Outcrop Characterisation of Transgressive Sandstone Reservoirs
Dr Gary Hampson (g.j.hampson@imperial.c.uk, +44 (0)20 7594 6475) of the Department of Earth Science and Engineering, Imperial College discusses the second phase (2006-8) of their Transgressive Sandstones Reservoir Study. The research outlined will be carried out as an ACHARR-approved Joint Industry Project (JIP).
Introduction
Transgressive sandstones form a significant component of many shallow-marine
reservoirs, including the Tarbert Formation (Brent Group) and Fulmar
Formation (Humber Group) in the UK North Sea. Our understanding of facies
architecture in transgressive sandstones reservoirs is poor, principally
because outcrop analogues of such reservoirs have been only rarely studied.
As a consequence, the detailed facies architecture and internal permeability
character of transgressive sandstone reservoirs may be highly variable,
complex, poorly constrained and difficult to predict.
Our work in the first phase (2002-5) of the Transgressive Sandstones
Reservoir Study focussed on developing generic, process-based 3D models
of the formation, preservation and facies architecture of transgressive
sandstones through analysis of an exceptionally exposed reservoir analogue,
the Hosta Sandstone in New Mexico, USA. The second phase (2006-8) of
the Transgressive Sandstones Reservoir Study will expand on our Hosta
Sandstone analogue work by examining a range of other outcrop analogues
(Figure 1) in order to quantify the key controls on transgressive reservoir
architecture.
Figure1: Schematic chronostratigraphic
cross section showing Upper Cretaceous rocks across the San
Juan basin, New Mexico, USA. Transgressive sandstones are highlighted.
The Hosta Sandstone was studied extensively in phase 1of our
work. Phase 2 will focus on quantitative comparative analysis
of the Hosta Sandstone with other transgressive sandstone units.
Shoreline Trajectory: A Key Tool in Predicting Transgressive Reservoir Architecture
Our Hosta Sandstone work documented that shoreline trajectory (defined as “the cross-section of the shoreline migration path in a depositional dip direction”) exerted a first-order control on preserved sandbody thickness, spatial extent and stacking pattern. We will develop and quantify this relationship via a comparative study of selected, additional transgressive sandstone units deposited under different shoreline trajectories (Figure 2) using tightly constrained outcrop analogue datasets. The results will provide the fundamental scientific insights to constrain predictions of transgressive reservoir architecture.
Figure 2: Cartoon illustrating the relationship
between transgressive shoreline, shoreface sandbody overlap/separation and
gross preservation potential of transgressive deposits, based on interpretation
of the Hosta Sandstone dataset (Phase 1). The cartoon shows the approximate
positions of a number of transgressive sandstone units to be studied in Phase
2 (those highlighted in red occur in the San Juan Basin, Figure 1).
Benefits
The second phase of the Transgressive Sandstones Reservoir Study will provide the following benefits for characterisation of transgressive sandstone reservoirs:
- robust predictive models of reservoir distribution, architecture and internal heterogeneity for all transgressive systems (including sandbody dimensions, distribution and connectivity, and preservation of mudstone barriers/baffles).
- correlation strategies at intra-reservoir and inter-well scales for transgressive sandstone reservoirs that allow the application of tools developed from outcrop correlation to subsurface wireline-log datasets.
- quantitative datasets (e.g. sandbody dimensions and geometries) and quantitative relationships (e.g. width of facies-tract deposits, vertical connectivity of shoreface sandbodies for different transgressive shoreline trajectories) for use in conditioning of reservoir models.
- “subsurface sedimentology toolkits” comprising diagnostic criteria that allow models to be readily applied to subsurface reservoir data (e.g. gross stratigraphic architecture derived from seismic data, vertical facies successions in cores and well-logs).
- earlier and more accurate prediction of hydrocarbon recovery, waterflood sweep efficiency and bypassed oil distribution in transgressive sandstone reservoirs.
Joint Industry Proposal
The research outlined above will be carried out as an ACHARR-approved Joint Industry Project (JIP). We thank the current sponsors of this JIP: Shell, Chevron, BP and the DTI. If your company is interested in being a sponsor, or if you would like more information on this JIP please contact Gary Hampson, Sanjeev Gupta or Howard Johnson at Imperial College London (g.j.hampson@imperial.c.uk, +44 (0)20 7594 6475).