An experimental study of two-phase flow behaviour through pipes and hydraulically-fractured rock specimens

The use of foam-based fracturing fluids for hydraulic fracturing has been identified as a promising technique to extract unconventional natural gases. However, lack of knowledge of foam properties and the two-phase flow behaviour of foam under high pressure makes it challenging to use in field conditions. Therefore, this comprehensive study was conducted to investigate (1) the properties and flow behaviour of foams, under relatively high-pressure (7 MPa) conditions using a newly-developed high-pressure viewing window and (2) two-phase flow behaviour through fractured rock using the high-pressure triaxial test apparatus. Fracture permeability tests were conducted for a series of confining and injection pressures, to evaluate the relative permeability coefficients. The experimental results show that foam flow can have bubble, plug, slug or disperse flow patterns, based on the gas flow rate, at a constant pressure. Moreover, the results show that, at pressures above 1 MPa, the foam flow is almost homogeneous with a fine texture, which is favourable for proppant transport. The findings of this study reveal that, during foam injection into a fractured rock mass under two-phase conditions, the nitrogen phase dominates the flow rate while having higher relative permeability coefficients than the water phase, irrespective of the confining pressure.