Forward modelling of a compartmentalised reservoir: Insights into changing oil water contacts across the Vincent Van Gogh Field, Southern Exmouth Sub-Basin, North Western Australia
Millard, Daniel T.
Honours Degree 2006
University of Adelaide
Reservoir compartmentalisation has a significant impact on field development, both economically and strategically. Development of the Vincent Van Gogh Field, in the Exmouth Sub-basin, is governed by a complex set of geological circumstances including stratigraphic compartmentalisation. Three separate oil water contacts have been encountered to date in an area devoid of known faults. With limited well penetration over the field, locating the barrier separating the Vincent and Van Gogh accumulations has proven a difficult proposition.
Interpreting oil water contact (OWC) depth from the seismic data is virtually impossible, due to the effect of geology and fluid fill on the geophysical response. Consequently, this forward modelling project was undertaken prior to the planned appraisal drilling, in an effort to quantify amplitude variations associated with the changing position of the OWC. Models were based on selected seismic traverses, and constructed in a rock physics package called RokDoc. Rock and fluid properties were incorporated from well data, while the appropriate hydrocarbon substitutions were performed via Gassmann theory.
Models were created with a constant OWC throughout the field, with one model for each of the three known contacts. Changing facies and interference effects complicate the OWC response, but while tuning is witnessed within the gas leg, it has minimal influence on the oil response, and ultimately is not a significant element in this study.
Despite the complex seismic response, amplitude comparisons from two events in the crestal model provide reasonable evidence to suggest that the deepest OWC extends as far north as the current P50 barrier interpretation, in the adjacent production licence. Seemingly due to the effects of resolution limitations, the actual oil response amplitudes to the north of this location match much better with the modelled (lower) amplitudes from the two shallower contacts.
If these results are correct, the 1314mSS Vincent OWC should be encountered with the proposed appraisal well. The recommendation would be to drill the northern option, into the interpreted P50 compartment. A successful result here would greatly improve confidence surrounding the current barrier interpretation, maximising reserve and unitisation information, whilst providing greater flexibility with respect to the initial phase of production well planning.