Assessment of the heterogeneity and petrophysical evaluation of reservoirs in the “Akbar Field”, Niger Delta, Nigeria

Abstract

Abstract This study involved the use of well logs from four wells (JAP-1–4) to evaluate the reservoirs’ quality and to determine the clay distribution trends of the reservoirs using the neutron–density crossplot in the “Akbar Field” Coastal Swamp depobelt, Niger Delta. The results of the analysis show that a total of fifteen (15) reservoirs (A1–A15) were delineated and they are relatively laterally continuous. There is an increase in reservoir thickness as the delta prograded, giving rise to good sand development down-dip at the shallow and intermediate intervals. From the interpreted gamma ray log motifs, it was observed that reservoirs A1–A5, A8, A10 and A12–A14 are tidal channels; A7 and A11 are fluvial channels; A9 and A15 are shoreface sands, while only A6 is of coastal plain deposit. The reservoir porosities show good–excellent values that range from 0.15 to 0.38 v/v (15–38%) except in JAP-1 well where reservoirs A4, A5 and A9–A11 have poor to fair value of 0.11 v/v (11%). Also, the permeability values are good to excellent (1866.24–75873.41 md), except for the few sands in JAP-1 well that are low (3.42–72.82). Additionally, the neutron–density crossplots show that the reservoirs contain mainly laminated and structural clays with few dispersed clays. Despite the presence of these three clay types, the reservoir qualities of the reservoirs are not relatively affected. Although the horizontal fluid flow may not have been affected, the vertical flow could be impaired due to the presence of numerous laminated clay/shale baffles compartmentalizing the reservoirs.

Keywords

• Reservoir quality
• Clay volume/distribution
• Depositional environment