depositional facies has notional porosity-permeability values, which get changed with time. It is more of a presumption, than actual measurement.

Permeability is a measure of connectivity of pores; hence, measuring porosity gives more closer estimate than depositional facies based presumption.

Many thanks Ramkumar for your response. I agree absolutely with your position. Please I'll also request for an article that I can cite on this issue if you can please forward same to me.

Many thanks once again for your assistance.

I'm afraid the answer is fairly complex, Ebong. In several chapters of his book Geology of Petroleum, A.I. Levorsen considers the relationship between porosity and permeability in great detail.  A brief summary would be that the factors bearing on the permeability of a reservoir rock include temperature, hydraulic gradient, grain shape and packing, cementation and compaction. Even when you think you can correlate reservoir beds between wells, there are important differences in permeability - porosity relationships between bedded carbonate reservoirs and detrital reservoirs. This is because 'sandy' reservoirs are much more susceptible to subtle stratigraphic traps than bedded carbonates, which are more susceptible to widespread diagenetic changes as they get buried deeper. In theory, permeability is related to rock geometry by an equation that includes measurable porosity and hypothetical grain surface area, which in turn constricts the passage of fluids in proportion to how diagenesis affects individual pores. I'd recommend fracking any recalcitrant reservoir rather than getting involved with all this hypothetical complexity.

@Mcclure

Many thanks for your response to my question. I sincerely appreciate your stand point. I wish to request that, in situations where you have to choose constraints for estimation of permeability, which one of these two (i.e., porosity and either litho- or depositional facies) will favour permeability estimation?

I understand that a lot of factors affect the porosity-permeability relations as contained in literature.

My thinking is that facies distribution exhibit more variations with respect to diagenetic factors and depth of burial of sediments than porosity and so, for reservoir sands that are relatively clean, the relationship between porosity and permeability can be assumed to be direct.

A very simple (-minded) answer is that porosity and permeability are both petrophysical properties that can be readily measured, and thus statistical correlations can also be quantified. In contrast depositional facies are a qualitative interpretation that can be very useful in perm prediction, but less quantitatively.  In a given reservoir, field, or even on the scale of a formation or a depositional or diagenetic facies, there is commonly a strong (positive) correlation between porosity and permeability (generally log K).  Porosity is much the easier measurement and can be estimated from wire-line logs or high-resolution seismic records.  Thus, once a correlation has been established, reasonable estimations of permeability can be made from measurements or estimates of porosity.

A most useful reference on carbonate phi & K is: LUCIA, F.J., 2007, Carbonate reservoir characterization: an integrated approach: Springer Science & Business Media, 333 p.

@ Enos

I acknowledge your contribution and reference with thanks.

Since the porosity defines the volumes of moveable fluids in the reservoir, measurement of the effective porosity of the reservoir rock is basically required along with its permeability. In this case, porosity and permeability allows better control across the reservoir of spatial connectivity in studied wells. However, porosity/permeability relationships were better constrained away from the wells using depositional facies distribution and consequently improve the reliability of the depositional model.

@ Elfigih, many thanks for your response.

Any time>>>>Thanks for your question, really you raised a very debatable issue ...Thanks again....