Publications

The Mahogany Formation is a syn-rift Oligocene naturally fractured over pressured sandstone reservoir in the WNB. This reservoir was discovered in 2012 from the deepening of a platform development well to explore deeper gas sands. The Mahogany Formation underlies prolific producing sands separated by a massive shale barrier. As the formation can be produced with the existing producing facility, it becomes an attractive exploration/development target due to the ease to commercialize. Currently, two wells have been drilled into the reservoir. GESNE-1 discovery well was drilled in 2012 and penetrated 129 ft net-pay of Mahogany-D Sand and tested at a maximum gas rate of 18 MMScfd. The well was suspended for future recompletion to the sands above the shale. The second (appraisal) well was drilled in 2015 and penetrated the same Sand, but did not flow due to poor productivity. Later, utilizing existing 3D seismic data, it was found that the well was located in an area of low fracture density. The first well started producing gas in 2017 once facilities were upgraded for the higher pressures from this deeper sand. It was expected to deliver significant production as suggested by the simulation model. The initial gas rate was excellent with no water production. However, after 3 months and less than 15% of GIIP recovered, water unexpectedly broke through. A year later, water cut continued to rise eventually producing insignificant gas. In order to fully appraise the Mahogany Formation, an upper interval was perforated to see the fractures characteristics and test its productivity. Unfortunately, the gas production was insignificant. Production logs, water flow logs and reservoir pressure have been acquired to confirm the reservoir behavior. This paper describes the lessons learned by Premier Oil during the studies and activities which hopefully will help with exploration in this type of play concept.