煤层中CO2注入运移瞬变电磁法监测技术探索

TEM monitoring technology of CO2 injection and transport in coal seam

煤层中注入CO2,使煤层的CO2饱和度发生变化。根据阿尔奇经验关系公式,煤层电阻率在CO 2注入前后有明显的差异,为瞬变电磁法监测提供了条件。在柿庄北煤层气开发中,利用瞬变电磁法监测煤层中CO 2注入前后电阻率变化进行了实验探索,结果显示煤层中CO 2的注入能引起煤层电阻率的增加,并且可以通过瞬变电磁方法监测;同时感应电压能直观地反应CO 2注入所产生的地层电性特征的变化,利用地层等效电阻率的计算公式,计算地表至煤层的等效电阻率值,求解煤层附近地层的瞬变电磁采样延时及其对应的感应电压值。感应电压值相对于背景值的变化,反映了地层电性特性的变化,分析计算CO 2注入引起的地层感应电压的变化量和变化率,结合误差范围,可以推断出CO 2运移富集区范围。

The injection of CO2 into the coal seam changes the CO2 saturation of the coal seam.According to Archie's empirical formula,there are obvious differences in coal seam resistivity before and after CO 2 injection,which provides conditions for TEM monitoring.In the development of coalbed methane in Shizhuang North Block,the electrical resistivity changes of coalbed methane before and after CO2 injection were monitored by TEM.The results show that the increase of electrical resistivity of coal seam can be caused by CO2 injection in coal seam,and can be monitored by TEM.At the same time,the induced voltage can directly reflect the change of formation electrical characteristics caused by CO 2 injection.The equivalent resistivity from the surface to the coal seam is calculated by using the calculation formula of formation equivalent resistivity,and the transient electromagnetic sampling delay and the corresponding induced voltage of the formation near the coal seam are solved.The variation of induced voltage relative to background value reflects the change of formation electrical properties.The variation and rate of formation induced voltage caused by CO2 injection are analyzed and calculated.Combined with the error range,the range of CO2 migration enrichment zone can be inferred.