INTEGRATING ATTRIBUTE ANALYSIS AND STRUCTURAL MODELLING FOR EVALUATION OF THE HYDROCARBON POTENTIAL OF ‘BA’ FIELD, NIGER DELTA

Abstract

3D seismic and well log data have been used to map the stratigraphy and hydrocarbon potential of an offshore field in Niger Delta. This environment is a high risk environment characterized by complex geologic structures and low sand to shale ratio. The data base comprised 3D seismic lines, borehole logs from five wells and checkshot survey. Lithology interpretation was done using gamma ray log and hydrocarbon bearing reservoirs were mapped using a combination of gamma ray and deep resistivity logs. Well log correlation was carried out using similarity in log signatures. Computation of petrophysical parameters such as net to gross, volume of shale, porosity, permeability and hydrocarbon saturation was done using standard equations. Identification and mapping of network of faults was carried out on the basis of amplitude, reflection geometry and frequency. Seismic attributes such as variance edge, root mean square, minimum and maximum amplitudes were also utilized to compliment structural interpretation. Two horizons located at a time window ranging from 3 to 4 milliseconds were picked on the basis of prospectivity, event strength and continuity. Reservoir properties modelling were also carried out to evaluate the spatial distribution of facies and their effects on reserves estimation and hydrocarbon production. Uncertainty evaluation using deterministic and probability were analysed to reduce risk in oil and gas production. The stratigraphy is composed of alternating sands and shale units. The reservoirs located at a depth interval of 2.4 to 3.0m have average effective porosity of 32%, volume of shale 10%, net to gross 80%, hydrocarbon saturation 87% and permeability 1100 mD. Well correlation panel depicted the general stratigraphy, lateral and vertical extent of the reservoir units. The probable structure harboring oil and gas is a faulted anticline. The reserves of gas for reservoirs 1 and 2 are 1.4*10^6 and 1.8*10^6 MSCF. Integration of seismic structural analysis and reservoir facies modelling has contributed immensely in revealing structural complexities and economic potentials of the field with a view to reducing risk and enhancing future field development.