Characteristics of boundary layer under microscale flow and regulation mechanism of nanomaterials on boundary layer

Abstract

As a new functional material that can effectively reduce displacement pressure and increase injection, nanomaterials have attracted much attention in the development and research of tight oil and gas reservoirs with a low permeability. At present, the research on the technology of decreasing displacement pressure and increasing injection by nanomaterials, mostly focuses on improving the interface properties of nanomaterials such as wall wettability and roughness, and evaluates the performance from the macro-level to clarify the influence and application prospect of nanomaterials. However, there are relatively few studies on the micro influence of nanomaterials on fluid flow. At the same time, owing to the existence of a boundary layer in the pores of a tight reservoir with a low permeability, the fluid flow characteristics are also substantially different from those under the condition of a conventional-size flow channel. In this study, a porous medium was constructed with glass beads to simplify the physical model, and the variation trend of the boundary layer thickness under different treatment conditions and flow channel sizes was clarified through centrifugal experiments, and a formula that can effectively describe the variation in boundary layer thickness with displacement pressure was established, consistent with the functional relationship δ = δ0 + A × exp [− (Grad ΔP − B) / C]. Using the relationship, the static boundary layer thickness δ0 can be obtained. In addition, the regulation of nanomaterials on the thickness of the boundary layer was clarified. The results show that nanomaterials can effectively reduce the thickness of the boundary layer of the fluid in the flow channel, and their performance for this thickness reduction increases with the increase in the wall hydrophobicity after nanomaterials are adsorbed. The smaller the scale of the flow channel, the more clear the regulation effect. In this study, the influence of nanomaterials on the regulation of boundary layer during the fluid flow under a microscale flow channel was clarified from the micro-level. The mechanism for displacement pressure decrease and injection increase of nanomaterials was further elucidated, which is important for the application of nanomaterials in tight reservoirs with a low permeability.