Distributed Acoustic Sensing in Geophysics. Группа авторов

acoustic angular wavenumber K _z acoustic angular wavenumber along fiber K _e ratio of optical to physical length of fiber L fiber length L _P integration length L ₀ interferometer length also known as gauge length L _S scattering zones spacing M number of scattering zones n _eff fiber effective refractive index N _F noise figure of amplifier N number of photons per second p(z) averaging function P ₀ input peak power P number of different interferometric ports or pulses R _BS backscattering coefficient of fiber r₀(z) distribution of reflection/scattering coefficient along fiber axis r(z) distribution of reflection/scattering coefficient along fiber axis with optical phase shift included Re Z real part of interference output t′ “fast” optical time scale t “slow” acoustic time scale u(z, t) ground displacement u parameter of function v(z) fiber local speed along its axis and also ground speed V(z) interference visibility along fiber x parameter of integration: coordinate along fiber axis z coordinate along fiber axis z ₁ parameter of function z ₂ parameter of function β optical wave propagation constant of fiber β ₀ unperturbed optical wave propagation constant of fiber ΔΩ(z) distance variation of Doppler shift along fiber Δv distance variation of ground speed ΔF geophone bandwidth δ the Dirac delta function ε ₁ maximum recoverable strain for first order algorithm ε ₂ maximum recoverable strain for second order algorithm ε _min minimum strain level Φ_min phase noise Γ incident angle of seismic wave λ laser wavelength Λ spacing of geophones μ flicker noise coefficient ω circular frequency of light Ω(z) Doppler frequency shift of light ψ ₀ phase shift between delayed optical fields in interferometer Φ shift of backscattered light ρ backscattering intensity coefficient θ(z) Heaviside step function τ(z) input pulse τ optical pulsewidth

2 Important Aspects of Acquiring Distributed Acoustic Sensing (DAS) Data for Geoscientists

       Mark E. Willis1, Andreas Ellmauthaler1, Xiang Wu2, and Michel J. LeBlanc1

       1Halliburton, Houston, Texas, USA

       2Halliburton Far East Pte. Ltd., Singapore

      ABSTRACT

      Fiber‐optic