Proppant concentration variation in a hydraulic fracture across the fracture width is investigated using a slurry transport simulator. The result indicates that the proppant slurry dehydrates more near the fracture walls and thus has higher concentration at the wall than at the center of the fracture width. When fluid leak-off is high, this can lead to a proppant pack built on the wall, reducing the effective width of the flow channel and causing mid-fracture screen-out. Furthermore, since the slurry dehydration occurs mostly near the fracture wall, the slurry that travels down the middle of the fracture dehydrates slower than what the current hydraulic fracture models would predict based on the assumption of uniform slurry concentration across the width. Therefore, in tip-screen-out (TSO) designs, it may take longer to achieve TSO than what models predict. The effect of a localized high leak-off area within a fracture, which may represent faults or reservoir inhomogeneity, is also investigated. Again, proppant wall-building occurs and causes width restriction.
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