determined from packer tests are used to estimate the flow in and out of the open hole at each of the intervals tested for assessing the cross-connection effects under open borehole conditions. Understanding open-hole flow dynamics gives insight about the potential for vertical cross connection of chemical constituents caused by the open hole.RésuméLes forages en trou nu en roche fracturée connectent souvent entre elles des fractures de différente charge hydraulique, ce qui cause un écoulement vertical entre ces fractures dans la colonne d’eau. Cette connexion peut biaiser potentiellement les valeurs de transmissivité (T) obtenues à partir de tests entre packers. Cette étude démontre comment des mesures de la charge hydraulique composite dans les segments de forage en trou nu situés en dessus et en dessous de l’intervalle testé entre packers peuvent être utilisées pour corriger les essais entre packers des effets de connexion entre fractures. Une variation de pression observée dans le segment en trou nu situé au-dessus et/ou au-dessous des packers isolant un intervalle testé pendant un test hydraulique indique un court-circuit d’eau depuis l’intervalle d’injection vers des segments en trou nu, à travers le réseau de fractures connecté verticalement, ce qui conduit à surestimer T. Une méthode est présentée utilisant les concepts de charge composite pour minimiser cette erreur au moyen d’une procédure par essais et erreur pour déterminer le débit en court-circuit afin de prendre en compte les conditions de charge dans les segments en trou nu pendant chaque test hydraulique. Les différences observées entre les charges mesurées et la charge composite calculée dans les segments en trou nu au-dessus et au-dessous de l’intervalle testé sont attribuées aux effets de connexion autour des packers de 1 m de long. Les valeurs de charge et de T corrigée déterminées à partir des tests entre packers sont utilisées pour estimer les débits entrant et sortant par le trou nu au sein de chacun des intervalles testés afin d’évaluer les effets de connexion en conditions de forage en trou nu. La compréhension de la dynamique des écoulements en trou nu donne un aperçu du potentiel des interconnexions verticales, causé par les forages en trou nu, vis-à-vis des constituants chimiques.ResumenLos pozos abiertos en rocas fracturadas a menudo conectan fracturas con diferentes cargas hidráulicas y las diferencias de carga entre estas fracturas producen un flujo vertical en la columna de agua. Esta conexión cruzada tiene el potencial para sesgar los valores de transmisividad (T) obtenidos a partir de ensayos de straddle-packer. Este estudio demuestra como las medidas combinadas de carga en los segmentos del pozo abierto por encima y por debajo del intervalo de la prueba de straddle-packer pueden ser utilizados para corregir las pruebas de packer en relación con los efectos de la conexión cruzada. Una respuesta de presión observada en el segmento del pozo abierto por encima y/o por debajo del aislamiento de los packers de un intervalo de prueba durante un ensayo hidráulico indica un cortocircuito de agua desde el intervalo de inyección a través de la red de fracturas verticalmente conectadas a los segmentos del pozo abierto, lo cual resulta en la sobrestimación de T. Se presenta un método usando conceptos de carga combinada para minimizar este error utilizando un procedimiento de prueba y error para determinar el caudal del cortocircuito para dar cuenta de las condiciones de carga en los segmentos del pozo abierto durante cada ensayo hidráulico. Las diferencias observadas entre la carga medida y la carga combinada calculada en los segmentos del pozo abierto por encima y por…
Flow deviates from Darcian flow at low flow rates in fractured rockDarcy-Missbach equation is a b... more Flow deviates from Darcian flow at low flow rates in fractured rockDarcy-Missbach equation is a better alternative to the Forchheimer equationRec numbers calculated from field data compare well with laboratory values
ABSTRACT A series of rising and falling head slug tests with different initial applied head diffe... more ABSTRACT A series of rising and falling head slug tests with different initial applied head differentials (DHo) were conducted in open fractured dolostone and sandstone boreholes using straddle packers isolating specific depth intervals (1.5 m length) to examine the influence of non-Darcian flow. The open holes were developed and inspected using video and acoustic televiewing (ATV) to ensure that evidence of skin effects due to drilling were absent. The transmissivity (T) values obtained from both the rising and falling head slug tests were very similar at low initial applied head; however, the T values were progressively smaller at larger DHo, suggesting error due to non-Darcian flow. Non-Darcian flow behavior was confirmed by constant head step tests conducted in the same test intervals where the injection rate (Q) vs. applied head (dH) relationship became non-linear at relatively low injection rates, and the non-Darcian data also resulted in lower T values. For a series of slug tests conducted at different DHo, non-Darcian flow effects gradually increased as DHo increased, consistent with the trends for constant head step tests conducted in the same test intervals. To maintain Darcian flow conditions in the fractured dolostone and sandstone tested in this study, DHo must be kept small, generally less than 0.2 m. This study demonstrates that by conducting both ‘‘stepped’’ slug tests and constant head step tests, the Darcian flow assumption for both types of tests can be rigorously validated. However, when only slug tests are conducted, it is necessary to conduct a series of ‘‘stepped’’ slug tests, including tests with small applied head differentials, to avoid errors due to non-Darcian flow.
Equipment has been developed for straddle packer testing in fractured-rock boreholes to conduct f... more Equipment has been developed for straddle packer testing in fractured-rock boreholes to conduct four types of tests (constant-head step tests, slug tests, constant-rate pumping tests, and recovery tests) without deflating the packers or adjusting equipment in the hole between tests. The goal is to achieve improved accuracy and precision in the determination of transmissivity (T). Water-pressure measurements are recorded using pressure transducers positioned above and below the test interval to identify connections from the test interval to the open borehole. Insights concerning the nature of test conditions are gathered with this equipment to assess errors related to deviations from assumptions inherent in the mathematical models used to determine T, including validation of the Darcian flow assumption, validation of slug test assump-tions, cross-connection to the open borehole, inadequate borehole development, and dual permeability, thereby giving greater confidence in the calculate...
ABSTRACT Estimation of water and contaminant discharges is an important hydrological problem. Fra... more ABSTRACT Estimation of water and contaminant discharges is an important hydrological problem. Fractured rock aquifers are recognized as highly complex flow and transport systems, and the fractured rock passive flux meter (FRPFM) is a recently tested device to simultaneously measure cumulative water and contaminant mass fluxes in fractures intersecting an observation well (boring). Furthermore, the FRPFM is capable of indicating orientations and directions of flow in hydraulically active ("flowing") fractures. The present work develops a discharge estimator for when FRPFM measurements of fracture fluxes in the direction perpendicular to a transect (control plane) along one or more observation wells are available. In addition, estimation uncertainty in terms of a coefficient of variation is assessed based on a Monte Carlo approach under normalized conditions. Sources of uncertainty considered are spatially random fracture trace locations, random trace lengths, and orientations as well as variability of trace average fluxes (including smooth spatial trends), variability of local fluxes within traces, and flux measurement errors. Knowledge about the trace length distribution, which is commonly not available from borehole surveys, is not required for discharge estimation. However, it does affect the uncertainty assessment, and equations for upper uncertainty bounds are given as an alternative. In agreement with general statistical inference, it is found that discharge uncertainty decreases proportionally with the number of fluxes measured. Results are validated, and an example problem illustrates practical application and performance.
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Papers by Patryk Quinn