Production declines in hydraulically fractured shale gas wells are far higher than conventional wisdom predicts and gas yields are low. A science-based approach to understanding proppant flow and proppant-formation interaction could yield new technologies that extend well-life while better protecting the environment. To this end, a series of millifluidic experiments have been undertaken to elucidate proppant flow and placement in idealized fractures, where the size and shape of the fracture has been varied. In the field, hydrofracturing creates fractures radially around the well bore. Here we mimic that effect with pairs of duct-shaped cracks off a central cylindrical core. The size of the fractures is varied and the concentration of proppant in the cracks is estimated in flow visualization experiments. The millifluidic device is made by 3D printing the interior features and affixing these to clear Lexan plates, since the Lexan is much clearer than the printed plastic. This process creates low cost, easily visualized, test bed for understanding proppant flow.
Two idealized proppants are studied, each with 20vol% of 70mm aluminum oxide particles. First, a proppant with a Newtonian suspending fluid similar to slick water is studied. Second, a proppant with a time-dependent viscoelastic suspending fluid, guar, is studied. Rheological measurements are taken for both proppants and used to populate a diffusive flux suspension flow model, where the effects of guar are mimicked with a yield stress. Particle-scale simulations are also undertaken to estimate the permeability of the propped crack. Results from the experiments are compared to the both models and discrepancies and missing physics are discussed. Laboratory-scale tests have also been conducted on fracturing and placing proppant in shale. Here the volume of particles placed in the fractures is characterized post-test using micro-CT imaging. Results from the shale experiments will be discussed along with possibilities for modeling this more realistic system.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2014-18859A
See more of this Group/Topical: Engineering Sciences and Fundamentals