LITHOFACIES DISTRIBUTION AND DEPOSITIONAL ARCHITECTURAL STUDIES OF THE MIOCENE DEPOSITS OF THE “THOR” FIELD, COASTAL SWAMP DEPOBELT, NIGER DELTA BASIN, NIGERIA

Abstract

The study accesses the petrophysical data from the Eocene deposit of the “Thor” field, Coastal swamp depobelt, Niger Delta and process it to decipher the different lithological makeup, the reservoir units, the depositional architecture and how these factors influenced reservoir distribution within the field. The study made use of well logs consisting of gamma ray, resistivity, neutron and density logs. Gamma ray log aided lithological identification, resistivity logs help to isolate reservoir rocks from non-reservoir rocks while neutron and density logs was used to differentiate oil or gas zones. Three hydrocarbon reservoirs designated as R-1, R-2 and R-3 were interpreted from the logs and the sand bodies show a lateral continuity within the field in the north-eastern direction. Log sequences analysis of the field made use of a combination of gamma ray and restively logs via electro-sequence identification and mapping of key stratigraphic surfaces and the identification of para-sequences including retrogadational, aggradational and progradational stacking pattern leading to the delineation of the environment of deposition. The three stratigraphic surfaces enable the classification of the field into two depositional sequences and further subdivision into three system tracts. The first depositional sequence is interpreted as the oldest and lies at the base which is about 1201ft thick while the second depositional sequence overlies the first sequence with about 1605ft in thickness and is interpreted to be younger. Sediments within the two sequences are thought to be deposited in deltaic environment within the marginal to shallow marine settings.