The hydrofracturing method of in situ stress measurement has evolved in the last fifteen eyars into an indispensable tool in geophysical research. For example, a major objective of the first deep scientific drilling in the U.S. at Cajon Pass, California, is to measure the state of stress, primarily by hydrofracturing, in the vicinity of the San Andreas fault. Depsite the general reliability of hydrofracturing, uncertainties in its interpretation still exist and cases where the method is only partially successful or totally unsuccessful are now surfacing. There are at least three major sources of diffi- culties in hydrofracturing data interpretaion: (1) reading the correct pessures from field records, (2) using the correct model for calculating the in situ stresses and (3) evaluating the effect of preexisting fractures on hydrofrac pressures and directions. The research is an attempt to resolve some of these difficulties through laboratory testing and data analysis. In addition, experimental verification of suggested innovative improvements of the method will be carried out. Such confir- mation of one or more of these alternate techniques would enable their use in either complementing orreplacing conventional hydrofracturing.
