Malu Field Nigeria—Contributions of Ocean Bottom Cable Seismic Data to Field Development

Kelsch, Kenneth¹, Fola Soetan¹, Eugenia Rojas², Rex Hanson¹, Jim Magill³;.(1) ChevronTexaco, Lagos, Nigeria (2) University of Texas Houston, Houston, TX;.(3) ChevronTexaco, San Ramon, CA

     Chevron Nigeria Limited (CNL) acquired a four component (4C) ocean bottom cable (OBC) seismic survey over the Malu Field, Nigeria in 2002. Gas accumulations in several reservoirs produced large gas clouds coupled with large fault shadows affect the seismic image to define the subsurface. The survey was processed to provide both compressional (PP) and converted shear wave (PS) datasets. The project team, composed of CNL develop-ment/structural geologists and geophysicists, strongly supported by ChevronTexaco’s Exploration Technology Company (ETC) staff conducted a technical review of this data lead­ing to a detailed work program:

.                       • Review contractor processing techniques & impact on interpretation

.                       • Test & apply ChevronTexaco’s proprietary prestack processing

.                       • Create velocity models & depth uncertainty estimates

.                       • Identify & analyze amplitude & attribute anomalies

.                       • Create amplitude / attribute models from key wells

.                       • Complete integrated 4C interpretation of PP / PS data images & attributes

.                       • Update maps, field development plan and confirm prospects for infill drilling

Gas accumulations within the Malu oil field create large mis-ties using PP data volume alone. The effect of large gas accumulations is eliminated using the converted shear wave (PS) volume and improves the well to seismic ties. Interpretation of this new data and appli­cation of key work processes are helping to rejuvenate a field that proved difficult for past interpreters, contributed to a 17 year production high in 2004 and provided 3-5 additional infill drill opportunities for 2005-06.