The goal of dilute surfactant flooding is to reduce the interfacial tension of the oil/water system to very low values in order to release the residual oil. The question then arises whether oil that would normally be produced by imbibition is lost as a result of such flooding; since the surfactant decreases or eliminates the capillary forces that underlie imbibition.To study the imbibition behaviour of surfactant solutions, we first focussed on miscible-fluid systems. Both theoretically and experimentally we have shown that miscible fluids can indeed be imbibed, depending on the affinity of the different fluids for the solid.These effects persist as long as equilibrium (complete mixing) has not been attained. A similar behaviour is expected for low-tension immiscible fluid systems.We present experimental results showing that indeed the (equilibrium) interfacial tension between model oils and surfactant solutions is not the driving force behind imbibition. For the surfactant systems studied, the conclusion is that lowering the interfacial tension has some effect on the imbibition rate but no effect on ultimate recovery.
Improvement of the steam-injection process by surfactants or foaming agents has already been demonstrated in field tests.However, surfactants for steam-foam operations that perform well in tests at low temperatures often fail above 200 °C. Laboratory research on steam-foam processes as a means of profile modification in soak wells has been carried out with the aim of alleviating the temperature limitation.First, the effect of surfactant structure was studied. As a result, sulphonates, both aliphatic and aromatic, were selected for further investigations. Besides critical parameters such as steam quality and surfactant concentration, the effects of a non-condensable gas and electrolyte were screened.It was found that, for steam-mobility reduction by in-situ foam generation, surfactant concentration and molecular weight are the overriding parameters.The thermal stability of the new products were studied in detail and the most economic supply formulation of these surfactants was identified. A product providing the best balance of all these aspects was tested in the field in soak wells on a large scale.The data collected on surfactant structure and molecular weight make it possible to select surfactants with excellent performance combined with long-term thermal stability. This will enable a successful extension of the steam-foam process towards the more extreme temperature conditions encountered in various fields in the world.
kBSTRACT INTRODUCTION Laboratory research on the steam-foam process as The effectiveness of steam injection into a heavy a means of reducing steam mobility in steam-injection oil reservoir can be increased by improving the aerial projects indicates that steam-foam formulations, which and vertical distribution of the steam. llsiscan be are effective in pilot tests at low steam accomplished by reducing the steam mobility; one temperatures, are not necessarily effective at method of doing this is to inject steam with foaming temperatures over 200~. agents' as currently appliad in various US projects.However, long-chain alkylaryl sulphonates exhibit In a steam-soak well the development of a steam an excellent capability for reducing steam mobility at tongue, reaching deep into a reservoir, is beneficial elevated temperature; furthermore, this class of for the activation of oil production mechanisms. surfactants is thermally stable. The performance of However, reservoirs often consist of several permeable steam foam with these surfactants has been studied in sands separated by ehale breaks. If steam is injected core-flow experiments at steam-injection tefrperatures into such a reservoir, steam injection wL1l often be representative of steam operations in the Tia Juana restricted to the top sand. 'lW.ssituation can be field, Venezuela and as a function of the following improved by reducing the steam mobility with foam, parameters: surfactant molecular weight and which will cause the steam-injection pressure to concentration, the presence of an electrolyte, the increase and the steam to be diverted to lower sands. addition of small amounts of a non-condensable gas, and steam quality. me surfactant molecular weight and Most of the experience gained so far with steam concentration appear to be the main parameters for foam in the USA is related to shallcw reservoirs where reducing steam mobility.pressures and temperatures are relatively low. However, in other areas, for example, the Tia Juana The laboratory research was followed by a pilot field in Venezuela, much higher pressures an3 Lest, operated by Flaraven,in the Tia 3aana field, in corresponding temperatures are used. Furthermore, in attempt to improve the injection profile in steam-steam qualities are different, varying from 50 to 60% 3oak wells.in the California fields, and from 80 to 90% in the L%e results obtained so far indicate the feasibility Tia Juana field. >f: . reducing the effective steam permeability, This paper deals with the joint research efforts plugging the most depleted layers, of Shell and Maraven on the mobility-reducing . diverting the injected steam to non-producing sands, capability of foaming agents for the high temperatures . enhancing oil production.prevailing in the Tia JUana field (21 bar, Zls"c). 3ased on the test results and operational conditions, the possibility of optirrdsingsteam-soak operations The laboratory work involved selecting a under Solivar coast conditions has been established. candidate surfactant and evaluating the steam...
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