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

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• 作者：E. Konstantinovskaya^a ; ^{Elena.Konstantinovskaya@ete.inrs.ca} ; M. Malo^a ; D.A. Castillo^b
• 关键词：Stress orientation and magnitude ; Stress regime ; Slip tendency of fault and fracture ; Rock strength ; St. Lawrence Lowlands
• 刊名：Tectonophysics
• 出版年：2012
• 出版时间：20 January, 2012
• 年：2012
• 卷：518-521
• 期：Complete
• 页码：119-137
• 全文大小：3652 K

文摘

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¡ãE ¡À 20¡ã 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 ¡À 3 kPa/m, S_v 25.6 kPa/m, S_Hmax 40 ¡À 7.5 kPa/m, pore pressure P_p 9.8 kPa/m indicating a strike-slip stress regime S_hmin < S_v < S_Hmax. The high-angle NE-SW regional faults and fractures in the Paleozoic sedimentary succession and the Grenvillian basement are oblique to the S_Hmax stress orientations (10¡ã to 36¡ã) and could be reactivated (slip tendency 0.34 to 0.58) under the present-day stress field if fluid pressures exceeded the critical threshold. Further refinement of regional geomechanical model is required to estimate the maximum sustainable injection pressure necessary for shear reactivation along the regional faults. The regional pore pressure-stress coupling ratio under assumed parameters is about 0.5-0.65 and may contribute to reduce the risk of shear reactivation of faults and fractures. The maximum sustainable P_p that would not cause opening of vertical tensile fractures during CO₂ operations is about 18.5-20 MPa for the depth of 1 km.