In several oil fields of Iran with carbonate reservoir (Asmari Formation), I have studied open fractures and their effect on the reservoir properties. The effect of fractures on the conventional logs and reservoir properties is inevitable in the fractured reservoirs, however its not clear that which parameter of fractures (Density, aperture, length and dip) provide more effect. Previous studies emphasized on the fracture density but I think fracture aperture is the main fracture parameter which control reservoir properties and also conventional logs trend, particularly DT, NPHI, RHOB, GR, PEF and ...
Refer to this link
Article Calculation of fracture parameters and their effect on poros...
Cyril, seriously? The paper you are referring to is from the same author who posted the question...
Not sure I understand your question correctly. Are you asking what fracture parameter is most important for the RESERVOIR (i.e. what is the key factor determining the permeability in situ) or for a factor which is most "visible" in logs?
I'm afraid I can't provide a definite answer, but here is some brainstorming:
I wouldn't jump into a conclusion that the aperture is the most important. For permeability, what matters most is how these fractures are interconnected - for this, the aperture won't help you.
And what is most visible in logs? In imaging, the aperture will be a massive factor, I agree, but in temperature, resistivity or sonic logs, a zone of interconnected low-aperture fractures will have a stronger signal than a single high-aperture fracture.
Overall, if you are looking at different logs and just wonder what parameters matter most, I'd recommend doing principal component analysis, something like in this paper: http://onlinelibrary.wiley.com/doi/10.1002/ggge.20236/abstract
Dear Ghasem Aghli,
in my opinion reliably quantifying fracture properties such as fracture aperture(s) &/or effective fracture porosity, fracture density and fracture spacing using conventional logs (with the possible exception of Borehole Image logs) is a ‘mission impossible’. The reason is indicated by the attached photograh which shows that even quite sizeable fractures ( dipping white streak on left hand side) is MUCH smaller than the investigation volume of the various conventional logs ( shown on the poster banner). Only the BHI logs have an investigation volume small enough for the tool response to be dominated by the fracture itself rather than the surrounding matrix properties. However, even BHI tools in my view do not allow you to reliably calculate fracture apertures, fracture porosity or fracture fluid saturations. BHI logs do allow you to estimate fracture density, fracture spacing and fracture connectivity
If any further quiries please let me know,
Regards,
W.J.E. van de Graaff
The typical P10 value for fracture density one can derive from BHI logs is a conservative estimate of the actual fracture density as fractures parallelling the (horizontal) borehole are systematically underrepresented by the image log measurements.
Thank you so much for your kind responses (Dear Koehrer and Graaff).
I greatly appreciate you for your meticulous explanations. I agree with you that fracture parameters are not measurable by conventional logs, because other factors such as porosity, lithology and fluid flow considered as the main effective parameters on the conventional logs. However, during our studies on the carbonate Asmari reservoir (As you know this formation known as a typical fractured reservoir in the world), we found some zones which fractures mainly controlled the conventional logs behavior. In this zones, both of fracture density and fracture aperture show high values especially fracture aperture. For your more information, I attached 2 examples of studied wells in this formation. In this wells, FVDC is fracture density and FVAH is fracture aperture.
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