Experimental Study of Proppant Transport in Flat Fracture Based on PIV/PTV

In order to study the placement behaviors of proppants in fractures during hydraulic fracturing, proppant transport tests were carried out based on flat fractures, and the influence of pump injection displacement, fracturing fluid viscosity, injection position, and proppant type on the placement process of proppants was studied. By using particle image velocimetry (PIV)/ particle track velocimetry (PTV) technology, a two-phase flow velocity test of fracturing fluid–proppant was carried out, and the influence of different factors on final sand embankment shape was analyzed from the perspective of particle motion. The test results showed that: ① there were two typical modes of proppant placement in single flat fracture. The first one was that the front end of the fracture accumulated to the equilibrium height first, and the push-type back end was placed, while the second indicated the mode of overall longitudinal growth of sand embankments. The two modes could appear and transform at different stages of pumping. ② There were different controlling factors in the shape of sand embankments at different positions. The injection position and displacement primarily controlled the leading edge shape; the viscosity and displacement mainly controlled the middle shape, and the viscosity mainly controlled the trailing edge shape. ③ At the distal end of the fracture, there were two modes of proppant settlement, namely backflow type and direct type. The former was controlled by eddy current, while the latter only depended on gravity settlement. ④ Directional perforation + 70/140-mesh quartz sand with large displacement and medium-high viscosity (main proppant) + 40/70-mesh ceramsite bridging + long-distance transportation of 70/140-mesh quartz sand with large displacement and medium-high viscosity + 40/70-mesh ceramsite of displacement tail chasing could be considered in field construction, which took into account the long-distance placement in direction of fracture length and the high connectivity between fractures and wellbores in the near-wellbore area. It was concluded that the experimental study on the transport and placement of proppants in the flat fracture can provide a reference for the efficient placement of proppants in the main fracture of shale reservoir fracturing and the optimization of reservoir stimulation process parameters.