摘要
Based on the AVO theoretical modeling of the coalbed, this paper analyzes the AVO characteristics and influencing factors of the coalbed P-P reflection wave. On the top interface of the coalbed, the P-P reflection wave absolute value of reflective coefficient decreases when the incidence angle increases between 0 and 60 degrees, and then increases gradually. On the bottom interface of the coalbed, the total reflection occurs rather strikingly because the incident wave propagates from low impendence media to high one. And for the soft and fractured coal in particular, such a phenomenon takes place even at an incidence angle less than 15 degrees. So the reflection characteristics of the coalbed bottom interface are not conducive to AVO analysis. AVO response is closely relative to the coal structure, and AVO intercept and gradient of top interface of the coalbed reflection wave increases when the coal structure is destroyed severely. For coalbeds of the same coal structure, AVO intercept and gradient of the coalbed top interface with the sandstone roof is greater than that with the mudstone one. The tuning of coal-bed thickness has adverse influence on coalbed AVO attributes analysis obviously. Those AVO characteristics of coalbed are shown further by modeling from Well 9-10-15 and Well 10-E-3 in Huainan coalfield, China.
Based on the AVO theoretical modeling of the coalbed, this paper analyzes the AVO characteristics and influencing factors of the coalbed P-P reflection wave. On the top interface of the coalbed, the P-P reflection wave absolute value of reflective coefficient decreases when the incidence angle increases between 0 and 60 degrees, and then increases gradually. On the bottom interface of the coalbed, the total reflection occurs rather strikingly because the incident wave propagates from low impendence media to high one. And for the soft and fractured coal in particular, such a phenomenon takes place even at an incidence angle less than 15 degrees. So the reflection characteristics of the coalbed bottom interface are not conducive to AVO analysis. AVO response is closely relative to the coal structure, and AVO intercept and gradient of top interface of the coalbed reflection wave increases when the coal structure is destroyed severely. For coalbeds of the same coal structure, AVO intercept and gradient of the coalbed top interface with the sandstone roof is greater than that with the mudstone one. The tuning of coalbed thickness has adverse influence on coalbed AVO attributes analysis obviously. Those AVO characteristics of coalbed are shown further by modeling from Well 9-10-15 and Well 10-E-3 in Huainan coalfield, China.
