Interpretation of Mode Converted (P-SV) Shear Wave Data

An in-line (SY) shear wave is recorded when a conventional source is recorded on three component geophones. A cross-line (SH) shear wave may also be recorded if anisotropy rotates any of the shear wave data out of the recording plane.

How can the interpreter make use of this extra information? This paper illustrates interpretational techniques used on a Glauconite channel in Southern Alberta, a Nisku Reef in Central Alberta and a Cardium conglomerate in West-Central Alberta.

The key to interpretation of P-SY data is in relating differences between P-wave and S-wave response to differences in velocity. The use of array sonic or three component YSP data allows the interpreter to relate differences in response to changes in lithology.

There are three basic interpretational methods which are illustrated:

1. velocity changes at interfaces which produce different amplitude response on P and P-SY data,

2. velocity changes through formations which produce different travel times on P and P-SY data,

3. anisotropy, which causes differences between P-SY and P-SH data ties.

The examples review the fundamental relationship between mode-conversion and AVO changes.

Biography

John Boyd has been President of Boyd Exploration Consultants since 1977.

His interests, in addition to interpretation, have included siesmic modelling, AVO analysis and three component recording.

He graduated from the University of Toronto in Engineering Physics in 1960 and worked for Amoco, IBM and Digitech.

He is a member of the SEG, EAEG, APEGGA, and the CSEG and was President of the CSEG in 1986.