Washburn Kathryn E, Cheng Yuesheng
Ingrain, Inc., 3733 Westheimer Road, Houston, TX 77027, United States.
Halliburton, 3000 North Sam Houston Pwky E, Houston, TX 77032, United States.
J Magn Reson. 2017 May;278:18-24. doi: 10.1016/j.jmr.2017.02.022. Epub 2017 Mar 4.
The mechanism behind surface relaxivity within organic porosity in shales has been an unanswered question. Here, we present results that confirm the existence of intermolecular homonuclear dipolar coupling between solid and liquid phases in sedimentary organic matter. Transverse magnetization exchange measurements were performed on an organic-rich shale saturated with liquid hydrocarbon. Liquid and solid constituents were identified through both sample resaturation and through their T/T ratios. Extensive cross peaks are observed in the T-T exchange spectra between the solid and liquid constituents, indicating an exchange of magnetization between the two phases. This result cannot arise from physical molecular diffusion, and the dissolution energies are too high for chemical exchange, such that the magnetization exchange must arise from intermolecular homonuclear dipolar coupling. These results both confirm a possible source of surface relaxivity in organic matter and emphasize caution in the use of standard porous media interpretations of relaxation results in shales because of coupling between different magnetization environments.
页岩中有机孔隙内表面弛豫率背后的机制一直是个未解之谜。在此，我们展示的结果证实了沉积有机质中固相和液相之间存在分子间同核偶极耦合。对饱和液态烃的富有机质页岩进行了横向磁化交换测量。通过样品再饱和以及它们的T/T比率来识别液相和固相成分。在固相和液相成分之间的T-T交换光谱中观察到大量交叉峰，表明两相之间存在磁化交换。这一结果并非由物理分子扩散引起，且溶解能对于化学交换来说过高，因此磁化交换必定源于分子间同核偶极耦合。这些结果既证实了有机质中表面弛豫率的一个可能来源，也强调了由于不同磁化环境之间的耦合，在对页岩弛豫结果使用标准多孔介质解释时需谨慎。
