Structural characterization and water saturation evaluation of a shaly-sand reservoir rocks in an onshore, Niger Delta, Nigeria

Evaluation of shaly-sand reservoir units in an onshore field Niger Delta was undertaken. The study aim is to optimize recoverable hydrocarbon volumes/water saturation and structural style characterization using 3D seismic and composite well log data. The two delineated reservoirs were correlated with oil–water contacts estimated at 2628.02 m (8622 ft) and 2750.8 m (9025ft), respectively. The Larinov tertiary equation was applied in estimating the shale volume of the identified reservoirs. However, water saturation was estimated using Udegbunam, modified Simandoux, and Dual water models. The Formation water saturation value derived from the Pickett plots was inputted into the modified Simandoux, and Dual water models for each well. Furthermore, the reservoirs pay thicknesses were 32 ft and 50 ft, respectively, with projected average net-to-gross (NTG) ratios of 78% and 76%. From structural characterization, a total of four (4) fault features were identified with F1, F2, F3, and F4 focusing on the designated reservoir units. The identified synthetic faults are F1 and F2, whereas the antithetic faults are F3 and F4 based on the style. Using the time map layout of the picked horizons on the seismic volume, the reservoir peaks were deduced. The evaluation of the reservoir properties proved that the Dual water model is more robust owing to the values obtained from water saturation, NTG, and STOIIP of the identified reservoirs.