Effect of pressure gradient on the flow of oil and water in gel-filled pore

Water is injected into oil-bearing porous rock for displacement of oil. Water tends to flow through high permeablity streaks, leaving significant amount of oil in place, unless the streaks are plugged by structure-forming fluids such as, polymer–gels. Cr(III)–polyacrylamide gel finds an use even in production well, as this gel structure offers easy flow of oil, apart from restricting water flow. The resistances that water and oil encounter, while flowing through the gel structure are characterized in this paper.The permeability of Cr(III)–polyacrylamide gel, held in tubes was evaluated as function of oil and water flow rates. This was observed that immediately after the rupture, a new pore space was created by the injected fluid. Same pathways were used by the other phase, i.e., water or oil, injected subsequently. The volume of the pathway within the gel structure was also monitored during the flow experiments. After complete recovery of the new pore space, the permeability was found to increase at higher flow rates. The change in permeability was completely reversible, and a cycle of step-wise ascent and descent in flow rates did not show any significant hysteresis. A theoretical model is developed that accounts for the rupture in the gel, and the deformation of the fracture inside the gel due to imposed pressure gradient. The model explains the power-law relationship between permeability and flow rate, as observed in experiments. The model identifies a ratio of interfacial to elastic deformation, in terms of a dimensionless parameter, σ/(GL). This ratio controls the relative reduction in water permeability with respect to the reduction in oil permeability. Experiments were conducted in Berea sandstone rock, and similar trends, as described above were observed.

► Rupture of Cr(III)–polyacrylamide hydrogel in a tube at the centre under oil or aqueous pressure.
► New pathways arising from rupture - used by oil or water.
► The permeability increases at higher flow rate reversibly.
► The difference in permeability to oil and water controlled by the dimensionless parameter, σ/(GL).
► Similar results from the experiments in Berea sandstone.