Present-day stress analysis of the St. Lawrence Lowlands sedimentary basin (Canada) and implications for caprock integrity during CO2 injection operations

A geomechanical analysis of the St. Lawrence Lowlands sedimentary basin is important to reliably estimate the maximum sustainable fluid pressures for CO2 injection that will not reactivate pre-existing faults in the caprock thereby inducing a breeched CO2 reservoir. This requires the determination of prevailing stresses (orientations and magnitudes), fault and fractures geometries and rock strengths. The average maximum horizontal stress orientation (S-Hmax) is estimated N59 degrees E +/- 20 degrees in the St. Lawrence Lowlands. The stress orientations were obtained from stress-induced wellbore breakouts inferred from four-arm dipmeter caliper data in 17 wells. These wellbore failure features are confined to Paleozoic lithological units of the St. Lawrence Platform succession and frontal thrusts of the Quebec Appalachians at depths from 250 m to 4 km. Our results are consistent with the regional NE-SW S-Hmax stress orientation trend that is generally observed in eastern Canada and the U.S. The stresses/pressure gradients estimated for the St. Lawrence Lowlands (depths<4 km) are: S-hmin 20.5 +/- 3 kPa/m, S-v 25.6 kPa/m, S-Hmax 40 +/- 7.5 kPa/m, pore pressure P-p 9.8 kPa/m indicating a strike-slip stress regime S-hmin