SEISMIC INTERPRETATION JIM KELLOGG UNIVERSITY OF SOUTH CAROLINA

Instructor http://www.AndeanGeophysical.com http://www.KelloggInternational.com Dr. James Kellogg has 30 years experience in regional tectonics, satellite geodesy, structural modeling, and potential field studies. He is a Professor in the Department of Earth and Ocean Sciences and Director of the Andean Geophysical Laboratory, at the University of South Carolina, President of Kellogg International Associates, and Editor-In-Chief of the Journal of South American Earth Sciences. He obtained his M.A. (1978) and Ph.D. (1981) in geology and geophysics at Princeton University. In 1987 he joined the faculty of the University of South Carolina as professor of applied geophysics. He has coordinated regional geophysical basin studies for petroleum exploration using seismic, well, gravity, and magnetic data. He has published over 60 papers and taught short courses in volume balanced structural and seismic reflection interpretation, potential field modeling, 3-Dimensional modeling, and regional tectonics.

SEISMIC INTERPRETATION Seismic Data Acquisition and Processing Pitfalls Volume Balanced Solutions and Kink Method of Seismic Interpretation Extensional Tectonics Salt Tectonics Seismic Attributes for Reservoir Characterization 3D Seismic Data

SEISMIC DATA ACQUISITION AND PROCESSING

SEISMIC DATA ACQUISITION AND PROCESSING Acquisition – Shot, Wavelet, Trace Acoustic Impedence, Polarity Acoustic Well Logging Synthetic Seismic Traces Common Depth Point (CDP) Stack Processing and Migration

DATA ACQUISITION Shot – initial bang Shotpoint – geographical location Source pulse or wavelet – resulting sound Reflections – echoes Trace – stream of reflections recorded by geophone

SEISMIC ACQUISITION

SEISMIC ACQUISITION

Land Seismic Data Acquisition Transition Zone Arctic Highlands Jungle Heliportable Specialists Desert

Geophone Team

Marine Seismic Acquisition

Marine Seismic Acquisition

Ocean-Bottom Cables For some applications, it is desirable to put the receivers directly on the seafloor using ocean-bottom cables (OBC). The acquisition of shear wave seismic data is one such use. Shear waves do not travel through water, and so conventional marine sources do not generate them and hydrophones will not record them.

DATA ACQUISITION Seismic reflector or acoustic-impedence boundary – boundary across which the hardness changes. Reflection coefficient – type and size of acoustic impedence change.

DATA ACQUISITION Seismic reflector or acoustic-impedence boundary – boundary across which the hardness changes. Reflection coefficient – type and size of acoustic impedence change. Acoustic impedence (Z) = density (r) x velocity (V) Z = r V

TRACE ANALYSIS Positive reflection – overlying layer is softer than underlying layer Negative – upper layer is harder Polarity – peak or trough for positive reflection

TRACE ANALYSIS Positive reflection – overlying layer is softer than underlying layer Negative – upper layer is harder Polarity – peak or trough for positive reflection

TRACE ANALYSIS Two-way time – time from bang to recording Amplitude – reflection strength Wavelet shape

REFLECTION COEFFICIENT LOG AND NORMAL POLARITY WAVELET

Acoustic Well Logging Operation The main instrument used is called the sonde. A basic sonde consists of a source and two receivers one-foot apart. The sonde is lowered down the borehole and waves are generated and recorded continuously. The sonde is usually positioned in the borehole center using centralizing springs. Frequencies used are in the range of 2 - 35 kHz. Typical investigation radius is 0.2 – 1.2 m.

Acoustic Well Logging Sonde types

Acoustic Well Logging Transit time

Acoustic Well Logging Example

Note high resolution of sonic log vs the seismic trace

Synthetic Seismic Trace Reflection coefficients and velocity log used with a zero phase wavelet to produce a synthetic seismic trace

Wavelet minimum phase wavelet = front loaded energy i.e. at time zero minimum energy and elsewhere maximum. zero phase wavelet has maximum energy at time zero. Most seismic sources do not generate a zero phase pulse, because that implies output before time zero. For instance an air gun source generates a minimum phase pulse. We can use minimum phase wavelet for acquisition and during processing convert to zero phase.

EFFECT OF WAVELET FREQUENCY ON SEISMIC RESPONSE

Which display do you prefer?

Are the faults clearer in this display?

Or in this display?

CDP RECORDING METHOD TO INCREASE SIGNAL TO NOISE RATIO Common-depth-point (CDP) or Common-mid-point (CMP) – reflections recorded from the same subsurface point with different offsets. Fold – number of traces 2 fold – 2 traces 96 fold – 96 traces

SEISMIC ACQUISITION

CDP-CMP METHOD

SEISMIC ACQUISITION

MIGRATION Migrated – restore dipping reflector to correct subsurface position.