Inertia Controlled Capillary Pressure at the Juncture between Converging and Uniform Channels

An operational guide to resin 3D printing of geological macromodels

Stereolithography (SLA) is a form of 3D printing that is based on the curing of resin under UV light. There are a wide variety of 3D resin printers on the market that all follow the same general procedure. First, a slicing program is used to slice the model in a sequence of thin layers. The model will be printed in this sequence of layers after it is exported in a format recognizable by a 3D printer. In addition to this main function, slicing programs offer additional features to manipulate the model, adjust print settings, and add model supports. Next, after the printer is set up, the sliced model is loaded onto the printer and fabricated. Once the print is complete, the model can be washed, cured and sanded/polished to the desired finish. In this work, we utilize SLA 3D printing to print geological macromodels, to be utilized in flooding experiments. Images captured from the flooding experiments were then incorporated in a set of visual learning exercises for undergraduate students to enhance the study of immiscible fluid flow in porous media. SLA printing was selected in this use case as it provides important advantages over other common 3D printing technologies (e.g. Fused Depositional Modelling: FDM), such as high print resolvability of sub-millimeter scale pore geometry and a high degree of transparency within the resultant printed models. Overall, this method was found to:•

Provide an engaging learning experience for undergraduate students, as the captured flooding experiment image time series allowed students to directly visualize often obtuse fluid flow processes in porous media.

•

Be easily reproducible: after completing an initial print the method can be reproduced for many different pore networks, allowing for a wide array of comparative studies and learning exercises to be developed.

Understanding the role of wettability distribution on pore-filling and displacement patterns in a homogeneous structure via quasi 3D pore-scale modelling

Most numerical simulation studies have focused on the effect of homogenous wettability on fluid flow dynamics; however, most rocks display spatially heterogeneous wettability. Therefore, we have used direct numerical simulations (DNS) to investigate wettability heterogeneity at pore-scale. We have built a quasi-3D pore-scale model and simulated two-phase flow in a homogenous porous media with homogenous and heterogeneous wettability distributions. Five different heterogeneous wettability patterns were used in this study. We observed that heterogenous wettability significantly affects the evolution of fluid interface, trapped saturation, and displacement patterns. Wettability heterogeneity results in fingering and specific trapping patterns which do not follow the flow behaviour characteristic of a porous medium with homogenous wettability. This flow behaviour indicates a different flow regime that cannot be estimated using homogenous wettability distributions represented by an average contact angle. Moreover, our simulation results show that certain spatial configurations of wettability heterogeneity at the microscale, e.g. being perpendicular to the flow direction, may assist the stability of the displacement and delay the breakthrough time. In contrast, other configurations such as being parallel to the flow direction promote flow instability for the same pore-scale geometry.

Critical Pressure Asymmetry in the Enclosed Fluid Diode

Joint physically and chemically pattered surfaces can provide efficient and passive manipulation of fluid flow. The ability of many of these surfaces to allow only unidirectional flow means they are often termed fluid diodes. Synthetic analogues of these are enabling technologies from sustainable water collection via fog harvesting to improved wound dressings. One key fluid diode geometry features a pore sandwiched between two absorbent substrates-an important design for applications that require liquid capture while preventing back-flow. However, the enclosed pore is particularly challenging to design as an effective fluid diode due to the need for both a low Laplace pressure for liquid entering the pore and a high Laplace pressure to liquid leaving. Here, we calculate the Laplace pressure for fluid traveling in both directions on a range of conical pore designs with a chemical gradient. We show that this chemical gradient is in general required to achieve the largest critical pressure differences between incoming and outgoing liquids. Finally, we discuss the optimization strategy to maximize this critical pressure asymmetry.