Realistic laboratory simulation of fractures propped with sand, engineered ceramic proppants, and resin-coated proppants to determine the impact of temperature, stress, and stress cycling on proppant-pack structure and pack permeability is both difficult and expensive. Large, specialized testing equipment and long testing times are required, which can lead to high testing costs. This paper presents a new dynamic compression device (DCD) that permits rapid proppant-pack analysis to optimize proppant selection.
Understanding the mechanical and fluid dynamics of hard granular particle packs subjected to high closure stress and cyclic stress is important for understanding fracture conductivity and the impact of production operations. Few experimental studies have been reported where the compression of proppant with variable stress rates was used that also includes simultaneous direct visualization of the proppant structure.
The DCD imposes a controlled strain on the proppant pack while measuring the stress response, up to a compressive loading of 7,100 psi. Simultaneously, the liquid permeability and a detailed visualization of the proppant-pack structure are acquired. The stress loading and unloading process, performed in either a single or repeated (cycling) protocol, can be performed with precise measurement of the resulting system-level strain. Permeability results obtained using the DCD were comparable to those obtained using standard API linear conductivity determinations. Particle rearrangement by direct visualization during stress cycling was comparable to that predicted by use of a popular, commercial, three-dimensional particle-flow numeric simulator.
The DCD is a small, bench-top device that uses a small proppant sample. It has been demonstrated to be an efficient tool to experimentally determine the impact of closure stress, stress-change rate, proppant-packing properties, and the effect of multiple stress cycles on liquid permeability, while providing direct proppant-pack structure visualization. This new device enables rapid testing to determine the impact of expected downhole production conditions on proppant-pack permeability and permit selection of optimum proppant and proppant coatings.