Effects of Depositional Environments on Hydrocarbon Production from Sandstone Reservoirs

Peter Damian Emeka Agbata
University of Port Harcourt, Port Harcourt, Nigeria

Understanding the reservoir geologic characteristics is necessary for optimum recovery and effective reservoir management. The development scheme of a field can be strongly affected by the uncertainties in the connectivity of various reservoir units. A good knowledge of the environments of deposition of reservoir rocks and the prevalent geologic processes prior to and after hydrocarbon impregnation of these rocks is a key step in developing reservoir geologic description. This paper presents the common depositional environments of most reservoirs in the Niger Delta and their effects on fluid production. In the Niger Delta, reservoir quality is strongly dependent on the environment of deposition; known reservoir rocks are Eocene to Pliocene in age and are often stacked. Most important reservoir types are point bars of distributary channels and coastal barrier bars intermittently cut by sand filled channels. Deep-sea sands and proximal turbidites create potential reservoirs in the outer portion of the delta complex. Reservoir quality is affected by digenesis, compaction and shaliness. The paper further demonstrates how proper determination of the environment of deposition of a field was used for modeling two reservoirs in that field and for a water flood project.