Prediction of Reservoir Performance of Moby Field, Niger Delta Basin using Integrated Facies and Petrophysical Analyses

Abstract

To effectively predict reservoir performance, and make proper reservoir managements within the depleting Moby field, Niger Delta Basin of Nigeria, the effect of facies changes on reservoir quality has been studied. Well log and 3-D seismic facies analyses were used to determine the depositional facies within the study area, and have shown how the facies changes affect the petrophysical properties of the reservoirs. The facies analysis from the well log showed five subfacies environments and three facies associations. The identified subfacies include; up bar distributary channel subfacies (UD), distributary mouth bar subfacies (DM), intertidal subfacies (IT), sub tidal subfacies (ST), and Storm dominated shelf subfacies (SD). The UD and DM subfacies belong to the delta front facies association, the IT and ST subfacies are of Tidal flat facies association, while the SD subfacies is associated to the Shore face facies. Continuous high and low amplitude (D-facies), high amplitude convergent (CBH-facies), high and low amplitude convergent (CBHL-facies), and low amplitude discontinuous, shingled to chaotic (BLfacies) all make up the four identified seismic facies. The D-seismic facies correspond to the Delta front facies, CBHL-seismic facies correspond to the sub tidal subfacies, and CBH-seismic facies are of the intertidal subfacies, while the BL-seismic facies correspond to the storm dominated shelf facies. Calculation of the sand percentages for the seismic facies show that the D-seismic facies has the highest reservoir percentage, and is ranked highest than the other seismic facies identified. The paleoenvironment of the Moby field was therefore inferred to be marginal to shallow marine environments. Nine reservoirs (H1-H9) were identified from qualitative petrophysical analysis. The H1 and H2 reservoirs are deposits of the delta front facies, the H3-H6 reservoirs are deposits of the intertidal subfacies, while the H7-H9 reservoirs are deposits of the sub tidal subfacies. Quantitative Petrophysical analysis of the reservoirs shows that H1 and H2 reservoirs possess the best petrophysical properties. This is followed by that of the H7-H9 reservoirs, and lastly the H3-H6 reservoirs. The variations in petrophysical properties of the reservoirs within the study area are associated with different depositional conditions and settings.