Incorporation of Detailed Fault Structure into Reservoir Models

Yielding, Graham¹, Tom Manzocchi², Andy Heath³, Brett Freeman¹, Andy Foster¹ (1) Badley Geoscience Ltd, Lincolnshire, United Kingdom (2) University College Dublin, Dublin 4, Ireland (3) University of Liverpool, Liverpool, United Kingdom

Relay structures and local drag are geometric features of fault zones that are often too small to be incorporated in reservoir models, or even mapped directly on seismic data. To examine the sensitivity of oil production to fault-related uncertainties, we have developed functionality in the TrapTester/TransGen software to model the effects on flow of small-scale fault-zone structures within the full-field simulation model. Results indicate that these fault zone characteristics can have significant beneficial or detrimental effects on production.

For example, an unbreached relay ramp potentially provides additional across-fault communication via tortuous flow paths across the ramp-bounding faults and along the ramp in different layers. Depending on the original fault compartmentalisation, such features may double the total discounted oil production in a 30-year simulation.

We have also modelled realisations where the mapped fault throw is varied either systematically owing to drag, or following correlated variations owing to structural uncertainties; cases where the fault zone is taken up by paired slip surfaces; and cases where populations of new sub-seismic faults are introduced. Effects can be severe or subtle; for example some cases of sub-seismic faults increase the total oil production while reducing the discounted oil production, because the production profile over time is radically changed by a different sweep pattern.

The transmissibility solutions, combined with the deterministic and stochastic fault zone placement functionality, allow representation of a range of geological fault properties. Connection transmissibilities are calculated for the modified model and output with respect to the parent model using appropriate ECLIPSE(™) keywords.