Reservoir Induced Seismicity-3

1. Department of Earth Sciences KFUPM Introduction to Seismology Reservoir Induced Seismicity ( Reading Assignment: pp.384-386 ) Introduction to Seismology-KFUPM Ali Oncel [email_address]

3. Recall: Carthage Gas Field, East Texas Introduction to Seismology-KFUPM

4. Two event sub-clusters each delineating the intersection of two planes. Looking along line of intersection (top) and face-on views (bottom). Linear trends can be seen along fracture faces (bottom). The event sequences indicate early fluid invasion along linear trends. Recall

5. Event rate changes correlate with production rate changes. Seismic response lags production by 2–3 weeks. Introduction to Seismology-KFUPM Recall

6. Fracture planes are delineated by production-induced events occuring over a 6-month monitor period. Composite fault plane solutions indicate thrust displacement along the mapped, low-angle fractures. Induced stress changes are very small (<0.1 MPa). Introduction to Seismology-KFUPM

7. Small magnitude events were detected above the reservoir by placing a downhole receiver array within the upper 800 feet of an abandoned well. Event occurrence terminates near the base of the serpentine unit. WELL-BORE DEFORMATION The Geysers, California Introduction to Seismology-KFUPM

8. WELL-BORE DEFORMATION The Geysers, California Introduction to Seismology-KFUPM

9. Rangely Oil Field experiments • Following the Rocky Mountain Arsenal episode, USGS scientists experimented with controlling earthquakes through fluid injection at the Rangely oil field • Experiments suggested that pore pressure increases , decreasing the normal stress on faults, was the controlling factor Frictional stress = coefficient of friction x pressure of rock (pressure of water) Introduction to Seismology-KFUPM

10. Mining and induced seismicity • Quarry blasts may let off enough energy to be like an M 2 earthquake; many through California Introduction to Seismology-KFUPM

11. Mining seismicity • Mining destabilizes rocks; causes rock bursts , small earthquakes Introduction to Seismology-KFUPM

12. Nuclear Explosions An underground nuclear test can cause shaking like an M 5 earthquake . Introduction to Seismology-KFUPM

13. A natural earthquake or a bomb? • A lot of effort has gone into trying to being able to determine whether ground shaking is caused by a natural earthquake or a nuclear explosion • Establishment of the World Wide Seismic Network in the 1960s was actually funded based on the need to monitor bombs , not study earthquakes Introduction to Seismology-KFUPM

14. Earthquake or Bomb? • Radiation pattern of seismic waves: Bomb: compressional P wave first motion in all directions Slip on a fault: P wave first motion compressional and extensional How can we tell? Introduction to Seismology-KFUPM

15. Earthquake or Bomb? • Nuclear tests are shallower than most earthquakes • Nuclear tests generally have weaker surface waves and stronger P wave arrivals Nuclear test in China recorded in Oklahoma, vertical component India’s nuclear bomb Introduction to Seismology-KFUPM

16. Can nuclear tests could trigger tectonic earthquakes? Introduction to Seismology-KFUPM Some people take the connection between earthquakes and bombs a little too far? Debate

18. Could we induce earthquakes to make a fault safe? • People have thought about trying to induce many small earthquakes on a large fault; relieve the stress before a big one happens • Problem #1: It would take a lot of small earthquakes! • Problem #2: At present, there is no way of controlling the size of an induced earthquake! Introduction to Seismology-KFUPM