Capacity Of Aquifers Research Articles

Protection of Caprock Integrity for Large-Scale CO2 Storage on the Norwegian Continental Shelf

Large-scale CO2 storage requires advanced understanding of the geomechanical response of the caprock subject to pressure build- up in the reservoir. CO2 injection into basin systems will need to approach rates of 100 Mt/y in order to achieve significant reduction in worldwide emissions and realize the large capacity of saline aquifers. High pressure build-up is expected, which may activate existing fractures and faults in the seal and create leakage pathways for the CO2 plume. New fractures may also evolve at higher pressures. To avoid creating leakage pathways for the CO2 plume, the pressure must be kept under an upper bound that is determined by the caprock weakest point or initial stress. To date, there has been great uncertainty in critical knowledge needed for planning and execution of safe large-scale CO2 storage projects. Within the PROTECT project, we advance methods and reduce uncertainty regarding the mechanical response. The research study focuses on three subareas: data collection, experimental studies and computational tasks. The studies are performed at small scale (scale of individual cracks, cm to m) and at large scale (reservoir or basin scale, 10 m to km). Data are synthesized, and a benchmark study of large-scale geomechanical simulation is performed. The Utsira Formation on the Norwegian continental shelf has been used as a common case study for integration and benchmarking activities. Finally, recommendations are made for future research based on knowledge gained in this study.

Stratification of reactivity determines nitrate removal in groundwater

Biogeochemical reactions occur unevenly in space and time, but this heterogeneity is often simplified as a linear average due to sparse data, especially in subsurface environments where access is limited. For example, little is known about the spatial variability of groundwater denitrification, an important process in removing nitrate originating from agriculture and land use conversion. Information about the rate, arrangement, and extent of denitrification is needed to determine sustainable limits of human activity and to predict recovery time frames. Here, we developed and validated a method for inferring the spatial organization of sequential biogeochemical reactions in an aquifer in France. We applied it to five other aquifers in different geological settings located in the United States and compared results among 44 locations across the six aquifers to assess the generality of reactivity trends. Of the sampling locations, 79% showed pronounced increases of reactivity with depth. This suggests that previous estimates of denitrification have underestimated the capacity of deep aquifers to remove nitrate, while overestimating nitrate removal in shallow flow paths. Oxygen and nitrate reduction likely increases with depth because there is relatively little organic carbon in agricultural soils and because excess nitrate input has depleted solid phase electron donors near the surface. Our findings explain the long-standing conundrum of why apparent reaction rates of oxygen in aquifers are typically smaller than those of nitrate, which is energetically less favorable. This stratified reactivity framework is promising for mapping vertical reactivity trends in aquifers, generating new understanding of subsurface ecosystems and their capacity to remove contaminants.

Detecting dominant changes in irregularly sampled multivariate water quality data sets

Abstract. Time series of groundwater and stream water quality often exhibit substantial temporal and spatial variability, whereas typical existing monitoring data sets, e.g. from environmental agencies, are usually characterized by relatively low sampling frequency and irregular sampling in space and/or time. This complicates the differentiation between anthropogenic influence and natural variability as well as the detection of changes in water quality which indicate changes in single drivers. We suggest the new term “dominant changes” for changes in multivariate water quality data which concern (1) multiple variables, (2) multiple sites and (3) long-term patterns and present an exploratory framework for the detection of such dominant changes in data sets with irregular sampling in space and time. Firstly, a non-linear dimension-reduction technique was used to summarize the dominant spatiotemporal dynamics in the multivariate water quality data set in a few components. Those were used to derive hypotheses on the dominant drivers influencing water quality. Secondly, different sampling sites were compared with respect to median component values. Thirdly, time series of the components at single sites were analysed for long-term patterns. We tested the approach with a joint stream water and groundwater data set quality consisting of 1572 samples, each comprising sixteen variables, sampled with a spatially and temporally irregular sampling scheme at 29 sites in northeast Germany from 1998 to 2009. The first four components were interpreted as (1) an agriculturally induced enhancement of the natural background level of solute concentration, (2) a redox sequence from reducing conditions in deep groundwater to post-oxic conditions in shallow groundwater and oxic conditions in stream water, (3) a mixing ratio of deep and shallow groundwater to the streamflow and (4) sporadic events of slurry application in the agricultural practice. Dominant changes were observed for the first two components. The changing intensity of the first component was interpreted as response to the temporal variability of the thickness of the unsaturated zone. A steady increase in the second component at most stream water sites pointed towards progressing depletion of the denitrification capacity of the deep aquifer.

Groundwater capacity of a flysch-type aquifer feeding springs in the Outer Eastern Carpathians (Poland)

Abstract The aim of the study is to assess the capacity of the flysch aquifer feeding springs in the Outer Eastern Carpathians using spring recession curves. The four selected springs are located in an area generally believed to be poor in groundwater. However, the selected springs were characterized by remarkably high average discharge of 3.2–9.6 L s−1. Recession coefficients were estimated which enabled an aquifer capacity and groundwater residence time assessment. Despite similarities in elevation, precipitation, and lithology in the study area, a substantial variation in the recession coefficients and aquifer parameters was found. The average aquifer capacity of groundwater subsystems strongly varied in the small study area (4.9–49 m3 × 103). The mean groundwater residence time varied from 11 days to 50 days depending on the volume of groundwater drained by the springs. Differences in discharge, recession coefficients, groundwater capacity, and residence time were related to recharge areas of different size. Simple relationships between the topographic catchment areas of springs and their hydrologic parameters can become altered by local structural features: faults and fissures. The study demonstrates that tectonically produced structures may facilitate a larger supply of groundwater and the occurrence of high-discharge springs in a given area.

Effects of Na+, K+, Ca2+, and Mg2+ cations on CO2–brine interfacial tension under offshore storage conditions

AbstractThe laboratory determination of CO2‐brine interfacial tension is very important for estimating the storage capacity of saline aquifers during the CO2 sequestration process. In this paper, we measured CO2 and the brine interfacial tension using the pendant‐drop method at a temperature of 285–300 K and pressure of 3–9 MPa. The brine was composed of Na+, K+, Ca2+, and Mg2+ cations with different molalities. The experimental results indicate that interfacial tension increased with temperature and salinity but decreased with pressure until it reached a plateau. At the same temperature and pressure, the plateau value increased with increasing brine salinity for all types of brines used in this work. Moreover, the plateau exists whenever the CO2 is liquid. The interfacial tension between CO2 and brine with bivalent cations is larger than that between CO2 and monovalent brines. Finally, we established an empirical equation based on the relationship between interfacial tension and temperature, pressure, and salt molality grounded on experimental data, which allows the evaluation of CO2–brine interfacial tension values with a mean deviation of ±4 mN·m−1. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.

Assessing the Protective Capacity of Aquifers Using Very-Low-Frequency Electromagnetic Survey

The protective capacity of aquifers is a prerequisite for groundwater quality in areas prone to contamination from the ground surface. Aquifers without protective layers are more susceptible to contaminations from point and non-point sources. The protective capacity of an aquifer significantly correlates with the thickness of clay and organic materials that mantled it. To assess aquifer protective capacity, electrical conductivity property of saturated clay was determined from filtered imaginary and real components of Very Low-Frequency Electromagnetic (VLF-EM). The filtered real components against distance and current density pseudo-section produced from real components were concomitantly used for interpretation. Clays capping aquifers were delineated from those without capping from low and high values of filtered imaginary and real components and current density pseudo-section. The distribution of clay laterally across the area indicates that aquifers are poorly protected and susceptible to contaminations from a point and non-point sources. The apparent agreement between inferred geology from VLF-EM interpretation, borehole data and resistivity data underscores the efficacy of VLF-EM as an important tool that can be used or combined with other geophysical methods and borehole information/data for assessment of the protective capacity of the aquifer.

Groundwater Modeling in Agricultural Watershed under Different Recharge and Discharge Scenarios for Quaternary Aquifer Eastern Nile Delta, Egypt

Different scenarios of recharge and discharge were assessed for sustainable management of groundwater in Quaternary aquifer east of Nile Delta. MODFLOW was utilized to investigate the effect of land use change and damming construction in the upstream of the Nile River on the current and short-term groundwater management strategies. The interpretive transient simulation was performed between 2004 and 2016 after steady-state calibration in 2004, and transient state from 2004 to 2013 with different irrigation recharges associated with land use change in this period. Sensitivity analysis was performed for hydraulic conductivities, recharge, and conductance parameters. The predictive transient simulation was run till 2023 under three scenarios of increasing pumping rates by 15, 30, and 50% for agriculture expansion and specified head reduction of Port Said Canal by 0.2, 0.4, and 0.6 m associated with the reduction of Nile water levels after Grand Ethiopian Residence Dam, GERD operation in 2017. Results from the in- and out-flow budgets showed that groundwater aquifer is stable at the current rate of pumping till 2023. Groundwater heads decreased by 0.2 and 0.42 m in the southern section, and a slight increase in the northern part was noticed for the first and second scenarios, respectively. When additional pumping stress is applied (50% increase), groundwater head dropped by 0.66 m, and the storage is no longer able to maintain the aquifer capacity after 2020 (worst-case scenario).

Models and tools for the assessment of thermal-short circuit in open-loop geothermal systems

The use of Ground Water Heat Pumps (GWHPs) for the heating and cooling of buildings is getting more and more popular due to the sustainability and economic convenience of this technology. One of the most critical design issues of these systems is the hydraulic and thermal short-circuit between the abstraction and the injection well(s), which impairs the energy efficiency of the heat pump and may even lead to the plant failure. A number of mathematical tools has already been developed to assess thermal short-circuit in well doublets with a prescribed injection temperature (thermal feedback), but this assumption is rarely met in the reality. In order to assess thermal short-circuit for a prescribed temperature difference between injection and abstraction (thermal recycling), a numerical code called TRS (Thermal Recycling Simulator) was therefore developed and is presentedin this paper. The code is based on the potential flow theory and it has been validated against coupled flow and heat transport simulations with FEFLOW. TRS is freely available at http://goo.gl/AdjCp6 and works in MATLAB environment. An empirical formula, which describesthe time evolution of the extracted water temperature, has also been derived from a series of simulations with TRS. The developed mathematical tools can be used to assess the long-term sustainability of a certain plant setup, to perform sensitivity analyses and for largescale assessments of the thermal exchange capacity of aquifers.

Produced water re-injection in a non-fresh water aquifer with geochemical reaction, hydrodynamic molecular dispersion and adsorption kinetics controlling: model development and numerical simulation

An improved produced water reinjection (PWRI) model that incorporates filtration, geochemical reaction, molecular transport, and mass adsorption kinetics was developed to predict cake deposition and injectivity performance in hydrocarbon aquifers in Nigeria oil fields. Thus, the improved PWRI model considered contributions of geochemical reaction, adsorption kinetics, and hydrodynamic molecular dispersion mechanism to alter the injectivity and deposition of suspended solids on aquifer wall resulting in cake formation in pores during PWRI and transport of active constituents in hydrocarbon reservoirs. The injectivity decline and cake deposition for specific case studies of hydrocarbon aquifers in Nigeria oil fields were characterized with respect to its well geometry, lithology, and calibrations data and simulated in COMSOL multiphysics software environment. The PWRI model was validated by comparisons to assessments of previous field studies based on data and results supplied by operator and regulator. The results of simulation showed that PWRI performance was altered because of temporal variations and declinations of permeability, injectivity, and cake precipitation, which were observed to be dependent on active adsorption and geochemical reaction kinetics coupled with filtration scheme and molecular dispersion. From the observed results and findings, transition time tr to cake nucleation and growth were dependent on aquifer constituents, well capacity, filtration coefficients, particle-to-grain size ratio, water quality, and more importantly, particle-to-grain adsorption kinetics. Thus, the results showed that injectivity decline and permeability damage were direct contributions of geochemical reaction, hydrodynamic molecular diffusion, and adsorption kinetics to the internal filtration mechanism, which are largely dependent on the initial conditions of concentration of active constituents of produced water and aquifer capacity.

Modeling rock-fluid interactions due to CO2 injection into sandstone and carbonate aquifer considering salt precipitation and chemical reactions

Carbon dioxide is a greenhouse gas that has the most effect on the phenomenon of global warming. Saline aquifers have higher potential compared to other storage options to store carbon dioxide. Sandstone and carbonate aquifers have good reservoir characteristics and can be appropriate choices for CO2 storage. The modeling of the process has been performed combining salt precipitation, solubility, region specification and pressure drop models to study the effect of CO2 injection on gas saturation and pressure distribution profile, skin factor over time, the amount of salt precipitation, porosity and permeability. Sensitivity analysis has been done for temperature, pressure, permeability, porosity, salinity, critical gas saturation and CO2 injection rate. In order to study chemical reactions, long time simulation of rock-fluid interaction in carbonate and sandstone aquifer is also performed.The permeability reduction is in the range of 0.69–0.86 in all cases of salt precipitation simulation which is consistent with experimental results. The proposed salt precipitation model with an average relative deviation of about 5% for rock-fluid interaction parameters is able to predict the aquifer properties accurately during CO2 gas injection. The advantage of the model presented in this study compared to Zeidouni's model (2009) is that the proposed model predicts the pressure distribution after injection and estimates mole fraction of components in equilibrium with higher accuracy. The results of this study are shown that CO2 storage needs an aquifer with lower temperature, higher pressure and lower salinity compared to other options as the solubility trapping of carbon dioxide increases in this case. Permeability change does not influence on determining equilibrium regions and the only effect of the permeability is on the injectivity. Simulation of mineral reactions shows that chemical equilibrium is established after long time (more than 100 years) in sandstone aquifer and it is established in less than one day in carbonate aquifer. It should be noted that mineral trapping capacity of carbonate aquifer is less than sandstone aquifer in the CO2 storage process.

Evaluation of local groundwater vulnerability based on DRASTIC index method in Lahore, Pakistan

Groundwater vulnerability assessment shows an extreme sensitivity to in situ anthropogenic pollutants. A dichotomous assessment of geological and hydrological (inter alia) characteristics makes it possible to determine the vulnerability of an aquifer. The natural carrying capacity of aquifer can be severely compromised by human activities. The physical structure and material composition of aquifers shows resistance to contaminants transport from surface to water-table. Currently, numerous methods have been posited evaluating aquifer's vulnerability. Similarly the DRASTIC model utilizes computer algorithms and hydro-geological data within a Geographical Information System (GIS) environment to compute aquifer vulnerability.The degree of vulnerability for each parameter can be evaluated by computing sensitivity analysis of DRASTIC index using GIS, showing the contribution of each parameter to vulnerability sensitivity. The GIS was used to developed map which showed high risk area of 28.8% and moderately vulnerable areas of 46.3% while areas of no risk were 10.4%. Central regions within the study area showed low vulnerability due to dense human settlement and low water level. However, pasture type lands and agricultural areas recorded high risk.Lahore's environmental and socio-economic development is dependent on policy makers and planner's ability to use information effectively for decision making. The resultant groundwater vulnerability map provides a basis for this aimed at protecting the aquifer from pollutants. Additionally, land use and development activities can be informed by mapping variables, showing that industrial and agriculture areas are highly vulnerable as compare to settlement areas.

Analysis of Groundwater Advance Decline in Surakarta City

This research was intended to know the cause of a drawdown of artesian groundwater surface and analyze on exploiting its groundwater in Surakarta. The total amount of groundwater exploitation in Surakarta will be 69,206.4 m3 if it is compared the groundwater runoff capacity of unconfined aquifer as with 8,860.9 m3 a day and confined aquifer as 42,447.3 m3 a day. Thus, the total amount of groundwater runoff in Surakarta is 51,308.2 m3 a day. Groundwater exploitation has exceeded the capacity of groundwater runoff as 17,898.2 m3, so the reservoir of groundwater is going to reduce continually. Groundwater exploitation in the loation of the researh has caused a piezometric drawdown. In 1990, its piezometric was negative, it means that the position of the piezometric was under the surface of land, while in 1990 artesian well indicated that its piezometric was almost nearly positive. Thus, the piezometric drawdown average 9.4 m3. In the center of the ity, it happened the cone of depression at piezometric contour in 1990, so a piezometric drawdown that resulted from groundwater exploitation exceeding the runoff of groundwater was proved. As a result of groundwater exploitation excessively, it resulted in the inequilibrium of groundwater. This depession has been extending continually as a result of adding wells, so it result in a groundwater drawdown permanently, as happened in the location of the research.

Applying fractional flow theory to evaluate CO2 storage capacity of an aquifer

Abstract In this paper, an application of fractional flow theory is used to evaluate CO 2 storage capacity of an aquifer because of two trapping mechanisms: capillary snap-off and gas dissolution. The capillary snap-off and CO 2 dissolution into the resident aqueous phase are two major trapping mechanisms of the CO 2 sequestration in geological formations over intermediate time-scale. In practice, numerical simulations are used to assess the CO 2 storage capacity of a geological formation and evaluate various trapping mechanisms; however, the simulations are complex and time-consuming and they require detailed inputs. Whereas, the presented method requires limited inputs and provides fast results in agreement with the simulation that makes it suitable tool to compare and screen the CO 2 storage potential of various formations. The notion of optimal solvent-water-slug size is adopted as the ultimate CO 2 storage capacity for a given permeable medium. A combined graphical solution of multiple geochemical front propagation and fractional flow theory is used to determine the CO 2 storage capacity of one-dimensional (1D) models; i.e. the largest slug of injected CO 2 that is trapped because of the capillary trapping and the CO 2 dissolution. Injecting larger amount of CO 2 than the optimum slug size causes the CO 2 breakthrough (over capacity) while smaller slugs leaves the aquifer unfilled (under-capacity). We use numerical simulation to validate the accuracy of the predicted optimal slug size. Next, we incorporate gravity override as the governing two-dimensional (2D) phenomenon affecting the storage capacity. The impact of 2D effects is applied via a multiplying factor that reduces the ultimate storage capacity and depends on the reservoir aspect ratio and buoyancy number. In practice, the proposed method provides an efficient screening method to assess the CO 2 storage capacity of aquifers and significantly reduces the simulation costs while providing an interesting insight.

Groundwater in hard rocks of Benin: Regional storage and buffer capacity in the face of change

Groundwater plays a major role in supplying domestic water to millions of people in Africa. In the future, the ability to increase reliable water supplies for domestic and possibly irrigation purposes will depend on groundwater development. Groundwater storage is a key property because it controls the buffering behavior of the aquifer as it is subjected to time-varying conditions such as increased pumping or land-use change. However, quantitative knowledge of groundwater storage in Africa is very limited. This lack of knowledge is a major concern in hard rocks, which cover about 40% of the surface area of Africa. This paper presents a unique quantitative assessment of groundwater storage in different types of hard rocks and a first estimate of the capacity of hard rock aquifers to buffer changes in climatic and anthropogenic conditions. Our study area in Benin (West Africa) is composed of various grades of metamorphic rocks. We used the latest developments in the application of the magnetic resonance geophysical method to confront the methodological difficulty of quantifying groundwater storage. We successfully conducted 38 magnetic-resonance measurements in eight (8) different geological units; each measurement was quantitatively interpreted in terms of groundwater storage. We determined the groundwater storage of our study area to be 440 mm ± 70 mm (equivalent water thickness). To assess the buffer capacity of aquifers, we compared groundwater storage to groundwater discharge. Groundwater discharge is the sum of natural discharge plus human abstraction. We estimated natural discharge (i.e. deep drainage plus evapotranspiration) from water table fluctuations monitored in six (6) piezometers. Human abstraction was calculated based on the number of operating boreholes and their average daily abstraction. We found that human abstraction (0.34 mm/year ± 0.07 mm) is far less than natural discharge (108 mm/year ± 58 mm). We conclude that increased abstraction due to population growth will probably have a smaller impact on storage than observed land-use change, which may lead to a change in the evapotranspiration rate. We calculated buffer capacity as the ratio of current storage to total discharge, and obtained a result of 6 years ± 47 months. This buffer capacity confirms groundwater’s ability to buffer changes. Finally, our study is intended to promote a more quantitative approach to assessing groundwater resources in Africa and to support our ability to adapt to current and future changes.

Economic Assessment of Opportunities for Managed Aquifer Recharge Techniques in Spain Using an Advanced Geographic Information System (GIS)

This paper investigates the economic aspects of Managed Aquifer Recharge (MAR) techniques considered in the DINA-MAR (Depth Investigation of New Areas for Managed Aquifer Recharge in Spain) project. This project firstly identified the areas with potential for MAR for the whole of the Iberian Peninsula and Balearic Islands of Spain using characteristics derived from 23 GIS layers of physiographic features, spanning geology, topography, land use, water sources and including existing MAR sites. The work involved evaluations for 24 different types (techniques) of MAR projects, over this whole area accounting for the physiographic features that favor each technique. The scores for each feature for each type of technique were set based on practical considerations and scores were accumulated for each location. A weighting was assigned to each feature by “training” the integrated score for each technique across all the features with the existing MAR sites overlay, so that opportunities for each technique could be more reliably predicted. It was found that there were opportunities for MAR for 16% of the area evaluated and that the additional storage capacity of aquifers in these areas was more than 2.5 times the total storage capacity of all existing surface water dams in Spain. The second part of this work, which is considered internationally unique, was to use this GIS methodology to evaluate the economics of the various MAR techniques across the region. This involved determining an economic index related to key physiographic features and applying this as an additional GIS overlay. Again this was trained by use of economic information for each of the existing MAR sites for which economic data and supply or storage volume were available. Two simpler methods were also used for comparison. Finally, the mean costs of MAR facilities and construction projects were determined based on the origin of the water. Maps of potential sites for Managed Aquifer Recharge (or “MAR zones”) in the Iberian Peninsula and Balearic Islands of Spain and the results of the previous economic studies developed at the beginning of the project were used as the foundation for the economic analysis. Based on these data, a new specific mapping of the total expected costs for all “MAR zones” (€/m3) was proposed based on the techniques that were considered most appropriate for each Spanish study case. Capital costs ranged from Euro 0.08–0.58 per m3/year. Overall, this study investigates the opportunity and economic feasibility of implementing new MAR projects and provides support to decision makers in Spain. The novel mapping provides valuable guidance for the future development of Managed Aquifer Recharge projects for water managers and practitioners.

Investigation of Self-Similar Interface Evolution in Carbon Dioxide Sequestration in Saline Aquifers

In this work, we investigate numerically the injection of supercritical carbon dioxide into a deep saline reservoir from a single well. We analyze systematically the sharp-interface evolution in different flow regimes. The flow regimes can be parameterized by two dimensionless numbers, the gravity number, $$\Gamma $$ and the mobility ratio, $$\lambda $$ . Numerical simulations are performed using the volume of fluid method, and the results are compared with the solutions of the self-similarity equation established in previous works, which describes the evolution of the sharp interface. We show that these theoretical solutions are in very good agreement with the results from the numerical simulations presented over the different flow regimes, thereby showing that the theoretical and simulation models predict consistently the spreading and migration of the created $$\hbox {CO}_{2}$$ plume under complex flow behavior in porous media. Furthermore, we compare the numerical results with known analytic approximations in order to assess their applicability and accuracy over the investigated parametric space. The present study indicates that the self-similar solutions parameterized by the dimensionless numbers $$\lambda , \Gamma $$ are significant for examining effectively injection scenarios, as these numbers control the shape of the interface and migration of the $$\hbox {CO}_{2}$$ plume. This finding is essential in assessing the storage capacity of saline aquifers.

Projected impacts of climate change on farmers' extraction of groundwater from crystalline aquifers in South India

Local groundwater levels in South India are falling alarmingly. In the semi-arid crystalline Deccan plateau area, agricultural production relies on groundwater resources. Downscaled Global Climate Model (GCM) data are used to force a spatially distributed agro-hydrological model in order to evaluate Climate Change (CC) effects on local groundwater extraction (GWE). The slight increase of precipitation may alleviate current groundwater depletion on average, despite the increased evaporation due to warming. Nevertheless, projected climatic extremes create worse GWE shortages than for present climate. Local conditions may lead to opposing impacts on GWE, from increases to decreases (+/−20 mm/year), for a given spatially homogeneous CC forcing. Areas vulnerable to CC in terms of irrigation apportionment are thus identified. Our results emphasize the importance of accounting for local characteristics (water harvesting systems and maximal aquifer capacity versus GWE) in developing measures to cope with CC impacts in the South Indian region.

Development of Rainfall Recharge Model for Natural Groundwater Recharge Estimation in Godagari Upazila of Rajshahi District, Bangladesh

Estimation and forecast of groundwater recharge and capacity of aquifer are essential issues in effective groundwater resource management in Bangladesh. Godagari Upazilla is located in High Barind Tract situated in the northwestern part of Bangladesh. A typical dry climate with comparatively high temperature prevails in this Barind area. It is particularly significant in regions with large demands for groundwater supplies to meet irrigation needs, where such resources are the key to economic growth. However, the rate of aquifer recharge is one of the most complicated factors to assess in the evaluation of groundwater resources. Assessment of recharge, by whatever method, is normally subject to large uncertainties and errors. In this paper, an attempt has been taken to develop a rainfall recharge model by non-linear regression technique to determine groundwater recharge using only annual rainfall data in Godagari Upazilla based upon groundwater balance study carried out for a number of years. It was also proven that the developed model provided an accurate estimation for similar projects

Using Pressure and Volumetric Approaches to Estimate CO2 Storage Capacity in Deep Saline Aquifers

Various approaches are used to evaluate the capacity of saline aquifers to store CO2, resulting in a wide range of capacity estimates for a given aquifer. The two approaches most used are the volumetric “open aquifer” and “closed aquifer” approaches. We present four full-scale aquifer cases, where CO2 storage capacity is evaluated both volumetrically (with “open” and/or “closed” approaches) and through flow modeling. These examples show that the “open aquifer” CO2 storage capacity estimation can strongly exceed the cumulative CO2 injection from the flow model, whereas the “closed aquifer” estimates are a closer approximation to the flow-model derived capacity. An analogy to oil recovery mechanisms is presented, where the primary oil recovery mechanism is compared to CO2 aquifer storage without producing formation water; and the secondary oil recovery mechanism (water flooding) is compared to CO2 aquifer storage performed simultaneously with extraction of water for pressure maintenance. This analogy supports the finding that the “closed aquifer” approach produces a better estimate of CO2 storage without water extraction, and highlights the need for any CO2 storage estimate to specify whether it is intended to represent CO2 storage capacity with or without water extraction

Effects of capillary pressure – fluid saturation – relative permeability relationships on predicting carbon dioxide migration during injection into saline aquifers

Abstract Mathematical modeling and numerical simulations on carbon dioxide plume migration in confined saline aquifers have become important approaches to evaluate storage capacity and efficiency for carbon dioxide sequestration and to predict potential risks of leakage during and after carbon dioxide injection into subsurface formations. The effects of the characteristic functions relating capillary pressures and relative permeabilities to fluid saturations are critical in predicting carbon dioxide plume migration in saline aquifers. In this paper, four well known models, i.e. Brooks-Corey-Burdine model (BCB), Brooks-Corey- Mualem model (BCM), Van Genuchten-Burdine model (VGB), and Van Genuchten-Mualem model (VGM), were incorporated with an immiscible displacement process model to simulate carbon dioxide injection into saline aquifers. Parametric analysis was conducted to identify the influences of parameters in the Brooks-Corey based model on the predictions of carbon dioxide plume migration in a confined saline aquifer. A comprehensive comparison was carried out to reveal the different performances of the models with respect to the evolutions and patterns of carbon dioxide plume in the confined saline aquifer. The simulation results indicate that the saturation distributions of carbon dioxide are drastically sensitive to the capillary entry pressure. However, the parameters and in the Brooks-Corey based model, which are related to pore size distribution and tortuosity ratio of a porous medium, respectively, have little effects on predicting carbon dioxide plume migration in the saline aquifer. Moreover, different models may cause extensive influences on the carbon dioxide distributions at the region that is close to the injection well and at the leading edges of carbon dioxide plume in the saline aquifer. Hence, the results indicate that for the evaluation of the storage capacity and efficiency of a saline aquifer to trap carbon dioxide, the storage capacity of the saline aquifer could be over- estimated by using the BCB model, whereas it could be underestimated by using the VGM model. On the other hand, for evaluations of potential leakage of carbon dioxide in saline aquifers, where the movement of the leading edge of carbon dioxide plume is monitored, the VGM model is a safe choice in simulations. These results have potentially significant implications for estimation of carbon dioxide storage capacity of saline aquifers and assessments on potential risks of leakage.