Using a medical CT scanner, researchers from Danish Hydrocarbon Research and Technology Centre and TU Delft have investigated the effect of presence of soap (surfactant) in water on how fast water can move when gas and soapy water is pushed through Bentheimer sandstone. The short answer is that there is no effect. The long answer is that it depends on how the experiments are conducted and the data is interpreted.
Ali Akbar Eftekhari, Postdoc at DHRTC, and R. Farajzadeh, Assistant Professor at TU Delft and senior reservoir engineer at Shell, have investigated the validity of the assumption that foam in e.g. sandstone rock reduces the mobility of gas only and does not have an impact on the liquid phase mobility. The foam is generated by simultaneous injection of nitrogen gas and a surfactant solution.
“We found that the answer to this rather old question is that at the same saturation, soapy water moves as fast as pure water when gas and surfactant solutions are injected into the sandstone rock,” says Ali Akbar Eftekhari, Postdoc at DHRTC.
Ali Akbar Eftekhari continues and tells that their new experimental results and analyses resolve apparent discrepancies in the literature. Previously, some researchers erroneously applied relative permeability relationships measured at small to moderate capillary numbers to foam floods at large capillary number.
“Our results indicate that the water relative permeability in the absence of surfactant should be measured with the capillary pressure ranging up to values reached during the foam floods. However, to do that you should conduct a steady-state gas and water core flood with capillary numbers similar to that of the foam floods or measure the water relative-permeability curve using a centrifuge,” ends Ali Akbar Eftekhari.
Read the whole article in Nature.
Picture: CT scan images of the injection of nitrogen into a surfactant saturated sandstone core. Photo: Ali Akbar Eftekhari.