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Reservoir Characterization of the High-Impedance Tight Gas Sands in the Ada Field, North Louisiana

Shrestha, Rajendra K.1
1 Lower 48 Business Unit, ConocoPhillips Company, Houston, TX.

Objectives: The Upper Cotton Valley formation in the Ada field, North Louisiana comprises multiple sandstone reservoir zones that vary significantly in lateral extent and thickness. These reservoirs are situated in an anticline compartmentalized by a number of faults in multiple directions. Therefore, the primary objective of this study was to build a model with improved definition of the Cotton Valley sand pay zones facilitating well-to-well correlation and thickness estimation of the tight gas sands to aid optimization of location of the future infill and step-out wells.

Procedure: The Upper Cotton Valley sandstones are fine to medium grained, well sorted and highly compacted. Due to compaction and quartz cementation, these sandstones are tight with relatively low porosity and permeability. The Cotton Valley pay zones in this field are stimulated by hydraulic fracturing for completion.

The high-resolution impedance model was built using model-based seismic inversion technique. The prestack seismic data and the near-angle and far-angle stacks were used for AVO analysis to identify and predict the tight-gas pay zones in the Upper Cotton Valley formation. An AVO model was constructed for Well D using the P-wave, S-wave and density logs. The impedance and the ratio of the P-wave and S-wave velocities were cross plotted to characterize the pay zones.

Results: The impedance data aided in improving definition of the Cotton Valley sand pay zones facilitating well-to-well sand correlation and thickness estimation of the gas sands. The horizon slice of the pay zone provided the lateral distribution of the reservoir and non-reservoir facies and the faults. The impedance model was validated by the results of the test well E, drilled post seismic inversion which is currently producing gas. The analysis of the AVO model and the pre-stack data in Well D was used in characterizing the Cotton Valley sands as Class I gas sand

Conclusions: The improvement in definition, continuity and thickness estimate in the impedance model facilitated tracking the tight-gas sands in the Upper Cotton Valley formation, both vertically and laterally, aiding optimization of location of the future infill/step-out wells. The AVO modeling and analysis and the rock property analysis assisted in identification and prediction of the high-impedance, tight gas sand pay zones in the Ada field.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009