Flow-Based Effective Properties of Sub-Seismic Karst
- Gareth D Jones (ExxonMobil Exploration Company, a division of ExxonMobil Corporation)
- 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 Reservoir Desciption & Dynamics, 5.1.5 Geologic Modeling, 1.11 Drilling Fluids and Materials, 5.1 Reservoir Characterisation
- Model Assisted Characterization, Effective Properties, Karst, Geologic Modeling
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Evaluating uncertainty in reservoir performance related to karst is a fundamental challenge for field development planning and optimizing recovery. Deciding which karst features matter-to flow and how to capture their effect for flow simulation is a critical, but uncertain step in developing an appropriate reservoir characterization and modeling strategy.
Our ability to characterize karst is compromised by the type, resolution and relative abundance of different measurement methods. Many sub-seismic karst features fall in a "data gap" because they have dimensions and networks of pores that are not, or only partially, resolved in typical subsurface datasets. Outcrop analogs and cave maps provide a bridge to address this "data gap". A specific challenge is how to capture the flow significance of karst features that are smaller than a full field scale geological model cell.
This paper presents a workflow using high resolution geologic models termed element modes to address this karst characterization and modeling challenge. Element models were populated with distinct geological configurations of sub-seismic karst and matrix. Flow-based averaging was used to calculate the effective reservoir properties at the scale of a full field geologic model cell. Karst was populated using two different facies modeling methods: 1) Object Based Modeling (OBM) and 2) Multiple Point Statistics (MPS).
Results for two karst examples presented demonstrate that the presence of certain types of karst, even < 5% by volume in a geological model cell, can increase the vertical permeability by an order of magnitude or more relative to a matrix only case. In contrast the effect of karst on horizontal permeability is less significant. Permeability anisotropy (kz:kx) is therefore increased. The karst: matrix property is common to both the element and full field model and can be used as the link to populate effective properties at the field scale.
"Model Assisted Characterization" experiments with efficient fast-to-run high resolution element models, that capture distinct styles of karst, in combination with flow-based averaging optimizes the characterization workflow and provides a richer understanding of irreducible uncertainty that expedites geologic model design.
|File Size||2 MB||Number of Pages||10|