Seismic monitoring of the drilling of an exploratory well off the east coast of the Canary Islands

摘要

From November 2014 to January 2015, REPSOL, S.A. carried out the drilling of an exploratory well 50 km east of the east coast of Lanzarote and Fuerteventura (Canary Islands) at a depth of approximately 900 m below the sea level. This region is characterized by low seismic activity. However, moderate earthquakes have occurred in the region in recent years, some of them being felt by the population, such as the 6 September 2003 (M=4.5) event SE of Lanzarote. Moreover, the 11 June 2013 (M=3.7) earthquake occurred in the same location as the drilling area. Because of the increased awareness of the potential seismic hazard caused by hydrocarbon exploitation activities, the drilling of this exploratory well was monitored with an unprecedented level of detail for an activity of this kind.Two seismic networks, one consisting of land stations, and another of ocean bottom seismometers (OBS) were installed to monitor the drilling activities. The land stations consisted of 8 broadband seismometers and 2 accelerometers in the Canary islands, and 11 broadband stations in southern Morocco. All these stations transmitted their continuous data in real time via GPRS, and these data streams were automatically processed for earthquake detection and location. The marine network consisted of 18 OBSs with three-component, short-period geophones and a hydrophone, and was deployed in the vicinity of the well. Data from the OBSs were not available in real time and were processed offline in order to complement the information from the land stations.During the drilling activities, real time seismic monitoring was used to operate a ¿traffic-light¿ warning protocol, although during the drilling operations no seismicity was detected in the vicinity of the well. Here we report on the performance of the seismic networks, the seismicity recorded, and the lessons learned for future similar deployments.