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1.
The impact of lost circulation during rotary drilling near an existing monitoring well cluster was evaluated by periodic measurements of water levels and contaminant concentrations at the well cluster. Due to regulatory concerns, changes in water levels or VOC concentration in the well cluster during drilling would trigger monitoring well redevelopment. The borehole was drilled approximately 30 feet northeast of four nested monitoring wells that screen Devonian and Silurian carbonate bedrock at depths of 15, 60, 130, and 190 feet. Following complete circulation loss at depths of 177 and 1 S3 feet in the borehole, a rapid decrease in water levels was observed in the upper three monitoring wells. The water level in the well that was screened through the lost circulation zones increased slightly.
Decreasing water levels in formations located above the point of circulation loss appear to occur in response to a sudden decrease in borehole fluid pressure caused by the flow of drilling fluid into the formation. The relative contribution of contaminated formation water lo the borehole can be estimated by using the time-drawdown relationship and estimates of transmissivity. At the point of circulation loss, significant dilution of contaminant concentrations occurs from the loss of drilling fluid into the contaminated zone. Contaminated formation water entering the borehole during periods of complete lost circulation may mobilize contaminants from upper lo lower formations. Lost circulation into a formation would be signaled by a water level increase in monitoring wells. The wells would subsequently require development to remove the volume of fluid lost to the formation, including both drilling fluid and contaminated formation water. Monitoring wells exhibiting declining water levels following lost circulation would not require development since drilling water has not entered the zones screened by these wells.  相似文献   

2.
A New Multilevel Ground Water Monitoring System Using Multichannel Tubing   总被引：5，自引：0，他引：5  
A new multilevel ground water monitoring system has been developed that uses custom-extruded flexible 1.6-inch (4.1 cm) outside-diameter (O.D.) multichannel HOPE tubing (referred to as Continuous Multichannel Tubing or CMT) to monitor as many as seven discrete zones within a single borehole in either unconsolidated sediments or bedrock. Prior to inserting the tubing in the borehole, ports are created that allow ground water to enter six outer pie-shaped channels (nominal diameter = 0.5 inch [1.3 cm]) and a central hexagonal center channel (nominal diameter = 0.4 inch [1 cm]) at different depths, facilitating the measurement of depth-discrete piezometric heads and the collection of depth-discrete ground water samples. Sand packs and annular seals between the various monitored zones can be installed using conventional tremie methods. Alternatively, bentonite packers and prepacked sand packs have been developed that are attached to the tubing at the ground surface, facilitating precise positioning of annular seals and sand packs. Inflatable rubber packers for permanent or temporary installations in bedrock aquifers are currently undergoing site trials. Hydraulic heads are measured with conventional water-level meters or electronic pressure transducers to generate vertical profiles of hydraulic head. Ground water samples are collected using peristaltic pumps, small-diameter bailers, inertial lift pumps, or small-diameter canister samplers. For monitoring hydrophobic organic compounds, the CMT tubing is susceptible to both positive and negative biases caused by sorption, desorption, and diffusion. These biases can be minimized by: (1) purging the channels prior to sampling, (2) collecting samples from separate 0.25-inch (0.64 cm) O.D. Teflon sampling tubing inserted to the bottom of each sampling channel, or (3) collecting the samples downhole using sampling devices positioned next to the intake ports. More than 1000 CMT multilevel wells have been installed in North America and Europe to depths up to 260 feet (79 m) below ground surface. These wells have been installed in boreholes created in unconsolidated sediments and bedrock using a wide range of drilling equipment, including sonic, air rotary, diamond-bit coring, hollow-stem auger, and direct push. This paper presents a discussion of three field trials of the system, demonstrating its versatility and illustrating the type of depth-discrete data that can be collected with the system.  相似文献   

3.
An investigation of elevated concentrations of nickel and chromium in certain ground water samples collected at Williams Air Force Base (AFB) indicated that type 304 stainless steel well materials are the source. Chloride in the ground water has apparently caused crevice corrosion of the stainless steel well screens installed during site characterization. An evaluation of site geochemistry suggested that chromium released from the well screen would precipitate, while nickel would remain dissolved. Thus, low-flow purging and sampling significantly reduces the chromium found in the ground water samples because such sampling minimizes the collection of artificially entrained particulates. In contrast to chromium, nickel concentrations did not decrease during low-flow purging and sampling, indicating that it is dissolved. Nickel and chromium concentrations are both low following high-volume purging when turbidity levels are stabilized below 10 nephelometric turbidity units prior to sampling. In the latter case, chromium concentration is low because particulate collection is minimized, and nickel concentration is low because of increased dilution. Based on these results, it is recommended that elevated levels of nickel and chromium in ground water samples collected from stainless steel monitoring wells be carefully evaluated, because well materials may be the source. In addition, although low-volume purging is increasingly becoming the sampling method of choice, high-volume purging may be a useful means of determining whether the well materials influence nickel and chromium concentrations.  相似文献   

4.
The progressive packer/zone sampling method was used to identify the bottom of a plume of volatile organic compounds (VOCs) in the parts-per-million (ppm) range using one well in each of three separate locations. The method involves progressively drilling a 20-foot length of borehole through casing, setting an inflatable packer at the top of the drilled zone, purging the zone of three volumes of water using the airlift method, sampling the zone in situ through the packer string using a bailer, then repeating the procedure.
A plume consisting of chlorinated VOCs, alcohols, and vinyl chloride occurs in a low-yielding fractured bedrock aquifer located in the Passaic Formation at a site in central New Jersey. The thickness of the plume in total VOC concentrations exceeding 1 ppm was determined using the progressive packer/zone sampling method to a depth of 200 feet. The first borehole was completed as a monitoring well in the "hottest" zone encountered during testing. Additional wells were then clustered with this exploratory well to delineate the plume in the parts-per-billion (ppb) range. Cross contamination from previously sampled zones was not a problem as long as total VOCs in the ppm range were targeted and the sample interval was properly purged.
Instead of using a multiple well cluster consisting of an indefinite number of wells to determine the bulk thickness of a plume at a specific location, information from one borehole may suffice during the exploratory phase. Costs to the client and cross contamination potential to the aquifer can be minimized by limiting the number of boreholes needed for vertical delineation.  相似文献   

5.
Twenty monitoring wells were installed in fine-grained glacial till at two sites in southeastern Wisconsin to study the effects of monitoring well construction, installation, and development on the amount of fine-grained suspended material in the well. The types of well screens used were continuous slot, factory slot, factory slot with a filter wrap, and porous piezometer tips. Some of the wells were installed before the open borehole began to fill with water; others were installed after the water levels in the lower section of the borehole had begun to rise. About half of the wells were developed by surging while the others were simply bailed without surging. Installation of the wells in the initially dry holes resulted in wells that yielded samples with very low turbidity compared to wells installed in wet holes. Water samples from wells that were surged were more turbid than those that were not. The type of construction materials investigated had no effect on the turbidity of samples from the wells.  相似文献   

6.
State-of-the-art analytical techniques are capable of detecting contamination In the part per billion (ppb) range or lower. At these levels, a truly representative ground water sample Is essential to precisely evaluate ground water quality. The design specifications of a ground water monitoring system are critical in ensuring the collection of representative samples, particularly throughout the long-term monitoring period.
The potential interfaces from commonly used synthetic well casings require a thorough assessment of site, hydrogeology and the geochemical properties of ground water. Once designed, the monitoring system must be installed following guidelines that ensure adequate seals to prevent contaminant migration during the installation process or at some time in the future. Additionally, maintaining the system so the wells are in hydraulic connection with the monitored zone as well as periodically Inspecting the physical integrity of the system can prolong the usefulness of the wells for ground water quality. When ground water quality data become suspect due to potential interferences from existing monitoring wells, an appropriate abandonment technique must be employed to adequately remove or destroy the well while completely sealing the borehole.
The results of an inspection of a monitoring system comprised of six 4-inch diameter PVC monitoring wells at a hazardous well facility Indicated that the wells were improperly installed and in some cases provided a pathway for contamination. Subsequent down hole television inspections confirmed inaccuracies between construction logs and the existing system as well as identified defects in casing materials. An abandonment program was designed which destroyed the well casings in place while simultaneously providing a competent seal of the re-drilled borehole.  相似文献   

7.
Diffusion samplers installed in observation wells were found to be capable of yielding polyethylene to transmit other volatile compounds, such as benzene and toluene, indicates that the samplers can be used for a variety of volatile organic compounds. In wells at the study area, the volatile organic compound concentrations in water samples obtained using the samplers without prior purging were similar to concentrations in water samples obtained from the respective wells using traditional purging and sampling approaches. The low cost associated with this approach makes it a viable option for monitoring large observation-well networks for volatile organic compounds.  相似文献   

8.
Hydrogen gas was discovered within the steel casing above standing water in a percussion-drilled borehole on the Hanlord Site in south-central Washington state. In situ measurements of the borehole fluids indicated anoxic, low-Eh (<-400 mV) conditions. Ground water sampled from adjacent wells in the same formation indicated that the ground water was oxygenated. H2 was generated during percussion drilling, due to the decomposition of borehole waters as a result of aqueous reactions with drilled sediment and steel from the drilling tools or casing. The generation of H2 within percussion-drilled boreholes that extend below the water table may be more common than previously realized. The ambient concentration of H2 produced during drilling was limited by microbial activity within the casing-resident fluids. H2 was generated abiotically in the laboratory, whereby sterilized borehole slurry samples produced 100 times more H2 than unsterilizcd samples. It appears that H2 is metabolized by microorganisms and concentrations might be significantly greater if not for microbial metabolism.  相似文献   

9.
Dual-wall reverse-circulation drilling uses flush-threaded double-wall drill pipe and high-pressure air to provide continuous return of formation and water samples. Cuttings and formation waters are not contaminated with drilling additives or mixed with other borehole material. Up-hole velocity of about 70 ft/sec provides reliable logging of water, mineral or contaminant-bearing strata. Water samples representative of specific strata may be airlifted or bailed to the surface.
In the percussion hammer system, dual-wall drill pipe is advanced through chiefly unconsolidated material by the percussion action of an above-ground pile hammer. The borehole is drilled and temporarily cased in one pass. Wells or monitoring devices are installed as the drill pipe is hydraulically retracted during construction. A rotary head may be adapted as an option to allow dual-wall rotary drilling into consolidated or crystalline formations through a percussion hammer drill string temporarily left in place as a conductor.
The complex geology and variety of geoenvironmental problems in southern California has provided a testing ground for dual-wall drilling on hazardous material site investigations. Several case histories have demonstrated the capabilities and versatility of this method, including: (1) the installation of 4-inch and 6-inch diameter gasoline monitoring and recovery wells through gravels and cobbles at a filling station where hollow-stem auger drilling failed; (2) the confirmation of a dry borehole initially drilled by direct rotary at a landfill; and (3) multiple installations of monitoring devices through municipal refuse at a city of Los Angeles landfill.  相似文献   

10.
Monitoring well sand packs are theoretically capable of retarding metal ions and organic contaminants. If this retardation does indeed occur it may have a significant effect on the purging requirements of newly installed monitoring wells. Calculations based on mass balance and retardation concepts demonstrate that if common guidelines for well purging are followed, contaminants may not be detected or may be detected in lower concentrations than are actually present in the ground water. This problem is greatest in relatively shallow wells installed in low to moderate permeability materials. In most cases, the effect of solute retardation in the sand pack can be avoided simply by additional purging prior to the first sampling of the monitoring well. Common purging guidelines can then be applied to subsequent samplings. The methodology outlined in this paper can be used to calculate the purging requirements of existing monitoring wells or it may be applied to alternative monitoring well designs to test which will require the smallest volume of purged water.  相似文献   

11.
Hole stability problems occurring during construction of monitoring wells in coarse, unconsolidated alluvium can be overcome by using a drill-through casing driver mounted on a standard top-head drive rotary rig. Steel casing is driven contemporaneously with drilling, providing continuous hole stability. Samples of aquifer material and ground water can be taken at discrete depths as drilling proceeds. Monitoring well completion is accomplished by: (1) using the steel casing as an open-ended piezometer; (2) installing a telescoping well screen; (3) plugging the casing end and perforating desired intervals, (4) installing one or more smaller diameter wells, and then (5) pulling back the steel casing. Advantages of this drilling method include maintenance of hole stability during drilling and well completion, faster borehole construction time than traditional methods in coarse alluvial deposits and other poorly sorted formations, and collection of representative samples of the geologic formations and ground water; additionally, drilling fluids are not required.  相似文献   

12.
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13.
Hollow-stem augers are a widely used drilling method for constructing monitoring wells in unconsolidated materials. The drilling procedures used when constructing monitoring wells with hollow-stem augers, however, are neither standardized nor thoroughly documented in the published literature.
Variations in drilling procedures and techniques may occur as a result of the: (1) type of auger drill equipment and formation samplers used; (2) hydrogeologic conditions at the site, especially where heaving sands occur; and (3) known or suspected presence of contaminated zones, where there is a potential for the vertical movement of contaminants within the borehole.
In a saturated zone in which heaving sands occur, changes in equipment and drilling techniques are required to provide a positive pressure head of water within the auger column. This may require the addition of clean water or other drilling fluid inside the augers.
When monitoring the quality of ground water below a known contaminated zone, hollow-stem auger drilling may not be advisable unless protective surface casing can be installed. Depending on the site hydrogeology, conventional hollow-stem auger drilling techniques alone may not be adequate for the installation of the protective surface casing. A hybrid drilling method may be needed that combines conventional hollow-stem auger drilling with a casing driving technique that advances the borehole and surface casing simultaneously.  相似文献   

14.
The reliability of filter pack and annular seal emplacements, and the degree of integrity of installed seals, are two of the most important factors to be considered when both installing and later utilizing ground water monitoring wells.
Numerous, and often costly, problems of using existing methods of installing filter packs and annular seals during the construction of ground water monitoring wells have led to the development of a technique of installing these monitoring well components using a dry injection system.
The dry injection system has been used to construct monitoring wells in extremely complex overburden/bedrock environments with a variety of drilling techniques. The system has shown that a high degree of reliability in the, construction of monitoring wells and greater confidence in obtaining representative ground water samples can be achieved over existing methods of filter pack and annular seal emplacement. The system has also been more cost effective than existing methods, especially for deep boreholes and multilevel monitoring system installations.  相似文献   

15.
Boreholes drilled through contaminated zones in fractured rock create the potential for vertical movement of contaminated ground water between fractures. The usual assumption is that purging eliminates cross contamination; however, the results of a field study conducted in a trichloroethylene (TCE) plume in fractured sandstone with a mean matrix porosity of 13% demonstrates that matrix-diffusion effects can be strong and persistent. A deep borehole was drilled to 110 m below ground surface (mbgs) near a shallow bedrock well containing high TCE concentrations. The borehole was cored continuously to collect closely spaced samples of rock for analysis of TCE concentrations. Geophysical logging and flowmetering were conducted in the open borehole, and a removable multilevel monitoring system was installed to provide hydraulic-head and ground water samples from discrete fracture zones. The borehole was later reamed to complete a well screened from 89 to 100 mbgs; persistent TCE concentrations at this depth ranged from 2100 to 33,000 microg/L. Rock-core analyses, combined with the other types of borehole information, show that nearly all of this deep contamination was due to the lingering effects of the downward flow of dissolved TCE from shallower depths during the few days of open-hole conditions that existed prior to installation of the multilevel system. This study demonstrates that transfer of contaminant mass to the matrix by diffusion can cause severe cross contamination effects in sedimentary rocks, but these effects generally are not identified from information normally obtained in fractured-rock investigations, resulting in potential misinterpretation of site conditions.  相似文献   

16.
The HydraSleeve is a sampling device for collecting groundwater from the screened interval of a monitoring well without purging that uses a check valve to take in water over the first 3 to 5 feet of an upward pulling motion. If the check valve does not perform as expected, then the HydraSleeve has the potential to collect water from an incorrect depth interval, possibly above the screened interval of the well. We have evaluated volatile organic chemical (VOC) results from groundwater samples collected with the HydraSleeve sampler compared to other methods for sampling monitoring wells at three sites. At all three sites, lower VOC concentration results were observed for samples collected using the HydraSleeve. At two of these three sites, the low concentration sample results were most strongly associated with monitoring wells with more than 10 feet of water above the monitoring well‐screened interval. At the site with the largest dataset, the median bias for samples collected with HydraSleeve was ?20% (p < 0.001). At this site, a bias of ?26% (p < 0.001) was observed for the subset of monitoring wells with greater than 10 feet of water above the screened interval compared to a bias of ?7% (p = 0.21) for wells screened across the top of the water table. In addition to lower VOC concentrations, the monitoring records obtained using the HydraSleeve were more variable compared to monitoring records obtained using purge sampling methods, a characteristic that would make it more difficult to determine the long‐term concentration trend in the well.  相似文献   

17.
Lost circulation, the inadvertent injection of drilling fluids into a highly permeable and/or fractured aquifer during rotary drilling, may result in collection of spurious information if the lost drilling fluids are not adequately purged before sampling the ground water. The purpose of this study was to determine whether removal of the volume of water lost during coring of a monitoring well in the carbonate Scotch Grove Formation (Silurian, east central Iowa) necessarily ensures collection of representative ground water samples. To monitor dilution of the ground water due to lost circulation, rhodamine dye was added to the drilling water and dye recovery was measured in samples collected during purging of five separate 5- to 10-foot intervals.
Circulation loss occurred in all five intervals, ranging from nearly 200 gallons in the upper permeable portion of the Scotch Grove to 25 gallons in the less permeable Buck Creek Member below. When the volume of water purged from the upper three intervals corresponded to the volume of water lost during coring, the purge water still contained 11 to 20 percent dyed drilling water. As purging continued, the proportion of drilling water in the samples decreased slowly. After purging more than 200 gallons of water, 86 to 98 percent of the dyed drilling water was recovered from the five test intervals. Four traditionally measured water quality parameters-pH, temperature, specific conductance, and dissolved oxygen — were less useful than the dye recovery for distinguishing drilling water from formation water in those zones in which the ground water quality was similar to the drilling water. These results indicate that the determination of the quantity of water to be purged prior to sampling must be based, at least in part, on aquifer lithology and hydraulic characteristics.  相似文献   

18.
在定向井中,双侧向测井数据由于受井眼、围岩、井斜、径向侵入等环境因素的影响,难以准确地估算储层的电阻率和更准确地识别储层流体.本文拟提出图版法和反演法相结合的思路来研究地层视电阻率的校正问题.首先,针对研究区的测井环境和钻井液电阻率,计算了不同尺寸井眼的双侧向测井响应,绘制了井眼校正图版;然后,针对斜度井地层模型,采用三维有限元方法计算了不同井斜、不同厚度地层的测井响应,构建了井斜-围岩/层厚图版,利用该图版实现了井眼校正和井斜-围岩/层厚的电阻率快速校正.最后,针对钻井液侵入的影响,采用反演方法计算了侵入半径和地层真电阻率,最终实现了双侧向测井的环境校正.利用上述理论与方法对海洋中定向井的双侧向测井资料进行了环境校正,提高了储层流体定性识别和定量评价的精度.  相似文献   

19.
Two borehole geophysical methods—electromagnetic induction and natural gamma radiation logs—were used to vertically delineate landfill leachate plumes in a glacial aquifer. Geophysical logs of monitoring wells near two land-fills in a glacial aquifer in west-central Vermont show that borehole geophysical methods can aid in interpretation of geologic logs and placement of monitoring well screens to sample landfill leachate plumes.
Zones of high electrical conductance were delineated from the electromagnetic log in wells near two landfills. Some of these zones were found to correlate with silt and clay units on the basis of drilling and gamma logs. Monitoring wells were screened specifically in zones of high electrical conductivity that did not correlate to a silt or clay unit. Zones of high electrical conductivity that did not correlate to a silt or clay unit were caused by the presence of ground water with a high specific conductance, generally from 1000 to 2370 μS/cm (microsiemens per centimeter at 25 degrees Celsius). Ambient ground water in the study area has a specific conductance of approximately 200 to 400 μS/cm. Landfill leachate plumes were found to be approximately 5 to 20 feet thick and to be near the water table surface.  相似文献   

20.
Fracture aperture is an important transport property in subsurface hydrology because it influences well productivity and the volume of the water resource. Nuclear magnetic resonance (NMR) well logging measures the hydrogen‐bearing fluid molecules in porous or fractured strata, and the NMR signal intensity increases with the amount of fluid in the sensed region of the NMR sonde. Fluid confined in a large fracture of >>0.2 mm in aperture has T2 (i.e. spin‐spin relaxation time) values as long as those of the bulk fluid. The bulk‐fluid porosity (i.e. porosity calculated using this long T2 component in a T2 histogram data) increases linearly with aperture. Therefore, NMR logging enables quantitative estimation of fracture apertures of >>0.2 mm using the bulk‐fluid porosity data if the calibration of the NMR sonde is performed adequately. We applied NMR logging to a borehole in a Holocene andesite lava at Sumikawa, Japan, to estimate the aperture of open fractures within the lava. A test well of 100 m depth and 20 cm diameter, filled with bentonite drilling mud, was scanned with an NMR sonde to obtain a profile of the porosity and the T2 histogram of the andesite. The bulk‐fluid porosity was calculated from the T2 histogram data, as the porosity at which the T2 value is larger than or equal to a threshold T2 of bulk bentonite mud. The bulk‐fluid porosity of a specific inclined fracture responsible for the total loss of circulation at 61.2 m depth during drilling was calculated assuming a threshold or T2 cut‐off of 33 ms, and again for a cut‐off of 100 ms. Calibration of the NMR sensor in a laboratory and measurement of the fracture dip angle by electrical microimaging logging enabled us to estimate the fracture aperture as 1.7 cm, assuming a T2 cut‐off of 33 ms, or 1.6 cm for a T2 cut‐off of 100 ms. The method of aperture determination described in this study is independent of fluid species and lithology, and is applicable to various hydrogen‐bearing borehole fluids (clean water, mud and oil) and geological settings.  相似文献   

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