Effects of Gas Trapping on Foam Mobility in a Model Fracture

Abstract

In enhanced oil recovery, foam can effectively mitigate conformance problems and maintain a stable displacement front, by trapping gas and reducing its relative permeability in situ. In this study, to understand gas trapping in fractures and how it affects foam behavior, we report foam experiments in a 1-m-long glass model fracture with a hydraulic aperture of 80 $$\upmu $$ μ m. One wall of the fracture is rough, and the other is smooth. Between the two is a 2D porous medium representing the aperture in a fracture. The fracture model allows direct visualization of foam inside the fracture using a high-speed camera. This study is part of a continuing program to determine how foam behaves as a function of the geometry of the fracture pore space (AlQuaimi and Rossen in Energy & Fuels 33: 68-80, 2018a). We find that local equilibrium of foam (where the rate of bubble generation equals that of bubble destruction) has been achieved within the 1-m model fracture. Foam texture becomes finer, and less gas is trapped as interstitial velocity, and pressure gradient increase. Shear-thinning rheology of foam has also been observed. The fraction of trapped gas is significantly lower in our model (less than 7%) than in 3D geological pore networks. At the extreme, when velocity increases to 7 mm/s, there is no gas trapped inside the fracture. Our experimental results of trapped-gas fraction correlate well with the correlation of AlQuaimi and Rossen (SPE J 23: 788-802, 2018b) for fracture-like porous media. This suggests that the correlation can also be applied to gas trapping in fractures with other geometries. Article Highlights We have made a lab-scale 1-meter-long transparent glass model representing a geological fracture with roughened surface, and we have implemented a direct method of image analysis to quantify the texture of bubbles in the fracture and to link the texture with the strength of the foam; We have successfully created surfactant-stabilized foam flow inside the fracture and examined its stability along the 1-meter-long fracture; We explain the mechanism of gas trapping in fractures and how it affects foam behavior. We also discuss how viscous force and capillary force affect gas trapping in fractures at our experimental conditions. Graphic Abstract

A micro-scale rheometer to study foam texture and flow resistance in planar fractures

“…They observed noticeable foam trapping in fractures with apertures of less than 50 μm. Li and Rossen 32 confirmed that by increasing the interstitial velocity and pressure gradient, gas trapping decreased and foam texture becomes finer. In rough-walled fractures, foam propagation through permeable paths produces strong flow resistance.…”

“…Microscale observations using silicon-based micromodels are extensive for studying multiphase flow properties and fluid–fluid interactions. 19,32,36,37 An instrumented micromodel is useful to visualize the microscopic flow of foam in fractures. This instrument enables pressure drop measurements and foam microstructure observations for a wide range of flow rates and foam qualities.…”

Coarsening of Foam in Two Model Fractures with Different Roughness

“…Foam is further refined as it propagates through the model fracture due to in-situ bubble generation, mainly by lamella division [26]. After foam achieves steady-state, bubble generation and destruction rates are in local equilibrium in the second half of the model fracture [26]. In this study, the designed velocities ensure that foam reaches a stable pressure gradient, and they are not great enough to compromise the safety of our setup with glass model fractures.…”

“…Li et al diffusion between the mixing tee and the inlet of the fracture, the pregeneration step ensures that gas enters the fracture as relatively large bubbles instead of elongated gas slugs. Foam is further refined as it propagates through the model fracture due to in-situ bubble generation, mainly by lamella division [26]. After foam achieves steady-state, bubble generation and destruction rates are in local equilibrium in the second half of the model fracture [26].…”