A modular borehole monitoring concept has been implemented to provide a suite of well‐based monitoring tools that can be deployed cost effectively in a flexible and robust package. The initial modular borehole monitoring system was deployed as part of a CO2 injection test operated by the Southeast Regional Carbon Sequestration Partnership near Citronelle, Alabama. The Citronelle modular monitoring system transmits electrical power and signals, fibre‐optic light pulses, and fluids between the surface and a reservoir. Additionally, a separate multi‐conductor tubing‐encapsulated line was used for borehole geophones, including a specialized clamp for casing clamping with tubing deployment. The deployment of geophones and fibre‐optic cables allowed comparison testing of distributed acoustic sensing. We designed a large source effort (>64 sweeps per source point) to test fibre‐optic vertical seismic profile and acquired data in 2013. The native measurement in the specific distributed acoustic sensing unit used (an iDAS from Silixa Ltd) is described as a localized strain rate. Following a processing flow of adaptive noise reduction and rebalancing the signal to dimensionless strain, improvement from repeated stacking of the source was observed. Conversion of the rebalanced strain signal to equivalent velocity units, via a scaling by local apparent velocity, allows quantitative comparison of distributed acoustic sensing and geophone data in units of velocity. We see a very good match of uncorrelated time series in both amplitude and phase, demonstrating that velocity‐converted distributed acoustic sensing data can be analyzed equivalent to vertical geophones. We show that distributed acoustic sensing data, when averaged over an interval comparable to typical geophone spacing, can obtain signal‐to‐noise ratios of 18 dB to 24 dB below clamped geophones, a result that is variable with noise spectral amplitude because the noise characteristics are not identical. With vertical seismic profile processing, we demonstrate the effectiveness of downgoing deconvolution from the large spatial sampling of distributed acoustic sensing data, along with improved upgoing reflection quality. We conclude that the extra source effort currently needed for tubing‐deployed distributed acoustic sensing vertical seismic profile, as part of a modular monitoring system, is well compensated by the extra spatial sampling and lower deployment cost as compared with conventional borehole geophones.
Sirex noctilio Fabricius has a long history as an invasive insect species in pine plantations throughout the Southern Hemisphere and has been recently discovered in North America, where it is uncertain how this insect will behave in pine ecosystems. To assess the impact and attack behavior of S. noctilio, forest surveys and measurements from attacked and unattacked trees were taken in nine Pinus resinosa Ait. and Pinus sylvestris L. plantations in New York, USA, and Ontario, Canada. There was a trend of S. noctilio attacking suppressed trees with smaller live crowns and reduced growth. Some S. noctilio attacks were also found in dominant crown classes but at a lower rate than overtopped or intermediate classes. Sirex noctilio appeared to have more of an impact in P. sylvestris forests, as they attacked more stems (9%–18%) and higher basal area (1.6–5.5 m2/ha) than P. resinosa stands (3%–8% of stems and 0.4–2.4 m2/ha). Dead trees with signs of Siricidae and dead from other causes were also quantified, and in some P. resinosa stands, levels were greater in magnitude than S. noctilio losses. Data from this study suggest that silvicultural treatments should be a key component of integrated pest management plans for S. noctilio.
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