The relationship between the in situ stresses and wellbore stability in multi-lateral horizontal well about the coal withⅠandⅡstructures

It is one of effective measures to guarantee success rate about multi-lateral horizontal well drilling to prevent hole collapse, coal structure and situ stresses are two main factors to effect hole forming. Based on casing program about multi-lateral horizontal well and pore and fissures characteristics about coal body, elastic mechanics and coal with I and Ⅱs tructures, the corresponding targential stress models were established. Based on targential stress models, the force conditions in different states such as different sizes among horizontal stress and vertical stress, different drilling directions about main branch and collateral branches in multi-lateral horizontal well were analyzed. The results showed tha it is the easiest to hole-forming to drilling along the direction of the minimum horizontal stress to the coal with I structure, it is the hardest to drilling along the direction of the maximum horizontal stress to the coal with I structure; the drilling direction was controlled by the angle between the surface of exogenous fracture and the direction of the maximum horizontal stress to the coal with Ⅱstructure.