Abstract

Hydraulic fracturing is a pressure-induced fracture caused by injecting fluid into a target rock formation. In oil and gas industries, this method is commonly used to increase permeability by creating fractures in the formation that connect the reservoir and wellbore. Another purpose of hydraulic fracturing is to determine in-situ stresses. This research was performed in laboratory to validatefracture mechanism of hydraulic fracturing where fractures should be formed perpendicular to the minimum principal stress. Block samples with dimension of 25 cm × 25 cm × 25 cm were prepared in laboratory using two types of materials i.e. resin and concrete. Nozzle with diameter of 1 cm was mounted at the center of block samples to accommodate fluid injection. During the test, the block samples were given initial loads representing in-situ stress at three perpendicular directions. The initial loads were 12MPa, 9 MPa and 6 MPa for resin block sample, and 3 MPa, 2 MPa and 1 MPa for concrete block sample. Fracture pressures (breakdown pressure) were obtained from the tests giving values of 15.6 MPa and 7.0 MPa for resin and concrete block samples, respectively. The fractures were observed approximately parallel to direction of maximum principal stress. Numerical simulation using two dimensional finite element methods were performed to validate the test results, where fracture initiation was predicted using failure criteria of Griffith and Mohr-Coloumb. The fracture initiation should begin at the perimeter of the injected hole, and the location has been confirmed similar with the laboratory test results where fracture generates parallel to direction of maximum principal stress.

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