A Single-shot Method for Determining Drainage and Imbibition Capillary Pressure Curves

A single-shot method to determine the capillary pressure curve employed a single rotational velocity centrifugation experiment and one-dimensional Centric Scan SPRITE (single-point ramped imaging with T1 enhancement) MRI (magnetic resonance imaging) to determine the fluid saturation distribution, S(r), along the length (r) of the core. A full capillary pressure curve can be directly determined by the relation of S(r) and the capillary pressure distribution, Pc(r). The rotational speed required for the single-shot method can be determined with the Leverett J function value at the irreducible water saturation. Centric scan SPRITE MRI is an ideal method for measuring spatially resolved fluid saturation in rocks. The single-shot method has been applied to measure the primary drainage, as well as imbibition and secondary drainage capillary pressure curves for reservoir rocks. Proper boundary conditions are ensured by maintaining the free water level in contact with the outlet face of the core. Deuterium oxide (D2O) instead of H2O was employed to dissolve salt for preparing synthetic brine to determine fluid saturation with MRI unambiguously. Thus crude oil can be applied for centrifuging at reservoir temperature with the single-shot method. The single-shot method for determining the capillary pressure curve is rapid, cheap, accurate and adaptable. The capillary pressure curve can be obtained straightforwardly with approximately 40 data points. A desktop centrifuge and a desktop permanent magnet based one-dimensional MRI instrument can be employed for the single-shot method. After primary drainage and imbibition measurements, the rock core should be managed to reach a uniform irreducible water saturation distribution and uniform residual oil saturation distribution, respectively. MRI was also employed to check the saturation distribution. Since only a single rotational velocity is employed, there is no pressure effect on rock pore structure due to dramatic rotational speed changes required for traditional methods. The effect of gravity can also be neglected. In addition, the long rock cores preferred for the single-shot method result in a relatively small radial effect and reduced rotational speed; friable and unconsolidated samples may be measured. In addition, application of the single-shot method for a disk-shaped rock sample and the design of non-magnetic centrifuge disk-shaped rock sample holder will also be presented.