Wellhead Area Research Articles

ОПРЕДЕЛЕНИЕ ПРОСТРАНСТВЕННОГО ПОЛОЖЕНИЯ УСТЬЕВ ЛИКВИДИРОВАННЫХ СКВАЖИН В АКВАТОРИИ ТАЗОВСКОЙ ГУБЫ МЕТОДОМ МАГНИТНОЙ СЪЕМКИ

The article presents the results of magnetometric engineering work at the Semakovsky subsoil block within the water area of the Taz Bay of the Kara Sea. The purpose of the work was to determine the coordinates of the exact location of the wellheads of 6 abandoned wells and to examine the wellhead area for the presence of foreign magnetic objects. This paper examines the procedure for finding abandoned wells using marine magnetic surveys and shows their reflection in an abnormal magnetic field. The relevance of the work is related to ensuring the environmental safety of the water area and the requirements of the Safety Rules in the oil and gas industry. To meet the requirements, it is necessary to check the technical condition of the wellheads of abandoned wells for the presence of hydrocarbon omissions. A diving survey of the area in the wellhead zone did not reveal any hydrocarbon passes, however, it confirmed the presence of a number of man-made objects near the wellheads identified by magnetic surveys. When working at shallow depths, the original configuration of the magnetometer was proposed and used.

Validation of oil fate and mass balance for the Deepwater Horizon oil spill: Evaluation of water column partitioning

Model predictions of oil transport and fate for the 2010 Deepwater Horizon oil spill (Gulf of Mexico) were compared to field observations and absolute and relative concentrations of oil compounds in samples from 900 to 1400 m depth <11 km from the well. Chemical partitioning analyses using quantitative indices support a bimodal droplet size distribution model for oil released during subsea dispersant applications in June with 74% of the mass in >1 mm droplets that surfaced near the spill site within a few hours, and 1–8% as <0.13 mm microdroplets that remained below 900 m. Analyses focused on 900–1400 m depth <11 km from the well indicate there was substantial biodegradation of dissolved components, some biodegradation in microdroplets, recirculation of weathered microdroplets into the wellhead area, and marine oil snow settling from above 900 m carrying more-weathered particulate oil into the deep plume.

Spatial targeting approach for a payment for ecosystem services scheme in a peri-urban wellhead area in southeastern Brazil

In recent years, payments for ecosystem services (PES) have emerged as a form of financing for the conservation of natural resources, compensating landowners that generate positive environmental externalities. For the PES design process, the spatial targeting approach for identifying priority areas aiming at the environmental recovery and preservation is essential for the efficient allocation of limited financial resources. In this sense, the present work aims to spatially identify priority areas for the implementation of PES schemes, with emphasis on the conservation of water resources, using as case study the Feijão River watershed (FRW), the primary water source for the city of São Carlos-SP, Brazil. For such, we performed a multicriteria evaluation in geographic information system (GIS) environment for mapping priority areas for forest restoration based on relevant criteria for the provision of hydrological services. We then cross-referenced the resulted information plan with estimated opportunity costs for compensating landowners in order to identify higher restoration priorities associated with low cost sites for PES implementation. The results show that 25.6% of the eligible areas have very high priority to forest restoration and are located mainly along the Feijão River watercourse, in direct recharge areas of the Guarani Aquifer System and with predominance of pasture and sugarcane uses, the main driving forces of erosion processes in the watershed. Among the agricultural activities, livestock presented the lowest opportunity cost (US$ 57.91 ha−1.year−1), and 99 rural properties with areas of interest for PES schemes were identified (3.7% of the watershed area), corresponding in full to the payment amount of US$ 52,018.08 per year to producers. Finally, the use of multicriteria evaluation combined with economic analysis of land use presented as a flexible and straightforward methodological approach, whose results can support further watershed planning and management.

Reservoir Stimulation Technique Combines Radial Drilling Technology With Acid Jetting

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202661, “Combination of Radial Drilling Technology With Acid Jetting: New Approach in Carbonate Reservoir Stimulation,” by Ayrat Bashirov, Ilya Lyagov, and Ilya Galas, Perfobur, prepared for the 2020 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, held virtually 9–12 November. The paper has not been peer reviewed. The complete paper describes an approach to stimulate carbonate formations with bedding water or a gas cap. The technique is a combination of acid jetting and a radial drilling technology that uses mechanical radial drilling with a slim mud motor. The primary advantages of the technology include controlled trajectory and the possibility of re-entry into channels. The novelty of the technology is in its ability to deploy acids in the rock far away from the wellbore through the mechanically drilled holes with known depths and azimuths. Reservoir Description The mature field is in central Russia in the Republic of Bashkortostan. The field contains both sandstone and carbonate reservoirs. Oil depth is from 780 to 1830 m. Six reservoirs are in development. This study concentrates on projects in a carbonate formation that is a substage of the early Pennsylvanian Period. This formation is highly heterogeneous with closely underlying water. Permeability of the reservoir is approximately 43 md; reservoir pressure is 1,000 psi, and oil density is 0.891 g/cm3. Two adjacent well candidates with identical reservoir properties were selected for the study, with a distance between wells of approximately 136 m. Net oil thickness in Well A is 4.4 m and 3 m in Well B. Mechanical Radial Drilling Technology The technology described by the authors uses mechanical radial drilling with a slim mud motor. The technology allows the drilling of a network of radial channels up to 15 m long with up to four channels of different trajectories on one level. The technical system features a modular construction for ease of assembly at the wellhead area and increased operational efficiency. The main elements of the technical system include the following: - Pipe pusher connected at the top with an overflow valve module and, at the bottom, with a guiding device connected by means of a hydraulic pusher - Flexible pipe assembly with a small (nonstandard) sectional mud motor - Drilling bit (milling cutter for window cutting) - Special whipstock and an anchor module with an orienting funnel connected from below to the pipe frame

3D SIMULATION OF THE THERMAL REGIME OF A GROUP OF GAS WELLS IN THE SREDNETYUNGSKOE FIELD

The thermal interaction between a group of gas wells and the permafrost ground was simulated using the finite element method for the conditions of the Srednetyungskoe field. For the spacings between the wellheads of 10 m, 15 m, and 20 m, thermal regimes for the gas and surrounding ground massif are forecasted for 30 years of operation. The feature of the present work is that atmospheric conditions and the effect of the wells are modeled simultaneously in 3D, allowing for accurate characterization of the wellhead area. Field data on the ground temperature, the bottomhole pressure and temperature, the production rate, the gas composition, thermophysical properties of the ground, and weather conditions are used as input parameters. Temperature profiles of the ground, the position of the thawing front, and timing of merger of the thawing halos around the wells are estimated. The results of the survey can be used in development planning of the field.

Современное минералообразование в месте разгрузки рассолов Людмилинской скважины (г. Соликамск, Пермский край)

The minerals formed from cold (4°C) sodium chloride solutions discharged between 1923 and 2019 from the Lyudmilinskaya brine-producing well were studied. During this time, the mineralization dropped from 260 to 9 g/dc3, and, at the wellhead area, an ecosystem presented by invertebrate animals, diatoms, iron and sulfur bacteria has been formed. Minerals, such as calcite and pyrite, and micron precipitates of native phases (sulfur, copper, silver, nickel, bronze), sulphides (series chalcocite- covelline, marcasite, argentopentlandite, acantite, millerite, chalcopyrite), sulfochlorides ((Ag,Cu,Ni)3(Cl,S)), chlorides (Ag3Cl), iron hydroxides, barite and sahamalit(Ce), were deposited both on the surface of pebbles and in clay-sand alluvial sediments. The studied brines are enriched with respect to sea water by siderophilic (Co, Ni), chalcophilic (Zn, Ge, As, Se, Sn, Sb, Bi, Pb, Tl (Cu?), and lithophilic elements (Be, Al, Ti, Cr, Mn, Y, Zr, Nb, W, Th). The increased concentration of these elements is explained by the hydrolysis and metal leaching the suprasalt clayey rocks with chlorides and sulfates. It is shown that the deposition of minerals occurs both chemically and biochemically.

Risk Assessment and Reduction for an Innovative Subsurface Well Completion System

In recent years, many oil and gas fields have been discovered in ultra-deep sea (UDS). Some of these fields are evaluated to have no commercial value if existing oil field development approaches are used, especially while the oil prices remain low. A new alternative field development solution, termed as Subsurface Well Completion (SWC) system, is proposed with the aim to produce oil and gas in a cost-effective manner in UDS. This system primarily consists of four parts: a tethered subsurface platform, the rigid riser, SWC equipment and flexible jumper. Obviously, central to the evaluation and application of the new SWC technology is the inherent risk relative to acceptance level. In particular, an uncontrolled release of hydrocarbons to sea, which may lead to catastrophical consequences involving personnel risk, environmental damage and economic losses, is a main contributor to the total risk and of great concern to the offshore petroleum industry. As for the new SWC system, any failure will not be a direct source of risk for the personnel on the surface installation due to its offset feature. In this context, this paper proposes a quantitative risk assessment (QRA) framework to assess such uncontrolled releases to sea with regard to the SWC system for an oil field in the production phase based on the new Subsurface Tension Leg Production (STLP) facility. According to the QRA results presented in this paper, the identified scenarios representing uncontrolled releases to sea are subsea wellhead leaks, rigid riser leaks, subsurface wellhead leaks, releases from X-mas tree and flexible jumper leaks. Among these scenarios, subsea wellhead is found to be the high-risk area. Compared with the established risk acceptance criteria (RAC), the environmental risk levels for the subsea wellhead’s leak lie within the As Low As Reasonably Practicable (ALARP) region while other risks are all below ALARP limits, which means that there is a need for improved consideration of the existing design with regard to the subsea wellhead area, and the corresponding risk reduction measures are proposed. Furthermore, the sources and effects of uncertainties are reviewed and sensitivity studies are carried out to illustrate the effect of some of the important assumptions in the risk model. It can be found that some assumptions made are conservative or optimistic while others are unknown. However, the final QRA results can be regarded as somewhat conservative. This paper concludes that the new SWC technology has a distinct advantage with respect to the leakage duration time in UDS, and thus mitigates the environmental and commercial impacts to a large extent. Besides, relaxed design requirements for the X-mas tree and flexible jumper can be accepted. It is also concluded that there are no serious and major commercial losses for all the identified accidental release scenarios, which is of great importance and attractiveness to oil producers.

Surface runoff and accelerated erosion in a peri-urban wellhead area in southeastern Brazil

Degradation of hydrological conditions can adversely impact water resource quality and quantity. This degradation can generate social and economic losses, including losses for users outside the basin area. Therefore, studies focusing on surface runoff and accelerated erosion processes are needed to enable interventions that address degradation-induced challenges. In the present study, the surface runoff and accelerated erosion potential of the Feijão River basin were presented in charts at a 1:50,000 scale. The Feijão River basin has an area of 243.16 km2 and is used as the main water source for the city of São Carlos, Brazil. Geoenvironmental attributes, such as substrate, climate, relief, soil, water bodies and land cover and use, were integrated and assessed in a GIS environment, using a multicriteria analysis and weighted sum tool. The results show that a large part of the area (86.12% of the basin) exhibits a low surface runoff potential and a moderate accelerated erosion potential. Accelerated erosive processes are triggered by changes in soil cover and have a direct relationship with the removal of existing vegetation and implementation of anthropogenic activities. In this case, as well as for most of the areas in southeastern Brazil, extensive grazing followed by sugar cane cultivation was the main driving force of erosion, acting as trigger for accelerated erosive processes at the water source area.

Concentrations of some heavy metals in underground water samples from a Nigerian crude oil producing community.

Pollution due to oil exploration activities in the Niger Delta region of Nigeria and government under-investments in potable water infrastructure has led to the dependence of the population on personal boreholes. Yet, there are little quality or surveillance reports on such waters. The concentrations of heavy metals in underground water samples from an oil producing area, Umuebulu, in the Niger Delta were therefore investigated. Water samples were collected from three test points, each approximately 300m from (1) wellhead area (WHA), (2) flare area (FA) and (3) effluent discharge area (EDA), and one control point located 10km away from any oil-related activity. The concentrations of lead, arsenic and cadmium were determined in the samples using atomic absorption spectrophotometry. All three heavy metals were present in the test, and control water samples at concentrations significantly (P<0.05) exceeding the maximum contaminant levels recommended by the World Health Organization. The total hazard index of the water samples showed that their consumption constituted significant health risks in the order EDA>FA>WHA>Control. Appropriate water treatment and surveillance is warranted and therefore recommended for underground water resources of the studied community.

Distinct Bacterial Communities in Surficial Seafloor Sediments Following the 2010 Deepwater Horizon Blowout.

A major fraction of the petroleum hydrocarbons discharged during the 2010 Macondo oil spill became associated with and sank to the seafloor as marine snow flocs. This sedimentation pulse induced the development of distinct bacterial communities. Between May 2010 and July 2011, full-length 16S rRNA gene clone libraries demonstrated bacterial community succession in oil-polluted sediment samples near the wellhead area. Libraries from early May 2010, before the sedimentation event, served as the baseline control. Freshly deposited oil-derived marine snow was collected on the surface of sediment cores in September 2010, and was characterized by abundantly detected members of the marine Roseobacter cluster within the Alphaproteobacteria. Samples collected in mid-October 2010 closest to the wellhead contained members of the sulfate-reducing, anaerobic bacterial families Desulfobacteraceae and Desulfobulbaceae within the Deltaproteobacteria, suggesting that the oil-derived sedimentation pulse triggered bacterial oxygen consumption and created patchy anaerobic microniches that favored sulfate-reducing bacteria. Phylotypes of the polycyclic aromatic hydrocarbon-degrading genus Cycloclasticus, previously found both in surface oil slicks and the deep hydrocarbon plume, were also found in oil-derived marine snow flocs sedimenting on the seafloor in September 2010, and in surficial sediments collected in October and November 2010, but not in any of the control samples. Due to the relative recalcitrance and stability of polycyclic aromatic compounds, Cycloclasticus represents the most persistent microbial marker of seafloor hydrocarbon deposition that we could identify in this dataset. The bacterial imprint of the DWH oil spill had diminished in late November 2010, when the bacterial communities in oil-impacted sediment samples collected near the Macondo wellhead began to resemble their pre-spill counterparts and spatial controls. Samples collected in summer of 2011 did not show a consistent bacterial community signature, suggesting that the bacterial community was no longer shaped by the DWH fallout of oil-derived marine snow, but instead by location-specific and seasonal factors.

Root causes of hydrocarbon leaks on offshore petroleum installations

Hydrocarbon leaks on offshore installations may result in severe consequences to personnel, to the environment and to assets. In order to prevent such leaks, it is crucial to understand their root causes. The objective of this paper is to study the circumstances of hydrocarbon leaks on the Norwegian continental shelf (NCS). In the study, all reported hydrocarbon leaks from process inventories on all offshore installations on the NCS, with an initial leak rate higher than 0.1 kg/s in the period 2008–2014, have been considered. This includes 78 hydrocarbon leaks, of which about 60% have occurred during manual intervention on normally pressurized systems. The dominating activity when leaks occur is preventive maintenance. A significant fraction of the leaks occur during the preparation for maintenance; such a preparation is typically carried out during the night shift. About half of the leaks are associated with wellhead area and manifolds, separation and compression systems. A substantial fraction of the leaks can be associated with verification faults, dominated by the failure to comply with procedural requirements that are needed to carry out independent verification.

Influences of heterogeneity on three-dimensional groundwater flow simulation and wellhead protection area delineation in karst groundwater system, Taiyuan City, Northern China

Karstic limestone formation in Lancun spring area is one of the most important drinking water resources for Taiyuan City in Shanxi Province. The mapping of drinking water-protected areas is an effective way to protect drinking water sources. In this study, Lancun spring area in Taiyuan City was considered as a case study. Considering geological deposition and hydrogeological characteristics of this area, the stochastic idea was introduced to structural model establishment to determine the heterogeneity of karst groundwater system and clarify medium parameters. To analyze the influence of heterogeneity on groundwater flow simulation and wellhead-protected area delineation, homogeneous and stochastic hydrogeological parameter models were established and coupled with groundwater flow simulation models. Particle tracer analysis could be performed to determine capture zone. Results showed that stochastic methods could be used to generate a series of possible flow head field distributions and delineate a series of capture zones compared with homogeneous methods; thus, probability distribution was observed instead of a deterministic area. This result could provide a more scientific basis for the design and assessment of protective measures for wellhead areas in karst groundwater systems.

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...

Experiments on Large-Scale Fires Reveal Benefit of Greater Water Deluge

This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 164973, ’The Effect of Deluge Spray Systems on Large-Scale Fires,’ by Stian Hoiset and Eli Glittum, Statoil, prepared for the 2013 SPE European HSE Conference and Exhibition, London, 16-18 April. The paper has not been peer reviewed. A series of 56 large-scale fire experiments in the range of 40–120 MW has been carried out in a generic offshore module. The effect of deluge fire-water application has been measured for different setups. Both deluge nozzle type and water-application rate have been varied in the experiments. Introduction The use of water-spray systems for fire-fighting is standard for most offshore oil and gas installations. The requirements to and guidelines for control and mitigation of fires are stated in International Organization for Standardization (ISO) 13702, Petroleum and Natural Gas Industries—Control and Mitigation of Fires and Explosions on Offshore Production Installations—Requirements and Guidelines. Appendix C in ISO 13702 lists the recommended fire-water-application rates for areas and rooms on an oil- or gas-production installation. Typically, the minimum recommended water-application rate is listed as 10 (L/min)/m. NORSOK Standard S-001, applicable for installations on the Norwegian continental shelf, states that the effect of deluge may be taken into account for process equipment and piping, provided that there is proper documentation of the fire-water effect (and that there are requirements to the reliability of the fire-water system). In order to document the effect of the recommended fire-water-application rate, a set of full-scale fire experiments with application of fire water was carried out at SINTEF NBL. Background Today’s design of oil- or gas-production installations includes deluge-fire-water systems as standard. These are costly and may require extensive maintenance. Despite the costs involved, little knowledge is available on the actual effect of fire-water systems under different operating conditions. Appendix C in ISO 13702 recommends a typical water-application rate of 10 (L/min)/m. National Fire Protection Association (NFPA) 15: Standard for Water Spray Fixed Systems for Fire Protection recommends a design objective for control of burning of not less than 20 (L/min)/m. NORSOK S-001 refers to NFPA 15 but prescribes 10 (L/min)/m for process areas and equipment surfaces and 20 (L/min)/m for the wellhead area. American Petroleum Institute (API) 2030, Guidelines for Application of Water Spray Systems for Fire Protection in the Petroleum Industry, prescribes 20 (L/min)/m where pumps are present and 10 (L/min)/m for pipe racks and piping. To what extent do these water-application rates actually affect the fire?

Applicability of a Surveillance Methodology for the Microbiological Safety of Well Water Supplies, in a Highly Vulnerable Hydrogeological Setting——A Case Study Based Findings from the West Coastal Area of Sri Lanka

A well surveillance study carried out in nine Divisional Secretariat Divisions on the west coast of Sri Lanka showed that 70.3% of 101 well sampling points were microbially contaminated with equal to, or greater than, faecal coliform grade C (11 - 100 cfu/100 mL). Due to the very vulnerable hydro-geological setting of the coastal sand, laterite and alluvium aquifers occurring in the study areas, the recommended safe separation distance between an on-site sanitation system and a well could not be achieved. Hence, a cardinal rule of well protection was observed to be broken at almost every well study site. The existing excreta disposal systems need to be improved or replaced with more efficient ones before the impact of other sanitary hazards at the well, and wellhead area, on the microbial quality of well water, can be determined and addressed. The published (WHO, 1997) sanitary survey forms for open dug wells and tube wells need to be modified in the context of the study areas described. Based on a comparison of three different statistical methods used to assess the relative significance of each sanitary hazard modification to the methodology for determining the sanitary hazard index (SHI) was prescribed.

LARGE-BORE GAS WELL DESIGN—APPLICATION TO OFFSHORE GAS FIELD DEVELOPMENT

Offshore gas development projects including the North West Shelf of Australia continue to develop new technologies in order to reduce development costs. Given that the number of development wells directly relates to capital expenditure, past attempts have focussed on obtaining higher gas rates out of conventional well designs by carefully managing erosional limits, which, in turn, tend to restrict the use of higher offtake rates.A strategy based on safely flowing gas wells at higher rates results in fewer wells and delays the phasing-in of additional wells, both of which result in economic enhancement. In recent times the industry has increasingly moved to large-bore gas well technology as a means of realising this strategy. Large-bore gas wells are defined as wells equipped with production tubing and flow control devices larger than 7” or 177 mm. Originally developed for land-based operations, this technology is increasingly moving offshore into totally subsea systems. One factor limiting the speed of adoption of this technology is the trade-off that exists between the increased offtake rates offered by large-bore systems and the risks posed by wear due to erosion in and around the wellhead area caused by any solids entrained in the gas stream.The problem becomes more acute when different-sized well designs employ the same wellhead configurations, because the upper wellhead area is usually the critical and limiting wear component.This paper summarises the recent developments in large-bore offshore applications and presents a consistent methodology showing how different gas well designs can be compared using hydraulic and erosional considerations. Additional trade-offs posed by reliable solids monitoring and the adoption of untested wellhead and intervention designs are discussed. In many cases, hybrid designs based on large diameter tubulars but with conventional wellheads may offer a useful balance between higher well rates and adoption of proven technology. The results shown here are directly applicable to alternative well designs presently under consideration for a number of offshore reservoir developments.

Wellhead protection area delineation using a coupled GIS and groundwater model

The 1986 Amendments to the United States Safe Drinking Water Act (SDWA) made wellhead protection an important issue for water suppliers in the US. These Amendments mandate that each State develop a wellhead protection program (WHPP) to protect the wellhead areas of all public water systems from contaminants that may have adverse human health effects. Data requirements to support a WHPP can become unwieldy without the benefit of a system that can handle large databases involving spatial relationships. Geographic information systems (GIS) store, analyse, map and illustrate data sets of complex spatial information, and can therefore be used to integrate and analyse various types of spatial data needed to delineate wellhead protection areas. The Cheyenne-Arapaho tribe has initiated a study of the groundwater resources on the Concho Reserve in Canadian County, Oklahoma, US. Groundwater within the Concho Researve is vulnerable to contamination because of the high permeability of the alluvial aquifer associated with the North Canadian River. Pollutants of concern are associated with industrial agricultural and domestic sources in the recharge area.This paper describes the development of an interface allowing the Cheyenne-Arapaho tribe to delineate and manage wellhead protection areas (WHPAs). The system described herein provides for two modes of operation. The first, in which a well site is selected and possible sources of contamination are identified, is termed the forward problem. The second, where the ensemble area of possible well sites for which no known sources of contamination exist, is termed the backward problem. The system developed provides efficient management and protection of tribal drinking-water resources.1998 Academic Press

Radon in Quaternary Aquifers Related to Underlying Bedrock Geology

AbstractA survey of radon concentrations in water abstracted from 31 of Norway's largest waterworks, using ground water from Quaternary fluvial and glaciofluvial sediments, returned values of between 0.4 Bq/L and 83 Bq/L, with a median of 23 Bq/L. Significantly higher Rn concentrations were present in ground water from Quaternary aquifers underlain by gneissic and granitic lithologies compared with those underlain by metasandstones, phyllites and mica schists. Compared to the recommended national action level of 500 Bq/L and concentrations of up to 19,900 Bq/L, which have been detected in boreholes in Norwegian granite aquifers, the concentrations measured in Quaternary aquifers are regarded as unproblematic for consumers, although a more detailed assessment may be required for workers spending a lot of time in wellhead areas.

Integrated borehole logging methods for wellhead protection applications

Modeling of ground water infiltration and movement in the wellhead area is a critical part of an effective wellhead protection program. Such models depend on an accurate description of the aquifer in the wellhead area so that reliable estimates of contaminant travel times can be used in defining a protection area. Geophysical and hydraulic measurements in boreholes provide one of the most important methods for obtaining the data needed to specify wellhead protection measures. Most effective characterization of aquifers in the wellhead vicinity results when a variety of geophysical and hydraulic measurements are made where geophysical measurements can be calibrated in terms of hydraulic variables, and where measurements are made at somewhat different scales of investigation. The application of multiple geophysical measurements to ground water flow in the wellhead area is illustrated by examples in alluvial, fractured sedimentary, and fractured crystalline rock aquifers. Data obtained from a single test well are useful, but cannot indicate how conductive elements in the aquifer are connected to form large-scale flow paths. Geophysical and hydraulic measurements made in arrays of observation boreholes can provide information about such large-scale flow paths, and are especially useful in specifying aquifer properties in wellhead protection studies.

The use of ancrod to prevent thrombosis on prosthetic heart valves: An experimental study

<h3>Objectives</h3> After 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 characterise inhalation exposure on these vessels for various exposure groups (EGs) to total hydrocarbons (THCs). <h3>Method</h3> Approximately 100 EGs based on job title group, tasks and time period during the response effort were standardised across these vessels. Descriptive statistics were calculated from the measurements for each EG on each vessel. Since many of the data were censored (i.e., below the limit of detection), a Bayesian method was used to obtain estimates for the arithmetic mean (AM), geometric mean, and geometric standard deviation. <h3>Results</h3> During the first time period (April 20–May 14), the range of the AMs on the vessels was 1.9–24.2 ppm THC. Exposures were lower during the second period (May 15–July 15) when dispersant was used to reduce air concentrations (0.1–14.6 ppm). After top-capping the well, a substantial reduction was observed on all seven ships (0.1–1.9 ppm). After bottom capping (&gt;August 10), exposures generally increased on the ships (0.1–3.8 ppm), most likely due to decontamination activities. The vessel capping the well and the vessel burning waste oil and gas had significant differences from the vessels drilling the relief wells. <h3>Conclusions</h3> Differences were found by vessel and time period that likely reflected oil weathering and differences in job and vessel activities.