Generally, Steel to Steel FF is lower that Steel to Formation.
Typical values are respectively 0.1-0.15 and 0.2-0.25 in OBM. Higher in WBM.
Bear in mind that in drilling applications FF encompass more than just friction. Sometimes we call them Fudge Factor. The state of hole cleaning within open hole and cased hole will affect them, as well as many other things, such as casing wall rugosity, bore hole micro tortuosity, mud solids content, etc…Régis STUDER
thank you for your response. It's clear that this stand-off value cannor be achieve with solid centralisers. We are mainly interested in knowing if the pipe were well centralised can we assume that it can be turning as if it was supported on different points and therefore experience torque reduction (with less friction factor)
you're right. Can we imagine that the steel to steel friction factor will be less than steel to formation and therefore we can see less torque when rotating.
With a solid centralizer you will not achieve 80% Stand-off.
Proper placement of centralizers can reduce torque and drag,
suggest you contact Centek and let them run a simulation on
your well, their model is one of the few accurate ones on the
market, and their product can achieve 80% stand-off.
I work for BHGE, so have no affiliation with Centek, this advice is based on my 40 + years experience in primary cementing products and applications.