逆断层工区浅层天然气赋存及运移特征研究---以成都轨道交通30号线为例

Occurrence and Migration Characteristics of Shallow Natural Gas in Reverse Fault Area:a Case Study of Chengdu Metro Line 30

为解决逆断层工区浅层天然气频繁涌出的问题,依托成都轨道交通30号线工程,通过CH_(4)短期监测试验、CH_(4)补给试验、CH_(4)长期监测试验和气相色谱试验,探索逆断层工区浅层天然气的涌出、补给、赋存特征和聚集能力。结果表明:(1)活动逆断层区域浅层天然气短期聚集能力强、涌出量大、补给速度快,但补给的持续性较差。(2)在休止期逆断层的破碎带区域中,浅层天然气短期聚集能力强、涌出量大、补给效率和持久稳定性好,长期的敞孔通风措施可以有效降低该区域浅层天然气的短期聚集能力和涌出量;而在裂隙发育带中浅层天然气聚集能力弱、涌出量小、补给效率和持久稳定性差,长期敞孔通风条件可以排放掉钻孔周围的绝大部分浅层天然气。(3)休止期逆断层中,浅层天然气在破碎带区域连续分布,在裂隙发育带范围内以气囊的方式不均匀分布。(4)浅层天然气主要赋存在逆断层方圆1~2 km,气体体积分数随埋深增加而增大,CH_(4)与其他烃类气体的比值(C_(1)/C_(2)+)随埋深增加而减小。

To avoid frequent outbursts of shallow natural gas in the reverse fault area,a case study of the Chengdu metro line 30 is conducted,and CH_(4) short-term and long-term monitoring tests,CH_(4) recharge test,and gas chromatography test are employed to explore the characteristics of gas outburst,recharge,occurrence,and accumulation capacity of shallow gas in reverse fault areas.The results reveal the following:(1)The short-term accumulation of shallow natural gas in the active reverse fault area is strong,outburst volume is large,and recharge speed is high,but the sustainability of the replenishment is poor.(2)In the broken zone of the static reverse fault,the short-term accumulation of shallow natural gas is strong,outburst volume is large,recharge efficiency and sustainability are good,and long-term ventilation measures can effectively reduce the short-term accumulation ability and shallow natural gas outbursts in this area.However,in the fractured zone,shallow natural gas has weak accumulation ability,small outburst volume,poor recharge efficiency and sustainability,and most of the shallow natural gas around the borehole can be discharged by long-term ventilation.(3)In the static reverse fault,shallow natural gas is continuously distributed in the broken zone and unevenly distributed in the form of air bags within the fracture zone.(4)Shallow natural gas mainly accumulates within 1~2 km around the reverse fault.With the increase in depth,the concentration of gas increases,whereas the ratio of methane to other hydrocarbon gases(C_(1)/C_(2)+)decreases.