Calillary Pressure Curve Measurement Using a Single-moderate-speed Centrifuge and Quantitative Magnetic Resonance Imaging

For traditional centrifugal capillary pressure curve measurements, a short core plug is often employed. The capillary pressure is assumed to be zero at the outflow boundary of the core. The traditional experiments are time consuming. Measurement of the full capillary pressure curve often requires 7 to10 different centrifuge speeds, thus requiring one day to several days for measurement. Different approximate solutions may be employed to deduce the capillary pressure curve from experimental data of average saturation and the corresponding rotational speed. In the current work, we propose a new method to measure the capillary pressure curve using a single-moderate-speed centrifuge experiment and one dimensional centric scan SPRITE (Single-Point Ramped Imaging with T1 Enhancement) magnetic resonance imaging (MRI) technique for long rock samples. As a pure phase encoding quantitative MRI technique, centric scan SPRITE offers unique advantages in the measurement of spatially resolved fluid saturation in rocks. The proposed method is rapid and accurate. Because the new method uses a long core to directly measure a large range of saturation distributions along the length of the core, at a single moderate centrifuge speed, this process will be much faster than a traditional measurement. There is no requirement for an approximate solution; the capillary pressure curve is directly determined by the measured saturation profile. Long cores can be employed, which leads to a smaller radial effect than short core plugs. Since a moderate centrifuge speed is employed, the effect of gravity will be very small and the outlet boundary condition of the core plug can be satisfied. A comparison of capillary pressure curves obtained by a single-speed centrifuge and SPRITE MRI with mercury intrusion methods yields remarkably consistent results.