Interaction of helically wound fibre‐optic cables with plane seismic waves

Distributed acoustic sensing is a novel technology for seismic acquisition. In this technology, strain changes induced by seismic waves impinging on an optical fibre are monitored. Due to the fact that glass is relatively rigid, straight glass fibres are not sensitive to broadside waves. We suggest using distributed acoustic sensing systems with fibres helically wound around cables. One increases the fibre sensitivity to broadside waves by decreasing the fibre wrapping angle (the angle between the fibre axis and the plane normal to the cable axis). The optimal wrapping angle is chosen to minimize the impact of Rayleigh waves on the signal measured. This angle depends on the cable Poisson ratio, and it is approximately equal to 30◦ for cables composed of plastic. For reliable detection of seismic waves, one needs a good mechanical contact between the cable and the surrounding medium. On the other hand, the sensitivity of distributed acoustic sensing systems to primary waves can be significantly reduced if the cable is placed in a cemented borehole.

[1]  R. Posey,et al.  Strain sensing based on coherent Rayleigh scattering in an optical fibre , 2000 .

[2]  T. Marzetta.  Inverse borehole coupling theory and its application to hydrophone vertical seismic profiling , 1992 .

[3]  B. Kennett,et al.  Reflections, rays, and reverberations , 1974, Bulletin of the Seismological Society of America.

[4]  Wilfred Berlang,et al.  Distributed acoustic sensing for reservoir monitoring with vertical seismic profiling , 2014 .

[5]  J R Rice,et al.  Pressure sensitivity of a clad optical fiber. , 1979, Applied optics.

[6]  B. Kuvshinov.  Reflectivity method for geomechanical equilibria , 2007 .

[7]  G. Hocker,et al.  Fiber optic acoustic sensors with composite structure: an analysis. , 1979, Applied optics.

[8]  D. C. Finfer,et al.  Distributed Acoustic Sensing - A New Tool for Seismic Applications , 2012 .

[9]  K. Fuchs,et al.  Computation of Synthetic Seismograms with the Reflectivity Method and Comparison with Observations , 1971 .

[10]  M. Toksöz,et al.  Cased Borehole Effect On Downhole Seismic Measurements , 1993 .

[11]  J. H. Cole,et al.  Optimizing fiber coatings for interferometric acoustic sensors , 1982 .

[12]  K. Fuchs.  The Reflection of Spherical Waves from Transition Zones with Arbitrary Depth-dependent Elastic Moduli and Density , 1968 .

[13]  J. White.  Signals in a Borehole Due to Plane Waves in the Solid , 1953 .

[14]  Paul Lumens,et al.  Cable development for distributed geophysical sensing with a field trial in surface seismic , 2013, Other Conferences.

[15]  Kees Hornman,et al.  Field Trial of a Broadside-sensitive Distributed Acoustic Sensing Cable for Surface Seismic , 2013 .

[16]  Arthur H. Hartog,et al.  Vertical seismic optical profiling on wireline logging cable , 2014 .

[17]  J. Jarzynski,et al.  Static pressure sensitivity amplification in interferometric fiber-optic hydrophones. , 1980, Applied optics.