A Review of Alternative Methods to Classify Rock-Types from Capillary Pressure Measurements

Lab capillary pressure Pc measurements are routinely performed on core plug samples. Applications of Pc curve measurements are mainly to derive some relationships between water saturation Sw and the height H above the Free-Water-Level FWL. The resulting correlations can then be cross-checked vs. the Elogs-derived Sw so as to confirm the overall consistency of the Sw model. Ultimately, the Sw - H relationship can be used as input to the 3D model. In addition, screening of Pc – Sw relationships often allows defining robust rock-types, based on observation of Pc clusters vs. the sample porosity, permeability, mineralogy and geological facies. In the case of MICP, the rock-type classification may be further enhanced by looking at the Pore-Throat-Radius PTR distributions, related to the derivative of the Pc curve. Several methods to derive Sw – Pc relationships and classify Pc clusters are possible (e.g. Leverett, Thomeer, Johnson, Cuddy, Skelt, ..) and have been documented and published in the past. In this paper, we make a synthetic review of the pros and cons associated to each Pc classification method. Eventually, we propose an innovative way to take the best of several known Pc classification methods in defining a straightforward technique to derive robust Pc clusters and equations.