Wire Line

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Technical Note 2010-09

South Africa A History of Mineral Wireline Logging

Four-arm dipmeter sonde

Lowering a probe or ‘sonde’ into a borehole, in order to make measurements of rock properties, is based on geophysics in the sense that it is a remote, nondestructive, technique that does not involve taking rock samples. It is hardly surprising, then, that it was a geophysicist whoinvented wireline logging. Nor is it surprising that the application was oilfield exploration. Energy has always been a major driver of advances in exploration technology. In 1927, Conrad Schlumberger, a French geophysicist, was performing surface electrical prospecting work, with his brother Marcel, at the Pechelbronn oilfield near his home in Alsace. The brothers had been working on improving remotesensing to depth and had travelled to several countries, including the Union of South Africa. Their client, the Pechelbronn Oil Company, was struggling to identify a particular stratigraphic boundary from drill chippings and, as a result of an on-site conversation, Conrad thought it might be worth lowering an electrode array into the borehole and moving it up and down instead of along thesurface. Actually, it was not Conrad that captured the first log but his son-in-law, Henri Doll. Henri assembled a four-electrode array, as instructed by Conrad, and lowered the first ever logging tool down well Diefenbach 2905 The first log rig 7 on September 5th 1927. The contraption (From SEPM Society for Sedimentary Research) did not work well at first, mostly due to problems with the wireline (thelogger’s most important piece of equipment) but, eventually, Henri and his team were able to make point measurements of formation resistance, every one metre, to a depth of 600 metres. It was then necessary to place the measured values on a long graph and join up the dots in order to generate the first ever wireline log.

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The log was a success and, on 28 July 1928, the Schlumberger brotherssigned a contract to provide ‘Electrical Coring’ services to the owners of the Pechelbronn site, which was, surprisingly, the only oilfield in France at the time. The business grew steadily at first and, by 1931, the brothers had discovered SP or spontaneous potential, a natural voltage generated between bedding layers, occurring only as a result of the presence of a borehole (or perhaps asubmerged cave). The SP ‘noise’ had been problematic until it was realized that it was a stand-alone log and could help define permeable zones, which are, of course, important in oil exploration. SP was used later in the 1930s to create the first formation dipmeter tool. Over the next forty years wireline logging, as it became known, grew into a major oilfield service sector. Schlumberger and, later,Halliburton, Baker Hughes and others, developed a wide range of tools, dedicated to the exploration and production of oil and gas resources. New measurements included natural gamma ray, formation density, inductive conductivity, and sonic transit time. Continuous logs plotted on roll paper became available from 1936. In 1942, Gus Archie, working for Shell, described an empirical relationship betweenthe porosity of sandstone and its resistivity, known as the formation factor. If the resistivity could be predicted based on porosity then deviations from this prediction, on the resistivity high-side, would infer the presence of oil. What was needed was a reliable porosity log. At first, porosity was estimated based on local knowledge or the separation of resistivity logs due to borehole fluidinvasion. As density, sonic and neutron-based porosity logs appeared in the 50s and 60s and, with refinements to Archie’s original equations; wireline logging became a quantitative measure of oil in place. In South Africa, there was little use for wireline logging due to a rather unique lack of oil reserves. From the early 1950s, however, there was an application in uranium logging, using the new...