Weight Distribution Characteristics During the Process of Hole Enlargement When Drilling

The weight distribution between the pilot bit and reamer is the key factor to ensure the safety and performance of hole enlargement when drilling (HEWD) assembly when reaming. Based on the finite element method, a real-time model of HEWD assembly was proposed, in which it can simulate the interactions between the components. The characteristics of weight distribution and its effects on the dynamic of HEWD assembly were studied. The results indicate, in homogeneous formation reaming, the optimal rotary speed can improve the utilization of mechanical energy up to 97% and leads to a more reasonable weight distribution. The weight distribution will also be reasonable when the difference in strength between the upper soft and lower hard formation is less than 17 MPa. However, the reamer will be out of drilling when the difference exceeds 37 MPa. In addition, the weight distribution ratio is less than 0.3 when the difference in strength between the upper hard and lower soft formation is less than 32 MPa. But it will exceed 0.5 when the difference exceeds 37 MPa. The ROP keep on increasing 1.6 and 1.4 times when the HEWD assembly reams through the upper Quartzite and lower black sandstone formation, respectively. But the ROP drops by 52 and 11% when it reams through the upper black sandstone and lower Quartzite formation while the torque slightly increases. Based on the trend of ROP and surface torque, engineers can judge the working status of a HEWD assembly and make appropriate adjustments.