Rall Walsh and Mark Zoback

Transcription

1 Update to Oklahoma s Recent Earthquakes and Saltwater Disposal with 2014 Injection Data 1 Rall Walsh and Mark Zoback Fig. 1. Earthquakes and injection wells in Oklahoma. The map shows the locations of recent earthquakes ( as red dots), historical earthquakes ( as yellow dots) and EOR wells (black x s) and SWD injection wells (blue x s) that injected more than 30,000 barrels (~4800 cubic meters) in any month in the most recent three years of data. Eight study areas are outlined, each named for a nearby town, are presented in figures 3-5. This figure remains essentially unchanged. 1 Walsh, F.R. and M.D. Zoback, Oklahoma s Recent Earthquakes and Saltwater Disposal, Science Advances, 1, e June 2015

2 Fig. 2. Statewide injection and earthquakes. (Top) Cumulative number of M 2.5 or greater earthquakes in Oklahoma since (Bottom) The left axis shows total combined injection rate of all UIC wells in Oklahoma by well type. The right axis shows all earthquakes in the state by magnitude through time in the state. Earthquake data are complete through We ve added injection data for 2014 to this plot and we see an step up in total volume injected statewide.

3 Fig. 3. Injection and earthquakes in three study areas. Monthly injection rates from EOR, SWD and unknown wells within the Cherokee, Perry and Jones study areas as well as the times and magnitudes of earthquakes in each area. Detailed maps of each study area are also shown. The symbols for earthquakes and injection wells on the maps are the same as in figure 1. Each study area in figures 3 and 4 is 5000 km 2. We see significant increases in the rate of injection in the Cherokee area in Perry the increases continued, and in Jones, rates declined slightly but earthquakes remained.

4 Fig. 4. Injection and earthquakes in three additional study areas with fewer earthquakes and less Saltwater disposal. In contrast to those in figure 3, here are three comparable areas with comparatively few earthquakes. The vertical scale in the Enid and Oklahoma City study areas is the same as in figure 3. The Ardmore area has a different vertical axis because of the very large volumes of EOR injection. In 2014 earthquakes extended into the eastern edges of the Enid and Oklahoma City boxes, and there was a slight increase in earthquake rate in the Ardmore area, though both injection and Earthquakes are significantly lower than the areas of equal size in figure 3.

5 Fig. 5. Injection and earthquakes in two areas within the Prague and Jones study areas. These show monthly injection rates and locations of EOR, SWD and unknown wells as well as earthquakes. The symbols for earthquakes and injection wells are the same as in the maps in figure 3. Note that the vertical scales are different for each area as are the sizes of the study areas. In 2014 Injection increased in the Prague area, and earthquakes continued to occur. In Stillwater the injection rate in the one main well peaked and started dropping as rapidly as it rose. It will be interesting to see how the seismicity responds if this well continues its rapid decline in 2015.

6 Fig. 6. Saltwater disposal in the three seismically active areas shown in figure 3. Volumes injected into enhanced oil recovery wells (EOR) and saltwater disposal wells (SWD) in the Cherokee, Perry and Jones study areas are shown between 2009 and Also shown is an upper bound estimate of the volume of hydraulic fracturing flowback water that was disposed of in each area in any given year (green). Over 95% of the saltwater disposed of in SWD is produced water, not flowback water from hydraulic fracturing.