Seismic Attributes

Seismic Attributes Karenth, Takashi, Danielle, Mike, Scott

www.seismicatlas.org

What are seismic attributes? • A measurable property of seismic data, such as amplitude, dip, frequency, phase and polarity. Attributes can be measured at one instant in time or over a time window, and may be measured on a single trace, on a set of traces or on a surface interpreted from seismic data.

Schlumberger Oilfield Glossery

Why are they important? • The increasing reliance on seismic data requires that we gain the most information possible from the seismic reflection data • Seismic attributes empower interpreters to obtain more information from seismic data • Seismic geomorphology uses seismic attributes to extract geomorphologic insight using 3-D datasets

Application of seismic attributes • Check seismic data quality-identifying artifacts • Performing seismic facies mapping to predict depositional environments • Hydrocarbon play evaluation • Prospect identification and risk analysis • Reservoir characterization

Categorization of attributes • There are hundreds of seismic attributes • Taner et al. (1994) divide attributes into two general categories: geometrical and physical o The objective of geometrical attributes is to enhance the visibility of the geometrical characteristics of seismic data; they include dip, azimuth, and continuity. o Physical attributes have to do with the physical parameters of the subsurface and so relate to lithology. These include amplitude, phase, and frequency.

Workflow • Starts with the interpreter • Look for FLT (funny looking things) -typically a local amplitude bright spot, dim spot, or something that looks geological • Once FLT is identified it becomes the focus by applying one or several seismic attributes

• The point is to look for geological or geomorphological patterns in plan and section view. E.g. fluvial, deep water channels, slumps slides, carbonate reefs, shelf ridges, ect. • Develop one or more geologic hypotheses

www.seismicatlas.org

Examples of seismic attributes www.seismicatlas.org

• • • •

Amplitude Discontinuity Curvature Frequency

Horizon based amplitude

Tuning effects

Virtual Seismic Atlas, Leeds

Rayleigh Criterion

λ/4 Amplitude analysis allows us to operate outside the constraint of Rayleigh’s Criterion, allowing resolution in great detail of structures that would normally be considered on the margin of seismic resolution.2

Channel or deltaic sands

Direct hydrocarbon indicators

Virtual Seismic Atlas, Leeds

Gas and fluid accumulation

Virtual Seismic Atlas, Leeds

Mass transport complexes

Virtual Seismic Atlas, Leeds

Sills

Virtual Seismic Atlas, Leeds

Certain types of reefs

Virtual Seismic Atlas, Leeds

Complex deformation

Virtual Seismic Atlas, Leeds

Discontinuity Attributes and Fault Imaging The most obvious characteristic of geologic faults is lateral discontinuity of the geologic strata. The equivalent seismic representation is the discontinuity of siesmic reflectors.*

Discontinuity Attributes – What are they? • Variance – Uses statistical variance (squared differences) of “adjacent” seismic amplitudes. • Coherency – Dot product cross-correlation of “adjacent” wave packets. • Semblance – Computes the squared sum of vectors along the trace and off the trace. The maximum sum direction has most semblance. • Similarity – Checks a standard pattern of points around a central point for the most similar seismic amplitude and progresses to the most similar point as the next central point.

Similarity Patterns:

Steered Similarity:

2 Point

44 Point Point

Point 88 Point

2 Point

4 Point

8 Point

Minimum vs. Maximum Similarity

Better Fault Continuity

Better Fault Detail

Small Fault Flexure with Local vs. Regional Dip-Steering Regional Dip-Steering If the sub-regional dip (right) is used, discontinuity attributes will succeed at locating flexures associated with small faults.

Local Dip

Regional Dip: Better Fault Continuity

Regional Dip

Local Dip: Some Faults Not Imaged

Directional Decomposition of the Similarity Attribute

Better Fault Continuity

Seismic Geomorphology – Turbidite Fan Terminations (Thrust Faults)*

A - Time varying section through trubidite deposits where decollement surfsurface and thrust faults. B – A verticle section through the turbidite deposits showing thrust fault and duplex fault terminations.

Faults and Automated Horizon Tracking Combines Discontinuity Attributes and Seismic Amplitudes

Seismic amplitudes used to define the brown horizon. No explicit fault picks were used, only discontinuity attributes to define fault blocks.

A High Quality Discontinuity Volume

Better Fault Continuity

A – Fault continuity even in the presence of rollover and interfingering reflectors.

B – A discontinuity not associated with a fault is suppressed.

C – Local apparent continuity does not disrupt the fault trace.

Uses of Discontinuity Attributes • • • •

Automated fault delineation Assistance in manual fault picking Delineation of directional fault sets Seismic geomorphology (turbidite fan terminations (thrust faults) • Auto tracking of seismic horizons in time slices without fault picks

Curvature

Roberts et al. 2001; Seismicatlas.org

Dip, Azimuth, and Curvature

Roberts et al. 2001

Positive and Negative Curvature

Roberts et al. 2001; Chopra et al. 2010

Roberts et al. 2001

Curvature Attributes: Dip Angle

Roberts et al. 2001

Fault Detection through Dip Magnitude

Schuelke 2011

Curvature Attributes: Azimuth

Roberts et al. 2001

Curvature Attributes: Maximum Curvature

Roberts et al. 2001

Curvature Attributes: Most-Negative and Most-Positive Curvature

Roberts et al. 2001

Curvature Attributes: Most-Negative Curvature

Schuelke 2011

Fault Detection through Curvature

Treagold 2011

Fault Detection: Velocity Variations with Azimuth

Treagold 2011

Fault/Fracture Impact on Horizontal Drilling

Treagold 2011

Coherency vs. Curvature

Chopra et al. 2007

Neural Network and Application One of the methods to combine multiple input attributes in order to extract / isolate a target geological feature / property

Brouwer et al

What is the problem with single attribute? (1) Discontinuity attribute highlights any lateral features, including incised sedimentary features, faulting, gas chimneys, noises and so on (2) Attributes may not capture some of the target features (e.g. discontinuity attributes will not highlight small faults) Discontinuity Attribute

Curvature Attribute

Brouwer et al

Artificial Neural Network (ANN) Try to copy the cognitive capabilities of the human brain into computer This system/method can be trained to mimic human interpretation Training data for gas chimney = Weight

Training data for Nonchimney

Brouwer et al

Geo. Feature Attributes

(e.g. Chimney or nonchimney?)

Hou et al, 2008

Brouwer et al

Chimney Extraction by ANN

Brouwer et al

ANN with AVO + Frequency Attribute

Zeynal et al., 2012

AVO Attribute Analysis

Zeynal et al., 2012

Frequency Attribute Analysis

AQF attribute anomalies for 900’ Sand, Grand Bay Field

Zeynal et al., 2012

Neural Network Property Prediction

The Neural Network were trained based on well control data, AVO and absorption related attributes

GAS SAND MAP

Zeynal et al., 2012

Conclusion

Posamentier et al, 2007

References • • • • •

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Brouwer, F. C. G., Tingahl, K., and Connolly, D., A Guide to the Practical Use of Neural Networks, dDB Earth Sciences Brouwer and Huck, An Integrated Workflow to Optimize Discontinuity Attributes from Imaging of Faults, 31 st Annual GCSSEPM Foundation Bob F. Perkins Research Conference, December 4-7, 2011, Houston, Texas Cartwright, J. and Huuse, M., 3D seismic technology: the geological ‘Hubble’, Basin Research (2005). Chopra, S. and K.J. Marfurt, 2007, Seismic Attributes for Fault/Fracture Characterization, 2007 CSPG CSEG Convention. Chopra, S. and K.J. Marfurt, 2010. Integration of coherence and curvature images: The Leading Edge, v. 29, p. 1092-1107 Hou, J., Takahashi, T., Katoh, A., Jaroonsitha, S., Chumsena, K. P., and Nakayama, K., 2008, Application of seismic attributes and neural network for sand probability prediction — A case study in the North Malay Basin, Bulletin of the Geological Society of Malaysia 54, p.115 – 121 Posamentier, Integrated Seismic Stratigraphy and Geomorphology; Workflows and Techniques, 2010 GCSSEPM Foundation Conference Proceedings Roberts, A., 2001, Curvature attributes and their application to 3D interpreted horizons: First Break, 19, 85–99. Schuelke, J., 2011, Overview of Seismic Attribute Analysis in Shale Plays, Attributes: New Views on Seismic Imaging -- Their Use in Exploration and Production: 31st Annual GCSSEPM Foundation Bob F. Perkins Research Conference, February 2012, v. 1, p. 806-827 Treagold, G., et al., 2011, Eagle Ford Exploration and Development – The Application of Regional Geology and Geophysical Technologies, Attributes: New Views on Seismic Imaging -- Their Use in Exploration and Production: 31st Annual GCSSEPM Foundation Bob F. Perkins Research Conference, February 2012, v. 1, p. 806-827 Zeynal, A. R., Aminzadeh, F., Cliffod, A., 2012, Combining Absorption and AVO Seismic Attributes Using Neural Networks to High-Grade Gas Prospects, SPE Western Regional Meeting, Bakersfield, California, USA