Yusuke Kumano

Reservoir structure delineation by microseismic multiplet analysis at Basel, Switzerland 2006

Summary In order to develop an enhanced geothermal reservoir as part of the Deep Heat Mining project at Basel (Switzerland) a hydraulic stimulation program was conducted in deep geothermal well Basel 1 during December 2006. This EGS project is financed by Geopower Basel AG. The stimulation was operated and monitored by Geothermal Explorers Ltd for microseismic activity; more than 13,000 microseismic events were observed during the stimulation and afterwards. Hypocenters of approximately 2,900 events were located onsite. During subsequent analysis, we analyzed microseismic multiplet events that exhibit similar waveforms to those among the located events. 70% of the located events comprise multiplets which may be assigned to over 100 distinct multiplet clusters. We estimated relative hypocenters for 1,635 of the multiplet events using a double differential hypocenter location technique. The relocated hypocenter distribution clearly delineates the reservoir structure to an accuracy of typically less than 10 m. Each multiplet cluster defines a planar or streak structure which has vertical inclination and strikes predominantly along a NW-SE direction; this is generally consistent with local tectonic stress analyses. Hypocenter distribution is uniform within the stimulated volume, suggesting that the reservoir structure lacks any dominant fluid flow path. The temporal and spatial pattern of multiplet response corresponds clearly to the time line and injection volumes of the pumping operation.

Passive seismic monitoring of a stimulation of HDR geothermal reservoir at Cooper Basin, Australia

A team of Japanese researchers, with long experience in passive seismic monitoring in the area of development of hot dry rock (HDR) and hot wet rock (HWR) geothermal systems, carried out seismic monitoring at the Australian HDR site being developed by Geodynamics Limited in the Cooper Basin. The seismic network consisting of 4 near-surface stations and 4 downhole stations detected approximately 32,000 triggers during injection of 20,000 m3 of liquid into granitic basement over 3 weeks. The authors located the events on a semi-realtime basis and the locations were fed back to the pumping side. The locations of seismic events showed sub-horizontal extension of the reservoir to 1,800 m away from the injection well at a depth of around 4,500 m. The heterogeneous source migration suggest that the reservoir was close to a critically stressed state.

Reservoir Structure At Yufutsu Gas Field, JAPAN Determined By Analysis of Induced Microseismic Multiplets

Summary We examine induced microseismicity from a hydraulic stimulation at the Yufutsu gas field on Hokkaido Island, Japan, managed by Japan Petroleum Exploration Co., Ltd. (JAPEX), to delineate the fracture system in the reservoir. Over 3,700 seismic events were detected by a network of 4 deep downhole and 3 shallower seismic sensors. 701 of these events showed clear onsets of P and S waves and were located. The source distribution determined using conventional location methods was too diffuse to reveal detailed reservoir structure. We therefore re-examined the dataset by clustering the events using waveform similarity, and subsequently relocated using relative arrival times. 576 events (82% of located events) were identified as multiplet events based on waveform coherence. We relocated the multiplets using a double differential (DD) technique, and obtained a source distribution that delineates tens of sub-parallel streaks composed of multiplets. A synthetic test of the DD location technique with our station distribution suggests that the streaks are artifacts arising from the co-planar network arrangement.