| The paper does a systematic research on chemical mechanism of slurry stable wall, based on which it optimally selects various treating agents which are compatible with the silicate, and develops formula of silicate drilling fluids with great inhibition. The formula has been put into production in DaGang oilfield with remarkable effect.We can get the following conclusions from the experiment: the silicate solution with concentration of 7% has the smallest average size and best plugging effect. Modulus and pH have the most prominent effect on the size of silicate colloid: silicate with modulus between 2.8-3.2 has the narrowest distribution range; The absorption between the silicate and clay is mainly in the form of chemical absorption and greatly effected by the temperature; The isolation formed by the reaction of silicate and shale can hamper the pressure transfer and plug well wall.The formula of KCl /silicate drilling fluids with strong inhibition by research which is suitable for Dagang Oilfield is of excellent inhibition, rheology, filtration and temperature resistant. Its API filtration rate is less than 5mL, and HTHP filtration rate is less than 12mL,and cutting recovery rate can reach more than 90%, and it can resist the temperature of 120℃, the core permeability recovery value reaches more than 75%.The formula can protect the oil layer effectively ,and can act as the completion fluid when drilling into the layer(perforated completion as the premise), so different silicate drilling fluids project could be selected according to the conditions in practice. Besides, the silicate drilling fluids with strong inhibition have no corrosive effect on casing.The new silicate drilling fluids have been experimented in 5 wells. It is proved in the field experiments: silicate drilling fluids has superb inhibition, and the cuttings almost didn't disperse in the fluid, its recovery rate can reach more than 90%, the average ratio of hole enlargement is less than 4%. The drilling fluid system has excellent rheology, and is easy to maintain, and can satisfy the requirement of sand-carrying. In addition to these, the system has a prominent effect of protecting oil layer, and the average HTHP filtration rate of the target zone is 13.26mL,the core permeability recovery value reach more than 75%. The core permeability recovery value reach more than 90% when the polluted cores are removed. The effects of oil test in test wells are very good, among which Gang 561K Well is a flowing well with high output, and daily crude oil production reaches 55.08t .
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