(10b) Laboratory Evaluation of a Natural Gas-Based Foamed Fracturing Fluid

Foams have been used as hydraulic fracturing fluids to reduce water usage and minimize the potentially deleterious impact on water-sensitive formations. Traditionally, carbon dioxide (CO₂) and nitrogen (N₂) have been used as the internal phase in these foamed fluids. Hydraulic fracturing with natural gas is a relatively inexpensive option, particularly if natural gas produced from the wellhead can be used without significant processing. As part of a Department of Energy (DOE) sponsored program, we have previously identified an optimal thermodynamic pathway to transform wellhead natural gas into pressurized natural gas suitable for use as the internal phase in a foamed fracturing fluid.

The current study is focused on preparing a natural gas-based foam at surface conditions typically encountered in hydraulic fracturing and measuring the stability and rheological properties of the foam. In addition, the transient response of the foam and the pumping equipment used to break the formation down was simulated using a burst disc. A base fluid was prepared by batch mixing a viscosifier and foaming surfactant with water. The base fluid was then injected into a tee using a water pump. Simultaneously, liquefied natural gas (LNG) was pressurized using a cryogenic pump, vaporized using a heat exchanger, and injected into the tee to contact the base fluid and generate a foam. The mixture was then pumped through approximately 300 ft of 0.312-in ID tubing equipped with pressure transducers at several locations. The test fixture included a sight glass to visually determine the quality of the foam. Fluids were pumped at various natural gas/base fluid ratios (60 to 80% foam quality), pressures (2,500 to 7,500 psi), and flow rates (0.5 to 7 galUS/min); the resulting pressure gradients in the tubing were measured at each test condition. This presentation reports our findings related to foam stability and rheology and compares these results to previous studies on foamed fracturing fluids.