A rapid and accurate method for calculation of capillary pressure from centrifuge data

Centrifugation technique is among various methods for rock capillary pressure measurement. In this method, capillary pressure data is not directly measured and it should be calculated from production data. Calculation of capillary pressure data needs conversion of the measured fluid productions to the local saturation values. Considering frequent use of the conventional centrifuge method in the industry, an accurate and rapid technique is highly demanded. Several interpretation techniques have been reported in the literature. Simple methods can be found with less accuracy, while accurate methods usually require time consuming analysis. In this paper, a simple method is proposed based on a semi-analytical solution for calculation of local saturation from experimental data. In this method fundamental centrifuge equation, which is a Voltera equation, is converted by Laplace transformation. Inverse Laplace transformation is performed assuming a sub-polynomial equation for each segment of average saturation (S-). The performance of the proposed method is evaluated using two theoretical functions for capillary pressure. The results obtained by new method are compared with the results from the available methods in the literature.