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Proppant Damage Characterization Using Nuclear Magnetic Resonance Measurements

Abstract

Proppant performance can significantly affect production in unconventional plays. Quantifying the mechanical damage and conductivity of proppants are, however, challenging, and there are no existing methods for evaluating in-situ performance of proppants. This paper proposes a new method using Nuclear Magnetic Resonance (NMR) measurements to characterize pore-size distribution in proppant packs, which is directly correlated to their mechanical damage and conductivity. We first prepared and saturated proppant packs with water. A benchtop 2MHz-frequency NMR equipment was used to measure T2 (spin-spin relaxation time) distribution in the proppant packs. We carried out tests to investigate the sensitivity of the T2 distribution measurements to proppant packs that contain (a) different types of proppant with different surface relaxivity, (b) mixture of proppants with different sizes, and (c) proppants with different levels of mechanical damage. The results showed that NMR T2 distribution is sensitive to pore size distribution in the proppant packs which contained a mixture of proppants with different sizes and level of mechanical damage. These measurements reflect the contribution of fines to the pore-size distribution of the proppant pack, and the effect of mechanical damage on different combinations of proppant grain size. We also observed measurable sensitivity of T2 distribution to the different levels of mechanical damage in the proppant packs, which enabled quantifying damage in proppants. The loss of pore volume predicted by NMR T2 distribution was in agreement with direct measurements applied on the proppant packs. Furthermore, we quantified the sensitivity of the NMR measurements to the proppants composed of different materials and coating. The results showed that NMR T2 distribution is sensitive to the presence of paramagnetic materials such as iron in the proppants, especially if well distributed on the proppant surface. The new method enables evaluating mechanical damage in proppant packs through quantifying pore structure in the packs, which eliminates the challenges with fluid-flow-based conventional techniques. The results are promising for application of this characterization technique for in situ assessment of proppant conductivity. Finally, the introduced technique defines criteria necessary for strategic selection of proppants in stimulation design, which is a requirement for successful development of unconventional plays.