On the Use of Low-Frequency Distributed Acoustic Sensing Data for In-Well Monitoring and Well Integrity: Qualitative Interpretation

Abstract

Summary Distributed acoustic sensing (DAS) is used to monitor production and injection wells in real time. Here we present theory, data examples, and interpretation of low-frequency (LF)-DAS data acquired on fiber-optic (FO) cables clamped to the production tubing. We show that these data give unprecedented insights into the well and serve as a tool for qualitative analysis of well integrity, well operations, and production. By understanding these data, we show that we, for example, can detect leaks, monitor valve performance, and detect the liquid level in Annulus A. While in-well DAS’s sensitivity to changes in temperature over time is well known, its sensitivity to pressure and flow at low frequencies has not been well understood. Here, we show that the LF-DAS response is multifaceted and dependent on the fluid content of the different tubulars in a well, the casing, and completion design, and if a valve is open or closed. Very often a pressure response is seen due to an accompanied temperature effect; while this complicates the overall picture for quantitative data analysis, qualitative interpretation can be made simple. Understanding these processes in LF-DAS data forms the foundation for developing automated interpretation algorithms in the future.

Towards tsunami early-warning with Distributed Acoustic Sensing: Expected seafloor strains induced by tsunamis

“…The lower values of E and larger values of ν correspond to less armored cables. For a submarine cable with mid-range elastic properties (ν = 0.23 and E = 25 GPa) the Poisson's effect sensitivity is ϵ x ∼ 4.3 × 10 −11 ∆P , which falls within expectations based on previously reported theoretical estimates (Budiansky et al, 1979;Haavik, 2022).…”

“…This manifests as a slight increase of the slope of each curve at shallow depths in comparison to Figure 5a. responses of the fiber silica (Fernandez-Ruiz et al, 2022;Haavik, 2022;Hartog et al, 1979).…”

High resolution seafloor thermometry for internal wave and upwelling monitoring using Distributed Acoustic Sensing

“…Under these assumptions, a one nanostrain difference is approximately equivalent to a temperature increase of mK. In terms of relative optical phase variations , the same relationship can be expressed as 39 , 40 , 47 : An absolute normalization of each separate LF-DAS channel, i.e. between zero and the maximum value of each channel, is applied before conversion to temperature differences.…”

High resolution seafloor thermometry for internal wave and upwelling monitoring using Distributed Acoustic Sensing

“…However, only in recent years there have been publications demonstrating the diverse geophysical applications of low frequency DAS (LF-DAS) signals that are dominated by temperature [34,35,36,37,38,39]. In particular, Ide et al, 2021 [37] found distinctive patterns with several-hours periodicity on underwater LF-DAS data from a cable offshore Japan.…”

“…Under these assumptions, a one nanostrain difference ∆ε is approximately equivalent to a temperature increase of ∆T ≈ 0.1 mK. In terms of relative optical phase variations ∆Φ/Φ, the same relationship can be expressed as [38,39,46]:…”