Pore-scale dynamics of nanofluid-enhanced NAPL displacement in carbonate rock

Abstract

This study consists of a pore-scale investigation of two-phase flow dynamics during nanofluid flooding in subsurface formations containing non-aqueous phase liquids (NAPLs) such as crude oils. The goal was to gain fundamental understanding of the dominant displacement mechanisms of NAPL at different stages of nanofluid injection in a carbonate rock using x-ray microtomography integrated with a miniature coreflooding system. The nanofluid consisted of surfactant-based microemulsions with in-situ synthesized silica nanoparticles. After establishing its initial wettability state, the carbonate core sample was subjected to various pore volumes (PV) of nanofluid flooding (from 0.5 to 10) to examine the impact on NAPL flow dynamics. We found that most NAPL mobilization occurred within the first PV of injection, removing nearly 50% of NAPL from the rock. The nanofluid invaded into larger pores first with piston-like displacement due to a sharp decrease in NAPL/brine interfacial tension (from 14 to 0.5 mN/m) and contact angle (from 140 to 88). With higher amount of nanofluid delivered into the pores through advection and diffusion, over 90% of NAPL droplets were emulsified and their size decreased from 9 to 3 µm. Subsequent nanofluid injection could further remove NAPL from the smaller pores by altering the thickness of NAPL layers adsorbed on the rock. This dynamic solubilization process reached equilibrium after 5 PV of injection, leading to a reduced layer thickness (from 12 to 0.2 µm), a narrower in-situ contact angle distribution around 81, and an additional 16% of NAPL removal.

Pore-scale experimental investigation of oil recovery enhancement in oil-wet carbonates using carbonaceous nanofluids

“…A considerable amount of oil was displaced after the injection of the first PV of the aqueous solution (i.e., the blank brine and E-CNS mixture in the first and second flow tests, respectively). As the displacing fluid was injected under capillary-driven flow, oil inside the pores was gradually displaced in a sequence dictated by the relative magnitude of their threshold entry pressures 48 . Since most of the medium and large pores were oil-wet and small pores were water-wet at the beginning of the tests, the injection of an aqueous solution was a drainage process in the medium and large pores, and hence the oil recovery was dominated by a piston-like pore-scale displacement mechanism.…”

“…Information on the core-flooding system, data acquisition, and image analysis procedures are provided in the Supplementary Information. A detailed schematic diagram of the experimental setup is shown in Figure S2(a) 41,47,48 . The core-flooding procedure consists of six different steps ( Figure S2(b)).…”

Graphene Quantum Dots for the Mobilization and Solubilization of Nonaqueous Phase Liquids in Natural Porous Media

“…Arkose was selected for its heterogeneous mineralogy with nearly 60% quartz, 30% carbonate (calcite and dolomite), and a small fraction of other minerals such as feldspars and clays, as shown in Figure 1. 45 The in situ contact angles were measured on the dominant minerals (i.e., quartz and carbonate) before and after brine and nanofluid flooding. More than 200 images were considered for these measurements, and some of them are provided in Figure 10a.…”

Direct Pore-Level Visualization and Verification of In Situ Oil-in-Water Pickering Emulsification during Polymeric Nanogel Flooding for EOR in a Transparent Three-Dimensional Micromodel

“…Due to the difficulty of direct visualization of the fluid flow process within a core, the in situ emulsification phenomenon during nanogel flooding cannot be easily visualized . Therefore, microfluidic models become a powerful tool to investigate the microscopic mechanisms of NPs for EOR, including the in situ emulsification .…”

“…50 Due to the difficulty of direct visualization of the fluid flow process within a core, the in situ emulsification phenomenon during nanogel flooding cannot be easily visualized. 51 There-fore, microfluidic models become a powerful tool to investigate the microscopic mechanisms of NPs for EOR, including the in situ emulsification. 52 Since most available microfluidic studies were based on a two-dimensional (2D) micromodel, it is inherently difficult to study emulsion or foam flow due to the limited pore geometry, 53,54 most of which focused only on the investigations of IFT reduction and wettability alteration caused by NPs 55−58 while a few discussed the NP-stabilized emulsion flow using an emulsion generator or the so-called "2.5D micromodel" in the literature.…”