Hydraulic fracturing can increase the fracture conductivity by providing high-conductivity channels for hydrocarbon flow. Proppants flow back from the propped fracture during the early stage of production in the hydraulically fractured tight reservoirs, during which the fracture conductivity decreased due to the proppant flowback. In this paper, the conductivity of the proppant is quantified at different concentrations and closure stresses as baselines. Then, flowback experiment is conducted to understand the impacts of flowback rates, fracturing fluids, closure pressures, and proppant placement methods. When the pressure is higher than 40 MPa, the fracture conductivity of paving with sand will approach zero due to the crushing of sand under the high closure pressure, while the ceramic proppant has high conductivity due to a low crushing rate. The conductivity gradually decreases with time, during which the decline rate is large at the initial stage, and decreases with time till reaching a plateau. When the slickwater is used, the daily production of 70— 200 m3/d in conventional horizontal wells can reduce sand production. When the guar is used, the critical flow rate is expected to be doubled due to the guar residues after gel breaking. Proppant size has a larger impact on proppant flowback than the fracturing fluid. Combined proppant can also decrease the proppant flowback. It is found both fracturing fluids residue and special proppant paving methods can reduce the proppant flowback, which can guide the choke sizes in field conditions.
Hydraulic fracturing is used for shale reservoir stimulation to get more daily production to solve the problems of low natural productivity and difficult waterflood development due to the shale formation characteristics of small pore throat radius and low permeability. The proppant is pumped into the fractures to support artificial fractures in the hydraulic fracturing to create the hydrocarbon migration channel. The high conductivity of fractures is the guarantee of enhancing oil recovery in shale reservoirs. (Cohen et al., 2013; Gomaa et al., 2014)