VARIATION OF DRILLING MUD GAS COMPONENTS AT 350～800m INTERVAL OF No.2 BOREHOLE OF SCIENTIFIC DRILLING FOR WENCHUAN SEISMIC FAULTED ZONE

Based on data of some gas components in drilling mud at 350～800 m interval of No.2 borehole for WFSD and Richter earthquake magnitude ML≥3.5 catalog as well as lithologic character of cores from the faulted zone of Wenchuan earthquake,the authors investigated the relationships of anomalies of drilling mud de-gas gaseous components to tectonic environment and earthquake activity.The results show that the shattering of rocks is maximum at the interval of 660～680 m,the normalized values of various gases also show obvious positive and negative anomalies,and the intervals corresponding to the maximum and minimum values are places where aftershocks higher than the magnitude MS 3.0 frequently occur.The gas anomalies mostly occur in cracks in rocks,surface of fractures and faults.