Using Outcrop Analogs to Understand Deep-Water Reservoir Performance
Jonathan Stewart1, Kirt Campion1, Anthony Sprague1, Mike Farrell1, and Lisa Stright2
1ExxonMobil Upstream Research Company, Houston, TX
2School of Earth Sciences, Stanford University, Stanford, CA
In the last decade, many deep-water confined channel reservoirs have been discovered offshore West Africa. Recent production and 4D seismic data have revealed the geologic complexity of these reservoirs. In particular, the scale of features controlling reservoir connectivity appears to be close to or below the resolution of the seismic data. In this study, geologic and seismic models from detailed stratigraphic descriptions of deep-water reservoir outcrop analogs were used to better understand how fine-scale stratigraphy may or may not be expressed in seismic data and how it influences the production characteristics of these fields.
Forward seismic models of the Scripps Formation (Eocene), exposed in the sea cliffs near La Jolla, CA., were built at various frequencies and angles. The channel complex is typically the smallest stratigraphic element resolved using conventional datasets. Facies probability volumes were extracted from these datasets and used to generate geostatistical realizations of the outcrop.
These models failed to capture the organized nature of the stratigraphy observed in the outcrop. In order to demonstrate the importance of correctly capturing this sub-seismic stratigraphic heterogeneity in geologic models, a detailed model based on the Capistrano Formation (Miocene), exposed in the sea cliffs near San Clemente, CA., was built and flow simulated. Inclusion of a small fraction (~ 10%) of a stratigraphically organized lithofacies with strong permeability contrast (i.e., shales or gravels) had a significant impact on breakthrough time and recovery efficiency.
These outcrop-based models confirm the critical need for proper representation of the 3D distribution of organized stratigraphic heterogeneity, with particular regard to high contrast lithofacies, at scales below seismic resolution in geologic models of deep-water channel complex reservoirs.
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