3-D structural and seismic attribute analysis for field reservoir development and prospect identification in Fabianski Field, onshore Niger delta, Nigeria

Abstract

An integrated 3-D seismic data, suite of eleven well logs and checkshot data from Fabianski field, Coastal Depobelt, Niger Delta basin Nigeria were analysed and interpretations carried out using relevant algorithm models in the Petrel workstation for detailed 3-D structural and seismic attribute analysis. The method adopted involves well log interpretation for identification of reservoirs tops and base, well correlation for determination of lateral continuity of the reservoirs, seismic structural mapping, seismic attribute analysis, lead(s)/prospect(s) mapping and risk assessment. Twenty-three (23) faults were interpreted to offset the stratigraphic packages within the field at different seismic horizons. These faults created structures that are favourable for hydrocarbon trapping and accumulation. Three reservoirs have been identified: FAB-1, FAB-2 and FAB-3. Correlation of the reservoirs across five wells along depositional dip shows that the reservoirs are laterally continuous with varying thicknesses at well points. FAB-1 reservoir was studied in detail because it corresponds to a seismic flat spot identified in seismic volume. Four prospects were identified within the FAB-1 reservoir based on structural contour closures: FAB-1 southern prospect, FAB-1 northern prospect, FAB-1 northeastern prospect and FAB-1 northwestern prospect. Only FAB-1 southern prospect shows evidence of hydrocarbon accumulation. FAB-1 southern reservoir is characterized by localized bright amplitudes of root mean square (RMS) and envelope attributes which indicates porous and fluid filled lithologies; constant drop-off high frequencies of instantaneous frequency (12 Hz–25 Hz), and very bright localized high values of sweetness attribute indicative of hydrocarbon saturated sand. Positive values of apparent polarity attribute validate the presence of hydrocarbons in the southern prospect. Spectral decomposition analysis shows that the FAB-1 southern reservoir is better imaged by a frequency range of 15 Hz–25 Hz. It is therefore concluded that spectral decomposition techniques integrated with seismic attributes can unravel subtle indications that are not independently conclusive, and delineate hydrocarbon charged reservoir geometry and structural discontinuities within complex tectonic settings.