The authors describe a fast field-cycling NMR/NQR spectrometer with a switching time of only 0.7 ms between zero field and maximum field (1 T) which uses a novel air-cored magnet design in which the magnet is cut out of a solid copper tube by means of electric spark erosion. The pitch and cross section of the windings vary and have been optimized for small inhomogeneity of the field (6 parts in 105) and the highest field for the available power (20 kW). The design of the power supply, which uses one capacitor as energy storage, and considerations concerning the safety of the instrument are also described as well as the probe and the more conventional parts of the NMR spectrometer. The authors conclude with examples of the performance and the main applications: field-dependent spin-lattice relaxation time measurement (T1 dispersion), cross relaxation and nuclear quadrupole double resonance (NQDR).

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractNuclear Magnetic Resonance (NMR) was identified as a critical technology for reducing uncertainty and minimizing risk during the planning phase of a major field development project. The reservoirs in the subject field contain heavy oil/tar in the flanks, and accurate knowledge of viscosity trends becomes essential for the placement of water injectors. Since NMR logs can be used to estimate heavy oil viscosity, the development plan required running logging while drilling (LWD) NMR logs in the extended-reach horizontal injectors, in addition to some selected producers.A program heavily based on slim hole drilling presented a practical challenge for the execution of the development plan, since at the time no service company offered slim hole LWD NMR services. Considering the business impact of this technology gap, the operator decided to collaborate with the service industry to develop LWD NMR technology for hole sizes ranging from 5⅞-to 6⅛-in. Within a year, a joint project was established with a major technology provider for the development of a slim LWD NMR tool. The first two prototypes were delivered for field testing in less than 18 months.The prototypes have been run in nearly a dozen wells to date and in a variety of environments, including extended-reach wells with high salinity muds. Data obtained from drilling and reaming runs agree very well with those from other porosity tools, including wireline NMR. Furthermore, close coordination and cooperation between the operator and the service provider during testing runs have resulted in significant improvements in downhole firmware, data acquisition modes and signal processing.Two factors weigh heavily for the successful fast delivery of the project goals: clear requirements from the operator, and proven expertise in NMR tool design from the technology provider. Given continuing reliable and robust performance from the prototypes, the slim LWD NMR service is expected to be commercially available shortly. In fact, the high level of confidence gained from early field tests has already allowed the use of the data in critical well placement decisions in some wells.

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