Print this pageCharacterization of Shoreface and Incised Valley Fill Deposits in Gbokoda A-04 and A-05 Reservoirs, Niger Delta, Nigeria
Reginald E. Onyirioha1, Neil Hurley2, Timothy McHargue3, and Piret Plink-Bjorklund1
1Geology and Geological Engineering, Colorado School of Mines, Golden, CO
2Schlumberger Doll Research, Cambridge, MA
3Chevron Corporation, San Ramon, CA
Gbokoda field produces hydrocarbon in the Niger Delta, Nigeria, from predominantly shoreface deposits that were cut by incised valleys, and filled with fluvial and estuarine deposits. This interpretation integrates core studies with well-log cross sections and 3-D seismic data to establish a geologically consistent interpretation of the Gbokoda A-04 and A-05 intervals.
The facies tracts of Gbokoda A-04 and A-05 were deposited as shoreface and incised valley deposits. The shoreface facies of A-04 and A-05 are preserved in Block-7, in the eastern portion of Gbokoda field. The shoreface facies were eroded in the western portion, and subsequently filled with fluvial and estuarine deposits in the western part of the field. The Gbokoda A-04 interval in the eastern Block-7 is a vertical succession of two shoreface units, which are separated by marine shelf shales that were deposited in the upper marine shelf. The Gbokoda A-04 interval in the western Block-3 is a single amalgamation of incised valley fill deposits known as A-04.
Composite maps, comprised of paleogeography, net-sand thicknesses, oil-water contacts, RMS (root mean square) amplitude anomalies, and bottom-hole pressure anomalies demonstrate consistent barriers between the eastern shoreface deposits and the western IVF (incised valley fill) deposits. Cores and a field-wide grid of cross sections demonstrate stratigraphic boundaries between the shoreface and the IVF systems. RMS amplitude anomalies define trend lines, approximately corresponding to shoreface/IVF boundaries. Though sparse, time-lapse bottom-hole pressure data demarcates the eastern part of the A-05 interval from the western part, with an anomaly that corresponds to the approximate boundary between shoreface and IVF deposits.
The new correlations help explain anomalous shifts in the oil-water contacts.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas