Magnitude and Detailed Structure of Residual Oil Saturation

Abstract

Experimental results are presented that demonstrate the effect on residual oil, under water-wet conditions, of particle size, particle-size distribution, macroscopic and microscopic heterogeneities, microscopic dimensions such as ratio of pore-body to pore-throat size, and pore-to-pore coordination number. Experiments were performed in random packs of equal spheres, heterogeneous packs of spheres with microscopic and macroscopic heterogeneities, two-dimensional (2D) capillary networks having various pore geometries, and Berea sandstone. Detailed information on residual oil structure is presented, including blob-size distributions of residual oil. Major conclusions are (1) residual saturations are independent of absolute pore size, per se, in systems of similar pore geometry; (2) well-mixed two-component aggregates of spheres gave virtually the same residual saturations as random packings of equal spheres; (3) clusters of large pores accessible through small pores will retain oil; (4) high aspect ratios tend to cause entrapment of oil as a large number of relatively small blobs, each held in single pores; and (5) the role of pore-to-pore coordination number is generally secondary; hence, correlations that have been proposed between residual oil and coordination number are unreliable.