Evaluation of In-Situ Generation of Nitrogen Gas for Foam Applications using Two Salt Solutions

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Abstract
Foams are used in many oil and gas applications including conformance control during EOR processes, fracturing, and acidizing operations. Foams are defined as dispersions of gas bubbles into a continuous liquid phase. Typically, foams are generated when an injection gas such as nitrogen, carbon dioxide, or flue gas is mixed with an injection fluid containing a foaming agent. This method, however, requires a gas source to be present for foams to be generated. The objective of this study is to evaluate a new alternative technique for foam generation using two salt solutions. Nitrogen gas is generated as a result of the reaction of the two salt solutions at specific conditions. This generated nitrogen gas is then used for foam generation in porous media. The foam generated using the two salt solutions is tested in a microfluidic device (rock-on-a-chip) to study the gas mobility reduction in porous media. A Foam rheometer apparatus is also used to measure foam apparent viscosity when the two salt solutions are mixed with a foaming agent. The results are compared with those obtained when nitrogen gas is injected into the system independently in the absence of the two salt solutions. Results reveal that the amount of added salts significantly impact the produced nitrogen volume. Additionally, the test conditions especially the temperature, significantly impacts the reaction rate. The rate of nitrogen gas generation is directly proportional to the temperature when tested at 25-80°C. In addition, experiments demonstrate that the foams generated using the two salt solutions reaction have almost identical characteristics as those produced when nitrogen gas is injected into the foam rheometer apparatus independently. Both methods generate the same foams with comparable foam apparent viscosity. In the microfluidic system, the foam obtained using the two salt solutions in the presence of a foaming agent shows excellent resistance to gas flow and subsequently exhibit large gas mobility reduction. This experimental study, for the first time, confirms the ability of the two salt solutions reaction to generate nitrogen gas spontaneously upon contact under certain conditions. The generated gas is used to generate foams in the presence of a foaming agent. This newly proposed technique of foam generation could significantly impact many oil and gas operations including conformance control during EOR processes, fracturing, and acid stimulation operations.

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