The Mahogany field was discovered in 1968 and appraisal was completed in 1996. The field is located 50 miles offshore eastern Trinidad (Fig. 1) with the platforms situated in water depths of 230 feet and contains more than 30 stacked sands (17 of which are gas bearing) with a development footprint area of c. 10000 acres. Initially the field’s resources were booked assuming volumetric depletion was the dominant drive mechanism (Nandalal and Gunter 2003), however the updated understanding showed that water drive was the prevailing mechanism with near volumetric depletion being exhibited by only two reservoirs within the field, the TQ51 FB4 and TQ51 FB5.
There were two development wells in the TQ51 FB4, MA04 and MB13. MA04 became liquid loaded and stopped producing in March 2004 after fourteen months of concurrent production with MB13. MA04 showed volumetric behaviour until late life. Due to the volumetric response exhibited by the reservoir, the MB13 well was assigned low pressure access resources and was also used as a swing well to compensate for gas market demand fluctuations.
Conventional material balance techniques (P/Z, Havlena Odeh, van Everdingen Hurst aquifer match) led to the belief that the drive mechanism was volumetric to very weak aquifer support. Pressure Transient Analysis (PTA) and pore volume material balance estimates showed the presence of an edge drive aquifer. This was corroborated by geological studies which showed that although the two reservoirs had the same initial gas water contact (GWC), with production they became two separate compartments exhibiting different properties, the aquifer acting via an edge drive mechanism.