Zhang Junjian, Chu Xuanxuan, Wei Chongtao, Zhang Pengfei, Zou Mingjun, Wang Boyang, Quan Fangkai, Ju Wei
College of Earth Sciences & Engineering, Shandong University of Science and Technology, Qingdao 266590, China.
School of Resources and Earth Science, China University of Mining and Technology, Xuzhou 221116, China.
ACS Omega. 2022 Jul 20;7(30):26298-26307. doi: 10.1021/acsomega.2c02112. eCollection 2022 Aug 2.
Low-field nuclear magnetic resonance has become one of the main methods to characterize static parameters and dynamic changes in unconventional reservoirs. The research focus of this paper is process simulation of coalbed methane (CBM) production. The dynamic variation of pore volume with different pore sizes during pressure drop, methane desorption-diffusion process, and methane-water interaction during migration is discussed. Moreover, the calculation principles of NMR single and multifractal models are systematically described, and the applicability of NMR fractal models within different research contexts is discussed. Four aspects need urgent attention in the application of this technology in CBM production: (1) overburden NMR technology has limitations in characterizing the stress sensitivity of shale and high-rank coal reservoirs with micropores developed, and we should aim to enable an accurate description of micropore pore stress sensitivity; (2) dynamic NMR physical simulation of reservoir gas and water production based on in-situ and actual geological development conditions should become one of the key aspects of follow-up research; (3) low-temperature freeze-thaw NMR technology, as a new pore-fracture characterization method, needs to be further applied in characterizing the distribution characteristics of pores and fractures; and (4) NMR fractal model should be used as the main theoretical method to expand the simulation results. The applicability of different fractal models in characterizing pore-fracture structure (static) and CBM production process (dynamic) needs to be clarified.
低场核磁共振已成为表征非常规储层静态参数和动态变化的主要方法之一。本文的研究重点是煤层气（CBM）开采的过程模拟。讨论了压降过程中不同孔径孔隙体积的动态变化、甲烷解吸 - 扩散过程以及运移过程中的甲烷 - 水相互作用。此外，系统描述了核磁共振单分形和多分形模型的计算原理，并讨论了核磁共振分形模型在不同研究背景下的适用性。该技术在煤层气开采应用中急需关注四个方面：（1）覆盖层核磁共振技术在表征页岩和微孔发育的高阶煤储层的应力敏感性方面存在局限性，应致力于准确描述微孔孔隙应力敏感性；（2）基于原位和实际地质开发条件的储层气水产出动态核磁共振物理模拟应成为后续研究的关键方向之一；（3）低温冻融核磁共振技术作为一种新的孔隙 - 裂缝表征方法，需要进一步应用于表征孔隙和裂缝的分布特征；（4）应将核磁共振分形模型作为扩展模拟结果的主要理论方法。需要明确不同分形模型在表征孔隙 - 裂缝结构（静态）和煤层气开采过程（动态）中的适用性。
