SOURCE:

Faculty: Physical Sciences
Department: Geology

CONTRIBUTORS:

Aigbadon, G. O.
Okoro, A. U.
Orajaka, I. P.

ABSTRACT:

This study was carried out using seismic, geophysical well logs, core and temperature data to build reservoir and geothermal models for the sequence penetrated by the wells in the Usani oil field. Core data and well log were integrated to evaluate the petrophysical characteristics of the reservoirs and calculate the hydrocarbon reserves. A depositional model was built for the field.The model identified that the fluvial channel facies with highly permeable zones constituted the reservoirs. Eight reservoirs were mapped at depth range of 2886m to 3533m with thicknesses varying from 12m to 407m. Petrophysical results show that porosity of the reservoirs range from 14% to 28 %; permeability from 245.70 md to 454.7md; water saturation from 21.65% to 54.50% and hydrocarbon saturation from 45.50% to 78.50 %. Calculated stock tank oil in place range from 0.0030mbls – 2.520mbls; stock tank gas in place range from 0.0307mbls/scf – 0.652bbls/scfand calculated recoverable reserve for oil and gas range from 0.0014mbls – 1.62mbls and 0.015mbls/scf – 0.326bbls/scf respectively. Core data and the gamma ray log trends in reservoir A with irregular / serrated motif indicates barrier bar sand in shallow marine environment. Thesymmetrical shaped log pattern and core logs from reservoirs B2,C2,C3 and C4 in well 2,3 and 4 indicate offshore regressive barrier bars in delta front environment.Seismic attribute map revealed presence of hydrocarbon in sands A, B, C, D1, D2, D4, D5. By-passed hydrocarbons were identified in low resistivity pay sands D1, D2 at depth of 2884m – 2940m andsand D5 at depths of 3114m - 3126m respectively. The hydrocarbon reserve of the by-passed zones D1, 0.015mbls/scf ; D2, 0.037mbls/scf ; D4, 0.025mbls; D5, 0.041mbls was added to the hydrocarbon reserve in the field. From geothermal analysis, the linear model generated shows that the shale of the Agbada Formation at determined temperature of 101.8 – 120.49oC at depths of 1350m – 3500m isthermally mature. Earlier belief that the Agbada Formation is immature and cannot generate hydrocarbon is invalidated by this model.