Foam-enhanced oil recovery

An important and perspective application of foams is its use in petroleum and gas industries in drilling wells, in developing oil pools, in cleaning out wells from sand cork [142-148], in foam enhanced oil recovery (EOR) from underground formations [149-154]. 

In the following section we present results of our foam-enhanced oil recovery experiments in Berea Sandstone cores to assess the performance of the three a-olefin sulfonates discussed above. 

Tables 2 and 3 show the results of the foam-enhanced oil recovery tests for the constant pressure and the constant flow rate experiments respectively. The foam-enhanced oil recovery results from both sets of experiments are similar in that the recovery efficiency and gas bteakthrough time increased in the same order C 2 0S, AOS and C AOS.

Figure 13. Oil saturation during foam-enhanced oil recovery with...

Figure 16. Pressure data for foam-enhanced oil recovery with C AOS.

Our foam-enhanced oil recovery experiments in Berea Sandstones showed for the first time a striking correlation between basic foam... 

Interfacial tension is an important factor in chemical and physical processes involving a large interface, such as formation of emulsions, spreading of one liquid on another, wetting, foaming, enhanced oil recovery, and other processes of technical interest. Emulsification requires a low, near-zero, interfacial tension because a large interface has to be created. A low interfacial tension is a result of positive adsorption of the surfactant at the interface. The effect of a surfactant on interfacial tension depends on the extent of adsorption and the nature of the adsorbed film. 

An important application of foams arises in foam displacement, another means to aid enhanced oil recovery. The effectiveness of various foams in displacing oil from porous media has been studied by Shah and co-workers [237, 238]. The displacement efficiency depends on numerous physicochemical variables such as surfactant chain length and temperature with the surface properties of the foaming solution being an important determinant of performance. 

In addition to chemical synthesis and enhanced oil recovery, gaseous carbon dioxide is used in the carbonated beverage industry. Carbon dioxide gas under pressure is introduced into mbber and plastic mixes, and on pressure release a foamed product is produced. Carbon dioxide and inert gas mixtures rich in carbon dioxide are used to purge and fiH industrial equipment to prevent the formation of explosive gas mixtures. 

The use of AOS and other surfactants as steam-foaming agents has been studied by several oil companies in laboratories and in the field [55-62]. In the next section we will view olefinsulfonate structure-property relations [40] that have helped design optimum surfactants for enhanced oil recovery applications. 

Good thermal stability is a requirement for surfactants used in processes to enhance oil recovery. This applies most particularly to steam foam applications where surfactants such as AOS may be exposed to temperatures far above 100°C albeit for short times. Many authors have approached the problem of the thermal stability of a surfactant through a determination of the activation energy of the thermal degradation process. Once the activation energy is known, it can be used to estimate the rate of thermal degradation under various conditions. 

W. A. Rendall, C. Ayasse, and J. Novosad. Surfactant-stabilized foams for enhanced oil recovery. Patent US 5074358, 1991. 

Recent research and field tests have focused on the use of relatively low concentrations or volumes of chemicals as additives to other oil recovery processes. Of particular interest is the use of surfactants as CO (184) and steam mobility control agents (foam). Also combinations of older EOR processes such as surfactant enhanced alkaline flooding and alkaline-surfactant-polymer flooding have been the subjects of recent interest. Older technologies polymer flooding (185,186) and micellar flooding (187-189) have been the subject of recent reviews. In 1988 84 commercial products polymers, surfactants, and other additives, were listed as being marketed by 19 companies for various enhanced oil recovery applications (190). 

Foam is a promising fluid for achieving mobility control in underground enhanced oil recovery (1-3). Widespread application of this technology to, for example, steam, CO, enriched... 

By the addition of other liquid reservoirs, e.g. for water and crude oils, and replacement of the capillary test unit by a sand pack, the effectiveness of the same foams for enhanced oil recovery at reservoir temperatures and pressures will be investigated. 

The practical importance of monolayer formation is generally because of its relationship to reduction of surface tension. Air—water surface tension can affect such important phenomena as contact angle with a solid surface (affecting flotation), rate of wetting of a solid, or foaming (with applications in enhanced oil recovery or fire extinguishers), just to name a few. Reduction of air—water surface tension could, for example, cause a liquid to spread on a solid instead of beading up on it. 

This brief review has attempted to discuss some of the important phenomena in which surfactant mixtures can be involved. Mechanistic aspects of surfactant interactions and some mathematical models to describe the processes have been outlined. The application of these principles to practical problems has been considered. For example, enhancement of solubilization or surface tension depression using mixtures has been discussed. However, in many cases, the various processes in which surfactants interact generally cannot be considered by themselves, because they occur simultaneously. The surfactant technologist can use this to advantage to accomplish certain objectives. For example, the enhancement of mixed micelle formation can lead to a reduced tendency for surfactant precipitation, reduced adsorption, and a reduced tendency for coacervate formation. The solution to a particular practical problem involving surfactants is rarely obvious because often the surfactants are involved in multiple steps in a process and optimization of a number of simultaneous properties may be involved. An example of this is detergency, where adsorption, solubilization, foaming, emulsion formation, and other phenomena are all important. In enhanced oil recovery. 

Foams may contain not just gas and liquid (and usually surfactant), but also dispersed oil droplets and/or solid particles. Figure 1.5 shows a practical aqueous foam that contains dispersed oil droplets within the foam lamellae. This can occur, for example, when a foaming solution is used for detergent action in a cleaning process (see Section 12.2) or when a foam is propagated through an underground oil reservoir as part of an enhanced oil recovery process (See Section 11.2.2). 

Foams, in the form of froths, are intimately involved and critical to the success of many mineral-separation processes (Chapter 10). Foams may also be applied or encountered at all stages in the petroleum recovery and processing industry (oil-well drilling, reservoir injection, oil-well production and process-plant foams). A class of enhanced oil recovery process involves injecting a gas in the form of a foam. Suitable foams can be formulated for injection with air/nitrogen, natural gas, carbon dioxide, or steam [3,5]. In a thermal process, when a steam foam contacts residual crude oil, there is a tendency to condense and create W/O emulsions. Or, in a non-thermal process, the foam may emulsify the oil itself (now as an O/W emulsion) which is then drawn up into the foam structure the oil droplets eventually penetrate the lamella surfaces, destroying the foam [3], See Chapter 11. 

Micro-foam, or colloidal gas aphrons have also been reportedly used for soil flushing in contaminated-site remediation [494—498], These also have been adapted from processes developed for enhanced oil recovery (see Section 11.2.2.2). A recent review of surfactant-enhanced soil remediation [530] lists various classes of biosurfactants, some of which have been used in enhanced oil recovery, and discusses their performance on removing different type of hydrocarbons, as well as the removal of metal contaminants such as copper and zinc. In the latter area, the application of heavy metal ion complexing surfactants to remediation of landfill and mine leachate, is showing promise [541]. 

Any kind of dispersion that was useful in the reservoir may be, or may become, an undesirable dispersion when produced at a well-head. This could include used drilling fluid that has returned to the surface, conventional oil production that occurs in the form of a W/O emulsion, or foam from an enhanced oil-recovery process. These can present some immediate handling, process control, and storage problems. In addition, pipeline and refinery specifications place severe limitations on the water, solids, and salt contents of oil they will accept in order to avoid corrosion, catalyst poisoning, and process-upset problems. For pipeline transportation, an oil must usually contain less than 0.5% basic sediment and water (BS W). 

Enhanced oil recovery The process in which a foam is made to flow through an underground reservoir. The foam, which can either be generated on the surface and injected or generated in situ, is used to increase the drive fluid viscosity and improve its sweep efficiency. 

Heller, J.P. CO2 Foams in Enhanced Oil Recovery in Foams, Fundamentals and Applications in the Petroleum Industry, Schramm, L.L. (Ed.), American Chemical Society Washington, DC, 1994, pp. 201-234. 

Foam can be obtained also by simultaneous movement of liquid and gas in a tube, filled up with spherical particles (for example, polystyrene grains [46], beadpacks [49]), in coarse-pored medium [47] or movement through natural soil, such as sand packs) [48]. These ways of foam formation are used in modelling of enhanced oil recovery processes or controlling porous media permeability to gas [e.g. 48,50],... 

The stability of emulsion and foam films have also been found dependent upon the micellar microstructure within the film. Electrolyte concentration, and surfactant type and concentration have been shown to directly influence this microstructure stabilizing mechanism. The effect of oil solubilization has also been discussed. The preceding stabilizing/destabilizing mechanisms for three phase foam systems have been shown to predict the effectiveness of aqueous foam systems for displacing oil in enhanced oil recovery experiments in Berea Sandstone cores. 

T. "Enhanced Oil Recovery by COj Foam Flooding," Report, Contract No. DE-AC21-78MC03259 (February... 

Heller, J. P. "Reservoir Application of Mobility Control Foams in CO2 Floods, paper SPE/DOE 12644 presented at the SPE/DOE Fourth Joint Symposium on Enhanced Oil Recovery, Tulsa, Oklahoma, April 15-18, 1984. 

Foam exhibits higher apparent viscosity and lower mobility within permeable media than do its separate constituents.(1-3) This lower mobility can be attained by the presence of less than 0.1% surfactant in the aqueous fluid being injected.(4) The foaming properties of surfactants and other properties relevant to surfactant performance in enhanced oil recovery (EOR) processes are dependent upon surfactant chemical structure. Alcohol ethoxylates and alcohol ethoxylate derivatives were chosen to study techniques of relating surfactant performance parameters to chemical structure. These classes of surfactants have been evaluated as mobility control agents in laboratory studies (see references 5 and 6 and references therein). One member of this class of surfactants has been used in three field trials.(7-9) These particular surfactants have well defined structures and chemical structure variables can be assigned numerical values. Commercial products can be manufactured in relatively high purity. 

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