Seismic Interpretation and Attribute Mapping Of The Petrel Gas Field, Bonaparte Gulf, Northwestern Australia.
Honours Degree, 1997
University of Adelaide
The hydrocarbon reservoirs of the Petrel Gas Field on the Northwest Shelf occur in the Cape Hay Member of the Permian Hyland Bay Formation. The Cape Hay Member is bounded by the Dombey and Pearce Members, which are laterally consistent marine carbonates and generate two distinct, laterally extensive seismic marker horizons. Initial observations indicate that the reservoir intervals should be similarly consistent. However, the appraisal wells drilled to date have proven that the reservoirs are discontinuous and occur as `pockets' in a relatively geologically complex section. A thorough understanding of the depositional environment is required to predict the distribution of the reservoir units and estimate the lateral extent of the gas reservoirs.
The depositional environment of the Cape Hay Member proved to be one of the major problems encountered in this project, because the currently accepted depositional model conflicts with recent palynological data. The difficulty in applying a predictive geological model to the distribution of the reservoirs has been the conundrum responsible for the inconsistent results of the appraisal wells drilled to date. To overcome this problem, seismic attribute mapping was investigated as a method of directly mapping the lateral extent of the gas accumulations and/or the distribution of reservoir quality.
The methodology used to address this problem required the construction of synthetic seismogram models in order to demonstrate which physical property variations in the reservoir would have a substantial effect on the reflection response. Results from the modelling revealed that a number of physical properties, such as thickness and porosity variations, will have a significant effect. In a typical reservoir, the cause of its particular seismic response could not be unambiguously determined from the stacked seismic data alone.
Key seismic horizons were then interpreted across the field and seismic amplitude analyses were performed over the reservoir intervals. The results of the amplitude mapping were encouraging, with amplitude distributions correlating to the well data.