SWELLING INHIBITORS FOR CLAYS AND SHALES

Method for inhibiting the hydration of clays and shales during drilling operations comprising the use of a water base drilling fluid, which contains from 0.2 to 5% by weight of the condensation product of a dicarboxylic acid having 4 to 10 carbon atoms with alkanolamines, diamines or polyalkyleneamines of formula R'''R''N-R'-XH, where X is O or NR0; R0 is hydrogen or a linear or branched alkyl group having from 1 to 6 carbon atoms, R' is a linear or branched, aliphatic or cicloaliphatic alkylene group having from 2 to 10 carbon atoms or R' is R'''(NH-R''')n where R''' is ethylene or CH(CH3)CH2, n is a number from 1 to 6 and X is NR0; R'' and R''' can be equal or different from one another and are hydrogen or a linear or branched alkyl group having from 1 to 6 carbon atoms, optionally substituted with a hydroxyl group, the condensation product being in neutral form or in the form of salt.