11:00 AM - 11:30 AM
[SSS09-08] Fracture detection and properties estimation using fiber optic sensors
★Invited Papers
Keywords:fiber optic sensors, DAS-VSP, diffraction, fracture detection
The knowledge of fracture locations and connections which are pathways for fluid and solute transport are crucial information for developing the geothermal field. This information contributes that plan to drill the sidetrack within the suspended well and detection the drilling target for a make-up production well.
The development of Distributed Acoustic Sensing (DAS) technologies enables the operation under high temperature environment and dense spatial measurement. This could be particularly valuable for acquiring high spatial resolution images of seismic reflection survey and dipping faults in the vicinity of the well.
In the feasibility study, we acquired the overnight monitoring data and conducted SSP (surface seismic profiling) survey and DAS-VSP survey which was used the suspended well in the real geothermal field. We developed the fracture detection systems in the vicinity of the well described following and investigated their applicability for the real data set.
・acquire the seismic cross section with SSP and DAS
・FWI velocity model building which correspond with check shot
・extract the diffracted wave from overnight monitoring DAS data and evaluate the indicators that detect the fractures in the vicinity of the well.
The records of SSP and DAS provide seismic reflection section and represent the faults and fractures as the characteristics of each method. Fractures are represented as a gap in SSP section and as a fault plane in DAS-VSP section. It was confirmed the fracture locations in both reflection sections were consistent. Moreover, the result of joint FWI using SSP and VSP dataset showed a better agreement with the velocity along the well estimated by the zero-offset DAS-VSP analysis. This confirmed that accurate velocity information can be estimated from the DAS-VSP dataset.
The numerical studies were performed to simulate the DAS-VSP acquisition. In the synthetic experience, the presence of later phases including diffracted waves after direct P-wave and S-wave show the potential as seismic signatures that indicates the existence of fractures near wellbore.
These results stimulated us the development of diffraction enhancement workflow. We combine Plane Wave Destruction (Fomel, 2002) and Common Reflection Surface (Dell and Gajewski, 2011) to separate the diffractions from direct arrivals in the overnight monitoring data. Comparison with the wellbore information and the distribution of the extracted diffracted waves, it was confirmed that significant PS conversion waves after the direct P-wave which generated by the vicinity of the fracture zone were observed and significant amplification was also observed in the later phases which were identified as direct S-wave.
With the development of DAS sensing technology, its dense sampling could be possible to extract diffracted waves and to estimate accurate velocity model using FWI. In this presentation, the background and developed fracture detection systems will be explained and discussed these results and further works.
Acknowledgements:
We conducted this research as a part of Geothermal Borehole Exploration Techniques by JOGMEC. Nittetsu Mining Co., Ltd. and Kirishima Geothermal Co., Ltd. were kindly allowed us the use of their suspended well and fields. We want to thank these organizations.
The development of Distributed Acoustic Sensing (DAS) technologies enables the operation under high temperature environment and dense spatial measurement. This could be particularly valuable for acquiring high spatial resolution images of seismic reflection survey and dipping faults in the vicinity of the well.
In the feasibility study, we acquired the overnight monitoring data and conducted SSP (surface seismic profiling) survey and DAS-VSP survey which was used the suspended well in the real geothermal field. We developed the fracture detection systems in the vicinity of the well described following and investigated their applicability for the real data set.
・acquire the seismic cross section with SSP and DAS
・FWI velocity model building which correspond with check shot
・extract the diffracted wave from overnight monitoring DAS data and evaluate the indicators that detect the fractures in the vicinity of the well.
The records of SSP and DAS provide seismic reflection section and represent the faults and fractures as the characteristics of each method. Fractures are represented as a gap in SSP section and as a fault plane in DAS-VSP section. It was confirmed the fracture locations in both reflection sections were consistent. Moreover, the result of joint FWI using SSP and VSP dataset showed a better agreement with the velocity along the well estimated by the zero-offset DAS-VSP analysis. This confirmed that accurate velocity information can be estimated from the DAS-VSP dataset.
The numerical studies were performed to simulate the DAS-VSP acquisition. In the synthetic experience, the presence of later phases including diffracted waves after direct P-wave and S-wave show the potential as seismic signatures that indicates the existence of fractures near wellbore.
These results stimulated us the development of diffraction enhancement workflow. We combine Plane Wave Destruction (Fomel, 2002) and Common Reflection Surface (Dell and Gajewski, 2011) to separate the diffractions from direct arrivals in the overnight monitoring data. Comparison with the wellbore information and the distribution of the extracted diffracted waves, it was confirmed that significant PS conversion waves after the direct P-wave which generated by the vicinity of the fracture zone were observed and significant amplification was also observed in the later phases which were identified as direct S-wave.
With the development of DAS sensing technology, its dense sampling could be possible to extract diffracted waves and to estimate accurate velocity model using FWI. In this presentation, the background and developed fracture detection systems will be explained and discussed these results and further works.
Acknowledgements:
We conducted this research as a part of Geothermal Borehole Exploration Techniques by JOGMEC. Nittetsu Mining Co., Ltd. and Kirishima Geothermal Co., Ltd. were kindly allowed us the use of their suspended well and fields. We want to thank these organizations.