About the Course
The behavior of naturally fractured reservoirs (NFRs) is typically difficult to predict due to extreme heterogeneity of their flow-related character. This unpredictability affects most aspects of field management. Surprises can accompany each well.
From our well-based scale of observation, we sample and test reservoir fracture systems below their representative elemental volume (REV). This is the ultimate cause of the unpredictability of their flow behavior.
Heterogeneity is caused by the complex and variable geometry and connectivity of the plumbing system of the reservoir (well, fractures, and matrix). Connectivity is a function of:
a) Orientation of a well relative to reservoir fracture sets,
b) Spacing of fractures in each set,
c) Spatial variability of the fracture system,
d) Effective length of fractures,
e) Fracture height.
What do we know, what might we know, and what are the limits of our knowledge? Which of the controlling variables can we understand and measure, to help predict aspects of reservoir performance? Because we sample the reservoir below its REV, there are limits to what can be known from downhole data alone; it must be placed into a larger context. Our understanding of these data requires that the NFR be interpreted in light of a) competent geologic understanding of fracture systems, integrated fully with b) sound, creative engineering insight of observed flow behavior. This approach does not guarantee salvation, but it improves the odds.
This series of lectures on Heterogeneity in NFRs will use subsurface examples, outcrop analogs of subsurface fracture systems, and fracture system models to address:
• Heterogeneous production behavior of Naturally Fractured Reservoirs (NFRs)
• Causes of heterogeneity in NFRs
⎯ Well-fracture intersection probabilities
⎯ Fracture size (height, length, & aperture) variability
⎯ Geologically induced heterogeneity (stratigraphy & diagenesis)
⎯ Fracture connectivity variability
• Perspectives on fracture-induced heterogeneity – learning from models