Interfacial dynamics of gas–water displacement in fractured porous media under high pressure

To deeply understand the dynamics of gas–water displacement in fractured porous media, especially under extreme high-pressure conditions, is essential to prevent water invasion in natural gas reservoirs. To this end, we presented an experimental study on the interfacial dynamics of gas–water displacement in a microfluidic device with fractured porous media, in which the displacement pressure could reach as high as 25 MPa. We found that, under the condition of quasi-static imbibition (i.e., at quite low differential pressure), water preferentially invaded the matrix instead of the fracture. In contrast, invasive water tended to permeate the fracture under high differential pressure; as a consequence, a conical front edge was formed at the gas–water displacing interface. More importantly, the interfacial front in different fractures contacted at the cross junctions and led to the formation of trapped gas in the matrix, due to the velocity of gas–water interface in the fracture being higher than that in the matrix. Besides, with increase in differential pressure and fracture number, the difference in the interfacial velocity between fractures and the matrix increased and hence the gas in the matrix was more easily trapped. Finally, we established a theoretical model to predict the interfacial velocity of gas–water displacement in fractured porous media under high pressure, which was able to well reproduce experimental data.