Improved Calculation of Wellbore Steady Fluctuation Pressure in Tripping Operations

To eliminate the possibility of kicks, lost circulation and other complicated situations during tripping operations, it is necessary to enhance the accuracy of calculation for the wellbore fluctuation pressure. Based on the slot flow model and considering the actual velocity distribution in the wellbore, fluctuation pressure at laminar flows and turbulence flows was investigated in accordance with the continuity of wellbore fluids and corresponding boundary conditions. Eventually, steady fluctuation pressure calculation methods were established and numerical solutions were also introduced. Field production data were used to verify these models. When the velocity of the drilling string was increased from 0.2 m/s to 0.6 m/s, fluctuation pressures increased from 0.21 MPa to 0.27 MPa. Under stable drilling strings velocity and fluid rheology, fluctuation pressure of the wellbore increased from 0.3MPa to 0.5 MPa when ID/OD ratio increased from 0.55 to 0.9. Through comparison with experiment data in published literatures, calculation errors from the Burkhardt model was over 8%, while the calculation error from the new model was less than 5%. The new model met pressures accuracy requirements in drilling operations. Research results show that the high-precision steady fluctuation pressure calculation method could be used for accurate analysis of wellbore pressures during non-drilling operations and might provide necessary guidance for secure operation onsite.