Application Of Deterministic And Stochastic Analysis Of Fault Seal Integrity In Baka Field, Niger Delta.

ABSTRACT

Fault seal analysis in fault dependent reservoirs were carried out at different reservoir levels in the Baka Field, Niger Delta. These involved stratigraphic correlation, 3-D seismic interpretation of faults and horizons, time-depth conversion of all interpreted faults and structural maps using both check-shot and synthetic seismogram. Also, static models of all interpreted reservoir levels, and 3-D deterministic and stochastic fault seal integrity models were carried out. The deterministic approach applied in this study is sensitive to uncertainties associated with mapping of horizons in the proximity of faults and the inherent uncertainties in the static fault interpretation in both position and fault zone properties complexity. However, the integration of stochastic approach captured the uncertainties in the position of the reservoirs at all interpreted faults by allowing multiple realizations of stacking geometries relative to their lateral reservoir distribution. All hydrocarbon bearing reservoir levels and faults were interpreted in detail on seismic and a structural framework model was built for juxtaposition analysis and fault shale gouge ratio calculation. The interpreted hydrocarbon columns of the reservoirs in the field are mostly controlled by structural spill points, implying that the faults affecting the accumulation must be effectively sealed which is evident from calculated high SGR values. Some reservoirs are under filled, indicating that the faults are leaking. It was shown that these fault intervals have relatively low SGR. There is high degree of conformity between field hydrocarbon column heights and the stochastic column heights predicted from the shale gouge ratio. The calculated shale gouge ratio quite matched with the shale gouge ratio related column height distribution used in exploration. Top shale thickness played a role (impede up dip fluid conduit), but not a major factor in the Baka reservoirs as regards to column controls. Also, faults in the Baka Field leaks at 40% shale gouge ratio. Shale gouge ratios are higher at the boundary fault.

Key words: Fault seal, Shale Gouge ratio (SGR), Hydrocarbon column Height, Stratigraphic Juxtaposition, Structural Spill Points and Leaking points.