METHOD OF DEEPENING A HORIZONTAL BOREHOLE IN UNSTABLE BEDS OF A FORMATION Russian patent published in 2020 - IPC E21B21/00 

FIELD: oil and gas industry.

SUBSTANCE: invention relates to oil and gas industry, namely, to drilling of horizontal wells to restore open horizontal shaft. Method comprises assembly of drilling string bottomhole assembly – BHA, consisting from bottom upwards of bit, right branch pipe and calibrator, lowering to well BHA at drill string end, restoration of the barrel passability with reciprocation of the layout to normal without puffing and arranging passage of the assembly along the shaft, extraction from the well BHA, lowering the cutting head with the template to the open horizontal shaft interval, back-flushing deepening with respect to the open horizontal shaft along its entire length, preventing drill pipe string from landing in well over 5 tons of its own weight. Reservoir rock is analyzed, from which required rate of deepening and rate of liquid pumping are determined to obtain breakable particles with value which excludes build-up during pumping between BHA and well walls. Pumping rate is selected to ensure turbulent upward flow preventing particles deposition during deepening. Received parameters are used to select the downhole motor, which is installed before descent above the BHA. When deepening and removing the template and the cutting head, the liquid flow rate during direct and / or back flushing is maintained not less than providing a turbulent upward flow which eliminates precipitation of particles obtained during deepening.

EFFECT: reduced probability of emergency situations associated with incomplete washing of rock from horizontal borehole at direct and / or back flushing, practically to zero, expanded functionality due to possibility of use in horizontal shafts with any rock and any depth of occurrence.

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