Field experiment and prospect discussion of in seam seismic survey for CO2 source

Seismic source is the source of seismic records and the key part of seismic exploration，which directly affects the quality of seismic signal. Conventional explosive source is strictly controlled in high gas mine. Therefore，it is urgent to study new seismic source for seismic exploration in the mine. Based on this，in seam seismic survey of a new type of CO2 source was carried out in medium thick coal seam working face of outburst mine. Based on the methods of theoretical calculation，numerical simulation and field measurement，the kinematic and dynamic characteristics of seismic signals excited by a new type of CO2 source are studied，the results showed that:typical P wave，S wave and channel wave appear in the seismic sections of different roadway excitation receiving transmission detection and same roadway excitation receiving transmission detection，among which the main frequency of channel wave is the highest and the amplitude energy is the strongest;The frequency width of transmitted channel wave excited and received by different roadways is about 200-350 Hz，and the Airy phase is about 260 Hz;The amplitude energy of transmitted channel wave excited and received in the same roadway is concentrated in 250-450 Hz，and the Airy phase is about 280 Hz;The theoretical energy of 2 kg liquid CO2 source exceeds the equivalent to the TNT of 140 g. Therefore，the frequency and amplitude characteristics of CO2 source meet the needs of mine seismic exploration. Compared with explosive source excited in the roadway side，the excitation mode of concentrated force source of CO2 source is beneficial to the development of channel wave，and CO2 source has the advantage of deep borehole excitation，avoiding the influence of roadway and surrounding rock loose zone，and directional energy accumulation on coal seam. At the same time，CO2 source excitation has directionality，and it is the next key research direction to make use of the directional advantage of CO2 source energy accumulation to carry out structural fine detection. CO2 gas fracturing technology is often used for coal seam pressure relief and permeability enhancement，it is expected that the gas enrichment anomaly and stress variation anomaly in front of the coal roadway can be detected with the help of CO2 source.