This month’s Wireline Workshop Bulletin features articles such as an overview of the Formation Density Log, an in depth measurement focus on the Induced Polarization (IP) tool, and a discussion of field radiation safety including the use of radiation detectors.
The following are just a few examples of the insightful material in this bulletin:
“In oilfield logging, density and neutron porosity logs, as percentages of volume, are critical to the estimation of oil in place. Actual RD or density in grams per cubic centimetre is usually less critical. In mineral logging, density is arguably the most important measurement.
A large proportion, probably over 70%, of mineral logging is performed in coal exploration and mining. Coal, particularly good coal, has relatively low density… the lowest of any mineral that one is likely to intersect while drilling in a sedimentary basin. Coal seams stand out clearly.”
-in Overview- Formation Density Log
“A log of electrical resistance per rock mass volume, or resistivity, was the first wireline log and remains a fundamental measurement in oilfield exploration. In sedimentary basins, the log is used as a measure of water-filled porosity, as opposed to oil-filled porosity (the distinction is not available from sonic density and neutron porosity logs). In clean (no clay) formations, the resistivity of a rock depends on two things; relative volume of pore spaces and conductivity of the fluid therein. Brine is conductive and oil is resistive.
In some situations, most notably in hard rock environments more familiar to mineral explorers, a third factor will affect formation resistivity, the conductivity of the solid rock matrix. Some metallic minerals (and graphite) have conductive properties.”
-in The Induced Polarization (IP) Sonde
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