Structural Interpretation, Trapping Styles and Hydrocarbon Potential of Block-X, Northern Depobelt, Onshore Niger Delta

Abstract

Detailed structural interpretation had been carried out on the three fields within Block-X with the aim of better understanding the structural evolution, trapping styles and the influence of the fault system on the facies distribution within the Block. Well correlation was carried out on six wells for log analysis and to determine variation in lithology, which in turn was tied with seismic for horizon and structural interpretation to generate structure maps that formed inputs (fault polygon & depth structure maps) for static modelling. This allows for building a 3D spatial framework, facies and property distribution models and ultimately determine probabilistic hydrocarbon–in–place volume.

Structures interpreted include listric growth faults, roll-overs, synthetic and antithetic faults. The synthetic faults are dominant across the Block and they formed the main boundary of the three Fields within the Block. The faults showed a dominant NW-SE trend, and the variance attribute also validated the interpreted fault trend. Impact of a mobile clay substratum was more noticeable around ‘FLO’ and ‘A’ Fields around the Upper Eocene to Lower Oligocene strata of the Agbada Formation. Four-way closures dominate ‘OGEY’ Field, the traps on ‘FLO’ Field are fault assisted while ‘A’ Field at best have some good leads which given some more control on the seismic acreage could possibly have good prospects.

A 3D structural model was built for the hydrocarbon zone in which grid cells were assigned values for facies (discrete) and property model (continuous) to estimate the hydrocarbon in place. An oil-down-to was picked at -1763 m SSTVD on the depth structure map of Shale marker (SM) 3. The facies model showed minor shale content localised at the western part of the Block with good reservoir sand and some silty sand making up the remaining Block. The fault system of the Block was not observed to have any significant effect on the facies and property distribution. A probabilistic volume of hydrocarbon-in- place determination yielded a volume of 69.8 x 10³ MMbbls. The fluid contact model revealed communication across the fields and that the reservoir is not compartmentalised.

This integrated approach in determining the hydrocarbon potential of Block – X, Northern Depobelt of Niger delta reduces the effect of under estimation and over estimation of hydrocarbon –in – place volume, thus assisting in well planning and input into running Petroleum economics.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018