Oil recovery using slug comprising aq. polymer soln. - of varying surfactant concn. and aq. drive fluid contg. solubilising agent

摘要

Oil is recovered from an underground formation which has an injection well and a prodn. well by (a) injecting a slug consisting of an aq. polymer soln. contg. a small amt. of a surfactant with an increase in the concn. of the surfactant as the slug is injected, (b) injecting water contg. a small amt. of a solubilising agent of formula (i) R-NR2-R1O(CH2CH2O)mA, (ii) R-NR3-R1O(CH2CH2O)mSO3A or (iii) R-NR4-R1O(CH2CH2O)nCH2CH2SO3A (where R is 1-16C alkyl, R1 is 2-4C alkylene, R2 is H, 1-16C alkyl or -R1O(CH2CH2O)mA; R3 is H, 1-16C alkyl or R1O(CH2CH2O)mSO3A; R4 is H, 1-16c alkyl or -R1O(CH2CH2O)nCH2CH2SO3A, A is H, Na, K or NH4, m = 4-60 and n = 4-60); and (c) recovering oil through the prodn. well. Pref. polymer is (hydrolysed) polyacrylamide or a polysaccharide. Interfacial tension between the water and the crude is decreased and fingering is inhibited.