大倾角煤层浅部露出区煤层气溢出问题数值仿真模拟

Numerical simulation of coalbed methane leakage from shallow exposed area of steep coal seam

中国新疆阜康白杨河矿区42号煤层倾角大,浅部煤系地层露出,为研究煤层气从该区域溢出问题,防止煤层气资源浪费,基于大倾角煤层中气-水分异现象,修正了大倾角煤层三维气-水两相渗流模型,结合阜康白杨河矿区42号煤层实际地质资料与历史拟合储层再描述,展开了大倾角煤层浅部露出区煤层气溢出问题数值模拟仿真研究。研究结果表明:大倾角煤层浅部露出区煤层气溢出问题的存在;埋深300、500和700 m直井生产15 a累计溢出量分别为1.02×10^(5)、1.08×10^(7)以及1.33×10^(7) m^(3),和产量比值分别是5.06%、668.02%以及335.77%,直井生产时会造成大量的煤层气资源浪费;溢出现象并非伴随整个生产周期,溢出量先增后降直到溢出现象结束,使用顺层井生产时可以完整观测这一过程,溢出现象持续了1918 d,日溢出量上升和下降过程近似对称,累计溢出量为7.18×10^(5) m^(3),和累计产气量比值为1.54%。补充400 m和600 m埋深直井模拟方案后,发现煤层气最大溢出量和累计溢出量与直井埋深呈正相关线性关系,而溢出现象开始时间随着埋深增加逐渐提前,500 m以深溢出现象开始时间保持不变。综合分析煤层气溢出现象是造成该区直井产能较差的原因之一,使用顺层井排采能有效提高经济效益和降低煤层气溢出现象。

Based on the gas-water gravity differentiation in the steep coal seams,the three-dimensional gas-water two-phase seepage for steep coal seam was revised.Combined with the actual geological data of the No.42 coal seam in the Baiyanghe mining area of Fukang,a numerical simulation study on the leakage of coalbed methane from the shallow exposed area of steep coal seam was carried out.The research results indicated the existence of coalbed methane leakage in the shallow exposed area of steep coal seam;when vertical wells with buried depths of 300,500,and 700 m were produced,the amount of leakage and production ratio are 5.06%,668.02%and 335.77%,respectively.During production,a large amount of coalbed methane resources will be wasted;the leakage phenomenon did not accompany the entire drainage stage.The amount of leakage firstly increased and then decreased until the phenomenon ends.When using lateral wells for production,the leakage phenomenon lasted for 1918 days,and the ratio of the amount of overflow and cumulative production is 1.54%.After adding simulation cases of 400 m and 600 m burying depth vertical well,it is found that the maximum and cumulative amount of coalbed leakage are positively correlated with the vertical well burying depth.The starting time of leakage phenomenon reduce with the buried depth increases,and the start time remains constant in the deeper area.In conclusion,coalbed methane leakage is one of the reasons for poor productivity of vertical wells in this area.The use of lateral wells can effectively improve economic benefits and reduce coalbed methane leakage.