Combining porosimetry and Purcell permeability modeling to calibrate FZI and define a dynamic permeability cut off.

摘要

An integrated algorithmic workflow is proposed for the interpretation of MICP experiments. By combining,among other features,the detection of local minima,maxima and inflexion points of the distribution of Pore Throat Size(PSD)and the permeability modeling of the latter by Purcell method,it introduces new possibilities to calibrate RCA poro-perm on MICP and thus to improve the reliability of the FZI method and the definition of a dynamic permeability cut off. Saturation/height modeling is also part of this workflow which,to date,has been used over 4000 MICP measurements in complex carbonates of varied geological settings. Because the Purcell’s method for permeability modeling quantifies the contribution of each class of pore throat size to the permeability,the set of those classes which actually controls the fluid flow can be accurately delineated,even if the PSD does not exhibit clearly individuated subsets,and characterized by its lower and upper(entry pressure)limits,its equivalent pore throat radius,the radius of the pore throat class contributing most to permeability and the fraction(PHIZ)of the effective porosity involved. The entry pressure is defined according to the experimental results of Katz and Thompson(1987)and,so far,the observations support the idea that a good approximation of the lower limit of this subset is the Mean Hydraulic Radius(MHR)which roughly corresponds to the apex of the trial solutions proposed by Pittman or Walls and Amaefule. We show that,in formation exhibiting complex porous network,PHIZ should be used for the computation of”true”RQI and FZI,instead of the effective porosity which inevitably results in degrading FZI. The impact of the change of porosity values is illustrated and its relationship with the complexity of PSD curve shape is examined in terms of texture. We expose how the calibration of RCA poro-perm on SCAL porosimetry allows retrieving the true RQI from RCA poro-perm and its associated PHIZ value and how a dynamic permeability cut off can be defined.