Abstract：Aiming at the problem of the deviation of gas extraction boreholes along seam in coal mines, the basic parameters of the drilling trajectory were measured by inclinometer through field test. With the method of the equal angle and total distance, the drilling borehole offset was calculated and the general rule of the deviation of borehole along seam was studied. Combined with the field constructions, the reasons led to the deviation of the borehole were analyzed. The results showed that the trajectory of boreholes along seam generally was of an upward trend; with an inspection interval of 20 m in drilling direction, the maximum change rate of borehole dip angle was in the range of > 40 ~ 60 m. Technical factors, geological factors and artificial construction factors were the main factors led to borehole deviation. The conclusions provided a scientific basis for preventing borehole deviation and for further researching of straightening anti-slanting technology in drilling along seam.

Keyword：coal mine;gas extraction;borehole along seam;deviation rule;