Technical Paper
Technical Paper

A Probabilistic Multi-Scenario Seismic Inversion Scheme for Field Development and Appraisal

Written by: Ehsan Naeini and Jalil Nasseri

Field appraisal and development plans aim to provide the best technical solution for optimizing the production and require integration between various disciplines including geology, geophysics, engineering, well planning and environmental sciences. Of course this is a broad definition and the geophysics loop itself can consist of many studies. On that note, one could argue that seismic inversion is the fundamental, and perhaps the most critical, step in the quantitative interpretation (QI) workflows (and generally in the seismic discipline) to provide the final deliverables for field appraisal and development evaluations. It is therefore of significant importance in seismic inversion to assess all the possibilities and incorporate all the uncertainties involved in the reservoir definition and extension.

The case study in this paper centres on a recent Paleocene discovery, known as Avalon, in block 21/6b of the UK Central North Sea located at the north-western edge of the Central Graben just south of the Buchan Field. The reservoir sands lie within the proximal part of the prolific northwest to southeast late Paleocene Forties and Cromarty depositional trend. Generally, Cromarty and Forties members have high porosities, high net-to-gross and, as a result of these rock properties, the reservoirs provide a natural laboratory for applying AVO-based inversion techniques. Zabihi Naeini and Exley (2017) presented a facies-based inversion to delineate the discovery and to optimize the location of a further appraisal well, the third well on the structure (well-3 in this work) after a dry well (well-1) and a successful discovery well (well-2; 85 ft column of oil in good quality sands). In this study we assess the success of the new well, and further employ the same facies-based seismic inversion method as in the previous study, albeit this time in a probabilistic mode to assess uncertainties to optimize field development. I.e. whilst the previous work was focused on de-risking via QI for a successful exploration toward drilling appraisal well program, this paper is dedicated to the application of facies-based inversion for field appraisal studies toward development planning.

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