Interpretation theory in applied geophysics: Grant, F S ... Interpretation theory in applied geophysics Unknown Binding – January 1, 1965 5.0 out of 5 stars 1 rating. See all formats and editions Hide other formats and editions. The Amazon Book Review Book recommendations, author interviews, editors' picks, and more. Read it now. Enter your mobile number or email address below and we'll send you a ...

Interpretation Theory in Applied Geophysics Grant (McGraw-Hill, 140s.)

Scaling of fault attributes: A review

Conditions and implications for compaction band formation in the Navajo Sandstone, Utah

Factors controlling permeability of cataclastic deformation bands and faults in porous sandstone reservoirs

This work presents results from a series of triaxial compression tests on two quartz sands (differing principally in grain shape), at confining pressures high enough to cause grain breakage during shearing. Tests are performed inside an X-ray scanner, which allows specimens to be imaged non-destructively as they deform. Observation of the acquired images clearly shows different mechanisms of deformation, including shearing, dilation, compaction and grain breakage. These mechanisms are investigated quantitatively through 3D measurements of local porosity, as well as strain (obtained by 3D Digital image correlation), which is analysed in terms of volumetric and shear components. These tools allow the transition between macroscopically dilative (typically of a dense sand at low mean stress) and compactive behaviour to be investigated. The analysis reveals that at the high end of the confining pressure range studied (100–7,000 kPa), the more rounded sand deforms with highly localised shear and volumetric strain—the porosity fields show a dilative band within which a compactive region (due to grain crushing) grows. The more angular material shows shear strain localisation; however, its faster transition to compactive behaviour (due to a higher propensity for individual grains to crush) translates to much more distributed compactive volumetric strain.

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Strain localisation and grain breakage in sand under shearing at high mean stress: insights from in situ X-ray tomography

[1] Millimeter-thick strain localization structures in porous sandstones, known as deformation bands, are reported to perturb the permeability structure of petroleum reservoirs and aquifers. However, the internal permeability structure of deformation bands is difficult to assess by means of classical methods. We have used spatial correlation functions to estimate the porosity and specific surface area in deformed sandstones from high-resolution backscatter images. This work demonstrates the use of a modified version of the Kozeny-Carman relation to calculate permeability based on the information obtained from image processing. We have identified anisotropy with regard to petrophysical properties in deformed sandstones, and demonstrated variations in microstructure and properties across and along the deformation bands. Our results show that properties outside the deformation bands (in the host rock) differ significantly from those inside the band (up to three orders of magnitude). Moreover permeability varies by up to two orders of magnitude along a single band. Furthermore, our porosity and permeability estimates are lower than those obtained from plug measurements. While plug measurements measure the effective permeability across a 2.54 cm (inch) long sample, the method demonstrated here provides a means to estimate porosity and permeability on the microscale, and to map out the variations in these properties both along and across deformation bands and similar structures.

/pdf/application-of-spatial-correlation-functions-in-permeability-3lgf6fc98x.pdf

Application of spatial correlation functions in permeability estimation of deformation bands in porous rocks

Abstract Damage zones of different fault types are investigated in siliciclastics (Utah, USA), carbonates (Majella Mountain, Italy) and metamorphic rocks (western Norway). The study was conducted taking measurements of deformation features such as fractures and deformation bands on multiple 1D scanlines along fault walls. The resulting datasets are used to plot the frequency distribution of deformation features and to constrain the geometrical width of the damage zone for the studied faults. The damage-zone width of a single fault is constrained by identifying the changes in the slope of cumulative plots made on the frequency data. The cumulative plot further shows high deformation frequency by a steep slope (inner damage zone) and less deformation as a gentle slope (outer damage zone). Statistical distributions of displacement and damage-zone width and their relationship are improved, and show two-slope power-law distributions with a break point at c. 100 m displacement. Bleached sandstones in the studied siliciclastic rocks of Utah are associated with a higher frequency of deformation bands and a wider damage zone compared to the unbleached zone of similar lithology. Fault damage zones in the carbonate rocks of Majella are often host to open fractures (karst), demonstrating that they can also be conductive to fluid flow.

Fault zone architecture and its scaling laws: where does the damage zone start and stop?

Normal fault 3D geometry and displacement revisited: Insights from faults in the Norwegian Barents Sea

Fault seismic attribute volumes (such as volumetric coherence and curvature) represent an efficient and objective way to visualize and identify faults in seismic cubes. Fault geometric attributes such as length, height, and fault segmentation can be extracted from such fault seismic attribute volumes. We evaluate the strengths and pitfalls of using coherence volumes for characterization of fault geometry. The results are obtained using a database from the Barents Sea, which contains 35 3D seismic cubes, together with conceptual synthetic seismic models. A high signal-to-noise ratio is a requirement for the extraction of accurate fault geometric data. Noise attenuation methods improve fault visualization, but our results indicate that the effect of noise attenuation on the extracted fault geometric attributes is only clear in areas of low signal-to-noise ratios. The choice of coherence algorithm is important when extracting fault length data. Semblance-based coherence performs better than gradient structure tensor-based coherence in low-displacement areas near the fault tips, and it produces more accurate fault length data. Faults can appear segmented in coherence volumes if relatively similar reflectors are juxtaposed across a fault. In such areas, it is important that the interpreter does not overlook the fault. The size of the analysis window used in coherence calculations controls the resolution and continuity of the imaged faults. Our results support an optimal temporal window size of one to two times the dominant period of the seismic data (typically 7–17 samples in conventional 4 ms sampled 3D seismic data). Larger temporal window sizes can result in an overestimation of fault height, especially for small faults. A large spatial window can smear out segmentation along the fault and make the fault traces wider. Even though a large spatial window can have some positive effects, we recommend using a relatively small spatial window (five traces) when extracting subtle fault geometric attributes.

Behzad Alaei

Papers

Application of spatial correlation functions in permeability estimation of deformation bands in porous rocks

Fault zone architecture and its scaling laws: where does the damage zone start and stop?

Normal fault 3D geometry and displacement revisited: Insights from faults in the Norwegian Barents Sea

Fault visualization and identification in fault seismic attribute volumes: Implications for fault geometric characterization

Faults and fractures in basement rocks, their architecture, petrophysical and mechanical properties