Pore-Water Occurrence Characteristics in High-Rank Coal Based on NMR and Its Water-Blocking on Coalbed Methane Production
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摘要: 沁水盆地南部高阶煤层气开发存在显著的井间产能差异，水锁效应是制约煤层气解吸与高效产出的关键微观因素.为揭示高阶煤储层孔隙赋水分布规律、水锁效应程度及其对煤层气排采的控制作用，以樊庄区块南部（A区块）、沁南东区块（C区块）为研究对象，对应采集寺河煤矿（SH，无烟煤）、古城煤矿（GC，贫煤）3号煤样，开展低场核磁共振（NMR）孔隙流体测试和甲烷高压等温吸附实验，结合研究区煤层气井长期排采数据，系统分析煤孔隙的赋水特征与水相赋存状态差异，阐明煤孔隙赋水-水锁效应-煤层气解吸排采的响应机制.SH煤样以小孔（10~100 nm）赋水为主（55.97%），微孔（<10 nm）赋水为40.87%；GC煤样微孔赋水占比高达81.72%，小孔赋水仅14.51%.经1.61 MPa离心后，SH煤样吸附水占比73.89%，显著低于GC煤样的97.94%，表明C区块微孔发育、吸附水滞留量大，毛管束缚力强，水锁效应伤害风险远高于A区块.在储层压力条件下，A区块煤样甲烷平均解吸速率达5.27 m3·t-1·MPa-1，远高于C区块的1.45 m3·t-1·MPa-1，解吸驱动力更强、流体运移阻力更小.排采数据验证显示，单相排水阶段C区块排水周期更长、降压解吸难度更大；两相流上产阶段压降漏斗扩展受限、产能提升缓慢；A区块单井累计产气量和峰值日产气能力均显著优于C区块.分析了高阶煤微观孔隙赋水特征对宏观排采效果的影响，明确微孔吸附水富集诱发高程度水锁、抑制气水高效运移是区块产能差异化的关键，可为高阶煤储层产能评价、水锁伤害防控及排采参数优化提供理论支撑.Abstract: Significant productivity differences exist among high-rank coalbed methane (CBM) wells in the southern Qinshui Basin, and the water-blocking effect is a key microscopic factor limiting CBM desorption and efficient production. To reveal the pore-water occurrence law, water-blocking effect, and the control on CBM production in high-rank coal, the southern Fanzhuang Block (Block A) and eastern Qinnan Block (Block C) were selected, and the No.3 coal samples were collected from Sihe Coal Mine (SH, anthracite) and Gucheng Coal Mine (GC, lean coal). Low-field nuclear magnetic resonance (NMR) pore-fluid test and high-pressure methane isothermal adsorption experiment were conducted. Combined with long-term production data from CBM wells, the differences in pore-water occurrence and water-phase distribution in coal pores were systematically analyzed, and the coupling response mechanism of pore-water occurrence, water-blocking effect, and CBM desorption-production was clarified. SH coal is dominated by water in transition pores (10-100 nm) with a proportion of 55.97%, while micropores (<10 nm) account for 40.87%. In contrast, GC coal has a micropore water proportion of 81.72% and a transition pore proportion of 14.51%. After centrifugation at 1.61 MPa, the adsorbed water proportion of SH coal is 73.89%, significantly lower than 97.94% of GC coal, indicating that Block C has well-developed micropores, a high volume of adsorbed water, and strong capillary binding forces, making the risk of damage from water-blocking effect significantly higher than that in Block A. Under reservoir pressure, the average methane desorption rate of Block A reaches 5.27 m3·t-1·MPa-1, far exceeding 1.45 m3·t-1·MPa-1 of Block C, demonstrating stronger desorption driving force and lower fluid migration resistance. Production data confirm that Block C exhibits a longer single-phase water drainage period, greater difficulty in pressure reduction and desorption, limited pressure-drop funnel expansion during the two-phase flow stage, and slow productivity improvement. Both the cumulative gas production and the peak daily gas production capacity in Block A are significantly higher than those in Block C. This paper analyzes the effect of the microscopic pore-water occurrence on macroscopic CBM production performance of high-rank coal. It is clarified that enriched adsorbed water in micropores induces high-intensity water blocking and restricts efficient gas-water migration, which is the core cause of block productivity differentiation. The results provide theoretical support for productivity evaluation, water-blocking damage prevention, and production parameter optimization of high-rank coal reservoirs.
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图 2 饱水样与离心样（1.61 MPa）T2谱图
Fig. 2. T2 spectra of water-saturated and centrifuged (1.61 MPa) coal samples
图 7 A、C区块日均产气量对比
Fig. 7. Comparison of average daily gas production between A and C blocks
图 8 A、C区块累计产水量对比
Fig. 8. Comparison of cumulative water production between A and C blocks
表 1 煤样基本性质
Table 1. Basic properties of the coal samples
样品
编号Ro, max
（%）煤阶 工业分析（%） 煤岩有机显微组分（%） Mad Ad Vdaf 镜质组 惰质组 SH 3.24 无烟煤 2.79 9.21 8.92 92.5 7.5 GC 2.22 贫煤 1.44 7.31 10.51 83.9 16.1 
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表 2 孔隙水赋存特征
Table 2. Pore-water occurrence characteristics of the coal samples
样品号 核磁孔隙度
（%）原始干质量
（g）饱和水质量
（g）单位质量吸附的水体积
（mL/g）不同孔径范围内赋存的水体积占比（%） 0~10 nm 10~100 nm 100~1 000 nm >1 000 nm SH 6.86 31.996 33.578 0.049 4 40.87 55.97 0.71 2.45 GC 4.76 34.534 35.703 0.033 8 81.72 14.51 1.5 2.27
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表 3 不同离心力下煤样含水饱和度
Table 3. Water saturation of the coal samples under different centrifugal pressures
样品 含水饱和度（%） 0.46 MPa 0.69 MPa 0.92 MPa 1.15 MPa 1.38 MPa 1.61 MPa 1.84 MPa SH 96.21 94.94 94.06 93.24 92.35 91.85 91.84 GC 97.55 92.56 91.62 90.59 89.91 89.39 89.39 注：含水饱和度=（离心后质量‒干重）/（饱和水质量‒干重）×100%.
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表 4 煤样孔隙中水的相态分布
Table 4. Phase distribution of pore waters
样品 离心压力
(MPa)不同相态水占比（%） 吸附水 毛管束缚水 自由水 <2 ms 2~100 ms >100 ms SH 0 69.13 28.42 2.45 1.61 73.89 25.68 0.43 GC 0 95.15 2.58 2.27 1.61 97.94 2.05 0.01
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表 5 储层压力对应解吸阶段
Table 5. Desorption stages under reservoir pressures
区块 煤样 储层压力
（MPa）平均储层压力
（MPa）平均储层压力下解吸速率
（m3·t-1·MPa-1）解吸阶段 A SH 0.9~3.44 1.92 5.27 敏感解吸 C GC 3.79~6.43 4.53 1.45 快速解吸、缓慢解吸
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表 6 单相排水阶段排采特征参数
Table 6. Production-performance parameters during the single-phase water-production stage
区块 W1（m3） R1（%） 日均产水量(m3/d) 解吸时间（d） A 0.7~1 648.8（171.6） 0.01~27.76（7.87） 0.57~9.75（2.8） 1~229（45.5） C 31~10 436（584.1） 4.1~69.46（32.91） 0.24~28.36（3.26） 24~659（145.3） 注：括号内为平均值，下同.
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表 7 单相排水阶段井底流压特征参数
Table 7. Bottom-hole flowing-pressure parameters during the single-phase water-production stage
区块 储层压力（MPa） 临界解吸压力（MPa） 临储比（%） 压降速率（kPa/d） A 0.9~3.44（1.92） 0.99~2.51（1.72） 40.48~100（85.13） 0~131.4（7.68） C 3.79~6.43（4.53） 0.25~3.23（2.12） 0~80.48（43.96） 3.3~147.7（18.8）
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表 8 两相流初期上产阶段排采特征参数
Table 8. Production parameters during initial two-phase flow stage
区块 最高日产气量（m3） W2（m3） R2（%） 日均产水量(m3/d) 上产时间（d） A 985~21 456（5 795） 75.3~62 720.4（2 300.7） 7.59~95.21（44.42） 0.18~50.1（3.02） 69~2 132（560.7） C 305~4 743（1 051） 68.1~29 705.3（1 108.7） 6.78~72.97（31.28） 0.13~44.87（1.52） 122~1 765（626.3）
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表 9 A区块和C区块典型井排采参数
Table 9. Production-performance parameters of representative wells in A and C blocks
井号 单相排水阶段 两相流初期上产阶段 总累产水(m3) 最高日产气(m3) 解吸天数(d) W1(m3) R1(%) 日均产水(m3/d) 上产天数(d) W2(m3) R2(%) 日均产水(m3/d) A-14 58 104.1 13.7 1.8 394 437.7 57.6 1.1 759.9 8 270 C-170 130 163.9 30.2 1.3 551 159 29.3 0.3 542.6 1 831
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