The Forties Field, the largest oilfield in the UK North Sea, has been a prolific producer since its initial development. With an initial plateau rate of 500 000 bopd the field had produced some 2500 mmbo and the field rate had declined to 41 000 bopd by 2003 when the operatorship changed from BP to Apache. From 2004 to 2012, over 100 bypassed pay targets were drilled with a success rate of 75%, establishing a late life plateau of 50 000–60 000 bopd.The Forties reservoir is provided by Paleocene turbidites of the Forties Sandstone Member of the Sele Formation, deposited in a channelized proximal area of the Forties Fan. In this paper, the reservoir architecture is described, and bypassed pay examples are discussed in the context of the reservoir architecture and the production history. Bypassed pay is shown to occur in both the high net to gross channel axes and the heterogeneous wing deposits. Oil is trapped by subseismic channel architecture and subtle faulting. The occurrence of bypassed pay at a particular location is also shown to be dependent on the continually evolving pattern of injection and production within the field.
Apache discovered the Maule field in October 2009 with the 21/10-A52 wellbore drilled from the Forties Alpha production platform. The discovery of a 14m TVD net oil column in Eocene aged Brimmond sands led to the development of the Maule field under the UK government's small field allowance scheme. The field was taken from completion of the discovery well to first oil from a horizontal production well in under 9 months. The Maule field is located on the western margin of the Brimmond Formation turbidite fairway where re-mobilised sands are also present. Steep dips as seen in the development well and steep seismic features indicate that the Maule field reservoir was formed by remobilsation of Brimmond sands. The A52 exploration well was drilled on the basis of a seismic amplitude anomaly. This seismic data along with LWD density image data was used to successfully place the horizontal production well which accessed a 114m MD pay section and flowed in excess of 11,500 bopd. A 2010 4D snapshot taken in early July 2010, 5 weeks after production started, identified the source of the well's rapidly increasing water-cut and identified further infill locations. Despite modest production for an offshore North Sea development the first Maule producer has been an economic success for Apache as a result of integrated subsurface technical work, drilling performance, small field allowance incentives and a sense of urgency.
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