Effect of Pore Structure on Miscible Displacement in Laboratory Cores

Abstract

Observations of pore structure in thin-sections are related to the performance of stable, first-contact-miscible displacements in reservoir cores and then to simulations of displacement performance of CO 2 corefloods. Results of effluent composition measurements are reported for miscible displacements in seven core samples-three sandstones and four San Andres carbonates from west Texas or eastern New Mexico. Those displacements are interpreted by fitting the measured effluent compositions to the Coats-Smith (C-S) model, which represents the flow as occurring in flowing and stagnant fractions with mass transfer between them. Observations of thin-sections, including measurements of pore-size distributions and a simple measurement of spatial correlation of pore sizes, are also reported. Comparison of displacement results and thin-section data indicates that wide pore-size distributions and preferential flow paths are characterized in the C-S model by high dispersion coefficients and low flowing fractions. Simulations of the interactions of phase behavior and flow in nonuniform pore structures indicate that wide poresize distributions and preferential flow paths can significantly increase residual oil saturations (ROS's) in CO 2 floods over those for uniform pore structures. Thus, heterogeneities observable at the scale of a thin-section have significant effects in laboratory core but much smaller effects in displacements at field scale. Large-scale heterogeneities present in field floods, however, probably cause similar increases in residual saturation in some fields.

Enhanced gas recovery with CO2 sequestration: The effect of medium heterogeneity on the dispersion of supercritical CO2–CH4

“…This model has been used for several dispersion studies on carbonate rocks (Baker, 1977;Batycky et al, 1982;Bretz and Orr Jr., 1987;Bretz et al, 1988;Brigham, 1974;Spence Jr. and Watkins, 1980). Equation (4) and (5) may be analytically solved for a pulse input where semi-infinite initial-boundary conditions were assumed (Goltz and Roberts, 1986;van Swaaij, 1967;Villermaux and Van Swaaij, 1969):…”

“…Orr and co-workers systematically conducted miscible core flood experiments through four carbonates (Bretz and Orr Jr., 1987;Bretz et al, 1988;Orr Jr. and Taber, 1984). The cores were saturated with brine and step input or pulse experiments were conducted using a solution of the same brine containing 0.4% sucrose as the tracer.…”

Predicting the Performance of the Acid-Stimulation Treatments in Carbonate Reservoirs With Nondestructive Tracer Tests

“…Acidizing simulation models are calibrated on the basis of experimentally measured acid PV bt curves (Golfier et al 2002;Panga et al 2005;and Buijse and Glasbergen 2005). However, most of these models are calibrated on the basis of linear acid PV bt curves.…”

“…Several attempts were made to study the effect of carbonate pore structure on flow behavior, including the work of Bretz et al (1988); Xu et al (1998); and Hidajat et al (2004). However, all these studies focused on nonreactive flow.…”

Capacitance Effects in Porous Media

“…Spence and Watkins 2S and Bretz et al 29 have also carried out experiments that correlate the velocity and the parameters f and N Da • The Coats-Smith model has been modified by Salter and Mohanty31 for two-phase flow in porous media, and experiments with immiscible displacements were perfQtmed by Bretz et al 32 to determine the parameters for two-phase flow.…”