Javelin ----Overview----Features----Specifications----Case Studies
Microhole/Slimhole NMR Logging
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Javelin poster presented at the American Geophysical Union (AGU) Meeting, San Francisco, Dec 2010 Javelin featured in Environmental Engineering Geophysical Society (EEGS) publication FastTIMES |
Overview
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 and gas exploration, but the size, weight, and high cost of oil-field NMR instruments has precluded their use in hydrology and environmental investigations, until now. The first and only tool of its kind, Javelin enables economical NMR measurements in small-diameter "slimhole" boreholes, yielding key information about the subsurface at sub-meter resolution. Download a Javelin product brochure here.
Javelin Measurements Provide
- Direct detection and quantification of groundwater (including capillary and clay-bound water)
- Detection and quantification of other hydrocarbon fluids
- Precise determination of porosity and water content
- Reliable estimation of hydraulic conductivity, mobile/bound water content, pore/grain-size distribution
- Sensitivity to geometric and geochemical pore-scale properties
- Sub-meter depth resolution
Javelin Applications in Hydrology Include
- Groundwater exploration and aquifer characterization
- Precise delineation of small-scale hydrogeologic features including thinly layered flow barriers or preferential flow zones
- Detailed characterization of hydrogeologic units to parameterize hydrogeologic models
- Novel approaches to monitoring groundwater dynamics
- Integration of logging and surface-based NMR measurements
How Javelin Works
Javelin operates in a borehole like an inside-out MRI scanner and provides direct sensitivity to groundwater. The tool projects a magnetic field several inches beyond the borehole, creating a "sensitive region" that is approximately cylindrical in shape 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 have not been disturbed by drilling.
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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. |
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 of the groundwater. Generally, water in low-permeability silts and clays exhibits short decay times, while water in high-permeability sands and gravels exhibits long decay times.
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 at right show derived values of bound water (red), mobile water (blue) and total water (black).
More Javelin case study examples can be found here.
Small-Diameter Slimhole Tool
Many groundwater wells and boreholes are just a few inches in diameter and cannot accommodate large oil-field NMR logging instruments (even if funding permits the use of these expensive tools). The affordable Javelin tool is available in three sizes designed specifically for slimhole boreholes and wells. The smallest tool is designed to operate in holes as small as two inches. The largest tool operates in four to eight inch holes. An intermediately sized tool is designed to be operated with a GeoProbe direct push system for minimally-invasive surveys.
Advanced Noise Cancellation
NMR measurements in the near surface can be highly susceptible to noise from nearby infrastructure, particularly at very shallow depths <50 feet which are often of great interest in groundwater investigations. The Javelin system incorporates Vista Clara's advanced noise cancellation algorithms (patent pending) enabling the user to obtain high quality data in otherwise prohibitively noisy environments.
Fast Data Processing
The Javelin software package allows the user to easily monitor data quality and to process measurements while logging. The software also includes analysis tools to determine water content, T2 distributions, estimated hydrogeologic parameters including bound/movable water content and relative permeability.
Power Supply: 120V and 240V Models Available (Line or Generator)
Winch Options
- Motorized Mount Sopris 4WNA with 3WCA controller
- 220 m Custom Downhole Cable
- Custom Light-Weight Manual Winch
- 120 m Custom Downhole Cable