No abstract

No abstract

No abstract

No abstract

In this study, the performance of calcium hydroxide (Ca(OH) 2 ) flooding (CHF) was investigated with three-dimensional (3-D) experiments with microcomputed tomography and two-dimensional (2-D) micromodel experiments. In 3-D experiments for CHF, two stages of displacement occurred at high capillary numbers. First, streak-like patterns of viscous fingering developed up to the exit of the packed bed. After that, a stable displacement front propagated in the flow direction and resulted in an oil recovery of >50% of the initial oil in place. During the propagation of the stable displacement front, a high-pressure drop was established along the porous media. If CHF is followed by water flooding (WF), the stable front did not propagate and oil production declined promptly. CHF oil recovery is higher by approximately 30% than that of WF for all permeability ratios of heterogeneous layered porous media. We successfully demonstrated that CHF could improve significantly in homogeneous porous media and heterogeneous layered media. 2-D micromodel experiments suggest that a ganglion of Ca(OH) 2 blobs and folded membranes pushed out heavy oil at pore scale in a stable displacement front.

Crude oil often contains long-chain fatty acid components. The fatty acid usually exists as a dissociative anionic surfactant in the oil phase. This study introduced a novel cationic surfactant to absorb the in situ anionic surfactant. Thus, a dual surfactant system was formed, and surfactant aggregates were produced near the water–oil interface. Due to the viscoelastic and fragile aggregates, spontaneous oil deformation and splitting were discovered as a novel mechanism for chemical enhanced oil recovery (EOR). First, we used a water phase doped with stearyltrimethylammonium chloride to displace the heavy oil with palmitic acid in the Hele-Shaw cell. The fingering patterns were observed in the water flooding (WF) and chemical flooding (CF) systems under different flow rates. After that, the experiments were transferred to the wettability-altered micromodel to simulate real oil recovery applications. The Hele-Shaw cell experiments show that viscous fingering was intensive at a low flow rate whereas it was significantly suppressed at a high flow rate in the CF system. The micromodel experiments show that oil recovery is higher in the CF system than in the WF system. The spontaneous cocurrent and counter-current oil blebbing was observed in the dynamic CF process. As the blebbing developed to a certain degree, the oil phase split into tiny droplets that could easily pass through the pore spaces. Additionally, the wettability was also altered from oil-wet to water-wet. As a result, oil recovery was improved significantly. The residual oil was classified into cluster, ganglia, and singlet based on the circularity and Euler number. We found the large clusters dominated in the WF system, whereas the small size of ganglia and singlets were the main forms in the CF system. The new chemical used can be applied for large-scale industrial EOR fields due to its good performance and low cost.

Micromodels are important for studying various pore-scale phenomena in hydrogeology. However, the fabrication of a custom micromodel involves complicated steps with cost-prohibitive equipment. The direct fabrication of micromodels with a 3D printer can accelerate the fabrication steps and reduce the cost. A stereolithography (SLA) 3D printer is one of the best options because it has sufficient printing performance for micromodel fabrication and is relatively inexpensive. However, it is not without drawbacks. In this report, we explored the capability of an SLA 3D printer for micromodel fabrication. Various parameters affecting the printing results, such as the effects of geometries, dimensions, printing axis configurations, printing thickness resolutions, and pattern thicknesses were investigated using microtomography for the first time. Eventually, the most optimal printing configuration was then also discussed. In the end, a complete micromodel was printed, assembled, and used for fluid displacement experiments. As a demonstration, viscous and capillary fingerings were successfully performed using this micromodel design.

Solute transport through variably saturated porous media is ubiquitous in multiple subsurface flows, piquing the geoscience community's interest. This study adopts a novel experimental approach using microfocus x-ray computed tomography for real-time imaging of a three-dimensional NaI tracer plume in a partially saturated packing column. A stabilized two-phase flow field is achievable through continuous co-injection of two-phase fluids: NaCl solvent and pump oil. Thus, the critical role of the NaCl saturation Sw and Péclet number on dispersion can be fully studied by controlling the NaCl fractional flow rate and the total flow rate from the Buckley–Leverett theory. Furthermore, we study solute transport behavior based on statistical moments, the dispersion coefficient, the dilution index, and the mean scalar dissipation rate. Experimental results indicate that the solute transport is Fickian for high Sw ≥ 0.34. In contrast, anomalous transport behavior is found for Sw < 0.34, where the concentration distribution is initially left-tailed and leptokurtic before reaching a well-dispersed regime. The dispersion coefficient is 2–10 times larger for partially saturated cases compared with the fully saturated case and shows a non-monotonical dependency on Sw. Finally, the analysis of the dilution index indicates that the overall mixing strength increases when Sw decreases, whereas the mean scalar dissipation rate reveals that the time scaling of transverse mixing is the largest at an intermediate Sw. The results can be used to elucidate the solute transport behavior in a two-phase system.