Poor wellbore cleaning is the cause of many well construction incidents and complications. In fact, 30% of sticking incidents in vertical wells and 80% of sticking incidents in horizontal wells are due to poor wellbore cleaning. When using inhibiting polymer in composition of drilling mud in case of wells of large diameter in suprasalt clayey sediments of Astrakhan gas condensate field there are problems caused by their low carrying capacity. For modern drilling fluids, including polycationic drilling fluids, dynamic shear stress and plastic viscosity are not convenient parameters for providing cuttings transport to the surface, especially at high mechanical drilling speeds in clayey sediments. It is proposed to regulate the value of shear stress and effective viscosity determined in the range of shear rates corresponding to the speed of upward fluid flow in the annulus of the borehole as the relevant rheological indicators to ensure cuttings transportation to the surface in the intervals with large diameters. The minimum value of shear stress is selected based on the difference of upward flow velocity and slip velocity, and the value of effective viscosity is determined by the results of tests at the well by the volume of cuttings carried out. To increase the efficiency of cuttings transport to the surface, when drilling vertical intervals with large diameters, it is most rational to use solutions with increased rheology parameters in combination with periodic pumping of viscous packs.
References
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