CLAYLESS DRILLING MUD BASICALLY DESIGNED FOR BORING HORIZONTAL HOLES (VERSIONS) Russian patent published in 2002 - IPC

FIELD: oil and gas production and drilling fluids. SUBSTANCE: invention, in particular, relates to biopolymer clayless drilling muds for exposing productive formations by way of boring horizontal holes and holes with large deviation angles represented by carbonate and terrigene (sandstone) reservoir rocks and likewise for restoring wells by boring second boreholes under different hydrogeological conditions. Drilling mud contains, wt.%: biopolymer, 0.05-0.2; modified starch, 1.15-2.0; alkali metal hydroxide, 0.045- 0.16; water-soluble silicic acid salt, 0.23-1.2; surfactant, 0.3-1.0. and water, the balance Said alkali metal hydroxide and said silicic acid salt are taken at weight ratio 1:(2.5-15.0). According to another embodiment of invention, drilling mud contains, wt.%: biopolymer, 0.05-0.2; modified starch, 1.15-2.0; multianionic cellulose, 0.1-0.25; alkali metal hydroxide, 0.045-0.16; water- soluble silicic acid salt, 0.23-1.2; surfactant, 0.3-1.0; and water, the balance. Said alkali metal hydroxide and said silicic acid salt are taken at weight ratio 1:(2.5-15.0). Drilling muds may further contain weighing agents (sodium, calcium, and potassium chlorides, carbonate agent, bentonite) in amounts required to obtain products with specified density. Drilling muds so composed exhibit stability in filtration, structural-rheological, and lubricating properties under multisalt mineralization conditions within a wide temperature range (up to 90 C) and also ensure formation, on boring, of low- permeable filtration crust and mudding zone resistant against to mineralized formation water effects. Another advantage: reduced expenses on preparation and property control of drilling mud due to lower total consumption of reagents, increased enzymatic stability and more stable characteristics of drilling mud in what concerns resistance to formation fluids and drillings. EFFECT: improved working characteristics. 4 cl, 3 tbl, 2 ex