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Quantifying the Impact of Stratigraphic and Sedimentologic Heterogeneities on Flow in Carbonate Reservoirs through Integrated Flow Simulation Experiments

Peter J. R. Fitch, Matthew D. Jackson, Gary J. Hampson, and Cédric M. John
Department of Earth Science and Engineering, Imperial College London, UK

We present the results of an investigation into how stratigraphic heterogeneities impact on flow in carbonate ramp reservoirs. Although stratigraphic, sedimentologic, and diagenetic heterogeneities in carbonates reservoirs are well documented, the relative influence of different heterogeneities on recovery is poorly understood.

A hierarchy of heterogeneity in carbonate reservoirs (presented separately by Hampson et al. was used to catalogue the wide range of heterogeneities documented from outcrop and subsurface examples at progressively decreasing length-scales of observation. Using the hierarchy as a framework, surface-based models were constructed at progressively increasing levels of geologic detail, and an analysis of the impact of heterogeneities on flow is completed at each level. This top-down modeling approach, combined with the use of efficient, surface-based grids, avoids the problem of spending too much time constructing a very high resolution model which is not appropriate for direct flow simulation. Additionally, as increasing levels of detail are included into the models, simulated production behavior changes so that an understanding is generated of the interpretational details required to capture fluid flow patterns and of which heterogeneities are key in controlling flow. Well placements, fluid properties, and / or relative permeability and capillary pressure models may alter how geologic heterogeneities impact on flow. Additional simulations, incorporating different production schemes and rock type models, were used to identify and understand these effects.

Our modeling experiments use fractional factorial experimental design as a tool to investigate the relative impact of different heterogeneities on a number of flow-based performance criteria. A selection of heterogeneities relevant to hydrocarbon production were chosen from the hierarchy for inclusion in our geologic models. Each heterogeneity is assigned two end-member settings, which are chosen to be representative of a range of documented reservoirs and outcrop analogues. The experimental design is used to define the combination of heterogeneity settings that are incorporated into the resulting models. This approach allows efficient exploration of the parameter space defined by the end-member settings of the various heterogeneities, and establishes the rank order of heterogeneities that impact the simulated reservoir performance. The results serve as a screening study that can be used to direct effort in subsequent case-specific modeling studies.

Surface-based geologic models of an entire carbonate ramp are produced (depositional dip extent of 32 km, depositional strike extent of 8 km, thickness of 230 m) in order to constrain the stratigraphic context of smaller, reservoir-scale models taken from different locations on the ramp (depositional dip and strike extents of 4 km, thickness of 66 m) and used for flow simulation. No structural dip is added to the stratigraphic models.

Integrating our current investigation of stratigraphic and sedimentologic heterogeneities with research into the impact of diagenetic and structural heterogeneities on flow in carbonate reservoirs will produce a catalogue of what heterogeneities control flow and why. Such a catalogue will provide insights into where efforts should be focused to ensure representative geologic models are constructed and simulated with appropriate production scenarios. Expanding this integrated study, to include enhanced oil recovery (EOR) techniques, carbon dioxide sequestration, and the application of novel gridding and adaptive meshing approaches to geologic and flow simulation models will produce a comprehensive guide for future hydrocarbon production developments.

AAPG Search and Discovery Article #120034©2012 AAPG Hedberg Conference Fundamental Controls on Flow in Carbonates, Saint-Cyr Sur Mer, Provence, France, July 8-13, 2012