Deposits of Robertkiri field, in the central offshore area of Niger Delta, comprise a 4 km
thick succession of Pliocene to Miocene non-marine and shallow marine deposits. A
sequence stratigraphic framework for Robertkiri field strata was constructed by
combining data from 20 well logs and a seismic volume spanning 1400 km2. Major
sequences, hundreds of meters thick, define layers of reservoir and sealing strata formed
during episodic progradation and retrogradation of deltaic shorelines. These deposits
progress upward from fine-grained prodelta and deep water shales of the Akata
Formation through paralic sandstone-shale units of the Agbada Formation and finally to
sandy non-marine deposits of the Benin Formation. The Agbada Formation is divided
into six third-order sequences starting at the first seismic reflection that can be mapped
across the seismic volume. The Agbada Formation under Robertkiri field is complexly
deformed across a succession of major, cuspate, offshore-dipping, normal faults, and
associated antithetic faults and rollover anticlines within down-dropped blocks. Thickening of intervals between some reflections across major faults and away from the
crests of adjacent rollover anticlines suggest syndepositional displacement. Relationships
between major faults and the thickness of transparent seismic facies that comprise lower
parts of the seismic record suggest faulting was associated with movement of
undercompacted shales within the Akata and lower Agbada Formations.
Robertkiri field is located along the proximal margin of the Coastal Swamp I
depobelt, a subbasin within the Niger Delta clastic wedge formed by margin collapse
into underlying undercompacted shale. Accommodation and sequence development in
this setting is controlled by both structural faulting and sea level fluctuations. Upsection,
sequences become thinner, more laterally uniform in thickness, less structurally
deformed and contain less growth strata. Erosion along sequence boundaries becomes
progressively shallower and broader, as accommodation under Robertkiri field declined
and more sediment was bypassed basinward. Incisions along the base of older sequences
(>100 m) is greater than 3rd order sea level falls reported to occur during the Miocene,
which suggests that there were local areas of tectonic uplift within this dominantly
extensional setting.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4768 |
| Date | 25 April 2007 |
| Creators | Magbagbeola, Olusola Akintayo |
| Contributors | Willis, Brian J |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 10414980 bytes, electronic, application/pdf, born digital |
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