ABSTRACT: 4 Component Seismic - Seeing through the Haze
John Erick Battie, Martin Bennett, and Ivar Gimse
Four component seismic acquisition records pressure using a hydrophone and particle motion using three orthogonal geophones. This allows processing of the PP and the converted PS wave energy. Shear wave information allows us to perform more accurate reservoir imaging, characterization, and DHI prediction through such methods as S wave AVO analysis and Vp/Vs inversion. This paper concentrates on the use of converted waves to image through gas clouds and to predict reservoir gas presence and saturation.
To get the most form four component data, modeling is recommended using available well data to assist in survey design and to assess the feasibility of reservoir characterization work.
A number of examples have shown that 4C surveys can be extremely successful at improving imaging in areas of shallow gas, including an example which was acquired recently in Indonesia.
The technique for predicting fluid saturation involves band limited inversion of the PP and PS wave data resulting in Vp and Vs estimations. The method, which makes several assumptions about the geology and rock physics, worked successfully in the example study where both the PP and PS data were adequately imaged. The Vp/Vs ratio can theoretically be used to predict gas saturation. In practice, areas of relatively high gas saturation can be identified, but absolute values for the saturation are difficult to predict without adequate well calibration. The actual value of the gas saturation predicted in this example is yet to be verified by drilling.
AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia