Fast-Tracking Field Development in a Green Field by Eliminating the Need for Appraisal Using Multidisciplinary Evaluation Methods

Abstract

Field development is heavily contingent on the proper delineation of the field's resource volume along with the subsurface uncertainties. For green fields, appraisal drilling reduces uncertainties, but has the potential of cost escalation and delays in project timelines thus making projects less competitive. This study highlights how a fast tracked appraisal/development strategy for 1.7 Tcf of gas development project worth $800mln was developed and approved by the regulatory authorities. The GATOE field under review is in the South East of the Niger delta, Nigeria. The field is 80 km2 in aerial extent. It consists of 11 stacked hydrocarbon-bearing reservoirs of varying thicknesses and, is penetrated by 5 wells. Seven (7) of these reservoirs (3 AG and 4 NAG) with GIIP of 900 Bscf that are ‘ready-to-go’ gas resource were captured in the ‘Tranche-1’ development scope. The remaining 4 reservoirs which are AG reservoirs with uncertainties in the actual oil column were grouped for trench-2 development but will be appraised during the Tranche-1 execution phase. Usually regulatory approval for field development is secured post appraisal drilling. This study however, proposes a concurrent field development and appraisal scheme where development wells (for fairly known reservoirs) are used to also appraise reservoirs with appraisal needs. Thus significantly reducing the number of appraisal wells (from 3 to 1) and ensuring the delivery of fast-tracked field development (early ‘First-gas’ date). The only appraisal well will be drilled at the tranche-1 execution stage. In order to achieve this, a multidisciplinary evaluation of all available data was done in addition to the use of reliable technology. This is with the aim of demonstrating that the fast-tracked gas development will not jeopardise the recovery of any potential oil that may be proved from the appraisal exercise. This study demonstrates the viability of a field development strategy in which ‘freezing’ of a development concept prior to full field appraisal can be achieved. The outcome is a massive reduction in appraisal costs and accelerated field development.