Diplog analysis of paleocurrent and depositional energy of Miocene reservoir sands in the northwestern Niger Delta

Abstract

Dipmeter log is an invaluable tool in the description of paleocurrent and depositional energy associated with subsurface sediments due to its high depth resolution and uniqueness as a method for studies of this kind. Interpretation of dip patterns and variations in dip amounts, in conjunction with composite log and biostratigraphic data, shows that the Lower to Middle Miocene sand reservoirs identified in two onshore wells in the Niger Delta were deposited under high to low energy conditions. The paleocurrent directions are mainly to the southwest, northwest, and southeast. Transporting water currents, waves, tides, and longshore currents dictated both paleocurrent directions and depositional energy. The interaction of these nearshore influences and the resulting pattern of sedimentation of the reservoir sands reinforce the conclusions drawn from studies conducted on Quaternary sediments along the Nigerian southwest coast and on Cretaceous sediments in the adjoining Anambra Basin. The levels of depositional energy deduced are indicative of the bathymetry of the reservoirs and their petrophysical properties. High-energy deposits occur in shallower water depths than the low energy deposits and are likely to be better sorted and more permeable. High variability in energy levels in some sand zones have been shown to correlate with depth intervals having repeated sequences of very thin reservoir sands often separated by minor shale beds.


KEY WORDS: Dips, paleocurrent, energy, deposition, reservoir


Global Jnl of Pure and Applied Sciences Vol.10(4) 2004: 635-641