Multi-well Pumping Research Articles

Improving monitoring network design to detect leaks at hazardous facilities: Lessons from a CO2 storage site

Exploring the challenges posed by uncertainties in numerical modeling for hazardous material storage, this study introduces methodologies to improve monitoring networks for detecting subsurface leakages. The proposed approaches were applied to the Korea CO2 Storage Environmental Management (K-COSEM) test site, undergoing calibration, validation and uncertainty analysis through hydraulic and controlled-CO2 release tests. The calibration phase involved inter-well tracer and multi-well pumping tests, leveraging the Parameter ESTimation (PEST) model to determine the aquifer flow and solute transport properties of the K-COSEM site. To tackle uncertainties with limited observation data, we adopted Latin Hypercube simulation. Our uncertainty analysis confirmed model accuracy in simulating observed CO2 breakthrough curves. We also explored a probabilistic method to identify the environmental change point (EnCP) through correlation analysis with the distance from the CO2 injection well, revealing a linear trend and pinpointed potential preferential flow pathways by assessing detection probabilities. Evaluating CO2 detection capabilities was crucial for optimizing monitoring well placement, highlighting strategic well selection based on detection probabilities. This study advances managing uncertainties in hydrogeological modeling, underscoring the importance of sophisticated models in designing monitoring networks for hazardous leak detection in complex subsurface conditions.

Assessing the Connectivity of a Regional Fractured Aquifer Based on a Hydraulic Conductivity Field Reversed by Multi-Well Pumping Tests and Numerical Groundwater Flow Modeling

Assessing the Connectivity of a Regional Fractured Aquifer Based on a Hydraulic Conductivity Field Reversed by Multi-Well Pumping Tests and Numerical Groundwater Flow Modeling

LPS Rope Suspension Auxiliary Unloading Device Structure Design

In this paper, we propose a wellhead unloading protection system for a multi-well pumping unit with the functions of multi-pumping, energy efficiency, and intelligent control, and address the painful issue of having to shut down the entire well group for maintenance when the single well fails or during wellhead maintenance operations. An in-depth theoretical design was carried out and the structure was simulated and analysed using finite element software. The finite element analysis results show that the LPS auxiliary unloading device has a reasonable structure and high reliability, and can achieve the unloading protection function well, which provides a valuable reference for further optimization of the structure.

Identification of non-Darcian flow effect in double-porosity fractured aquifer based on multi-well pumping test

Well testing in double-porosity fractured aquifers or oil and gas reservoirs is one of the long-lasting research problems in subsurface hydrology and petroleum engineering, where the double-porosity implies that the media of concern can be approximated as a two interrelated continuums (fracture network and rock matrix) with two distinctively different porosities. However, most of those studies in double-porosity fractured aquifers only concern Darcian flow in the fractured continuum. In this study, we will expand such studies from Darcian flow regime to non-Darcian flow regime, which is most likely to be the case for the field well testing site reported in this investigation. New solutions based on power law and a linearization approximation are obtained for hydraulic heads in Laplace domain and subsequently inverted to give spatiotemporal distributions in real-time domain. The non-Darcian flow model in single porosity media is obtained by setting the leakage coefficient (C) to 0 or the storage coefficient of the matrix (Sm) to 0, where C is the rate of fluid transfer between the fracture and rock matrix. Parameter analysis is conducted using dimensionless formats. A larger dimensionless quasi conductivity coefficient KqD, a larger drawdown in the early stage, and a smaller drawdown in the late stage. The dimensionless parameters CD and ϕ influence the drawdown in transitional state, and the values get larger, the drawdown in transitional state drop smaller. A pumping test conducted in Huangtun, Anhui province of China has been applied to test the non-Darcian flow effect in a double-porosity aquifer, in which a particle swarm optimization (PSO) algorithm will be applied here to seek the optimal hydraulic parameters. As the result shows, the observed drawdown data fit well with the new model in the pumping stage. The predicted recovery drawdown curve with the calculated parameters of the new model also performs well with the field drawdown data, which supports the applicability of the new model to interpret the field data.

Laboratory Physical Experiments on the Saltwater Upconing and Recovery of Island Freshwater Lenses: Case Study of a Coral Island, China

The research of saltwater upconing is crucial for the development and utilization of island freshwater resources. In this paper, a laboratory physical experiment device was developed, and the saltwater upconing and recovery of island freshwater lenses were investigated using rainfall simulations and single-well and multi-well pumping tests with various pumping intensities. The results of the experiment revealed that: (1) The thickness of the freshwater lens increased continuously and linearly during the early stages of rainfall. As the rainfall continued, the upward trend slowed and eventually leveled off. (2) Under the same pumping duration, when the pumping intensity was less than the critical pumping intensity, the increasing height rate of the saltwater upconing increased linearly at a small gradient, and when the pumping intensity was greater than the critical value, the rising height rate of the saltwater upconing increased linearly at a large gradient. (3) Under the same pumping intensity conditions, the pumping duration of the multi-well was longer than that of the single-well pumping, and the pumping volume of the multi-well was also greater than that of the single-well pumping. The experiment results can provide support for the development and utilization of island freshwater lens.

Approaching geoscientific inverse problems with vector-to-image domain transfer networks

We present vec2pix, a deep neural network designed to predict categorical or continuous 2D subsurface property fields from one-dimensional measurement data (e.g., time series), thereby offering an alternative approach to solve inverse problems. The performance of the method is investigated through two types of synthetic inverse problems: (a) a crosshole ground penetrating radar (GPR) tomography experiment with GPR travel times being used to infer a 2D velocity field, and (2) a multi-well pumping experiment within an unconfined aquifer with time series of transient hydraulic heads being used to retrieve a 2D hydraulic conductivity field. For each type of problem, both a multi-Gaussian and a binary channelized subsurface domain with long-range connectivity are considered. Using a training set of 20,000 examples (implying as many forward model evaluations), the method is found to recover a 2D model that is in much closer agreement with the true model than the closest training model in the forward-simulated data space. Further testing with smaller training sample sizes shows only a moderate reduction in performance when using 5000 training examples only. Although these 5000 to 20,000 forward runs can be performed offline in parallel, the associated computational expense may still be prohibitive for very demanding forward solvers. In addition, re-training is required for each new measurement configuration. Even if the recovered models are visually close to the true ones, the data misfits associated with their forward responses are generally larger than the noise level used to contaminate the true data. Uncertainty of the inverse solution is partially assessed using deep ensembles, in which the network is trained repeatedly with random initialization. Overall, this study advances understanding of how to use deep learning to infer subsurface models from indirect measurement data. More work is needed to evaluate the suitability of our proposed approach for real data, for which model errors and uncertainty in the geologic scenario will bring additional complexities.

Multi-Well Pumping System Design and Field Application

Abstract In view of the low efficiency of cluster wells, a multi-well pumping system with phase-division balance is put forward based on the idea of overlapping load-dislocation vectors. In this article, the kinematics and dynamics of the system are analyzed and the torque fluctuation characteristics of the system and the changing law of the motor energy consumption are studied under theory and actual working conditions. Additionally, a comparative analysis of a computer simulation and field test is carried out from the single-well to four-well pumping system. The results show that the dynamic performance of the multi-well pumping system based on phase-division balance is obviously better than that of single-well pumping unit. In addition, the system has remarkable high-efficiency energy-saving characteristics and good dynamic characteristics with coefficient of load fluctuation approaching 1 and a markedly reduced root mean square torque. The influence of inertia force on driving moment is considered by establishing the dynamic equation of the main mechanism and doing dynamic simulation. The friction power is equivalent to the corresponding additional driving power, so the influence of friction on driving moment is considered. The computer simulation results also show that the effect of multi-wells is good. According to field test data, a four-well pumping system can save 361 kWh of electricity per day.

Management and Utilization of High-Pressure Floor-Confined Water in Deep Coal Mines

This study analyzed the failure characteristics of the coal seam floor induced by longwall mining to manage and eliminate possible hazards associated with high pressure (8.0 MPa) floor-confined water in the Xinjulong coal mine. The disturbed floor was divided into mining failure (MF), water-resistant (WR), and confined water intrusion (CWI) zones. The MF and CWI zones have lost their ability to resist the confined water, so the WR zone is the key for preventing water inrush from the floor aquifer. A thin-plate model for the WR zone indicated that the water pressure had to be decreased to 2.4 MPa or less. Multi-well pumping was used to decrease the floor aquifer water pressure from 8.0 to 2.1 MPa. Moreover, grouting was used to block water-conducting fractures in the floor strata. In addition, classification, purification, and recycling techniques enabled 84.8% utilization of the produced mine water.

Experimental study on the artificial recharge of semiconfined aquifers involved in deep excavation engineering

Artificial recharge measures have been adopted to control the drawdown of confined aquifers and the ground subsidence caused by dewatering during deep excavation in Tianjin, Shanghai and other regions in China. However, research on recharge theory is still limited. Additionally, confined aquifers consisting of silt and silty sand in Tianjin have lower hydraulic conductivities than those consisting of sand or gravel, and the feasibility and effectiveness of recharge methods in these semiconfined aquifers urgently require investigation. A series of single-well and multiwell pumping and recharge tests was conducted at a metro station excavation site in Tianjin. The test results showed that it was feasible to recharge silt and silty sand semiconfined aquifers, and, to a certain extent, the hydrogeological parameters obtained from the pumping tests could be used to predict the water level rise during single-well recharge. However, the predicted results underestimated the water level rise near the recharge well (within 7 m) by approximately 10–25%, likely because the permeability coefficient around the well was reduced during the recharge process. Pressured recharge significantly improved the efficiency of the recharge process. Maintaining the recharge and pumping rates at a nearly equal level effectively controlled the surrounding surface and building settlement. However, the surrounding surface subsidence tended to rapidly develop when recharge stopped. Therefore, the recharge process should continue and gradually stop after the pumping stops. The twin-well combined recharge technique can be used to control the head loss of an aquifer when one of the recharge wells requires pumping to solve the associated clogging problems.

Random errors in the hydrogeological parameters of a two-layer stratum evaluated by multi-well pumping tests

Random errors in estimates of flow and storage parameters of a two-layer stratum, derived from multi-well pumping test data are examined. It was found that the relative random error with a confidence probability of 0.954 is appreciably less than 100% only for the estimates of aquifer transmissivity, while the estimates of the hydraulic conductivity and the specific yield of the overlying deposits show relative random errors with the same confidence probability in excess of 100%. Therefore, the random errors of parameters are to be given as multiples of the established values.

Analysis of multiwell pumping tests in a confined aquifer under variations in the production rate and atmospheric pressure

Problems of the interpretation of long-term multiwell pumping tests that account for variations in the production rate and atmospheric pressure are considered. The barometric efficiency and corrections of actual drawdowns are calculated for the Udomlya groundwater basin; spatiotemporal development of the depression cone is analyzed. The hydrogeodynamic parameters are used for calibration of a numerical model of the groundwater basin and prediction of the periodic compensation water system for recharging the cooling lakes of the Kalinin Nuclear Power Plant.

Analysis of multi-well pumpingtest under atmosphere pressure and anisochronous schedule of pumping rate

Interpretation problems of long-term anisochronous multi-well pumping test under oscillating atmosphere pressure is analyzed. The barometric efficiency and corrections of measured drawdowns are calculated to Udomlya groundwater basin, evaluation of space and temporal moving of depression cone is investigated. Obtained hydraulic parameters is used for numerical model of groundwater basin and forecasting of periodical compensation wells pumping for recharge lake-coolers of Kalininskaya Nuclear Power Plant.

Numerical simulation and evaluation of groundwater resources in a fractured chalk aquifer: a case study in Zinder well field, Niger

Groundwater is often a unique water source for agriculture, industry and domestic use for local inhabitants in semi-arid African continent owing to shortage of surface water and rainfall. It is of significance to quantify and assess the groundwater resources for local sustainable development in order to correctly evaluate groundwater resources of Zinder well field with fractured media in Zinder, Niger. A conceptual model of hydrogeology was set up by a geological and hydrogeological survey. For simulating the real conditions, a large multi-well pumping test with designed pumping rate was conducted. In addition, a two-dimensional finite-element transient flow model was developed to simulate groundwater flow at the site. Results show that generally good agreements have been found between the simulated and observed hydrogeology heads for the test. The hydraulic parameters were obtained from the pumping test. A 11-year prediction of groundwater resources has been made under three exploitation schemes, respectively, and it indicates that the well field can offer 7,000 m3/day when the aquifer remains confined. An optimal scheme of exploitation is provided.

A case history of field pumping tests in a deep gravel formation in the Taipei Basin, Taiwan

33 large-diameter wells embedded in 2-m thick, 63-m deep diaphragm walls were constructed to reduce both the uplift pressures and the groundwater inflow during the excavations. As the actual thickness of the pumped aquifer is unknown, the installed wells are regarded as partial penetration wells. Single-well and multi-well pumping tests were conducted in the deep gravel formation of Taipei Basin to derive the hydraulic parameters and to investigate the drawdown characteristics at both the construction and remote sites. However, the tidal effect on the drawdown of both the pumping well and nearby observation wells was found significant. Additionally, wellbore storage, skin, and leakage need to be taken into account for deriving the hydraulic parameters. Hence, a method to remove these five factors influencing the drawdown curve is developed, which takes advantage from the late-time characteristics of drawdown data and the early-time behavior of drawdown. Some currently available semi-log graphic techniques are therefore proven applicable for parameter determination. Validity of the proposed method is verified by the good agreement between the calculated and the measured drawdown of both the pumping well and observation well.

What can be learned from sequential multi-well pumping tests in fracture-karst media? A case study in Zhangji, China

A fracture-karst aquifer is a karst aquifer with a fractured rock matrix, and its parameters are difficult to determine. Two sequential pumping tests in a fracture-karst aquifer system at the Zhangji well field of China are considered, one carried out before (in 2000) and one after (in 2005) the operation of a pumping station in the well field (2003–2005). The sequential tests serve multiple purposes. First, they provide a cross check of the parameters obtained. Second, they can be used to assess the effect of long-term groundwater exploitation of the aquifer. A three-dimensional finite-element transient flow model has been developed to simulate groundwater flow at the site. Generally good agreement has been found between the simulated and observed hydraulic heads for both tests. The hydraulic parameters obtained from the 2005 test are generally consistent with their counterparts from the 2000 test. However, a small but steady increase of hydraulic conductivities from 2000 to 2005 at the site has been observed. A 10-year prediction of groundwater resources has been made and indicates that the well field can accommodate the proposed 8.0 × 104 m3/day exploitation rate under relative drought conditions without causing a steady decline of groundwater levels.

INVERSE ANALYSIS OF ESTIMATING DISTRIBUTION OF HYDRAULIC CONDUCTIVITY AND RADIUS OF INFLUENCE USING FFT AND MULTI-WELL PUMPING TEST

This study aimed at determining the distribution of hydraulic conductivity and radius of influence from the results of multi-well pumping test and natural distribution of piezometric head in a non-uniform phreatic aquifer. The inverse analysis was performed by using the Fast Fourier Transform (FFT) and the constrained simplex method. These results showed that the method presented here could estimate mean value of hydraulic conductivity and the radius of influence more accurately than the conventional method using an analytical model of aquifer flow. And the distribution of hydraulic conductivity were well reproduced except the case of that the heterogeneity of hydraulic conductivity was not reflected in the distribution of drawdown and piezopmetric head.

Site Characterization in Densely Fractured Dolomite: Comparison of Methods

One of the challenges in characterizing fractured-rock aquifers is determining whether the equivalent porous medium approximation is valid at the problem scale. Detailed hydrogeologic characterization completed at a small study site in a densely fractured dolomite has yielded an extensive data set that was used to evaluate the utility of the continuum and discrete-fracture approaches to aquifer characterization. There are two near-vertical sets of fractures at the site; near-horizontal bedding-plane partings constitute a third fracture set. Eighteen boreholes, including five coreholes, were drilled to a depth of approximately 10.6 m. Borehole geophysical logs revealed several laterally extensive horizontal fractures and dissolution zones. Flowmeter and short-interval packer testing identified which of these features were hydraulically important. A monitoring system, consisting of short-interval piezometers and multilevel samplers, was designed to monitor four horizontal fractures and two dissolution zones. The resulting network consisted of >70 sampling points and allowed detailed monitoring of head distributions in three dimensions. Comparison of distributions of hydraulic head and hydraulic conductivity determined by these two approaches suggests that even in a densely fractured-carbonate aquifer, a characterization approach using traditional long-interval monitoring wells is inadequate to characterize ground water movement for the purposes of regulatory monitoring or site remediation. In addition, traditional multiwell pumping tests yield an average or bulk hydraulic conductivity that is not adequate for predicting rapid ground water travel times through the fracture network, and the pumping test response does not appear to be an adequate tool for assessing whether the porous medium approximation is valid.

Groundwater resources evaluation case study via discrete fracture flow modeling

The Arizona Department of Transportation (ADOT) is preparing to upgrade State Route 260 between Payson and Heber. It is estimated that a total of about one million cubic meters of water will be required for embankment construction during a period of about 84 months to upgrade the first 33.8 km of the highway. ADOT is investigating various sources of construction water for use in the highway improvement project, including groundwater resources along the highway corridor. A region known as the RV site, underlain by fractured granite, is located 12.9 km east of Payson. The site includes three springs, a creek and several wells. Several boreholes and observation wells were made to a maximum depth of 157 m to obtain fracture data and to conduct pumping tests with monitoring. Fracture data recorded by acoustic televiewer logs were used to build a fracture network model for the rock mass. Results of a 24-hour and a 7-day pumping tests were used to calibrate hydraulic parameters of a finite element discrete fracture fluid flow model considering the region as a heterogeneous, anisotropic, fractured medium. A 38-day multi-well pumping test was used to validate the calibrated numerical model. The calibrated model showed the capability to provide reasonably accurate predictions for new pumping tests conducted in the same well field. The validated model was then used to simulate pumping exceeding a 7 year period under different scenarios incorporating different sets of boundary conditions and different pumping rates at multi-wells, with and without recharge, to evaluate the yield of the aquifer and to assess the effect of long-term pumping on the environment. The results indicated that (a) the combined yield of the wells in the RV site is sufficient to meet the water demand for the ADOT highway project and (b) the water levels in the well field would decline between 3.0 and 7.6 m after one year of pumping and by 12.2 to over 30.5 m during the life of the project.

An evaluation of Jacob's Method for the interpretation of pumping tests in heterogeneous formations

Most pumping tests are interpreted using the classical Theis assumption of large‐scale homogeneity with various corrections to account for early time behavior of drawdown curves. When drawdowns are plotted versus log time, late time data often delineate a straight line, which is consistent with Jacob's approximation of Theis' solution but may seem surprising in view of the heterogeneity of natural media. The aim of our work is to show that Jacob's method leads to a good approximation of the effective transmissivity of heterogeneous media when constrained to late time data. A review of several multiwell pumping tests demonstrates that when drawdown curves from each observation well are interpreted separately, they produce very similar transmissivity T estimates. However, the corresponding estimates for storativity span a broad range. This behavior is verified numerically for several models of formation heterogeneity. A very significant finding of the numerical investigation is that T values estimated using simulated drawdown from individual observation wells are all very close to the effective T value for parallel flow. This was observed even in nonmultiGaussian T fields, where high T zones are well connected and where the effective T is larger than the geometric average of point values. This implies that Jacob's method can be used for estimating effective T values in many, if not most, formations.

Cardiff Bay Barrage: investigating groundwater control in a tidal aquifer

Abstract The Cardiff Bay Barrage Act requires any impact caused by groundwater rise as a consequence of the construction of the Barrage to be remedied. A possible strategy is to control groundwater levels, obviating any rise. Such control would require groundwater abstraction adjacent to rivers which are presently strongly tidal. This strong tidal fluctuation makes difficult the measurement of parameters needed for the design of the scheme. Two multi-well pumping tests were performed during feasibility investigations. One of these is described, together with two different approaches to interpreting the strongly tidally affected results--a correlation method and a spectral analysis method. Similar results are obtained from both methods, which are compatible with the other results, although both methods are found to have limitations. The results are then used to constrain analytic and numerical models of the interaction with the rivers, and to assess the feasibility of future groundwater control.