Volumetric re-evaluation of the Seahorse Oil Field, Gippsland Basin
Goedecke, Alison P.
Honours Degree 2008
University of Adelaide
The Seahorse Field is located in the offshore Gippsland Basin, southeast Australia. It is a relatively small oil field and has been producing since 1990. The initial completion allowed production from two reservoir levels with different OWCs, the N1 and N2.6. In 2005 the N2.6 was isolated and production continued from the upper zone only.
The purpose of this study was to estimate the reserves remaining in the field, based on interpretation of the 2001 Northern Fields 3D Seismic Survey. This was done using a material balance approach which compared production to date with volumetric OOIP calculations. Quadrature phase seismic data was interpreted and combined with well data from the study area to produce volumetric estimates for each of the five reservoir sands, the N1.1 to N1.4 and the N2.6.
Results show that the field structure splits the reserves in each reservoir sand into three separate sections. The producible volume can in principle be drained from the current producer, Seahorse 1. In addition, there are two attic sections, one in the western part of the field and the other above the well penetration. The western attic is formed due to the rising of the two OWCs above a saddle point on the structure and is smaller than the main attic at each reservoir level.
Deterministic volumetric analysis concludes that a potential 1.5 MMbbl remains recoverable from Seahorse 1. An additional 1.8 MMbbl is potentially recoverable from the attic regions of the field, based on average reservoir parameters. The uncertainties in these numbers can be attributed to those in the individual parameters used in the volumetric calculations. In particular, the low relief of the structure makes the gross rock volume very sensitive to even relatively small velocity variations across the field, and depth conversion is a significant source of uncertainty in the results.