Sequence Stratigraphy Study of UNIABR Field in Northern Delta Depobelt of Niger Delta, Nigeria

Abstract

Integrated  interpretation of wireline logs and high resolution biostratigraphic data has enhanced the subdivision of the stratigraphic column within the Uniabr Field ( fictitious) (OML 4) in the Niger Delta  of Nigeria into five sequences and different  systems tracts.  It has also aided the identification of maximum flooding surfaces and type – 1 sequence boundaries.

Lowstand systems tract with basin floor fans, slope fans and prograding  wedge complex plus transgressive systems tracts and highstand  systems tracts occur in the field.  Five maximum flooding surfaces and five sequence boundaries are recognized with their average depths tie to their absolute ages.  All except the second sequence boundary are clearly type – 1 sequence boundaries.  Lowstand systems tract is missing on top of the second sequence boundary and is directly overlain by transgressive systems tract, hence it cannot convincingly be pass for a type – 1 sequence boundary.  Again, five sequences are identified from the base to the top of the stratigraphic column (of the field) with varying average thicknesses and cyclicities.  Based on their cyclicities of between 1.0  and 5.0 Ma, all the sequences identified in this field are third order type.  They have potential of both serving as excellent source rocks and providing stratigraphic traps.  A structural trap is speculated between the second and third sequences at 2417m (7930ft) depth below the mean sea level.

Based on palynological zonation of Uniabr – 1 Well (P450 – P650), the age range of the sediments penetrated in the Uniabr  Field is from Late Eocene to Early Miocene, thus placing the field within the northern delta depobelt of the Niger Delta.

Keywords : OML 4, Systems tracts, Maximum flooding surfaces, Type-1 sequence boundaries,Niger Delta.