Why do microchannels form in cold production of heavy oil?

Though high-temperature oil recovery techniques easily decrease oil viscosity for extraction, they are expensive and less environmentally friendly than cold production done at the reservoir’s natural temperature. But the heavy oil’s viscosity remains a problem: Recovery ratios are low, even with viscosity-reducing chemicals.

In light oil recovery, injecting water into a reservoir repels the oil and guides it toward the collection point. When done with heavy oil, the viscosity reducer creates an unstable boundary between the water and oil, forming microchannels that hinder the recovery efforts. These microchannels carry most of the injected water and chemical agents directly to the production well, bypassing the surrounding oil and leaving much of it unrecovered.

Meng et al. set out to explain this microchannel formation in hopes of improving heavy oil cold production. They first created a theoretical model based on a linear stability analysis of the displacement front, the interface between the oil and the injected water.

“The analysis shows that in the heavy-oil system, disturbances longer than a few centimeters are amplified into dominant channels, whereas in the light-oil system, only meter-scale defects can grow, a sharp contrast that explains why the same reservoir heterogeneity is harmless for light oil but catastrophic for heavy oil,” said author Bofeng Bai.

They tested their theory with a 2D sand-packed displacement experiment. Here, the researchers wanted to see if spontaneous channeling occurred in a clean, uniform medium, which would provide evidence for their theory of intrinsic instability.

“Indeed, during viscosity-reducer flooding, water broke through early toward one well, and the four producers diverged sharply, confirming that even microscopic imperfections suffice to trigger dominant channels,” Bai said.

Their results provide a theoretical and experimental basis for the microchanneling issue that plagues cold production.

Source: “Microchannel formation driven by instability in heavy oil chemical cold production,” by Lin Meng, Xi Lu, Bofeng Bai, Mengyun Zhao, Lili Cao, Haibo Wang, and Changbo Zhai, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0341453 .