Relief Wells Research Articles

Evaluation on the Effect of Relief Wells by 3D Numerical Analysis on the Embankment of an Agricultural Reservoir

Evaluation on the Effect of Relief Wells by 3D Numerical Analysis on the Embankment of an Agricultural Reservoir

Effect of jet grouting and dewatering on an adjacent tunnel in a Shanghai deep excavation

In general, jet grouting is usually adopted in deep excavation projects to improve the soils inside and outside the pit to protect surrounding tunnels or building foundations. A cost-effective way is to keep the deformations caused by pit excavation within limitations with the minimum jet-grouting. In this study, different types of jet-grouting soils around tunnels or inside pits were compared and analysed in detail using three-dimensional finite-element modelling. Tunnels on one side of the pit or underneath the formation level were considered. A dewatering method was also introduced in some finite-element models to explore the effect of pore-water pressure (PWP) relief wells in soft clay with very low permeability. The finite-element modelling results indicated that enhancing the soils around tunnels is more profitable than only improving the soils between tunnels and retaining walls. The positive effect of jet-grouting soils above the tunnel may exert only when the excess PWP dissipates. This study may assist engineers who are seeking more cost-effective ways to protect surrounding tunnels or building foundations during deep excavation in soft clay.

Variable pathways, residence time, and geochemical evolution of seepage beneath the Mississippi River levee during the 2011, 2015, and 2016 floods

Seepage beneath artificial levees is a common concern during flooding events. Risk of levee failure is elevated when piping erodes channels beneath the levee, evidenced by the formation of sand boils where transported sediments discharge. Along the lower Mississippi River, pathways of floodwater beneath the levee vary with surface geology, following deeper paths where the levee overlies fine-grained channel-fill deposits, and shallower (higher risk) paths where it overlies sand-bar deposits. Shallow, organic-rich alluvial aquifers are often geochemically stratified into upper oxic and lower anoxic zones, raising the possibility of using the geochemical signatures of discharging water from sand boils to differentiate flow pathways. A preliminary investigation north of Vicksburg, MS, (USA) during the 2011 Mississippi River flood demonstrated the potential of using geochemistry to identify deep and shallow pathways, though the study was limited to cation and trace element analyses. Sampling during the 2015 and 2016 floods for temperature, conductivity, redox potential (Eh), dissolved oxygen (DO), major ions, trace elements, tritium, and stable isotope ratios of oxygen, hydrogen, and strontium, facilitated a greater understanding of the nature of flow and geochemical evolution of groundwater in this environment. Characteristics of deeper flow pathways (relative to shallow) included (1) lower Eh and higher Fe and As, reflecting anoxic conditions and high-Fe sediments, (2) proportional increases in Fe and HCO3, indicating reductive dissolution of Fe-oxyhydroxides, and (3) higher ratios of Ba/Ca and Sr/Ca, reflecting differences in the elemental composition of minerals with depth. Tritium results indicate that subsurface flow pathways are dynamic, shifting spatially with the rapid changes in hydraulic gradients during and between flooding events. Estimated residence times of groundwater discharging from sand boils and relief wells ranged from essentially zero (discharge of concurrent floodwater) up to a quarter century. Lower strontium isotope ratios (87Sr/86Sr) were observed in the aquifer relative to river water, though with no clear variation with flow depth. Oxygen and hydrogen isotope ratios (δ18O and δ2H) show evidence of partial evaporation prior to recharge, also with no apparent variation with subsequent flow depth.

Influence of the opening timing of recharge wells on settlement caused by dewatering in excavations

In deep excavation engineering, the head of the confined aquifer below the excavation bottom must be lowered when the anti-uprush safety factor is not satisfied. However, the drawdown of the confined aquifer may cause ground settlement around the excavation and endanger adjacent buildings, tunnels or municipal pipes. Artificial recharge (AR) is a measure that has been applied in such situations to recover the water level and control the settlement. However, practical engineering cases have shown that AR could control only the development of settlement and could hardly recover the settlement caused by long-term dewatering. Therefore, three recharge schemes, namely, “recharge first”, “simultaneous pressure relief and recharge” and “pressure relief first”, are studied using numerical modeling. The results show that the opening timing of the recharge wells and pressure relief wells has a significant impact on the final settlement. In different recharge schemes, different stress paths of the soil in the confined aquifer and overlying aquitards cause different plastic compressive deformations. To reduce plastic deformation, recharge should begin at the same time as pressure relief when the surrounding environment of the deep excavation must be strictly protected. Additionally, the case study and numerical simulation both show that the most significant settlement or uplift occurs in the deep soil layer rather than at the ground surface, a phenomenon that occurs because the vertical displacement of the soil adjacent to the relief and recharge wells is larger than that in the soil far away, leading to a vertical soil arching in the strata above the confined aquifer.

Method and equipment for the safe development of preparatory workings in the gas-bearing coal seams

The article describes a method and equipment for the safe development of preparatory working on a gas-bearing, outburst hazardous coal seam by a heading machine. The described method significantly prevents the gas emission during mining operations. Determination of the amount of degassing and relief wells is performed according to the given in article mathematical formulas. This ensures a significant increase in the level of safety processing the preparatory roadway on a gas-bearing, prone to outbursts coal seam by a heading machine. Due to this, the speed of conducting excavation increases and the cost of mining is reduced. The proportionality coefficients of the mathematical models were determined. Mathematical models are used to calculate the number of relief and degassing wells, which are drilled during the impulse hydraulic loosing of the nearby part of the coal seam. Also the duration of liquid injection into a coal seam is also determined. Mathematical models for calculating the number of injection, unloading and degassing boreholes can be used in development of the passports for conducting preparatory workings on a gas-bearing, prone to outburst coal seam by a heading machine with a preliminary impulse hydraulic loosing of the nearby part of a coal seam.

Analysis of the impact of Shifosi Reservoir water level on underground water

Abstract Shifosi Reservoir is a plain reservoir. High groundwater level in the nearby area caused by impoundment of the reservoir has not only submerged the nearby farmland and village, but also reduced production and affected farmers' living. To analyze the influence of reservoir impoundment on surrounding groundwater level, Visual MODFLOW software was used to simulate the groundwater in Zhujiapu and Chenpingpu areas on the right auxiliary dam of Shifosi Reservoir. Results show that with the rise of the reservoir water level from 45.5 m to 46.2 m and 46.5 m, the area under the critical groundwater table (45 m) in the study area decreased in turn. In 2008, when the reservoir water level was 46.2 m and 46.5 m, the area under the critical groundwater level was reduced by 0.64 km2 and 0.84 km2, respectively, compared with the case of reservoir water level of 45.5 m, and would decrease by 0.38 km2 and 0.45 km2, respectively, by 2022. This indicates that the impact of reservoir impoundment on groundwater level is great. Therefore, relief wells or drainage ditches should be arranged along the auxiliary dam axis to effectively lower the groundwater level, and improve the surrounding ecological environment of the reservoir.

Blowout Prevention and Relief-Well Planning for the Wheatstone Big-Bore Gas-Well Project

Summary The offshore Wheatstone liquefied natural gas (LNG) project in Western Australia uses subsea big-bore gas wells as the preferred method of producing the field. Wheatstone wells use a 9⅝-in. production conduit from the top of the gas pay zone to the ocean floor. Wellbores of this size are necessary to match the large productive capacity of the gas reservoirs they penetrate. This producing scenario provides the obvious benefit of yielding large volumes of gas through the use of relatively few wells. Each of those highly productive wells, however, also represents a source of gas that, if accidentally allowed to flow unhindered, could present an uncommonly difficult well-control challenge. It is for this reason that the Wheatstone Drilling and Completions (D&C) Team evaluated a wide range of possible reservoir- and well-architecture scenarios to fully understand the possible scale of relief-well responses that might be necessary in the event of a blowout. The conclusions from this evaluation were surprising. Our original well-design concept called for penetrating the Wheatstone gas reservoirs with a casing shoe set 3,100 ft vertically above. Our analysis indicated that three or four relief wells would be simultaneously required to bring a blowout under control. Because of these results, both the well- and drilling-execution plan were redesigned to minimize the number of required relief wells. In summary, the redesign amounted to setting the casing immediately (i.e., ≤ 10 ft) above the gas reservoir before actually penetrating it, with the resulting benefit of reducing the required number of relief wells to two. Although this reduction is beneficial, it should be noted that there is only one documented subsea case where two or more relief wells have been drilled with the intent of simultaneously pumping into both to effect a dynamic kill. Given this fact, our well-control-related preparations for executing this project were more extensive than those of preceding projects. This paper chronicles the full extent of the engineering and operational planning performed to ensure that no uncontrolled hydrocarbon releases occurred during the execution of the Wheatstone Project's subsea big-bore gas wells and, if a blowout were to occur, that the response to such an unprecedented event would be sufficient and robust. Covered in this paper are reservoir-deliverability modeling, dynamic-kill modeling, gas-plume modeling, relief-well trajectory and mooring planning, pilot-hole-execution planning, a newly applied logging-while-drilling (LWD) technology for sensing resistivity vertically below the drill bit, and a discussion of future research identified as necessary to better define the fluid-injectivity capabilities of subsea relief wells.

How To Develop a Well-Specific Capping-Stack Blowout Contingency Plan

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 181393, “How To Develop a Well-Specific Blowout Contingency Plan That Covers Engineering Analysis of the Deployment, Installation, and Soft Shut-In of a Subsea Capping Operation,” by Ray T. Oskarsen, SPE, Morten H. Emilsen, SPE, and Amir S. Paknejad, Add Energy; Mike Cargol, Trendsetter Engineering; and Kwee Choong See, SPE, Shell International Exploration and Production, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed. The planning process for developing a well-specific subsea-capping contingency plan involves assessing the feasibility of deploying a capping stack from a floating vessel, determining the weight and stability of the capping stack to overcome the force of the blowout jet, and performing dynamic-flow simulations of closing the capping stack outlets without loss of well integrity. This process not only assesses the feasibility, complexity, and risk exposure of the capping operation but also may justify further planning, studies, or expenditure. Introduction Blowout-kill techniques can be classified as either surface-intervention or relief-well methods. Relief wells aim to kill a blowout from the bottom by injecting fluid into the wellbore until the influx of formation fluid is stopped and the well is static when pumping stops. In many cases, a relief well will be the safest intervention and have the highest likelihood of success, and often it is considered the last line of defense against a blowout. Surface interventions are kill attempts aimed at controlling the discharge at the wellhead or at the fluid-exit point. An example is to install a capping stack on top of the wellhead and close its openings, which can be gate valves, chokes, or rams. Blowout Contingency Planning. Blow-out contingency plans ensure that people understand and can manage risks, thus ensuring safe and sustainable operations at all times. All blowouts are inherently different; thus, it would be both impractical and impossible to attempt to cover every possible blowout scenario in a contingency plan. For source-control planning, an operator should, at a minimum, address a worst credible scenario to demonstrate how the well will be brought under control. This scenario may be different from the worst-case discharge, which is used to estimate spill potential and necessary resources for containment and cleanup. As an example, if there is uncertainty about the gas/oil ratio (GOR), a low-case GOR may cause more oil spill, while a high-case GOR may make source control more challenging.

Blowout Prevention and Relief-Well Planning for the Wheatstone Big-Bore Gas-Well Project

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 174890, “Blowout Prevention and Relief-Well Planning for the Wheatstone Big-Bore Gas-Well Project,” by Eric R. Upchurch, SPE, Sam Falkner, Andrew House, SPE, Chinh Nguyen, SPE, and Ken Russell, Chevron Australia, prepared for the 2015 SPE Annual Technical Conference and Exhibition, Houston, 28–30 September. The paper has not been peer reviewed. The offshore Wheatstone project in Western Australia uses subsea big-bore gas wells as the preferred method of producing the field. Each of the highly productive wells represents a source of gas that, if accidently allowed to flow unhindered, could present an uncommonly difficult well-control challenge. This paper details the engineering and operational planning performed to ensure that no uncontrolled hydrocarbon releases occur during the execution of the subsea big-bore gas wells and that, if a blowout were to occur, the response to such an event would be sufficient and robust. Introduction The Wheatstone high-rate gas-well design, with its 9⅝-in. production conduit, represents the company’s initial attempt at implementing such a well. Because the design team’s combined engineering and execution experience included neither big-bore wells nor reservoirs of Wheatstone’s productive magnitude, well-control expectations were limited to anticipating needing only a single relief well in the event of a blowout. However, upon receipt of dynamic-kill simulations performed by consulting experts in that field, a new reality became obvious. That is, the combination of a large wellbore connected to the multidarcy Wheatstone gas reservoir has the potential to produce at more than 1 Bscf/D if flow is unconstrained; in some scenarios, this could require the use of up to four relief wells simultaneously injecting 15-lbm/gal drilling fluid to regain control. Analyses suggest that it is improbable that a dynamic kill at Wheatstone can be performed successfully using only a single relief well, given the large diameter of the production wellbore. Therefore, the well-control risk of drilling a Wheatstone well was mitigated not by limiting its productive capacity (i.e., reducing the well diameter) but by (1) optimizing casing-setting depths to minimize the number of required relief wells, (2) designing the well to be completely pressure competent, even if it were totally filled with gas, and (3) formulating a blowout-response plan that is reflective of the complexities of executing a two-well dynamic kill on any of the nine foundation wells drilled at Wheatstone.

Location selection of deepwater relief wells in South China Sea

Abstract By analyzing affecting factors on deepwater relief well location selection, and focusing on the regional deepwater operating environment in South China Sea and different rig positioning types, a calculation method for minimum safety distance between reliefs well and blowout well was proposed. In addition to the affecting factors on shallow-water relief well location selection, difficulties which are specific for deepwater operating considerations should be considered for deepwater relief well location selection, including metocean conditions, site survey results, blowout situation and evolution, influences of relief well location on relief well trajectory design, ranging procedure, ranging tool usage and dynamic killing operation, and fire hazard heat radiation and rig positioning types. The most significant factors for deepwater relief well location selection in South China Sea are typhoon and internal solitary wave. For a mooring positioning rig, the main considerations are mooring deployment, internal solitary wave and typhoon. For a dynamic positioning rig, the main considerations are operation window and other vessels. Based on analyses of affecting factors on deepwater relief well location selection in South China Sea, the well location selection method was demonstrated through the discussion of an existing regional well.

Semi-Analytical Model of Pressure Perturbations Induced by Fault Leakage in Multilayer System

Lateral and vertical migration capacity of faults has been studied for applications related to fluid extraction and injection from and into the subsurface. Fluid exchange between formations connected by a fault can cause pressure perturbations in nonoperating formations. An analytical model was previously developed to evaluate the leakage rates through a fault in a multilayer system. However, the effect of the fault’s lateral resistance to flow was neglected and therefore the model was not applicable in evaluating the pressure changes caused by fault leakage. Pressure perturbations induced by fault leakage are important to determine the safety of injection operations near faults and/or in characterizing and remediating fault leakage. Here, the previous model on fault leakage to evaluate the pressure changes is extended by accounting for the lateral resistance to flow in all modeling components. As a result, the leakage rates at the two sides of the fault are no longer identical. Also, the model presented here allows for well perforation in any layer compared with the previous model where perforation must be in the bottom layer of the system. This modification is important to enable estimation of pressure changes in multilayer operation [e.g., injection in one or more aquifers while producing from other aquifer(s)]. Hence, the model can be used to determine basin-scale pressure changes considering multiple injection or production wells in multiple layers. The semianalytical solution presented here involves obtaining a set of coefficients to determine the pressure changes in Laplace and Fourier domains followed by numerical Fourier-Laplace transforms inversion. The model is applied to two example problems. In the first example, the model is verified against results of a two-layer system and compared to pressure perturbations in a three-layer system where the solution behavior is investigated. In the second example, the model is applied to investigate pressure management close to a critically stressed fault zone using relief wells, which is of interest in CO2 sequestration and/or waste disposal applications.

The Application of Magnetic Guidance Drilling Technology in Shengli Oilfield

The magnetic guidance drilling technology could use the magnetic guidance instrument to measure the distance between the signal source and the instrument, which is used to control the well trajectory. It is an essential supplement of the existing steering drilling technology. At present, the magnetic guidance drilling technology is mainly applied to dual horizontal wellslls for heavy oil reservoir, CBM horizontal connected wells, wells to mine underground soluble minerals, and relief wells. This paper mainly introduces the working process of magnetic guidance drilling technology and connected wells. In order to test the overall performance of this technology, an experimental study is conducted on it, and the field test was carried on Shengli oil field.

Slurry trenches and relief wells installed to strengthen Ohio and Mississippi river levee systems

I n April of 2011, the Ohio River began flooding farmland and cities in Ohio, Indiana, Kentucky, and Illinois, which were not protected by levees. Cairo, Illinois, and many of the other cities on the Ohio and Mississippi rivers protected by levees did not flood, but their levees and floodwalls were in danger of failing due to the constant water pressure against and under the levees and floodwalls. The extra weight of the river at flood stage pushes water under-neath levees and floodwalls increasing the potential for sand boils and undermining the strength of the levee and its capacity to hold back floodwater (Camillo 2012; Morton and Olson 2015). By early May of 2011, the Ohio River gage at Cairo, Illinois, had reached 18.7 m (61.7 ft) (NOAA 2012), and floodwaters were starting to put significant pressure on both Ohio and Mississippi river levee and floodwall systems to the north of Cairo (figure 1). Although, the New Madrid Floodway south of the Ohio and Mississippi river confluence at Cairo was deliberately breached on May 2, 2011, by the United States Army Corps Engineers (USACE) to reduce levee pressure, the levee system north of Cairo, the levee system south of Hickman, Kentucky,…

Use of Numerical Simulation to Measure the Effect of Relief Wells for Decreasing Uplift in a Homogeneous Earth Dam

Relief wells are used extensively to relieve excess hydrostatic pressure in pervious foundation strata overlain by impervious top strata, conditions which often exist landward of levees and downstream of dams and hydraulic structures. Placing well outlets in below-surface trenches or collector pipes helps dry up seepage areas downstream of levees and dams. Relief wells are often used in combination with seepage control measures, such as upstream blankets, downstream seepage berms, and grouting. Draining seepage water into relief wells decreases uplift and prevents piping. This study examined the effect of relief wells with different diameters at different distances downstream of a homogeneous earth dam using Seep/W software. Also the effect of upstream water level of reservoir on seepage flow to each well was carried out. Results show that by decreasing the distance between relief wells and increasing the diameter of the relief wells, total uplift pressure decreases. The optimum distance between relief wells to decrease uplift pressure was found to be 5 m. The proposed method is recommended in designing relief wells by providing optimum diameter and distance of wells for the sustained yield.

Comments: Macondo 5 Years Later

Editor's column The Macondo explosion and oil spill occurred 5 years ago this month, freezing activity in the US Gulf of Mexico and putting the industry in a negative spotlight for weeks. But, in addition to drawn-out legal consequences, the accident spawned new technology, improved safety practices, and better operations awareness. Some of the improvements are still a work in progress. On 20 April 2010, a blowout and explosion on the Deepwater Horizon rig on the Macondo prospect in the deepwater US Gulf of Mexico killed 11 crewmen. On 22 April, the rig sank, leaving the well gushing and causing the largest oil spill in US waters. The spill continued until 15 July when it was finally capped, and relief wells permanently sealed the well. Five years later, the impact of the disaster is clearer. Despite fears from some in the oil and gas industry, the accident and resulting regulation did not greatly harm US offshore oil output. The government temporarily stopped drilling in the US Gulf but operators were able to obtain new drilling permits within a year. Now, several large new oil projects are on the horizon, including ones by Shell, ExxonMobil, Hess, and Chevron. The new projects, with a potential to produce close to 1 million B/D, promise to return the Gulf into a major source of US production, although the greatest threat now is not regulation stemming from the oil spill but from the recent steep drop in oil prices. In 2001, the Gulf of Mexico accounted for a fourth of US oil output, but production has dropped since then because of well decline and the drop in permits issued after Macondo. With the recent dramatic rise in onshore unconventional output in the US, the Gulf now accounts for only about 10% of US oil production. But Macondo did hurt the industry’s reputation—the oil spill dominated news headlines for weeks. The recent concern about the safety of hydraulic fracturing operations and crude oil transport by pipeline or railcar stem in part from the fallout of the Macondo disaster. All of this plays into the industry’s “license to operate” in communities around the globe. Any dramatic, high news impact industry incident— upstream or downstream—heightens public awareness about industry operations and their potential impact. The industry has, in fact, improved operations since Macondo: new technologies have been developed to prevent and arrest blowouts and spills, and the industry has improved engagement with the public. The Macondo incident has also transformed risk management in offshore operations, although there is still work to be done, according to DNV GL. The consultancy maintains that there are still lessons to be learned from Macondo; for one thing, companies are tempted to skirt long-term management of risk for shorter-term decisions about profitability. The worry is that sharply lower oil prices will lead to cost cutting and neglecting safety ideas, which will make the industry even more vulnerable when the next Macondo comes around. JPT

Construction of relief wells under artesian flow conditions at dam toes: engineering experiences from Karkheh earth dam, Iran

We report engineering experiences from the critical task of relief well installation under high artesian flow conditions at the downstream toe of the Karkheh earth dam, Iran. Due to the establishment of excessive uplift pressure at the downstream toe of the Karkheh dam, installation of a series of new relief wells was considered to permanently relieve part of these pressures. The mentioned uplift pressure, as high as around 30 m above the ground level, was produced in a confined conglomerate aquifer bounded above and below by relatively impervious mudstone layers which reduced the safety factor of the dam toe to below 1.0. Investigations on the shortcomings of the old relief wells installed at the dam site showed that the main problems were: insufficient well numbers, insufficient well diameters, irregular well screens causing their blockage by time passing, and insufficient total opening area. Despite engineering difficulties and associated risk of downstream toe instability, installation of new relief wells was successfully completed under high artesian flow conditions” was successfully completed. The employed technique for the construction of the new relief wells under flowing artesian conditions was based on: 1) cement grouting and casing of the well, 2) telescopic drilling, 3) application of appropriate drilling fluid, and 4) controlling the artesian flow by adding a long vertical pipe to the top of the relief wells. Numerical modeling of seepage for the Karkheh dam foundation showed that, as a result of the installation of the new relief wells, the safety factor of the downstream toe increased to the safe value of 1.3 for the normal reservoir water level.

New Gyro While Drilling Technology Delivers Accurate Azimuth and Real-Time Quality Control for All Well Trajectories

Summary In response to the increasing demand for a reduction in the uncertainty of wellbore placement to minimize drilling risks and potential liabilities, a new gyroscopic survey tool capable of operating at any attitude during the drilling process has been developed: an all-attitude gyro while drilling (GWD) tool. Gyro survey systems determine the direction of the survey tool in the wellbore, the tool azimuth, by use of measurements of the horizontal components of Earth's rotation in a process known as gyrocompassing or north finding. Current GWD systems are based on angular rate measurements taken about two axes only. These measurement axes are perpendicular to the direction of the wellbore and perpendicular to each other. Although two-axis systems provide accurate estimates of azimuth near vertical, this accuracy degrades as inclination increases, with the azimuth becoming indeterminate because of a mathematical singularity at 90° inclination. To overcome this, an additional rate measurement about the along-hole axis of the tool needs to be performed. Only gyroscopic instruments with three orthogonal sensitive axes, as adopted in the new tool, are capable of measuring the full horizontal Earth rate signal in all wellbore geometries. This paper describes a number of innovative technological developments that have allowed all-attitude GWD to become a reality, including a new gyroscope designed specifically for the downhole drilling environment, a new system mechanization to control gyroscope biases, a signal-processing technique known as continuous adaptive processing that estimates the g-sensitive bias errors at each gyrocompass station, and a more robust quality control scheme. The new high angle GWD system is well-suited to handle any wellbore-placement needs. These include high inclination kickoffs, infill drilling, relief wells, and the provision of improved accuracy in east/west wells. With the improved reliability of the data comes increased confidence that the resulting survey is representative of the true wellbore trajectory. The detection of gross errors can also be accomplished by comparing real-time GWD and measurement-while-drilling (MWD) data. Further, with the memory multishot capability that is available, reliable high accuracy surveys from section total depth (TD) to surface are generated, verifying both MWD and GWD performance on the trip out and eliminating the need for separate and rig-time-dependent gyroscopic surveys. Finally, a number of case studies are presented to illustrate the performance capabilities of the new gyroscopic system over a range of well trajectories and latitudes. The all-attitude GWD system not only allows the survey-reliability goals to become a reality in a cost-effective manner—as set out in the earlier quality control papers published in conjunction with the SPE Well Positioning Technical Section—but also does this in real time while drilling.

0304 The NIEHS GuLF STUDY: Estimate of workers’ exposures through the inhalation route on seven response vessels near the well-site during the Deepwater Horizon oil spill

ObjectivesAfter the Deepwater Horizon, response vessels were brought near the wellhead area to stop the leak, collect oil and drill the relief wells. The objective of this paper is to...

Analysis of the Influential Factors of Waterlogging Caused by a Reservoir Impoundment and Evaluation of the Related Solutions

After the impoundment of large reservoirs, the cut-off wall, originally built into the bedrock to cope with the immersion effects, can block the river backwater zone and minimize the risk of the consequential submergence. However, it also hinders the groundwater at the reservoir bank from flowing into the river, resulting in some sort of waterlogging disasters and causing some impact on the crops and buildings alongshore. This paper mainly focuses on the following three factors, i.e. the water table of the backwater zone, the rising height of capillary water and the characteristics of infiltration and evaporation. All of them are the most straightforward factors of the waterlogging of a reservoir. To tackle the issue, the paper has proposed a solution that combines the relief wells and drainage channels on the basis of the numerical simulation methods.

Elemental chemistry of sand-boil discharge used to trace variable pathways of seepage beneath levees during the 2011 Mississippi River flood

Shortly after peak stage of the 2011 Mississippi River flood, water samples were collected from the river, from sand boils near the toe of the levee, and from actively flowing relief wells over a 55 km stretch north of Vicksburg, MS. Two distinct pathways for seepage under the levee were identified based on the elemental composition of water samples. Sand boil discharge was similar to water from relief wells only at a location where the levee sits on ancient channel fill deposits. Seepage at this site is forced along a deeper pathway beneath the fine-grained channel fill. Where the levee sits on sandy point bar deposits, shallow flow beneath the levee is unimpeded. The chemical composition of discharge from sand boils at these sites was clearly not just river water, nor a simple mixture of river and groundwater, but appears to reflect unique weathering or redox interactions occurring within the upper portion of the alluvial aquifer. Distinguishing shallow and deep seepage pathways may prove useful for evaluating site specific risk of levee failure.