Practical Fracture Modeling Workflows: An Example from a Large Carbonate Field Development
- R. L. Vaughan (ExxonMobil Upstream Research Company)
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Oil & Gas Show and Conference, 8-11 March, Manama, Bahrain
- Publication Date
- Document Type
- Conference Paper
- 2015. Society of Petroleum Engineers
- 5.8.7 Carbonate Reservoir, 5.8.6 Naturally Fractured Reservoir, 5.6.3 Pressure Transient Testing, 5.6 Formation Evaluation & Management, 5 Reservoir Desciption & Dynamics, 5.1 Reservoir Characterisation, 5.1.5 Geologic Modeling, 5.8 Unconventional and Complex Reservoirs
- Workflow, Fracture, Modeling, Carbonates, DFN
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- 273 since 2007
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To borrow from Shakespeare, fractures are the "undiscovered country" of reservoir modeling. Despite decades of research and the application of sophisticated tools and processes, building a model of a naturally fractured reservoir (NFR) that reliably predicts key aspects of reservoir performance often proves to be an elusive and costly goal.
Some of the reasons for disappointing NFR modeling results—system complexity, paucity of data, and software/computing limitations—are often beyond our control. Other reasons we bring on ourselves. These include a reluctance to use modeling early in the process to aid and guide reservoir characterization, and an adherence to high levels of precision despite great uncertainty.
In this example from early development of a large carbonate reservoir, a concerted effort was made to design and apply a workflow that stresses integration, visualization, ease-of-use, flexibility, and speed. The high degree of uncertainty and long characterization times typical of NFRs are addressed by promoting early investigation of parameters impacting both volumes and fluid flow. A key component is to quickly test concepts to identify irreducible uncertainty and avoid unnecessary work.
The workflow relies on sector models that are copied directly from the full-field model and are representative of large regions of the field, primarily with respect to degree and distribution of cements and solution-enlarged fractures. Discrete fracture networks (DFNs) are built within the sectors for various concept scenarios and converted to effective properties using flow-based scale averaging. Fracture intensity is used as the "bridging" property between sector and full-field models, and to facilitate calibration to pressure-transient-test estimates of permeability-thickness. Permeability continuity is estimated using experimental variograms derived from the scaled-up properties. Simulation-ready models take only a few weeks to complete and can quickly alter assumptions on parameters such as fracture distribution and porosity.
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Pan, Y., Hui, M., Narr, W., King, G., Tankersley, T.H., Jenkins, S.D., Flodin, E.A., Bateman, P.W., Laidlaw, C., Vo, H.X. 2013. Integration of Pressure Transient Data in Modeling Tengiz Field, Kazakhstan – A New Way to Characterize Fractured Reservoirs. Paper SPE 165322 presented at the SPE Western Regional and AAPG Pacific Section Meeting, 2013 Joint Technical Conference held in Monterey, California, 19-25 April.