Enhanced oil recovery from heterogeneous formations - by injecting graded sequence of 3 slugs contg. surfactants, opt. formed from the oil

摘要

A process for enhanced recovery of oil from a reservoir comprises sequential injection of the following slugs from an injection well: (i) a macroemulsion of 2-50 (pref. 10-30)% of crude oil and water with emulsifying cpds., to homogenise the flow from the injection well by increasing the flow resistance; (ii) an emulsion of crude oil and an aq. phase contg. a high concn. of surfactants as active slug to release oil from the formation; and (iii) an emulsion of crude oil and an aq. phase similar to that of (ii), to protect (ii) from dilution with water. Water is injected after (iii). The total vol. of (i)-(iii) is 5-50 (pref.10-30)% of the formation pore vol. Process is used in formations where water is much more mobile than oil, because of formation heterogeneity, high oil viscosity or high multivalent ion concn. More oil is released.