HYDROCARBON CHARACTERIZATION AND PROSPECT IDENTIFICATION OF YZ FIELD, NIGER DELTA

Abstract

3D seismic data interpretation and well log analysis have been carried out for hydrocarbon characterization and additional prospect identification in YZ field, in the Northern Ughelli Depobelt of Niger Delta. Recently, major focus within the Niger Delta has been tending towards the regeneration of older fields and the identification of new prospects from these old fields. To this end, indigenous companies have been involved in developing marginal fields and the search for additional prospects is pertinent in developing and expanding the profitability of these fields. The data utilized for the analysis of YZ field were 3D migrated seismic data, 6 composite well logs and check shot. The well logs were correlated in the North to South direction. Synthetic seismogram was generated to aid mapping of the reservoir tops across the 3D seismic data coverage. Faults were delineated and mapped on the 3D seismic data by identifying abrupt terminations of seismic reflections. Seismic attributes analysis including RMS, maximum amplitude, sum of energy, sum of amplitude were extracted from the time map to enhance interpretation. From the well log correlation, five reservoirs namely Sand 1, Sand 2, Sand 3, Sand 4 and Sand 5 were identified. The pay thickness ranges from 3 to 39m across the reservoirs. The net to gross of the reservoirs ranges from 76 to 97% and effective porosity ranges from 18 to 22.2%. Petrophysical analysis have shown that the hydrocarbon type in Sand 2 is predominantly gas, Sand 4 is partly oil and gas and Sand 5 is predominantly oil. The hydrocarbon saturation ranges from 58 to 76 %. On the other hand, Sand 1 and Sand 3 has indicated no accumulation of hydrocarbon within the tested trap. It was also observed that four major growth faults are present in YZ field while other faults are either synthetic or antithetic to the major faults. Four horizons corresponding to the top of Sand 1 to 4 in the well log analysis were mapped across the 3D migrated seismic data. The structural maps from the mapped horizons, reveals structural highs and closures that are observed as fault assisted and dependent traps. Four to five additional prospects were observed across the mapped Sand reservoirs. The attribute analysis has shown high anomalies on some of the prospects which is supportive of possible accumulation of hydrocarbon. The identified prospects were ranked partly based on type of closure (fault assisted versus fault dependent), attribute support and volume estimates. In conclusion the additional STOIIP for YZ field is 194,025,188stb and GIIP is 193,804,479scf. Therefore, YZ field can be considered viable and encouraging for further development.