Seismic monitoring of CO2 injection at an enhanced oil recovery site in Wellington, Kansas Available to Purchase

CO₂-EOR is an attractive enhanced oil recovery (EOR) technique that offers both economic and environmental benefits – 1) CO₂-EOR recovers additional oil from depleted reservoirs and 2) CO₂-EOR provides safe and permanent storage of injected CO₂ in the subsurface. According to the U.S. Chamber of Commerce, CO₂-EOR accounts for almost 6% of domestic onshore production, which is proof of its significance for fulfilling U.S. energy requirements. However, to derive the long-term environmental benefit of CO₂-EOR, it is essential that the injected CO₂ is permanently stored in the reservoir-caprock system. Although the balanced injection and production of fluids at CO₂-EOR sites should not result in significant reservoir-wide pore pressure increase, local pressure abnormalities do exist that may change the local stress condition sufficiently to trigger displacement along critically stressed, pre-existing faults in the reservoir or in the overlying caprock. Recently, public attention has focused on infrequent reports of seismicity around CO₂-EOR sites. To address this concern, we analyzed surface seismic data collected at a CO₂-EOR site near Wellington, Kansas. We focused our analysis on low frequency events of long duration (LPLD events) likely linked with slow shear slip or tensile opening of pre-existing fractures in the injection formation or the caprock. We identified multiple low frequency (1-5 Hz) events of exceptionally long duration (120-180 seconds) during six months of CO₂ injection. The LPLD events were recorded by a local seismic network (within 2 km) but not by a nearby seismic network (approximately 15 km away), and there is no corresponding record in the regional earthquake catalog. Together, this suggests that the observed LPLD events are of local origin and may be linked to the CO₂ injection. We compared the location of selective LPLD events with the reservoir model of the CO₂ plume and the alkalinity response polygon around the treatment well. We suggest that the uniquely recorded LPLD events in this study are perhaps linked with local CO₂ injection that triggered slow slip along pre-existing faults and fractures in the subsurface.

Presentation Date: Tuesday, October 13, 2020

Session Start Time: 9:20 AM

Presentation Time: 10:10 AM

Location: Poster Station 4

Presentation Type: Poster