Schlumberger

Technical Paper: New Generation Magnetic Resonance While Drilling

Society: SPE
Paper Number: 160022
Presentation Date: 2012
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In this paper, a new series of Logging-while-drilling (LWD) nuclear magnetic resonance (NMR) tools is introduced. The tools incorporate a magnet arrangement which provides a low field gradient minimizing adverse lateral motion effects. T2 distributions are measured while drilling or sliding in a range of hole sizes, including large holes previously inaccessible to LWD NMR measurements. Benefits and trade-offs of key tool design features are presented. Emphasis is placed on measurement quality, operational simplicity and log quality control in real time and memory mode through example logs from operator wells. Real-time T2 distributions provided by the new generation LWD NMR tool enable a full range of NMR answers, including lithology-independent total porosity, bound fluid volume and permeability. Real-time log quality controls monitor tool noise, antenna sensitivity, tuning quality and lateral motion. Acquisition sequences are optimized for porosity precision and accuracy in different environments. Drilling data have been acquired in several operator wells and a test well covering diverse ranges of formations and logging conditions. Environmental factors affecting porosity precision and T2 quality are discussed with reference to log quality indicators and comparison with wireline NMR logs is made where available. In general, the LWD tools deliver NMR answers comparable to the analogous wireline logs in terms of precision, accuracy and vertical resolution. With increased industry focus on LWD services and heightened sensitivity to downhole chemical sources, the need for reliable LWD NMR measurements continues to grow. In addition to a sourceless porosity measurement, NMR provides unique quantitative information on the disposition of producible fluids, which is not available from other logs. Real-time producibility information can be used to optimize formation pressure measurements and sampling as well as for timely completions and well placement decisions. The new generation LWD NMR tools introduced here addresses this need.

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