By Nick Jervis Bardy
The WIREBmrTM or Borehole Magnetic Resonance is a downhole geophysics tool that measures water contained in subsurface environment safely and accurately. WIREBmrTM is specifically tuned to sense fluids within pore network, enabling precise determination of rock’s total porosity, mobile fluid content (specific yield), bound fluid content (specific retention) and permeability (convertible to hydraulic conductivity). The technology differentiates between moveable and non-moveable water fractions and reliably predicts how easily groundwater flows through an ore body eliminating the need for other traditional methods that require radioactive sources and produces a lithology independent result in contrast to traditional methods such as density and neutron logging.
Theory
Nuclear magnetic resonance (NMR) is a phenomenon that results from the interaction of these nuclei with external magnetic fields. In a volume of water, or other hydrogen-containing fluids, the magnetic fields of the various hydrogen nuclei in the different molecules will be randomly oriented. If an external magnetic field is introduced, these nuclei will align themselves with the external magnetic field.
The application of a second with appropriate frequency for an appropriate time interval will tip the nuclei by 90 generating an oscillating electromagnetic field that can be detected. A series of subsequent secondary magnetic field pulses, called a CPMG pulse sequence, to refocus the nuclei and generate a measurable decay.
In the subsurface the rate of this decay is controlled, primarily, by interactions between the hydrogen nuclei being stimulated and the pore walls. This interaction directly reflects the pore size distribution of the rock. The measured decay can be processed into a T2 distribution that reflects total water measured in the rock as well as the pore size distribution.
Application
NMR has been used in the oil and gas industry to measure pore fluid and for fluid typing for 30+ years, WIREBmrTM brings this technology to other markets with a smaller size and lower price point than its oil and gas equivalents. has been used for broad application across. It has been applied across hard rock mining, in-situ recovery mining, groundwater and geotechnical spaces including:
- Mapping total porosity, specific yield and dry bulk density in iron ore deposits to determine blend for feed stock to the crusher, quantify resource and pick open/closed fractures (in combination with ATV/OTV).
- Developing dewatering strategies in and around underground and open pit mines.
- Mapping aquifer hydrogeology to guide development of comprehensive groundwater management strategies.
- Mapping brine hydrogeology to determine the economic viability and shaping development strategy of brine mining operations.
- Map coal seam gas content and permeability distribution for optimization of gas production for both coal and CSG.
Data Processing
Data processing involves QAQC of raw data to properly mark data that has been affected by hole conditions (washouts, magnetics, conductivity) as well as the generation of a T2 fluid distribution, fluid volume estimates and permeability / hydraulic conductivity estimates that using multiple models.
Further Reading
Contact Orica Orebody intelligence at www.orica.com/wirebmr or Orica’s APAC Regional Manager, Calvin Lau, directly at: calvin.lau@orica.com for more information as well as processing, interpretation, and training services.
Service Agreement
The WireBMR service is run by Borehole Wireline through a 3rd party agreement with Orica Digital Solutions.