Abstract: Considering the situation of Well Yunaba 272H,such as smaller adjustment space,HTHP,poor drill ability and smaller hole diameter of sidetracking intervals,the sidetracking method,sidetracking point and bottom-hole assembly were selected.Relevant technical measures were taken,including conventional open hole sidetracking method for the purpose of safety in long directional section.As the sidetracking point is deeper than 6,600 m,and the over-all angle changes beyond the designed rate,the sidetracking point was selected at 1.00-5.00 m beneath the casing shoe.Due to the sidetracking point retained in hard rocks,the bottomhole assembly was determined as"roller bit+straight PDM+2.75° bending sub"to increase the sidetracking force.Additionally,certain operation measures were taken,such as suspended lower sidetracking,reasonable control over sidetracking speed and direction,strengthening the monitoring of operation,and ensuring drilling fluid performance,etc.These measures were successfully applied in Well Yuanba 272H,the well path,concentration of cuttings and drilling parameters show that new and old holes were completely separated at the depth of 6 672.30 m.This success is significant for sidetracking in similar wells.