1940s

World War II inevitably slowed the rapid spread of logging technology, but Schlumberger nonetheless continued to make significant advances during the 1940s. In 1940, the company moved its headquarters to Houston to take advantage of the US's position as a global technology leader, especially in electronics. However, Marcel Schlumberger remained based in France, where he and his team continued to invent and innovate.

Logging trucks were modernized, equipped with a winch and an electrical cable capable of operating a wide range of services in ever-deeper boreholes. New devices designed to complement electrical logging tools, provided measurements of borehole parameters such as diameter, temperature, and inclination.

Significant contributions were being made to technological knowledge. In 1942, Gus Archie of Shell Oil published a report on the relationship between electrical resistivity, porosity, and water saturation in oil-bearing rocks, known as "Archie's Law." This was to become the foundation of petrophysical log interpretation.

As the decade progressed, logging applications began to expand beyond formation evaluation. In 1946, the casing collar locator (CCL) was first deployed to measure changes in magnetic flux at the collar's location. This breakthrough made it much easier to correlate openhole and cased hole logs taken from the same wellbore. The first induction log was recorded in an Humble Oil well in Tyler, Texas, helping to distinguish oil- from water-bearing rock layers when the borehole contains fluid that does not conduct electricity. The late 1940s was also the period when the first offshore oil rigs were being deployed in the Gulf of Mexico, opening up new possibilities for Schlumberger technology.

Meanwhile, the nature of the oilfield services sector was changing. Henri Doll said increasing competition between companies provided Schlumberger with an extra incentive to advance and grow—and, having rebuffed a takeover attempt by Halliburton, that is what the company did. "Wherever the drill goes, Schlumberger goes" became a rallying cry. As the company expanded globally, it took on increasing numbers of local recruits, providing the cultural diversity that still defines SLB's character today.

Keeping ahead of competitors required substantial investment in cutting-edge research. In 1948, Doll was charged with establishing a new research center in Ridgefield, Connecticut—the Schlumberger–Doll Research Center. This provided the springboard for the technological breakthroughs that would define Schlumberger success in the second half of the 20th century. The Center, which still plays a significant role in the company's R&D activities, is now located in Cambridge, Massachusetts.

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