Abstract: A three-stage, hybrid solvent and water injection process is provided for the enhanced oil recovery from an oil-bearing formation. The three-stage process includes the sequential steps of: (i) injecting part of a selected total amount of solvent into the formation in a "single slug" injection stage, (ii) injecting the remainder of the total amount of solvent with water into the formation, in a water-alternating-gas (WAG) injection process, and (iii) injecting water into the formation until the water content in the produced mixture of oil and water reaches at least about 90 percent. The process includes deriving, for the selected total amount of solvent, a relationship between different first injection stage amounts of solvent and corresponding projected incremental oil recovery rates and selecting from such relationship the part of the solvent to be injected in the single slug injection stage.

Abstract: A method for tagging an oil so that subsequently it may be identified as to source by incorporating into the oil as a tracer material an oil-soluble or oil-dispersible Group VIB, Group VIIB or lanthanum series rare earth metal salt of a fatty acid. The so-tagged oil may be utilized in any desired manner. Thereafter, an oil suspected to contain at least a portion of the so-tagged oil is analyzed for the presence of the added metal moiety. The method is especially useful in tracing a complex oleaginous and petroliferous material so that it may be recovered and identified following a theft or spill or to trace the flow of such oil injected through a subterranean reservoir.