Stress Transfer Characteristics of Double Casing Shear Deformation in Surface Borehole

Aiming at the problem of failure and fracture of drilling well under mining condition, through using numerical simulation, we researched the stress transfer feature in the shear deformation progress of double casing for surface drilling. Results show that the peak stress and the stress concentration area of outer casing are all bigger than the inner casing; the stress transfer coefficient presents a variation trend which increases quickly and then increases slowly; besides, the stress transfer coefficient of double casing decreases with increase of thickness of fill layer or decreases with elasticity modulus of filling material. Therefore, the structure optimization suggestion of borehole is: increasing the thickness of the filling layer and selecting the flexible filling material.