Assessment of wellbore integrity failure risk and hazardous zones in depleted reservoirs underground gas storage during the operation processes.

Depleted reservoirs are widely used for underground gas storage due to their advantages of low construction cost and easy development. Under the influence of complex geological conditions and frequent operations, the integrity of the wells in depleted reservoirs is prone to failure, which would potentially lead to gas leakage. In this study, by using a finite element-based computational fluid dynamics model, we have developed evaluation criteria for assessing the severity of the occurred wellbore integrity failure and the risk of the un-occurred wellbore integrity failures respectively to identify hazardous zones potentially prone to wellbore integrity failure. The study results indicate that the gas storage wellbore integrity failure is prone to occur inside the wellbore structure in the direction of the minimum ground stress near the lower boundary of the formation interlayer. The wellbore integrity failure hazardous zones are mainly concentrated at the formation interlayer boundaries. The practical guidelines and solutions derived from current research results can provide an accurate direction for monitoring and protecting work of wellbore integrity and avoid environment pollution problems caused by natural gas leakage.

Methane Emissions from Non-producing Oil and Gas Wells and the Potential Role of Seismic Activity: A Case Study in Northeast British Columbia, Canada.

Increasing seismic activity due to fluid injections for oil and gas production may be contributing to leakage along non-producing oil and gas wells and emitting methane, a potent greenhouse gas. However, the extent to which nearby seismicity may drive or exacerbate methane emissions and cause well integrity issues is unknown. Therefore, we analyze field evaluations at 448 non-producing oil and gas wells in Northeast British Columbia (NEBC) and geospatially analyze oil and gas well and fluid injection data alongside locations of 3515 earthquakes from 2001 to 2021 and 130 faults. Through analysis of ground and helicopter-based field evaluations of non-producing wells in NEBC, we show that methane emission rates of non-producing wells average at 8301 mg/h/well but vary by 10 orders of magnitude. We find that higher methane emission rates (milligrams of methane/h/well) are observed at wells with larger flowing pressures at the wellhead during completion (kPa) and with shorter distances (m) to earthquakes, particularly at plugged wells. These results imply that seismicity may increase the likelihood of non-producing well integrity issues and methane leakage, thereby also exacerbating groundwater contamination and environmental degradation risks.

Using groundwater monitoring wells for rapid application of soil gas radon deficit technique to evaluate residual LNAPL.

The application of the 222Radon (Rn) deficit technique using subsurface soil gas probes for the identification and quantification of light non-aqueous phase liquids (LNAPL) has provided positive outcomes in recent years. This study presents an alternative method for applying this technique in the headspace of groundwater monitoring wells. The developed protocol, designed for groundwater monitoring wells with a portion of their screen in the vadose zone, is based on the use of portable equipment that allows rapid measurement of the Rn soil gas activity in the vadose zone close to the water table (i.e., smear zone) where LNAPL is typically expected. The paper first describes the step-by-step procedure to be followed for the application of this method. Then, a preliminary assessment of the potential of the method was carried out at two Italian sites characterized by accidental gasoline and diesel spills into the subsurface from underground storage tanks. Although the number of tests conducted does not allow for definitive conclusions, the results obtained suggest that, from a qualitative point of view, Rn monitoring in the headspace of monitoring wells is a promising, fast, and minimally invasive screening method that could also potentially reduce the costs associated with field data acquisition. This method proves to be suitable for detecting the presence of LNAPL in both the mobile and residual phases with results consistent with the other lines of evidence available at the sites, such as groundwater and soil gas monitoring. Future efforts should be directed toward evaluating the accuracy of this method for a quantitative assessment of residual LNAPL saturations.

Race, Racism, and Drinking Water Contamination Risk From Oil and Gas Wells in Los Angeles County, 2020.

Objectives. To evaluate the potential for drinking water contamination in Los Angeles (LA) County, California, based on the proximity of supply wells to oil and gas wells, and characterize risk with respect to race/ethnicity and measures of structural racism. Methods. We identified at-risk community water systems (CWSs) as those with supply wells within 1 kilometer of an oil or gas well. We characterized sociodemographics of the populations served by each CWS by using the 2013-2017 American Community Survey. We estimated the degree of redlining in each CWS service area by using 1930s Home Owners' Loan Corporation security maps, and characterized segregation by using the Index of Concentration at the Extremes. Multivariable regression models estimated associations between these variables and CWS contamination risk. Results. A quarter of LA County CWSs serving more than 7 million residents have supply wells within 1 kilometer of an oil or gas well. Higher percentages of Hispanic, Black, and Asian/Pacific Islander residents and a greater degree of redlining and residential segregation were associated with higher contamination risk. Conclusions. Redlining and segregation predict drinking water contamination risks from oil development in LA County, with people of color at greater risk. (Am J Public Health. 2023;113(11):1191-1200. https://doi.org/10.2105/AJPH.2023.307374).

Implementing a Community-Led Arsenic Mitigation Intervention for Private Well Users in American Indian Communities: A Qualitative Evaluation of the Strong Heart Water Study Program.

Arsenic is a naturally occurring toxicant in groundwater, which increases cancer and cardiovascular disease risk. American Indian populations are disproportionately exposed to arsenic in drinking water. The Strong Heart Water Study (SHWS), through a community-centered approach for intervention development and implementation, delivered an arsenic mitigation program for private well users in American Indian communities. The SHWS program comprised community-led water arsenic testing, point-of-use arsenic filter installation, and a mobile health program to promote sustained filter use and maintenance (i.e., changing the filter cartridge). Half of enrolled households received additional in-person behavior change communication and videos. Our objectives for this study were to assess successes, barriers, and facilitators in the implementation, use, and maintenance of the program among implementers and recipients. We conducted 45 semi-structured interviews with implementers and SHWS program recipients. We analyzed barriers and facilitators using the Consolidated Framework for Implementation Research and the Risks, Attitudes, Norms, Abilities, and Self-regulation model. At the implementer level, facilitators included building rapport and trust between implementers and participating households. Barriers included the remoteness of households, coordinating with community plumbers for arsenic filter installation, and difficulty securing a local supplier for replacement filter cartridges. At the recipient level, facilitators included knowledge of the arsenic health risks, perceived effectiveness of the filter, and visual cues to promote habit formation. Barriers included attitudes towards water taste and temperature and inability to procure or install replacement filter cartridges. This study offers insights into the successes and challenges of implementing an arsenic mitigation program tailored to American Indian households, which can inform future programs in partnership with these and potentially similar affected communities. Our study suggests that building credibility and trust between implementers and participants is important for the success of arsenic mitigation programs.

Modeling demonstrates minimal ecological risks of cuttings discharges associated to oil and gas drilling with deep water wells.

To assess the impacts of drill cutting discharges in the Gulf of Mexico, a particle dispersion modeling study was conducted on hypothetical drilling scenarios. The goal was to assess cumulative seabed deposition, and potential hydrocarbon loading from non-aqueous drilling fluids (NADF). Cuttings drilled with NADF showed to have minimal impact on local fauna at the deep-water well simulated. A hypothetical drill site was modeled under 3 different seasonally representative met-ocean conditions. The site is located approximately 260 km from the coast in water roughly 3500 meters (m) deep. Cumulative deposition was assessed for all materials released, whereas hydrocarbon loading was assessed based on the potential for NADF fluids to be retained on cuttings. Smothering effects on the benthic community are not anticipated. Hydrocarbon deposition was also very limited, ≤165 ppm of TPH. Overall, the cuttings drilled with NADF are predicted to have minimal impact on local fauna.

Evaluation the feasibility of using clinoptilolite as a gravel pack in water wells for removal of lead from contaminated groundwater.

The ability of clinoptilolite zeolite as a filter in water wells to remove lead from polluted groundwater was tested in batch and fixed-bed column experiments. XRF, XRD, SEM, and BET were used to characterize the zeolite. Because of the pH variation in groundwater, batch experiments were performed at pH = 6, 7, and 8, with the highest removal efficiency (84.2%) at pH = 6 and 298 K within 90 min. The Freundlich model accurately predicted metal ion adsorption behavior and indicated a multilayer adsorption of Pb(II) molecules on the inhomogeneous surface of clinoptilolite. The best-fitting kinetic model for clinoptilolite is the pseudo-second order equation, highlighting that the rate of adsorption is dependent on absorbent capacity. Next, the effect of flow rate, bed depth, and grain size of clinoptilolite on lead removal was investigated in column experiments at an initial concentration of 450 mg pb/L. The highest removal efficiency was achieved in column experiments with a flow rate of 1 mL/min, a bed height of 10 cm, and a grain size of 0.6 to 0.8 mm. Breakthrough curves were predicted by the Thomas and Yoon-Nelson models, with excellent agreement with the corresponding experimental data. This research will be used to develop a new in situ remedial approach for removing lead from polluted groundwater.

In-Well Degassing of Monitoring Wells Completed in Gas-Charged Aquifers.

Total dissolved gas pressure (PTDG ) measurements are useful to measure accurate in situ dissolved gas concentrations in groundwater, but challenged by in-well degassing. Although in-well degassing has been widely observed, its cause(s) are not clear. We investigated the mechanism(s) by which gas-charged groundwater in a recently pumped well becomes degassed. Vertical PTDG and dissolved gas concentration profiles were monitored in the standing water column (SWC) of a groundwater well screened in a gas-charged aquifer for 7 days before and 15 days after pumping. Prior to pumping, PTDG values remained relatively constant and below calculated bubbling pressure (PBUB ) at all depths. In contrast, significant increases in PTDG were observed at all depths after pumping was initiated, as fresh groundwater with elevated in situ PTDG values was pumped through the well screen. After pumping ceased, PTDG values decreased to below PBUB at all depths over the 15-day post-pumping period, indicating well degassing was active over this time frame. Vertical profiles of estimated dissolved gas concentrations before and after pumping provided insight into the mechanism(s) by which in-well degassing occurred in the SWC. During both monitoring periods, downward mixing of dominant atmospheric and/or tracer gases, and upwards mixing of dominant groundwater gases were observed in the SWC. The key mechanisms responsible for in-well degassing were (i) bubble exsolution when PTDG exceeded PBUB as gas-charged well water moves upwards in the SWC during recovery (i.e., hydraulic gradient driven convection), (ii) microadvection caused by the upward migration of bubbles under buoyancy, and (iii) long-term, thermally driven vertical convection.

Composition and Origin of Surface Casing Fluids in a Major US Oil- and Gas-Producing Region.

Fluids leaked from oil and gas wells often originate from their surface casing─a steel pipe installed beneath the deepest underlying source of potable groundwater that serves as the final barrier around the well system. In this study, we analyze a regulatory dataset of surface casing geochemical samples collected from 2573 wells in northeastern Colorado─the only known publicly available dataset of its kind. Thermogenic gas was present in the surface casings of 96.2% of wells with gas samples. Regulatory records indicate that 73.3% of these wells were constructed to isolate the formation from which the gas originated with cement. This suggests that gas migration into the surface casing annulus predominantly occurs through compromised barriers (e.g., steel casings or cement seals), indicative of extensive integrity issues in the region. Water was collected from 22.6% of sampled surface casings. Benzene, toluene, ethylbenzene, and xylenes were detected in 99.7% of surface casing water samples tested for these compounds, which may be due to the presence of leaked oil, natural gas condensate, or oil-based drilling mud. Our findings demonstrate the value of incorporating surface casing geochemical analysis in well integrity monitoring programs to identify integrity issues and focus leak mitigation efforts.

Application of machine learning in predicting oil rate decline for Bakken shale oil wells.

Commercial reservoir simulators are required to solve discretized mass-balance equations. When the reservoir becomes heterogeneous and complex, more grid blocks can be used, which requires detailed and accurate reservoir information, for e.g. porosity, permeability, and other parameters that are not always available in the field. Predicting the EUR (Estimated Ultimate Recovery) and rate decline for a single well can therefore take hours or days, making them computationally expensive and time-consuming. In contrast, decline curve models are a simpler and speedier option because they only require a few variables in the equation that can be easily gathered from the wells' current data. The well data for this study was gathered from the Montana Board of Oil and Gas Conservation's publicly accessible databases. The SEDM (Stretched Exponential Decline Model) decline curve equation variables specifically designed for unconventional reservoirs variables were correlated to the predictor parameters in a random oil field well data set. The study examined the relative influences of several well parameters. The study's novelty comes from developing an innovative machine learning (ML) (random forest (RF)) based model for fast rate-decline and EUR prediction in Bakken Shale oil wells. The successful application of this study relies highly on the availability of good quality and quantity of the dataset.

Documented Orphaned Oil and Gas Wells Across the United States.

Orphaned oil and gas wells are unplugged nonproducing wells with no solvent owner of record to plug and mitigate them, such that the responsibility often falls on government agencies and the general public. Unplugged wells pose risks to the environment, climate, and human health. To develop a national framework to quantify the environmental benefits of plugging and optimize mitigation, we analyze oil and gas well data from state agencies across the United States to estimate the number of documented orphaned wells over time and evaluate their attributes. We find at least 81,857 documented orphaned wells as of September 2021 and 123,318 as of April 2022, representing 2% and 3%, respectively, of all estimated abandoned wells in the United States. We identify at least 20,286 potentially documented orphaned wells as of September 2021 (0.5% of all estimated abandoned wells in the country), of which 8% became documented orphaned wells as of April 2022. We estimate annual methane emissions to average 0.016 ± 0.001 MMt of CH4 for the 123,318 documented orphaned wells as of April 2022, corresponding to 5-6% of the total methane emissions estimated by the U.S. EPA for all abandoned wells. Although well type (i.e., oil vs gas) is generally available (83% of the 81,857 documented orphaned wells as of September 2021), only 49% and 16% of the wells have information on depth and last production date, respectively. Overall, documented orphaned wells and their attributes, including location, well type, depth, and last production date, require additional characterization and studies to constrain the uncertainties. Nevertheless, our identification and analysis of documented orphaned wells represent the first steps toward characterizing the full set of wells eligible to be plugged and remediated with the federal funding available in the U.S. via the Infrastructure Investment and Jobs Act. Our results can also be useful for the management of the hundreds of thousands, potentially a million, undocumented orphaned wells likely to exist across the nation.

Proximity and density of unconventional natural gas wells and mental illness and substance use among pregnant individuals: An exploratory study in Canada.

BACKGROUND: Hydraulic fracturing (fracking) is a method used to extract unconventional natural gas (UNG). Living near UNG operations has been associated with various health outcomes, but few have explored the association between UNG and mental health and substance use. Our objective was to evaluate the association between metrics of residential UNG well density/proximity and mental illness and substance use among pregnant individuals in Northeastern British Columbia, Canada. METHODS: Individuals who gave birth at the Fort St John hospital between December 30, 2006 and December 29, 2016 (n = 6278) were included in the study. Exposure was determined using inverse distance weighting (IDW) to calculate the density and proximity of UNG wells to the postal code centroid ofindividual's residential address at delivery. Four exposure metrics, categorized by quartiles, were calculated based on 50, 10, 5 and 2.5 km buffer zones around each postal code centroid. Logistic regression was used to separately evaluate associations between IDW quartiles of each metric and diagnosis of depression and anxiety prior to or during pregnancy, and self-reported substance use during pregnancy, controlling for relevant and available confounders. RESULTS: The second and third quartile (Q) of the 10 km IDW were associated with greater odds of depression (Q2: adjusted (aOR) 1.30, 95% (confidence interval) CI 1.03-1.64; Q3: aOR 1.35, 95% CI 1.07-1.70) compared to the first quartile, but not the fourth. Using the 5 km IDW, we observed a suggestive positive association with depression in the second and third quartile (aOR Q2: 1.21, 95% CI 0.96-1.53; aOR Q3: 1.24, 95% CI 0.98-1.57) compared to the first quartile. No statistically significant association was observed using the 2.5 km IDW exposure metric. CONCLUSION: We observed some evidence of greater odds of mental illness prior to or during pregnancy, and substance use during pregnancy in pregnant individuals living in postal codes with increased UNG well density/proximity, although associations were not observed in smaller buffer zones. This study adds to the growing literature on the adverse health outcomes surrounding living in proximity to UNG operations.

Spatial and temporal dynamics and potential pathogenicity of fecal coliforms in coastal shallow groundwater wells.

Access to water through shallow groundwater wells is a common practice in coastal settlements. This, coupled with a lack of planning for wastewater disposal promotes fecal contamination of groundwater and poses a threat to human health. Here, the spatial and temporal dynamics of groundwater fecal contamination was evaluated during summer and winter (2013 and 2014) in a coastal protected area having a high touristic relevance (Cabo Polonio, Uruguay). Fecal coliforms (FC) abundance in groundwater was significantly higher during summer, related to an influx of ~ 1000 tourists per day. A significant spatial autocorrelation was found in 2014, when the abundance of FC in a well was influenced by its three nearest wells (Moran and Geary tests). The applied statistical models (mixed models) indicated that total phosphorus and organic matter were the variables significantly explaining FC abundance. The risk for human health was estimated using groundwater-extracted DNA and qPCR of genes encoding for E. coli virulence factors (stx1, stx2, and eae). Potential Shiga toxin-producing enteropathogenic and enterohemorrhagic pathotypes were detected, even at FC abundances ≤ 1 CFU (100 mL-1). Moreover, we found that contaminated groundwater reached the beach, being the presence of FC in sand detected even in winter and showing its highest frequency nearby groundwater wells consistently having high FC abundance (hot spots). Altogether, the results show that fecal contamination of shallow groundwater in Cabo Polonio involves a risk for human health that intensifies during summer (associated to a significant increase of tourists). This contamination also impacts the beach, where FC can remain through the whole year.

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.

Water leak control for the oil-producing wells using Downhole Water Sink Technology.

Casing or tubing leaks cause unwanted water production from oil-producing wells. Many chemical and mechanic water control technologies can be used to solve this problem, including squeezing chemical shutoff fluids into the targeted zone or using plugs, cement, packers, patches to block the leakage. Although those methods are field-proven to be effective, the mechanical solutions may require well logs to detect the water entry point in the well. Chemical methods may present environment risks. In this study, an alternative method, Downhole Water Sink, is proposed to solve the problem of unwanted water production from a casing or tubing leak. The effectiveness of this method to control water production in a well with casing or tubing leaks is tested using the Hele-Shaw experimental model. The results show that this method can control unwanted water production via dynamic control of the pressure drawdown in the reservoir. From a technical standpoint, the advantage of this technology is that it eliminates the need to run logs to locate the water entry point and does not require chemical injection into the formation. From an environmental standpoint, this technology has the circular economy elements. Because the produced water in this technology contains little or no oil, it can be reused for reinjection into the reservoir for water flooding or pressure maintenance purposes. Therefore, a production-reinjection process to recycle the produced water is established to reduce the pollution caused by discharging the wastewater into the environment.

Free-Phase Gas Detection in Groundwater Wells via Water Pressure and Continuous Field Parameters.

Detection of free-phase gas (FPG) in groundwater wells is critical for accurate assessment of dissolved gas concentrations and the occurrence of FPG in the subsurface, with consequent implications for understanding groundwater contamination and greenhouse gas emissions. However, identifying FPG is challenging during routine groundwater monitoring and there is poor agreement on the best approach to detect the occurrence of FPG in groundwater. In this study, laboratory experiments in a water column were designed to mimic nonflowing and flowing conditions in a groundwater well to evaluate how the presence of FPG affects water pressure and commonly used continuous field parameters. The laboratory results were extrapolated to interpret field data at an abandoned exploration well with episodic release of free-gas CO2 . The FPG effect on water pressure varied between flowing and nonflowing wells, and depending on whether the FPG was above or below the sensor. Electrical conductivity values were decreased and/or behaved erratically when FPG was present in the water column. Findings from this study have shown that the combined measurement of water pressure, electrical conductivity, and total dissolved gas pressure can provide information about the occurrence of FPG in groundwater wells. Measurement of these parameters at different depths can also provide information about relative depths and amounts of FPG within the well water column. This approach can be used for long-term monitoring of groundwater gases, managing gas-locking in production wells with gassy groundwater, and measuring fugitive greenhouse gas emissions from groundwater wells.

Assessing cumulative water impacts from shale oil and gas production: Permian Basin case study.

Quantifying impacts of unconventional oil and gas production on water resources and aquatic habitats is critical for developing management approaches for mitigation. The study objective was to evaluate impacts of oil and gas production on groundwater and surface water and assess approaches to reduce these impacts using the Permian Basin as a case study. Water demand for hydraulic fracturing (HF) was compared to water supplies. We also examined contamination from surface spills. Results show that water demand for HF peaked in 2019, representing ~35% of water use in non-mining sectors. Most HF water was sourced from aquifers with ~1,100 wells drilled in the Ogallala aquifer in 2019. The State monitoring network did not show regional groundwater depletion but was not sufficiently dense to address local impacts. Groundwater depletion is more critical in the western Delaware Basin within the Permian Basin because groundwater is connected to large flowing springs (e.g. San Solomon Springs) and to the Pecos River which has total dissolved solids ranging from ~3000 to 14,000 mg/L. Most produced water (70-80%) is disposed in shallow geologic units that could result in overpressuring and potential groundwater contamination from leakage through ~70,000 abandoned oil wells, including orphaned wells. While there is little evidence of leakage from abandoned wells, the state monitoring system was not designed to assess leakage from these wells. Oil spill counts totaled ~11,000 in the Permian (2009-2018). Approaches to mitigating adverse impacts on water management include reuse of PW for HF; however, there is an excess of PW in the Delaware Basin. Treatment and reuse in other sectors outside of oil and gas are also possibilities. Data gaps include reporting of water sources for HF, PW quality data required for assessing treatment and reuse, subsurface disposal capacity for accommodating PW, and spills from PW in Texas.

Low-Level Groundwater Atrazine in High Atrazine Usage Nebraska Counties: Likely Effects of Excessive Groundwater Abstraction.

Recent studies observed a correlation between estrogen-related cancers and groundwater atrazine in eastern Nebraska counties. However, the mechanisms of human exposure to atrazine are unclear because low groundwater atrazine concentration was observed in counties with high cancer incidence despite having the highest atrazine usage. We studied groundwater atrazine fate in high atrazine usage Nebraska counties. Data were collected from Quality Assessed Agrichemical Contaminant Nebraska Groundwater, Parameter-Elevation Regressions on Independent Slopes Model (PRISM), and water use databases. Descriptive statistics and cluster analysis were performed. Domestic wells (59%) were the predominant well type. Groundwater atrazine was affected by well depth. Clusters consisting of wells with low atrazine were characterized by excessive groundwater abstraction, reduced precipitation, high population, discharge areas, and metropolitan counties. Hence, low groundwater atrazine may be due to excessive groundwater abstraction accompanied by atrazine. Human exposure to atrazine in abstracted groundwater may be higher than the estimated amount in groundwater.

CFD study of the water production in mature heavy oil fields with horizontal wells.

Excessive water production in mature heavy oil fields causes incremental costs, energy consumption, and inefficiency. Understanding multiphase flows near the wellbore is an alternative to improve production efficiency. Therefore, this study conducts a series of numerical experiments based on the full set of the Navier-Stokes equations in 3D to simulate multiphase flows in porous media for heavy oil production horizontal wells. The solution given by this advanced mathematical formulation led to the description of the movement of the fluids near the wellbore with unprecedented detail. A sensitivity analysis was conducted on different rock and fluid properties such as permeability and oil viscosity, assuming homogeneous porous media. The influence of these parameters on the prediction of the breakthrough time, aquifer movement, and the severity of water production was noticed. Finally, the numerical model was verified against field data using two approaches. The first one was conducting a history match assuming homogeneous rock properties. In contrast, the second one used heterogeneous rock properties measured from well logging, achieving a lower deviation than field data, about 20%. The homogeneous numerical experiments showed that the breakthrough occurs at the heel with a subsequent crestation along the horizontal well. Moreover, at adverse mobility ratios, excessive water production tends to happen in water connings at the heel with an inflow area less than 1% of the total inflow area of the completion liner. Different aquifer movement dynamics were found for the heterogeneous case, like the breakthrough through multiple locations along the horizontal well. Finally, critical hydraulic data in the well, such as the pressure and velocity profiles, were obtained, which could be used to improve production efficiency. The numerical model presented in this study is proposed as an alternative to conducting subsurface modeling and well designs.

A novel, direct-push approach for detecting sulfidated nanoparticulate zero valent iron (S-nZVI) in sediments using reactive and non-reactive fluorophores.

Injection of microparticulate and nanoparticulate zero valent iron has become a regularly used method for groundwater remediation. Because of subsurface inhomogeneities, however, it is complicated to predict the ZVI transport in the subsurface, meaning that tools capable of determining its distribution after injection are highly useful. Here, we have developed a new direct-push based technique, which combines fluorescent and visible imaging, for detection of sulfidized nanoparticulate zero valent iron (S-nZVI) in the subsurface. Laboratory experiments show that the redox sensitive fluorophore riboflavin is rapidly reduced by S-nZVI within 200 s. Because the reduced riboflavin losses its green fluorescence, it can be used as S-nZVI sensitive indicator. Secondly, S-nZVI is black and tints light coloured sediment to a degree that allows detection in images. For quartz sand, 70 mg/kg of S-nZVI can be detected by visible imaging. Based on these results, a new direct-push probe (Dye-OIP) was designed based on Geoprobe's Optical Image Profiler (OIP), which was equipped with a fluorophore injection port below the OIP-unit. The injectant consisted of the redox active riboflavin mixed with the redox inactive fluorophore rhodamine WT, which fluoresces red and was used to verify that the mixture was indeed injected and detectable. Small scale experiments show that the fluorescence of this mixture in S-nZVI amended sand changes within 150 s from green with a hue of ~50 to red with a hue of ~30 when imaged with Dye-OIP. Tests of the Dye-OIP after a S-nZVI injection in a 1 m3 sized tank show that the tool could detect S-nZVI via fluorescence and visible imaging, when S-nZVI concentration was >0.2 mg per g dry sediment. Thus, these novel methods should be able to detect S-nZVI in the subsurface, without relying on infrastructure such as wells. Based on our results, the Dye-OIP could be further improved to make it suitable for regular use in the field.