Geological characteristics and development effect evaluation of coalbed methane reservoirs in Panguan syncline, Guizhou Province
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摘要: 贵州省上二叠统龙潭组煤层多，煤层气资源丰度高，具备煤层气开发的资源基础，但煤层渗透率较低，影响气、水产出，需探索适应贵州省低渗、多煤层条件下的煤层气开发关键技术。根据盘关向斜煤储层地质特征及煤层气井工程资料，从地质、压裂、排采指标3个维度开展研究分析，总结低渗、多煤层的煤层气开发技术。盘关向斜工程实践表明：①该向斜12#、18#煤层合层开发煤层气，渗透率、储层温度、破裂压力、每米煤层的加液量及加砂量、压降速率、提产速率对煤层气井产气的影响较大；②提高每米煤层的加液量及加砂量指标，能够显著提高压裂改造后的储层渗透率，YP-1井改造后渗透率达到64.158×10-3 μm2，提高1 304倍；③控制合适的压降速率、提产速率能够提高煤层气井的压裂液返排率及扩大压降漏斗半径，YP-1井排采210 d后压裂液累计返排率达到82.53%，产水半径达到压裂影响半径的91%，对扩大有效解吸半径及提高产气效果有利。针对盘关向斜低渗、多煤层的地质条件，建议采取“选层射孔、分段压裂、合层排采”的工艺技术进行煤层气开发，从而提高煤层气开发的地质及工程潜力。Abstract: The Upper Permian Longtan Formation in Guizhou Province contains multiple coal seams with abundant coalbed methane (CBM) resources, providing a solid base for CBM development. However, the low permeability of the coal seams hinders gas and water production, necessitating the development of key technologies for CBM development under conditions of low permeability and multiple coal seams in Guizhou. Based on the geological characteristics of coal reservoirs in the Panguan syncline and CBM well engineering data, the study analyzed geological, fracturing, and drainage and production parameters, and summarized development technologies for low-permeability and multi-seam CBM reservoirs. Engineering practices in Panguan syncline show that: (1) For commingled development of coal seams 12# and 18# in the syncline, factors such as permeability, reservoir temperature, fracture pressure, liquid and sand addition per meter of coal seam, pressure drop rate, and production enhancement rate significantly influence gas production of CBM wells. (2) Increasing the liquid and sand addition per meter of coal seam can significantly increase the reservoir permeability after fracturing. The permeability of well YP-1 after fracturing reached 64.158×10-3 μm2, 1 304 times higher than before. (3) Controlling pressure drop rate and production enhancement rate to appropriate levels can improve the fracturing fluid flowback rate and expand the pressure drop funnel radius of CBM wells. The cumulative fracturing fluid flowback rate of well YP-1 reached 82.53% after 210 days of drainage and production, with the water production radius reaching 91% of the fracturing influence radius. This helps to expand effective desorption radius and improve the effectiveness of gas production. For the Panguan syncline with low permeability and multiple coal seams, the study suggests adopting the technical approach of "selected layer perforation, segmented fracturing, and commingled drainage and production" to improve the geological and engineering potential of CBM development.
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图 1 贵州省盘关向斜煤层气参数井连井剖面
Figure 1. Connecting-well profile of coalbed methane parametric wells in Panguan syncline, Guizhou Province
图 2 贵州省盘关向斜YV-1井煤层等温吸附曲线
Figure 2. Isothermal adsorption curves of coal seams in well YV-1 of Panguan syncline, Guizhou Province
图 3 贵州省盘关向斜12#、18#煤层压汞体积比例
Figure 3. Mercury injection volume ratios for coal seams 12# and 18# in Panguan syncline, Guizhou Province
图 4 贵州省盘关向斜12#、18#煤煤体结构
Figure 4. Coal structure of coal seams 12# and 18# in Panguan syncline, Guizhou Province
图 5 贵州省盘关向斜YP-1井压裂施工曲线
Figure 5. Fracturing operation curves of well YP-1 in Panguan syncline, Guizhou Province
图 6 贵州省盘关向斜YP-1井放溢流产水及出气情况
Figure 6. Overflow water and gas production from well YP-1 in Panguan syncline, Guizhou Province
图 7 贵州省盘关向斜YP-1井排采曲线
Figure 7. Drainage and production curves of well YP-1 in Panguan syncline, Guizhou Province
表 1 贵州省盘关向斜YV-1井含气性数据
Table 1. Gas content of well YV-1, Panguan syncline, Guizhou Province
煤层号 煤层深度/m 兰氏体积/(m3/t) 兰氏压力/MPa 实测含气量/(m3/t) 含气饱和度/% 12# 723 22.90 1.85 15.52 88 18# 774 17.63 1.43 12.05 82 
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表 2 贵州省盘关向斜压力梯度
Table 2. Pressure gradient of Panguan syncline, Guizhou Province
井号 煤层号 煤层深度/m 破裂压力/MPa 破裂压力梯度/(MPa/hm) 闭合压力/MPa 闭合压力梯度/(MPa/hm) YV-1井 12# 723 13.85 1.92 12.17 1.69 18# 774 14.17 1.83 12.18 1.57 YV-3井 12# 567 13.22 2.30 11.59 2.02
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表 3 贵州省盘关向斜煤层气井射孔数据
Table 3. Perforation data of coalbed methane wells in Panguan syncline, Guizhou Province
井号 压裂段 压裂煤层 煤层深度/m 煤层结构/m 射孔段/m 射孔厚度/m 孔密/(个/m) 相位/(°) 射孔数/个 射孔枪弹/mm 备注 YP-1井 第1段 18# 771.4 1(0.6)0.7 771.4~772.4 1.0 16 60 16 102/127 只射煤层夹矸避射 773.0~773.7 0.7 16 60 12 第2段 12# 719.7 3.6 719.7~722.7 3.0 16 60 48 注：煤层结构数据1(0.6)0.7表示煤(夹矸)煤的厚度。
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表 4 贵州省盘关向斜煤层气井压裂规模
Table 4. Fracturing scale of coalbed methane wells in Panguan syncline, Guizhou Province
井号 煤层编号 煤层深度/m 煤层厚度/m 压裂液量/m3 压裂砂量/m3 每米煤层液量/ m3 每米煤层砂量/m3 加液量与加砂量比值 YP-1井 18# 771.4 1.7 803 38.16 472.35 22.45 21.04 12# 719.7 3.6 1 257 64.37 349.17 17.88 19.53 综合 / 5.3 2 060 102.53 388.68 19.35 20.09
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表 5 贵州省盘关向斜煤层气井压裂及测压降数据
Table 5. Fracturing and pressure drop data of coalbed methane wells in Panguan syncline, Guizhou Province
井号 压裂段 压裂煤层 煤层深度/m 煤层厚度/m 加液量/ m3 加砂量/ m3 停泵压力/ MPa 测压降时间/min 测压降后压力/MPa 压力降幅/ MPa 压力降幅与停泵压力比值/% YP-1井 第1段 18# 771.4 1.7 803 38.16 17.1 60 13.0 4.1 23.98 第2段第1次 12# 719.7 3.6 695 35.03 9.9 30 7.3 2.6 26.26 第2段第2次 12# 719.7 3.6 562 29.34 12.4 60 10.7 1.7 13.71
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