Jotun Field reservoir geology and development strategy: pioneering play knowledge, multidisciplinary teams and partner co-operation – key to discovery and successful development

Abstract

Accumulated knowledge from the early pioneering wells and subsequent exploration history led to the discovery of several fields in the Utsira High area during the 1990s. One of these, the Jotun Field, was discovered in 1994. The Jotun Field consists of three structures and is located on the western flank of the Utsira High, close to the eastern pinchout of the Tertiary submarine fan system. The reservoir at Jotun comprises Paleocene Heimdal Formation sands shed from the East Shetland Platform and transported across the Viking Graben area onto the Utsira High by high density gravity flow processes dominated by sandy turbidites. These distal gravity flow deposits display both thin-bedded sands alternating with shales and thicker, more massive sandstones (tens of metres thick). Minor sand injections occur throughout the field but are volumetrically insignificant. The production wells in one of the structures are completed in a slump and injection complex above thick massive reservoir sands. The Jotun Field development strategy was designed to optimize oil capture and minimize risk based on the interpreted reservoir geology. The initial development comprised 14 development wells: 12 horizontal producers, 1 water injector and 1 water disposal well. Production from the Jotun Field started in October 1999 and reached peak production in June 2000, with 140 000 BOPD. After exceeding initial expectations, declining production and rising water cut prompted an infill well programme, time-lapse seismic data acquisition and production logging in 2002. The first two wells were disappointing due to facies transition to interbedded sands and shales on the flanks of the structure and underprediction of oil–water contact movement. The newly available time-lapse seismic data were then integrated with production logging and updated depositional facies studies to evaluate additional drilling opportunities. The discovery, appraisal and development history of the Jotun Field serves as a good example of the key challenges in the Tertiary Utsira High play and the strength of applying multidisciplinary team efforts, partner co-operation and involvement to optimize asset value through tailored drilling and data acquisition programmes.