Petrophysical Analysis and Volumetric Estimation of Otu Field, Niger Delta Nigeria, Using 3D Seismic and Well Log Data

Petrophysical analysis and volumetric estimation was carried out using 3D seismic and well log data to evaluate the reservoir potentials of Otu Field in the Niger Delta of Nigeria. Three hydrocarbon bearing reservoirs (C10, D10 and D31) were mapped out of several identified sands. The tops of these reservoirs were tied on the seismic section using checkshots and were traced throughout the seismic volume. Faults were mapped and structure maps for the three reservoir tops were produced. For C10 reservoir mapped at the depth of about 4512 feet, gas-down-to (GDT) was picked at 4525 feet and Oil-water contact (OWC) was picked at 4592 feet. For D10 reservoir mapped at the depth of about 5337 feet, oil-water contact was picked at 5404 feet and D31 reservoir which was mapped at depth 5536 feet has oil-water contact at 5675 feet. The gross thickness of the C10 reservoir sandstone formation ranges from 45 ft to 78.5 ft. Since the reservoir was intercalated with shale, the net thickness varied between 11.5ft and 54.5ft. The gross thickness of the D10 reservoir varied between 55.5 ft and 103 ft; while the net thickness varied between 13 ft and 51 ft. The gross thickness of D31 reservoir varied between 127.5 ft and 273 ft and the net thickness varied between 11 ft and 114 ft. The petrophysical parameters obtained were porosity (ϕ) ranging from 0.32 to 0.34, water saturation (Sw) ranging from 0.23 to 0.29, hydrocarbon saturation (SH) varies between 0.71 and 0.77 and net to gross (N/G) which ranges from 0.21 to 0.47. The volume of the closures (GRV) gotten from the structure maps were combined with the relevant petrophysical parameters to estimate the volume of hydrocarbon in place. The estimation of the volume of hydrocarbon revealed that C10 contains 45.98b ft3 of gas and 95.18 million stock tank barrels of oil. The D10 and D31 reservoirs have oil with the volume estimated at 21.41 million stock tank barrels and 54.32 million stock tank barrels respectively. The study revealed that the field is prolific and the estimated volumes of hydrocarbon in the closures are satisfactory for further exploration work.