| Title | Interpretation of Microseismicity at the Rotokawa Geothermal Field, 2008 to 2012 |
|---|---|
| Authors | Steven SEWELL, William CUMMING, Jeff WINICK, Jaime QUINAO, Candice BARDSLEY, Irene WALLIS, Steve SHERBURN, Sandra BOURGUIGNON |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | Rotokawa, microseismic, MEQ |
| Abstract | At the Rotokawa Geothermal Field, the integration of microseimic (MEQ) data into a space and time visualization of geoscience data has helped identify and constrain important elements of the reservoir model, including a major structure that likely influences reservoir fluid flow. MEQ monitoring at Rotokawa began in 2006 when 140 ˚C injection fluid was moved to wells with deeper permeability in higher temperature rock, initially at more than 300 ˚C. An array of 8-10 seismometers has been operating continuously since mid-2008. Double-difference hypocenter analysis and seismic velocity tomography have supplied sufficient MEQ location accuracy to support the use of 4D visualization tools to interpret MEQ patterns in space and time with respect to a wide range of geoscience and reservoir engineering data sets. Detailed correlation of the MEQs with changes in injection and production well flow rate, pressure and temperature has been particularly important to understanding likely causes of the MEQs and their implications for reservoir properties. Most MEQs at Rotokawa appear to be triggered by injection cooling and by the field-wide pressure transients caused by changes in production, although other mechanisms are possible. Many MEQs occur in swarms of more than 10 events/day along a linear, northeast trending structure – the Central Field Fault (CFF). The majority of the remaining MEQs are clustered on the southeast side of this structure that separates injection wells to the southeast and production wells to the northwest. The location and timing of the MEQs relative to major changes in production and injection are consistent with other geoscience data sets suggesting that the northeast trending structure acts as a barrier to fluid flow across strike and a zone of enhanced permeability along strike. This structure and the effective base of the reservoir permeability are the main features interpreted from the MEQ data that have been incorporated into the Rotokawa conceptual and numerical models, which are used to guide field management. |