Collecting data while drilling - PetroWiki

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No other technology used in petroleum-well construction has evolved more rapidly than measurement while drilling (MWD) and logging while drilling (LWD). Early in the history of the oil field, drillers and geologists often debated conditions at the drillbit. With advances in electronic components, materials science, and battery technology, it became technically feasible to make measurements at the bit, and transmit them to the surface so that the questions could be answered. Directional measurements were the first measurements to have commercial application, with almost all use in offshore, directionally drilled wells. As long as MWD achieved certain minimum-reliability targets, it was less costly than single shots, and it gained popularity accordingly.