Stable core-annular horizontal flows in inaccessible domains via a triple-layer configuration

Recently we have introduced a novel methodology for efficient transport of heavy oil via a triple-layer core-annular flow. Pumping pressures are significantly reduced by concentrating high shear rates to a lubricating layer, while ideas from visco-plastic lubrication were used to eliminate the possibility of interfacial instabilities. Specifically, we purposefully position a shaped unyielded skin of a visco-plastic fluid between the transported oil and the lubricating fluid layer. The shaping of the skin layer allows for lubrication forces to develop as the core settles under the action of transverse buoyancy forces: adopting an eccentric position where buoyancy and lubrication forces balance. In later work we have explained how to sculpt the interface in a stable controlled way to achieve a desired shape. Here we show an explicit advantage of the proposed method: namely that we are able to produce stable core-annular flows in regimes where conventional core-annular flows are unsuitable, i.e. either dispersed phases or instability result. Essentially the method can give stable flows for a very wide range of fluid input ratio, although not all will produce the desired reduction in frictional pressure losses.