Stabilization mechanism of fly ash three-phase foam and its sealing capacity on fractured reservoirs

Water and gas channelling are important limiting factors for the development of fractured reservoirs. A three-phase foam system stabilized by fly ash is optimized as a sealing system to plug fractured reservoirs. The analysis covers the interfacial properties, particle adsorption effect and rheological properties to reveal the stabilization mechanism of fly ash on the three-phase foam. A sealing experiment was performed to evaluate the sealing capacity of the optimized foam system on fractured reservoirs using a natural core with artificial fracture. Results showed the optimized foam system, which consists of 0.5 wt% AOS + 4 wt% suspending agent + 8 wt% fly ash, has excellent stability with a foam half-life of more than 7 days. The adsorption of fly ash particles on the surface of the liquid film can reduce surface tension and improve viscoelasticity of the bubble films, prevent drainage of the liquid layer effectively and delay the aggregation and rupture speed of foam. The optimized fly ash three-phase foam can plug the channelling path of fractures in reservoirs efficiently with a sealing effect 20 times more than that of the conventional foam without particles. Hence, the optimized fly ash three-phase foam is an effective sealing system for plugging fractured reservoirs.