Seismic Reservoir Surveillance in the Alba Field, UK North Sea

摘要

The feasibility of a time-lapse seismic response to productionrnwas identified early on in the life of the Alba field, UK NorthrnSea. The reservoir rocks and fluid properties (oil and water),rnwere conducive to a change in seismic properties in responsernto water encroachment. The acquisition of appropriate seismicrndata took longer to obtain, due in part to the vintage of the 3Drnbaseline survey (acquired in 1989) and the focus on lithologyrnidentification in a subsequent repeat survey (acquired inrn1998), shot using ocean bottom cable. The acquisitionrndifferences between the two surveys made it difficult tornextract more than the simplest 4D response from the surveys.rnIn 2002, the Britannia coventurers acquired a long offsetrnsurvey in response to their subsurface requirements. This datarnprovided an opportunity to revisit the overlying Alba 4Drnresponse, using a more recent baseline survey and monitor andrnmore similar acquisition geometries.rnThe intepretation of this more recent baseline and monitorrnpair showed that the amplitude of the direct hydrocarbonrnindicator (representing the oil water contact) was reduced byrnproduction. The contact was no longer a flat surface nearrnactive producers and the Direct Hydrocarbon Indicator (DHI)rnwas seen to be tilted. This was probably in response to thernproduction as the effect was not observed in the vicinity ofrnabandoned producers. Comparison of the observed response tornforward modeling of the seismic response from the reservoirrnsimulator confirmed that the effect was water coning under thernproducers. The forward modeling also identified thernpossibility for amplitude changes at the top of the reservoir.rnThese areas are being evaluated along with production andrnreservoir simulation to identify infill producer andrninjector locations.