CLAY-FREE DRILLING FLUID FOR EXPOSING PRODUCTIVE FORMATIONS Russian patent published in 2001 - IPC

FIELD: oil and gas production. SUBSTANCE: clay-free drilling fluid used as washing fluid when exposing productive formations contains 0.3-1.8 % of xanthane series biopolymer, 0.3-3.0% of associative binary product, in particular polyalkylene glycol component, and water. Polyalkylene glycol component more particularly consists of water-soluble ethylene oxide/propylene oxide copolymer with at least 85 mol % ethylene oxide and oil-soluble ethylene oxide/propylene oxide copolymer with no more than 15 mol % ethylene oxide at their ratio from 1:1 to 1:3. Fluid may also contain filtration reducer, clay swelling inhibitor, biocyde, mudding agent, and weightening agent. EFFECT: reduced filtration characteristics, increased clay rock inhibition efficiency, and improved surfactant and waterproofing properties. 6 cl, 5 tbl, 4 ex