This is not a scientific paper in the normal sense. It is more like a lecture in which I try to point out that in conducting in situ stress measurements by hydraulic fracturing the exception is often the rule. Results of measurements can often be bewildering, requiring thorough investigation of the reasons for the unexpected stress conditions. I focus on effects of lithology, inhomogeneity, topography, and fault zones on stress regimes, and emphasize the importance of field experience and correct interpretation of test data.
This keynote is a collection of briefly described hydraulic fracturing case histories with which I have been personally involved in the last 40 or so years. They are all related to in situ stress measurements conducted on different continents and for different purposes, from purely scientific, like understanding crustal stress and the causes of man-made earthquakes, to practical, such as assisting in the design of stable underground caverns for hydro-electric plants or mine openings. The purpose of the talk is to highlight some of the many causes that interfere with a neatly uniformstress regime that varies linearly with depth, and possesses consistent principal stress directions. I also emphasize through a case history the importance of field experience in the proper interpretation of hydraulic fracturing stress measurements. Finally I recommend that whenever available, independent supporting evidence of hydraulic fracturing results be sought and used to enhance the confidence in the measured stress field.
At Darlington, Ontario (Haimson & Lee, 1980) hydraulic fracturing (HF) measurements in a 300 mdeep borehole yielded consistent results within the Ordovician limestone between 50 and 220m depth, with the minimum and maximum horizontal stresses (σh and σH) and the σH direction averaging 9MPa, 13.5MPa, and N70°E, respectively.