Capillary pressure determination using the micropore membrane technique

Generation of capillary pressure curves is essential to the evaluation of fluid flow phenomenon in the multi-phase region of a reservoir. It is used chiefly for the determination of oil and gas water contacts, the location of transition zones and modeling oil displacements through either water or gas flooding. Unfortunately its measurement is made unattractive by the time-consuming nature of its generation which could be up to six months in some cases. The micropore membrane technique of capillary pressure determination is a novel approach introduced by the Institut Français du Pétrole- IFP, which has the capacity to reduce the time required to generate a full suite of capillary pressure curves, namely – spontaneous imbibition, drainage and imbibition cycles to about a tenth of the time required for conventional methods such as the porous diaphragm restored state method.

This research work was conducted to build a setup for capillary pressure measurement that replaces the conventional mercury injection and restored state techniques currently in use in the department’s core analysis laboratory. The setup was used to perform four distinct drainage runs on sandstones and dolomite with different petrophysical properties. Soltrol130-Brine pair was used for the fluid system while all the rock samples were characterized as water-wet. The drainage capillary pressure curves generated were analyzed on the basis of petrophysical analytical tools like pore entry pressure, irreducible water saturation and pore size distribution index. A homogeneity and heterogeneity correlation was established amongst the samples based on the shape of the drainage curves and the analytical tools and this trend was validated using CT scan images which were carried out on the dry core samples. Mercury injection capillary pressure (MICP) test was conducted on one of the samples and a very good match was obtained between the micropore membrane technique and MICP. Further validation of this method was carried out by conduction a re-run on one sample to ensure repeatability of the procedure and accuracy of data collected. The results of the re-run showed an excellent match with the initial run to validate the procedure and accuracy of the data acquisition process of this technique. The success of the validation process and the functionality, flexibility and dynamism of the experimental setup and also the reliability of the procedure all borne out of the reliability of results obtained, with each experiment concluded in about 24hours using reservoir fluids confirms the micropore membrane technique to be a robust, simple, convenient and time efficient method for the generation of representative capillary pressure data for reservoir rock samples.