The strength and conductivity of proppant packs are key parameters for assessing their performance. Mechanical damage in the propping agents, leading to compaction and crushing, significantly reduces the conductivity of the proppant pack. Mechanical damage of proppants is usually analyzed using crush tests. However, measurements from these tests remain questionable because of discrepancies in procedures and test results. Therefore a need emerges to develop techniques for characterizing the properties and mechanical damage in proppant packs.
In this paper, we introduce a new technique based on interpretation of acoustic measurements to quantify mechanical damage in propping agents. We performed uniaxial compression tests in the laboratory and measured the compressional- and shear-wave velocities in proppant packs loaded at axial stress ranging from 10 MPa to 110 MPa. After unloading the tests in which maximum axial stress of 28, 55, 69, 97 and 110 MPa were applied, we conducted sieve analysis on the proppant packs. We applied an effective medium theory based on the Hertz-Mindlin model to approximate the effective elastic properties. We then calibrated the model using the elastic properties estimated from the experimental measurements to characterize the mechanical damage of the proppant packs.
Proppants are used to create conductive pathways for reservoir fluids by keeping the created fractures propped open in hydraulic fracture stimulation treatments. The application of proppants in stimulation treatments is largely influenced by properties such as permeability, conductivity, and resistance to crush. The reduction in fracture conductivity is usually associated with proppant failure and fines migration. The failure of proppants can occur as a result of geochemical reactions and/or mechanical damage.
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