微地震监测技术在气田水回注中的应用

Microseismic monitoring for water reinjection in a gas field

气田开采过程中产生的大量气田废水,去污之后回注处理时,若处理不当,则可能诱发安全事故甚至对地下环境造成污染。因此,采用微地震监测方法对水体回注过程进行实时监测。通过震源速度联合反演方法对速度模型进行优化数据处理,并利用扫描叠加算法对微地震事件进行定位,最终根据微地震事件定位结果刻画水流通道,了解水体扩展规律,判断回注过程是否存在安全隐患,及时调整注水参数。结果表明:①在监测期间,回注水体基本存贮在目的层中,并未出现严重串层现象;②水体波及一些小的裂缝带,且回注水体更易沿小断层、裂隙流动。微地震监测技术对水体回注过程起到很好的监控作用。

A large amount of wastewater produced during gas field operation is usually decontaminated and re-injected for gas production.As the injected water is in the underground for a long time,it may lead to safety accidents and even cause environment pollution if not properly handled.Therefore,it is necessary to monitor the water flow direction and affected range in the injection process.To prevent this problem we use microseismic to monitor water re-injection process.We adopt the source-velocity joint inversion to optimize velocity models,and use the scanning superposition algorithm to locate microseismic events.Based on the positioning results of microseismic events,water channels are depicted,the water expansion zone is estimated,and safety risks in the injection process are predicted.So water injection parameters can be adjusted in time.Our application results show the following observation:(1)The injected water is basically stored in targets during the monitoring period,there is no serious water leakage into other strata;(2)The injected water may expand to some minor faults and small fractures in the zone;and it flows easily along these faults and fractures.Our application demonstrates that the microseismic monitoring can be very useful in monitoring water injection process.