Impact of Bioturbation on Quality of Early-Middle Miocene Shoreface Reservoirs, Coastal Swamp Depobelt, Niger Delta Basin (Nigeria)

Abstract

AbstractCore sections from two wells (M-11 and M-22) from the lower Miocene interval, in the Coastal Swamp Depobelt, Niger Delta Basin, were studied to determine the depositional environments and the impact of bioturbation on the reservoirs. Plots of average porosity and permeability values against the bioturbation intensity (BI), for the upper shoreface (USF) and lower shoreface (LSF) sections in each well, indicate that the burrowed intervals in the USF sections show a decline in porosity values with an increase in bioturbation intensity, reaching a maximum of 12% in M-11 well and 51% in M-22 well. The burrowed LSF section in M-11 well showed an increase in porosity with an increase in bioturbation intensity reaching a maximum of 38%, while the burrowed LSF section in M-22 exhibited a decline in porosity value to 45%. However, the burrowed USF and LSF sections in both M-11 and M-22 cores, showed a general decline in porosity/permeability with an increase in bioturbation intensity. The trends between bioturbation intensity and porosity/permeability in this study suggests that intervals with: (i) Moderate and rare bioturbation (BI: 2–3) have better reservoir quality, probably due to limited impact on the sediment fabrics (ii) Intense bioturbation (BI: 4–5), affected reservoir quality negatively due to the decrease in grain sorting resulting in porosity/permeability loss in the USF. However, in the LSF the reduction of porosity and permeability may be, related to siderite cementation.KeywordsBioturbation intensityShoreface reservoirsReservoir qualityNiger delta Basin