COMPRESSIVE STRESSES IN HYDRAULIC FRACTURES

Abstract

In hydraulic fracturing of producing formations in oil and gas reservoir engineering, as well as in coal gas drainage, hydraulic fractures are propped by solid particles—proppant that prevents closure of fractures under the action of compressive stresses in rocks. It is shown that alongside with lateral earth pressure, the compressive stresses in fractures are governed by additional compression generated by fracturing and by compression of rock in depression zone formed in the reservoir fluid inflow to the fracture. The compressive effect in the depression zone can be adjusted by reducing the rate of depression growth in time. This method of compression decrease in fractures is the most efficient in reservoir engineering and in shallow coal seam gas drainage. The compressive stresses in the depression zone are comparable with the lateral earth pressure, thus, the differential pressure step-up can make it possible to keep the stress–strain behavior of rock in the neighborhood of a hydraulic fracture within the limits of elastic deformation and to prevent the fracture closure with irreversible pressing-in of proppant in rock.