We present an NMR measurement technique which has the unique ability to determine the in-situ adsorbed gas concentration within coal seams. The measurement of adsorbed gas content is of critical importance for operational safety and commercial resource evaluation in the development of coal mining operations and coal seam gas (CSG) resources. The current measurement technique involves laboratory core analysis, using a canister desorption measurement which is subject to significant measurement uncertainty due to the gas lost between coring and analysis. The NMR measurement technique enables in-situ measurement of fluid content within the coal seams without disturbing the coal seams. The technique utilises the stimulated echo diffusion editing (SEDE) pulse sequence which simultaneously captures relaxation and diffusion behaviour of fluids contained within coal seams. In this work, we have optimised the SEDE pulse sequence by using two diffusion times which are appropriate for capturing the diffusive behaviour of water and adsorbed gas. The measured signal captured by the SEDE sequence is inverted to provide a T₂-StimD distribution. The appropriate interpretation of the T₂-StimD distribution enables the determination of the free and adsorbed gas concentrations. The adsorbed gas concentration measured using the optimised SEDE sequence shows very good agreement with core canister desorption measurements. The sequence also enables the detection of free gas which is important for understanding the depressurisation of the coal seams and the impact on development strategies.

我们提出了一种 NMR 测量技术，该技术具有确定煤层内原位吸附气体浓度的独特能力。吸附气含量的测量对于煤矿开采作业和煤层气 (CSG) 资源开发中的作业安全和商业资源评估至关重要。当前的测量技术涉及实验室岩心分析，使用罐解吸测量，由于取心和分析之间的气体损失，该罐解吸测量具有显着的测量不确定性。核磁共振测量技术能够在不干扰煤层的情况下现场测量煤层内的流体含量。该技术利用受激回波扩散编辑 (SEDE) 脉冲序列，该序列同时捕获煤层内流体的弛豫和扩散行为。在这项工作中，我们通过使用两个适合捕获水和吸附气体扩散行为的扩散时间来优化 SEDE 脉冲序列。SEDE 序列捕获的测量信号被反转以提供T ₂ -StimD 分布。T ₂ -StimD 分布的适当解释能够确定游离气体和吸附气体的浓度。使用优化的 SEDE 序列测量的吸附气体浓度与核心罐解吸测量结果非常吻合。该序列还能够检测游离气体，这对于了解煤层减压及其对开发战略的影响非常重要。