TECHNICAL PROGRAM
AND
ABSTRACTS
EIGHTH
INTERNATIONAL SYMPOSIUM
ON
BOREHOLE GEOPHYSICS
FOR MINERALS, GEOTECHNICAL
AND GROUNDWATER APPLICATIONS

AUGUST 21-23, 2002
TORONTO, ONTARIO

SPONSORED BY THE
CANADIAN EXPLORATION GEOPHYSICAL SOCIETY (KEGS)
AND THE
MINERALS & GEOTECHNICAL LOGGING SOCIETY (MGLS)

ABSTRACTS

(* = Poster Paper)

1.

ON THE PATH OF THE ELUSIVE GAMMA RAY: TRAVELS ON SIX CONTINENTS TO SPREAD THE GOSPEL OF CALIBRATION
Patrick G. Killeen

Geological Survey of Canada,
Ottawa, Ontario

As one’s career unfolds, opportunities to act as an advisor, or in ‘collaborative research’ in foreign lands often presents itself. The International Atomic Energy Agency (IAEA), for example calls them ‘Expert Missions’. The Canadian International Development Agency (CIDA) also has technical advisory missions. These missions present the geophysicist with two problems; the geophysical problem at hand, and the cultural problems/experiences to be encountered. These affect each other. There is also the consideration of the meaning of ‘Developing Nations’ and how it will impinge on the mission. The mission will be affected by everything from the weather, the power supply voltage, the language, the availability of parts and supplies, to the politics and religion.
The author has been involved over a period of years in an IAEA International Intercalibration Project to tie together calibration models around the world with a ‘standard’ gamma-ray logging system. He has also participated in an advisory capacity in the construction of calibration facilities around the world, for airborne, surface and borehole gamma-ray spectrometry. Instructions on the use of concrete model borehole facilities to derive calibration factors, and the application of these factors to uranium, gold and phosphate exploration data acquired in the field to produce quantitative measurements, has also taken the author to many different countries.
This presentation is a lighthearted look at some experiences (mostly good) and technical (and non-technical) observations. These are from a geophysicist traveler on a mission to pass on knowledge of the use of gamma-ray spectrometry in boreholes in particular, but also on the ground and in the air, and the importance of proper calibration of equipment. Besides the transfer of knowledge and meeting interesting people, one of the advantages of such travel is to be able to see and experience different and sometimes exotic cultures. For this ‘expert mission overview’ the author draws upon experiences on six continents: Asia- India, Iran, Thailand, Malaysia, and Indonesia; Africa- Egypt, Europe; Norway, Denmark, Sweden, Czechoslovakia (then), Hungary, Poland, and Greece; South America- Argentina and Venezuela; Australia; and North America- USA and Canada.
This might be considered as a pseudo-technical travelogue, perhaps useful to the young geophysicist looking forward to some future world traveling experiences....as told by one who’s been there, done that.

2.

BOREHOLE GEOPHYSICAL TECHNIQUES TO DEFINE STRATIGRAPHY, ALTERATION AND AQUIFERS IN BASALT
Catherine M. Helm-Clark and David W. Rodgers
Department of Geosciences, Idaho State University,
Pocatello, ID

Richard P. Smith
Idaho National Engineering and Environment Laboratory,
Idaho Falls, ID

The interpretation of borehole geophysical data in basalt is commonly different from the default interpretations used in sedimentary strata. In support of ongoing efforts at the Idaho National Engineering and Environmental Laboratory in southeastern Idaho, we have made both an extensive review of previous borehole geophysical research in basalt world-wide for geological, geothermal, environmental, and geohydrological purposes, as well an evaluation of the effectiveness of the various wireline tools for studying the properties of basalt useful for stratigraphic and structural characterization, especially in basalt provinces with fractured-basalt-hosted aquifers. Datasets from basaltic terranes reviewed in this study include those from flood basalts (central India, southern Africa, and the Pacific Northwest of North America); the tholeiitic volcanic sequences of shield volcanoes and associated structures (Hawaii and Iceland); oceanic basalts (Deep Sea Drilling Program and Oceanic Drilling Program data); and plains-style basalt volcanism (North American Snake River Plain). These four types of basalt terranes include most of the basalt exposed on the surface of the earth, and cover every hydrological condition found in basalt.
The result of this work is a schema of interpretations for various tools to enhance their usefulness in basaltic terranes. Specifically we deal with natural and active gamma, neutron, geochemical, resistivity, sonic, magnetic susceptibility, magnetometer, and temperature tools, and discuss each tool type individually. Based on the modifications in tool interpretations, we show how these tools can be most effectively used to determine compositional, textural and magnetic stratigraphy, aquifer boundaries and some common alteration features. For example, basalts flows with unique potassium composition can be distinguished by their (high or low) natural gamma signature, which can be used to establish stratigraphic correlations over tens of kilometers in some cases. Many flow breaks between lava flows are typically marked by a decrease in velocity, resistivity, and active gamma density; and an increase in natural gamma counts. Sedimentary interbeds (with poorly consolidated sand or clay) are usually marked by decreases in neutron flux, resistivity, and velocity, and in increases in natural gamma counts. Aquifer boundaries can be marked by changes in temperature gradient, neutron response, natural and active gamma flux, and fluid resistivity response. Hydrous alteration minerals in basalt can be recognized by comparing changes in neutron flux or resistivity vs. active gamma or velocity response. The closely related issue of apparent vs. actual porosity recognized in DSDP, ODP, Cascade Mountain geothermal and Snake River Plain studies is discussed in light of the problems of using neutron, resistivity and active gamma tools to determine porosity and density in basalt. We conclude with a list of suggested guidelines for logs and log combinations which will more effectively characterize different stratigraphic features of interest in structural, lithological, geohydrological and petrographic studies.

3.

BOREHOLE FLOWMETER APPLICATIONS IN IRREGULAR AND LARGE-DIAMETER BOREHOLES
Frederick L. Paillet
U. S. Geological Survey,
Denver, CO

High-resolution flow measurements such as those given by the heat-pulse and electromagnetic flowmeters are often analyzed to yield permeability profiles of heterogeneous aquifers in situ. However, the borehole environment exerts a strong influence on the effectiveness and accuracy of flow log interpretation. As many as five different kinds of corrections need to be applied to most flow log data sets. 1) Heat-pulse and electromagnetic flowmeter measurements may need to be adjusted to differentiate between very low and no flow environments. 2) Flow data may need to be normalized to account for changes in the total magnitude of the flow regime attributed to changes in pumping rate or relaxation of drawdown when measurements are made during water level recovery. 3) Flow log data may need to be multiplied by a constant factor to account for leakage around the flowmeter measurement section related to ineffective sealing of the annulus by packers or flexible disk diverters. Relatively minor conditions such as changes in borehole wall texture can have a significant effect on flow measurements. 4) Continuous flow logs are often run to define the depths where water enters or exits boreholes, but these profiles need to be corrected to remove the measurement bias introduced by the trolling speed. The trolling flow bias is easily removed by adjusting the zero point and scale of the log to match a few stationary flow measurements made with the same flowmeter. 5) Abrupt changes in borehole diameter can introduce fluctuations in flow logs that suppress any indications of vertical variation in borehole flow, and are especially severe in the case of trolled flow logs. Trolling a flowmeter probe with an under-fit diverter and calibrating flow measurements to account for the portion of flow bypassing the flowmeter measurement section can reduce the effects of borehole diameter variations. Specific examples of these corrections applied to heat-pulse and electromagnetic flowmeter data sets are given for flow logs obtained at sites in Hawaii, New Hampshire, North Carolina, Pennsylvania, Connecticut, Florida, and Kuwait. Scatter in flow measurements related to the efficiency of diverter operation or the presence of voids in the annulus surrounding well screens act to effectively limit the permeability detection capability of both heat-pulse and electromagnetic flowmeters to about two orders of magnitude regardless of the dynamic range and accuracy of either flowmeter as demonstrated by laboratory tests in smooth-walled calibration tubes.

4.

USE OF BOREHOLE RADAR TECHNIQUES TO CHARACTERIZE A FRACTURED GRANITIC ROCK AT AECL’S UNDERGROUND RESEARCH LABORATORY
M.H. Serzu, E.T. Kozak, G.S. Lodha, R.A. Everitt and D.R. Woodcock
Atomic Energy of Canada Ltd.,
Pinawa, Manitoba

Single-hole radar reflection and cross-hole radar tomography surveys have been used to assist in characterizing a 105 m3 block of granite rock at AECL’s Underground Research Laboratory (URL) in southeast Manitoba, Canada. The surveys were conducted in a series of seven boreholes drilled in moderately fractured rock from the URL 240 Level.
The RAMAC borehole radar system with dipole antenna frequencies of 22 and 60 MHz was used for these surveys. Results of single-hole radar reflection surveys revealed several linear reflectors and hyperbolic diffractions events. Some of the linear reflectors were interpreted to be reflections from fracture planes; others were from boreholes near or within the survey area. The hyperbolic diffractions are from point reflectors related to discrete vertical fractures or inhomogeneities in the rock. The 60 MHz surveys provided high-resolution reflection records and detected reflectors up to 50 m away from the boreholes. Compared to 60 MHz surveys, the 22 MHz reflection data showed marked decrease in resolution but considerable increase in probing-range (~ 100 m). Both the 22 and 60 MHz surveys were able to detect water-saturated discrete fractures and fractures zones a few cm thick. Reflections from the HQ size boreholes (96 mm diameter) were also detected in both the 22 and 60 MHz reflection surveys. The radar velocities in the study area varied from 105 m/_s to 125 m/_s, which translates to a total velocity variation of 8-10% in the URL granite (with average velocity 120 m/_s).
Results from borehole radar surveys were compared with core log data and hydrogeologic measurements from the test boreholes. The single-hole reflection surveys correlate well with fractures and fracture zones observed in core logs. Combined interpretation identified low dipping fracture zones (with 10 o - 30o dip) and two sets of subvertical fractures trending northeast and southwest. In addition, the radar velocity images from tomographic surveys show good correlation with the geology interpreted from core log data. Above average radar velocities correlate with less fractured rock and lower velocities with more fractured rock. The tomography interpretations are also consistent with transmissivity values from hydraulic tests in the boreholes. The regions of low radar velocity anomalies correspond to the transmissivity values of 1x10-6 - 1x10-8 m2/s in the boreholes, and above average radar velocities to the transmissivity values of 10-12 - 10-13 m2/s. In addition, the lower radar velocities correlate with increase in permeability as observed from groundwater flow measurements (e.g. 22 L/min in borehole MF12) and higher radar velocities corresponding to lower groundwater flow rate (e.g. 0.5 - 0.8 L/min in borehole MF6).

5.

MULTIWELL ANALYSIS OF DOWNHOLE PHYSICAL ROCK PROPERTIES OF KIMBERLITE: GUACHO KUE•, NORTHWEST TERRITORIES.
Susanne MacMahon
Earthfx Inc.,
Toronto, Ontario

Chris Wallace
Debeers Canada Exploration,
Yellowknife, NWT

Dirk Kassenaar
Viewlog Systems,
Toronto, Ontario

Bill Morris
McMaster University,
Hamilton, Ontario

Kimberlite pipes commonly comprise a number of different lithological phases. How these individual phases interrelate to one another often has major economic significance. If the individual lithological classes have distinct physical properties then it should be possible to construct a geophysical model that describes the internal morphology of each kimberlite pipe.
Multiparameter borehole geophysical measurements were collected from 71 boreholes, at the Guacho Kue• property in the Lac de Gras area, Northwest Territories. Four pipes surveyed in this study are; 5034, Hearne, Tuzo and Tesla. Measurements were made with the following tools; Natural Gamma, Neutron-Neutron, Gamma-Gamma, Inductive Conductivity, Spontaneous Potential, Point Resistance, Magnetic Susceptibility and 3 Arm Caliper. The key to interpreting multi-parameter borehole data is data integration. It is truly a multivariate data set with varying correlations between physical parameters for different lithological units. Spreadsheets and most graphical display packages are primarily 2-dimensional, whereas geophysical borehole data, is 4-dimensional (x,y,z position and physical parameter). To achieve easy access to data in a multi-well, multi-parameter setting requires construction of a relational database. In this type of setting it becomes relatively simple to test hypotheses on the basis of physical property, depth, location, or any combination of parameters.
Physical properties can discriminate lithoclasses on the basis of discreet clusters of points on 2D, or 3D cross plots. The degree to which the points cluster versus the separation between individual cluster centroids defines the "uniqueness" of each lithoclass. 2D cross plots from single holes allow the log analyst to verify that the geophysical (lithoclass) boundaries are compatible with known geological lithological boundaries. Multi-well cross plotting allows the analyst to determine if the same discriminant parameters are applicable across the whole body. Having picked correlative discriminant lithoclasses the analyst can then construct 3D models showing the geometry of lithoclass surfaces.
Within the Guacho Kue• property petrophysical analysis suggests three main lithoclasses of kimberlite; K1, K2 and K3. Each lithoclass can be further subdivided into secondary classes; K1a, K1b and K1c, K2a and K2b, K3a, K3b, K3d. The granite host rocks of the Guacho Kue• property exhibited physical properties that are substantially dissimilar from the kimberlites and can be subdivided into three distinct, granitic lithoclasses: G1, G2 and G3. Multiwell cross plotting indicates that Kimberlite bodies 5034 and Hearne appear to have similar physical rock properties, based on the degree on clustering from each defined lithoclass. Whereas, kimberlite bodies Tuzo and Tesla appear to have independent and unrelated physical rock properties as compared to 5034 and Hearne. Krigging the individual parameters along the selected sections allows the log analysts to develop an initial conception of the geometry of the kimberlite phases within each independent body. The process of multiwell analysis further allows the log analysist to derived the conceptual geometric model based on the ability to identify the unique interactions of measured parameters.

6.

PHYSICAL ROCK PROPERTIES FROM THE ATHABASCA FORMATIONS; AN AID IN THE DESIGN OF GEOPHYSICAL EXPLORATION MODELS FOR URANIUM DEPOSITS.
C. J. Mwenifumbo, M. Salisbury, B. E. Elliott, C.W. Jefferson, G. R. Bernius, and K. A. Pflug
Geological Survey of Canada,
Ottawa, Ontario

Multi-parameter borehole geophysical measurements were collected from 11 boreholes in the Eastern and Western Athabasca basin as part of the exploration technology initiative EXTECH IV to determine the geophysical characteristics of uranium deposits and their host rocks. The multi-parameter measurements included natural •-ray spectrometry, resistivity, density, and compressional wave velocity (Vp). Laboratory physical rock property measurements including resistivity, density, Vp and porosity were also made on several samples selected from the sandstone and basement rocks in the eastern Athabasca basin. These in-situ physical rock property data have been correlated with laboratory measurements and drill core geological data. The Athabasca sandstones overlying uranium mineralization have a relatively uniform mineralogical composition but the bulk resistivity, density and Vp varies as a function of porosity and pore fluid conductivity. Basement quartzites and gneisses are only slightly different from the overlying silicified sandstones, but graphitic zones are dramatically different in conductivity. Variations in acoustic properties (density, Vp and acoustic impedance) in the sandstone depend on the degree of silicification. Highly silicified zones have higher acoustic impedance than the unsilicified sandstone units and therefore seismic reflectivity in the sandstone is a function of silicification. The basement contact shows up as a velocity gradient, with the acoustic impedance of the sandstone increasing with depth towards the contact. The physical rock property data indicate that the sandstone/basement contact can be accurately imaged by electrical and seismic methods. High-resolution gravity measurements may also provide basement structural information. Mapping the alteration zones as a vector towards uranium mineralization may also be achieved with the use of electrical, seismic and gravity methods as there is significant variations in conductivity, acoustic impedance and density between altered and unaltered formations.

7.

A STATISTICAL ANALYSIS OF PHYSICAL ROCK PROPERTIES AT THE MATAGAMI MINING CAMP
Erick Adam
University of Toronto,
Toronto, Ontario

Bruno Maillard
Ecole Polytechnique de Montréal,
Montréal, Québec

To assist the interpretation of seismic surveys acquired in the Matagami mining camp, physical rock properties were measured in several boreholes and on rock samples to identify the causes of seismic reflectivity. This dataset was used to obtain statistical properties of the main lithologies found in the mining camp.
Because of the limited number of open boreholes through orebodies in the Matagami mining camp, the data set lacks sufficient information about the sulphides and the alteration zone that underlies the volcanogenic massive sulphide deposits. This al-teration zone is often larger than the massive sulphide portion of the orebody and is potentially an easier target for geophysical surveys but little is known about their physical properties. To fill this gap, our database was complemented by in-mine velocity measurements in the alteration zone of the Bell Allard orebody. This study confirms that lithological contacts are likely to produce moderate to strong seismic reflections in the Matagami mining camp. The new acoustic properties of the Bell Allard alteration pipe are used to explain the high amplitude reflections imaged by the 31D seismic survey.

8.

ORE DELINEATION USING CROSSHOLE TOMOGRAPHIC INVERSION WITH POSITIONING CONSTRAINTS
Calin Cosma and Nicoleta Enescu
Vibrometric,
Toronto, Ontario

To produce a resolved and reliable image, the crosshole tomographic method requires that the positions of the sources and receivers are determined very accurately and in practice, keeping the positioning errors to the level required by the tomographic method may prove to be a difficult task. The method presented here attempts to reconciliate the level of accuracy attainable by standard positioning techniques with the needs of the tomographic method. With certain constraints applied, distance residuals can be generated while performing tomographic inversions, which residuals can be used to reposition the borehole probes. The example given has been taken from a trial survey performed at the Fraser Mine, Ontario, during year 2000. A non-calibrated trial run was used for the example, as a means to evaluate the potential of the error recovery procedure. This study demonstrates that positioning errors can be evaluated and removed while processing the tomographic data, without increasing the overhead cost and without the need of repeating problematic measurements.

9.

ROCK STRENGTH ASSESSMENT FROM GEOPHYSICAL LOGGING
Peter Hatherly
CRC for Mining Technology & Equipment
CSIRO Exploration and Mining,
Australia

It has long been recognised that seismic velocity has a relationship with rock strength. In the case of sonic logging, empirical relationships between sonic transit time and UCS have widespread acceptance in Australian coal mining. While these provide a first order estimate of rock strength, it has been found at many mines that a local relationship is required to enable UCS to be estimated with sufficient accuracy. Sometimes a relationship cannot be found at all.
The reasons for these problems mainly arise because the UCS is a measure of inelastic rock properties while seismic velocity is a measure of elastic properties. These need not be related and while an empirical relationship might exist within a given rock type, there is no reason for this to be the case when different rock types are involved.
In this paper I develop a new approach to rock strength estimation which is based upon extracting the rich petrophysical data that can be obtained from geophysical logs. In particular the constituents of clastic sediments can be expressed as proportions of quartz, clay and pore space and I investigate the correlation between these and the UCS.

10.

AUTOMATED GEOTECHNICAL INTERPRETATION OF GEOPHYSICAL LOGS

Peter K. Fullagar
Fullagar Geophysics Pty Ltd.,
Taringa, QLD, Australia

Binzhong Zhou
CMTE/CSIRO Exploration & Mining,
Kenmore, QLD, Australia

Mark Biggs
Capricorn Coal Management, PMB Middlemount, QLD, Australia

To date, geotechnical information has been derived primarily from drill core. However, coring followed by geotechnical logging is expensive and slow, providing a strong incentive to characterise the rock mass via alternative means. Geophysical logging is a fertile source of geotechnical data from uncored as well as cored holes. Conventional petrophysical parameters such as sonic velocity, density, and resistivity are often correlated with in situ rock strength, porosity, degree of fracturing, and type of material occupying pore space. More detailed and comprehensive geotechnical characterisation can be performed if full waveform sonic and/or acoustic scanner logs are available.
The keys to expanded utilisation of geophysical logs for geotechnical purposes are
    (a) an improved understanding of the connection between petrophysics and geotechnical engineering, and
    (b) efficient means for extracting geotechnical parameters from large volumes of wireline logging data.
This paper describes progress towards automated geotechnical characterisation of geophysical logs from the German Creek Coal Mine in Queensland, Australia, using the computer program LogTrans. The aim was to efficiently generate a 3D geotechnical model using all available wireline logs. A previous auto-interpretation, based largely on UCS (uniaxial compressive strength) computed from sonic logs, successfully mapped variations in strength. In this paper the immediate roof and floor strata for the German Creek seam are interpreted in terms of "geotechnical units" which are differentiated by lithology, strength, and stratigraphic position. The geotechnical units are not uniquely defined in terms of their physical properties, e.g. strong fine-grained sandstones occur in both the roof and floor strata. Consequently, a new capability has been added to LogTrans in order to ensure that the auto-interpretation is stratigraphically consistent as well as mechanically valid.

11.

A NEW SLIMLINE, TEMPERATURE-COMPENSATED, 1024 CHANNEL SPECTRAL GAMMA LOGGING TOOL
James J. LoCoco, and Charles P. Oden
Mount Sopris Instrument Co.,
Golden, CO

Historically, slimline spectral gamma tools have been manufactured without providing for drifting response as ambient tool temperature changes. This drift varies with the type of detector employed and can be high when using a BGO scintillation crystal, but lower when using other crystals. A new tool has been developed utilizing sources with distinct gamma emission energy (Cs137, Co60) and a swept temperature bath ranging from 5 - 60°C. Calibration coefficients resulting from these tests are stored inside the tool so that real time temperature compensation can be performed. Users can select the type of scintillation crystal desired. A standard tool with a 19.7mm diameter x 76.2mm long NaI (Tl) scintillation crystal is used in this study. Depending on survey requirements the tool can be software-selected to sweep 256, 512, or 1024 channels from approximately 0.1 — 3000 KeV resulting in spectral peak resolutions of 11.7, 5.85, or 2.92 KeV/channel.
In Grand Junction, Colorado USA, and at Bells Corners Ottawa, Canada, there are some spectral gamma models in which concentrations of various radioisotopes (K, U, Th) are known, along with some percentage error for each model. Analysis software accompanying the new tool includes accounts for these errors and menus for calibrating gamma spectra versus time or temperature, averaging spectra over time or depth, generating new traces from user selected energy windows, calculating concentrations using an energy window for up to five isotopes, and calculating concentrations using a basis spectrum for each isotope. Essentially, the software allows users to generate an isotope concentration model using spectral stripping, or model basis spectra generated from known standards. Since the calibrations are modeled over a temperature range, the tool can be taken to the field so that accurate real-time, temperature-compensated, in situ isotope concentration in pC/gm (with % error) data can be determined on site if necessary.
Spectral stripping and basis spectra tool response results from the Grand Junction and Bells Corner models are described and presented. These calibration models are then used as a basis to generate potassium, uranium, and thorium isotope concentrations as a function of depth in a field situation.

12.

DOWNHOLE PHYSICAL PROPERTY MEASUREMENTS FOR SITE CHARACTERIZATION AND ANALYSIS OF REMEDIATION SYSTEMS
William J. Henrich
NORCAL Geophysical Consultants Inc.,
Petaluma, California

Susanne MacMahon
Viewlog Systems,
Toronto, Ontario

Site Characterization is an investigative process for developing an understanding of the geologic and hydrogeologic conditions affecting the subsurface distribution of contaminants, potential migration along more hydraulically conductive pathways and feasibility of remedial measures. Downhole physical rock/alluvium properties measurements are an essential element, supporting the integrated series of critical parameters used in the design and optimization of a remedial conceptual model. A malfunctioning remediation system (air sparging) installed at a hazardous waste site prompted a re-examination of the subsurface model assumptions concerning the lateral and vertical extent of permeable and relatively non-permeable fluvial sediments. Most importantly, additional subsurface data was required to either;

1. Qualify the existing subsurface model and/or;
2. Modify the model in terms of number and continuity of permeable/non-permeable.

To this end, an electrical resistivity and natural gamma survey was conducted in 18 wells/boreholes in the area containing the remediation system. Induction conductivity and natural gamma logs were collected in 12 PVC cased monitoring and air sparging wells and further supplemented by 6 open hole electrical resistivity and natural gamma logs.
Downhole physical properties measurements of electrical resistivity/conductivity and natural gamma intensity accurately discriminated between the sand, clay and silt layers. Resistivity magnitudes allowed a qualitative assessment of layer permeability.
Krigged cross sections of the inductive conductivity were constructed to examine the continuity of each of the units. Volume calculations and isopach plan view maps were also created. Krigging the individual sections provided additional and valuable characterization of the heterogeneous nature of the subsurface geology. Earlier work on the site had incorrectly established that the clay and silt units were minor semi-continuous layers in an alluvial section predominately composed of sand and gravel. The final krigged sections showed that these relatively impermeable layers were in fact significant, continuous at certain elevations and have laterally overlapped and coalesced to form barriers to the remediation system. Finally, the lateral projections of silt layers have intercepted screened sections of wells completed before the true heterogeneity of the site conditions were understood.

13.

SONIC LOGGING CASE HISTORIES USING ADVANCED EQUIPMENT AND DATA PROCESSING TECHNIQUES
Charles P. Oden and James J. LoCoco
Mount Sopris Instrument Co.,
Golden, CO

This paper is a summary of various field tests that have been conducted with a variable frequency sonic tool. These surveys illustrate that a variable frequency tool can obtain both compressional and shear velocities for most environments.
A variable frequency acoustic tool is quite useful in performing acoustic surveys in a wide range of conditions. For example, low frequency surveys (below P and S cutoff frequencies) are optimal for conducting Stoneley wave surveys. In this manner, the Stoneley wave does not have interference from other modes (i.e. shear and normal modes) and it’s velocity and amplitude can be accurately measured. Using a survey frequency that is too high on the other hand, can cause many different modes to be exited resulting in complicated waveforms that are difficult at best to process.
Shear velocity can be easily extracted from data where the shear wave is present (medium to hard rock data) using semblance processing. Conventional sonic tools cannot measure shear velocity in slow formations. In this case, the shear velocity can be found by inverse modeling the Stoneley velocity. A preferred alternative is to conduct a flexural mode survey using dipole transducers. Results from all of these techniques are presented.
The mechanical properties of rock are invaluable information for many applications. Compressional and shear velocities were measured in both unconsolidated and consolidated sediments and verified against results from other types of surveys. Calculating mechanical properties such as Poisson’s ratio from the measured velocities assesses the liquefaction risk in unconsolidated sediments. These methods were also used to determine rock competency in a mining environment.
Since shear waves cannot move through fluid, saturation can be measured by looking at changes in bulk modulus with no corresponding change in shear modulus. This is evident in cased hole logs in the vadose zone.
Permeability has been associated with Stoneley wave amplitude. Researchers modeling Stoneley wave amplitude have found that the amplitude is a function of many parameters, but that it is most sensitive to shear velocity and permeability. Empirical relationships for permeability as a function of shear velocity and Stoneley wave amplitude have been determined for specific locations. These results have been compared with permeability determined using other techniques.

14.

THE USE OF GYROSCOPES IN BOREHOLE ORIENTATION SURVEYS

S.J. Balch
Balch Exploration Consulting Inc,
Sudbury, Ontario

Accurate positioning of exploration boreholes and mining blastholes is critical for successful exploration, resource estimation, and mineral extraction. Instruments that are based on gyroscopes rather than magnetometers are increasingly preferred so that surveys can be run inside steel-cased boreholes or within highly magnetic environments containing magnetite and/or pyrrhotite.
Three types of gyroscopes are now available to the mining industry. The conventional or free-spinning gyro operates on the basis of a known preset direction, with changes in azimuth referenced to the starting direction, normally the collar azimuth. The rate gyro measures the point-to-point change in azimuth while the probe is in motion along the borehole. The output of the rate gyro is integrated to give a change in azimuth referenced to the collar. The north-seeking gyro measures an absolute borehole azimuth referenced to the Earth’s geographic axis. This measurement minimizes the systematic error that can be introduced from an inaccurate collar azimuth or poor calibration. The most accurate positional survey is a combination of the rate gyro for a continuous measurement of azimuth, and the north-seeking gyro for absolute accuracy. This is achievable with a single tool.

15.

THE HEMLO GOLD DEPOSIT: FROM PHYSICAL ROCK PROPERTIES TO ALTERATION HALO MAPPING
Bill Morris
McMaster University,
Hamilton, Ontario

Susanne MacMahon
Viewlog Systems,
Toronto, Ontario

Gold materialisation in the Hemlo mining camp is restricted to two thin sub-parallel layers possibly the limbs of a tightly folded syncline. Geochemical studies have established that the gold is preferentially associated with a region of potassium alteration. However, since many of the parent rocks are potassium-rich delineation of the alteration zone is challenging.
Physical rock property measurements on cored hand samples, together with in-situ measurements on surface and underground outcrops have shown that the ore zone can be characterized by: a) increased potassium and depleted uranium, b) reduced magnetic susceptibility, and c) increased conductivity. Broad scale contouring of these point readings suggested the presence of a possible physical property halo associated with the gold deposit.
An extensive multi-parameter multi-well survey performed on the Hemlo gold deposit included both surface and underground boreholes. In attempting to establish the physical characteristics of a spatially constrained alteration halo it is first necessary to recognise the physical property signature of unaltered rock units. This was made possible by logging a suite of boreholes located outside the deposit. Characterization of individual lithologies was achieved through conventional single well cross-plotting techniques.
Multi-well cross-plotting of data from all holes surveyed enables the log analyst to examine data distributions for evidence of any systematic changes in physical property variations. Having identified the physical property changes that are indicative alteration it is then possible to use the borehole trajectory information to illustrate the extent and spatial distribution of the halo. Three dimensional kriging of the physical property variations provides an insight into the spatial variation of the extent of alteration. When associated with known gold mineralisation variations this leads to a procedure whereby the log analyst can use additional borehole information to vector towards potential economic grade mineralisation.
On a regional scale the deposit is characterized by very low thorium, and an inverse relationship between potassium and uranium. The halo surrounding the deposit has depleted potassium, and significant increases in uranium and in particular thorium. Potassium counts in proximity of the gold horizon are up to an order of magnitude greater than out side the halo. Magnetic susceptibility increases with respect to increasing distance from the deposit, although this is highly dependant upon lithology. Within the mine ore bearing porphyry can be uniquely discriminated from non-ore bearing porphyry classes on the basis of decreased conductivity.
Distribution of gold within the Hemlo camp is closely associated with the fold structure. Integration of structural information derived from borehole logs could have helped resolve the overall geometry of the alteration halo.

16.

OREBODY MODELLING AND GRADE CONTROL UTILISING GEOPHYSICAL BLAST HOLE LOGGING

Rodney Anderson, Ian Kelso, Mathew Clifford and Paul Habermann
Pasminco Century Mine Limited,
Australia

Bill Smith
Scintrex / Auslog

Australia

Implementation of the current system of geophysical blast hole logging is an integral process in the development of a high-resolution short-term mining model for grade control and ore production. Development of the system has evolved after an initial period of experimentation and feasibility in year 2000. Since then it has become an essential part of the grade control process for orebody definition. The system also represents significant cost savings compared with ongoing in-fill diamond drilling programs.
The logging system utilises two geophysical parameters, natural gamma and magnetic susceptibility to discriminate between the mineralised black carbonaceous shale and interbedded siderite altered siltstone of the Century Ore Sequence.

36 17.

EM MODELING OF A PLATE CONDUCTOR REVISITED

W. Qian
Consultant,
North York, Ontario

G. West
University of Toronto,
Toronto, Ontario

N. Hughes and W. Ravenhurst
Crone Geophysics & Exploration Ltd.,
Mississauga, Ontario

Since the works of Lamontagne and West (1971), Annan (1974), Dyck et al. (1980) and Ravenhurst (1986), the EM modeling of a plate conductor has been widely known and used in the mineral exploration industry. This mathematically elegant and numerically tidy work quickly gained popularity and is now almost routinely used in the industry. West and Sun (1995) have made steps towards improving the mathematical rigidity, numerical convergence and basis function selection. This work is a continuation which emphasizes convergence and numerical accuracy in close proximity of the plate. We will show that when the eigen-terms are increased to 36, the modeling can produce the secondary field, at very early times, to cancel the primary field anywhere on the surface of the plate for rather inhomogeneous primary field excitation. We will use this example to demonstrate truncation errors and finally make comparison between old and new modeling for various practical situations encountered in borehole EM logging.

18.

STRATEGIES AND PRACTICAL CONSIDERATIONS IN THE SEARCH FOR HIGH CONDUCTANCE ORE

Kevin W. Ralph, Neil A. Hughes and William R. Ravenhurst
Crone Geophysics & Exploration Ltd.
Mississauga, Ontario

Acquisition, modeling and interpretation of DHEM data can be costly and time consuming, however given the great success of the DHEM technique and the great depths to which the modern explorer has to search for economic massive sulphides there is little doubt of the value of the method to the explorer.
The residual step response (either measured or calculated) has been shown to be the best means of detecting highly conductive (massive sulphide) targets. The criteria required for an accurate Step Response are a well controlled and adequately sampled transmitter current waveform and the ability to minimize geometric errors through accurate positioning of the transmit loop and an accurate knowledge of the borehole trajectory. The theoretical basis for this is well established, but in the practical search for High Conductance Ores survey planning and logistics remain the key to success. Chief among these are two important considerations are: (1) transmitter to target coupling (you can’t see what you can’t energize!) and (2) choice of base frequency (good things come to those who wait). Both are extremely important, particularly in complex, multiple conductor environments where low base frequency surveys are required for conductivity discrimination of potential targets and multiple loops are required if the geology is complex or ill defined. To deal with complex anomalies, both spatial and temporal, numerical modeling is required.

19.

FLEXIBLE LINER APPLICATIONS TO GEOPHYSICAL MEASUREMENTS

Carl Keller
Flexible Liner Underground Technologies,
Santa Fe, NM

Flexible liners offer a wide variety of aids to logging of boreholes and other slender passages. This paper describes how a flexible liner works, the use in sealing of boreholes while still allowing many kinds of measurements within the borehole interior, the use in support of boreholes against collapse and entrapment of tools, the use for towing of tools in long sloped holes, and the use of a blank liner for the direct measurement of the fluid conductivity distribution in the formation. Applications to special temperature, sonic, electrical/tomographic and video tools are described.

20.

NEW DEVELOPMENTS IN REAL TIME PROCESSING OF FULL WAVEFORM ACOUSTIC TELEVIEWER DATA

Jean-Luc Deltombe and Reinhard Schepers
ALT (Advanced Logic Technology)
Grande-Duché de Luxembourg

As compared to the existing Televiewer tools, which measure one echo (amplitude and traveltime), the new full waveform Acoustic Borehole Imager tool (ABI) is a multi-echo system. This is achieved by digital recording of each reflected acoustic wave train. Then, on-line processing of the acoustic data is made by an attached DSP to extract all valuable information, which is further compressed before sending to the surface such that no special requirements are imposed on logging cable, data transmission rates or logging speed. Recording of full acoustic signals enables major improvements of the dynamic range of the system. Indeed, knowledge about the echo from the acoustic window gives the possibility to predict tool generated coherent noise and allows to detect an echo from the borehole wall which is much smaller than coherent noise signals.
In a Cased Hole context the system can automatically adapt to situations where the tool is run inside plastic casing to record both reflections at the casing and at the borehole wall. Effective imaging of formations through PVC-casing requires the casing to be centralized in the borehole.
In a Casing Thickness context the tool can detect the reflections from the inner wall and the outer wall of any casing to calculate inner corrosion, outer corrosion, and remaining casing thickness. If cementation was made information can be gathered about the absence of cement and the quality of cement bonding.
Under the new concept future challenges and costumer requirements can be solved with the same tool hardware just by upgrading the DSP software. Upgrades can be made by software from the surface unit.

21.

TELEVIEWER LOGGING OF EXPLORATION BOREHOLES FOR MINE DESIGN.

W.G. Maybee, M. Cai, P.K. Kaiser and S.M. Maloney
MIRARCO,
Sudbury, Ontario

G.M. McDowell
INCO,
Sudbury, Ontario

Acoustic televiewer surveys were run in sulphide exploration boreholes at three INCO properties in Canada. The televiewer logs provide valuable structural and geotechnical information for mine design purposes. Examples illustrating the analysis and interpretation of Acoustic televiewer logs are given.

22.

MULTIPARAMETER BOREHOLE GEOPHYSICS IN ORE DELINEATION, ORE GRADE ESTIMATION AND SULPHIDE DISCRIMINATION.

C. J. Mwenifumbo, B. E. Elliott, and K. A. Pflug
Geological Survey of Canada,
Ottawa, Ontario

Multiparameter borehole geophysical measurements including natural •-ray, spectral •-• density, compressional wave velocity (Vp) and conductivity have been carried out at several polymetallic VMS deposits and mono-minerallic basemetal sulphide, deposits in Canada. These measurements show that different basemetal sulphides besides having distinct geophysical signatures from the host rocks, exhibit different characteristics from each other. The •-ray activity is extremely low in massive sulphides compared to host rocks (except for ultramafics) especially in VMS deposits. Variation in radioactivity usually reflects the degree of host rock percentage within the sulphides and hence provides a means of estimating the percent sulphides. The spectral •-• ratio (SGG), a ratio of the high-energy •-ray intensities to low-energy intensities in selected energy windows of the backscattered •-ray spectrum, is a function of the effective atomic number (Z). Since the SGG ratio can be directly related to the increase in the effective Z, it provides a means of estimating the percentage of basemetal sulphides with significantly high effective Z values compared to common minerals that constitute host rocks.
Borehole SGG data acquired at a sandstone-hosted lead deposit correlate so well with lead assays that log-based predictions of lead content were possible. In polymetallic sulphide deposits, good correlation between the total base metal content and the SGG ratio show that the SGG technique is equally effective in estimating total base metal content. Non-economic sulphides (pyrite and pyrrhotite) can be differentiated from economic sulphides (chalcopyrite, galena and sphalerite) by SGG ratio, Vp and conductivity. Pyrite, sphalerite and galena, for instance, can be distinguished on the Vp-density cross-plot and hence can be fairly easily distinguished from each other. Conductivity is extremely high in chalcopyrite rich zones compared to other basemetal sulphides. This paper presents the utility of multiparameter borehole geophysics in accurately defining ore boundaries and providing in-situ base metal assays. In addition, it shows the potential of these techniques for discriminating between economic and non-economic sulphides.

23.

STATISTICAL ANALYSIS OF DOWNHOLE PHYSICAL PROPERTY MEASUREMENTS: CLASSIFICATION AND PREDICTIVE ANALYSIS

Susanne MacMahon
Earthfx Inc.,
Toronto, Ontario

Gary Hodgkinson
Debeers Exploration Canada,

Toronto, Ontario

Dirk Kassenaar
Viewlog Systems,
Toronto, Ontario

Bill Morris
McMaster University,
Hamilton, Ontario

One of the challenges of geophysical interpretation, whether purely descriptive (Exploratory Data Analyses) or mathematical (Classical Analysis), is the ability to accurately analyze and quantify the results. Most EDA techniques are graphical in nature with a few quantitative techniques. The reason for the heavy reliance on graphics is that by its nature the main role of EDA is to explore the patterns and clusters in the data. For classical analysis, the data collection is followed by the imposition of a model (normality, linearity, etc.) and the analysis, estimation, and testing that follows is focused on the parameters of that model. The Classical Analysis approach may include both deterministic and probabilistic models. Deterministic models include, for example, regression models and analysis of variance (MANOVA) models. The Exploratory Data Analysis approach does not impose deterministic models on the data. The two approaches differ substantially in focus. For classical analysis, the focus is on the model-- estimating parameters of the model, and generating predicted values from the model. Most log analysts will use a mix of graphical and classical quantitative techniques. The skill involved, is balancing the EDA approach, which is more subjective, against the more rigorous model fitting and testing algorithms. The questions that arise from the exploratory stage can then be further quantified and verified in the Classical Analysis stage.
The Guacho Kue•, 1999 Borehole Logging Project resulted in a vast amount of downhole geophysical data, 71 holes, each with eight physical properties, a data set that lends itself naturally to multivariate statistical analysis. The challenge was to accurately classify and quantify the physical properties to allow for lithology predictions. The creation of the relational database allowed for a quantitative, integrated interpretation of the data from multiple boreholes. This was a primary factor in establishing the physical property relationships between holes and establishing confidence in the classification results. Multiwell cross plotting (EDA) allowed for preliminary qualitative assessments in establishing the lithoclass boundaries. Multiple analysis of variance, MANOVA, is the primary step to establish the underlying structure of the main and interaction effects on the categorical variables (lithoclass) and the multiple dependent interval variables (physical property parameters). Analysis showed that the fundamental modelling assumptions for multivariate analysis were met and that in all cases the results were significant at the 0.01 level. This provided a preliminary indication as to which physical property(s) would best discriminate certain lithoclasses. In general MANOVA can be viewed as a rigorous test for the subjective interpretations that result from EDA.
Multiple discriminant analysis (MDA) shares many of the same principles as MANOVA, but is used primarily to classify the categorical dependant, investigate the difference between the lithoclasses and test the theory that the lithologies are classified as predicted. Analysis established that MDA was not the best method for classifying and predicting physical rock properties beyond a primary level of lithoclass distinction i.e. between distinct kimberlite phases and granite host rocks.
Analysis of the statistical parameters used in the predictive algorithms involved interpretation of the correlation matrix, matrix eigenvectors and principle component scores (PCA) to determine if the lithoclasses were uniquely defined. Ideally, the significant majority of the variation in the correlation matrix should be described by the first three eigenvectors i.e. PC1, PC2 and PC3. The most important factors are determined by the component matrix in PC Analysis. Analysis established that three parameters, Point Resistance, Sonic Velocity and Spontaneous Potential, best describe the uniqueness of each lithoclass. The accuracy of the classification and prediction depends primarily on the uniqueness of the downhole physical property responses of each lithoclass. If inconsistent or non-unique lithoclasses are used, classification results will be poor. The use of too few physical property parameters can inhibit classification, by not providing enough discrimination between units. Conversely, the use of too many parameters may smear the classes and result in poor discrimination. The log analyst must bring together both quantitative observations (EDA) and qualitative results (Classical Analysis), while simultaneously integrating his or her intuition of what is geologically viable.

24.

RPDS: A ROCK PROPERTY DATA BASE SYSTEM

John McGaughey and Gervais Perron
Mira Geoscience,
Westmount, Québec

Rock properties are the foundation of any quantitative relationship amongst data from the various earth science disciplines: geology, geophysics, geochemistry, hydrogeology, and geotechnical engineering. A broad-based, accurate, and queryable archive of rock properties is prerequisite to establishing project-specific relationships amongst multi-disciplinary geoscientific data sets as well as understanding their wider context.
"RPDS" (Rock Property Database System) was created to answer the growing need for a capability to archive, manage, and query large volumes of rock property data. It was a joint design venture between a government R&D and data acquisition organisation (Geological Survey of Canada), a borehole wireline logging contractor (Quantec Logging Services) and a major mining company consumer of rock property data (Noranda Inc). Since its commercialisation in early 2002 its use has grown beyond the original partners.
The special needs of handling the immense amount of data acquired by geophysical borehole wireline logging instruments are not met by standard drillhole database systems. Rock properties measured by these geophysical borehole probles cannot be treated as "just numbers" but require proper management of acquisition, calibration, and processing history metadata. RPDS manages both raw and processed logging data. The system automatically maintains a "Forced Interval Table" where different log parameter data values share a common reference sampling interval to speed query of co-located data. A "Physical Property Table" is maintained as a composite table where data are correlated with geological information, and where property statistics as a function of geological classification are precomputed and stored for rapid query. Meta-data related to the entire logging process and other types of information such as core photos, processing logs, and reports can be archived in the database.
RPDS was designed to be used as either a stand-alone application on a laptop or as a corporate or institutional database system where an organisation’s critical rock property data reside. It can be used in conjunction with existing drillhole databases or serve as a fully functional drillhole database on its own. The database uses a modern "3-tier" client-server architecture to enable a variety of access mechanisms from stand-alone to local-area network to remote internet access.

25.*

GEOPHYSICAL CHARACTERISTICS OF THE VOISEY’S BAY NICKEL DEPOSIT, NEWFOUNDLAND-LABRADOR.

B. E. Elliott, C. J. Mwenifumbo, and K. A. Pflug
Geological Survey of Canada,
Ottawa, Ontario

Multi-sensor borehole geophysical measurements were collected from the Voisey’s Bay nickel deposit, Newfoundland and Labrador to determine the geophysical characteristics and physical rock properties of the mineralization and the host rocks to aid in the delineation and exploration of the deposit. The Voisey's Bay mineralization is hosted by a medium-grained, even-textured troctolite intrusive; a varied-texture troctolite containing wall rock clasts; and a basal breccia, composed of abundant clasts of wall rock and mafics in a troctolite gangue. These intrusives are cut by syenite and granite dykes. The footwall rocks consist of orthogneisses. Mineralization at the Voisey’s Bay nickel deposit consists primarily of pentlandite and pyrrhotite with irregular chalcopyrite and cubanite within troctolite. Magnetite is scattered through the pyrrhotite.
The geophysical logs define the mineralization that has significant contrast to the host rocks. The compressional wave velocity (Vp) and density data show good contrasts between sulphides and the host rocks. Nickel sulphides exhibit high densities and low P-wave velocities relative to the host rocks. The low velocities are characteristic of nickel sulphide ores. The acoustic impedance (a product of density and velocity) is significantly lower in the massive sulphides compared to the host rocks. Therefore this type of mineralization is easier to delineate and is a good target for surface and hole-to-hole seismic exploration techniques. The natural •-ray logs are useful in identifying different lithologies. The highest •-ray activity is observed in syenite dykes followed, in decreasing order of •-ray activity by granite, orthogneiss, troctolite and, finally, sulphides. Low radioactivity, high density, low Vp and high electrical conductivity are characteristic of the nickel sulphides. These in-situ physical rock property data provide fundamental information for interpreting ground and airborne geophysical surveys. This poster presents the log responses that illustrate the geophysical characteristics of this type of nickel deposit.

26.*

USE OF MULTI-CHANNEL •-• MEASUREMENTS TO IMPROVE THE ACCURACY OF LOG-DERIVED DENSITIES OF MASSIVE SULPHIDES.

C. J. Mwenifumbo, M. Salisbury, B. E. Elliott, and K. A. Pflug
Geological Survey of Canada,
Ottawa, Ontario

In-situ rock densities derived from borehole •-• density measurements may be in error for two reasons; 1) the Z/A ratio varies for various chemical elements; and 2) the photoelectric absorption, formerly neglected in calibration, becomes significant when heavier elements are present. For most rocks, the atomic number of the constituent elements is fairly low (Z<=20) and the Z/A ratio is roughly constant at about 0.5. Rocks containing significant amounts of base-metal sulphide minerals, however, have high effective atomic numbers (Z>=26) with densities > 4.0 g/cm3and the Z/A ratios are appreciably less than 0.5. In these cases, the assumption of a constant Z/A ratio is not valid and the standard density calibration procedures result in densities that are underestimated.
The second major problem of density determinations in massive sulphides is that photoelectric absorption is considerable in the density window where Compton scattering is assumed to be the dominant •-ray interaction with the rock mass. This becomes severe when the sulphides contain a significant percentage of galena (Pb-sulphide). Lead has an extremely high atomic number (Z=82) compared to other base metals (Z<=30), and photoelectric absorption, rather than Compton scattering, becomes the dominant interaction in the density window.
The GSC has calibrated the density logging tool for use in high density/high Z sulphide zones. Spectral •-• density logging data were acquired in several underground boreholes at Brunswick No. 12 mine, New Brunswick. Core densities were also measured in the field on several drill core sections that were selected to be representative of waste rock, massive pyrite and Pb-Zn-Cu sulphide mineralization. A multiple regression analysis of core density against six energy windows covering the •-ray energy spectrum from 50 to 500 keV gave fairly accurate density estimates in both the low and high-Z media.

27.*

A PERSPECTIVE ON THE PROBLEMS OF BOREHOLE MAGNETIC SUSCEPTIBILITY AND CONDUCTIVITY MEASUREMENTS IN HIGHLY MAGNETIC AND CONDUCTIVE BASE METAL MASSIVE SULPHIDE ENVIRONMENTS.

C. J. Mwenifumbo, and B. E. Elliott

Geological Survey of Canada,

Ottawa, Ontario

The basic system for single-coil induction probes for measuring magnetic susceptibility and conductivity consists of an induction coil in an electrical bridge circuit with an alternating field driving the circuit. When the probe passes through magnetically susceptible material, the coil inductance changes, causing the bridge to become unbalanced. There is a change in the signal amplitude across the coil arising from magnetic changes in the rock formation due to the inducing field and this is converted to magnetic susceptibility units. There is also a phase shift (imaginary component) arising from eddy currents and hysteresis losses. The eddy currents are normally assumed to be negligible in common rocks, because of extremely low conductivity. Magnetic hysteresis effects in the magnetic susceptibility anomalies can cause apparent conductivity signals that are not separable from true conductivity signals generated by eddy currents in the formation. Negative magnetic susceptibilities are observed in highly conductive environments and the magnitude of this effect appears to be a function of instrumentation.

In this poster we present data that illustrate the cross-talk between the magnetic susceptibility and conductivity signals. These data were acquired at a several sites including nickel sulphide deposits that are highly conductive and also contain pyrrhotite and magnetite with a high magnetic susceptibility. Data are also presented from two VMS deposits; the Kidd Creek mine (Cu-Zn-Ag-Pb) and the Heath Steele mine (Zn-Cu-Pb) where magnetic pyrrhotite and/or magnetite are common occurrences within the massive sulphides. We also compare the response characteristics of two commercially available single-coil conductivity/magnetic susceptibility probes (IFG and OMS-Logg).

28.*

APPLICATION OF GROUND-PENETRATING RADAR, DIGITAL OPTICAL BOREHOLE IMAGES, AND CORES FOR CHARACTERIZATION OF POROSITY AND PALEOKARST IN THE BISCAYNE AQUIFER, SOUTHEASTERN FLORIDA, USA

Kevin J. Cunningham
U.S. Geological Survey,
Miami, FL

This paper presents examples of ground-penetrating radar (GPR) data from two study sites in southeastern Florida where karstic Pleistocene platform carbonates that comprise the unconfined Biscayne aquifer were imaged. Important features shown on resultant GPR profiles include: (1) upward and lateral distribution of porosity; (2) paleotopographic relief on karstic subaerial exposure surfaces; and (3) vertical stacking of chronostratigraphic high-frequency cycles (HFCs). These characteristics were verified by comparing them to rock properties observed and measured in rock samples from continuously drilled cores, and identified in digital optical borehole images.
Results demonstrate that an empirical relationship exists between measured whole-core porosity, observed porosity on digital optical borehole images, formation conductivity, and GPR reflection amplitudes–as porosity determined from core and borehole images increases, formation conductivity increases, and GPR reflection amplitude decreases. This relationship allows for qualitative interpretation of the vertical and lateral distribution of porosity within HFCs.
Two subtidal HFCs in the uppermost Biscayne aquifer have significantly unique populations of whole-core porosity values. Porosity measurements from one cycle averages about two to three times greater than the values from the other HFC. The HFC with the higher porosity values is shown as a discrete package of relatively low-amplitude reflections, whereas the HFC characterized by lower porosity measurements is expressed by higher amplitude reflections. Porosity values measured from whole-core samples and vuggy porosity identified on digital borehole images from shallowing-upward, peritidal HFCs show that the highest porosity occurs at the base of the cycles, moderate porosity at the middle of the cycles, and lowest porosity occurs at cycle tops. This change in porosity from bottom to top is visible as an upward variation in reflection amplitude on GPR profiles–lowest amplitudes at the base and highest at the cycle tops.
This study demonstrates that GPR can be used to show the qualitative distribution of porosity within a cycle stratigraphic framework composed of carbonate HFCs. The distribution of porosity within HFCs is mostly controlled by depositional textures. The upward and lateral patterns of the rock facies within the HFCs can be translated to geophysical-log properties and radar facies configurations that could aid in interpretation and prediction of ground-water flow through a carbonate aquifer.

29.*

NEW METHOD FOR QUANTIFYING VUGGY POROSITY FROM DIGITAL OPTICAL BOREHOLE IMAGES AS APPLIED TO THE KARSTIC PLEISTOCENE LIMESTONE OF THE BISCAYNE AQUIFER, SOUTHEASTERN FLORIDA

Kevin J. Cunningham
U.S. Geological Survey
Miami, FL

Janine I. Carlson and Neil F. Hurley
Colorado School of Mines,
Golden, CO

Vuggy porosity is gas- or fluid-filled openings in rock matrix that are large enough to be seen with the unaided eye. Well-connected vugs can form major conduits for flow of ground water, especially in carbonate rocks. This paper presents a new method for quantification of vuggy porosity calculated from digital borehole images collected from 47 test coreholes that penetrate the karstic Pleistocene limestone of the Biscayne aquifer, southeastern Florida. Basically, the method interprets vugs and background based on the grayscale color of each in digital borehole images and calculates a percentage of vuggy porosity. Development of the method was complicated because environmental conditions created an uneven grayscale contrast in the borehole images that makes it difficult to distinguish vugs from background. The irregular contrast was produced by unbalanced illumination of the borehole wall, which was a result of eccentering of the borehole-image logging tool. Experimentation showed that a simple, single grayscale threshold would not realistically differentiate between the grayscale contrast of vugs and background. Therefore, an equation was developed for an effective subtraction of the changing grayscale contrast, due to uneven illumination, to produce a grayscale threshold that successfully identifies vugs. In the equation, a moving average calculated around the circumference of the borehole and expressed as the background grayscale intensity is defined as a baseline from which to identify a grayscale threshold for vugs. A constant was derived empirically by calibration with vuggy porosity values derived from digital images of slabbed-core samples and used to make the subtraction from the background baseline to derive the vug grayscale threshold as a function of azimuth. The method should be effective in estimating vuggy porosity in any carbonate aquifer.

EXHIBITORS

MOUNT SOPRIS INSTRUMENTS

As the world's premier logging equipment supplier for nearly 50 years, MSI exhibits new multi-frequency full waveform sonic and temperature-compensated spectral gamma tools.

17301 W. Colfax, #255

Golden, Colorado

80401, USA

Contact: James LoCoco

Tel: 303-279-3211

Fax: 303-279-2730

Email: jim.lococo@mountsopris.com

www.mountsopris.com

TERRAPLUS INC

Terraplus markets a wide range of borehole systems including Seismic (VSP), Radar, Sonic, Spectral Gamma, Resistivity, Conductivity. Overhauser Magnetometer, Magnetic Susceptibility, Optical & Accoustical Televiewers, Calipers, Flowmeters, Video Camera, Density, etc.

17 - 52 West Beaver Creek Road

Richmond Hill, Ontario

L4B 1L9, Canada

Contact: Claude Meunier

Tel: 905-764-5505

Fax: 905-764-8093

Email: terraplus@compuserve.com

www.terraplus.com

EARTHFX INC

Earthfx offers the VIEWLOG and Sitefx software for borehole database management, log interpretation, rock properties analysis, automated litho-classification and 3D geologic modelling.

71 Cranbrooke Avenue

Toronto, Ontario

M5M 1M3, Canada

Contact: Susanne MacMahon

Tel: 416-481-6287

Fax: 416-481-0069

Email: susanne@earthfx.com

www.viewlog.com

MIRARCO - MINING INNOVATION

An applied R&D / service organization offering the only immersive virtual reality facility focussed on mining & geotechnical applications - ideal for 3D borehole data interpretation. www.mirarco.org

Laurentian University

Willet Green Miller Centre

933 Ramsey Lake Road

Sudbury, Ontario

P3E 6B5, Canada

Contact: Jane Djivre

Tel: 705-675-1151

Fax: 705-675-4838

Email: jdjivre@mirarco.org

www.mirarco.org

QUANTEC LOGGING SERVICES INC.

Quantec provides complete petrophysical logging and analysis expertise for mining, mineral exploration, geotechnical, and environmental applications. (multi-parameter logging, optical & acoustic televiewer, predictive logging.)

Suite 400

116 Spadina Avenue

Toronto, Ontario

M5V 2K6, Canada

Contact: Rob Gordon

Tel: 416-306-1941

Fax: 416-306-1949

Email: info@quantecgeoscience.com

www.quantecgeoscience.com

ROBERTSON GEOLOGGING (USA) INC

Robertson Geologging manufactures state of the art acquisitions systems, winches, and sondes for borehole logging, imaging, and video inspection.

17 - 11115 Mills Road

Cypress, Texas 77429, USA

Contact: John Mims

Tel: 281-807-6209

Fax: 281-807-6165

Email: sales@geologging.com

www.geologging.com

NETWORK INNOVATIONS

As a wide area network enterprise, we specialize in the service and distribution of portable satellite communications equipment and airtime, always striving to bring the best solution to meet our customer's need and budget.

4424 Manilla Road S.E.

Calgary, Alberta

T2G 4B7, Canada

Contact: Peter Ferguson

Tel: 403-640-0550

Fax: 403-640-0342

Email: main@networkinv.com

www.main@networkinv.com

IFG CORPORATION

IFG Corporation designs and manufacturers, slimhole borehole sensors for mining and environmental applications. A variety of multi parameter sensors for exploration are available. Visit www.ifgcorp.com.

26 Bramsteele Road

Brampton, Ontario

L6W 1B3, Canada

Contact: Detlef Blohm

Tel: 905-451-5228

Fax: 905-459-2877

Email: ifg@idirect.com

www.ifgcorp.com

CRONE GEOPHYSICS & EXPLORATION LTD

Crone Geophysics & Exploration Ltd. manufactures the leading 3-D time-domain Electromagnetic system for mineral exploration, with programmable gates and precise waveforms (Pulse EM).

3607 Wolfedale Road

Mississauga, Ontario

L5C 1V8, Canada

Contact: Bill Ravenhurst

Tel: 905-270-0096

Fax: 905-270-3472

Email: cronegeo@compuserve.com

www.cronegeophysics.com

GEONICS LIMITED

Geonics Limited manufactures electromagnetic (EM) geophysical equipment. This includes our near-surface EM39 Borehole Conductivity, Magnetic Susceptibility and Gamma Probes. For deeper mining applications our BH43 borehole time-domain system is used with our 3D receiver probe.

8-1745 Meyerside Drive

Mississauga, Ontario

L5T 1C6, Canada

Contact: Mike Catalano

Tel: 905-670-9580

Fax: 905-670-9204

Email: geonics@geonics.com

www.geonics.com

GEOVISTA

Geovista manufacture borehole camera and borehole logging systems featuring compact dimensions and sonde stacking capability allowing for sensor combinations that would otherwise not be available.

Unit 6, Cae Ffwt Business Park

Glan Conwy

Conwy, LL28 5SP

United Kingdom

TEL: +44 (0) 1492 57 33 99

FAX: +44 (0) 1492 58 11 77

SCINTREX - AUSLOG

Booth No. 12

Scintrex-Auslog provides a full solution to your logging needs to suit every application. NEW DLS-5 logging system utilizing the powerful AusWIN-Software.

222 Snidercroft Road

Concord, Ontario

L4K 1B5, Canada

Contact: Paolo Berardelli

TEL: 905-669-2280

FAX: 905-669-6403

email: pberardelli@scintrexltd.com

www.scintrexltd.com

SPONSORS

KEGS/MGLS sincerely thanks the sponsors of the 8^th International Symposium on Borehole Geophysics.

CANADIAN EXPLORATION GEOPHYSICAL SOCIETY (KEGS)
5863 Leslie Street - Suite 517
Willowdale, ON, M2H 1J8
www.kegsonline.org

MINERALS AND GEOTECHNICAL LOGGING SOCIETY
A Chapter-at-Large of the
Society of Professional Well Log Analysts
www.mgls.org