entry key
5.The technology of hole trajectory primary section is the key of drilling in re-entry horizontal wells.
8.Aiming at the abnormal strata behavior in the advance entry of 1303 fully-mechanized working face in Xinglongzhuang coal mine, the movement rule, characteristic, step distance of fracturing, position and mode of fracturing of the overlying strata in mining process is analyzed by using the key strata theory.

