Faults, fracture corridors and diffuse fracturing: ranking the main structural heterogeneities within onshore Abu Dhabi fields

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOne of the most challenging issues within Abu Dhabi onshore fields is the definition, characterization and modeling of the main structural heterogeneities. Integration of structural, geometrical and dynamic understanding is the key to defining what is important from a field development and production viewpoint, since it may affect the economics of the fields.A consistent analysis and approach is essential to be able to compare the fields taking into account the three different types of fracture (i.e. faults, fracture corridors and diffuse fracturing), and the potential geological events that postdate the fracturing (fluid circulation, diagenesis).Diffuse fracturing was commonly described across most fields based on core observations and image log interpretation. However, this fracture type alone cannot explain the behavior of many wells.A new look at the data reveals that several fields exhibit fracture corridors and/or subtle faults. Integrating the well behavior suggests this fracture type may have a significant impact in some fields. Unfortunately, this style of deformation is often below the seismic detection threshold.The recent acquisition of 3D seismic across most of the Abu Dhabi onshore fields reveals all fields are faulted at the seismic scale. The fault style is often characterized by small throws. Recent improvements in seismic resolution reveal that what was previously interpreted as one fault is in fact made of numerous fault segments separated by relay areas. This new interpretation has obvious implications for the dynamic behavior of these fault zones. Indeed great discrepancies of the fault zone behavior are observed and discussed using six example fields which encompass a wide variety of carbonate reservoirs with varied depositional environments and reservoir properties. Given such a range of reservoir properties, faults and fractures with similar properties might be expected to have very different expressions in the way they affect fluid flow.

Mechanical insights into the development of fracture corridors in layered rocks

“…Fracture corridors are believed to have a considerable practical impact on production in fractured reservoirs, by forming drains for fluids or providing permeability enhancement and/or anisotropy (Fig. 2a; Cosentino et al, 2001;Bockel-Rebelle et al, 2004Elrafie et al, 2008;Caetano et al, 2014). Drilling experience reveals their link to localized enhanced production (Hart et al, 2002), water breakthrough (local intrusion of water), and major drilling mud losses.…”

Investigating the controls on fault rock distribution in normal faulted shallow burial limestones, Malta, and the implications for fluid flow

“…Although there are documented examples of carbonate-hosted fault zones acting as barriers to fluid flow (e.g. Bockel-Rebelle et al, 2004;Birkle and Angulo, 2005;Vega Riveros et al, 2011;Corona et al, 2012), their impact on flow is poorly understood, despite the global importance of carbonate reservoirs in hydrocarbon reserves; around 60% of global oil reserves and 40% of global gas reserves are stored in carbonates (Schlumberger, 2007). Past research into the sealing potential of faults has been primarily directed towards siliciclastic hydrocarbon reservoirs (e.g.…”