Pacific Section AAPG Convention

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A Simple Wireline Measurement Screening Technique For Identifying Commercial Potash Deposits


Wireline identification of commercial potash mineralization can be both simple and straight forward or quite complex, depending upon the mineralogy present.

Potash minerals are radioactive because of the presence of the radioactive 40K isotope. This characteristic has led to developing core based log transforms of total gamma ray log measurements to estimate potash ore grades. Unfortunately the core transform approach is compromised by the occurrence of 232Th decay series and/or 238U decay series isotopes. Potassium/Uranium/Thorium (K-U-T) spectral gamma ray logs can isolate 40K from the uranium and Thorium series isotopes. While this removes some of the problems of identifying commercial potash deposits, not all potash minerals are commercial, so more sophisticated multi-mineral techniques have been utilized.

Multi-mineral analyses have been successfully utilized to estimate potash assays in Saskatchewan and Cape Breton Island. This approach is limited, however, by the number of wireline measurements available. For example, the McNutt Member of the Salado Formation in the SE New Mexico Potash Area, contains 6 different potash minerals, only 2 of which are commercial, and 4 non-radioactive evaporite minerals, as well as radioactive “Marker Beds”, and claystones. Multi-mineral analyses, for this situation would require 11 different physical property measurements, to be most effective.

A simple screening technique utilizing only two log measurements: Gamma Ray and Neutron Porosity, is proposed and successfully demonstrated for potash deposits in Michigan, New Mexico, Nova Scotia, and Saskatchewan.