Foaming agents for foamed fracturing

In low-pressured reservoirs (either naturally under-pressured or depleted reservoirs), the concern is that during a flow-back operation to remove fracturing fluid from the reservoir, the energy of the reservoir will be too low for an efficient clean-up. Therefore, a solution is to use foamed fracturing fluids, which will lighten the fluid column during fracturing, and ensure a large enough pressure differential to recover the fluid, while still placing sufficient proppant in the formation. The foam can also add to the viscosity of the fluid system, as well as help to control leak-off to a certain extent. To generate a foamed fracturing fluid, Nitrogen or Carbon Dioxide can be injected into the system, as well as foaming stabilizers to maintain the foam quality (percentage of foam as designed for a specific well) with exposure to shear. Often these foaming agents will be surfactants. Care must be taken during foamed fracturing operations with the involvement of gas injection systems, and the high surface pressures required for exceeding fracturing gradients at the reservoir level.