A revolution in groundwater science, Javelin combines advanced electronics and precise measurements in a small package to deliver economical NMR logging of boreholes as small as 2 inches in diameter.  For decades, NMR logging has proven to be an invaluable tool in oil exploration, but the size, weight, and high cost of oil-field tools has precluded their use in groundwater and environmental investigations, until now.  The first and only tool of its kind, Javelin enables economical NMR logging in small-diameter “slimhole” boreholes, yielding key aquifer and subsurface properties at sub-meter resolution.

Javelin Measurements Provide

  • Direct detection and quantification of groundwater (including capillary and clay-bound water)
  • Detection and quantification of hydrocarbons and fluid diffusion
  • Precise determination of porosity and water content
  • Estimation of permeability, mobile/bound water fraction, pore-size distributions
  • Sensitivity to geometric and geochemical pore-scale properties
  • Sub-meter depth resolution

Javelin Applications in Hydrology Include

  • Groundwater exploration and aquifer characterization
  • High resolution characterization of small-scale hydrogeologic features, including thinly layered flow barriers or preferential flow zones
  • Detailed characterization of hydrogeologic units to parameterize groundwater and site conceptual models
  • Long-term monitoring of groundwater dynamics

How Javelin Works

information graphic

Overhead view of NMR sensitive region of the 3.5″ diameter NMR probe, with respect to the probe, the casing and the undisturbed earth formation. The 3.5″ diameter probe is sensitive to water at a radius of about 7.5″, which is outside of the disturbed zone for most 4″ and 6″ wells.

Javelin operates in a borehole, like an inside-out MRI scanner, to provide direct sensitivity to groundwater.  The tool projects a magnetic field several inches beyond the borehole, creating a cylindrical-shaped “sensitive region” from which the groundwater NMR signal is detected.  This thin sensitive region is ideally located within the undamaged region of the formation, where the rocks and sediments are not disturbed by drilling.

By emitting a series of radio-frequency pulses and recording the returning signal, Javelin measures the NMR response of groundwater in the sensitive zone, much like an MRI scanner measures the NMR response of tissues in the body.  The characteristics of the measured NMR signal reflect the quantity of groundwater, as well as the hydrogeologic properties at a given depth.  Specifically, the total amplitude of the signal directly and unambiguously indicates the total amount of groundwater.  The decay behavior of the signal over time, which is summarized by the decay-time (T2) distribution, conveys more detailed information about the pore environment.  Generally, water in low-permeability silts and clays exhibits short T2, while water in high-permeability sands and gravels exhibits long T2.

The recorded NMR signal at each depth is processed and analyzed to provide reliable estimates of hydrogeologic parameters, including bound/mobile water content, pore size, and permeability. By repeating logging measurements at successive depth intervals, a high resolution profile of the NMR T2 distribution and hydrogeologic properties is obtained.

An example of a Javelin NMR log from a borehole in Central Nebraska. The color panel at the left shows T2 distributions at each depth. Signals with short T2 (towards left) indicate water in silts and clay; signals with long T2 (towards right) indicate water in sands and gravels. Profiles in center show derived values of bound, mobile, and total water content. Two hydraulic conductivity estimators derived from the NMR data shown at right.

Read more Javelin case study examples.