Abstract - Faults may have either a positive or a negative impact on production from hydrocarbon reservoirs. Fracture permeability enhances flow in chalks and carbonates with low matrix permeabilities, whereas faults in clastic reservoir units are often detrimental to fluid flow on the production time-scale. This talk outlines the main methods for mapping and analysing faults in clastic hydrocarbon reservoirs, and describes the principal geometric characteristics and flow properties of fault arrays and how their effects can be incorporated in reservoir flow modelling.
The use of 3-D seismic data is now standard in both the exploration and production stages of hydrocarbon exploitation and fault throw resolution down to ca 20m and a lateral resolution better than 100m at depths of 3km is common. We review a variety of software implementations of new seismic interpretation techniques which allow better definition of the displacement geometries of individual faults and of fault arrays than was possible even a few years ago. Interpretation of seismically imaged faults is supplemented by prediction of sub-seismic fault populations.
Definition of horizon and fault geometries allows assessment only of the geometric effects of fault displacements on reservoir continuity and flow paths. Assessment of fault seal characteristics, usually due to shale smears or the presence of shaley gouge, is an additional requirement for reservoir characterisation and modelling. Fault seal prediction is largely empirical and generally is limited to prediction of the maximum difference in oil column height which can be supported by a fault surface. The empirical approach is complemented by outcrop data on fault rocks developed within fault zones, which highlight the complex and heterogeneous nature of fault zones and the relative persistence of shale smears and shaley gouge compared with other fault rock components.
Incorporation of the flow properties of faults into reservoir simulation models is severely hampered by the lack of quantitative data on the hydraulic properties and spatial distribution of fault rocks within fault zones, and also by the limited resolution of the reservoir geological models which can be modelled routinely using existing numerical flow modelling systems. Future development is likely to concentrate on determining the sensitivity of reservoir flow to a variety of quantified geological uncertainties.
Abstract of talk given to:
Structural Control and Genesis of Economic Resources (Minerals and Hydrocarbon deposits), Dave Johnston Memorial Meeting, Trinity College Dublin, November 1997