Distributed Acoustic Sensing in Geophysics. Группа авторов

F. Wang

      Erik Westman

      Ethan Williams

      Mark E. Willis

      Xiangfang Zeng

      Ge Zhan

      Zhongwen Zhan

      Haijiang Zhang

      Ran Zhou

      Ding Zhu

      Tieyuan Zhu

      PREFACE

      Distributed acoustic sensing (DAS) systems are optoelectronic instruments that measure acoustic interactions (distributed strain or strain rate) along the length of a fiber‐optic sensing cable. DAS observation systems can record sound and vibration signals along several tens of kilometers of sensing optical fiber with fine spatial resolution (1–10 m) and over a wide frequency range (from millihertz to tens of kilohertz). DAS provides a large sensing aperture for acquiring high‐resolution acoustic data in both time and space domains. The advantages of DAS technology have enabled its rapid adoption across a range of applications, including geophysics geohydrology, environmental monitoring, geotechnical and civil engineering (railroad, tunnel, and bridge monitoring), hazard mitigation and prevention, and safety and security fields.

      This monograph focuses on various DAS applications in geophysics. The use of DAS in the oil, gas, geothermal, and mining industries for high‐resolution borehole and surface seismic imaging, and microseismic monitoring for hydraulic fractures has accelerated with improvements in the sensitivity of DAS instruments, advances in real‐time big data processing, and flexible and economic deployment of fiber‐optic sensing cables. There is also growing interest in using DAS for critical geophysical infrastructure applications, such as earthquake and near‐surface passive seismic analysis, including the development of tailored or novel numerical techniques. This book aims to engage both the scientific and industrial communities to share their knowledge and experiences of using DAS for novel geophysical applications.

      The origin of this book was the 2017 American Geophysical Union (AGU) Fall Meeting, when scientists and engineers from both industry and academia gathered in New Orleans to present their fantastic research outcomes on DAS instrumentations and applications in geophysics and seismology. As DAS technologies have continued to advance, more and more successful geophysical DAS applications have been reported and published in different geophysical and seismological journals, abstracts, and proceedings of technical conferences, such as the AGU, the Society of Exploration Geophysicists (SEG), the European Association of Geoscientists and Engineers (EAGE), the Society of Petroleum Engineers (SPE), and the Seismological Society of America (SSA). However, few DAS books are available on DAS principles, instrumentation, and geophysical applications. Many attendees at the DAS sessions at the 2017 AGU Fall Meeting expressed that there was a need for a book on DAS geophysical applications. We had interesting discussions with many scientists and engineers working on the frontier of DAS geophysical applications about the potential for a book. We specially recognize Biondo L. Biondi, Thomas M. Daley, William Ellsworth, Mahmoud Farhadiroushan, Barry M. Freifeld, Albena Mateeva, Robert Mellors, Clifford H. Thurber, Herbert Wang, and Mark E. Willis, as well as many others for their encouragement.

      During the 2017 AGU Fall Meeting in New Orleans, we fortunately got an opportunity to meet with the AGU Books Editor, Dr. Bose, who was already aware of this rapidly growing scientific field. We discussed a potential book on DAS geophysical applications, and she was very supportive and invited us to submit a book proposal for an AGU monograph. With no surprise, this DAS book proposal received very positive comments and constructive suggestions from all reviewers. Several reviewers also asked for an opportunity to submit their own contributions to this monograph. We are grateful to those anonymous reviewers of the book proposal for their positive comments and constructive suggestions that led this book to be initiated.

This monograph is organized into four parts. Part I starts with principles of DAS measurements and instruments. DAS interrogation units transmit a pulse of laser light into the fiber. As this pulse of light travels down the fiber, interactions within the fiber result in light reflections known as backscatter (Rayleigh scattering). Backscatters are determined by tiny strain events within the fiber, which in turn are caused by localized acoustic energy. This backscattered light travels back up the fiber toward the interrogation unit where it is sampled. Part II introduces various DAS applications in the oil and gas, geothermal, and mining industries. Part III looks at DAS applications in seismic monitoring. DAS microseismic monitoring of hydraulic fracturing is an industry application but with passive seismic sources. The microseismic DAS method has been shown to have sufficient sensitivity to record very small magnitude microearthquakes with DAS deployed in boreholes. Microseismic DAS systems can be naturally extended to monitoring larger earthquake activity, and slow deformation of Earth’s structure with large‐scale fiber‐optic networks. Part IV discusses DAS environmental and shallow geophysical applications such as geological carbon dioxide sequestration. The final chapter presents a review of fiber optical sensing applications in geophysics including historical developments and recent advances. The list of over 900 literature references of DAS and related technologies will benefit readers, especially newcomers who have just stepped into this fast-growing field.

      We would like to thank the AGU Books Editorial Board for supporting this monograph. Without the efforts from contributing authors it would not have been possible to accomplish this project. We would also like to thank the many volunteer reviewers who spent tremendous amounts of time and effort to ensure that each chapter is of the highest quality. We appreciate Jonathan B. Ajo‐Franklin, Biondo L. Biondi, Mahmoud Farhadiroushan, Albena Mateeva, and Siyuan Yuan for providing their pictures as candidates for the book cover design. Thanks are also extended to the AGU Books editorial team at Wiley, especially Dr. Rituparna Bose, Layla Harden, Noel McGlinchey, Vaishali Rajasekar, Sangaprabha Mohan, Bobby Kilshaw, Nithya Sechin, and Emily Bae, for their organization, management, and cover design.

      This monograph will be the first comprehensive handbook for anyone interested in learning DAS principles and applications. We hope that the book will have a wide spectrum of readers – such as geophysicists, seismologists, geologists, and geoscientists; environmental scientists; and graduate and undergraduate students in geophysics and geoscience – with a common interest in DAS geophysical applications. This book also provides a common platform to the scientific and industry communities to share state‐of‐the‐art DAS technology.

       Yingping Li

       BlueSkyDas (formerly Shell), USA

       Martin Karrenbach

       OptaSense Inc. (A LUNA Company), USA

       Jonathan B. Ajo‐Franklin

       Rice University and Lawrence Berkeley National Laboratory, USA

Part I Distributed Acoustic Sensing (DAS)Concept, Principle, and Measurements

1 High Definition Seismic and Microseismic Data Acquisition Using Distributed and Engineered Fiber Optic Acoustic Sensors

       Sergey Shatalin, Tom Parker, and Mahmoud Farhadiroushan

       Silixa Ltd. Elstree, UK

      ABSTRACT

      The distributed acoustic sensor (DAS) offers a new versatile tool for geophysical applications. The system allows seismic signals to be recorded along tens of kilometers of optical fiber and over a wide frequency range. In this chapter we introduce the concept of DAS and derive an expression for the system response by modeling the superposition of the coherent backscatter