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Magnetic-resonance-image (MRI) logging while drilling
Use of magnetic-resonance-image (MRI) logging is growing as a logging while drilling (LWD) tool.
The use of chemical nuclear sources downhole has been a logistical and management headache. MRI, by measuring in real time the free-fluid, capillary-bound-water, and clay-based-water volumes, offers an alternative, lithology-independent porosity measurement in complex lithologies. It can be used for geosteering and geostopping when sufficient productive formation has been exposed to the wellbore.
Like most measurements, at an initial phase there are specialist applications that are more susceptible to realizing the value of magnetic-resonance logging. In this case, applications of interest are the evaluation of shaly sands and low-resistivity pays, particularly in deepwater and exploration wells.
Tool designers have had to meet a number of challenges in converting the measurement to a drilling environment. Shock, vibration, rotation, and general tool movement mitigate against the use of the T2 measurement, which is sensitive to excessive motion while drilling. As a result, the T1 measurement has been adopted as a de facto standard in real-time (reconnaissance) applications. This is supplemented by T2 measurements when a more-detailed characterization of the formation is required. Devices in use investigate a rotationally symmetric volume with a diameter of 14 in. They benefit from the generally lower ROP experienced in the drilling environment. Some care needs to be taken in the relative position of the large permanent magnets in the magnetic-resonance device and the magnetometers in the directional module, although correction algorithms can be used to eliminate interference.
Noteworthy papers in OnePetro
1. Arve K. Thorsen, Tor Eiane 2008. Magnetic Resonance in Chalk Horizontal Well Logged With LWD, SPE Annual Technical Conference and Exhibition, 21-24 September 2008. 115699-MS. http://dx.doi.org/10.2118/115699-MS
2. M.G. Prammer, E. Drack, G. et al. 2001. The Magnetic-Resonance While-Drilling Tool: Theory and Operation, SPE Reservoir Evaluation & Engineering Volume 4, Number 4. 72495-PA. http://dx.doi.org/10.2118/72495-PA