![]()
Within a few years after the first successful observations of NMR in 1946, and the demonstration of free-precession NMR in the earth's magnetic field in 1948, the petroleum industry recognized the potential of NMR measurements for evaluating reservoir rocks, pore fluids, and fluid displacement (flow). In the early 1950s, several companies--particularly California Research (Chevron), Magnolia (Mobil), Texaco, Schlumberger, and Shell--began extensive investigations to understand the NMR properties of fluids in porous media for the purpose of characterizing reservoir rocks (porosity, permeability, and fluid content).[1][2][3] In addition to laboratory research, these investigations included proposals for logging devices and the development of well-logging methods to permit formation evaluation in situ.[1][4] Although a number of patents for logging tools were issued in the 1950s, it was not until Chevron completed an experimental Earth's field nuclear-magnetic-log (NML) logging device in 1958 that a functioning device was actually developed.[1][5] Limited commercial service of these devices was introduced in 1962 by Atlas, using the Chevron centralized design, and followed in 1965 by Schlumberger, using a pad-type tool of its own design. An improved version of the Schlumberger tool was introduced in 1978. Although the potential applications for this measurement were significant, particularly in the shallow, heavy-oil fields of the San Joaquin Valley,[6] in general, they did not live up to expectations and were not commercially successful.[7] Tool reliability and operational limitations proved to be major obstacles: the tool was not combinable, it required high (surface) power; the signal level varied geographically and was generally very low as a result of the low-operational frequency (2 kHz); and the borehole had to be doped with powdered magnetite to suppress the proton signal from the mud.[1][2] [8] The final version of the Schlumberger NML tool--a centralized tool introduced in 1984--proved reliable and commercially successful and was in service until the advent of modern pulse-echo tools in 1994.
Site News