Beyond Parasequences: Reservoir Characterization Using High-Resolution (Bedset-Scale) Physical Stratigraphy in Shallow-Marine Strata

Hampson, Gary¹, Peter Sixsmith², Oliver Jordan¹, Richard Sech¹, Sanjeev Gupta¹, Matthew Jackson¹, Howard Johnson¹ (1) Imperial College London, London, United Kingdom (2) Chevron Energy Technology Company, San Ramon, CA

Shoreline-shelf deposits contain a high-resolution physical stratigraphy that is below parasequence scale, and which records the evolution of the shoreline-shelf system over short geological time-scales (10⁰-10⁵ years). This presentation aims: (1) to document outcrop and subsurface examples of this high-resolution stratigraphy, (2) to demonstrate its impact on rock-property distribution and fluid flow, and (3) to present generic correlation templates for use in reservoir characterization and modelling.

Physical stratigraphy at sub-parasequence scale is defined by discontinuity surfaces that bound packages of beds (“bedsets”). Discontinuity surfaces are marked by: (1) erosion or non-deposition, (2) small (typically <1 km) landward or basinward facies shifts, and/or (3) localized changes in the depositional process regime. The geometry of the surfaces approximates the shoreface-shelf profile, while “bedsets” are comparable in geometry and scale to geomorphic elements of analogous modern shoreline-shelf systems.

Insights from outcrop datasets of net-regressive, wave-dominated shoreface-shelf successions (Cretaceous Blackhawk Formation, Book Cliffs, USA) and net-transgressive, mixed wave- and tide-dominated shoreface-shelf successions (Cretaceous Hosta and Cliff House Sandstones, San Juan Basin, USA) allow construction of templates of detailed sub-parasequence-scale stratigraphy. Key aspects of these templates include: (1) the shoreface-shelf geomorphic profile, (2) depositional process regime (e.g. wave climate, which determines the depth of wave-base erosion), and (3) shoreline trajectory, which determines the preservation potential of “bedsets”. The templates can be used in the subsurface to guide well-log correlations and predict inter-well facies volumes and architectures, but their accurate incorporation into reservoir models requires a surface-based approach to reservoir model construction and flow simulation.