--> ABSTRACT: Optimising the Rewards of Appraisal Drilling, by John Gdula; #91019 (1996)

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Optimising the Rewards of Appraisal Drilling

John Gdula

Management of the uncertainties associated with the development of a hydrocarbon resource is essential to minimise economic risk. In many instances these uncertainties can only be reduced by appraisal drilling. This presentation illustrates the efforts being made to manage uncertainty by determining its impact on overall project profitability. The Value of Information (VOI) approach is described. VOI aims at quantifying the benefits of appraisal by determining its economic reward in terms of its contribution to a development plan which is economically robust over the uncertainty range.

Appraisal drilling costs can be reduced by combining appraisal and development objectives in one well. The growing use of horizontal drilling technology has resulted in novel approaches to appraisal. As examples, in the Osprey and Brent Fields (UK North Sea) wells were designed to satisfy both appraisal and development objectives. In Osprey, a well was drilled from a central production platform to provide water injection support in a satellite structure while at the same time appraising the saddle area between the two structures. In Brent, horizontal wells are used to appraise and develop the so called slump blocks, characterised by being highly faulted and compartmentalised.

Another increasingly common application of horizontal wells is for the flank appraisal of hydrocarbon bearing structure. Examples from the Rabi Field (Gabon) and Batan Field (Nigeria) show how appraisal was achieved by extending the reach of horizontal development wells from the central core of the structures.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California