Jubilee Field Reservoir Description & Waterflood Performance Overview

The Jubilee Field is a unitized deepwater oil development located approximately60 km offshore Ghana. The field was discovered in June 2007 with firstproduction achieved on November 28, 2010. This paper reviews the field'sreservoir description, gives an overview of the static and dynamic reservoirmodeling process used to plan the first phase of field development, anddescribes how the uncertainty inherent in these models was reduced usingdynamic data from long term interference testing conducted prior to fieldstartup. Interference test results were used to evaluate inter-well reservoirconnectivity over distances of several kilometers in a subsea environment andplayed an integral role in the reduction of uncertainty. This paper alsodescribes the Phase 1 development strategy and reviews Jubilee waterfloodperformance. Introduction The Jubilee Field is located 60 km offshore Ghana in water depths averaging1200 meters (Fig. 1). The field was discovered by Kosmos in June 2007 with theMahogany-1 exploration well and contains two primary reservoir intervals, theUpper and Lower Mahogany. Fig. 2 is a type log showing the current and initialreservoir zonation nomenclature. The seventeen well Phase 1 development programtargets the two most volumetrically significant reservoirs in these intervals, the MH4 (UM3) and the MH1 (LM2), and comprises nine producers, six waterinjectors, and two gas injectors. Fig. 3 shows the Phase 1 development welllocations relative to the Jubilee Field unit boundary and the developedreservoir outlines. The dynamic inter-well connectivity and water injectivitylevels achievable during waterflood were identified early on as key reservoiruncertainties. A June 2008 DST in the Mahogany-2 appraisal well had indicatedpotential compartmentalization within the Lower Mahogany interval. To reducethese uncertainties a four well long term interference test was initiated inthe MH1 (LM2) reservoir in May 2009, eighteen months prior to field startup. Results from the interference testing established pressure continuity throughthe reservoir over distances exceeding 5 km, reduced the uncertainty inoriginal-oil-in-place (OOIP), and confirmed pre-test water injectivityestimates. Field startup occurred November 28, 2010 and production hascontinued to ramp up as additional Phase 1 wells have been brought on line. Astatic and dynamic reservoir model uncertainty analysis constrained with ahistory match through January 2011 of the interference test pressures and onlythe first two months of field performance significantly reduced the uncertaintyassociated with Phase 1 waterflood performance. The work described in thispaper was performed by a Kosmos-led multi-disciplinary Integrated Project Team(IPT) that included team members from Kosmos, Tullow, and Anadarko. Reservoir Description The exploration of the Tano Basin and the discovery of the Jubilee Field havebeen described previously by others (Ref. 1). The Mahogany-1 (M-1) explorationdiscovery well location was selected to test Late Cretaceous Turonian fanobjectives identified with 3D seismic data. The well was drilled to a totaldepth of 3,802 m TVDss and encountered an estimated 98 m of net oil-bearing paywithin a 271 m gross interval. The Hyedua-1 (H-1), Mahogany-2 (M-2), andHyedua-2 (H-2) appraisal wells were drilled by the end of 2008 and confirmed a250 m average gross interval of stacked, amalgamated turbidite channel and fansands with net pay intervals ranging from 20 - 100 m TVD. Fig. 4 is an RMSamplitude extraction on the Mahogany Fan from 2009 showing the Jubilee Fieldunit boundary and the locations of the discovery and appraisal wells.