Earth Resources Laboratory :: Abstracts

Seismic Stratigraphic Analysis in the Niger Delta:
A Case Study of the Benin River 3-D Seismic Cube

Elliot Ede Ibie

Submitted to the Department of Earth, Atmospheric, and Planetary Sciences on October 17, 1997 in partial fulfillment of the requirements for the degree of Masters of Science in Geology/Geophysics

Abstract

Regional unconformity surfaces in the Niger Delta are important stratigraphic features that bound successions of genetically related strata (sequences) and serve, in some cases, as stratigraphic traps. The Benin River 3-D seismic cube was thus studied in order to map depositional sequences and their boundaries, establish their ages and environments of deposition, and calibrate well log character and biostratigraphy.

The analysis involved initially generating a structural framework for the seismic cube by carrying out a detailed fault interpretation, and then defining genetic reflection packages by identifying stratigraphic discontinuities on the basis of reflection termination, seismic stratal onlap, downlap or toplap. Seismic facies analysis was also introduced by determining variations in seismic pattern within individual seismic sequences and studying the geometry of reflectors, as well as their amplitudes and continuity.

Six sequence boundaries were identified within the project area largely from an analysis of the seismic sections, but with input from the well logs. These sequence boundaries range in age from the Lower Oligocene to the Middle Miocene. The oldest identified sequence boundary was denoted as Sequence Boundary_A, while the youngest was denoted as Sequence Boundary_F. Four sequence boundaries are recognized based on the presence of incised topography, while the other two sequence boundaries are identified by a combination of the analysis of seismic sections and well logs.

The sequences bounded by these sequence boundaries were analyzed based on their seismic attributes and a tie-in was made with their hydrocarbon potential to provide a framework for possible reservoir prediction. The sequences are second- and third-order frequencies. Stratigraphic seismic markers were also identified, corresponding to distinct episodes within sequences, the most prominent of which was the Top basin floor fan mapped within the deepest studied sequence.

Of the six sequences studied Sequence_A, C, D and E were found to contain hydrocarbon accumulations, while Sequence_B and F were observed to be composed of sands with no measurable accumulations of oil or gas.