Influential Factors on Permeability Recovery during Flowback of Fractured Reservoirs

During drilling and completion in fractured low-permeability reservoirs,filtration and particle invasion would cause damage to reservoir.Shielding temporary plugging is an effective way to protect reservoir by forming tight plugging zone,in which permeability recovery during flowback is an important index in plugging quality evaluation.The experiment of plugged zone buildup and flowback were conducted on fractured sand core samples using the same fluid but different particle size.The impact of particle size and pressure gradient on flowback recovery was studied.Results show that the flowback recovery increases at first then decreases with the pressure gradient increase.The matching between particle size and fracture width directly affects the invasion depth of particles.The recovery is high when solid particle invasion is shallow,while it is low when solid particle invasion is deep.For sand core samples with fracture width of 20 to 70 microns,the best pressure gradient is from 7.8 to 24.2 MPa/m and the best matching ratio is from 1/3 to 2/3 and close to 2/3 bridge.Optimal pressure gradient exists in the process of flowback in fractured reservoirs.The matching between particle size and fracture width would affect the invasion depth of particles and,in turn,the permeability flowback recovery.