Analysis of pressurizing borehole wall in a hydraulic fracturing test in laboratory

Hydraulic fracturing (HE) test is one of the available methods to determine the magnitude and the direction of in-situ stresses. This method is simple and can be applied at a great depth, but the result is less accurate than other methods. Among others of important parameters are determinations of the tensile strength value used to predict the breakdown pressure, and the process during pressurization by packer and by hydraulic fluid in HE test. Experiments were carried out using three boreholes each of 6 meters depth at a limestone quarry, concrete-blocks of 50 cm x 50 cm x 160 cm, and concrete thick-walled cylinders at laboratory. To simulate the maximum horizontal stress, a pressure of 0.03 MPa was applied. The result of the experiment showed that tensile strength value obtained from Brazilian test (2.48 MPa) lower than that of obtained from HE test (4.20 MPa). Analysis of the pressurizing by packer and by HE fluid revealed that the breakdown pressure from pressurizing by packer (7 MPa) was higher than that of breakdown pressure obtained from pressurizing by hydraulic fluid (4.17 MPa).