Mechanism of multi-stage sand filling stimulation in horizontal shale gas well development

Fracturing operations in shale gas reservoirs of the Sichuan–Chongqing area are frequented by casing deformation, failures in delivery of mechanical staging tools and other down-hole complexities. In addition, limitation in volumes of tail-in proppant in the matrix area significantly restricts the conductivity in the near zones of the wellbore. Eventually, flowback performance and productivity of shale gas horizontal wells are negatively affected. With consideration to the limitations in the implementation of the mechanical staging technique with bridge plug for shale gas development in the Sichuan–Chongqing area, the technique of multi-stage sand filling stimulation in horizontal wells was proposed to solve the above-mentioned problems. By filling sands in fractures, it is possible to divert fluids to maintain long-term high conductivity of fractures, which is the key to satisfactory EOR performances. By introducing the Hertz contact and fractal theory in the analysis of sand plug strength, and in combination of lab engineering simulation test results, the mechanical model for sand plugs in fractures with proppant was constructed. In terms of strength criteria and friction, the stability criteria of sand plug were put forward. Thus, the permeability fractural model for sand plugs in fractures was perfected. Test results show that the stability of sand plug in the earlier stage of production is mainly affected by fluid washing during flowback, so it is necessary to control the flowback rate strictly. In the later stage of production, the stability is mainly affected by fracture closure stress and flow pressure, so it is necessary to enhance the yield strength of proppant to maintain high conductivity of fractures. In conclusion, the multi-stage sand filling stimulation provides a new technique for multi-stage clustering fracturing operations in shale gas horizontal well development.