Microresistivity and ultrasonic imagers: tool operations and processing principles with reference to commonly encountered image artefacts

Cheung, Philip

doi:10.1144/gsl.sp.1999.159.01.02

Cited by 16 publications

(8 citation statements)

References 10 publications

(8 reference statements)

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“…All structural orientation data undergo statistical correction to address systematic undersampling of features subparallel to the borehole axes (Table ; Hudson & Priest, ; Massiot et al, ; Terzaghi, ). In addition, apparent fracture apertures measured at the borehole wall are processed to determine fracture normal (true) aperture (Cheung, ; Davatzes & Hickman, ; Lofts & Bourke, ). Fracture density measurements from borehole imaging are known to be strongly dependent on image quality variation in image logs.…”

Section: Methodsmentioning

confidence: 99%

Tectonic Controls on Taupo Volcanic Zone Geothermal Expression: Insights From Te Mihi, Wairakei Geothermal Field

et al. 2019

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Information on structure, stress, and their interrelationship is essential for understanding structurally controlled geothermal permeability. Active fault mapping, borehole image analysis, and well testing in the Te Mihi geothermal area, New Zealand, allows us to refine structural and fluid flow architecture of this resource. The Te Mihi area is structurally complex, comprising a set of NW dipping master faults containing pervasive SE dipping antithetic and splay structures in their hanging walls. These faults are also intersected by E‐W striking faults. A localized, N‐S striking structural trend is also observed at Te Mihi. In consideration with Global Navigation Satellite System velocity vectors, both active NE‐SW and E‐W striking faults create biaxial extension at Te Mihi, though the observed NE‐SW SHmax direction suggests that contemporary extension is NW‐SE dominated. Stress field perturbations coincide with structural complexities like fault splays and intersections and/or proximity to recently active E‐W and NE‐SW striking structures. Borehole fluid flow at Te Mihi is concentrated at NW dipping master fault intersections, travel time fractures on acoustic image logs, halo fractures on resistivity image logs, NE‐SW and E‐W striking fractures, intervals of high fracture density, and spatial concentrations of wide aperture fractures and recently active NE‐SW and E‐W striking fractures. This study suggests Te Mihi geothermal expression results from biaxial extension evident from active structural trend intersections and the predominance of NE‐SW and E‐W striking structures within permeable well zones. Biaxial extension is therefore an important control on crustal fluid flow within the Taupo Volcanic Zone and thus geothermal resource delineation.

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Section: Methodsmentioning

confidence: 99%

Tectonic Controls on Taupo Volcanic Zone Geothermal Expression: Insights From Te Mihi, Wairakei Geothermal Field

et al. 2019

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“…Fracture apertures were measured directly from the acoustic image and scaled to the average diameter of the borehole and, as such, are only approximations. Although apparent aperture can be proportional to the true aperture of a fracture, it does not directly correspond to the hydraulic aperture as many other physical properties can influence the acoustic impedance contrasts associated with a structure [ Cheung , ; Valley , ; Davatzes and Hickman , ]. Therefore, apparent aperture measurements presented here are most likely maximum estimates [ Davatzes and Hickman , ] and are presented to provide insight into the relative importance of aperture variation.…”

Section: Methodsmentioning

confidence: 99%

Heterogeneity of structure and stress in the Rotokawa Geothermal Field, New Zealand

et al. 2015

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Geometric characterization of a geothermal reservoir's structures, and their relation to stress field orientation, is vital for resource development. Subsurface structure and stress field orientations of the Rotokawa Geothermal Field, New Zealand, have been studied, for the first time, using observations obtained from analysis of three acoustic borehole televiewer logs. While an overall NE-SW fracture strike exists, heterogeneity in fracture dip orientation is evident. Dominant dip direction changes from well to well due to proximity to variously oriented, graben-bounding faults. Fracture orientation heterogeneity also occurs within individual wells, where fractures clusters within certain depth intervals have antithetic dip directions to the well's dominant fracture dip direction. These patterns are consistent with expected antithetic faulting in extensional environments. A general S Hmax orientation of NE-SW is determined from induced features on borehole walls. However, numerous localized azimuthal variations from this trend are evident, constituting stress field orientation heterogeneity. These variations are attributed to slip on fracture planes evidenced by changes in the azimuth of drilling-induced tensile fractures either side of a natural fracture. Correlation of observed fracture properties and patterns to well permeability indicators reveal that fractures play a role in fluid flow in the Rotokawa geothermal reservoir. Permeable zones commonly contain wide aperture fractures and high fracture densities which have a dominant NE-SW strike orientation and NW dip direction. Studies of this kind, which show strong interdependency of structure and stress field properties, are essential to understand fluid flow in geothermal reservoirs where structural permeability dominates.

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“…Differentiating between in situ natural geological features, generally also visible on cores, and drilling-induced or logging-related features is part of the data quality control process and is critical for the interpretation of well-log data. Logging-related and drillinginduced features have been described in several studies (e.g., Lofts and Bourke, 1999;Cheung, 1999); here, we provide examples from Site M0077. We focus mainly on acoustic borehole images that provide invaluable source of information for sub-surface geology characterization.…”

Section: Introductionmentioning

confidence: 93%

Drilling-induced and logging-related features illustrated from IODP–ICDP Expedition 364 downhole logs and borehole imaging tools

Lofi¹,

Smit²,

Delahunty³

et al. 2018

Sci. Dril.

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Expedition 364 was a joint IODP and ICDP mission-specific platform (MSP) expedition to explore the Chicxulub impact crater buried below the surface of the Yucatán continental shelf seafloor. In April and May 2016, this expedition drilled a single borehole at Site M0077 into the crater's peak ring. Excellent quality cores were recovered from ∼ 505 to ∼ 1335 m below seafloor (m b.s.f.), and high-resolution open hole logs were acquired between the surface and total drill depth. Downhole logs are used to image the borehole wall, measure the physical properties of rocks that surround the borehole, and assess borehole quality during drilling and coring operations. When making geological interpretations of downhole logs, it is essential to be able to distinguish between features that are geological and those that are operation-related. During Expedition 364 some drilling-induced and logging-related features were observed and include the following: effects caused by the presence of casing and metal debris in the hole, logging-tool eccentering, drilling-induced corkscrew shape of the hole, possible re-magnetization of low-coercivity grains within sedimentary rocks, markings on the borehole wall, and drilling-induced changes in the borehole diameter and trajectory.Published by Copernicus Publications on behalf of the IODP and the ICDP. J. Lofi et al.: Expedition 364 downhole logging 375 m DSF: artesian water flow up pipe when pipe unhooked from drill head 15.5 m DSF 503.6 m DSF 701.7 m DSF 1334.69 m DSF Cased 9 5/8" (24.45 cm)

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Microresistivity and ultrasonic imagers: tool operations and processing principles with reference to commonly encountered image artefacts

Cited by 16 publications

References 10 publications

Tectonic Controls on Taupo Volcanic Zone Geothermal Expression: Insights From Te Mihi, Wairakei Geothermal Field

Tectonic Controls on Taupo Volcanic Zone Geothermal Expression: Insights From Te Mihi, Wairakei Geothermal Field

Heterogeneity of structure and stress in the Rotokawa Geothermal Field, New Zealand

Drilling-induced and logging-related features illustrated from IODP–ICDP Expedition 364 downhole logs and borehole imaging tools

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