3-D Seismic Attribute Expressions of Deep Offshore Niger Delta Basin, Nigeria

Abstract

Structural and stratigraphic interpretation of 3D seismic data for reservoir characterization in an area affected by dense faulting is typically difficult and strongly model driven because of problems with imaging. In the Freeman field, located about 120km offshore southwestern Niger Delta at about 1300m water depth, 3D seismic attribute-based analogs, and structural and stratigraphic based geometric models are combined to help enhance and constrain the interpretation. The objectives being to show how 3D seismic attribute analysis enhances seismic interpretation, helps in the development of structural and stratigraphic architecture models and identifies trap mechanisms; with the main purpose of aiding prospecting of Miocene to Pliocene Agbada Formation reservoirs in the deep offshore Niger Delta Basin. A multidisciplinary approach which involved analyses of calculated variance-based coherence cube, spectral decomposition box probe and root-mean-square amplitude attributes, sequence stratigraphy based well correlation, and structural modeling; were undertaken to achieve these objectives. Results reveal a massive northwest-southeast trending shale cored detachment fold anticline, with associated normal faults; interpreted to have been folded and faulted by localized compression resulting from a combination of differential loading on the deep-seated overpressured-ductile-undercompacted-marine Akata shale, and gravitational collapse of the Niger delta continental slope due to influx of sediments. Crestal extension resulting from this localized compression is believed to have given rise to the synthetic, antithetic and newly observed crossing-conjugate normal faults in the study area. Presence of crossing-conjugate structures could have significant implications on permeability anisotropy, thereby modifying production. Detection of structure with crossing-conjugates is new for the entire Niger Delta and may be present in other principal oil fields in the basin. The Mid-Miocene to Pliocene age Agbada Formation reservoirs of the Freeman field occur as part of a channelized fan system, mostly deposited as turbidites in an unconfined distributary environment, except one reservoir sand that occurs as channel sand within a submarine canyon that came across and eroded a previously deposited distributary fan complex, suggesting likely presence of prospective areas for hydrocarbon exploration southwest of the Freeman field.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016