Integration of 4D Seismic to Add Value: The Enfield ENC01 Sidetrack Story

Abstract

Abstract The Enfield oil field, on Australia's Greater North-West Shelf, has now produced over 50 million barrels of oil. The field is a water flood development with both downdip and updip water injection wells. Faults and baffles within the reservoir create a complex dynamic system that can only be understood with the integration of 4D seismic data. Monitor surveys in 2007 and 2008 have made major contributions to reservoir management and identification of infill drilling opportunities. This paper highlights the value of fully integrating 4D seismic into reservoir management, and the rationale for sidetracking a water injector well at short notice to provide pressure support to the field's largest producing oil well. Oil production from this well was dropping rapidly and the need to improve pressure support was clearly evident. It only became clear how best to achieve this upon delivery of new 4D results. The reservoir model directed attention towards insufficient water injection downdip and the opportunity to sidetrack these injection wells closer to the production wells was under consideration. However, results of the December 2008 4D monitor survey became available at this time, and indicated a reservoir baffle between the oil producer and the downdip injectors, which diverts water away from the producer. Thus improving injectivity at these downdip water injector wells would have had little impact on the failing producer. The 4D seismic data also indicated that water from a key updip injector was being deflected away from the producer. The difference here was that the baffle was close to the water injector and not the oil producer. The opportunity to sidetrack this water injector across the baffle was rapidly progressed, with the injector sidetrack drilled and completed in mid 2009. Pressure support at the oil producer was seen within days of commencing injection in the sidetracked well. Revenue from increased oil production paid back the cost of the injector sidetrack and the 4D monitor survey within two months of startup. The involvement of all subsurface disciplines was a key success factor in the outcome.