Summary

Present crude oil prices are too low for the economic implementation of chemical EOR processes based on surfactants and polymers. However, considering recent progress made in use of surfactants, polymers, and alkalis in a synergistic way, it appears that significant improvements can be made in the efficiency/cost ratio of the process, which could make it attractive within a more favorable oilprice context. To illustrate this, the method used in developing the process is applied to a field case characterized by some properties not really suitable for chemical processes (i.e., a high clay content that magnifies ion exchange and related permeability effects, a pore-diameter distribution that prevents complete tertiary oil recovery, and an acid number that is not high enough to give substantial oil production when alkalis alone are used). Nevertheless, relatively reasonable performances have been obtained by combining the different chemicals.

In the first series of oil-recovery tests, the process was implemented conventionally with the aim of taking advantage of ion-exchange mechanisms. With an optimal micellar system, tertiary oil recovery did not exceed 50% original oil in place (OOIP). In a second series of tests, calcium ions contained in the connate water and those fixed on the clays were first removed by an alkaline solution. Then surfactants and polymer were injected, both with the same alkali. In this way, oil production was boosted to 70% OOIP, while the efficiency/ cost ratio was improved by a factor of 3. These performances were ascribed to low interfacial tensions (IFT's), appropriate mobility control, and a drastic reduction of surfactant and polymer retention. From these results, the alkali-surfactant-polymer process could be expected to be used in a wide range of field conditions and, in particular, with crude oils that do not necessarily have a high acid number.

Introduction

In a general price environment that has not been very favorable since 1986, with crude oil prices fluctuating at around $113/m3, chemical EOR processes have been progressively moving away from the petroleum companies' concerns; as a consequence, a spectacular drop in the number of field projects and in chemical EOR oil production has occurred. The technical cost of this extra oil, which depends mainly on the cost of chemicals, does not ensure the profitability of these processes in the present economic climate.

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