Microscale Visual Study of End Effects at Permeability Discontinuities

Abstract

The physical effect of multiphase fluid distribution and flow at permeability boundaries has not been fully investigated, particularly at the pore scale (1-100 µm), although such behaviour can significantly affect the overall scaled-up reservoir trapping capacity and production performance. In this article, microscale physical models have been used to qualitatively study the pore scale flow events at permeability boundaries, both high to low and vice versa, to gain a better understanding of the role of these boundaries and water saturation on multiphase displacement behaviour at the pore scale. We have used etched glass models of stripes of large and small (a factor of two) pores with circular matrix. Capillary pressure, which is the controlling parameter is itself dependant on pore size and its spatial distribution, the magnitude of the interfacial tensions and the wettability between the fluids and the solid surface of the models. Sometimes, the only way the non-wetting fluid can penetrate the boundary is through a fortuitous leakage, whereby the presence of an initial saturation reduces the controlling capillary pressure. Examples are demonstrated including mechanisms of end-effects and how capillary boundary resistance (due to capillary forces) can be broken down and fluid movement across the boundary can develop. These micromodel experiments show vividly that connate water can assist in these processes, particularly oil trapping and leakage of water across a permeability boundary.

Immiscible Displacement in Cross-Bedded Heterogeneous Porous Media

“…It will change the flow patterns in immiscible displacements from that observed in miscible displacements, especially at low flow rates where capillary effects dominate viscous effects, (Dawe and Grattoni 1998;Dawe et al 2010), which will be further discussed in Sect. 5.…”

“…For instance, at saturation discontinuities capillary pressures (interfacial curvatures) can change over a few grain diameters giving rise to large pressure gradients. In homogeneous media, such discontinuities may occur across immiscible displacement fronts and at porous media boundaries, such as end effects (Dawe et al 2010). In heterogeneous media, capillary pressure effects are also created at the boundaries between areas with different properties, such as permeability, porosity or wettability changes (Dawe et al 2010).…”

High-Resolution X-Ray Computed Tomography of Liquid CO<SUB>2</SUB> Permeation in Water-Saturated Sandstone

“…On the other hand, previous studies in which supercritical CO 2 was used indicate a thicker permeation front region with 3 to 13.4 PV injected before CO 2 saturation reached a steady distribution (14,15) . The influence of the sub-core scale heterogeneity was discussed by Perrin et al (14) and Shi et al (15) , and recent studies noted that permeability discontinuities cause saturation discontinuities (18,19) . In this study, a thin laminar structure in a large-diameter sandstone sample can be observed by employing microfocus X-ray CT.…”

“…During the CO 2 permeation from a higher to a lower porosity region, the boundary forms a temporary barrier to the flow of CO 2 and prevents CO 2 flow until the threshold pressure at the boundary is overcome (18,19) .…”

Pore-scale simulation of effects of coal wettability on bubble-water flow in coal cleats using lattice Boltzmann method

“…However, most of them are either based on laboratory core flooding experiment data or field data, and they cannot explain the factors controlling the multiphase flow at pore scale (Dawe et al, 2011;Ofori et al, 2010;Shen et al, 2011). To fill this knowledge gap, a detailed research of gas/water two-phase flow behaviours in coal seams at pore scale is essential.…”