Leaky Wells Research Articles

Development and performance test of an expansive particle temporary plugging agent

Addressing the problems found in some wells in the carbonate reservoirs of Tahe and Shunbei blocks, such as wide natural fractures and large leakage, an efficient temporary plugging agent is developed to effectively seal up large fractures and leaky wells without affecting the flow path after acid fracturing. The temporary plugging agent is prepared by crosslinking an organic zirconium crosslinker with starch-grafted polyacrylamide. Among the materials, starch-grafted polyacrylamide shows good viscoelasticity, water absorption, expansion, and degradable properties; an organic zirconium crosslinker can improve the sealing effect. The temporary plugging agents produced from the two-boast have good performance in water absorption and expansion, temporary plugging pressure, and degradability. Experimental tests evaluated the developed expansive particle temporary plugging agent’s performance. According to the results, the particle size of the temporary plugging agent can expand 4 times larger; its final degradation under formation conditions reaches 99%. A larger plugging agent particle size and a higher concentration of the plugging agent can increase the plugging pressure. The plugging pressure can be as high as 15.5 MPa at a 5% concentration of the plugging agent with a particle size of 2 mm, which fully meets the needs of temporary plugging fracturing on site.

A framework to simulate the blowout of CO2 through wells in geologic carbon storage

It is important to evaluate the risks associated with CO2 leakage in large scale carbon capture and storage (CCS) projects. Leaky wells are considered a major concern for potential CO2 leakage in geologic carbon storage. The most rapid and spectacular mode of CO2 leakage is the blowout of a CO2 storage well. The Sheep Mountain CO2 blowout in March 1982 is an example of this type of catastrophe wherein several thousand tons of CO2 were released into the atmosphere every day. The blowout was stopped only in early April. In the current work we present a numerical framework to simulate blowouts of CO2 wells accounting for the supercritical-liquid–gas–solid phase transitions of CO2 during the process. It is an in-house finite volume method based code for CO2 transport in open wells, relying on a hybrid Span–Wagner equations of state. We present extensive verification and validation of the code against numerical and experimental data in the literature. When applied to well blowouts, our numerical method is able to identify the locations along the well where CO2 transitions between its different phases. Our simulations show that while the heat transfer between CO2 and the casing has a significant impact on the transient characteristics of the blowout, it does not affect the steady-state leakage rate significantly. We also find that the CO2 leakage rate increases as the total depth of the well increases, with an average leakage rate of 2.09×104 tons per day across all the well depths simulated ranging between 1 km and 3.5 km. Our simulations show that when the temperature and pressure at the well bottom are appreciably lower than the geothermal temperature and hydrostatic pressure at the given depth, CO2 is released as dry ice at the wellhead. The dry ice modeled here has a significant time-averaged mass fraction of 30% at quasi-steady state, and causes rapid fluctuations in the CO2 leakage rate.

A semi-analytical model for multi-well leakage in a depleted gas reservoir with irregular boundaries

Depleted gas reservoirs are potential sites for CO2 geo-sequestration (CGS). Improperly sealed wells may provide leakage pathways and increase the risk of environmental contamination. A fast and efficient method for injection performance monitoring and leakage risk assessment is essential for implementing CGS projects. This paper presents a new semi-analytical model for predicting the transient behavior of the injection pressure and leakage rate during CO2 injection. The proposed model considers the leakage through multiple abandoned wells and the effect of boundary irregularities on the injection performance. First, the CO2 seepage model for the depleted gas reservoir and the overlying aquifer is derived. Then, the boundaries are discretized into segments, given the boundary irregularities. Using the boundary element method (BEM), Laplace transform, and Duhamel’s principle, the mathematical model is solved, and the solutions are compared with those from numerical simulations for verification. Based on a case study of the Dongfang 1-1 gas field, the impacts of the parameters of the reservoir and leaky well on the injection performance and leakage rate are analyzed.The proposed model has a good fit with the results of the numerical simulations. The sensitivity analysis demonstrates that the cumulative leakage ratio increases linearly with the upper limit of injection pressure and reservoir permeability. The leakage risk induced by the leaky wells is relatively low in the reservoir with low permeability because of high seepage resistance and limited pressure propagation. However, the storage potential is restricted due to the poor injectability. The rate of CO2 inter-layer flow is determined by the leakage permeability of all of the abandoned wells, not just those with a high leakage permeability. Reservoirs with multiple abandoned wells and a large overlying aquifer are still at the risk of gas leakage even if the leakage permeability of the abandoned wells is low.

A multi-stage screening approach to evaluate risks from inter-aquifer leakage associated with gas well and water bore integrity failure

Integrity failure of wells in gas resource developments poses a potential risk to groundwater resource quality and quantity by enhancing the connectivity and fluid migration between a gas reservoir and overlying aquifers, which may support groundwater dependent ecosystems or be used as a water source. This study assessed the potential for impact on groundwater resources from flow pathways created by well integrity failure in decommissioned coal seam gas (CSG) wells, deep water bores or gas wells repurposed as water bores and legacy coal exploration drillholes using an example based on a proposed CSG development near Narrabri, Australia. The study only considered the flow of water. A multi-stage screening method for likelihood and consequence assessment was used, which included (i) a semi-quantitative risk prioritisation of potential pathways for inter-aquifer leakage and development of metrics for impact assessment, (ii) assessment of the consequences of each of these pathways through an analytical model, and (iii) numerical groundwater modelling of single and multiple leaky wells. All three approaches indicated that increases in inter-aquifer leakage, drawdown in upper aquifers are not likely to be significant for high flow leaky gas wells (effective well conductivity, Kw <10−1 m/d) based on conditions reported in previous studies and for the case study. It is theoretically possible that extremely high flow leaky wells (Kw >102 m/d) could have an impact where aquitard conductivity is 10−4 m/d or less, or well failure density is higher than 1 well per km2, however Kw values for compromised gas wells of >1 m/d have not been identified in previous studies. The most extreme case tested, open legacy coal exploration drillholes or petroleum bores repurposed into water bores across an aquitard, should it occur, has the potential to deplete or contaminate groundwater resources in connected aquifers, the magnitude of which will depend on aquifer and production zone transmissivity. However, current Australian regulations for petroleum exploration make this an extremely unlikely case. More effort is required to determine Kw and failure rates of gas wells, water bores and exploration drillholes in Australian conditions to better quantify the potential risks associated with leaking infrastructure.

Leakage From Coexisting Geologic Forcing and Injection‐Induced Pressurization: A Semi‐Analytical Solution for Multilayered Aquifers With Multiple Wells

AbstractAbnormal fluid pressures (above or below hydrostatic pressure) can develop and persist in sedimentary basins. The common occurrence of abnormal pressures may cause challenges for project permitting of geological carbon sequestration (GCS), particularly in reservoirs with pre‐injection overpressure. The leaky wells that may exist in some sedimentary basins can provide flow paths between deep brine aquifers and shallower freshwater aquifers. Pre‐injection relative overpressures can cause brine leakage through leaky wells even before any injection occurs. The tendency for flow through leaky wells is coupled with the process of pressure dissipation that occurs through aquitards. Specifically, with non‐zero permeability, aquitards can dissipate pressure over large areal extents and thereby reduce leakage rates through leaky wells. This study presents development of a semi‐analytical solution for hydraulic head and brine leakage in multilayered aquifer–aquitard systems with geologic pressure forcing. The geologic forcing that causes abnormal pressures in the multilayered system can coexist with any number of injection, extraction, and leaky wells that also affect fluid pressure. The semi‐analytical model is applied to explore how leakage through leaky wells varies as functions of pressurization rate, along with aquitard and leaky well properties in an overpressured multilayered system. The results show that although injection‐induced pressures can dissipate rapidly through suitably permeable aquitards, coexisting geologic forcing may create sustained rates of brine leakage into freshwater aquifers through leaky wells. In GCS, a very low‐permeability aquitard with high capillary entry pressure to free‐phase CO2 is desired to serve as the caprock to prevent leakage of CO2 from the storage reservoir. Nevertheless, the results from this study show that the brine leakage impact to shallow freshwater aquifers through leaky wells might substantially decrease with increasing aquitard permeability values, as long as small aquitard permeability and high capillary entry pressure serve to prevent CO2 leakage.

Enhanced Passive Stormwater Infiltration Improves Urban Melia Azedarach Functioning in Dry Season

Urban water management projects involving stormwater harvesting, detention, and infiltration are being increasingly combined with urban greening to support adaptation and resilience to the changing climate. A novel stormwater harvesting device, the TREENET Inlet, intercepts stormwater runoff from roads and soaks it into the soil through a leaky well to provide passive irrigation directly into street tree root zones. This study investigated the effects of stormwater harvesting through these inlet systems on the growth, water-use, leaf-level gas exchange and productivity of white cedar (Melia azedarach) street trees in a semi-arid climate in South Australia. The results indicated that mature trees with TREENET Inlets and leaky wells transpired 17% more water per unit of canopy area per day, on average for about a year, and 21% more during the dry season. White cedar saplings with stormwater harvesting grew 65% more in height and 60% more in diameter at breast height over a 3-year period than saplings without stormwater harvesting. This is consistent with observed 106% greater stomatal conductance and up to 169% greater photosynthesis rate in the dry season for saplings supported by harvested stormwater. This study shows that stormwater harvesting and infiltration by TREENET Inlets provides significant benefit to white cedar trees growing in a suburban street.

Stormwater runoff reduction benefits of distributed curbside infiltration devices in an urban catchment

Distributed infiltration systems can benefit downstream water bodies by reducing the runoff flowrate and volume discharges from the catchment. Investigating their runoff flowrate and volume reduction potential at the catchment scale will inform decision makers regarding their efficacy for managing catchment outflows. To this end, we conducted field investigations at the residential catchment scale for three years. The study monitored the catchment for one year before the installation of leaky well systems (preinstallation) and two years after installation (postinstallation). The hydrological model, calibrated to preinstallation catchment outflows, acted as a virtual control tool. Runoff flow outputs from the control model and two years of monitored runoff flow data from the postinstallation period were analysed using statistical methods. The statistical tests showed a significant 13% reduction in average flowrates in storms with a corresponding runoff flowrate of up to 50 L/s. The study further reported the ability of infiltration systems to reduce runoff volume in the catchment by 9%. This reduction was not significant, however, as per the results of the statistical analysis. We then fitted the generalized linear model (GLM) to the monitored and simulated runoff volume data. This enabled us to break down the effect of curbside infiltration systems on runoff volume according to corresponding peak flowrates during the storm. The results of the two-way ANOVA performed to detect significant differences in the regression slopes of the GLM indicated that curbside infiltration systems significantly reduced runoff volume for storms when the runoff flowrates remained below 100 L/s.

A Semi-Analytical Model for Injection Pressure and Co2 Leakage Calculation Considering Irregular Boundaries and Multiple Leaky Wells

A Semi-Analytical Model for Injection Pressure and Co2 Leakage Calculation Considering Irregular Boundaries and Multiple Leaky Wells

Characterizing the Stormwater Runoff Quality and Evaluating the Performance of Curbside Infiltration Systems to Improve Stormwater Quality of an Urban Catchment

The conveyance of stormwater has become a major concern for urban planners, considering its harmful effects for receiving water bodies, potentially disturbing their ecosystem. Therefore, it is important to characterize the quality of catchment outflows. This information can assist in planning for appropriate mitigation measures to reduce stormwater runoff discharge from the catchment. To achieve this aim, the article reports the field data from a typical urban catchment in Australia. The pollutant concentration from laboratory testing is then compared against national and international reported values. In addition, a stochastic catchment model was prepared using MUSIC. The study in particular reported on the techniques to model distributed curbside leaky wells with appropriate level of aggregation. The model informed regarding the efficacy of distributed curbside leaky well systems to improve the stormwater quality. The results indicated that catchment generated pollutant load, which is typical of Australian residential catchments. The use of distributed storages only marginally improves the quality of catchment outflows. It is because ability of distributed leaky wells depended on the intercepted runoff volume which is dependent on the hydrological storage volume of each device. Therefore, limited storage volume of current systems resulted in higher contributing area to storage ratio. This manifested in marginal intercepted volume, thereby only minimum reduction in pollutant transport from the catchment to outlet. Considering strong correlation between contributing impervious area and runoff pollutant generation, the study raised the concern that in lieu of following the policy of infill development, there can be potential increase in pollutant concentration in runoff outflows from Australian residential catchments. It is recommended to monitor stormwater quality from more residential catchments in their present conditions. This will assist in informed decision-making regarding adopting mitigations measures before considering developments.

Towards quantifying subsurface methane emissions from energy wells with integrity failure

The expansion of petroleum resource development has led to growing concern regarding greenhouse gas emissions from fugitive gas migration, which occurs at some wells due to well integrity failure. In this study, we quantify methane surface expression and emissions resulting from gas migration using a number of complementary techniques, and thereby evaluate surface expression processes as well as the strengths and limitations of the monitoring techniques. Methane emissions were found to be highly localized and variable over time. Injected gas reached the surface via preferential pathways through the soils and also along an installed groundwater monitoring well. Cumulative emissions were estimated from flux chamber measurements to be 3.8–6.5% of the injected gas; whereas eddy covariance (EC) data inferred approximately 26% of the injected gas was released to the atmosphere. Together these methods provide enhanced interpretation of surface expression at the site, advance our understanding on fugitive gas migration from integrity compromised energy wells and provide insights to improve monitoring and detection strategies with a view to reducing future greenhouse gas emissions. Moreover that, up to 75% of fugitive gas released at the site remained in the subsurface, shows that capillary barriers will mitigate greenhouse gas emissions from leaky wells; however, may infer greater potential for impacts on groundwater resources, if present.

Fate of Fugitive Natural Gas in Heterogeneous Near‐Surface Sediments in a Region of Extensive Petroleum Resource Development

AbstractFugitive natural gas released in the subsurface from leaking oil and gas wells can affect groundwater quality and generate significant greenhouse gas emissions to the atmosphere. We released natural gas into a Western Canada Sedimentary Basin (WCSB) groundwater system located in an area of petroleum resource development. Through 55 depth‐discrete monitoring points installed up to 26 m deep, we tracked spatiotemporal evolution of dissolved gases over 760 days. Fugitive gas was diverted and mostly retained in the subsurface by capillary barriers, resulting in highly irregular distribution and dissolution of multicomponent gas constituents. Gas wetness changed significantly during migration, although stable‐carbon isotope ratios did not. We expect that where a surface diamict is present, typical of the WCSB, a significant portion of fugitive gas released from leaky wells will be retained in the subsurface, mitigating greenhouse gas emissions to the atmosphere but inferring greater risk on groundwater.

Changes in Deep Groundwater Flow Patterns Related to Oil and Gas Activities.

Large volumes of saline formation water are both produced from and injected into sedimentary basins as a by-product of oil and gas production. Despite this, the location of production and injection wells has not been studied in detail at the regional scale and the effects on deep groundwater flow patterns (i.e., below the base of groundwater protection) possibly driving fluid flow toward shallow aquifers remain uncertain. Even where injection and production volumes are equal at the basin scale, local changes in hydraulic head can occur due to the distribution of production and injection wells. In the Canadian portion of the Williston Basin, over 4.6 × 109 m3 of water has been co-produced with 5.4 × 108 m3 of oil, and over 5.5 × 109 m3 of water has been injected into the subsurface for salt water disposal or enhanced oil recovery. Despite approximately equal values of produced and injected fluids at the sedimentary basin scale over the history of development, cumulative fluid deficits and surpluses per unit area in excess of a few 100 mm are present at scales of a few 100 km2 . Fluid fluxes associated with oil and gas activities since 1950 likely exceed background groundwater fluxes in these areas. Modeled pressures capable of creating upward hydraulic gradients are predicted for the Midale Member and Mannville Group, two of the strata with the highest amounts of injection in the study area. This could lead to upward leakage of fluids if permeable pathways, such as leaky wells, are present.

Semi-Analytical Solution to Assess CO2 Leakage in the Subsurface through Abandoned Wells

Geological carbon storage is an effective method capable of reducing carbon dioxide (CO2) emissions at significant scales. Subsurface reservoirs with sealing caprocks can provide long-term containment for the injected fluid. Nevertheless, CO2 leakage is a major concern. The presence of abandoned wells penetrating the reservoir caprock may cause leakage flow-paths for CO2 to the overburden. Assessment of time-varying leaky wells is a need. In this paper, we propose a new semi-analytical approach based on pressure-transient analysis to model the behavior of CO2 leakage and corresponding pressure distribution within the storage site and the overburden. Current methods assume instantaneous leakage of CO2 occurring with injection, which is not realistic. In this work, we employ the superposition in time and space to solve the diffusivity equation in 2D radial flow to approximate the transient pressure in the reservoirs. Fluid and rock compressibilities are taken into consideration, which allow calculating the breakthrough time and the leakage rate of CO2 to the overburden accurately. We use numerical simulations to verify the proposed time-dependent semi-analytical solution. The results show good agreement in both pressure and leakage rates. Sensitivity analysis is then conducted to assess different CO2 leakage scenarios to the overburden. The developed semi-analytical solution provides a new simple and practical approach to assess the potential of CO2 leakage outside the storage site. This approach is an alternative to numerical methods when detailed simulations are not feasible. Furthermore, the proposed solution can also be used to verify numerical codes, which often exhibit numerical artifacts.

Evaluating probability of containment effectiveness at a GCS site using integrated assessment modeling approach with Bayesian decision network

AbstractImproved scientific and engineering understanding of the behavior of geologic CO2 storage together with established regulatory framework and incentive structures raise the prospects for accelerated, large‐scale deployment of this greenhouse gas emissions reduction approach. Incentive structures call for the establishment of appropriate verification and accounting approaches to support claims of the integrity of a geologic storage complex and to justify taking credit for long‐term storage. In this study, we present a framework for assessing the probability of containment effectiveness over the lifetime of a geologic carbon storage site (e.g., after 70 years of injection and postinjection site performance) using forward stochastic model realizations based on site characterization data and using a monitoring‐informed Bayesian network based on hypothetical detectability from surface seismic surveys over the site injection and post‐injection phases. The National Risk Assessment Partnership's open‐source Integrated Assessment Model (NRAP‐Open‐IAM) was utilized to develop an ensemble of 10,000 a priori stochastic forecasts of CO2 containment. Those simulations were used to train the Bayesian network model to estimate the prior probabilities of the CO2 leakage mass into overlying, monitorable aquifers considering the uncertainties in the reservoir properties, permeability of potentially leaky wells and the overlying aquifers. The conditional probabilities in the Bayesian network were either learned from the NRAP‐Open‐IAM simulations or derived from the predefined detection thresholds for the monitoring method. Observations obtained from monitoring, over time during the site operation phases were then used to generate updated posterior probabilities of containment (and any loss from containment) in the Bayesian network by propagating the prior probabilities through the conditional probabilities. We demonstrate how to construct and use the Bayesian network for verifying the long‐term storage complex effectiveness informed by monitoring based on the NRAP‐Open‐IAM simulations previously developed for the FutureGen 2.0 site. This approach may have relevance for stake holders to demonstrate secure geologic storage, provide a defensible, probabilistic approach to claim credit for geologic storage, and to estimate the likelihood that any fraction of the claimed credit may need to be refunded to the creditor based on available monitoring information. © 2021 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Benchmarking a reduced order finite element method for multiphase carbon sequestration models

Carbon sequestration in deep saline aquifers has been proposed for long-term storage of CO2 as an alternative to the release of CO2 into the atmosphere. In this article, we present a computationally efficient numerical model based on a sequentially coupled Finite Element Method (FEM) and Streamline Upwind Finite Element Method (SU-FEM)-Finite Difference Method (FDM). An adaptive timestep strategy is implemented which allows computationally efficient and stable solutions as time progresses. The computational efficiency of the formulation is demonstrated by four examples that consider nonuniform permeability, multiple injection wells, an upsloping aquifer, and a dome-shaped aquifer. The adaptive timesteps reduce the computational cost by 75-82% compared to constant timesteps in the four examples considered. The proposed formulation is compared against a benchmark study where eleven different simulators were used to determine the arrival time of the CO2 plume at a leaky well. The original benchmark study did not include an FEM-based discretization of the reduced order equations. To the authors’ best knowledge, the current work is the first FEM based implementation of reduced order (vertically averaged) multiphase flow equations evaluated against this benchmark. The proposed formulation is in good general agreement with the results from the various simulators studied in the benchmark, and excellent agreement with an FDM discretization of the vertically averaged governing equations.

Analytical model of leakage through an incomplete-sealed well

This study presents a new analytical model to predict the pressure changes in a monitoring well and the leakage rate due to the leakage through an incomplete-sealed well in a closed system. Different from previous analytical models, herein we develop a new model to simulate the leakage of a leaky well which is incomplete-sealed and connects with the storage aquifer in a certain segment. Based on the problem description and assumptions, the governing equations with corresponding definite conditions are presented and solved by means of Laplace transform, Fourier cosine transform and Duhamel's principle. Verification of the developed model is achieved by comparing with existing analytical model. Then, the leakage rates and pressure changes are calculated for different key factors and sensitivity analyses are conducted. Obviously, a higher permeability accelerates the fluid exchange between the storage aquifer and the monitoring aquifer. Thus, with the increase of the leakage permeability, the leakage from the storage aquifer is more intensive but the ultimate leakage rate is invariable. With the decrease of the dimensionless distance, the seepage resistance along the leakage path is decreasing, resulting in the greater leakage between the two aquifers. Similarly, the dynamic equilibrium is unaffected by the position of the leakage segment. The incomplete seal of the leaky well only affects the spherical flow stage and this effect is relatively small. Therefore, the dimensionless leakage height has no obvious effect on the leakage. The increase of the storativity ratio enlarges the pressure difference between the two aquifers and increases the ultimate leakage rate to achieve the dynamic equilibrium. The leakage in the case with greater storativity ratio increases more significantly. This paper presents a simple and efficient analytical solutions for the leakage through an incomplete-sealed well and extends the applicability of the previous models.

Optimum numbering and sizing of infiltration-based water sensitive urban design technologies in South Australia

ABSTRACT The existing drainage systems consider storm water as a waste product and its main focus is on collecting the runoff from urban catchments as quickly as possible and discharging it into the nearby outlets. These traditional drainage systems cannot consider important utilisation of storm water. Therefore, a decentralised storm water management option, known as, Water Sensitive Urban Design (WSUD) technologies, can be implemented in the urban catchments to minimise the negative hydrological impacts due to urbanisation. Hydraulic designs of three different types of infiltration-based WSUD technologies (leaky wells, soakaways and infiltration trenches) were designed for South Australian contexts. Modelling equations to estimate optimum numbering of infiltration systems were developed using SPSS and six different independent variables, such as soil hydraulic conductivity, size of the device, average recurrence interval of rainfall events, critical storm duration, rainfall intensity and roof size, were considered. The developed modelling equations were statistically significant and were applied in the real-case scenarios of South Australian catchments.

A portrait of wellbore leakage in northeastern British Columbia, Canada.

Oil and gas well leakage is of public concern primarily due to the perceived risks of aquifer contamination and greenhouse gas (GHG) emissions. This study examined well leakage data from the British Columbia Oil and Gas Commission (BC OGC) to identify leakage pathways and initially quantify incident rates of leakage and GHG emissions from leaking wells. Three types of leakage are distinguished: "surface casing vent flow" (SCVF), "outside the surface casing leakage" (OSCL), and "cap leakage" (CL). In British Columbia (BC), the majority of reported incidents involve SCVF of gases, which does not pose a risk of aquifer contamination but does contribute to GHG emissions. Reported liquid leakage of brines and hydrocarbons is rarer. OSCL and CL of gas are more serious problems due to the risk of long-term leakage from abandoned wells; some were reported to be leaking gas several decades after they were permanently abandoned. According to the requirements of provincial regulation, 21,525 have been tested for leakage. In total, 2,329 wells in BC have had reported leakage during the lifetime of the well. This represents 10.8% of all wells in the assumed test population. However, it seems likely that wells drilled and/or abandoned before 2010 have unreported leakage. In BC, the total GHG emission from gas SCVF is estimated to reach about 75,000 t/y based on the existing inventory calculation; however, this number is likely higher due to underreporting.

A field and laboratory investigation of kerb side inlet pits using four media types

Kerb side inlets with adjacent leaky wells are an emerging tool to harvest stormwater and to reduce runoff volumes and peak flow rates. This is achieved by collecting the first flush runoff into kerb side storages and infiltrating this water into the surrounding soil, thereby also reducing stormwater pollutant loadings. The hydraulic performance of the kerb side inlet, filter media and surrounding soil are key factors in the performance of these systems. However, no field or laboratory data are currently available for the hydraulic performance of a kerb side tree inlet pit. In this study, 12 tree inlet pits were constructed and filled with various media types including gravel, water treatment solids (a recycled waste product), sandy loam and clay to examine (1) leaky well infiltration rates (2) emptying times of the wells and (3) the well capacity (runoff storage volume) before and after runoff filtering through the wells. Using a laboratory model, the water harvesting performance of the kerb side inlet plate was also examined for various road longitudinal slopes. Using the field and laboratory data, simulation of the well performance was undertaken using the Model for Urban Stormwater Improvement Conceptualisation (MUSIC) to assess the capacity of these systems to reduce runoff volumes at the residential street scale. It was hypothesised that the type of filter media used in leaky well systems has a significant impact on the infiltration rate, regardless of the native soil type through which the stormwater eventually infiltrates. The results showed that the infiltration rates of systems filled with gravel were significantly higher than for the other media types, and this was followed by water treatment solids, sandy loam and clay. The results of the MUSIC modelling indicated that 2.8% of the mean annual runoff volume in the catchment could be harvested by the systems at the case study site. It was found that selection of high infiltration rate media and regular maintenance are the key factors for maintaining long-term performance of these systems.

Estimates of CO2 leakage along abandoned wells constrained by new data

The viability of carbon capture and geological storage (CCS) projects depends in part on the risk that injected CO2 or displaced pore fluid will leak out of the target formation into surrounding formations or to the surface. Abandoned oil and gas wells, of which millions exist both throughout the United States and globally, form a potential conduit for this leakage. Recently, specific field measurements have been made to quantify the range of effective permeabilities that can be expected in abandoned wells, enabling us to, for the first time, combine field-scale numerical simulations of CO2 sequestration in deep saline aquifers with real data on effective permeabilities of leaky wells. Using a previously developed semi-analytical reservoir simulator that can accommodate an arbitrary sequence of alternating aquifers and aquicludes, as well as an arbitrary number of leaky wells, we investigated how the amount of CO2 that leaks out of the target formation depends on the spatial density of nearby abandoned wells and their effective permeability. Furthermore, we assess the influence that variations in pressure and temperature found between geological targets have on this dependency. We find that the observed differences in leakage between geological targets are controlled almost exclusively by differences in density of CO2 at the local subsurface conditions, causing the CO2 plume to contact a different number of wells when injecting at the same constant mass rate. We quantitatively assess the results obtained from our numerical experiments by combining them with the permeability data that have recently become available, typical spatial densities of abandoned wells, and performance requirements put forward in the literature. Our results indicate that leakage of CO2 through abandoned wells is unlikely to be a major limitation in storage security of CCS projects.