An Evidentiary List of Naturally Fractured Reservoirs
Blog Article
By Wayne Narr, PhD
When we're trying to recognize a naturally fractured reservoir, we often find ourselves asking: "is this a naturally fractured reservoir?" And, “are there are a lot of fractures...do they dominate the behavior of the reservoir?”
I deal with a full evidentiary list of naturally fractured reservoirs to help you identify these geologic phenomenon in my course (here), which covers the 5 tables below:
- Geologic evidence of natural fractures
- Drilling data-based evidence of natural fractures
- Single-well flow-related evidence of natural fractures
- Multi-well flow-related evidence of natural fractures
- Geophysical indications of fractures
In this article, however, I will introduce the first table, Geophysical Indications of Fractures. The table is comprised of three columns. The first column is the observation, the second is the possible explanation of that observation, and the third is the level of precision that we can apply to observation within a reservoir.
Geologic evidence of natural fractures
The first observation is “open natural fractures that are evident in core or an image log”. The explanation of that could be there are open natural fractures in the reservoir itself of course. And the precision is very high. That is we know the specific depth in the well of any given fracture that we see.
The second observation is “Fracture samples evident in cuttings based on mineralogy and texture”. If we're looking at cuttings carefully, you can often see evidence of natural fractures. And what that might tell us is there are fractures in the reservoir. We know approximately the depth in the well that those cuttings may have come from, but not nearly as precisely as we would looking at a core for example.
The third item here is “response of wireline logs”, this tells us generally there are fractures in the reservoir and that they're open. We tend not to see them on wireline logs unless they are open fractures, with the exception of portal image logs. And the precision with which we obtain this data is specific depths in the well.
If you would like to hear more about the list, you can watch my lectures here.
Or, if you would like to get a pdf version of all 5 tables, simply send an email to [email protected].
Your Instructor
Wayne Narr is a structural geologist with interest in characterization and modeling of naturally fractured reservoirs. He held the title of Senior Research Consultant for Chevron Energy Technology Company where he worked for 27 years on an array of international projects that included reservoir structural geology studies, consulting, technology development, training, and exploration. Prior to this he worked 8 years for Gulf Oil where his work included both R&D and exploration.
Wayne has worked extensively with reservoir engineers as well as geologists, with the goal of integrating engineering and geological data to improve understanding of naturally fractured reservoirs, often culminating in construction of fracture models for flow simulation. His work has included studies and synthesis of reservoir data as well as outcrop analogs. The reservoirs he has studied include naturally fractured carbonates and clastic rock, and both conventional and unconventional reservoirs as well as geothermal reservoirs.
Wayne currently teaches courses on naturally fractured reservoirs, leads field trips, and consults. He has written research articles on NFRs as well as co-authored a book. In 2008 he was honored to be an SPE Distinguished Lecturer, in which he traveled the world to talk about naturally fractured reservoirs. Wayne holds a Ph.D. in Structural Geology from Princeton University, an M.Sc. in Structural Geology from University of Toronto, and a B.S. in Geology from Pennsylvania State University.