Large-diameter Wells Research Articles

Estimating apparent thermal diffusivity using temperature time series: A comparison of temperature data measured in KMA boreholes and NGMN wells

Two different time series data sets, shallow ground temperatures of 58 synoptic stations of the Korea Meteorological Administration (KMA) and groundwater temperatures of 67 wells of the National Groundwater Monitoring Network (NGMN), were analyzed to estimate the apparent thermal diffusivity by using the analytical solution of the one-dimensional heat conduction equation. The KMA temperature data measured at 1–5 m depths illustrated values of the phase delay and the amplitude decay coincident with their theoretical relationship, indicating that the conductive heat transport should prevail over the nonconductive processes. On the contrary, some of the estimates from temperatures at a depth of 0.5 m were away from the theoretical values. It is most likely that the deviation would be caused by the effects of latent heat associated with freezing and thawing of the near ground surface. In contrast to KMA data, results obtained from the NGMN data highly deviated from the theoretical ones, and thereafter yielded unacceptably high values of thermal diffusivities as compared to the representative values of soils and rocks. Implication of the discrepancy between two data sets was discussed in conjunction with perturbation of the conductive heat transport by free convection of water and air occurring in large diameter wells as well as the convective heat transport by groundwater flow.

Discussion of “Approximation of Well Function for Large Diameter Wells” by Sushil K. Singh

Discussion of “Approximation of Well Function for Large Diameter Wells” by Sushil K. Singh

Closure to “Approximation of Well Function for Large Diameter Wells” by Sushil K. Singh

Closure to “Approximation of Well Function for Large Diameter Wells” by Sushil K. Singh

Aquifer Parameters from Drawdowns in Large-Diameter Wells: Unsteady Pumping

An optimization method is proposed for estimating transmissivity, storage coefficient, and effective well radius from drawdowns in large-diameter wells. Unsteady pumping is considered; any variation in pumping discharge can be accounted for. Pumping and residual drawdowns can be analyzed simultaneously using the new method. The application of the method is illustrated through the examples of prior studies. The new method reliably estimates the parameters. For the examples considered, the estimates of transmissivity and effective radius of well are more accurate than the estimate of storage coefficient. The proposed method is superior to the prior method because it is objective, more quantitative, and more general.

Estimating Aquifer Parameters from Early Drawdowns in Large-Diameter Wells

The existing equation applicable for large diameter wells in confined aquifers is transformed into a convenient form and a set of semilogarithmic diagnostic curves is developed for identifying the aquifer parameters (storage coefficient and transmissivity) from early drawdowns in large diameter wells. A scaled well function is proposed for the diagnostic curves. The aquifer parameters are estimated by matching the diagnostically plotted drawdowns to one of the diagnostic curves by a parallel shift of only one axis. The substantial curvature of the diagnostic curves and shifting of only one axis facilitate matching and reduce subjectivity. The proposed method is an improvement over the existing matching methods. The new method can reliably identify the aquifer parameters from only early drawdowns and would result in a 100-fold saving in time and money. It is hoped that this method would be helpful to field engineers and practitioners.

Simulating the Well Function for Large-Diameter Wells Using MODFLOW

An approach for incorporating large-diameter wells into MODFLOW is presented. A transformation of transmissivity in the flow field is devised to simulate the well function for a large-diameter wells. Transformations for accounting for the well radius and well storage are also developed. Using these transformations, MODFLOW is used to obtain the drawdowns. It is observed that the flow to a large diameter well can be accurately modeled using the proposed transformations and MODFLOW.

Estimating Storage Coefficient and Transmissivity from Slug Test Data

A new accurate approximation for the well function for instantaneous charge of water for large diameter wells is proposed. Using this approximation with an optimization method, storage coefficient and transmissivity are estimated from slug test data on large diameter wells. The proposed method is void of the subjectivity of curve matching procedure.

Approximation of Well Function for Large Diameter Wells

A computationally simple and accurate algebraic approximation of the well function for large diameter wells is proposed. This approximation can be used to calculate drawdown in a large diameter well due to steady pumping. Using this approximation, a method is proposed for calculating drawdowns in large diameter wells due to unsteady pumping discharge. The proposed method is also applicable for calculating residual drawdowns in large diameter wells. In principle, the proposed method that uses the approximation of the well function should yield more accurate results than the previously proposed kernel methods.

Optimizing Aquifer Parameters from Drawdowns in Large Diameter Wells

An optimization method is proposed for estimating the storage coefficient and transmissivity of an aquifer from drawdowns in large diameter wells consequent to an unsteady pumping. The concept of an optimal time step size is propagated in the proposed method. The estimate of the aquifer parameters corresponding to the optimal time step size is termed final estimate. The estimates for any other time step size are not reliable. The proposed method can also take into account the residual drawdowns. The application of the method is illustrated using an example.

Simple Equations for Aquifer Parameters from Drawdowns in Large-Diameter Wells

Simple equations are proposed for estimating storage coefficient and transmissivity of an aquifer from drawdowns in large- diameter wells. The proposed method requires determination of the peak and time to peak of a unimodal curve. Using these values and utilizing the provided set of equations, the aquifer parameters are estimated through an iterative procedure. The proposed method is void of subjectivity involved in the previously proposed curve matching methods. Also, the new method can be used when the conventional curve matching methods cannot be applied to estimate the aquifer parameters. The new method can be used to estimate the aquifer parameters from the drawdown data observed only up to a time so that the peak could be determined.

Simplified Kernel Method for Flow to Large Diameter Wells

A computationally simple kernel method is proposed for obtaining drawdowns due to unsteady pumping of large diameter wells. The kernels can be worked out even on a hand-held calculator. The new method can also be used to obtain residual drawdowns. The new method yields results as good as those obtained using earlier methods.

Type Curves for Unsteady Flow to a Large-Diameter Well in Patchy Aquifers

This paper analytically considers unsteady flow to a large-diameter well with the well storage in patchy aquifers that is cylindrically composed of two distinctive regions around the well with different hydraulic properties. The solution involves the usage of the independent variable transform. This approach gives, for both regions, the type curves that are dependent on the distance from the pumping well to the interface between two regions and the hydraulic parameter. The parameter is implied as the ratio of the transmissivity and the storage coefficients of two regions. A new well function expression—different from the well-known Theis well function—is defined to evaluate the field data. The function is seen as an approximation and is easily applicable to estimate the transmissivity and the storage coefficients of the patchy aquifers.

Well storage effect during pumping tests in an aquifer of low permeability

Well storage effect is generally considered while interpreting pumping test data from large diameter wells. However, in an aquifer of low permeability, the well storage is found to be significant during pumping tests conducted on bore wells. The interpretation of such data gives ambiguous results unless well storage effect is taken into account. A field example is presented to illustrate the difficulty in interpretation of the pumping test data. In order to take into account the well storage effect, a finite difference approach of interpreting pumping test data is suggested.

Characterization of an aquifer system in the Upper Palar Basin: a case study

Hydrodynamics of the groundwater flow regime in hard rock regions, and its quantification, are not yet fully understood. This is mainly a result of several uncertainties involved in quantifying the hydrogeological parameters. Numerical techniques are potential tools in interpreting hydrogeological parameters in hard rock regions. Such a study was carried out in the Palar River Basin, Tamilnadu (India), where pumping tests carried out on large diameter wells were interpreted using a numerical technique.

Modelling an inland Delta aquifer system to evolve pre-development management schemes: a case study in Upper Thamalakane River valley, Botswana, southern Africa

Groundwater modelling studies have been found to be a potential tool in planning the pre-development management of groundwater resources in newly developing aquifer systems. One such study was attempted in Upper Thamalakane River valley, Okavango Delta, Botswana (southern Africa). There are three major aquifers separated by two aquitards in the valley portion. The top two aquifers are freshwater bearing zones and the bottom one is saline. The hydrological set-up of the basin is complex, as the groundwater flow directions are opposite in the upper-unconfined and in the lower-confined aquifers. A preliminary multilayer model was developed for this aquifer system by making use of only available data. The hydrodynamic behavior was then studied under two prediction scenarios to evolve appropriate management decisions for locating the well field (large diameter wells) in the upper aquifer by making use of induced river infiltration during the flood season. The aquifer response for variable river-flow conditions was studied and the induced river infiltration was quantified.

Managing Groundwater in Hard-rock Areas through Agro-well Design and Development

Water shortage in the dry season is a major problem facing agriculture in the dry and intermediate zones of Sri Lanka. Large diameter wells (agro-wells) have been introduced to use the groundwater as a supplement to rainfall. The underlying crystalline hard-rock formations have very low storage and transmissivity, which limit the groundwater resource. The haphazard development of agro-wells may seriously threaten sustainable groundwater use in the future. Based on field studies and a groundwater hydrological model, this paper explains a methodology for determining the dimensions of agro-wells that limit a farmer to abstracting no more than the volume of water recharged under his/her land. This methodology can be used to regulate groundwater in hard-rock aquifers by identifying the safe volume of water that can be abstracted, establishing the optimum well dimensions for constructing a new well, and matching crop-water requirements to the abstractable volume of water. Farmers themselves can regulate groundwater resources to limit exploitation to equal their entitlement.

Interpretation of pumping test data from large diameter wells on an oceanic island

Estimation of aquifer parameters is vital for the assessment of groundwater potential and groundwater flow regime. On an oceanic island where fresh water lens is fragile and sensitive to various stresses, it is even more essential that in order to assess the potential of fresh water lens and the effect of various stresses on the fresh groundwater regime the parameters should be representative to the field hydrogeological set up. Pumping tests conducted on existing large diameter wells on an oceanic island have been analyzed. A finite difference method has been used to take into account the well storage, partial penetration and upconing effect into the aquifer. Forward modeling has been carried out to estimate aquifer parameters from the pumping test data. Field examples are described.

Seepage Face Modeling for Large-Diameter Well in Unconfined Aquifer

Modeling of the seepage face in the case of flow toward wells has received considerable attention in the literature. It is evident from the literature that the models applicable to describe the well loss in the confined flow situation have been also employed to represent the seepage face variation in the case of unconfined flow situations. It is only during the past decade that attempts have been made to describe the seepage face in the case of wells located in an unconfined aquifer. In these studies, the seepage face has been related to the aquifer discharge, the duration of pumping test, the time since the start of pumping, etc. With a view to further simplifying the existing seepage face models, the present study approaches the problem of seepage face modeling in the case of a large-diameter well located in an unconfined aquifer using the velocity of flow at the well face. The resulting expression of the seepage face is not only simpler but also converts to the existing seepage face models, or their si...

Optimising the dimensions of agrowells in hard-rock aquifers in Sri Lanka

A case study was conducted into the use of large diameter wells (agrowells) for supplementary irrigation from the hard-rock aquifer in the North-Western province of Sri Lanka. Two existing models, a radial groundwater flow model and a soil water balance, were used together to represent the agrowell irrigation system. A technique is described to optimise new agrowell systems by deciding the optimum well radii for given aquifer characteristics and well spacings, or to optimise existing agrowell systems by deciding the sustainable irrigable command areas

Use of slim holes with liquid feedzones for geothermal reservoir assessment

Production and injection data from slim holes and large-diameter wells at four geothermal fields (Oguni, Japan; Sumikawa, Japan; Takigami, Japan; Steamboat Hills, U.S.A.) were analyzed in order to establish relationships (1) between injectivity and productivity indices, (2) between productivity/injectivity index and borehole diameter, and (3) between discharge capacity of slim holes and large-diameter wells. The productivity and injectivity indices for boreholes with liquid feedzones are more or less equal. Except for the Oguni boreholes, the productivity and injectivity indices display no correlation with borehole diameter. Thus, the productivity index (or, more importantly, the injectivity index in the absence of discharge data) from a slim hole with a liquid feed can be used to provide a first estimate of the probable discharge capacity of a large-diameter geothermal production well. The large-diameter wells at the Oguni, Sumikawa and Steamboat Hills geothermal fields have a more or less uniform inside diameter, and the discharge capacity of these wells (with liquid feedzones) can be predicted using Pritchett's “scaled maximum discharge rate” in conjunction with discharge data from slim holes. Because of the non-uniform internal diameter for large-diameter Takigami wells, it is not possible to use a simple scaling rule to relate the discharge capacities of slim holes and large-diameter wells at Takigami; therefore, a numerical simulator was used to model the available discharge data from Takigami boreholes. The results of numerical modeling indicate that the flow rate of large-diameter Takigami production wells with liquid feedzones can also be predicted using discharge and injection data from slim holes.