Abstract:
The detection of subsurface reservoir structures and the estimation of reservoir parameters from well logs and seismic data remain the most widely used tools in the study of the subsurface The database which comprised 3-D seismic lines, borehole logs from three wells and checkshot survey data were used to study the structures, stratigraphy and hydrocarbon potential of a field offshore Niger delta sedimentary basin. Lithology interpretation was done using gamma ray log and hydrocarbon bearing reservoirs were mapped using a combination of gamma ray log and deep resistivity measuring log. Well log correlation was carried out using similarity in log signatures. Computation of reservoir parameters such as net to gross, volume of shale, porosity and hydrocarbon saturation was done using standard equations. The stratigraphy is composed of alternating sands and shale units. The shale units increase in thickness with depth and the sand units reduces in thickness. The reservoirs located at a depth range of 8326 ft to 10596 ft have average effective porosity of 28 , volume of shale of 12, net to gross sand 78 , hydrocarbon saturation 66 and permeability 21 . Eight distinct faults designated as F1 to F8 were mapped on the basis of amplitude, reflection geometry and frequency. Variance seismic attribute was also utilized to compliment the structural interpretation. Three horizons located at depth of 8236 ft, 8465 ft and 9198 ft were picked on the basis of prospectivity, events strength and continuity. The horizons were located within a time window ranging from 2.14 to 2.41seconds. Reservoir properties modelling were also carried out to evaluate the spatial distribution of facies and their effects on reserves estimation and hydrocarbon production. Seismic structural maps of the mapped horizons were also generated and the structures harbouring oil and gas are fault assisted and fault dependent anticlinal structures. Inaddition, the quantity of original gas-in-place (OGIP) and original oil in place (OOIP) were estimated to be 1,208 MMscf and 86 MMB respectively.
Integration of seismic structural maps and reservoir properties modelling provided detailed information on the structure and hydrocarbon prospectivity of the field.
