This document is an expanded abstract.
Summary
The estimation of oil in place is a key to the industry, both for an early discovery and to monitor sweep efficiency in a mature field. Saturation can be obtained from the interpretation of capillary pressure curves, and from different logging techniques such as: resistivity, NMR (Nuclear Magnetic Resonance), dielectric, and pulsed neutrons. However, resistivity measurement is the only tool capable of giving information in the virgin zone around the well but need to be interpreted using Archie’s law to obtain saturations. The knowledge of cementation factor (m) and saturation exponent (n) is required in order to perform this interpretation.
A widely used laboratory method, allowing the acquisition of both capillary pressure curve and saturation exponent measurement is the porous plate method. However, the main drawback of this technique is that it is extremely long.
Here, we present a radically faster method to measure both capillary pressure and saturation exponent based on the combination of centrifugation with NMR imaging and resistivity profiling. Drainage and imbibition processes can be carried out in matter of weeks.
This technique was validated by performing experiments on outcrop samples and comparing the results with the ones obtained from conventional methods. It has also been proven to work on heterogeneous carbonate samples from a Middle East reservoir.
Introduction
Accurate evaluation of hydrocarbon in place requires the knowledge of rock volume, porosity and fluid saturations. Fluid saturations can be estimated from capillary pressure curves or from the interpretation of resistivity logs using empirical equations such as Archie (Archie, 1942). Thus, both capillary pressure curves and Archie parameters (cementation factor and saturation exponent) are essential to estimate the hydrocarbon saturation in a reservoir. The determination of all these parameters requires laboratory measurements to be performed on core samples. The cementation exponent is quickly determined by measuring the resistivity on a 100% water saturated sample; while the capillary pressure and saturation exponent measurements are long and prone to experimental artefacts.
