Assessing the Impact of Incorporating Low Throw Faults on Reservoir Connectivity and Simulation Response

Wood, Victoria ¹; Freeman, Steve R.¹; Harris, Simon D.¹; Campbell, Jez ¹; Smith, Stewart ¹
(1) Rock Deformation Research Ltd, Leeds, United Kingdom.

Often low throw faults are not incorporated into reservoir simulation models and this may impact the simulated performance of those fields. There are a variety of reasons for this practice including i) the faults are below seismic resolution, ii) they are thought to have throws not likely to strongly influence field performance and iii) they are too time-consuming to model. We show that failing to include minor faults can have a major impact on modelled flow behaviour for many reservoir types.

In this contribution we demonstrate a new method for direct incorporation of low throw faults, with realistic displacement-length profiles, into fully populated geological models, without the need to rebuild the static reservoir model. This approach is different to the common practice of including these structures as transmissibility barriers with zero throw.

Multiple geological realisations were derived from a base case model containing only seismically resolvable faults. This was achieved using an uncertainty workflow which generated multiple models containing different proportions of low throw faults. The structures incorporated into the base case model were added using specific rules for orientation and linkage relative to the pre-modelled faults.

The realisations were taken forward to simulation where assessment of the relative impact of including these minor faults on predicted production histories was made. Investigation into cross-fault juxtapositions and predicted fault properties of the low throw faults indicate that they generally enhance reservoir connectivity, rather than impede flow, as is often assumed; generating more even sweep patterns during simulated production, compared to the base case.

This workflow was repeated for different base case structural models and permeability populations to create a matrix of generalised responses, defining the likely impact of adding low throw faults on simulated sweep patterns through reservoirs with different structural-stratigraphic architectures and reservoir conditions.

Incorporating low throw faults into geological and simulation models with realistic throws can induce marked differences compared to either ignoring them or including them as flow barriers. The technique shown, incorporated into a standard workflow manager, provides an effective means for quantifying this structural uncertainty on simulated responses hopefully leading to more realistic evaluations of reservoir production performance.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.