Correlative conformity Extension of an unconformity where the geologic time ... Density log A record of rock bulk density as a function of depth in a borehole.
Figure G.1 Types of coral reefs. Source: http://pubs.usgs.gov/fs/2002/fs025-02/. (See color plate section for the color representation of this figure.)
Correlative conformity Extension of an unconformity where the geologic time break disappears. Crustal subsidence Down warping of the Earth’s crust due to sediment loading. Cubic spline A method of interpolation using up to cubic power. Curvature The amount by which a geometric object deviates from being flat or straight. Decimation In wavelets, is the downsampling. Density log A record of rock bulk density as a function of depth in a borehole. Diagenesis Alteration of a sedimentary rock after its deposition by physical and chemical processes. Diagenesis can enhance or destroy primary porosity. Differential geometry Discipline that uses differential calculus and linear algebra to study problems in geometry. Dim spot A decrease of amplitude caused by hydrocarbon accumulation. Dix velocity The seismic velocity of a layer determined from stacking velocities and time. Dolomite Calcium–magnesium carbonate mineral CaMg(CO3 )2 and the main constituent of dolomites. Dolomitization Transformation of calcite to dolomite through ion replacement of Ca ions by Mg ions. It can enhance porosity because dolomite’s volume is smaller than that of calcite. Fault dip angle The angle that the fault plane makes with the horizontal. Fault throw The amount of vertical separation of a layer generated by the fault. Finite-difference method A method of approximating a derivative by taking the difference of the function at two discrete points.
Glossary
Flat spot A horizontal seismic reflection attributed to an interface between two fluids, such as gas and water or gas and oil. Foot wall The side of a fault that lies below a dipping fault plane (see Hanging wall). Fresnel zone The area of a reflector from which most of the energy of a reflection is returned. Gas chimney A region of low-concentration gas escaping and migrating upward from a gas accumulation. Graben A down-dropped block bounded by normal faults. Grain solution It occurs in shallow limestones where water is rich in carbonic acids that can dissolve calcite grains. Hanging wall The side of a fault that lies above the fault plane (see Foot wall). Horizon slice A view of 3D seismic data showing points lying on the same horizon (reflector). Isotropic Having the same physical property no matter which direction it is measured. Kerogen Organic matter after initial burial in a source rock. It matures into bitumen, which produces oil or gas depending on the kerogen type. Klauder wavelet The autocorrelation of a Vibroseis sweep. Lithology The mineral composition of a rock. Magmatic intrusion Forceful emplacement of magma beneath sedimentary rocks causing them to rise and form convex-up structures. Meandering Extensive curvature of a river channel due to low ground relief. Migrated seismic data Seismic data after performing the seismic migration process. The main objective of migration is to move dipping reflectors to their correct positions to produce a more accurate image of the subsurface. Mistie Occurs when interpreted seismic data do not match results of drilling a well. Multiple (reflection) A reflection more than once from the same interface. Permeability Ability of a sedimentary rock to allow fluids to flow. Petroleum Crude hydrocarbon products, including oil and gas. Pinnacle and patch reefs Isolated, round, comparatively small coral reefs. Polarity reversals Occur when the cap rock has a slightly lower seismic velocity than the reservoir and the reflection has its sign reversed. Porosity Ability of a sedimentary rock to store fluids. Primary (reflection) The first reflection from a subsurface interface. P-wave without S-wave anomaly An anomaly in multicomponent seismic data sets that is observed only on P-wave data but not on S-wave data, indicating its fluid origin. Quartz Silicon oxide mineral SiO2 and the main constituent of sandstones. Radial and concentric normal faults These are often associated with arches and domes. Figure G.2 shows a plan view of a typical dome with prominent concentric faults. Random noise Irregular part of signal that is not coherent. Reflection Seismic wave that is reflected from an interface where there are changes in acoustic impedance. Reflectivity Reflection coefficient (reflectance). Reflectivity series A time series of reflection coefficients at normal incidence. Ricker wavelet A zero-phase wavelet that represents the second derivative of the Gaussian function.
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Figure G.2 Horizon slice from a 3D seismic volume over a mud dome showing prominent concentric (T) normal faults (VSA source: Butler, 2015). Source: courtesy of Virtual Seismic Atlas (VSA), 2015 (www.seismicatlas.org). (See color plate section for the color representation of this figure.)
T
Rock matrix The solid part of a sedimentary rock. Seismic depth section Seismic section after converting its vertical axis from time to depth. Seismic horizontal resolution The ability to distinguish closely spaced features laterally on a seismic section. Seismic vertical resolution The ability to distinguish closely spaced reflections vertically on a seismic section. Seismic wavelength The distance between successive peaks or troughs of a seismic wave. Sonic log A record of rock P-wave velocity as a function of depth in a borehole. Speckle Granular noise that inherently exists in a signal. Stacked seismic data Seismic data after going through normal move-out correction, muting, and stacking processes. It represents an initial image of the subsurface. Stacking velocity The average velocity we get by fitting a hyperbola to the true time–distance curve of a primary seismic reflection.
Glossary
Static shift A constant vertical shift in a seismic trace due to lateral variations in shallow layers. Stratigraphy The study of rock strata and their classification. Subsampling Resampling of a signal at a coarser sampling interval. Synthetic aperture radar (SAR) Image representation form of radar data. Synthetic seismic data Seismic data generated by forward modeling on a computer. Tectonic Deformation and/or fracturing of rocks under stress. Time-average equation An equation that relates the seismic P-wave velocity V in a sedimentary rock to those of its solid matrix Vm and pore fluid Vf in terms of porosity 𝜙: 𝜙 1−𝜙 1 + . = V Vm Vf Time slice A view of 3D seismic data showing points having the same two-way time. Time-variant A physical property that changes with time. Unconformity Surface representing rock erosion or nondeposition. It represents a break in the geologic record. Vertical seismic profiling (VSP) Measurements of the response of a geophone at various depths in a borehole to sources on the surface. Welllog A record of one or more physical measurements as a function of depth in a borehole.
