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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 253

Last Page: 253

Title: Evaluation of Direct Hydrocarbon Indicators Through Comparison of Compressional- and Shear-Previous HitWaveNext Hit Data: Case Study of Myrnam Gas Field, Alberta: ABSTRACT

Author(s): Ross Alan Ensley

Article Type: Meeting abstract


A recent paper documents a new method of evaluating bright spots or other direct hydrocarbon indicators (DHIs). The technique involves the qualitative comparison of compressional (P)-Previous HitwaveNext Hit and shear (S)-Previous HitwaveNext Hit1 seismic data. In practice, such a comparison offers a viable means of evaluating DHIs previously observed on P-Previous HitwaveNext Hit data. The application of SH-Previous HitwaveNext Hit seismic data for evaluation of DHIs was documented with a case study of P- and SH-Previous HitwaveNext Hit data from the Putah Sink field of central California. As a second case history, this paper presents an interpretation of P- and SH-Previous HitwaveNext Hit seismic data from the Myrnam field of Alberta.

Shear waves differ from compressional waves in both the direction of particle motion relative to the direction of Previous HitwaveNext Hit propagation and in the rock properties that control the Previous HitwaveNext Hit velocity. A P-Previous HitwaveNext Hit is an elastic Previous HitwaveNext Hit in which the particle motion is perpendicular to the direction of Previous HitwaveNext Hit propagation. Because of this relationship between P- and S-waves, the velocities of the two are functions of different rock properties.

Consideration of the elastic properties that control the velocity of P- and S-waves in a rock indicates that P-waves are sensitive to the type of pore fluid present within a rock whereas S-waves are only affected slightly by changes in fluid type. Thus, if the presence of gas within a reservoir rock gives rise to an anomalous seismic expression on P-Previous HitwaveNext Hit data, a DHI, there will be no comparable expression on S-Previous HitwaveNext Hit data. However, a P-Previous HitwaveNext Hit anomaly generated by a lithologic feature, a false DHI, will have a corresponding S-Previous HitwaveNext Hit anomaly. One consequence of this relationship is that it is possible to evaluate the potential of P-Previous HitwaveNext Hit DHIs through a comparison of P- and S-Previous HitwaveTop seismic data recorded over a prospect.

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Copyright 1997 American Association of Petroleum Geologists