The hydrogeologic principle of superposition explains long-range fluid pressure transients caused by oilfield wastewater disposal

Fluid pressure increases when oilfield wastewater is injected into deep geologic formations. This lowers effective stress in the subsurface and may trigger earthquakes on faults that are critically-stressed and optimally-aligned with the regional stress field. The image below is a model of oilfield wastewater disposal from a single injection well operating at 13,000 bbl/day for 10 years. The resulting fluid pressure accumulation is shown as isosurface contours in 10 kPa intervals and shading is fluid density.

One recent study from our lab shows that the hydrogeologic principle of superposition reasonably explains the long-range earthquake triggering reported by Peterie et al. (2018) and quantified statistically by Pollyea et al. (2018).  Superposition means that the cumulative effects of multiple pumping wells are additive, so the pressure fronts from closely spaced wells interact to drive fluid pressure over much longer distances. This process is shown in the image below, which is a simulation result from nine high-rate (13,000 bbl/day) injection wells operating for 10 years on a 6 km grid. Fluid pressure accumulation is shown as isosurface contours in 10 kPa intervals. The model uses 4-fold symmetry, so the 1/4 model domain depicts four wells.

© 2019 by Ryan M. Pollyea. Created with Wix.com

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