METHOD OF INSTALLING A CEMENT PLUG FOR DRIVING UNSTABLE ROCKS WHEN DRILLING A WELL Russian patent published in 2019 - IPC E21B33/13 

FIELD: soil or rock drilling.

SUBSTANCE: invention relates to drilling of oil and gas wells, namely to methods of prevention of destruction and collapse of well walls at drilling intervals with unstable rocks. Proposed method comprises lowering of pipe string to the specified depth, pumping of cement solution volume, maintenance of cement mortar till its setting, removal of pipe string, removal of excess cement plug. Method comprises preliminary determining interval of unstable bed rock, enlarging borehole with diameter increase by at least 50 mm from nominal diameter of well for entire length of unstable rock interval, then in interval with unstable rock on tubing string easily drilled pipe string is lowered, which is preliminary in upper part is equipped with passing cork with through hole and saddle, and in lower part – stop ring, pumping cement slurry into pipe string and extruding design volume of cement slurry into gap between outer wall of easy-drilled column and wall of well with unstable rock by flushing cork until plug is fitted on stop ring, disconnecting pipe string from easy-to-drill pipe string and withdrawing from well, after setting cement grout excess cement plug is removed by expander equipped with centering cutter, wherein diameter of expander corresponds to nominal diameter of well shaft, diameter of centering mill is smaller than inner diameter of easily drilled pipe string.

EFFECT: improving efficiency and quality of installation of cement plug, which enables to exclude unstable rock collapse during well drilling due to creation and preservation of strong frame from cement stone and maintaining well cross-section after removal of excess cement plug without limitation of technological capabilities of well and quality improvement.

1 cl, 4 dwg