MEASUREMENT TECHNIQUE AND APPARATUS FOR HIGH-RESOLUTION MULTI-VOLUME NMR WELL LOGGING

摘要

The present invention uses a side-looking gradient NMR logging tool with 12 different sensitive volumes. An auxiliary electromagnet winding is placed so that the plane of the winding is substantially parallel to the symmetry axis of the permanent magnet configuration. The electromagnet is switched on and a CPMG sequence is performed. Immediately following this sequence the current in the electromagnet winding is reversed and a second CPMG sequence is acquired. The data from these two sequences comprise a phase-alternate pair and are combined using standard methods. The electromagnet current is sufficient to prevent the overlap of the sensitive volumes. The operating frequency of the tool can be switched and the process repeated until data from all the required sensitive volumes are acquired.