Flowmeter Tests Research Articles

Inverse modeling of flow tomography experiments in fractured media

The accurate characterization of the location, hydraulic properties, and connectivity of major fracture zones is essential to model flow and solute transport in fractured media. Cross‐borehole flowmeter tests, which consist of measuring changes in vertical borehole flows when pumping a neighboring borehole, were shown to be an efficient technique to provide information on the properties of the flow zones that connect borehole pairs. The interpretation of such experiments may, however, be quite uncertain when multiple connections exist. In this study, we explore the potential of flow tomography (i.e., sequential cross‐borehole flowmeter tests) for characterizing aquifer heterogeneity. We propose a framework for inverting flow and drawdown data to infer fracture connectivity and transmissivities. We demonstrate that successively exchanging the roles of pumping and observation boreholes improves the quality of available information and reduces the under‐determination of the problem. The inverse method is validated for several synthetic flow scenarios. It is shown to provide a good estimation of connectivity patterns and transmissivities of main flow paths. It also allows the estimation of the transmissivity of fractures that connect the flow paths but do not cross the boreholes, although the associated uncertainty may be high for some geometries.

Hydrodynamic and isotopic characterization of a site contaminated by chlorinated solvents: Chienti River Valley, Central Italy

Contaminant sources have been attributed to shoe manufacturers in an alluvial aquifer located along 26km2 in the Chienti River Valley, Central Italy. During the 1980s and 1990s, the main chlorinated compound used in the study area was 1,1,1-Trichloroethane (1,1,1-TCA), which was substituted by Perchloroethene (PCE) in the last 15years. A hydrogeological conceptual model has been developed for the alluvial aquifer taking into account the presence of low permeability lenses, forming a multilayer semi-confined aquifer. Hydrodynamic tests (pumping and flowmeter heat-pulse tests) coupled with standard and multilevel hydrochemical and isotopic samplings were performed. Flowmeter tests showed the existence of vertical flow between aquifer levels having different permeability. Physical–chemical parameter logs agreed with the existence of a multilayer aquifer. Concentration data collected in 21 wells located downgradient of the different sources revealed VOC (Volatile Organic Compound) levels lower than 100μg/L in the upper part of the valley and levels reaching about 200μg/L in the near shore areas. PCE is the main compound present in the aquifer. No evidence of the presence of TCA was found in the upper areas of the Chienti Valley, but in the areas near the shore, TCA and its degradation products are predominant. Data collected at multilevels located at two sites (upper and near shore areas) to refine the results obtained in the regional survey show a stratification of the VOC concentrations; values of each compound are higher than those measured in the conventional wells during the standard sampling (e.g. PCE: 150μg/L instead of 2μg/L). In addition, the vertical distribution of the contaminant reflects the vertical flow pattern inferred from hydrogeological data. The hydrogeological, VOC and isotope data showed that dilution is the main process controlling VOCs concentration in the aquifer. Degradation also played a role in the attenuation of the parent compounds in some localized areas of the aquifer. The role of the low permeability layers on VOC degradation was documented by the presence of cis-1,2-DCE, a main daughter product of PCE, in some zones of the upper area, and 1,1-Dichloroethene (1,1-DCE) and 1,1-Dichloroethane (1,1-DCA), byproducts of 1,1,1-TCA degradation, in the near shore areas.

Systems for calibration testing of coriolis flowmeters

A method of in-situ calibration testing of flowmeters is proposed. The design of the system, operating principles, and results of a simulation of the action of pulse interference are considered.

Three‐dimensional Bayesian geostatistical aquifer characterization at the Hanford 300 Area using tracer test data

Tracer tests performed under natural or forced gradient flow conditions can provide useful information for characterizing subsurface properties, through monitoring, modeling, and interpretation of the tracer plume migration in an aquifer. Nonreactive tracer experiments were conducted at the Hanford 300 Area, along with constant‐rate injection tests and electromagnetic borehole flowmeter tests. A Bayesian data assimilation technique, the method of anchored distributions (MAD) (Rubin et al., 2010), was applied to assimilate the experimental tracer test data with the other types of data and to infer the three‐dimensional heterogeneous structure of the hydraulic conductivity in the saturated zone of the Hanford formation.In this study, the Bayesian prior information on the underlying random hydraulic conductivity field was obtained from previous field characterization efforts using constant‐rate injection and borehole flowmeter test data. The posterior distribution of the conductivity field was obtained by further conditioning the field on the temporal moments of tracer breakthrough curves at various observation wells. MAD was implemented with the massively parallel three‐dimensional flow and transport code PFLOTRAN to cope with the highly transient flow boundary conditions at the site and to meet the computational demands of MAD. A synthetic study proved that the proposed method could effectively invert tracer test data to capture the essential spatial heterogeneity of the three‐dimensional hydraulic conductivity field. Application of MAD to actual field tracer data at the Hanford 300 Area demonstrates that inverting for spatial heterogeneity of hydraulic conductivity under transient flow conditions is challenging and more work is needed.

Interpretation of flowmeter data in heterogeneous layered aquifers

Summary We analyze numerically the impact of key assumptions which are usually adopted to interpret borehole flowmeter test data. We base our work on a set of detailed numerical simulations of transient and pseudo-steady state convergent flow to a fully penetrating well that pumps at a constant total flow rate in a confined three-dimensional system formed by well demarcated facies. Our results allow identifying the effects of (i) the presence of a skin zone around the well, (ii) the contrast of hydraulic conductivities of the aquifer facies and the gravel pack, and (iii) the dynamics of the flow regime on the ability to characterize the local aquifer conductivities of a stratified system through the typical interpretation of downhole flowmeter tests. Vertical intervals along the wellbore, where reliable estimates of the aquifer conductivities can be obtained through classical formulations are identified in terms of a set of dimensionless parameters. These parameters involve the thickness of the facies constituting the stratified aquifer and the contrast of conductivities amongst different facies and between them and the skin zone.

Efficiency verification of a horizontal flow barrier via flowmeter tests and multilevel sampling

AbstractThe remediation strategy for an industrial site located in a coastal area involves a pump and treat system and a horizontal flow barrier (HFB) penetrating the main aquifer. To validate the groundwater flow conceptual model and to verify the efficiency of the remediation systems, we carried out piezometric measurements, slug tests, pumping tests, flowmeter tests and multilevel sampling. Flowmeter tests are used to infer vertical groundwater flow directions, and base exchange index is used to infer horizontal flow directions at a metric scale. The selected wells are located both upstream and downstream of the HFB. The installation of the HFB produced constraints to the groundwater flow. A stagnant zone of contaminated freshwater floating over the salt wedge in the upper portion of the aquifer is detected downstream of the HFB. This study confirms that the adopted remediation system is efficiently working in the area upstream of the HFB and even downstream in the bottom part of the aquifer. At the same time, it has also confirmed that hot spots are still present in stagnant zones located downstream of the HFB in the upper part of the aquifer, requiring a different approach to accomplish remediation targets. The integrated approach for flow quantification used in this study allows to discriminate the direction and the magnitude of groundwater fluxes near an HFB in a coastal aquifer. Copyright © 2012 John Wiley & Sons, Ltd.

3-D Numerical Simulation and Analysis on V-Cone Flowmeter Based on LES Method

The rear pressure measurement position of V-cone flowmeter is in the complex vortex structure area after fluid around the cone. The non-uniformity of the fluid field will influence the measurement precision of V-cone flowmeter. Large eddy simulation (LES) has been used to study the V-cone flowmeter’s 3-D flow field structure with different Reynolds number in this paper. The better fluid area information can gain by this way. The results show that the values of discharge coefficient (Cd) obtained from LES are more close to the experiment data than the values obtained from k-ε model. Different turbulence intensity with different Reynolds number effects the velocity distribution in the V-cone flowmeter’s flow field. When Reynolds number equals to 20000, the flow field within 8d distance from V-cone tail should keep from being disturbed while the flowmeter under working condition. The non-interfering distance from V-cone tail flow field increases with the Reynolds number raising. These analysis results can offer optimizational information for V-cone flowmeter performance and testing method improvement.

Quantitative comparison of impeller-flowmeter and particle-size-distribution techniques for the characterization of hydraulic conductivity variability

Hydraulic conductivities associated with measurement scale of the order of 10–1 m and collected during an extensive field campaign near Tubingen, Germany, are analyzed. Estimates are provided at coinciding locations in the system using: (1) the empirical Kozeny-Carman formulation, providing conductivity values, K GS, based on particle-size distribution, and (2) borehole impeller-type flowmeter tests, which infer conductivity, K FM, from measurements of vertical flows within a borehole. Correlation between the two sets of estimates is virtually absent. However, statistics of the natural logarithm of K GS and K FM at the site are similar in terms of mean values (averages of ln K GS being slightly smaller) and differ in terms of variogram ranges and sample variances. This is consistent with the fact that the two types of estimates can be associated with different (albeit comparable) measurement (support) scales. It also matches published results on interpretations of variability of geostatistical descriptors of hydraulic parameters on multiple observation scales. The analysis strengthens the idea that hydraulic conductivity values and associated key geostatistical descriptors inferred from different methodologies and at similar observation scales (of the order of tens of cm) are not readily comparable and should not be embedded blindly into a flow (and eventually transport) prediction model.

Geological modeling of submeter scale heterogeneity and its influence on tracer transport in a fluvial aquifer

We developed a new model of aquifer heterogeneity to analyze data from a single‐well injection‐withdrawal tracer test conducted at the Macrodispersion Experiment (MADE) site on the Columbus Air Force Base in Mississippi (USA). The physical heterogeneity model is a hybrid that combines 3‐D lithofacies to represent submeter scale, highly connected channels within a background matrix based on a correlated multivariate Gaussian hydraulic conductivity field. The modeled aquifer architecture is informed by a variety of field data, including geologic core sampling. Geostatistical properties of this hybrid heterogeneity model are consistent with the statistics of the hydraulic conductivity data set based on extensive borehole flowmeter testing at the MADE site. The representation of detailed, small‐scale geologic heterogeneity allows for explicit simulation of local preferential flow and slow advection, processes that explain the complex tracer response from the injection‐withdrawal test. Based on the new heterogeneity model, advective‐dispersive transport reproduces key characteristics of the observed tracer recovery curve, including a delayed concentration peak and a low‐concentration tail. Importantly, our results suggest that intrafacies heterogeneity is responsible for local‐scale mass transfer.

Permeability Profiles in Granular Aquifers Using Flowmeters in Direct-Push Wells

Numerical hydrogeological models should ideally be based on the spatial distribution of hydraulic conductivity (K), a property rarely defined on the basis of sufficient data due to the lack of efficient characterization methods. Electromagnetic borehole flowmeter measurements during pumping in uncased wells can effectively provide a continuous vertical distribution of K in consolidated rocks. However, relatively few studies have used the flowmeter in screened wells penetrating unconsolidated aquifers, and tests conducted in gravel-packed wells have shown that flowmeter data may yield misleading results. This paper describes the practical application of flowmeter profiles in direct-push wells to measure K and delineate hydrofacies in heterogeneous unconsolidated aquifers having low-to-moderate K (10(-6) to 10(-4) m/s). The effect of direct-push well installation on K measurements in unconsolidated deposits is first assessed based on the previous work indicating that such installations minimize disturbance to the aquifer fabric. The installation and development of long-screen wells are then used in a case study validating K profiles from flowmeter tests at high-resolution intervals (15 cm) with K profiles derived from multilevel slug tests between packers at identical intervals. For 119 intervals tested in five different wells, the difference in log K values obtained from the two methods is consistently below 10%. Finally, a graphical approach to the interpretation of flowmeter profiles is proposed to delineate intervals corresponding to distinct hydrofacies, thus providing a method whereby both the scale and magnitude of K contrasts in heterogeneous unconsolidated aquifers may be represented.

Capabilities of the simulation method of studying electromagnetic flow meters

Different techniques for simulation modeling used in primary and subsequent testing of electromagnetic flow meters are considered.

Three‐Dimensional Geostatistical Inversion of Flowmeter and Pumping Test Data

We jointly invert field data of flowmeter and multiple pumping tests in fully screened wells to estimate hydraulic conductivity using a geostatistical method. We use the steady-state drawdowns of pumping tests and the discharge profiles of flowmeter tests as our data in the inference. The discharge profiles need not be converted to absolute hydraulic conductivities. Consequently, we do not need measurements of depth-averaged hydraulic conductivity at well locations. The flowmeter profiles contain information about relative vertical distributions of hydraulic conductivity, while drawdown measurements of pumping tests provide information about horizontal fluctuation of the depth-averaged hydraulic conductivity. We apply the method to data obtained at the Krauthausen test site of the Forschungszentrum Jülich, Germany. The resulting estimate of our joint three-dimensional (3D) geostatistical inversion shows an improved 3D structure in comparison to the inversion of pumping test data only.

Comparison of alternative methodologies for identifying and characterizing preferential flow paths in heterogeneous aquifers

One of the main difficulties encountered when characterizing the hydrodynamic properties of a fractured aquifer is to identify the preferential flow paths within it. Different methods may be applied to determine the variability of the permeability at the borehole scale and to image the structure of the main flow zones between boreholes. In this paper, we compare the information obtained from different measurement techniques performed in a set of three 100 m depth wells (well-to-well spacing: 5­10 m) in a fractured crystalline rock setting. Geophysical logging and borehole-wall imaging are used to identify open and closed fractures intersecting the boreholes and their orientation. The comparison with flowmeter and single packer tests shows that few of the fractures interpreted as open from geophysical logs are significantly transmissive. Cross-borehole connectivity is first investigated from single packer tests with pressure monitoring in adjacent boreholes. To determine fracture zone connectivity, we propose a methodology simply based on the variation with packer depth of the ratio of the drawdown in the observation well and the drawdown in the pumping well. The results are compared to the analysis of cross-borehole flowmeter tests. We show that both methods provide consistent results with a similar level of information on connectivity.

Characterizing flow zones in a fractured and karstified limestone aquifer through integrated interpretation of geophysical and hydraulic data

A detailed and integrated geologic–hydraulic–geophysical–geochemical study of groundwater flow in the near-vicinity of a borehole drilled into fractured and karstified limestone demonstrates the power of such an integrated approach in localising and characterising preferential groundwater flow pathways and ambient borehole flow. The study, conducted in the vicinity of a 100-m-deep research borehole on the island of Mallorca, achieves such characterisation on a scale from millimetres to tens of metres in scale. More specifically, it adds single packer and open-hole pumping test interpretations to the results obtained during fluid logging, impeller flowmeter testing, borehole imaging, core descriptions and an innovative fracture analysis. This approach allows the delineation of the main flowing features and showed that such features are directly or indirectly linked to karst phenomena. Understanding this complex flow system is critical for an appropriate assessment of groundwater resources and the design of sustainable groundwater production schemes.

Tidal effects on variations of fresh–saltwater interface and groundwater flow in a multilayered coastal aquifer on a volcanic island (Jeju Island, Korea)

Summary We conducted various field studies at the seawater intrusion monitoring wells located in the eastern part of Jeju Island, Korea, to observe the tidal effect on groundwater–seawater flow in the coastal aquifer. Studies included monitoring the fluctuations of groundwater and tide levels, electrical and temperature logging, and 2-D heat-pulse flowmeter tests. According to time-series analysis, tidal effects on groundwater level reached up to 3 km inland from the coastline. Water-level variation was more sensitive to tidal fluctuations near the coast, and more related to rainfall toward inland areas. Temporal and spatial variations in the shape and location of the freshwater–saltwater interface were analyzed using data from nine monitoring wells. The results indicated that the interface toe is located at a distance of 6–8 km from the coastline and its location was related to geological layers present. Long-term seasonal variations revealed no major changes in the interface; minor variations were due to moving boundary conditions induced by tidal fluctuations. Using the two-dimensional heat-pulse flowmeter, groundwater flow directions and velocities at four tidal stages were measured on three monitoring wells drilled into the multilayered aquifers. This direct measurement enabled us to relate the differences of flow velocities and directions with geology and tidal fluctuations. Combining the results of EC logging and flowmeter tests, we found a zone where freshwater and saltwater moved alternately in opposite directions, as influenced by the tidal fluctuations. Integrating various physical logging and flowmeter data with water-level fluctuations improved our understanding of the behavior of fresh and seawater flow in the coastal aquifers.

Focus on sensors

Focus on sensors

Development of a joint hydrogeophysical inversion approach and application to a contaminated fractured aquifer

This paper presents a joint inversion approach for combining crosshole seismic travel time and borehole flowmeter test data to estimate hydrogeological zonation. The approach is applied to a complex, fractured Department of Energy field site located at the Oak Ridge National Laboratory in Tennessee, United States. We consider seismic slowness (the inverse of seismic velocity) and hydrogeological zonation indicators as unknown variables and use a physically based model with unknown parameters to relate the seismic slowness to the zonation indicators. We jointly estimate all the unknown parameters in the model by conditioning them to the crosshole seismic travel times as well as the borehole flowmeter data using a Bayesian model and a Markov chain Monte Carlo sampling method. The fracture zonation estimates are qualitatively compared to bromide tracer breakthrough data and to uranium biostimulation experiment results. The comparison suggests that the joint inversion approach adequately estimated the fractured zonation and that the fracture zonation influenced biostimulation efficacy. Our study suggests that the new joint hydrogeophysical inversion approach is flexible and effective for integrating various types of data sets within complex subsurface environments and that seismic travel time data have the potential to provide valuable information about fracture zonation.

Assessment of preferential flow path connectivity and hydraulic properties at single-borehole and cross-borehole scales in a fractured aquifer

Summary Preferential flow path connectivity is generally cited to explain scaling effects in hydraulic properties [Hsieh, P.A., 1998. Scale effects in fluid flow through fractured geological media, Scale dependence and scale invariance in hydrology. Cambridge University Press, pp. 335–353; Illman, W.A., in press. Strong evidence of directional permeability scale effect in fractured rock. Journal of Hydrology]. However, this information is rarely available in the field. In this study, we present a characterization of flow paths connectivity at the Plœmeur fractured crystalline aquifer from cross-borehole flowmeter tests. We show that high transmissivity zones are connected over distances of at least 150 m all over the site. In parallel, we synthesize hydraulic properties estimates obtained at this site from field techniques having distinct scales of investigation: single borehole flowmeter experiments, cross borehole flowmeter experiments and long term pumping tests. We find that borehole scale variability of transmissivity estimates vanishes at larger scale and that the transmissivity converges towards the high values of the transmissivity distribution. This effect may be explained by the organization of the flow field in the subsurface, and particularly the good connectivity of the permeable zones all over the site.

Field, laboratory, and modeling investigation of the skin effect at wells with slotted casing, Boise Hydrogeophysical Research Site

Understanding and quantification of wellbore skin improves our ability to accurately measure or estimate hydrologic parameters with tests at wells such as pumping tests, flowmeter tests, and slug tests. This paper presents observations and results from a series of field, laboratory, and modeling tests which, together, explain the source of wellbore skin at wells at a research wellfield and which support estimation of skin thickness ( d s) and skin hydraulic conductivity ( K s). Positive wellbore skin effects were recognized at wells in the shallow, unconfined, coarse-grained fluvial aquifer at the Boise Hydrogeophysical Research Site (BHRS). Well development efforts at the BHRS removed residual drilling fines but only marginally reduced the skin effect. Likely causes for the remaining wellbore skin effect were examined; partial clogging of screen slots with sand is consistent with field observations and can account for the magnitude of wellbore skin effect observed. We then use the WTAQ code ( Barlow and Moench, 1999) with a redefinition of the term for delayed observation well response to include skin effects at observation wells (in addition to pumping wells) in order to analyze aquifer tests at the BHRS for average K s values at individual wells. Systematic differences in K s values are recognized in results at pumping ( K s_Q) and observation ( K s_obs) wells: larger values are seen at observation wells (average K s_obs=0.0023 cm/s) than pumping wells. Two possible causes are recognized for the occurrence of higher K s values at observation wells than pumping wells: (1) flow diversion between aquifer layers on approach to a pumping well with positive skin; and (2) larger portion of flow passing through lower-K zones in the heterogeneous aquifer near the pumping well than the observation wells due to strongly radially convergent flow near the pumping well. For the well-aquifer system at the BHRS, modeling analyses of drawdown vs time at observation wells provide better K s estimates than those from pumping wells.

Cross‐Borehole Flowmeter Tests for Transient Heads in Heterogeneous Aquifers

Cross-borehole flowmeter tests have been proposed as an efficient method to investigate preferential flowpaths in heterogeneous aquifers, which is a major task in the characterization of fractured aquifers. Cross-borehole flowmeter tests are based on the idea that changing the pumping conditions in a given aquifer will modify the hydraulic head distribution in large-scale flowpaths, producing measurable changes in the vertical flow profiles in observation boreholes. However, inversion of flow measurements to derive flowpath geometry and connectivity and to characterize their hydraulic properties is still a subject of research. In this study, we propose a framework for cross-borehole flowmeter test interpretation that is based on a two-scale conceptual model: discrete fractures at the borehole scale and zones of interconnected fractures at the aquifer scale. We propose that the two problems may be solved independently. The first inverse problem consists of estimating the hydraulic head variations that drive the transient borehole flow observed in the cross-borehole flowmeter experiments. The second inverse problem is related to estimating the geometry and hydraulic properties of large-scale flowpaths in the region between pumping and observation wells that are compatible with the head variations deduced from the first problem. To solve the borehole-scale problem, we treat the transient flow data as a series of quasi-steady flow conditions and solve for the hydraulic head changes in individual fractures required to produce these data. The consistency of the method is verified using field experiments performed in a fractured-rock aquifer.