A method based on spontaneous imbibition for characterization of pore structure: Application in pre-SCAL sample selection and rock typing

- Spontaneous imbibition theory can be used for rock typing.
- An inexpensive, fast and universal method is presented for rock typing.
- The new method guaranties efficient sampling for SCAL tests.

In the context of reservoir engineering, the common methods used to select representative rock samples for expensive and time-consuming special core analysis (SCAL) tests are porosity-permeability relationships and flow zone indicator (FZI). These methods are based on the assumption of modeling porous media as a bundle of capillary tubes, ignoring many complexities associated with real porous media. Generally, these methods fail when studying the pore structure of heterogeneous porous media particularly in carbonate reservoirs. In this work, a novel method based on the immiscible two-phase flow characteristics of real porous media is presented to characterize pore structure and ensure reliable sample selection for SCAL tests. The presented method offers an index (FZI**) which is derived from the existing universal scaling equation of counter-current spontaneous imbibition (COUCSI) problem. This index can be determined using an additional inexpensive, simple, and relatively fast water-air COUCSI experiment at ambient conditions on strongly water-wet dried plug samples during routine core analysis (RCAL) stage. Using different sets of experimental data, benefits, and applicability of the presented method are demonstrated.