There's a body of literature out there about the Niger Delta, but it is not as extensive as the literature on other parts of the world, particularly onshore areas, probably because of the scarse data available to the academic community and very limited publications by operators working the offshore blocks in Nigeria.
From my time working the Niger Delta, understanding the structure of the region and the timing of that structure relative to maturation and migration seemed to be the hotbutton basin-scale issues.
Mining the references of a paper such as "A simple method of determining sand/shale ratios from seismic analysis of growth faults: An example from upper Oligocene to lower Miocene Niger Delta deposits" S. Pochat, S. Castelltort, J. Van Den Driessche, K. Besnard, C. Gumiaux (AAPG Bulletin, V. 88, No. 10 (October 2004), P. 1357-1367) might be a good place to start.
Alternately, I'd recommend checking the references on some of the broader, survey papers such as "Fifty Years of Exploration in the Niger Delta (West Africa)" Luc Saugy, Jerome A. Eyer, M. T. Halbouty, 2003, Giant oil and gas fields of the decade 1990-1999: AAPG Memoir 78, p. 211-226.
Plenty of proprietary basin analysis for the Niger Delta exists within the major operators, but that won't help you.
Haack, R. C., Sundarara, P., Diedjomahor, J. O. et al. 2000. Niger Delta petroleum systems, Nigeria. In: Petroleum systems of South Atlantic Margins. (ed. by M. R. Mello and B. J. Katz), AAPG, Tulsa, OK, 213-231.