New Magnetic Resonance Wireline Sensor for High-Resolution, Faster Logging, and Better Fluid Typing

Abstract

A new wireline nuclear magnetic resonance (NMR) logging tool is capable of providing high-resolution logs at a logging speed that is twice that of the typical current MRIL® tool logging speeds. The new sensor features a stronger magnetic gradient to enhance the sensitivity of diffusion-based fluid typing; it also provides a much shorter inter-echo spacing (Te) to increase the data density per echo train. Consequently, the new sensor reduces the requirement of vertical averaging, which enhances the resolution of thin bed formation evaluation. The new NMR sensor addresses industry requirements for reliable porosity, organic vs. intergranular porosity discrimination, and free vs. adsorbed fluid fractions in low porosity, heterogeneous unconventional reservoir evaluations. The paper discusses optimization aspects of the sensor, including antenna aperture, maximized packing density of frequency bandwidth, and multi-frequency short inter-echo spacings. The new NMR sensor is fully combinable with several nuclear, electromagnetic (EM), and acoustic logging instruments with a log vertical resolution that is comparable to that of wireline density logs. Field tests from North American unconventional wells have demonstrated that only minimal stacking is needed to meet the 1 PU porosity repeatability and moderate stacking for reliable fluid typing, even in low porosity unconventional reservoirs. With an optimal number of frequencies used for unconventional reservoir applications, an advantage is realized from the total frequency bandwidth for optimal signal-to-noise ratio (SNR). The optimized SNR, in addition to the short Te, also improves the 1D T2 spectral and 2D map resolution and, consequently, free light hydrocarbon and organic pore fluids. Intergranular fluid signals are also resolved in several wells with porosity as low as ≤ 5 PU.