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12th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 14 Mar 1999 - 18 Mar 1999
- Location: Oakland, California, USA
- Published: 14 March 1999
81 - 100 of 108 results
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Characterization Of Shear-Wave Velocity Anisotropy In The Upper 33 M Of A Dipping, Consolidated Sandstone
Authors Gilein J. Steensma, Paul E. Murray, Michael L. Batzle and Thomas M. BoydThe extraction of groundwater or hydrocarbons from the subsurface and the effective remediation
of contaminated sites depend upon knowledge of preferential fluid migration. Shear-waves (s-waves)
have proven to be an effective tool to ascertain fracture orientation and the stress regimes responsible for
fractures. Grain and void alignment due to stratigraphy, rock texture and intergranular pore space can
cause s-waves velocity anisotropy, or variations in velocity with direction. S-waves with particle motion
parallel to the stiffer direction of the medium propagate faster than those parallel to the more compliant
direction of the medium.
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Object Identification Using Multifrequency Emi Data
Authors Dean Keiswetter, I.J. Won, Bruce Barrow and Tom BellUnexploded ordnance (UXO) cleanup is the number one priority Army Cleanup Problem
requirement and is identified as a major problem throughout the Department of Defense (DOD).
A recent SERDP technical report summarizes the status of capability for buried UXO detection,
discrimination, and identification as follows: (a) can detect UXO, within definable limits; (b)
cannot effectively discriminate UXO anomalies from ‘false alarm’ anomalies; and (c) cannot
identify UXO. False alarm anomalies are defined here as geophysical anomalies caused by
buried UXO debris, other metallic objects, gravel and cobbles, soil heterogeneities, tree roots,
and other natural and cultural features. False alarm anomalies significantly contribute to the cost
of UXO remediation due to the large number of unnecessary excavations, A major initiative in
the research and development community, therefore, is to develop discrimination (target
identification) capabilities. One potential methodology for target identification involves utilizing
the broadband scattered electromagnetic induction response. This technique, which is known as
Electromagnetic Induction Spectroscopy (EMIS), h as recently become feasible due to the
development of the GEM-3 sensor. The GEM-3 is an efficient, broadband, handheld EMI sensor
than employs a unique monostatic coil design. Analyzing the EMI spectral content for target
identification is not new. In fact, elementary EM theory states that an object must exhibit
different responses at different frequencies. All fundamental EM equations involving a timevarying
source testify as such. By fully characterizing and identifying an object without
excavation, we should be able to significantly reduce the number of false targets. EMIS should
be fully applicable to many other problems where target identification and recognition (without
intrusive search) are important.
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Geophysical Qa/Qc For A Uxo Eeka, Fort Ritchie Army Garrison, Md
Authors Kent Boler, Mike Ervine, Alex Smith, John Breznick and Chris EvansICF Kaiser, under contract to the US Army Corps of Engineers, Baltimore District
(CENAB) performed an engineering evaluation/cost analysis (EE/CA) in support of Base
Realignment and Closure (BRAC) to assess potential hazards due to unexploded
ordnance (UXO) in former and suspected range areas at Fort Ritchie Army Garrison, MD
(Fort Ritchie). EM61 geophysical surveys were conducted over portions of the now
developed cantonment area as part of a statistically based sampling plan to locate and dig
metallic anomalies potentially representing UXO. Select QA/QC aspects of the EM61
based ordnance location and sampling program are presented. Performance testing
documents a significant decrease in non-UXO anomalies vs mag-and-flag techniques at
this site. EM61 calibration pit results for simulated UXO items and analysis of 10%
replicate grid data show acceptable data accuracy, precision, and comparability.
Tracking of calibration pit test results show negligible variation of peak amplitudes
between instruments, or with variations in temperature and precipitation.
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Locating And Determining Dimensionality Of Uxos Using Time Domain Electromagnetic Induction
Authors Leonard R. Pasion and Douglas W. OldenburgIn this paper we assume that the Time Domain Electromagnetic (TEM) response of a buried
axisymmetric metallic object can be modelled as the sum of two dipoles centered at the midpoint of
the body. The strength of the dipoles depends upon the relative orientation between the object and
the source field, and also upon the shape and physical properties of the body. Upon termination of
the source field, each dipole is assumed to decay as k (t + a)-’ e-‘/y. The parameters k, LY, p and y
depend upon the conductivity, permeability, size and shape of the object, and these can be extracted
from field or laboratory measurements by using a nonlinear parametric inversion algorithm. Our
preliminary work, carried out using an analytic solution for a sphere and laboratory measurements
of steel plates, suggest the following methodology. The value of p might be used as a diagnostic
to assess whether the metallic object is non-magnetic or magnetic. If the object is thought to be
magnetic, then the ratios of ICI/k2 and pi//3 2 are diagnostic indicators as to whether the geometry
is plate-like (uninteresting) or rod-like (a high candidate for being a UXO).
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A Field Evaluation Of Airborne Techniques For Detection Of Unexploded Ordnance
Authors W.E. Doll, P. Hamlett, J. Smyre, D. Bell, T.J. Gamey and J.S. HolladayUnited States Defense Department estimates indicate that as many as 11 million acres of
government land in the U. S. may contain unexploded ordnance (UXO), with the cost of
identifying and disposing of this material estimated at nearly $500 billion. The size and
character of the ordnance, types of interference, vegetation, geology, and topography
vary from site to site. Because of size or composition, some ordnance is difficult to
detect with any geophysical method, even under favorable soil and cultural interference
conditions. For some sites, airborne methods may provide the most time and cost
effective means for detection of UXO. Airborne methods offer lower risk to field crews
from proximity to unstable ordnance, and less disturbance of sites that may be
environmentally sensitive.
Data were acquired over a test site at Edwards AFB, CA using airborne magnetic,
electromagnetic, multispectral and thermal sensors. Survey areas included sites where
trenches might occur, and a test site in which we placed deactivated ordnance, ranging in
size from small “bomblets” to large bombs. Magnetic data were then acquired with the
Aerodat HM-3 system, which consists of three cesium magnetometers within booms
extending to the front and sides of the helicopter, and mounted such that the helicopter
can be flown within 3m of the surface. Electromagnetic data were acquired with an
Aerodat 5 frequency coplanar induction system, deployed as a sling load from a
helicopter, with a sensor altitude of 15m. Surface data, acquired at selected sites,
provide a comparison with airborne data. Multispectral and thermal data were acquired
with a Daedelus AADS 1268 system. Preliminary analysis of the test data demonstrate the
value of airborne systems for UXO detection and provide insight into improvements that
might make the systems even more effective.
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A Comparison Of Towed And Mounted Helicopter Magnetometer Systems For Uxo Detection
Authors T. Jeffrey Gamey and Reinhold MahlerTraditional helicopter magnetic surveys have always utilised a towed platform, or bird, to
remove the need to compensate for the magnetic effects of the helicopter. Such platforms have
evolved to include total field, vertical gradient and triaxial gradient configurations. For detection
of small objects in the near surface, the principle limitation of towed systems is positional control
in three dimensions. In particular, the sensor height above the ground (Z) is critical for small
objects, and consistency as much as the actual altitude is an important consideration for
interpretation.
For environmental surveys with towed systems, nominal survey heights are reduced from 30 to 5
or 10 metres above ground level, tree cover permitting. In order to achieve these altitudes safely,
air speed is reduced which subsequently reduces aerodynamic stability. Speed changes also alter
the distance between helicopter and platform making control more difficult. Higher speeds drag
the bird back and upwards, and usually into a nose down orientation. Platform altitude is
monitored by laser altimeter and displayed to the pilot, but most pilots find this insufficient
warning, preferring direct visual observation. Depth perception from the top of a 30m cable is
still marginal, and minimum survey heights are limited by caution to 5m clearance under ideal
conditions (+/-3m) with 7-10m being more typical altitudes. For positioning in X&Y, lines can
theoretically be flown as close as the budget will allow. In practice, X&Y control is limited to
10m line spacing due to +/-5m of bird swing.
One solution to this problem is to mount sensors directly onto the helicopter in the tips of
stingers or booms. This provides a significant improvement in the pilot’s control, but requires a
more sophisticated data acquisition and processing system. When the mounting platform is a
direct extension of the helicopter and is placed at eye level for perspective, positional control can
be improved to +/-lm in any direction.
IABG in Germany has supported several years of airborne platform development through
European field projects. In 1997/98, the first phase of a research project consisted of comparison
surveys of Aerodat’s towed triaxial gradiometer and their boom mounted system. Tests were
conducted over a controlled test site, which included targets such as UXO, barrels, UST’s, pipes
and debris in varying amounts and configurations. This paper presents some of the results of
these comparative tests. Other tests by IABG at this site included multi-spectral and
photogrammetric surveys, but are not discussed within the scope of this paper.
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The Application Of An Integrated Magnetometer/Global Positioning System For An Unexploded Ordnance Investigation
More LessGeophysical techniques have been used for many years to detect unexploded
ordnance (UXO) buried in the subsurface. UXO detection can be performed by using
either “mag and flag” methods where anomalous metallic items are located without data
collection and flagged for excavation or dug immediately, or using a data collection
system where anomalous areas are selected from the data record and the positions are
reacquired for excavation. In recent years, recorded data surveys have begun to take
precedence over unrecorded surveys.
There are two elements to a successful recorded data geophysical survey:
1. Data collection (magnetic/electromagnetic field)
2. Location tracking.
Having only one of the above elements without the other yields nearly useless
information and certainly makes for an unsuccessful survey. Traditional methods of
tracking the location of data collected by the geophysical survey instrument have been to
use either a time/distance method or a mechanical measurement tool (i.e. wheel
odometer). Technological developments in survey equipment and the Global Positioning
System (GPS) have added a new way of tracking position during surveys in select
environments.
A geophysical investigation was conducted at a former military range in Mississippi
using an integrated magnetometer/GPS system. The use of the integrated system yielded
extremely good results in open areas but had limited use in areas under heavy tree
canopy. Results of the surveys performed indicate that the integration of GPS with
geophysical instruments is a viable tool and may become the standard operating
procedure in certain environments. The limitations of the integrated system primarily
stem from the ability of the GPS system to “speak” with satellites through tree cover.
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Mapping Buried Metallic Objects And Titaniferous Placers In The Mississippi Sound, Gulf Of Mexico
Authors Jeff Wynn and Kevin LaurentRecent experiments with a marine induced polarization (IP) streamer system have shown
that it can find and map titaniferous placers on and beneath the sea floor (Wynn and Laurent,
1998) and facies changes in the substrate beneath sandy shoals (Wymr and others, 1998). Close
examination of profile data acquired in the Mississippi Sound, however, shows that the system
can also detect certain conductive, polarizing objects that are buried beneath the sea floor and not
discernible with conventional bathymetry. The streamer system is designed to detect
polarizeable materials down to at least 6 meters below the sediment-water interface. The recent
data show broad phase-shift (IP) anomalies along the east side of Cat Island, off the coast of
Biloxi. MS. Dark, titaniferous sands can be seen in dissected benches and berms on the island’s
coastline, reinforcing the conclusion that the IP system is mapping the ilmenite-rich (FeTiO,)
sediments reported in shoals there (Foxworth, 1962). Interspersed in these data, however, are
several narrow electrical anomalies of two kinds: resistivity, and resistivity-IP anomalies. Both
kinds show pronounced drops in the already-low resistivity, and several of these also have
coincident phase-shift anomalies. The polarizing objects observed are -10 to 20 meters across,
but the IP anomalies can be seen - 20 to 40 meters laterally from their centers. The sources of
these anomalies are probably man-made in origin, buried under a veneer of modern sediments.
We speculate that these are shipwrecks, sunken buoys or parts thereof, lost and later buried (in
water now about 3 meters deep) by Hurricane Camille, which passed through the area in 1969.
We cannot, however, preclude emplacement and burial at an earlier time.
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New Field And Modeling Results From A Simulated Waste Pit Using The Enhanced Very Early Time Electromagnetic (Vetem) Prototype System
Tests in July, 1998, of an improved version of the prototype VETEM system demonstrated
improved depth of investigation at the Cold Test Pit (CTP) at the Idaho National Environmental
and Engineering Laboratory (INEEL). The improved depth of investigation is due primarily to
the development of larger loop antennas and a new transmitter capable of driving up to 30 times
more current than the original transmitter into the larger loop. An overlapped antenna
configuration was tried and proved effective in detecting buried objects. New display software
allows us, for the first time, to generate area1 time-slice displays of our data in the field for fast
qualitative evaluation. Comparisons of results using two different antenna configurations over
the Large Object Pit portion of the CTP show generally good agreement, but show an apparent
position offset of the two data sets from each other. The test over the Calibration Cell portion of
the CTP using the overlapped antenna configuration successfully located most of the indicated
targets in the cell. Results over both portions of the CTP suggest that the indicated locations of
some of the buried objects may not be completely accurate. New antenna and 3D forward
modeling codes run using an input waveform, antenna size and configuration, and system
bandwidth matching those of the VETEM system produce waveforms and show sensitivities
similar to those seen in recorded field data.
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Vertical Radar Profiling To Determine Dielectric Constant, Water Content And Porosity Values At Well Locations
Authors Michael D. Knoll and William P. ClementA vertical radar profiling (VRP) experiment was conducted at the Boise Hydrogeophysical
Research Site to determine if direct arrivals and reflections can be recorded using the surface-toborehole
survey geometry. The receiving antenna was deployed downhole to insulate it from
cultural noise. The transmitting antenna was located on the surface near the wellhead and
oriented radially to the well axis. Although the antenna polarizations are perpendicular, we were
able to record radar direct-arrivals and reflections. Picked first-arrival traveltimes were inverted
to determine layer interval velocities. The VRP-derived velocity estimates fall in the same range
as velocity estimates determined from crosshole radar tomography at the site; average velocities
for the unsaturated and saturated zones are 0.140 rn/ns and 0.080 m/ns, respectively. Resolution
of the VRP-derived velocity estimates is significantly better than the resolution of CMP-derived
velocity estimates. Dielectric constant and porosity estimates were also derived from the VRP
data using a simple petrophysical model, and compared to porosity estimates derived from
neutron logging. Correlation between the two porosity estimates is encouraging. While the VRP
method has not been widely used in site investigations to date, the results of this study suggest
that VRPs provide an accurate, high-resolution, and cost-effective means of obtaining dielectric
constant, EM velocity, volumetric moisture content and porosity values at well locations.
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Borehole Geophysics Applied To The Study Of Landfill Sites In Fractured Bedrock Terrains
Authors Horatio Ferriz and William PedlerGeotechnical and hydrogeologic studies for landfill sites in the fractured bedrock environment can
be a technically challenging prospect. Many of the problems involved in landfill construction in
fractured bedrock can be solved by detailed surface mapping of fracture density and orientation,
but ultimately data has to be collected from the subsurface via exploratory wellbores. Fracture
density and orientation can be obtained through acoustic televiewer logs or digital borehole
imaging logs, but identifying the fracture or fracture group that is water-bearing (hydraulically
conductive) is critical in characterizing the flow of water at the study site.
Hydrophysical logging and digital borehole imaging were used to log 13 wells to evaluate a
prospective canyon landfill site in weathered crystalline rocks. Hydrophysical cross-hole testing
was employed to evaluate hydraulic connections between wells and estimate medium scale
hydraulic conductivity. The results of this study found that: (1) For most wells, the more highly
transmissive intervals were within 30 feet of the piezometric level. This behavior is consistent
with the deeply weathered nature of the bedrock, which behaved in a manner hydraulically similar
to a silty sand. The hydraulically conductive intervals ranged in thickness between 2 and 8 feet,
and represented between 1% and 5% of the total length of the bedrock section, (2) In all but one
instance, the water bearing intervals were within 60 feet of the piezometric surface. In other
words, groundwater flow was largely concentrated in shallow fracture zones. (3) Based on the
hydrophysical logging results for ambient horizontal flow, a typical range of specific discharge
values for a discrete fractured interval between 0.3 and 0.02 A/day was observed at the study site.
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A Wireline-Operated Downhole Packer For Eiydraulic Measurements In Boreeoles
Authors F.L. Paillet, J.H. Williams and A.E. HessA wireline-operated packer was designed for reconnaissance logging in open boreholes and
field tested at a site in Belvidere, Illinois. Although the wireline packer uses a single downholeinflated
packer, analysis converts the wireline-packer data to estimates of hydraulic properties of
zones between adjacent packer measurement stations. A synthetic data example shows how the
single packer can be used to efficiently and effectively identify the depth intervals where
hydraulically active fractures or bedding planes intersect a borehole. Data analysis subsequently
provides estimates of the hydraulic head, transmissivity, and water quality for each of these zones.
Field tests of the wireline packer in Illinois produced estimates of zone hydraulic head and relative
transmissivity that agreed with values given by conventional straddle-packer hydraulic tests.
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Use, Comparison, Presentation, And Interpretation Of Borehole Image And Acoustic Televiewer Technology
By T.M. StaatzBorehole televiewers and image systems are used to accurately show sub surface
structural features. The borehole image system can show features not evident with the
acoustic televiewer under ideal conditions. Depending on the hole conditions, and the
data desired, either the image system or the televiewer may be the preferred instrument.
This paper will address:
1. General - The operation, calibration, survey setup, and complimentary logs to run
with each of these instrument types.
2. Comnarisons - The strengths, weaknesses, and similarities of the image system and
acoustic televiewer.
3. Data acauisition - Data gleaned from surveys can include: fractures and fracture
orientation; lithology and lithlogic changes; strike and dips; bedding planes, joint
sets, and foliation; compressional, extensional and horizontal stress determination;
information on how the borehole was drilled; and orientation of core. Interpretation
of this data will be discussed.
4. Presentation and annlication - Real examples will be used to show how a geoprofessional
would apply this data to varying situations. Data from a range of diverse
environments will be included, and various data formats will be presented.
Applications for when and type of surveys to run will be investigated.
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Field Evaluation Of A New Borehole Resistivity Probe Using Capacitive Electrodes.
Authors C.J. Mwenifumbo and Q. BristowA prototype resistivity probe using capacitive electrodes has been built under a collaborative
project funded jointly by the Geological Survey of Canada (GSC) and IFG Corporation, a
Canadian manufacturer of borehole geophysical instrumentation. The GSC carried out field tests
at its borehole test facilities in Ottawa and at the New Calumet massive sulphide deposit in
Quebec. Results indicate that the capacitive technique is sensitive in the resistivity range 100-
10,000 ohm-m and compares well with galvanically and inductively measured resistivities. Field
tests were also carried out for several transmitter-receiver spacings and in plastic-cased fluidfilled
boreholes. Capacitive resistivity logs acquired in a plastic-cased borehole are almost
identical to those acquired in the same but uncased borehole. Therefore, capacitive resistivity
logs promise to be valuable for use in environmental applications where boreholes drilled in
unconsolidated sediments are often plastic-cased.
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Assessing Exploratory Borehole Seals With Electrical Geophysical Techniques
Authors Stanford A. Gibson, Craig H. Benson and Tuncer B. EdilThis paper describes how time domain reflectometry (TDR) and electrical resistivity
logging were used to examine the integrity of seals placed in exploratory boreholes. Laboratory
tests were conducted in PVC columns containing layers simulating sealants and defect materials.
TDR or resistivity probes were installed in the columns and used to log the materials in the
column. Column testing showed that the TDR method could be used to identify defect types and
sizes. However, conduction losses limited the useful length of the TDR probe to less than 3-m.
Resistivity logging proved more suitable and thus field tests were conducted with the resistivity
probes. Resistivity logs clearly delineated portions of a borehole seal that contained either
sealant or defect materials.
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Characterization Of Well Seals Using An Ultrasonic Method
Authors Martin C. Christman, Tuncer B. Edil and Craig H. BensonA downhole ultrasonic method was modified and used to test water well seals. The
method analyzes reflections of ultrasonic waves off interfaces to determine the presence of
different materials between the casing and formation. The method of waveform analysis was
modified for thicker well casings. Indices for characterizing waveforms were compared, and
delineation between water and bentonite grout was improved. Laboratory tests using sand as an
annular material also led to changes in the method of interpretation. Test results from two water
wells are presented. Bentonite grout and sand were detected in the armulus of both wells.
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A Three-Dimensional Interpretation Of An Aem Survey In The Upper San Pedro Basin, Arizona
Authors Mark W. Bultman, Mark E. Gettings and Jeff WynnIn March 1997, a time-domain Airborne ElectroMagnetic (AEM) survey was flown over the
upper San Pedro basin, Arizona, by Geoterrex-Dighem Ltd. of Ottawa, Canada. This survey was
contracted and analyzed by the U.S. Geological Survey Geologic Division. A mathematical
transformation of the AEM data, referred to as a conductivity depth transform or CDT, was used
to build a three-dimensional model of resistivity in the basin. Comparisons of the CDTs and
resistivity measured in electric well logs from nine Fort Huachuca test wells show that the CDTs
are a good representation of the electrical conductivity of basin sediments for the upper 150 m.
Below 150 m trends in conductivity systematically decrease with depth, and therefore conductors
deeper than 150 m represented on the CDTs are underestimated. The depth to the water table
generally corresponds to the uppermost maximum of conductivity, but there are many
exceptions. It is possible that the relationship is coincidental with those areas where the water
table happens to fall in a zone of (more conductive) silts and clays. The eastern half of the basin
near the Tombstone Hills contains an increasing proportion of silts and clays with depth. We
infer that this is due to weathering of the volcanic rocks off of the Tombstone Hills into a low
energy environment during the filling of the basin. This resulted in a southwestward extending
wedge of silt and clay which is most extensive at depth and least at the surface. The lower part of
this wedge may include outflow tuff from the Tombstone caldera. This material limits the
permeability of much of the aquifer and thus is hydrologically significant.
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A World Of Applications For Helicopter Electromagnetics To Environmental And Engineering Problems
By Greg HodgesThe variety of environmental and engineering applications for helicopter-borne
electromagnetic surveys has increased in recent years. Helicopter EM surveys
undertaken by Geoterrex-Dighem have been used for:
l measuring soil conductivity near oil pipelines to assess corrosion risk,
l estimating soil type and depth for pipeline planning,
l mapping sand and gravel deposits for aggregate resource exploration,
l measuring the extent of salt water invasion into the Florida Everglades,
l mapping soil salinity in Australian farmland, assessing groundwater resources,
l locating brine leaks from abandoned Texas oil wells,
l site characterization and detection of leaks in mine tailings dams,
l assessing land slumping hazards in Japan,
l measuring ocean bathymetry
l locating igneous dikes in coal mines.
Magnetic and radiometric data can be collected simultaneously, and have been used to
find buried metal structures, and illegally abandoned radioactive sources.
The major advantages of helicopter EM over ground EM surveys are the reduced cost for
surveys over large areas, the speed of surveying coverage (approx 1000 hectares/hour),
and the multiple frequency/multiple depth sample nature of the data, which render a 3-
dimensional conductivity image of the ground conditions.
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A Case History Of The Scintrex Helicopterborne Pds3M Pipeline Detection System To Aid In The Safety And Planning Of 3D Seismic Surveys
Authors Terry McConnell and Bob LoThe Scintrex PDS-3M Pipeline Detection System was engineered to detect steel pipelines as
small as 2 inches in diameter under favourable conditions. Using three Scintrex CS-2 cesium
vapour magnetometer sensors arranged in a triangular fashion in a helicopter towed bird, the
PDS-3 system measures all three components of the magnetic gradient and the total magnetic
intensity. The data is interpreted to yield the location, likely layout of the magnetic responses.
The combination of high sensitivity gradient measurements and data collection from an airborne
platform allows for rapid surveying over areas which are difficult to access, such as over
swamps. The PDS-3M survey yields a good infrastructure maps for the 3D seismic acquisition
companies to plan their survey. The presented case history is taken from a PDS-3M survey over
an oil field in Mexico. It shows that the existing infrastructure maps are often grossly simplified
- creating uncertainty in the “safe areas” for seismic shot point locations. With the increased
confidence of the pipeline locations due to a PDS-3M survey, the safe areas for shotpoints were
identified and gaps in the seismic coverage were tilled in.
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Gem-2A Broadband Airborne Em System
Authors Bill SanFilipo and I.J. WonA helicopter towed bistatic EM system capableofsimultaneously transmitting and receiving at
several user-selected frequencies has been developed, and is currently operational in mineral
exploration programs in Australia. This system employs advanced digitally controlled
transmitter electronics providing flexible user selections for current waveforms, as well as
advanced built-in digital signal acquisition and processing including real-time sine/cosine
correlation for spectral analysis of the data. A reference, or “bucking” coil is incorporated,
which is wired in reverse polarity to the primary receiver coil, thus removing the direct system
response as observed iq the absence of a conductive target (i.e. at high altitudes). This feature
is critical in maximizing the observability ofthe weaker response from currents induced in the
earth. A case study is presented with presentations of apparent conductivity maps for real
survey data.
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