The Centrifuge as a Tool To Determine the Pore-Throat Size Distribution in Plugs

CARLOS A. MARTIN, MAXIMO E. RAMIA, AND LUCAS BARBERIS

Latin American & Caribbean Petroleum Engineering Conference

CCPE

Año: 2007 p. 1 - 7

The standard use of the centrifuge is to determine capillary pressure in plugs. What is proposed in this work is to extend its application making it possible to determine the pore-throat size distribution in plugs in addition to the capillary pressure indicated above. To this end we start with a plug properly cleaned and saturated with the corresponding brine. The plug is then placed in the centrifuge and the collected data consists of the total evacuated brine volume VT(n) as a function of the centrifuge rotation speed n. A simple model, consisting of capillary tubes running from one end of the plug to the other, is proposed to describe the complex system network of pores and the corresponding interconnecting pore-throats. The corresponding theory, based on treating the capillary pressure as that due to the water-air interphase, is worked out in such a way as to link the capillary size distribution to VT(n) vs. n. The mathematical procedures turn out to be straightforward and the solution is unique. This original analysis of the centrifuge data was successfully applied to a large number of plugs. As an example the corresponding data and analyses are fully given and described. In a companion paper these results are compared with those obtained by MICP (Mercury Injection Core Porosimetry), and the agreement found may be considered as excellent. There is a practical limitation of the method proposed in this work. The capillary pressures that can be reached with the centrifuge are not as high as those that can be reached by MICP. This limitation manifests itself in the fact that pore-throat sizes below 1 mm are poorly detected or not detected at all. However, for pore-throat sizes above that value the agreement is excellent. The main result obtained in this work is that it is shown that similar information to that produced in a MICP run with two main advantages (1) the centrifuge is a non-destructive experiment, and (2) is a non-contaminating experiment.