If you have elastic well log data available in your area, then Sharp Reflections has a number of QAI tools to help you understand your expected prestack seismic response and determine which prestack attributes may be useful for reservoir and fluid interpretation.

• Elastic well log cross plots can help determine whether it is possible to differentiate lithologies and fluids from their elastic properties.

Well log zonation for elastic property cross-plotting 

• Prestack synthetic well-to-seismic ties help you understand whether those differences can be detected at the seismic bandwidth, and whether the seismic data is of a sufficient S:N level to detect the expected response shown in our prestack synthetics.

Prestack well-to-seismic tie 

• 3D parametric modeling facilitates further understanding of expected prestack response by generating synthetic “what-if” scenarios, such as changes in thickness or fluid saturation of your target reservoir. This kind of modeling helps to establish which scenario changes could be discriminated in your recorded prestack data.

3D prestack parametric modeling of thickness and saturation changes 

There are many ways to interpret the prestack response within your 3D dataset with the QAI toolkit. Horizon tools can be used to pick and autotrack events on any stack or gather volume, which can then be used to extract attributes from your data.

Pick on stacks (left) Pick on gathers (right)

Migrated gathers are loaded as a single data object. You can perform attribute extraction at all angles within the gather volume in a single, instantaneous computation. Panning through the extracted attributes by angle in 2D or 3D viewers provides rapid insights into amplitude vs angle (AVA) behavior at your target.

Amplitude extraction at target direct from angle gathers

Screening prestack response in a 3D viewer

A full suite of two-term and three-term AVA attributes can be generated directly from your input gathers, on the fly in real time. These attributes can be analyzed on a volumetric and target horizon basis to gain further insights into your reservoir targets.

Simultaneous generation of multiple AVA attributes directly from input gathers 

Cross-plot polygon masking of attributes such as intercept and gradient is another interactive real-time way to screen prestack data for evidence of reservoir or fluid signals within the Sharp Reflections QAI environment. Cross-plot polygons can be edited to provide real-time updates in the map viewer, and vice versa, to reach deeper understanding of prestack response.

Cross-plot polygon masking for fluid anomalies 

AVA attribute cross-plot rotations such as Chi-angle reflectivity can also be used to screen quantitatively for fluid and reservoir responses in your prestack data.

Chi 45° reflectivity for reservoir (left) Chi 20° reflectivity for fluid (right)

Extended elastic impedance (EEI) volume generation is the logical extension to prestack reflectivity attribute analysis, and is another integrated workflow in the QAI toolkit. Colored inversion operators are designed in the Wavelet tool to phase-rotate and spectrally shape Intercept & Gradient or Chi reflectivity volumes to produce EEI volumes at desired angles. Where reservoir targets lie within the tuning-thickness range of the seismic data, this approach provides a quick way to approximate relative elastic interval properties. Well log data can also be used to help determine target EEI angles for targeting specific reservoir properties such as Sw or Vclay.

Colored inversion operator design (left) Colored inversion preview/parameter testing (right)

Relative acoustic impedance (EEI 0°) (left), Relative Vp/Vs ratio (EEI 45°) (right)

A particularly powerful QAI tool is the interactive spectral decomposition. Spectral decomposition is a method of analyzing seismic amplitude response at different frequencies and combining the response at multiple target frequency bands to identify thickness variations within a target reservoir (the frequency at which an interval reaches peak tuning amplitude is dependent upon its thickness).

Sharp Reflections provides the additional capability of analyzing spectral decomposition on an angle dependent basis, directly from the gathers, facilitating the separation of angle dependent (fluid) amplitude effects from reservoir thickness effects.

• Interactive spectral decomposition directly from prestack angle gathers

Spectral decomposition at target horizon 10° (left) Spectral decomposition at target horizon 50° (right)

The Sharp Reflections QAI toolkit allows you to work with multiple horizons in a single data object called a horizon deck. The deck can be a collection of interpreted horizons, or it can be a series of iso-proportionally interpolated surfaces between horizon picks.

Efficiency comes through the performance of operations using the horizon deck to compute attributes for all horizons in a single step. For example, with 12 input horizons in a deck and an angle gather volume with 60 angle planes, amplitudes can be extracted at every angle for every horizon in a single operation. The resulting 720 maps (12 horizons x 60 angles) are stored in a single data object for efficient screening of results and for use in further computations.

Horizon deck containing 12 horizons (left). Horizon deck attribute map creation (right)

Prestack horizon deck attribute maps can be interrogated by horizon and prestack attributes from a single, ordered data object.