UBC Theses and Dissertations
Large fluid injection induced seismicity events : empirical and numerical investigation of causes, mechanisms and mitigation strategies Mehrabifard, Ali
Fluid-injection-induced seismicity, e.g., that associated with hydraulic fracturing operations, is of high importance and interest to various stakeholders, including indigenous and local communities, regulators, operators and insurance companies. Failure to perform a thorough hazard assessment may result in undesired large magnitude events (>Mw2) that could impact safety, cause damage to infrastructure, and delay or stop projects. This thesis focuses on three key objectives: 1) to investigate whether hazard assessment relationships established for natural earthquakes can be used for fluid-injection-induced seismicity, 2) to understand the mechanism(s) of fluid-injection-induced seismicity events with focus on hydraulic fracturing operations in the Montney play of northeastern British Columbia (NEBC), and 3) to propose mitigation measures to potentially reduce fluid-injection-induced seismicity hazards. The methodology employed integrates empirical analyses with advanced 3-D numerical modelling. The empirical analyses are first applied broadly to a database compiled from global records of induced seismicity over a wide range of industrial operations, and then specifically using datasets from two well-pads in the Kiskatinaw area of NEBC. Numerical modelling supported these analyses and provided mechanistic understanding of them. Main findings include: 1) The commonly held belief that larger earthquakes occur in compressional stress regimes (as observed for natural earthquakes) is not necessarily true for fluid-injection-induced seismicity, and thus the use of focal mechanisms and b-values to assess hazard susceptibility and maximum magnitude potential should be approached with caution. 2) The dominant mechanism for large magnitude induced events in the Kiskatinaw area was found to be the direct effect of fluid-injection pressure perturbation associated with geological structures in the targeted reservoir volume that were limited in their hydraulic connectivity (i.e., where fracture intensity is low). 3) Higher injection pressurization rates were found to result in higher magnitude events, while lowering the rate was observed to cause the seismic moment release through many smaller events. The results point to mitigation measures such as monitoring and controlling the pressurization rate to control the rate of seismicity and event magnitudes, and increasing hydraulic fracturing fluid viscosity to reduce the fluid pressure front propagation to unfavorable (i.e., susceptible) areas outside the designed hydraulic fracturing zone.
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