Erosion Mechanism Analysis And Residual Strength Prediction For Pipe String During Nitrogen Well Drilling

The effect of impact angle and rate on the erosion behaviors of pipe strings(drill string, casing and tubing) materials under different conditions were investigated by analyzing the erosion rates and surface morphologies. The erosion mechanism of the pipe string materials was also discussed. Moreover, Fluent software was used to simulate annulus gas-solid flow pattern under Nitrogen Well Drilling conditions. Finally, predict the residual strengths of pipe strings(drill string, casing and tubing) in different conditions.The results showed that with increasing of the erosion rate, the average weight loss rate and average thinning rate of the pipe string material increase. In the drilling conditions, the critical velocities of drill string of BG13Cr-110 and S135 are 20m/s. Critical velocity of TP140 casing material in the drilling conditions is 20m/s at the impact angle of 18 ° and 30m/s at the impact angle of 75 °. In the producing conditions, there was no obvious critical velocity for P110 tubing string.The serious erosion occurred at lower angle for ductile materials 30 Cr Mo and at higher angle for brittle materials Cr2O3. When the erosion angle is same, the weight loss rate of Cr2O3 specimen is higher than 30 Cr Mo.Two-phase flow erosion model for pipe string was established based on the computational fluid dynamics(CFD) method. Through the analysis of the annular gas flow velocity, pressure, rock debris concentration, shear stress distribution and the erosion rates of drill string and casing, it can be concluded that the flow rates of gas and debris in the central region of the annulus are largest. From the center to the inner of casing and the outer of drill string, the flow rate decreases gradually until the velocity is zero on the wall. On the female joints of drill string, the debris concentration is maximum and the shear stress on the connector ramp of drill string is maximum.On the basis of erosion test, the residual strengths of and the remaining life of the drill strings(BT13Cr-110 and S135) in the drilling conditions were calculated; the residual strengths of and the remaining life of casing TP140 in the drilling conditions were calculated; the residual strength of and the remaining life of tubing P110 in the producing conditions also were calculated.