A GENERAL PURPOSE MICROCOMPUTER AQUIFER TEST EVALUATION TECHNIQUE

Abstract. Although determination of aquifer characteristics from pumping test data is generally carried out using type curves or other graphical techniques, a number of computer methods have been developed recently for this purpose. Based on the principle of least squares, these methods of nonlinear regression analysis can be applied to any flow system for which analytical expressions of the drawdown distribution are known. In view of the growing general interest in the application of microcomputers in ground-water hydrology, a BASIC routine has been developed for estimating any number of aquifer parameters. The least squares solution is calculated by Marquardt's algorithm, using the singular-value decomposition of the Jacobian matrix. The robust computing method obtained can be applied to all kinds of pumping tests. Aquifer characteristics as well as their standard deviations are computed with optimal speed and accuracy. The technique is demonstrated by a simple application to steady flow in a leaky aquifer and an example is provided. Other applications are easily implemented and programs for unsteady-state aquifer tests, recovery tests and multiple aquifer tests are available.     

Identification of Pumping Influences in Long‐Term Water Level Fluctuations

Identification of the pumping influences at monitoring wells caused by spatially and temporally variable water supply pumping can be a challenging, yet an important hydrogeological task. The information that can be obtained can be critical for conceptualization of the hydrogeological conditions and indications of the zone of influence of the individual pumping wells. However, the pumping influences are often intermittent and small in magnitude with variable production rates from multiple pumping wells. While these difficulties may support an inclination to abandon the existing dataset and conduct a dedicated cross‐hole pumping test, that option can be challenging and expensive to coordinate and execute. This paper presents a method that utilizes a simple analytical modeling approach for analysis of a long‐term water level record utilizing an inverse modeling approach. The methodology allows the identification of pumping wells influencing the water level fluctuations. Thus, the analysis provides an efficient and cost‐effective alternative to designed and coordinated cross‐hole pumping tests. We apply this method on a dataset from the Los Alamos National Laboratory site. Our analysis also provides (1) an evaluation of the information content of the transient water level data; (2) indications of potential structures of the aquifer heterogeneity inhibiting or promoting pressure propagation; and (3) guidance for the development of more complicated models requiring detailed specification of the aquifer heterogeneity.     

Inexpensive Electronic Water Level Recorders for Hydrologic Studies

Hydrologic investigations typically involve the collection of water level measurements at discrete points in space and time. The high cost of commercial electronic recorders can be a burden. We have developed an inexpensive (∼$200) electronic water level recorder consisting of a Motorola microcontroller, a clock, memory, pressure transducers, and associated circuitry. The instrument is powered by a 6-V battery. These devices, each capable of monitoring up to eight channels of analog input, are presently providing continuous monitoring of nested piezometers, tide gauges, and rain gauges in hydrologic studies at the Savannah River site and the North Inlet (South Carolina) Long-Term Ecological Research (LTER) site. The instruments can be custom tailored to record water levels at any specified time interval, or whenever the water level changes by a specified amount, and can store up to 32,000 water level observations. These instruments have been used to conduct slug tests and can be configured to monitor observation wells for pumping tests. Simplicity of construction and availability of components offer hydrologists an inexpensive but reliable method of water level recording. Several examples of the use of this instrumentation in diverse hydrologic settings are described.     

Analytical and Semi‐Analytical Tools for the Design of Oscillatory Pumping Tests

Oscillatory pumping tests—in which flow is varied in a periodic fashion—provide a method for understanding aquifer heterogeneity that is complementary to strategies such as slug testing and constant‐rate pumping tests. During oscillatory testing, pressure data collected at non‐pumping wells can be processed to extract metrics, such as signal amplitude and phase lag, from a time series. These metrics are robust against common sensor problems (including drift and noise) and have been shown to provide information about aquifer heterogeneity. Field implementations of oscillatory pumping tests for characterization, however, are not common and thus there are few guidelines for their design and implementation. Here, we use available analytical solutions from the literature to develop design guidelines for oscillatory pumping tests, while considering practical field constraints. We present two key analytical results for design and analysis of oscillatory pumping tests. First, we provide methods for choosing testing frequencies and flow rates which maximize the signal amplitude that can be expected at a distance from an oscillating pumping well, given design constraints such as maximum/minimum oscillator frequency and maximum volume cycled. Preliminary data from field testing helps to validate the methodology. Second, we develop a semi‐analytical method for computing the sensitivity of oscillatory signals to spatially distributed aquifer flow parameters. This method can be quickly applied to understand the “sensed” extent of an aquifer at a given testing frequency. Both results can be applied given only bulk aquifer parameter estimates, and can help to optimize design of oscillatory pumping test campaigns.     

Estimating hydraulic parameters when poroelastic effects are significant

For almost 80 years, deformation-induced head changes caused by poroelastic effects have been observed during pumping tests in multilayered aquifer-aquitard systems. As water in the aquifer is released from compressive storage during pumping, the aquifer is deformed both in the horizontal and vertical directions. This deformation in the pumped aquifer causes deformation in the adjacent layers, resulting in changes in pore pressure that may produce drawdown curves that differ significantly from those predicted by traditional groundwater theory. Although these deformation-induced head changes have been analyzed in several studies by poroelasticity theory, there are at present no practical guidelines for the interpretation of pumping test data influenced by these effects. To investigate the impact that poroelastic effects during pumping tests have on the estimation of hydraulic parameters, we generate synthetic data for three different aquifer-aquitard settings using a poroelasticity model, and then analyze the synthetic data using type curves and parameter estimation techniques, both of which are based on traditional groundwater theory and do not account for poroelastic effects. Results show that even when poroelastic effects result in significant deformation-induced head changes, it is possible to obtain reasonable estimates of hydraulic parameters using methods based on traditional groundwater theory, as long as pumping is sufficiently long so that deformation-induced effects have largely dissipated.     

A Field Terminal for Collection and Analysis of Geological and Hydrogeological Data

Having immediate, automated field access to data gathered during geological and hydrogeological investigations can be crucial to definition of the scope and direction of test procedures, as well as to the interpretability of results. A portable, briefcase-sized data collection and analysis instrument has therefore recently been developed. It is capable of operating as a standalone or operator-guided field unit. This terminal is pre-programmed for a number of standard applications, several of which involve BAT® tools, e.g., permeability tests made using the BAT Ground Water Monitoring System. It can, however, be used with a wide range of other tools for controlling data collection during pumping, penetration and pressometer tests, etc.
An operator's terminal and independent data collection microcontroller are the major components of this system. Data may be collected from any combination of four ports: an internal, programmable interval timer, a pulser (shaft encoder), and two 14-bit analog-to-digital (A/D) inputs. The latter are primarily used for pressure or resistance transducers. Reading of data may be triggered automatically by the timer and/or pulser, or be performed upon operator command. Many thousands of data points may be stored in the microcontroller, representing one or several tests of any type, intermixed. Via the operator's terminal, any subset of this stored data may be examined, erased, modified or analyzed. A 26-character LCD display and a four-color printer/plotter are used to record data and results of analyses. Data may also be transferred to an external computer for more extensive manipulation.
Three examples of how this terminal may be used in the field in connection with site investigations are presented in this paper. They involve (a) measurement of saturated hydraulic conductivity, (b) determination of soil stratigraphy using pore pressure sounding, and (c) water network profiling.     

Improved Kakioka automatic standard magnetometer (KASMMER)

The KASMMER (Kakioka Automatic Standard Magnetometer) has been constructed in 1972 for the standard magnetic observation at Kakioka (Yanagiharaet al., 1973). Then KASMMER system has been improved successively for the high level standard magnetic observation. The purpose of the present paper is to introduce an outline of the improved KASMMER system.The KASMMER system consists of four parts which are four optical pumping magnetometers, a fluxgate magnetometer (Supporting system to the optical pumping magnetometers), a calibration system and a data acquisition system (computer system). The calibration system consists of a proton magnetometer and a magnetic theodolite (Di-72). Details for each part are described and the ability of the improved system is shown to be higher than that of classical magnetic observatory systems.     

Does Pumping Volume Affect the Concentration of Micropollutants in Groundwater Samples?

Information on concentrations of micropollutants (such as pharmaceuticals, pesticides, and industrial chemicals) in most highly dynamic riverbank filtration (RBF) systems is lacking, in contrast to data on standard chemical parameters. Sampling protocols have thus far been based on the stabilization of standard chemical parameters in relatively pristine environments. To determine whether groundwater samples for micropollutant analysis can be taken at a similar pumping volume as samples for testing standard chemical parameters in both environments, three groundwater monitoring wells in an RBF system were sampled at two points in time (after pumping of 3 well volumes and after pumping of 15 well volumes). Micropollutant concentrations were not significantly different between the two sampling points; therefore, appropriate samples can be drawn after pumping 3 well volumes. For a specific microbiological parameter (leucin incorporation), a statistically significant difference was found.     

A State-Of-The-Art Approach to Hydrologic Data Management

High-accuracy electronic data acquisition equipment, a solid-state memory, computer interface and software have been developed to provide a complete system for measuring and recording water level changes.
A small, stand-alone hydrologic instrument (SE1000) provides the automation and accuracy of solid-state electronics in pump tests, slug tests, and long- and short-term ground water monitoring. The unit is powered by a high-performance battery pack with a minimum life of four years. This instrument can be buried at the monitoring site for protection from vandals, animals and temperature extremes. Ten pre-programmed 949-point data schedules are standard. One schedule is logarithmic with an initial data interval of 0.2 seconds. Nine linear schedules provide data intervals ranging from 15 minutes to 1.5 days and corresponding test durations ranging from 10 days to 46 months. The stored data can be recovered directly via the LCD display or transferred to a computer. Software provides automatic data reduction with hard copy tables and plots.
This instrument has been used successfully in various locations in the United States.     

ANALYSIS OF AQUIFER TESTS CONDUCTED IN FRACTURED ROCK: A REVIEW OF THE PHYSICAL BACKGROUND AND THE DESIGN OF A COMPUTER PROGRAM FOR GENERATING TYPE CURVES

Abstract. Assessing the hydrogeological character of fractured bedrock between two or more wells is usually accomplished through an analysis of the results of traditional pumping tests. Because these tests are subject to field boundary conditions that may be different from those conducted in porous media, alternative testing techniques or analytical methods are required. To provide an adaptable interpretive package for analyzing interwell hydraulic tests in fractured rock, a FORTRAN program was developed to generate type curves for pumping tests and pulse interference tests. A review of the physical conditions which most influence the results of these tests is conducted to provide the background for the development and use of the program. The analytical solutions included in the program consider inner boundary conditions such as wellbore storage, infinitesimally thin skin and finite-thickness skin. In addition, a solution is included to analyze results influenced by wellbore storage and infinitesimally thin skin at both the pumping and observation wells. The solutions are given in the Laplace domain and are numerically inverted to generate data for the type curves. The curves can be plotted using any standard plotting program, or they can be plotted manually. The program is menu driven, easily adaptable to include additional solutions, and can be executed on a personal computer.     

Optimized system to improve pumping rate stability during aquifer tests

Aquifer hydraulic properties are commonly estimated using aquifer tests, which are based on an assumption of a uniform and constant pumping rate. Substantial uncertainties in the flow rate across the borehole-formation interface can be induced by dynamic head losses, caused by rapid changes in borehole water levels early in an aquifer test. A system is presented that substantially reduces these sources of uncertainty by explicitly accounting for dynamic head losses. The system which employs commonly available components (including a datalogger, pressure transducers, a variable-speed pump motor, a flow controller, and flowmeters), is inexpensive, highly mobile, and easily set up. It optimizes the flow rate at the borehole-formation interface, making it suitable for any type of aquifer test, including constant, step, or ramped withdrawal and injection, as well as sinusoidal. The system was demonstrated for both withdrawal and injection tests in three aquifers at the Savannah River Site. No modifications to the control system were required, although a small number of characteristics of the pumping and monitoring system were added to the operating program. The pumping system provided a statistically significant, constant flow rate with time. The range in pumping variability (95% confidence interval) was from +/- 2.58 x 10(-4) L/sec to +/- 9.07 x 10(-4) L/sec, across a wide range in field and aquifer conditions.     

Extraction Rate Problems Lead to Increased Costs at Pump-and-Treat Facilities: A Call to Improve Reporting of Rates

Experiences at five pump-and-treatment (P&T) facilities provide three important lessons:
1. To reduce future costs, it is important to use the best hydraulic information possible for designing P&T systems, and to incorporate flexibility to compensate for uncertainties in hydraulic conditions. A phased approach to P&T system construction and hydraulic testing has been successful.
2. In practice, downtimes and maintenance problems result in significant reductions in the average ground water extraction rates. This indicates that operation and maintenance were more difficult than expected and warrant more attention. Furthermore, P&T systems are generally designed to attain the model optimized extraction rates only when the system is in full operation. Designers must recognize that P&T systems have downtimes, and, therefore, the uptime pumping must be sufficient to maintain capture. Generally, P&T systems should achieve model-optimized extraction rates on an average basis rather than only when the system is in full operation.
3. During operation of P&T systems, the average extraction rates should be routinely correlated to capture zone evaluations and included in monitoring reports. The average extraction rates should be compared to the model-derived extraction rates to assess whether the design objectives are being met and should be included in routine monitoring reports to confirm maintenance of pumping rates under which capture has been demonstrated.     

A Computerized Ground Water Monitoring System

This article describes a computer automated, hydrologic analysis system designed to allow the collection of high quality, long-term pumping test data. The instrument solves two of the major problems encountered in the field during aquifer tests: insufficient data, particularly during the early part of a test when drawdown is rapid; and high labor costs associated with long-term monitoring.
To illustrate the system's application, results are presented from the test of a highly transmissive aquifer. The aquifer's drawdown response was rapid; thus the time-drawdown curve was essentially flat after the first two minutes of the test, and correspondingly rapid data acquisition was essential for a unique solution of the aquifer's three-dimensional hydraulic conductivities.     

地层测试评价仪(FET)及其在中国海域的应用

地层测试评价仪(Formation Evaluation Tool)是中海油田服务股份有限公司引进澳大利亚 CROCKER公司技术而自行开发、制造的新一代地层测试评价系统。该仪器已经在中国近海渤海、南海等海域取得了成功应用,其精确地层压力测试能帮助判断多套油水系统,尤其在一些薄层和边水油藏也取得了可靠的测压资料,很好的解决了油水、气水界面确定问题;此外在目的层取样时所具有的污染流体抽排和地层流体特性实时检测功能保证获取不受泥浆污染的真实地层流体样品,对确定流体性质和分析流体成分起到了重要作用。本文主要介绍地层测试评价仪(FET)的原理和用途,以及在中国海域的成功应用实例。     

Fiber Optic Pressure Measurements Open Up New Experimental Possibilities in Hydrogeology

Fiber-optic (FO) technology is being used increasingly for measurement methods in a variety of environmental applications. However, FO pressure transducers are rarely used in hydrogeological applications. We review the current state of Fabry-Pérot interferometry-based FO pressure transducers, including their advantages and limitations, as another option for high-resolution pressure- or head-change measurements in conventional or advanced aquifer testing. Resolution and precision specifications of FO transducers meet or exceed commonly used non-FO pressure transducers. Due to their design, FO transducers can be used in small-diameter (inner diameter ≥1/4 inch) and continuous multichannel tubing (CMT), sampling points, multilevel packer systems, and Direct Push-based in situ installations and testing. The small diameter of FO transducers provides logistical advantages—especially for tests with monitoring at many zones in a number of wells and/or CMTs (e.g., no reels, placement just below water level in access tubes vs. within isolated zones, reduced weight and volume, small footprint at single point of data acquisition). Principal limitations are small measurement drift that may become evident for tests longer than a few hours, and higher-than-average cost. We present field examples of FO transducer performance in short-term tests with high consistency of acquired data and higher resolution (i.e., capturing significant hydrologic information) compared with commonly used non-FO transducers. Given the above, including advantageous logistical features, FO transducers can open new experimental possibilities in areas of high-resolution three-dimensional (3D) heterogeneity (flow and transport, remediation, critical zones); 3D fracture networks and fundamental hydromechanical behavior; complex 3D flow and leak detection (mines, dams, repositories, geothermal systems).     

Time‐Elevation Head Sections: Improved Visualization of Data from Multilevels

Hydrogeologic investigations of fractured rock are evolving toward increasing spatial and temporal resolution with increasing use of multilevel systems with 10 or more intervals in a single borehole, each with auto‐sampling sensors monitoring pressure, temperature or chemistry for weeks or months, creating large quantities of densely sampled data (time and space). These data are typically displayed as hydrographs for analysis of site‐specific controls on groundwater flow. We present a method for presentation of high density pressure head data from multilevel installations referred to as time‐elevation head (TEH) sections that improves visualization of spatial and temporal responses of the hydrogeologic system to external stresses. Data collected from two multilevel installations, each with 13 functioning pressure transducers monitoring the upper 40 m of a dolostone aquifer, over a period of 83 d, prior to, during and after a pumping test are used to present TEH sections and examples of data processing. TEH sections are produced using commercially available software designed for geophysical data collected at closely spaced intervals along sub‐parallel lines. These algorithms perform calculations orthogonally either in time (“X” axis) or elevation (“Y” axis) to interpolate a regular grid of head and subsequently when filtering is used to identify subtle trends within the data. The base and filtered TEH sections are used to interpret response of the system to transients and infer hydrogeologic characteristics of the site. The utility of the process is dependent on the precision and accuracy of the head data as well as an informed user to avoid introducing spurious features into the sections.     

天津王4井抽水观测水汞影响因素的探讨

王4井因受井区地热开发的影响,于2008年12月断流停测。2010年对原观测井口装置进行改造,开始进行抽水观测水汞试验研究。在新的观测方式下,为确保观测数据稳定、可靠,本文从抽水观测的观测条件方面,对不同取样位置和抽水时间对水汞测值的影响进行了试验。试验结果表明,不同抽水时间和不同取样位置抽水观测对水汞测值影响不大,这一结论与水汞本身的化学特性相一致。认为在没有自流井的地区,只要选择灵敏的观测点使用抽水方式采样,固定观测条件,依然可以进行水汞监测。     

Introduction to hydromechanical well tests in fractured rock aquifers

This article introduces hydromechanical well tests as a viable field method for characterizing fractured rock aquifers. These tests involve measuring and analyzing small displacements along with pressure transients. Recent developments in equipment and analyses have simplified hydromechanical well tests, and this article describes initial field results and interpretations during slug and constant-rate pumping tests conducted at a site underlain by fractured biotite gneiss in South Carolina. The field data are characterized by displacements of 0.3 μm to more than 10 μm during head changes up to 10 m. Displacements are a hysteretic function of hydraulic head in the wellbore, with displacements late in a well test always exceeding those at similar wellbore pressures early in the test. Displacement measurements show that hydraulic aperture changes during well tests, and both scaling analyses and field data suggest that T changed by a few percent per meter of drawdown during slug and pumping tests at our field site. Preliminary analyses suggest that displacement data can be used to improve estimates of storativity and to reduce nonuniqueness during hydraulic well tests involving single wells.     

A method for evaluating horizontal well pumping tests

Predicting the future performance of horizontal wells under varying pumping conditions requires estimates of basic aquifer parameters, notably transmissivity and storativity. For vertical wells, there are well-established methods for estimating these parameters, typically based on either the recovery from induced head changes in a well or from the head response in observation wells to pumping in a test well. Comparable aquifer parameter estimation methods for horizontal wells have not been presented in the ground water literature. Formation parameter estimation methods based on measurements of pressure in horizontal wells have been presented in the petroleum industry literature, but these methods have limited applicability for ground water evaluation and are based on pressure measurements in only the horizontal well borehole, rather than in observation wells. This paper presents a simple and versatile method by which pumping test procedures developed for vertical wells can be applied to horizontal well pumping tests. The method presented here uses the principle of superposition to represent the horizontal well as a series of partially penetrating vertical wells. This concept is used to estimate a distance from an observation well at which a vertical well that has the same total pumping rate as the horizontal well will produce the same drawdown as the horizontal well. This equivalent distance may then be associated with an observation well for use in pumping test algorithms and type curves developed for vertical wells. The method is shown to produce good results for confined aquifers and unconfined aquifers in the absence of delayed yield response. For unconfined aquifers, the presence of delayed yield response increases the method error.     

Hydraulic Tomography Offers Improved Imaging of Heterogeneity in Fractured Rocks

Fractured rocks have presented formidable challenges for accurately predicting groundwater flow and contaminant transport. This is mainly due to our difficulty in mapping the fracture‐rock matrix system, their hydraulic properties and connectivity at resolutions that are meaningful for groundwater modeling. Over the last several decades, considerable effort has gone into creating maps of subsurface heterogeneity in hydraulic conductivity (K) and specific storage (S_s) of fractured rocks. Developed methods include kriging, stochastic simulation, stochastic inverse modeling, and hydraulic tomography. In this article, I review the evolution of various heterogeneity mapping approaches and contend that hydraulic tomography, a recently developed aquifer characterization technique for unconsolidated deposits, is also a promising approach in yielding robust maps (or tomograms) of K and S_s heterogeneity for fractured rocks. While hydraulic tomography has recently been shown to be a robust technique, the resolution of the K and S_s tomograms mainly depends on the density of pumping and monitoring locations and the quality of data. The resolution will be improved through the development of new devices for higher density monitoring of pressure responses at discrete intervals in boreholes and potentially through the integration of other data from single‐hole tests, borehole flowmeter profiling, and tracer tests. Other data from temperature and geophysical surveys as well as geological investigations may improve the accuracy of the maps, but more research is needed. Technological advances will undoubtedly lead to more accurate maps. However, more effort should go into evaluating these maps so that one can gain more confidence in their reliability.