Tonto Field - The Application of AVO Inversion to Fast-track Development of a New Small Field at Forties

Over the past decade, lithology and fluid prediction from seismic has played a key role in optimizing well placement at the Forties field. To improve those predictions, 2010 vintage seismic data was recently reprocessed to broaden bandwidth while preserving AVO fidelity. This data was taken through AVO inversion constrained by depth dependent shale trends derived from well data. The results delivered a step-change improvement in lithology prediction at Forties.

An unexpected benefit of this work was improved imaging of steeply dipping Brimmond sands positioned above the Forties reservoir. These sands have been historically challenging to interpret on seismic data due to their complex morphology and highly variable AVO response to different fluid types. The new inversion results made it possible to confidently map these sands. The data was further interrogated for fluid effects when an oil-water contact was identified and mapped defining a new 3-way dip closure named Tonto.

Tonto became focus of an expedited development project targeting ∼2.5 MMBO of recoverable reserves from the Forties Bravo platform. One year after initially mapped, the field has two producers online with a cumulative oil production of ∼0.5MMBO. This paper describes the instrumental role seismic played in the decision to develop Tonto.