Date of Award

Spring 1-1-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Shemin Ge

Second Advisor

Anne Sheehan

Third Advisor

Paul Weimer

Abstract

Raton Basin, in southeastern Colorado and northern New Mexico, is known for coal bed methane (CBM) production. Raton Basin also has been a site of wastewater injection, a byproduct of the CMB production since the 1990s. Raton Basin has experienced an increase in earthquakes since wastewater injection began with over 130 M ≥ 3 events between 1990 and 2016. Seismicity has been attributed to anthropogenic causes because of a significant increase since 2001 following commencement of wastewater disposal. The largest earthquake is a moment magnitude (Mw ) 5.3 in 2011. Peer-reviewed studies have attributed the increase in earthquakes to pore pressure increase due to injection. However, other studies have presented the possibility of a naturally high geothermal gradient to the increase in earthquake activity. The average geothermal gradient is 49 °C/km and may also be the cause of seismicity in the Basin. The goal of this study was to assess if there is a spatial relationship between wastewater injection wells, seismicity, and the geothermal gradient. Cool wastewater has the ability to change the stress of the warmer rocks in the subsurface, thus leading to failure.

I hypothesized that injection wells in areas with a higher geothermal gradient would have a stronger correlation with earthquakes. Results of coupled fluid and heat transport modeling do not show a clear correlation between the role of the geothermal gradient in induced seismicity from wastewater injection. Modeling results show a temperature change of a few degrees °C at an observation point 100 m away from the disposal wells. This temperature change is at the same depth of disposal. The modeling results indicate most fluid moves laterally and thus the temperature decrease does not reach the depths at which earthquakes are occurring.

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