METHOD OF BOREHOLE DRILLING Russian patent published in 1997 - IPC

FIELD: oil and gas production. SUBSTANCE: borehole is drilled to target well depth with washing of bottom using natural aqueous suspension until confining productive bed is attained followed by replacing natural aqueous suspension by mud solution. Before replacement, borehole walls are covered with quickly- hardening impermeable cement crust by means of pumping through cement mortar treated by polyvinyl alcohol-vinyl acetate copolymer, cement before tempering being mixed with above-said copolymer and tempering water being supplemented with ethylene glycol aqueous solution. EFFECT: increased quality of formation isolation and reduced borehole drilling time. 3 tbl