Optimization of multi-layer commingled coalbed methane production in Zhijin area, Guizhou province
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摘要: 贵州省织金地区龙潭组煤层具有多、薄特点。与单一厚层状煤层相比，多煤层合采存在合采兼容性问题，易发生层间干扰，影响合采效果及资源动用程度。为了发挥煤层气井生产潜力，提高开发效益，亟需开展合采层位优选，建立多煤层开发序列。在研究织金区块地质特征的基础上，开展了多煤层地质条件差异研究，结合排采实践及解吸理论，探讨了织金地区多煤层合采影响因素，优选了合采层位。多煤层合采主要受解吸液面高度、纵向跨度、压力梯度、供液能力、渗透率差异影响。织金区块上二叠统龙潭组主力煤层地层供液能力、压力梯度、渗透率差异较小，对合采效果影响较小。层间跨度和解吸液面高度差异是影响区块合层开采的关键因素，16，17，20，23，27，30号煤层90 m跨度可作为一个开发组合，大井组优选此6层煤合采获得2 000 m3/d稳定产量，证实合采层位优选方法正确。Abstract: Coal seams of the Longtan Formation in the Zhijin area of Guizhou province present the characteristics of multiple layers and small individual thickness. Compared with single thick-layered coal seam, multiple coal seams have differences in reservoir pressure gradient, formation liquid supply capacity, permeability and desorption pressure, which affect the efficiency of combined mining and the degree of resource utilization. In order to enahance the production potential of coalbed methane and improve the economics, it is valuable to optimize commingled production and establish a multi-seam development sequence. In view of these problems, this paper carried out a study on the differences of geological conditions of multiple coal seams. Combined with drainage practice and desorption theory, the influencing factors of multi-layer commingled production in the Zhijin area were discussed, and the production strategy was optimized. The results showed that desorption liquid level height, longitudinal span, pressure gradient, liquid supply capacity and permeability difference are the key factors affecting multi-layer commingled production. The main coal seams in the Upper Permian Longtan Formation in the study area have small differences in liquid supply capacity, pressure gradient and permeability, hence these have less impact on commingled production. The differences in longitudinal span and desorption liquid level height are the key factors affecting commingled production in the study area. A 90 m span can be used as a development combination for coal seams no. 16/17/20/23/27/30. A practice in large well group obtained a stable production of 2 000 m3/d, proving that commingled production is viable.
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图 1 贵州省织金区块岩脚向斜构造
据参考文献[10]，有修改。
Figure 1. Tectonic setting of Yanjiao syncline, Zhijin area, Guizhou province
图 2 贵州省织金区块岩脚向斜上二叠统含煤地层综合柱状图
据参考文献[10]，有修改。
Figure 2. Stratigraphic column of upper Permian coal bearing strata in Yanjiao syncline, Zhijin area, Guizhou province
图 3 贵州省织金区块解吸液面高度、合采跨度对多煤层合采影响模式
Figure 3. Influences of desorption liquid level height and longitudinal span on commingled production, Zhijin area, Guizhou province
图 4 贵州省织金区块煤层中深及解吸液面高度柱状图[10]
Figure 4. Histograms of medium depth and desorption liquid level in Zhijin area, Guizhou province
图 5 贵州省织金区块大井组归一化生产曲线
Figure 5. Normalized production curves of Dajing Formation in Zhijin area, Guizhou province
表 1 贵州省织金区块主力煤层厚度统计
Table 1. Thickness statistics of main coal seams in Zhijin area, Guizhou province
煤组 主力煤层 煤层厚度/m 煤层跨度/m 厚度/m Ⅰ煤组 6号 $ \frac{1.5 \sim 5.1}{2.1}$ $\frac{1.5 \sim 6.0}{4.3} $ $ \frac{15.4 \sim 29.8}{18.9}$ 7号 $ \frac{1.3 \sim 6.0}{2.1}$ $ \frac{49.3 \sim 61.2}{56.2}$ Ⅱ煤组 12号 $ \frac{0.8 \sim 1.4}{1.0}$ $ \frac{2.1 \sim 5.0}{4.2}$ $\frac{19.2 \sim 25.6}{20.1} $ 14号 $ \frac{0.8-2.1}{1.2}$ $ \frac{29.2 \sim 36.1}{29.8}$ 16号 $ \frac{0.9 \sim 4.1}{2.0}$ $ \frac{8.2 \sim 11.4}{9.9}$ 17号 $\frac{0.8 \sim 1.4}{1.2} $ $ \frac{17.8 \sim 23.9}{19.7}$ Ⅲ煤组 20号 $ \frac{0.8 \sim 3.2}{1.3}$ $\frac{1.2 \sim 7.9}{4.5} $ $ \frac{20.1 \sim 26.2}{22.3}$ 23号 $\frac{0.9 \sim 2.3}{1.3} $ $ \frac{18.8 \sim 24.1}{20.7}$ 27号 $\frac{0.8 \sim 1.9}{1.3} $ $ \frac{17.6 \sim 24.7}{20.1}$ 30号 $\frac{0.8 \sim 4.0}{1.9} $ 注：表中分式意义为：$ \frac{ { 最小值 \sim 最大值 }}{\text { 平均值 }}$。 
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表 2 贵州省织金区块试气压力梯度、渗透率统计
Table 2. Statistics of gas test pressure gradient and permeability in Zhijin area, Guizhou province
井号 煤号 测点深度/m 储层压力/MPa 压力梯度/(MPa·hm-1) 渗透率/10-3 μm2 X-2 16 374 2.95 0.79 0.017 9 X-2 23 427 3.04 0.71 0.000 2 X-3 16 732 6.86 0.93 0.000 5 X-4 27 510 5.52 1.08 0.074 4
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表 3 贵州省织金区块多煤层合采跨度与降压空间关系
Table 3. Spatial relationship between commingled production span and depressurization of multiple coal seams in Zhijin area, Guizhou province
合采煤层 跨度/m 下部解吸上部可降压空间/MPa 可行性 6-30号 240 0~0.3 不可行 12-30号 130 0.9 基本可行 16-30号 90 1.7 可行 20-30号 60 小井组证实可合采
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