Faults, Fracture Corridors and Diffuse Fracturing: Rranking the Main 
Structural Heterogeneities within Onshore Abu Dhabi Fields

Bockel-Rebelle, Marie-Odile; Hassall, John; Silva, Fernando; Lozano, José A.; Deeb, Maged; El, Abd Salem; Vesseron, Marc; Mehsin, Khalil

doi:10.2523/88676-ms

Cited by 3 publications

References 1 publication

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Toward the creation of models to predict static and dynamic fault-seal potential in carbonates

Solum

Huisman

2016

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In contrast to faults in clastic reservoirs, rules to predict the exploration and production timescale fault-seal potential in carbonates are lacking. This paper provides a summary of carbonate reservoirs with cross-fault column height differences that represent examples of apparent static fault seal, and a summary of observed examples of dynamic fault seal in carbonate reservoirs and aquifers. These include cross-fault differences in water table depths across carbonate–carbonate juxtapositions, cross-fault pressure differences in carbonate aquifers separated by faults, production-induced cross-fault pressure differences in carbonate hydrocarbon reservoirs, sealing behaviour of faults in carbonate reservoirs inferred from well tests, and examples of low fault transmissibilities from history-matching exercises from carbonate reservoirs. This paper also documents the range of compositions of fault rocks in carbonates and the range of permeabilities that have been reported from low-permeability fault cores in carbonate fault zones, as well as the implications of the observed range of fault permeabilities in carbonates for sealing behaviours. The purpose of this paper is not to argue that every fault in a carbonate reservoir will seal or will even be capable of sealing. There are, however, enough examples of faults in carbonates that are sealing in a dynamic sense, and in a static sense, that the topic of carbonate fault seal should warrant much more study. Creation of predictive models will ultimately require a considerable amount of subsurface data, but these models should be created.

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Toward the creation of models to predict static and dynamic fault-seal potential in carbonates

Solum

Huisman

2016

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The Impact of Hierarchical Fracture Networks on Flow Partitioning in Carbonate Reservoirs: Examples Based on a Jurassic Carbonate Ramp Analog from the High Atlas, Morocco

Agar

Geiger²,

Matthäi

et al. 2010

SPE Annual Technical Conference and Exhibition

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Hydrocarbon reservoirs commonly contain an array of fine-scale structures that are below the resolution of seismic images. These features may impact flow behavior and recovery, but their specific impacts may be obscured by the upscaling process for sector and field-scale reservoir simulations. It is therefore important to identify those situations in which subseismic structures can introduce significant departures from full-field flow predictions. Using exposures of Jurassic carbonate outcrops near the village of Amellago in the High Atlas Mountains of Morocco, we have developed a series of flow simulations to explore the interactions of a hierarchical fracture network with the rock matrix of carbonate ramp strata. Model geometries were constructed in CAD software using field interpretations and LiDAR1 data of an outcrop area that is 350 m long by 100 m high. The impact of water injection on oil recovery between an injector and producer pair was investigated. Simulations were performed by a single medium reservoir simulator using a single mesh to represent fracture planes as well as rock-matrix volumes. The effects of changing scenarios for rock permeability and porosity as well as facture permeability distributions were investigated. First-order results show that the best recovery was achieved by a model with a high permeability, homogeneous matrix combined with a heterogeneous fracture network. The worst recovery scenario was given by a model with low, homogeneous permeability and high fracture permeabilities. After approximately 450 days there is a divergence in recovery profiles. Three models continue to recover oil while average oil saturations for the other 4 models start to plateau. The divergence does not simply reflect homogeneous vs. heterogeneous matrix models but captures a threshold between high and medium fracture-permeability scenarios that determines whether recovery continues in late time or the well starts to water out. The results highlight the importance of the permeability contrasts between the matrix and the fractures for overall recovery and the very significant impact that fractures can have on recovery by creating shadow zones and providing critical connections between permeable layers. The presence of the hierarchical fracture network developed strong fingering even in homogeneous matrix cases and evolving velocity patterns reveal competing fluid pathways among matrix and fracture routes. Insights from these models can help to develop production strategies to improve recovery from fractured carbonate reservoirs and provide an initial platform from which to extend further evaluations of different populations of conductive and baffling structures, spatial variations in wettability and capillary pressures and well positions.

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Fault and Fracture Corridors—How to Reduce the Structural Uncertainty for Reservoir Management Optimization

Bockel-Rebelle

Dabbour

Salem

et al. 2005

SPE Middle East Oil and Gas Show and Conference

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The occurrence of discontinuities such as faults, fractures or fracture corridors in the porous rock matrix usually has a strong impact on fluid flow and needs to be addressed carefully during the life cycle of the reservoirs. The major difficulty in characterizing the hydraulic properties of such systems frequently relates with our ability to integrate all the information in a meaningful way in order to derive the key factors constraining the development, intensity and role of the main fracture type in a given reservoir[1]. When the faults/fracture corridors act as baffles or barriers they may delineate compartments and blocks with differential drainage rates and variations in pore pressure. Where flow takes place in both the matrix and along/across the discontinuities, the flow paths can become very complex and the way the two systems interplay may even change with time or with injected/produced fluids. Likewise, the occurrence of faults identified from seismic or fractures brings some extra complexity to the strategies used for reservoir simulation. Issues like how to characterize the faults at different scales and to perform fault ranking and upscaling may have a strong impact on the way simulation results will match actual reservoir dynamics. Introduction This paper illustrates the role faults and fracture corridors play in two heterogeneous carbonate fields located onshore Abu Dhabi and their impact on different aspects of reservoir development highlighting some of the solutions to manage such situations. The focus is made on the impact of faults and/or fracture corridors; for they represent the main structural heterogeneities within Abu Dhabi onshore reservoirs[2] (diffuse fracturing is rarely observed). Reservoirs in Field 1 and Field 2 are different in age. Furthermore, the main structural heterogeneity is different. Yet, in both case, specific studies were conducted, aiming at reducing the uncertainties linked to the main type of fractures (i.e. fault zone within Field 1, fractured corridors and/or sub seismic faults within Field 2). As a result, the specific studies allowed; - Characterizing the damaged zone for the main fault system of Field 1, both in term of geometry (thickness, location, and associated fracturing) and dynamic behavior (the fault segments are probably barrier to oil, but locally allow gas to migrate). Consequently, some well trajectories were re-designed. - Achieving excellent history-matched models by using different strategies depending upon the characteristics at each well (the well performance is dominated by matrix or fracture) for Field 2. Consequently, the history-matched models will be used to quantify the uncertainties in the future development options.

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Faults, Fracture Corridors and Diffuse Fracturing: Rranking the Main Structural Heterogeneities within Onshore Abu Dhabi Fields

Cited by 3 publications

References 1 publication

Toward the creation of models to predict static and dynamic fault-seal potential in carbonates

Toward the creation of models to predict static and dynamic fault-seal potential in carbonates

The Impact of Hierarchical Fracture Networks on Flow Partitioning in Carbonate Reservoirs: Examples Based on a Jurassic Carbonate Ramp Analog from the High Atlas, Morocco

Fault and Fracture Corridors—How to Reduce the Structural Uncertainty for Reservoir Management Optimization

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