14:15 〜 14:35
[BH-06] Quantitative Characterization of Natural Fractures in Far Field from Borehole with Sonic 3D STC: Case Study from a Geothermal Field, Japan
This paper presents a case study from a geothermal field in Japan where natural fractures extending away from borehole are mapped and characterized in 3D using a new borehole sonic reflection processing workflow.
During the exploration phase of geothermal fields in Japan, it is critical to locate and exploit high temperature and permeable zones. These permeable zones are mainly driven by natural fractures or conductive faults in the volcanic geothermal field. Understanding the spatial distribution of these fracture zones is, however, challenging because of the geological complexity. This fact actually affects the entire geothermal field exploration planning.
A novel borehole sonic reflection processing workflow was recently developed. With the multi-level multi-azimuth borehole sonic data, the 3D slowness time coherence (STC) and a ray tracing inversion provide quantitative true dip and azimuth information of fractures in both near and far field around the wellbore. The results are also utilized as prior information for the migration processing. Here the workflow is applied in the borehole dipole sonic dataset acquired with 13-station and 8-azimuth receivers in a geothermal field, Japan. Clear sonic reflection events extended from near wellbore to far field are depicted. The 3D STC results provide true dip and azimuth information of those reflectors. Since the true dip and azimuth are consistent with the fractures interpreted from the borehole image log, the observed reflectors probably indicate a fracture zone crossing the well and extending from near wellbore to far field.
During the exploration phase of geothermal fields in Japan, it is critical to locate and exploit high temperature and permeable zones. These permeable zones are mainly driven by natural fractures or conductive faults in the volcanic geothermal field. Understanding the spatial distribution of these fracture zones is, however, challenging because of the geological complexity. This fact actually affects the entire geothermal field exploration planning.
A novel borehole sonic reflection processing workflow was recently developed. With the multi-level multi-azimuth borehole sonic data, the 3D slowness time coherence (STC) and a ray tracing inversion provide quantitative true dip and azimuth information of fractures in both near and far field around the wellbore. The results are also utilized as prior information for the migration processing. Here the workflow is applied in the borehole dipole sonic dataset acquired with 13-station and 8-azimuth receivers in a geothermal field, Japan. Clear sonic reflection events extended from near wellbore to far field are depicted. The 3D STC results provide true dip and azimuth information of those reflectors. Since the true dip and azimuth are consistent with the fractures interpreted from the borehole image log, the observed reflectors probably indicate a fracture zone crossing the well and extending from near wellbore to far field.
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