Dover-33, Michigan, US

Two microseismic monitoring surveys were conducted 39 months apart during re-pressurization (i.e., CO2 fill up) of the Dover 33 reef (located in Otsego County, Michigan) to evaluate the potential for CO2-injection induced seismicity in Silurian-age carbonate reef depleted oil reservoirs.

The baseline monitoring experiment was conducted over a 14-day period in March 2013 during the start of CO2 injection under the MRCSP III project when the reservoir pressure was low (approximately 800 psi).

Repeat monitoring was conducted over a 28-day period in June and July 2016 when reservoir pressure was near original discovery pressure. Monitoring was performed in 2016 after more than 285,000 tonnes of CO2 had been injected and the reservoir pressure had increased to approximately 3,700 psi.

Baseline monitoring was performed by Seismic Reservoir 2020 with 80 three-component (3C) geophones with a 50-ft spacing.

The repeat microseismic monitoring survey was conducted by Paulsson Inc. using 16 OpticSeis™ 3C fiber optic seismic sensors (accelerometers connected through a fiber optic cable that extended to ground surface) with 25-ft spacing.

CO2 injection-rate was continuously recorded during both the baseline and repeat monitoring surveys and these data are available. No valid microseismic events were detected during the baseline period; however, thousands of microseismic events were detected during the repeat monitoring period.

Analyses of the recorded microseismic data were performed by SR2020 (Baseline survey) and Paulsson Inc./NORSAR (repeat survey).