Abstract

Enhancing formation permeability through hydraulic fracturing has become a common tool for oil and gas, as well as enhanced geothermal systems reservoir production. Nanodarcy permeability is common in unconventional oil and gas reservoirs requiring the production to greatly depend on the complex network of induced and natural fractures. Proppant is used in these complex fracture networks to keep conductive pathways open and connected to the wellbore for flowback after fracture closure. The quality and mechanical properties of proppant directly impact the conductivity of the fracture network. Numerous proppant and proppant pack characterization tests can be performed to understand the behavior of the proppant pack in a fracture, some of which were initially outlined in API RP-56/58/60 and later in ISO 13503-2. According to ISO 13503-2 section 11, proppant pack crush strength is determined based on the amount of fines generated at specific loading conditions. Although this method gives an idea of proppant pack failure in a stress range, numerous tests are required to deconvolve the actual pack strength but still do not provide any information regarding partial pack yielding and precise full pack crush strength providing only wide application strength limits for a group of proppants. To study this problem, numerous proppant crush tests were performed according to this standard with the inclusion of acoustic emission (AE) monitoring. Two AE piezoelectric transducers were placed on the crush cell to observe sound waves stemming from grain friction as well as particle fracture initiation. The observed AE rate throughout the test showed stress level at pack grain alignment as well as the initiation of particle fracture, or proppant pack yield. Testing was performed on 20/40 mesh white sand, manmade proppant, resin pre-coated proppant, as well as other saturated and unsaturated conditions, including surface-modification agent (SMA) coatings. Information gained from AE analysis was compared to post-test particle size distribution. As a simple, non-invasive technique, AE monitoring proved to be a valuable and effective tool in evaluating proppant pack yield and strength performance at downhole conditions, allowing the well operator to select the optimal proppant material used in the hydraulic fracturing treatments for his well.

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