remove it. DAS data quality is intrinsically lower than that from geophones; however, because there is frequently one or two orders of magnitude more density of information, the signal quality can be greatly improved. Finally, while the native measurement of a DAS system is phase, it can be converted to relative strain, strain rate, particle velocity, and an equivalent geophone response.
Figure 2.10 Relationship among the various products created from a DAS data set.
REFERENCES
1 Bakku, S. K. (2015). Fracture characterization from seismic measurements in a borehole (PhD thesis). Cambridge, MA: MIT.
2 Barfoot, D. A. (2013). Efficient vertical seismic profiling using fiber‐optic distributed acoustic sensing and real‐time processing. Paper presented at EAGE Borehole Seismic Workshop II, Malta. doi: 10.3997/2214‐4609.20142554
3 Chen, J., Ning, J., Chen, W., Wang, X., Wang, W., & Zhang, G. (2019). Distributed acoustic sensing coupling noise removal based on sparse optimization. Interpretation, 7(2). doi: 10.1190/INT‐2018‐0080.1
4 Cheng, D., Zhao, X., Willis, M.E., Zhou, R., & Quinn, D. (2019). Receiver decimation and impact on DAS VSP processing quality. Paper presented at EAGE Workshop on Borehole Geophysics, The Hague. doi.org/10.3997/2214‐4609.2019X604020
5 Daley, T. M., Miller, D. E., Dodds, K., Cook, P., & Freifield, B. M. (2016). Field testing of modular borehole monitoring with simultaneous distributed acoustic sensing and geophone vertical seismic profiles at Citronelle, Alabama. Geophysical Prospecting, 64(5), 1318–1334. doi: 10.1111/1365‐2478.12324.
6 Ellmauthaler, A., Willis, M., Wu, X., & Barfoot, D. (2016). Factors affecting the quality of DAS VSP data. Paper presented at SEG Distributed Acoustic Sensing Workshop.
7 Ellmauthaler, A., Willis, M., Wu, X., & LeBlanc, M. (2017). Noise sources in fiber‐optic distributed acoustic sensing VSP data. Paper presented at 79th EAGE Conference and Exhibition, Paris, France. doi: 10.3997/2214‐4609.201700515
8 Ellmauthaler, A., Seabrook, B. C., Wilson, G. A., Maida, J., Bush, J., LeBlanc, M., et al. (2020) Distributed acoustic sensing in subsea wells. The Leading Edge (Nov), 39(11), 801. doi.org/10.1190/tle39110801.1
9 Giallorenzi, T. G., Bucaro, J. A., Dandridge, A., Sigel, G. H., Cole, J. H., Rashleigh, S. C., & Priest R. G. (1982). Optical fiber sensor technology. IEEE Transactions on Microwave Theory and Techniques, 30(4), 472–511. doi: 10.1109/TMTT.1982.1131089
10 Hartog, A. H. (2017). An introduction to distributed optical fibre sensors. Boca Raton, FL: CRC Press.
11 Higginson, P., Purkis, D., & Webster, M. (2017). Advancing the application of downhole fiber optics with a novel low cost disposable deployment method. Paper presented at SPE Offshore Europe Conference & Exhibition. SPE‐186124‐MS. doi: 10.2118/186124‐MS
12 Hull, R., Meek, R., Bello, H., & Miller, D. (2017). Case history of DAS fiber‐based microseismic and strain data, monitoring horizontal hydraulic stimulations using various tools to highlight physical deformation processes. Paper presented at Unconventional Resources Technology Conference, Austin, Texas. URTEC‐2695282‐MS. doi: 10.15530/URTEC‐2017‐2695282
13 Jin, G., & Roy, B. (2017). Hydraulic‐fracture geometry characterization using low‐frequency DAS signal. The Leading Edge, 36(12): 975–980. doi: 10.1190/tle36120975.1
14 Martin, E. R., Castillo, C. M., Cole, S., Sawasdee, P. S., Yuan, S., Clapp, R., et al. (2017). Seismic monitoring leveraging existing telecom infrastructure at the SDASA: Active, passive, and ambient‐noise analysis. The Leading Edge, 36(12): 1025–1031. doi: 10.1190/tle36121025.1
15 Martin, E. R., Lindsey, N. J., Dou, S., Ajo‐Franklin, J. B., Wagner, A., Bjella, K., et al. (2016). Interferometry of a roadside DAS array in Fairbanks, AK. Paper presented at SEG International Exposition and 86th Annual Meeting. doi: 10.1190/segam2016‐13963708.1
16 Mateeva, A., Lopez, J., Chalenski, D., Tatanova, M., Zwartjes, P., Yang, Z., et al. (2017). 4D DAS VSP as a tool for frequent seismic monitoring in deep water. The Leading Edge, 36(12). doi: 10.1190/tle36120995.1
17 Mestrayer, J., Cox, B., Wills, P., Kiyashchenko, D., Lopez, J., Costello, M., et al. (2011). Field trials of distributed acoustic sensing for geophysical monitoring. Paper presented at 2011 SEG Annual Meeting. SEG‐2011‐4253. doi: 10.1190/1.3628095
18 Ning, I. L. C., & Sava, P. (2018). High‐resolution multi‐component distributed acoustic sensing, Geophysical Prospecting, 66(6), 1111–1122. doi: 10.1111/1365‐2478.12634
19 Olofsson, B., & Martinez, A. (2017). Validation of DAS data integrity against standard geophones – DAS field test at Aquistore site. The Leading Edge, 36(12). doi: 10.1190/tle.36120981.1
20 SEAFOM. (2018). DAS Parameter Definitions and Tests, Measuring Sensor Performance Document – 02 (SEAFOM MSP‐02).
21 Tribolet, J. (1977). A new phase unwrapping algorithm. IEEE Transactions on Acoustics, Speech, and Signal Processing, 25(2), 170–177. doi: 10.1109/TASSP.1977.1162923.
22 Willis, M. E., Barfoot, D., Ellmauthaler, A., Wu, X., Barrios, O., Erdemir, C., et al. (2016). Quantitative quality of distributed acoustic sensing vertical seismic profile data. The Leading Edge, 35(7). doi: 10.1190/tle35070605.1
23 Willis, M. E., Palacios, W., Ellmauthaler, A., & Zhao, X. (2020). Mitigation of zigzag noise on DAS VSP records acquired in vertical wells. Paper presented at 2020 EAGE Annual Conference & Exhibition Online. doi.org/10.3997/2214‐4609.202011089
24 Wu, X., Willis, M. E., Palacios, W., Ellmauthaler, A., Barrios, O., Shaw, S., & Quinn, D. (2017). Compressional‐ and shear‐wave studies of distributed acoustic sensing acquired vertical seismic profile data. The Leading Edge, 36(12), 987–993. doi: 10.1190/tle36120987.1
Chapter 3 Distributed Microstructured Optical Fiber (DMOF) Based Ultrahigh Sensitive Distributed Acoustic Sensing (DAS) for Borehole Seismic Surveys
Qizhen Sun1, Zhijun Yan1, Hao Li1, Cunzheng Fan1, Fan Ai1, Wei Zhang1, Xiaolei Li2, Deming Liu1, Fei Li3, and Gang Yu3
1School of Optical and Electronic Information, National Engineering Laboratory for Next Generation Internet Access System, Huazhong University of Science and Technology, Wuhan, China
2OVLINK Inc., Wuhan, China
3BGP Inc., China National Petroleum Corporation, Zhuozhou, China
ABSTRACT
Distributed acoustic sensing (DAS) can record acoustic or seismic waves along the optical fiber with advantages of long distance, short operation time, full well coverage, and cost saving, which has important significance in borehole seismic surveys. By designing and fabricating a distributed microstructured optical fiber (DMOF) with successive longitudinal microstructures, the signal‐to‐noise ratio (SNR) of the Rayleigh backscattering light is enhanced and random interference fading is greatly eliminated, which are beneficial to improve the sensing performance of the system. Combined with coherent detection and phase demodulation, a DMOF‐based fiber optic DAS system with a wide frequency bandwidth from 0.01 Hz to 60 kHz and an ultrahigh strain resolution of 3.4 pε/√Hz around 10 Hz was explored and demonstrated. By employing the DMOF‐DAS system as data acquisition (DAQ) equipment (interrogator), zero‐offset vertical seismic profile (VSP), offset VSP, and walkaway VSP test surveys were conducted in two oil fields in China, respectively, with DMOF cables deployed inside a water‐filled borehole and cemented outside the