Quantifying the Impact of Fault Damage Zones on Reservoir Performance

While most motion along a fault zone is accommodated within a relatively narrow core, additional damage is incurred by the surrounding rock. Depending on the mechanics of the lithology and timing of deformation, this damage can have a major impact on reservoir performance by introducing either open fractures or low permeability deformation bands. In fine-grained clastic, tight sand, or most carbonate systems, the fractures can act as the main source of porosity and pathways for hydrocarbon migration. In high porosity, sand-rich clastic systems, the deformation band damage zones can decrease effective permeability thereby acting as baffles to flow. Understanding of the intensity and spatial arrangement of these features is crucial for making predictions about reservoir performance.

Using outcrop exposures of damage zones, a number of scenarios for damage zone width and internal deformation have been identified. Attempts to quantify the extent of damage zone intensity finds an approximately logarithmic relationship between density and distance from fault core for each specific case, but these fail to define a single mathematical relationship for all fault zones. The same limitation is found when investigating damage zones related to a kinematic parameter, such as fault throw. While a detailed knowledge of the fault zone architecture can be useful for working out detailed flow models, it is possible to estimate a transmissibility multiplier for the damage zone, which can be most useful to derisk the impact on hydrocarbon recovery.

Average values can be utilized for given lithologies or structural settings, or can be refined when additional data are available. Consideration of damage zones can aid in history matching when other transmissibility considerations (such as shale gouge) are unable to account for pressure differentials over a production timescale. This understanding can improve prediction of fault/fracture impact on hydrocarbon migration and reservoir compartmentalization in the appraisal and early-stages of field life, and understanding of underperforming reservoirs and potential remaining oil late in field life.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California