ESTIMATING THE STATE OF STRESS FROM SUBHORIZONTAL HYDRAULIC FRACTURESAT THE UNDERGROUND RESEARCH LABORATORY, MANITOBA

We conducted 9 complete hydraulic fracturing in situ stress measuremen ts in vertical borehole HF1 at the 420 Level of AECL's Underground Res earch Laboratory (UPL), near Pinawa, Manitoba. The tests did not resul t in vertical fractures. Thus, a generalized least-squares criterion w as employed to compute the estimated principal horizontal in situ stre sses. The large number of redundant test results enabled us to estimat e the stress condition with confidence, even though the hydraulic frac tures were only gently inclined. The estimated in situ stress regime w ithin the range between 25 and 95 m below the 420 Level (445-515 m bel ow the surface) is S(v) = 12-14 MPa; S(h) = 36(+/-16) MPa; S(H) = 54(/-13) MPa at 120-degrees(+/-32-degrees). The results are consistent wi th other independently conducted measurements at the URL.