Processing and analysis of high temperature geothermal acoustic borehole image logs in the Taupo Volcanic Zone, New Zealand

Massiot, Cécile; McNamara, David D.; Lewis, B.

doi:10.1016/j.geothermics.2014.05.010

Cited by 59 publications

(81 citation statements)

References 35 publications

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“…All natural features are interpreted as fractures which have morphological relationships (as defined in Massiot et al . []) that are parallel (46%, fractures with <1 m spacing with strike and dip orientation differences <15° that do not crosscut on the BHTV log), crosscutting (25%, fractures that crosscut each other on the BHTV), and solitary (29%, neither parallel nor crosscutting). Fractures observed in wells RK18L2 and RK32 have dominantly parallel relationships (52% and 46%, respectively), and those in well RK30L1 have mainly parallel or crosscutting relationships (40% and 38%, respectively).…”

Section: Resultsmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

“…BHTV logs were analyzed using Recall 5.4™ software and image features classified using the Massiot et al . [] system for TVZ geothermal acoustic image logs. Image quality is assessed qualitatively based upon visual assessment of the percentage of the image suitable for interpretation over 5 m intervals.…”

Section: Methodsmentioning

confidence: 99%

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

et al. 2015

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“…The BHTV logs acquired at Rotokawa commonly have only partial coverage of the borehole and contain a number of logging‐ and drilling‐induced artifacts that decrease the image quality [ Lofts and Bourke , ; McNamara et al , ]. Image quality has been qualitatively assigned using a five‐class ranking scheme [ Massiot et al , ]. Fracture detection can be hindered in zones of low‐ or very poor‐quality images, which may adversely affect the statistical analysis of fracture attributes, particularly the spacing.…”

Section: Datamentioning

confidence: 99%

Statistical methods of fracture characterization using acoustic borehole televiewer log interpretation

et al. 2017

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Acoustic borehole televiewer (BHTV) logs provide measurements of fracture attributes (orientations, thickness, and spacing) at depth. Orientation, censoring, and truncation sampling biases similar to those described for one‐dimensional outcrop scanlines, and other logging or drilling artifacts specific to BHTV logs, can affect the interpretation of fracture attributes from BHTV logs. K‐means, fuzzy K‐means, and agglomerative clustering methods provide transparent means of separating fracture groups on the basis of their orientation. Fracture spacing is calculated for each of these fracture sets. Maximum likelihood estimation using truncated distributions permits the fitting of several probability distributions to the fracture attribute data sets within truncation limits, which can then be extrapolated over the entire range where they naturally occur. Akaike Information Criterion (AIC) and Schwartz Bayesian Criterion (SBC) statistical information criteria rank the distributions by how well they fit the data. We demonstrate these attribute analysis methods with a data set derived from three BHTV logs acquired from the high‐temperature Rotokawa geothermal field, New Zealand. Varying BHTV log quality reduces the number of input data points, but careful selection of the quality levels where fractures are deemed fully sampled increases the reliability of the analysis. Spacing data analysis comprising up to 300 data points and spanning three orders of magnitude can be approximated similarly well (similar AIC rankings) with several distributions. Several clustering configurations and probability distributions can often characterize the data at similar levels of statistical criteria. Thus, several scenarios should be considered when using BHTV log data to constrain numerical fracture models.

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“…14,43,58,59 In a vertical well, the orientation of the minimum (Sh min ) and maximum (SH max ) horizontal stress can be determined from borehole breakouts and drilling-induced fractures assuming one of the principal stresses to be vertical ( Figure 5), 16,43,47,[59][60][61][62][63][64][65] Borehole breakouts (wellbore enlargements) are easily to be picked out and are recognized as broad and dark bands and are suggested to be parallel to the orientations of Sh min ( Figure 5). 14,43,58,59 In a vertical well, the orientation of the minimum (Sh min ) and maximum (SH max ) horizontal stress can be determined from borehole breakouts and drilling-induced fractures assuming one of the principal stresses to be vertical ( Figure 5), 16,43,47,[59][60][61][62][63][64][65] Borehole breakouts (wellbore enlargements) are easily to be picked out and are recognized as broad and dark bands and are suggested to be parallel to the orientations of Sh min ( Figure 5).…”

Section: In-situ Stress Analysismentioning

confidence: 99%

In‐situ stress determination and fracture characterization using image logs: The Paleogene Dongying Formation in Nanpu Sag, Bohai Bay Basin, China

Niu

Liu

Lai

et al. 2019

Energy Science & Engineering

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Fracture detection and in‐situ stress determination via well logs are important for exploration and exploitation of subsurface hydrocarbons. Cores, thin sections, and image logs are used to describe and interpret the subsurface fractures and in‐situ stress in the Paleogene Dongying sandstones in Nanpu Sag, Bohai Bay Basin, China. The maximum horizontal stress (SHmax) indicates a nearly east‐west trend according to the borehole breakouts and drilling‐induced fractures. Natural fractures in the Dongying sandstones are classified into: (1) open fractures and (2) closed fractures. The cement‐filled (closed) fractures are commonly detected by image logs as bright discontinuous sinusoidal waves due to resistive filling materials, while the open fractures are evident on image logs appearing as dark sine waves. The open fractures are of dominantly high dip angles, and the rose diagrams confirm the presences of two sets of fractures: northwest‐southeast and northwest‐southeast orientation. Fractures with strikes approximately parallel to the SHmax have good connectedness, making a significant contribution in hydrocarbon production. In addition, the oil‐bearing layers are mainly associated with the intervals with open fractures. The presence of natural fractures provides important pore spaces and fluid flow conduits. Insights can be provided into the subsurface fracture (natural and induced) detection and characterization using image logs.

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Processing and analysis of high temperature geothermal acoustic borehole image logs in the Taupo Volcanic Zone, New Zealand

Cited by 59 publications

References 35 publications

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

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

Statistical methods of fracture characterization using acoustic borehole televiewer log interpretation

In‐situ stress determination and fracture characterization using image logs: The Paleogene Dongying Formation in Nanpu Sag, Bohai Bay Basin, China

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