De-risking via objective quantitative interpretation (QI) is an essential part of successful hydrocarbon exploration and appraisal. Given suitable subsurface scenarios QI using AVO inversion can be used to identify lithologies, indicate pore fluid fill and determine net rock volume. However, the detail that can be extracted from a conventional AVO inversion workflow is limited by the averaging effects of not taking into account facies variations and adopting a simplified, rigid low frequency model input to supplement band limited seismic input. An alternative emerging technology, joint-impedance facies inversion, is presented here and provides rock physics models for each individual facies, whilst simultaneously updating the low frequency model; thereby removing one of the main sources of error in conventional AVO inversion routines.

The case study shown in this paper centres on a 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 discovery was initially made using conventional simultaneous pre-stack inversion followed by a discovery well that successfully drilled an 85 ft column of oil in good quality sands. The reservoir sands lie within the proximal part of the prolific northwest to southeast late Paleocene Forties and Cromarty depositional trend. This fairway includes the giant Forties Field.

Author associations - *Ikon Science and **Summit Exploration & Production Ltd