Experimental analysis of optimal viscosity for optimizing foamy oil behavior in the porous media

Foamy oil flow is one reason that contributes to the high recovery factor observed in the heavy oil reservoirs. Although the viscosity of heavy oil, as a critical fundamental property, has been noticed by many researchers, the viscosity effect on foamy oil flow remains unclear. Therefore, this work conducted experimental analysis to study the viscosity effect on the foamy oil and oil recovery factor. Based on the experimental analysis, optimal oil viscosity was determined for optimizing foamy oil behavior in the porous media. Stronger foamy oil flow was observed with higher oil viscosity. Due to the low mobility of high oil viscosity, a stronger foamy oil flow does not necessarily mean a higher oil recovery factor. With the increases of dead oil viscosity from 2200 mPa.s to 6600 mPa.s, oil recovery increases from 10.55% to 14.10%. When the dead oil viscosity further increases to 144,000 mPa.s, oil recovery drops to 10.43%. Another important observation is the second foamy oil flow, which occurs during the late stage of oil production for experiments of relatively high oil viscosity. During secondary foamy oil flow, the oil production rate increases again with an increased pressure gradient of the sand-pack and gas production rate drops. All those phenomenal indicate that given preferable oil viscosity and gas-oil ratio (GOR), foamy oil can occur multiple times, which provides significant understanding of current foamy oil study. Therefore, optimizing oil viscosity during each production stage will result in stronger foamy oil flow AND maintained the oil mobility during production.