Laboratory Testing on Proppant Transport in Complex-Fracture Systems

In the fields of unconventional gas and tight oil development, stimulated-reservoir-volume (SRV) fracturing is a key technology. Injecting low-viscosity sand-laden fluid at a high flow rate has the capacity to form complex-fracture networks. Therefore, placing proppant deep into these complex-fracture networks results in a conductive path for production enhancement. In addition, this technique reduces flow resistance when fluid flows from the rock matrix to the wellbore. Currently, the sand features in low-viscosity, sand-laden, high-flow-rate fluid are not fully understood. How this type of fluid can be used for proppant transportation in subsidiary fractures is particularly unclear. This study offers a full exploration of the practical conditions of engineering. Considering the similarity criterion of geometry and velocity, this experiment features the construction of a large-scale device used for proppant placement in visualization of complex-fracture networks. The device can change fracture angles, width, and quantity. Building on the single factors experiment, this paper presents a series of tests to evaluate the transport of proppant in complex-fracture networks. A variety of slickwater-treatment tests are simulated by pumping sand slurry through the visualization-of-complex-fracture-networks device while varying parameters of perforation, fracture angles, proppant size, pump rate, and proppant concentration. As the experiment shows, treatment tests that are used with variable factors obtain different laws regarding traction-carpet features, traction-carpet areas, and balance height and time in complex-fracture networks. In addition, this paper describes a 3D physical model designed by SolidWorks (2011) grid software to make complex-fracture grids. The paper also discusses the process of simulating proppant-concentration-distribution fields in a model of complex-fracture networks. A comparison of the results between the physical and numerical models reveals that during the process of SRV, the law of proppant placement in complex-fracture networks can serve as a guideline for engineering design.