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Application of Attribute Axis Rotation to Maximize Lithology Discrimination: Indonesia Deepwater Gendalo Field Example

Hariyannugraha, Febry²; Romero, Art E.¹; Royle, Andrew¹
¹Chevron Energy Technology Pty Ltd, Perth, WA, Australia.
²Chevron Indonesia Ventures Ltd, Jakarta, Indonesia.

In 2011, Chevron Energy Technology Company undertook a quantitative seismic project with the goal of estimating rock and fluid properties for four major reservoirs in the Indonesia Deep Water Development (IDD) Gendalo-Hub fields. This study generated rock property volumes that were used as input for subsurface mapping and static modeling generation.

After going through data scoping, QC analysis and seismic data conditioning, simultaneous inversion was initiated to generate impedance volumes. Well log analysis for all reservoir zones identified VP/VS ratio and far stack elastic impedance as the best attributes for sand vs. shale discrimination and also can be used to distinguish between gas and wet sands. Quakenbush et. al (2006) showed that the axis of the cross-plot between acoustic impedance vs. shear impedance can be rotated and new attribute defined by rotated axis, which is called Poisson impedance, is a good pore-fluid discriminator. The same technique was applied to VP/VS ratio vs. acoustic impedance cross-plot.

Log-based VP/VS ratio vs. acoustic impedance cross-plot from control wells exhibited a good linear shale trend. The shale trend linear function was chosen as a new reference axis to rotate the VP/VS ratio and acoustic impedance attribute cross-plot, resulting in a single attribute called VP/VS ratio rotated to distinguish sand vs. shale. Additionally, a cut-off was used to discriminate between gas and wet sands.

The histogram of seismic-derived rotated VP/VS ratio has significantly increased gas and wet sand separation compared to the original VP/VS ratio. After rotation, the seismic data show more contrast between sand and shale response and can be utilized for delineating the sand extent. Furthermore, extracted attribute maps exhibit a good correlation with gas-water contact and depth conformance. Cutoff values are used as an alternative to distinguish pay and non-pay zones.

In summary, the VP/VS ratio rotated attribute combines both VP/VS ratio and acoustic impedance information into a single attribute resulting in improved reservoir characterization. This attribute has greatly assisted in the subsurface mapping and in turn the static modeling framework generation.

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012