Seismic Attribute Analysis for Reservoir Description and Characterization of M-Field, Douala Sub-Basin, Cameroon

Abstract

Complexity of discontinuous reservoir units occurring within the shale-rich N’kapa Formation and the limitation of well-articulated interpretations deduced from 2D seismic data, led to a new approach of interpretation of the 3D seismic data of M-Field located offshore Douala Sub-Basin, Cameroon. The study aimed at determining the subsurface distribution of the delineated reservoir units in terms of geology, structures, stratigraphic architecture as well as the lateral and vertical distribution of each of the reservoir units across the field.Well log signatures were analyzed and interpreted to identify hydrocarbon bearing sands, which were subsequently mapped to the 3D seismic record using the generated 1D synthetic seismogram to tie the well information to the seismic volume. The delineated hydrocarbon bearing sand bodies were mapped as horizons on the 3D seismic record in addition to subsurface structural mapping to generate subsurface depth structure maps. Further still, amplitude variation surface seismic attribute analyses aid the delineation of geometry of depositional channels across the M-Field. Two horizons (X₁ and Y₁) were interpreted and used to generate surfaces attribute maps. The M-Field reservoirs present stratigraphic architecture which suggests levees or confined channel sands deposit as the dominant channel deposit. X₁and Y₁ are stratigraphic trappedhydrocarbon systems, however, while X₁ is located up-dip, Y₁is situated on a monoclinic slope in the down dip area of X₁, such that Y₁ stratigraphically seats on X₁but eroded around X_1. The high amplitude associated with the delineated erosional surface likely results due to difference in acoustic properties across the interface owing todifference in age and composition of the two units. This suggests that the delineated reservoirs are two different units which are not correlateable as earlier postulate.