STRATIGRAPHIC FRAMEWORK OF THE BARROW GROUP AND IMPLICATIONS FOR THE HYDROCARBON POTENTIAL OF THE WEST BARROW AREA

Abstract

An integrated sequence stratigraphic approach has been used to resolve, with high resolution, the chronostratigraphy of the Barrow Group in the West Barrow area. Assessment of the hydrocarbon potential has resulted in identification of various play concepts and exploration risks.

Five Barrow Group sequences are identified; each developed in response to tectonically or eustatically induced changes in sea level. The sequence stratigraphic framework provides an explanation for the distribution of reservoir and overpressure encountered in the area, and insight to the sealing potential within the Lower Barrow Group.

Utilising the sequence analysis results, two strategies for geophysical mapping were established; structural mapping of reservoir/seal interfaces identified in Top Barrow and intra-Lower Barrow Group intervals, and secondly, amplitude mapping of seismic events associated with sandstones within the overpressured Lower Barrow Group. Amplitude extraction mapping of a seismic reflection generated by the submarine fan complex intersected by the West Barrow wells demonstrates a lobate areal geometry with well developed apparent channel axes. The occurrence of lobate sands within an overpressured shale, combined with hydrocarbon shows within the interval, highlight the stratigraphic potential in the area. Petrographic studies, however, indicate that diagenetic occlusion of pore space has downgraded the reservoir quality of these sands.

At Top Barrow Group level, depth conversion of time structure maps using the midpoint depth technique has revealed structures not evident with time mapping. The largest closure encompasses the West Barrow-1A location where log analysis and gas homologue ratios indicate that a potential light oil/condensate hydrocarbon column may remain untested.