2. Geophysical Logging for Elastic Properties in Hard Rock: A Tutorial

Schmitt, Douglas R.; Mwenifumbo, C. J.; Pflug, K A; Meglis, I.L.

doi:10.1190/1.9781560802396.ch2

Cited by 6 publications

(5 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Other high-porosity zones are associated with cataclastic zones and large aperture fractures. Even in the most intact zones, the porosity is, however, still higher than common values of the matrix porosity in crystalline rocks of ∼1% or less (Schmitt et al, 2003).…”

Section: Porosity Estimationmentioning

confidence: 60%

Characteristics of a fracture network surrounding a hydrothermally altered shear zone from geophysical borehole logs

Caspari¹,

Greenwood²,

Baron³

et al. 2019

Preprint

View full text Add to dashboard Cite

Abstract. Hydrothermally active and altered fault/shear zones in crystalline rocks are of practical importance because of their potential similarities with petrothermal reservoirs and exploitable natural hydrothermal systems. The petrophysical and hydraulic characterization of such structures is therefore of significant interest. Here, we report the results of corresponding investigations on a prominent shear zone of this type located in the crystalline Aar massif of the central Swiss Alps. A shallow borehole was drilled, which acutely intersects the core of the shear zone and is entirely situated in its surrounding damage zone. The focus of this study is a detailed characterization of this damage zone based on geophysical borehole measurements. For this purpose, a comprehensive suite of borehole logs, comprising passive and active nuclear, full-waveform sonic, resistivity, self-potential, optical televiewer, and borehole radar data, was collected. The migrated images of the borehole radar reflection data together with the optical televiewer data reveal a complicated network of intersecting fractures in the damage zone. Consequently, the associated petrophysical properties, notably the sonic velocities and porosities, are distinctly different from intact granitic formations. Cluster analyses of the borehole logs in combination with the structural interpretations of the optical televiewer data illustrate that the variations in the petrophysical properties are predominantly governed by the intense brittle deformation. The imaged fracture network and the high-porosity zones associated with brittle deformation represent the main flow pathways. This interpretation is consistent with the available geophysical measurements as well as the analyses of the retrieved core material. Furthermore, the interpretation of the self-potential and fluid resistivity log data suggests a compartmentalized hydraulic behavior, as evidenced by inflows of water into the borehole from different sources, which is likely to be governed by the steeply dipping structures.

show abstract

Section: Porosity Estimationmentioning

confidence: 60%

Characteristics of a fracture network surrounding a hydrothermally altered shear zone from geophysical borehole logs

Caspari¹,

Greenwood²,

Baron³

et al. 2019

Preprint

View full text Add to dashboard Cite

show abstract

“…Comparison of the impedance log with lithology suggests that the massive sulphides will make strong reflectors. Modified from Schmitt et al (2003).…”

Section: Sudburymentioning

confidence: 97%

Enhancing base-metal exploration with seismic imagingThis article is one of a series of papers published in this Special Issue on the themeLithoprobe — parameters, processes, and the evolution of a continent.

et al. 2010

View full text Add to dashboard Cite

Commencing in 1988 and continuing for 5 years, Lithoprobe acquired a series of high-resolution seismic experiments within and near base-metal mining camps in Canada, including the Abitibi subprovince of Quebec and Ontario, the world-class Sudbury Ni-Cu mining district, the Buchans mine in Newfoundland, and the Thompson Ni belt in Manitoba. This work, undertaken in close cooperation with the Geological Survey of Canada and major Canadian mining companies, stimulated an intensive and broadened series of followup studies with the common objective of assessing potential applications of multichannel seismic (MCS) imaging for deep mineral exploration and mine development. This research was motivated by a widely recognized disparity between the depths from which ores can be profitably mined (up to 2 km or more) and the resolving depths (typically <500 m) of commonly used geophysical methods for mineral exploration. Initial rockproperty studies established that the expected contrast in acoustic impedance between ores and host rocks should be sufficient to generate observable reflections and (or) scattered waves. For an ore deposit to be directly detectable with MCS, however, it is also necessary for it to meet geometrical criteria including a minimum thickness of 1/8 wavelenth (typically *5 m) and a lateral extent similar to the Fresnel radius (typically *100 m). Both Lithoprobe and followup seismic studies, calibrated with borehole data, reveal that lithologic contacts that are characterized by large impedance contrast and significant lateral continuity, such as igneous intrusive contacts between mafic and felsic rocks, are the most likely features to be imaged with the MCS techniques. In some camps such as Buchans, however, faults and shear zones are better imaged than lithologic contacts. In either case, these studies show that well-designed and carefully processed seismic profiles can provide a valuable geophysical tool for interpreting the stratigraphic and structural framework of mineral systems and, more rarely, direct-detection capabilities for deep ore deposits.Résumé : Débutant en 1988 et se poursuivant pendant 5 ans, Lithoprobe a acquis une série d'essais sismiques de haute ré-solution à l'intérieur et à proximité de camps miniers de métaux de base au Canada, incluant la sous-province de l'Abitibi au Québec et en Ontario, le district minier Ni-Cu de classe mondiale de Sudbury, la mine Buchans à Terre-Neuve et la ceinture de nickel Thompson au Manitoba. Ce travail, entrepris en collaboration étroite avec la Commission géologique du Canada et de grandes compagnies minières canadiennes, a stimulé une série d'études de suivi, intensives et élargies, dont l'objectif commun était d'évaluer des applications potentielles d'imagerie sismique par canaux multiples « MCS -Multichannel Seismic » pour l'exploration minérale en profondeur et le développement de mines. Cette recherche a été motivée par la disparité largement reconnue entre les profondeurs desquelles les minerais peuvent être extraits rentablement (jusqu'à 2 k...

show abstract

“…In addition, the velocity depends on many other factors such as porosity, pressure, temperature, saturation, texture and lithology (Huenges ; Wang ; Schmitt et al . ). The interrelationship between these rock properties creates non‐linear and complicated relations between the various properties and sonic velocities.…”

Section: Introductionmentioning

confidence: 97%

“…Their work demonstrated that the prediction of compressional, shear and stoneley wave velocities from porosity, resistivity, bulk density and shale volume using “committee machines” is superior to using the individual techniques alone. Another tool is the adaptive neuro‐fuzzy inference system (ANFIS) (Jang ) that combines fuzzy models with artificial neural networks; this method appears to outperform the other networks (Singh, Sinha and Singh ; Singh, Vishal and Singh ). ANFIS is also a better predictor compared to multiple linear regression (Rajabi et al .…”

Section: Introductionmentioning

confidence: 99%

“…The P-wave velocity (Vp) and S-wave velocity (Vs) can be estimated by using empirical relationships with other rock properties; for example, Vp is a function of density (Brocher 2005) and a function of the composition (Behn and Kelemen 2003). In addition, the velocity depends on many other factors such as porosity, pressure, temperature, saturation, texture and lithology (Huenges 1997;Wang 2001;Schmitt et al 2003). The interrelationship between these rock properties creates non-linear and complicated relations between the various properties and sonic velocities.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Prediction of sonic velocities from other borehole data: An example from the Kevitsa mine site, northern Finland

Kieu

Kepic

Kitzig

2018

Geophysical Prospecting

View full text Add to dashboard Cite

P‐wave and S‐wave velocities are vital parameters for the processing of seismic data and may be useful for geotechnical studies used in mine planning if such data were collected more often. Seismic velocity data from boreholes increase the robustness and accuracy of the images obtained by relatively costly seismic surface reflection surveys. However, sonic logs are rarely acquired in boreholes in‐and‐near base metal and precious metal mineral deposits until a seismic survey is planned, and only a few new holes are typically logged because the many hundreds of holes previously drilled are no longer accessible. If there are any pre‐existing petrophysical log data, then the data are likely to consist of density, magnetic susceptibility, resistivity and natural gamma logs. Thus, it would be of great benefit to be able to predict the velocities from other data that is more readily available. In this work, we utilize fuzzy c‐means clustering to build a “fuzzy” relationship between sonic velocities and other petrophysical borehole data to predict P‐wave and S‐wave velocity. If boreholes with sonic data intersect most of the important geological units in the area of interest, then the cluster model developed may be applied to other boreholes that do not have sonic data, but do have other petrophysical data to be used for predicting the sonic logs. These predicted sonic logs may then be used to create a three‐dimensional volume of velocity with greater detail than would otherwise be created by the interpolation of measured sonic data from sparsely located holes. Our methodology was tested on a dataset from the Kevitsa Ni‐Cu‐PGE deposit in northern Finland. The dataset includes five boreholes with wireline logs of P‐wave velocity, S‐wave velocity, density, natural gamma, magnetic susceptibility and resistivity that were used for cluster analysis. The best combination of input data for the training section was chosen by trial and error, but differences in the misfit between the various training datasets were not particularly significant. Our results show that the fuzzy c‐means method can predict sonic velocities from other borehole data very well, and the fuzzy c‐means method works better than using multiple linear‐regression fitting. The predicted P‐wave velocity data are of sufficient quality to robustly add low‐frequency information for seismic impedance inversion and should provide better velocity models for accurate depth conversion of seismic reflection data.

show abstract

2. Geophysical Logging for Elastic Properties in Hard Rock: A Tutorial

Cited by 6 publications

References 0 publications

Characteristics of a fracture network surrounding a hydrothermally altered shear zone from geophysical borehole logs

Characteristics of a fracture network surrounding a hydrothermally altered shear zone from geophysical borehole logs

Enhancing base-metal exploration with seismic imagingThis article is one of a series of papers published in this Special Issue on the themeLithoprobe — parameters, processes, and the evolution of a continent.

Prediction of sonic velocities from other borehole data: An example from the Kevitsa mine site, northern Finland

Contact Info

Product

Resources

About