FLUID-PRESSURE MODELING OF INJECTION IN THE RATON BASIN, COLORADO-NEW MEXICO: A CASE STUDY OF INDUCED SEISMICITY

Injection of wastewater from oil and gas production has been linked to the recent increase in U.S. mid-continent seismicity. This study uses fluid flow modeling to analyze the link between wastewater injection from coal-bed gas production and recent seismicity in the Raton Basin of southern Colorado and northern New Mexico. Since the onset of wastewater injection in 1994, 108 earthquakes greater than M3.0 have occurred in the basin, representing a more than 11-fold increase in seismicity compared to the prior 30 years. Recent earthquakes, including a M5.3 that caused damage to structures in the region, have nearly all occurred within 5 to 10 km of one of the 28 injection wells in the basin. Rubinstein et al. [2014] identified earthquake epicenters for two distinct sequences of seismicity in 2001 and 2011 that were co-located spatially and temporally with high-rate injection wells. Here we use the USGS MODFLOW model to calculate injection-induced fluid-pressure changes relative to ambient reservoir conditions. The modeled reservoir includes the Dakota Sandstone, a fluvial and conglomeratic sandstone sequence which is the primary injection target; the Sangre De Cristo Formation, a conglomeratic sandstone; and crystalline basement. We compare the spatial and temporal evolution of fluid pressure to the migration and timing of earthquake hypocenters. Preliminary results using a realistic range of hydrogeologic parameters suggest that injection-induced fluid-pressure changes at earthquake hypocentral depths are sufficient to trigger the two distinct sequences of seismicity in 2001 and 2011.

J. L. Rubinstein, W. L. Ellsworth, A. McGarr and H. M. Benz (2014), The 2001-present induced earthquake sequence in the Raton Basin of northern New Mexico and southern Colorado, BSSA 104, 2162-2181.