Hydraulic fracturing experiment at the University of Regina Campus

A hydraulic fracturing stress determination was carried out during May and June, 1979, in a water well intended for the Geothermal Feasibility Project on the campus of the University of Regina, Saskatchewan. Four intervals between depths of 2062 and 2215 m were fractured successfully, one in the Winnipeg Formation (2034-2083 m), two in the Deadwood Formation (2083-2209 m), and one under the Phanerozoic sequence near the top of the Precambrian basement (2209-2215 m).Over the depth range (2062-2215 m) covered by this hydrofracture experiment, the results and inferences are as follow. Downhole breakdown pressure ranges from 42 to 45 MPa, and downhole shut-in pressure from 35 to 42 MPa. The minimum horizontal stress component, σ hmin , is taken as being equal to the corresponding shut-in pressure. The vertical stress component, σ v , is assumed to be essentially equal to the overburden pressure and varies from 51 to 56 MPa. Whereas σ v and σ hmin apparently vary smoothly across the Deadwood Formation, the maximum horizontal component, σ hmax , appears to undergo a discontinuity in the upper part of the Deadwood Formation, as σ HMAX varies from 40 MPa in the Winnipeg Formation to 53 MPa in the upper part of the Precambrian basement. In so far as seismotectonics is concerned, the physical implications of these measurements are that normal faulting should prevail in the Winnipeg (and overlying) formations whereas strike-slip faulting could occur in the Precambrian basement; however, the latter inference has not been firmly established. Breakdown pressure is a useful guide (upper limit) for the potential geothermal demonstration project. Key words: hydraulic fracture, fracture mechanics, faulting, stresses, in situ, breakdown, shut-in pressure, seismotectonics.