No. There is no consistent definition of Reservoir Quality or Reservoir competency for hydraulic fracturing.

"Brittleness", "fracability", "producibility", "stiff rock", "hard rock," and other modern terms have nothing to do with real processes during hydraulic fracturing and can be used as statistical tools only. With all limitations of statistical tools. You believe that wt% of clays cannot be >35% for "brittle" formation? Marcellus has 65% of clays.

Correlation does not mean causation.

There is no one to one correspondence and in fact hydraulic fracturing is used to increase the permeability in the target rock by creating deep fractures or cracks. So these measures are generally used in tight and poor reservoirs to increase the flow and produce the otherwise locked oil contents in the rock.

When performing a very big (several years) review of potential links between geophysics and rock mass quality, including rock joint properties,

I 'discovered' that there seems to be a strong link (even 1:1) between seismic quality (Qp) based on P-wave attenuation, and the static deformation modulus of rock masses, as derivable from the Q-value used in rock engineering - if E mass was expressed in GPa. So if static deformation modulus has some positive influence on the 'fracability' of reservoirs (others need to give opinion here), then seismic quality Q (the inverse of attenuation) may help. ( A 'sweet spot' has low Qp and low Q, and low Emass, but don't ever look for values lower than about 5 or 5 GPa even near the surface. Depth increase and confining pressure (in rock physics experiments) soon pushes Qp into the 100 + area, and our semi-empirical rock mechanics data for E mass thereafter struggles to keep pace. The degree of saturation, 'squirt' losses, frequency, all complicate the above. This may be of interest:

Barton, N. 2007. Near-surface gradients of rock quality, deformation modulus, Vp and Qp to 1km depth. First Break, EAGE,October, 2007, Vol. 25, 53-60.

There are many definitions of reservoir quality, for a reservoir engineer, this means that it has seals, reasonably clean and can deliver the fluids (Po, K), for geologist it will be different. From a fracturing point of view you are interested in the rock "mechanical" properties so you can actually break the rock and carry out the frac therefore, strength, Young modulus, pore pressure, barriers and stresses are what might define "competency" of the reservoir for fracturing purposes. You can not discard the reservoir engineerng definition of quality since after all it is this quality that will deliver the fluids to the fracture. I hope it helps

@Juan, your contribution helped greatly. Thank you.

Thank you Umesh. Your contribution is appreciated.

Brittleness is very important for hydraulic fracturing.

Thank you Jadhav. I obviously believe it is one of the most important factors to consider.

I think, we need to understand what reservoir qualit is, and what kínd of reservoir is! For example, the resevoir quality is better in conventional reservioirs than in unconventional (i.e., tight and shale reservoirs) where hydraulic fracturing does the big difference.

In this case we need to differentiate between the type of reservoir before venturing further and then accordingly think about the correlation. A small example is talking about clastic unconventional and conventional reservoirs.

In Shale gas reservoirs there is no clear cut correlation between the reservoir quality and the completion quality. A good shale gas reservoir may have high percentage of clay rendering it ductile and unfit for fracturing.

However when we talk of tight oil reservoirs like Bakken and Wolfcamp then often the organic lean and clay deficient intervals are the reservoirs. Since the good tight oil reservoirs have relatively low clay content they are more brittle and easy to frac therefore more or less reservoir and completion quality are related in tight oil reservoirs.

In conventional sand reservoirs case , the interval has maximum amount of quartz content therefore possess high Young's Modulus and Low Poisson's ratio and is brittle.

Therefore excluding the shale gas reservoirs in tight oil and conventional reservoirs the reservoir quality and completion quality go hand in hand.