首页| Influencing mechanics and correction method of nuclear magnetic resonance measurement in igneous rocks reservoir
Influencing mechanics and correction method of nuclear magnetic resonance measurement in igneous rocks reservoir
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Nuclear magnetic resonance (NMR) measurement provides lithology-independent porosity and pore structure for sedimentary reservoirs. Recently, oil and gas were discovered in igneous rock formations, however, NMR logging porosity is substantially lower than the true porosity, and the T_ distributions does not characterize the pore-size distributions. These observations limit the use of NMR logging in igneous rock formations and new research is needed to be developed. To address this gap in the literature, using numerical simulation of NMR behavior, we conduct a theoretical study to examine the impact of magnetic susceptibility, echo spacing, and fluid type on the T2 distributions in igneous rock. The simulation results and laboratory experiment show that, the paramagnetic minerals affect the magnetization of fluids in pores and rate of the echo decay, and NMR porosity is thus significantly reduced. To effectively correct the NMR measurement, a new approach is proposed to improve the underestimation of NMR porosity and T2 distribution shifting to shorter times. For a pore model, the corrected porosity and T2 distribution are both in good agreement with the model. In a case study from Chepaizi area of Junggar Basin, China, the corrected NMR porosity matches well with core measurement, and the corrected T2 distribution shifts to longer times more than before. Moreover, bound fluid volume and movable fluid volume are both corrected, and the NMR permeability also agrees well with core laboratory measurement, which proves that the correction method effective. Therefore, this technology enables NMR log for evaluating the igneous rock reservoir quality.
NMR LoggingPorosity correctionT2 distribution shape correctionDiffusion relaxationSusceptibility
Maojin Tan、Hongliang Wu、Jinyan Zhang
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School of Geophysics and Information Technology, China University of Geosciences (Beijing), Beijing 100083, China
Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China
Sinopec Shengli Well Logging Co., Dongying 257096, China
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