Stresses induced near a hydraulic fracture are calculated in an elastoplastic Mohr-Coulomb type formation. While an effective compressive stress increase may reduce the permeability in the formation, the induced shear stresses and dilatant zone developed can increase the stimulated reservoir volume (SRV) and the size of an enhanced permeability zone. Therefore, the induced shear stresses and dilatant zone are used in this article in order to quantify the size of the SRV. It is emphasized that when the SRV can be characterized by elastic strains generated during a fracturing process, this reversible SRV may not be maintained during production. It is those irreversible SRV (ISRV) or dilatant volumetric strains that are the key for producing low-permeability reservoir economically. It is suggested therefore that a production enhancement in these formations is dominated by the possible ISRV which are quantified by the cohesion, the orientation of the natural fracture network and in-situ stress ratios.

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