Effect of Choke Valve Action on Annular Pressure with Micro-Flux Control in MPD Drilling

To address effectively the complex pressure profile with narrow density window,the effects of choke valve action on fluctuation pressure in annulus have been studied during drilling operations.Based on the mass and momentum conservation equations,the model was established to simulate fluctuation pressure in annulus caused by choke valve action,and calculated by central difference method.In the calculation example,the fluctuation pressure in annular space will be higher with the increases of flow rate and the shorter time of choke valve action.The fluctuation pressure in the valve core is higher than that in the annulus,and the maximum fluctuation pressure increased from 1.26 MPa to 1.56 MPa with the flow rate of drilling fluids increased from 0.036 m3/s to 0.056 m3/s.The maximum fluctuation pressure is 0.22 MPa in drill collar section.When adjusting choke valve,the trouble probability at the casing shoe is 35% greater than that at the bottomhole.The research results indicate that the two-step or multi-step valve closing linearly is more flexible than the one-step valve closing,and can effectively lower the peak fluctuation pressure in annular space.