Abstract The movable-water saturation (MWS) of coal is critical for the flow of coalbed methane (CBM), however, there is a relative lack of research on it, especially of different-scale pores. The relative permeability of coal is another crucial parameter for CBM development due to its strong control on the characteristics of both gas and water production, but it also remains relatively unexplored. Naturally, little attention has been paid to the connections between the MWS and the relative permeability. In this study, an innovative experiment combining water-saturated coal core displacement test with low-field nuclear magnetic resonance (LNMR) was designed to obtain the MWSs of different-scale pores and gas-water relative permeabilities of coals simultaneously. The relative permeability results show that low-medium coals from the Southern Junggar Basin (SJB) were characterized by low MWSs, narrow spans of two-phase flow, and low end-point relative permeabilities to water (Krw*) and gas (Krg*), which were all disadvantageous for CBM development. The calculated MWSs of different-scale pores through the amplitude of T2 spectrum show that “macropores and fractures (MF)” have the highest MWS, with mesopores following next, “micropores and transition pores (MT)” possess the lowest MWS. Correlation analyses show that the total MWSs and movable porosities both present strong positive correlations with the Ka, Krw*, and Krg*. The irreducible water causes a greater obstacle to gas flow than to water flow. The MWSs of different-scale pores all exhibit positive impacts on the coal permeabilities. However, compared with MWSs of MT and MF, the MWSs of mesopores exhibit the strongest correlation with Ka, Krw*, and Krg*, indicating the critical role in affecting the fluid flow of coal. Besides, two significant parameters, cleat tortuosity (η) and cleat size distribution index (λ) of SJB coals, were determined. η and λ were rank-dependent. Coal macerals also have impacts on η and λ.

中文翻译：

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南准噶尔盆地中低阶煤不同尺度孔隙动水饱和度及相对渗透率试验研究

摘要 煤的可动水饱和度（MWS）是煤层气（CBM）流动的关键，但对其尤其是不同尺度孔隙的研究相对缺乏。煤的相对渗透率是煤层气开发的另一个关键参数，因为它对产气和产水的特征有很强的控制，但它也仍然相对未开发。自然，人们很少关注 MWS 与相对渗透率之间的联系。本研究设计了水饱和煤芯置换试验与低场核磁共振（LNMR）相结合的创新实验，以同时获得煤的不同尺度孔隙的MWS和气水相对渗透率。相对渗透率结果表明，南准噶尔盆地（SJB）低中煤煤具有低MWS、窄两相流跨度、低端点相对渗透率（Krw*）和气体（Krg*）的特点)，均不利于煤层气开发。通过T2谱幅值计算出的不同尺度孔隙的MWS表明，“大孔和裂缝（MF）”的MWS最高，其次是中孔，“微孔和过渡孔（MT）”的MWS最低。相关分析表明，总MWS和可动孔隙度均与Ka、Krw*和Krg*呈强正相关。束缚水对气体流动比对水流动造成更大的障碍。不同尺度孔隙的 MWS 对煤的渗透率均表现出积极的影响。然而，与 MT 和 MF 的 MWSs 相比，介孔的 MWSs 与 Ka、Krw* 和 Krg* 表现出最强的相关性，表明在影响煤的流体流动中起关键作用。此外，还确定了 SJB 煤的割理曲折度 (η) 和割理尺寸分布指数 (λ) 两个重要参数。η 和 λ 是秩相关的。煤质也对 η 和 λ 有影响。