Analysis of running depth and study of combined tubing of drill-grinding string in horizontal wells

To solve the difficulty of running drill-grinding string in oilfields, the joining pattern of two-line weight tubing combination is used to increase the running depth of drill-grinding string. There are currently few theoretical bases and systematic researches on the combined tubing. Thus, a calculation model of the combined tubing was established. Meanwhile, an experimental study of running drill-grinding string was conducted. The accuracy of the calculation model was discussed based on the experimental results. The field application of the calculation model was discussed. Finally, the combined characteristics and sensitivity analysis were studied. The results indicate that the critical condition for the optimal combination proportion of two-line weight tubing is a well depth of 1.236 rad deviated angle. The parameters affect running drill-grinding string, including frictional coefficient, running velocity, liquid density, and inner diameter. The work presented provides an effective solution and theoretical evidence for solving this difficulty.