This article reexamines the classical PKN model of hydraulic fracture Perkins and Kern (J. Pet. Tech. Trans. AIME, 222:937-949 (1961)) and Nordgren (J. Pet. Tech. 253:306-314 (1972)) using novel approaches, which have recently been developed to tackle this class of problems that are characterized by a moving boundary and strong non-linearities in the governing equations. First, we demonstrate, using scaling arguments only, that a PKN hydraulic fracture has two limiting time asymptotic behaviors: storage-dominated at small time, and leak-off-dominated at large time. Next, we investigate the multiscale nature of the tip asymptotics and its implication for the construction of a robust and efficient numerical algorithm. In particular, we show that in the storage-

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This brief note presents an alternative explanation to the fact that in the imbibition experiments with active ultrasonic monitoring the amplitude of the recorded P waves detects imbibition front before any changes in the P wave velocities are observable. The model is based on P wave interaction with the imbibition front. The qualitative estimation is in agreement with previously published experimental data.

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In-situ nuclear magnetic resonance (NMR) core flooding system has enabled researchers to monitor several rock properties such as porosity, pore size distribution, and fluid saturation along the tested samples with high resolutions and under reservoir conditions. However, spatially resolved rock strength/mechanical property alteration coupled to fluid migration/substitution remains poorly characterized. To this end, Fiber Bragg Grating (FBG) multiplex sensors were integrated with NMR core flooding system to monitor rock strength changes, or generally speaking, to observe hydro-mechanical-chemical coupling mechanisms during core flooding tests. In this study, we present a novel approach on how to conduct core flooding experiments, while simultaneously monitoring NMR and FBG strain response of the tested limestone plug. The NMR cell was modified to integrate FBG technology without impeding the NMR signal and core flooding high pressure/temperature capacity. A high spatial resolution optical fiber was attached onto the sample radial surface. The results show the successful association of NMR and FBG sensors to track any change at each stage of brine injection. The FBG is capable of measuring the rock strain variations induced by rock-fluid interactions during brine injection, allowing it to capture the fluid front location along with the sample and at a faster rate than the NMR.