Polymer/Surfactant Transport in Micellar Flooding

1981 ◽  
Vol 21 (05) ◽  
pp. 603-612 ◽  
Author(s):  
C.S. Chiou ◽  
G.E. Kellerhals
Keyword(s):  
Porous Media ◽  
Phase Separation ◽  
Crude Oil ◽  
Phase Behavior ◽  
Xanthan Gum ◽  
Water Soluble ◽  
Mobility Control ◽  
Rich Phase ◽  
Surfactant Systems ◽  
Polymer Transport

Abstract For the surfactant formulations used (particular surfactant concentration, surfactant type, cosolvent type, cosolvent concentration, etc.), the results show that surfactant systems containing polymer as a mobility control agent may exhibit adverse polymer transport behavior during flow through porous media. Polymer generally lagged behind the surfactant even though the two species were injected simultaneously in the surfactant slug. This poor polymer transport definitely could have a detrimental effect on the efficiency of a micellar flooding process in the field. Phase studies show that when some surfactant systems containing xanthan gum are mixed with crude oil at various salinities, a polymer-rich, gel-like phase forms. The polymer lag phenomenon in core tests can be related to phase separation due to divalent cations generated in situ as a result of ion exchange with the clays and the surfactant. Introduction and Background Proper design for mobility control is important in micellar or surfactant flooding to maintain stable displacement and prevent or reduce viscous fingering. Generally, effective mobility control is obtained by having the mobility of the polymer drive less than the mobility of the surfactant slug and the mobility of the surfactant slug less than the mobility of the oil/water bank. Oil-external and aqueous surfactant systems are designed to attain mobility control by two distinct approaches. In the oil-external case, increases in viscosity (compared with water) are largely a result of the presence of oil and the relatively high concentration of surfactant in the slug. The viscosity of aqueous surfactant systems frequently is increased by the addition of a polymer, usually either xanthan gum or polyacrylamide. There are drawbacks to both of these approaches. Use of a hydrocarbon such as crude oil (in the surfactant slug) to increase viscosity may result in injectivity problems due to wax and/or asphaltenes in the crude oil.Trushenski investigated the effects of sulfonate, cosurfacant, water, and salt concentrations on sulfonate/polymer incompatibility (multiple phases may form when polymer solution dilutes with a sulfonate containing micellar fluid). In dynamic core tests, this phase separation may result in one phase being trapped in the porous media. For the sulfonate/cosurfactant system (Mahogany AA and isopropyl alcohol) used, the results of static phase studies correlated with the incidence of phase trapping in dynamic core tests. Trushenski concluded that increasing the concentration of cosurfactant or cosolvent in the surfactant and polymer slugs could eliminate or reduce sulfonate/polymer incompatibility. In his dynamic core tests, the absolute brine permeability of the Berea cores was characteristically about 500 md. Polymer type (polyacrylamide or polysaccharide) did not appear to affect phase behavior appreciably. He identified sulfonate/polymer incompatibility as a previously unreported source of sulfonate loss. Trushenski also concluded that invasion of a surfactant slug by a water-soluble polymer can be eliminated or minimized if the surfactant slug contains low concentrations of crude oil.Pope et al. studied the phase behavior of surfactant/brine/alcohol systems both with and without polymer. Some of their various combinations also were equilibrated with a synthetic oil consisting of n-octane or an n-octane/benzene mixture. Both anionic and nonionic polymers were used. At a sufficiently high sodium chloride concentration, the oil-free (no added oil) mixtures showed phase separation into an aqueous polymer-rich phase and an aqueous surfactant-rich phase. They termed the salinity at which phase separation occurred the critical electrolyte concentration. SPEJ P. 603^

Surfactant Retention in Berea Sandstone- Effects of Phase Behavior and Temperature

1982 ◽  
Vol 22 (06) ◽  
pp. 962-970 ◽  
Author(s):  
J. Novosad
Keyword(s):  
Porous Media ◽  
Crude Oil ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Liquid Interface ◽  
Divalent Ions ◽  
Surfactant Precipitation ◽  
Wide Range ◽  
Solid Liquid Interface ◽  
Solid Liquid

Novosad, J., SPE, Petroleum Recovery Inst. Abstract Experimental procedures designed to differentiate between surfactant retained in porous media because of adsorption and surfactant retained because Of unfavorable phase behavior are developed and tested with three types of surfactants. Several series of experiments with systematic changes in one variable such as surfactant/cosurfactant ratio, slug size, or temperature are performed, and overall surfactant retention then is interpreted in terms of adsorption and losses caused by unfavorable phase behavior. Introduction Adsorption of surfactants considered for enhanced oil recovery (EOR) applications has been studied extensively in the last few years since it has been shown that it is possible to develop surfactant systems that displace oil from porous media almost completely when used in large quantities. Effective oil recovery by surfactants is not a question of principle but rather a question of economics. Since surfactants are more expensive than crude oil, development of a practical EOR technology depends on how much surfactant can be sacrificed economically while recovering additional crude oil from a reservoir.It was recognized earlier that adsorption may be only one of a number of factors that contribute to total surfactant retention. Other mechanisms may include surfactant entrapment in an immobile oil phase surfactant precipitation by divalent ions, surfactant precipitation caused by a separation of the cosurfactant from the surfactant, and surfactant precipitation resulting from chromatographic separation of different surfactant specks. The principal objective of this work is to evaluate the experimental techniques that can be used for measuring surfactant adsorption and to study experimentally two mechanisms responsible for surfactant retention. Specifically, we try to differentiate between the adsorption of surfactants at the solid/liquid interface and the retention of the surfactants because of trapping in the immobile hydrocarbon phase that remains within the core following a surfactant flood. Measurement of Adsorption at the Solid/Liquid Interface Previous adsorption measurements of surfactants considered for EOR produced adsorption isotherms of unusual shapes and unexpected features. Primarily, an adsorption maximum was observed when total surfactant retention was plotted against the concentration of injected surfactant. Numerous explanations have been offered for these peaks, such as a formation of mixed micelles, the effects of structure-forming and structurebreaking cations, and the precipitation and consequent redissolution of divalent ions. It is difficult to assess which of these effects is responsible for the peaks in a particular situation and their relative importance. However, in view of the number of physicochemical processes taking place simultaneously and the large number of components present in most systems, it seems that we should not expect smooth monotonically increasing isotherms patterned after adsorption isothemes obtained with one pure component and a solvent. Also, it should be realized that most experimental procedures do not yield an amount of surfactant adsorbed but rather a measure of the surface excess.An adsorption isotherm, expressed in terms of the surface excess as a function of an equilibrium surfactant concentration, by definition must contain a maximum if the data are measured over a sufficiently wide range of concentrations. SPEJ P. 962^

Favorable Attributes of Alkaline-Surfactant-Polymer Flooding

SPE Journal ◽  
2008 ◽  
Vol 13 (01) ◽  
pp. 5-16 ◽  
Author(s):  
Shunhua Liu ◽  
Danhua Zhang ◽  
Wei Yan ◽  
Maura Puerto ◽  
George J. Hirasaki ◽  
...  
Keyword(s):  
Crude Oil ◽  
Phase Behavior ◽  
Anionic Surfactants ◽  
Naphthenic Acids ◽  
Mobility Control ◽  
Alkaline Solutions ◽  
Synthetic Surfactant ◽  
Optimal Salinity ◽  
Interfacial Tensions ◽  
Alkaline Surfactant Polymer

Summary A laboratory study of the alkaline-surfactant-polymer (ASP) process was conducted. It was found from phase-behavior studies that for a given synthetic surfactant and crude oil containing naphthenic acids, optimal salinity depends only on the ratio of the moles of soap formed from the acids to the moles of synthetic surfactant present. Adsorption of anionic surfactants on carbonate surfaces is reduced substantially by sodium carbonate, but not by sodium hydroxide. The magnitude of the reduction with sodium carbonate decreases with increasing salinity. Particular attention was given to a surfactant blend of a propoxylated sulfate having a slightly branched C16-17 hydrocarbon chain and an internal olefin sulfonate. In contrast to alkyl/aryl sulfonates previously considered for EOR, alkaline solutions of this blend containing neither alcohol nor oil were single-phase micellar solutions at all salinities up to approximately optimal salinity with representative oils. Phase behavior with a west Texas crude oil at ambient temperature in the absence of alcohol was unusual in that colloidal material, perhaps another microemulsion having a higher soap content, was dispersed in the lower-phase microemulsion. Low interfacial tensions existed with the excess oil phase only when this material was present in sufficient amount in the spinning-drop device. Some birefringence was observed near and above optimal conditions. While this phase behavior is somewhat different from the conventional Winsor phase sequence, overall solubilization of oil and brine for this system was high, leading to low interfacial tensions over a wide salinity range and to excellent oil recovery in both dolomite and silica sandpacks. The sandpack experiments were performed with surfactant concentrations as low as 0.2 wt% and at a salinity well below optimal for the injected surfactant. It was necessary that sufficient polymer be present to provide adequate mobility control, and that salinity be below the value at which phase separation occurred in the polymer/surfactant solution. A 1D simulator was developed to model the process. By calculating transport of soap formed from the crude oil and injected surfactant separately, it showed that injection below optimal salinity was successful because a gradient in local soap-to-surfactant ratio developed during the process. This gradient increases robustness of the process in a manner similar to that of a salinity gradient in a conventional surfactant process. Predictions of the simulator were in excellent agreement with the sandpack results. Background Although both injection of surfactants and injection of alkaline solutions to convert naturally occurring naphthenic acids in crude oils to soaps have long been suggested as methods to increase oil recovery, key concepts such as the need to achieve ultralow interfacial tensions and the means for doing so using microemulsions were not clarified until a period of intensive research between approximately 1960 and 1985 (Reed and Healy 1977; Miller and Qutubuddin 1987; Lake 1989). Most of the work during that period was directed toward developing micellar-polymer processes to recover residual oil from sandstone formations using anionic surfactants. However, Nelson et al. (1984) recognized that in most cases the soaps formed by injecting alkali would not be at the "optimal" conditions needed to achieve low tensions. They proposed that a relatively small amount of a suitable surfactant be injected with the alkali so that the surfactant/soap mixture would be optimal at reservoir conditions. With polymer added for mobility control, the process would be an alkaline-surfactant-polymer (ASP) flood. The use of alkali also reduces adsorption of anionic surfactants on sandstones because the high pH reverses the charge of the positively charged clay sites where adsorption occurs. The initial portion of a Shell field test, which did not use polymer, demonstated that residual oil could be displaced by an alkaline-surfactant process (Falls et al. 1994). Several ASP field projects have been conducted with some success in recent years in the US (Vargo et al. 2000; Wyatt et al. 2002). Pilot ASP tests in China have recovered more than 20% OOIP in some cases, but the process has not yet been applied there on a large scale (Chang et al. 2006).

Surfactant Phase Behavior and Retention in Porous Media

1979 ◽  
Vol 19 (03) ◽  
pp. 183-193 ◽  
Author(s):  
C.J. Glover ◽  
M.C. Puerto ◽  
J.M. Maerker ◽  
E.L. Sandvik
Keyword(s):  
Porous Media ◽  
Phase Behavior ◽  
Surfactant Concentration ◽  
Divalent Cations ◽  
Reservoir Rock ◽  
Residual Oil ◽  
Optimal Salinity ◽  
Interfacial Tensions ◽  
Production Research ◽  
Surfactant Systems

Glover, C.J.,* SPE-AIME, Exxon Production Research Puerto, M.C., SPE-AIME, Puerto, M.C., SPE-AIME, Exxon Production Research Co. Maerker, J.M., SPE-AIME, Exxon Production Research Co. Sandvik, E.L., SPE-AIME, Exxon Production Research Co. Abstract Surfactant retention in reservoir rock is a major factor limiting effectiveness of oil recovery using microemulsion flooding processes. Effects of salinity and surfactant concentration on microemulsion phase behavior have a significant impact on relative phase behavior have a significant impact on relative magnitudes of retention attributed to adsorption vs entrapment of immiscible microemulsion phases.Surfactant retention levels were determined by effluent sample analyses from microemulsion flow tests in Berea cores. Data for single surfactant systems containing NaCl only and multicomponent surfactant systems containing monovalent and divalent cations are included. Retention is shown to increase linearly with salinity at low salt concentrations and depart from linearity with higher retentions above a critical salinity. This departure from linearity is shown to correlate with formation of upper-phase microemulsions. The linear trend, therefore, is attributed to surfactant adsorption, and retention levels in excess of this trend are attributed to phase trapping.Divalent cations are shown to influence microemulsion phase behavior strongly through formation of divalent-cation sulfonate species. A useful method for predicting phase behavior in systems containing divalent cations is described. This method combines equilibrium expressions with a relationship defining the contribution of each surfactant component to optimal salinity. Observed experimental data are compared with predicted data. Introduction Two essential criteria that must be met for successful recovery of residual oil by chemical flooding arevery low interfacial tensions between the chemical bank and residual oil and between the chemical bank and drive fluid andsmall surfactant retention losses to reservoir rock. If retention is excessive, interfacial tensions eventually will become high enough to retrap residual oil in the remainder of the reservoir.Previous studies have described several mechanisms responsible for surfactant retention in porous media. These include adsorption, porous media. These include adsorption, precipitation, partitioning into a residual oil phase, precipitation, partitioning into a residual oil phase, and entrapment of immiscible microemulsion phases. Of particular interest is Trushenski's discussion of microemulsion phase trapping as a consequence of surfactant-polymer interaction, and a supporting statement that similar behavior often was observed when microemulsions were diluted with polymer-free brine. Here, we attempt to provide some understanding of this surfactant dilution phenomenon by examining phase behavior as a function of salinity, divalent-ion content, and surfactant concentration. Experimental Procedures Surfactant Systems Two surfactant systems were used in this study. (Specific microemulsion compositions are discussed later.) One system was the 63:37 volumetric mixture of the monoethanol amine salt of dodecylorthoxylene sulfonic acid and tertiary amyl alcohol (MEAC12OXS/TAA) described by Healy et al. The oil component for these microemulsions was a mixture of 90% Isopar M TM and 10% Heavy Aromatic Naptha.(TM)** The brine contained NaCl only. SPEJ P. 183

Use of Perspective Plots To Aid in Determining Factors Affecting Interfacial Tensions Between Surfactant Solutions and Crude Oil

1982 ◽  
Vol 22 (03) ◽  
pp. 350-352
Author(s):  
G.E. Kellerhals
Keyword(s):  
Crude Oil ◽  
Aqueous Phase ◽  
Oil Recovery ◽  
Surfactant Concentration ◽  
Reservoir Rock ◽  
Surfactant Flooding ◽  
Rich Phase ◽  
Interfacial Tensions ◽  
Surfactant Systems ◽  
The Impact

Abstract In surfactant flooding, low interfacial tensions (IFT's) are required for recovery of additional significant quantities of crude oil from a reservoir rock. This paper indicates the usefulness of perspective plots to facilitate comparison of sets of IFT data. Such perspective plots simplify the process of screening various surfactant systems for enhanced oil recovery. Introduction Numerous articles have been written about the effects and/or importance of IFT between oil and aqueous phases in determining ultimate oil recovery during a phases in determining ultimate oil recovery during a secondary (waterflooding) or tertiary oil-recovery process. In the area of micellar/polymer or surfactant process. In the area of micellar/polymer or surfactant flooding, IFT has been studied extensively both by industrial and by academic investigators. A simplistic summary of this work is that low IFT's (generally corresponding to high capillary numbers ( are required for recovery of additional significant quantities of crude oil from a reservoir rock. Method Development Several variables influence between an oil-rich phase and a surfactant-containing aqueous phase. During phase and a surfactant-containing aqueous phase. During a surfactant flood, variations in surfactant concentration and salt concentration will occur as a result of mixing of the chemical slug with the pre flush (or formation brine) and polymer drive (" rear mixing" ). Nelson investigated salt concentrations required during a chemical flood to achieve efficient oil displacement. Since these variables (and others) change during the progress of a flood, it is desirable to determine the impact of these changes on the IFT between the oil- and water-rich phases. To assess the importance of changes in these two key variables (surfactant concentration and salinity) on IFT, an x-y plot may be constructed with values of each variable along the axes. The IFT for a particular surfactant concentration and salinity then is obtained experimentally and the numerical value placed at the corresponding (x, y) point on the plot. The resultant figure/table can be referred to as an IFT map. Points of equal, or about equal, IFT can be connected to produce an IFT contour map. In the investigation of the effect(s) of temperature on a given surfactant system and crude oil, IFT maps might be constructed for each of the pertinent temperatures. IFT's might be determined at six different sodium chloride concentrations (e.g., 1.0, 1.5, 2.0, 3.0, 4.0, and 5.0 wt%) and four surfactant concentrations (e.g., 0.085, 0.064, 0.042, and 0.021 meq/mL), resulting in IFT maps (for each temperature) each consisting of 24 IFT values. A comparison of the values of one map to the values of a second map (measurements made at different temperature) then is required to determine the impact of the temperature change. A single value for IFT for a given salinity and surfactant concentration assumes that the system is two-phase, because two IFT's can be measured for a three-phase system consisting of an oil-rich phase, a water-rich phase, and a microemulsion phase. phase. A method to allow easier comparison for the relatively large number of IFT data points that may be obtained during the study/screening of various surfactant systems at various conditions is described in this paper. The technique consists of interpolating between IFT values and then plotting the data with a perspective plotting routine. The method allows comparisons of IFT values for different crude oils, temperatures, cosolvent types, surfactant types, hardness ion concentrations, etc., through visual scanning of a perspective plot ranter than through trying to judge or compare numerical IFT values of an IFT map. SPEJ p. 350

Flow of Hydrophobically Modified Water-Soluble Polymers in Porous Media: Controlled Resistance Factors vs. Flow-Induced Gelation in the Semidilute Regime

SPE Journal ◽  
2012 ◽  
Vol 17 (04) ◽  
pp. 1196-1206 ◽  
Author(s):  
Guillaume Dupuis ◽  
David Rousseau ◽  
René Tabary ◽  
Bruno Grassl
Keyword(s):  
Porous Media ◽  
Oil Recovery ◽  
Membrane Filtration ◽  
Water Soluble ◽  
Mobility Control ◽  
Throat Radius ◽  
Water Soluble Polymers ◽  
Resistance Factors ◽  
Soluble Polymers ◽  
Hydrophobically Modified

Summary The associative properties of hydrophobically modified water soluble polymers (HMWSPs) are attractive for improved oil recovery (IOR) because of both their enhanced thickening capability, compared with classical water-soluble polymers (for mobility-control applications), and their permeability-reduction, or plugging, ability (for well-treatment applications). In previous works, we have studied the injectivity of HMWSP made of sulfonated polyacrylamide backbones and alkyl side chains in the dilute regime and have shown, in particular, that it was largely governed by adsorption. In this paper, we report new experimental data on the injectivity of the same class of HMWSP solutions in the semidilute regime. From membrane filtration tests at imposed flow rate, we have first observed the formation of a filter cake made of HMWSP physical gel, which remained largely permeable to polymers. Our observations are compatible with the creation of channels within the gel. This leads to a gel-filtration process, entailing modifications of the solution's viscosimetric properties, which can be explained by a rearrangement of the intra- and interchain hydrophobic bonds in the solution. The second part of our work consisted of injectivity tests in model granular packs. We have performed comparative experiments in porous media with variable permeabilities, but at the same shear rate in the pore throats. Results show that, above a critical permeability kC, or a critical pore-throat radius rpC, HMWSP injection led to stable resistance factors, with values close to the solution's viscosity, and that, at less than kC or rpC the very high resistance factors observed suggest that flow-induced gelation of the HMWSP takes place. Furthermore, resistance factors measured over the core internal sections are compatible with an in-depth formation of the gel. These insights could be of use for designing HMWSP better suited to mobility-control operations and for tuning HMWSP-injection conditions for profile/conformance-control operations.

Influence of Polymer-Molecule/Wall Interactions on Mobility Control

1981 ◽  
Vol 21 (05) ◽  
pp. 613-622 ◽  
Author(s):  
J.L. Duda ◽  
E.E. Klaus ◽  
S.K. Fan
Keyword(s):  
Porous Media ◽  
Shear Rate ◽  
Pore Volume ◽  
Xanthan Gum ◽  
Mobility Control ◽  
Permeability Reduction ◽  
Polymer Flow ◽  
Inaccessible Pore Volume ◽  
Wall Interactions ◽  
Low Shear

Abstract This paper presents the results of a study of molecule/wall interactions on permeability modification of consolidated porous media by polymer solutions. The experiments were conducted with a newly developed low-shear porous media viscometer. This is a simple-to-use, versatile instrument that is particularly useful for measurements at the low shear rates characteristic of reservoir flooding. The key for obtaining reproducible, steadystate results was to expose the porous medium to several hundred pore volumes of polymer solution to saturate it with polymer. The effective permeability during polymer flow and the residual permeability were determined for xanthan gum and polyacrylamide solutions in Berea sandstone, Bradford sandstone, filter papers, and Nuclepore filters. A mechanistic interpretation of the coupling of adsorption, mechanical entrapment, shear rate, and inaccessible pore volume effects on the effective and residual permeabilities was developed. This is the first study to show that inaccessible pore volume can influence the residual permeability significantly. Introduction Solutions of high-molecular-weight polymers are being used as modified waterfloods and to control the mobility of the waterflood that follows the chemical slug in enhanced oil recovery. Currently, two distinctly different polymers are used most commonly for this application. The most popular mobility-control polymer is partially hydrolyzed polyacrylamide. This polyelectrolyte is sensitive to electrolytes and is susceptible to mechanical degradation. The second most frequently used mobility-control polymer is a polysaccharide called xanthan gum. This biopolymer is produced by a fermentation process and is less sensitive to electrolytes and shear degradation than polyacrylamide. Polyacrylamide increases the viscosity of aqueous solutions and causes changes in the permeability of porous media by adsorption and mechanical entrapment in pores whose dimensions are the same order of magnitude as the dimensions of the polymer in solutions. Numerous investigators have shown that polyacrylamide reduces the permeability of porous media during flow and that some of this permeability reduction is permanent. It generally is considered that xanthan gum reduces the mobility of a solution in porous media mainly by increasing the viscosity of the solution and that the action of the xanthan gum on the permeability is insignificant.The purpose of this study is to investigate the influence of polymer-molecule/wall interactions on mobility control. This investigation uses studies on the flow of xanthan gum and polyacrylamide solutions in various kinds of porous media with a wide range of characteristics. Although the permeability modification caused by xanthan gum molecules is not as pronounced as that caused by polyacrylamide, the polymer/wall interactions with this biopolymer are significant. Results of permeability-reduction studies during polymer flow and the residual permeability reduction as functions of shear rate, initial permeability, hydrodynamic size of polymer molecule in solution, electrolyte (NaCl) concentration, polymer concentration, and porous media characteristics are reported. The experiments were conducted with a newly developed low-shear porous media viscometer. Permeability modifications during and after polymer flow can be determined accurately with this simple instrument that eliminates the need for pumps and pressure measuring devices. The results of this investigation have been used to develop a mechanistic interpretation for the influence of molecule/wall interactions on mobility, which incorporates adsorption, mechanical entrapment, shear rate, and inaccessible pore volume effects. SPEJ P. 613^

Foamlike Dispersions for Mobility Control in CO2 Floods

1985 ◽  
Vol 25 (04) ◽  
pp. 603-613 ◽  
Author(s):  
John P. Heller ◽  
Cheng Li Lien ◽  
Murty S. Kuntamukkula
Keyword(s):  
High Pressure ◽  
Porous Media ◽  
New Mexico ◽  
Crude Oil ◽  
Mobility Control ◽  
Field Conditions ◽  
Reservoir Rock ◽  
Research Center ◽  
Displacement Efficiency ◽  
Foam Flow

Heller, John P., SPE, New Mexico Petroleum Recovery Research Center Petroleum Recovery Research Center Lien, Cheng Li, SPE, New Mexico Petroleum Recovery Research Center, Kuntamukkula, Murty S., SPE, New Mexico Petroleum Recovery Research Center Petroleum Recovery Research Center AUGUST 1985 Abstract At the reservoir temperature and pressure at which CO2 can displace a crude oil with high microscopic-displacement efficiency, its density and compressibility are close to those of the crude oil-and not greatly different from those of water itself. Because of this, the mechanical and chemical characteristics of a high-pressure, CO2-in-water "foam" cannot be assumed to be the same as those of an air/water foam at near-atmospheric pressure. pressure. This paper reports information on the mobility of foamlike dispersions in reservoir rock. The data come both from the recalculation of selected experimental work reported in the literature and from new experiments. An important criterion for these experiments is to eliminate or greatly reduce the influence of fluid compressibility, so as to approximate field conditions in CO2 floods more closely. The core flow experiments performed for this work meet this condition by use of the nonaqueous phase of either liquid CO2 at high pressure, or a light hydrocarbon to simulate dense CO2 in experiments performed at low pressure. We postulate that to be effective in retarding the growth of fingers or other instability patterns in CO2 floods while maintaining a high microscopic displacement efficiency, a foamlike dispersion of dense CO2 in surfactant/water should have the following characteristics. 1. Its aqueous-phase content should be as low as possible, to minimize oil trapping and to permit maximum possible, to minimize oil trapping and to permit maximum contact between CO2 and the crude oil. 2. Its effective mobility in the reservoir rock should be adjustable, by some parameters accessible during its generation, to about that of the oil bank it is expected to form and to displace. Introduction Since the classical flow and model experiments, and calculations of the 1950's and 1960's, it has been well known that adverse mobility ratio prevents the attainment of high areal sweep efficiencies in both miscible and immiscible displacements. The mechanism responsible for this is the formation of "fingers" of an unstable displacement front, which leads to early breakthrough and lowered oil production rates. The only apparent remedy is to thicken or to decrease the mobility of the injected fluids. An early suggestion along this line was to use foams to displace the oil. Several dozen papers over the intervening years have studied this idea further in both laboratory and field, and there is general agreement that the method holds great promise for selected plugging or diversion of flow from high-permeability streaks. Although the literature points out that large pressure drops ate required to move foam through porous media, and although this is very promising for mobility control, serious questions remain unresolved for that application. One such problem is that in most of the reported experiments, considerable expansion in volume occurred over the length of the flow system. Thus, it is difficult to separate the effects of the foam's compressibility from its inherent flow-resisting properties. An even more fundamental question concerns the mechanism of foam flow itself and the task of describing it quantitatively. We reject the idea that a useful description can be given in terms of a "foam viscosity" as measured in any standard viscometer. To explain this view, and to justify a more modest description in terms only of measurable quantities, we present a section on the rheological background of the problem. problem. This work is directed specifically toward the development of foamlike dispersions of dense CO2 in aqueous surfactant solutions for use in the control of mobility ratio in CO2 floods. We have searched the literature for applicable information, and have re-examined several studies of foam flow in porous media. In most cases the given results have been recalculated to cast them all into a common form that, it is hoped, offers a basis for calculation of the pressure gradients associated with foam flow in a reservoir. This paper also contains the results of original, steady-state experiments, performed under approximate field conditions and designed to permit the calculation of the mobility of foam-like dispersions of CO2 in reservoir rock. Finally, some general conclusions are drawn concerning the use of such foams for mobility control. Rheological Background The concept of "viscosity" to represent the resistance offered by a fluid to continuous deformation under the influence of shearing force has been a cornerstone of classical fluid mechanics and is of paramount importance in engineering practice involving fluid flow. The viscosity of a fluid is given by the ratio of shear stress to the rate of shear and is generally a strong function of temperature and weakly dependent on pressure. SPEJ p. 603

Interfacial Tension and Phase Behavior of Surfactant Systems

1978 ◽  
Vol 18 (04) ◽  
pp. 242-252 ◽  
Author(s):  
W.H. Wade ◽  
James C. Morgan ◽  
R.S. Schechter ◽  
J.K. Jacobson ◽  
J.L. Salager
Keyword(s):  
Molecular Weight ◽  
Interfacial Tension ◽  
Crude Oil ◽  
Phase Behavior ◽  
Oil Recovery ◽  
Surfactant Concentration ◽  
Low Molecular Weight ◽  
Middle Phase ◽  
Surfactant Systems ◽  
Low Tension

Abstract The conditions necessary for optimum low tension and phase behavior at high surfactant concentrations are compared with those required at low surfactant concentrations, where solubilization effects are not usually visible. Major differences in tension behavior between the high and low concentration systems may be observed when the surfactant used contains a broad spectrum of molecular species, or if a higher molecular weight alcohol is present, but not otherwise in the systems studied. We compared the effects of a number of aliphatic alcohols on tension with phase behavior. An explanation of these results, and also of other observed parameter dependences, is proposed in terms of changes in surfactant chemical potential. Surfactant partitioning data is presented that supports this concept. Introduction Taber and Melrose and Brandner established that tertiary oil recovery by an immiscible flooding process should be possible at low capillary process should be possible at low capillary numbers. In practice, the required capillary number, which is a measure of the ratio of viscous to capillary forces governing displacement of trapped oil, may be achieved by lowering the oil/water interfacial tension to about 10(-3) dyne/cm, or less. Subsequent research has identified a number of surfactants that give tensions of this order with crude oils and hydrocarbon equivalents. Interfacial tension studies tended to fall into two groups. Work at low surfactant concentrations, typically 0.7 to 2 g/L, has established that a crude oil may be assigned an equivalent alkane carbon number. Using pure alkanes instead of crude oil has helped the study of system parameters affecting low tension behavior. Important parameters examined include surfactant molecular structure, and electrolyte concentration, surfactant concentration, surfactant molecular weight, and temperature. At higher surfactant concentrations, interfacial tension has been linked to the phase behavior of equilibrated systems. When an aqueous phase containing surfactant (typically 30 g/L), electrolyte, and low molecular weight alcohol is equilibrated with a hydrocarbon, the surfactant may partition largely into the oil phase, into the aqueous phase, or it may be included in a third (middle) phase containing both water and hydrocarbon. Low interfacial tensions occur when the solubilization of the surfactant-free phase (or phases) into the surfactant-containing phase is maximized. Maximum solubilization and minimum tensions have been shown to be associated with the formation of a middle phase. Both the high and low surfactant concentration studies have practical importance because even though a chemical flood starts at high concentration, degradation of the injected surfactant slug will move the system toward lower concentrations. This study investigates the relationship between tension minima found with low concentration systems, and low tensions found with equivalent systems at higher surfactants concentrations, particularly those in which third-phase formation occurs. Many of the systems studied here contain a low molecular weight alcohol, as do most surfactant systems described in the literature or proposed for actual oil recovery. Alcohol originally was added to surfactant systems to help surfactant solubility, but can affect tensions obtained with alkanes, and with refined oil. Few systematic studies of the influence of alcohol on tension behavior exist. Puerto and Gale noted that increasing the alcohol Puerto and Gale noted that increasing the alcohol molecular weight decreases the optimum salinity for maximum solubilization and lowest tensions. The same conclusions were reached by Hsieh and Shah, who also noted that branched alcohols had higher optimum salinities than straight-chain alcohols of the same molecular weight. Jones and Dreher reported equivalent solubilization results with various straight- and branched-chain alcohols. In this study, we fix the salinity of each system and instead vary the molecule; weight of the hydrocarbon phase. SPEJ P. 242

Recent Advances in Surfactant EOR

SPE Journal ◽  
2011 ◽  
Vol 16 (04) ◽  
pp. 889-907 ◽  
Author(s):  
George J. Hirasaki ◽  
Clarence A. Miller ◽  
Maura Puerto
Keyword(s):  
Phase Separation ◽  
Crude Oil ◽  
Oil Recovery ◽  
Surfactant Solution ◽  
Naphthenic Acids ◽  
Mobility Control ◽  
Wettability Alteration ◽  
Recent Advances ◽  
Carbonate Formations

Summary In this paper, recent advances in surfactant enhanced oil recovery (EOR) are reviewed. The addition of alkali to surfactant flooding in the 1980s reduced the amount of surfactant required, and the process became known as alkaline/surfactant/polymer flooding (ASP). It was recently found that the adsorption of anionic surfactants on calcite and dolomite can also be significantly reduced with sodium carbonate as the alkali, thus making the process applicable for carbonate formations. The same chemicals are also capable of altering the wettability of carbonate formations from strongly oil-wet to preferentially water-wet. This wettability alteration in combination with ultralow interfacial tension (IFT) makes it possible to displace oil from preferentially oil-wet carbonate matrix to fractures by oil/water gravity drainage. The alkaline/surfactant process consists of injecting alkali and synthetic surfactant. The alkali generates soap in situ by reaction between the alkali and naphthenic acids in the crude oil. It was recently recognized that the local ratio of soap/surfactant determines the local optimal salinity for minimum IFT. Recognition of this dependence makes it possible to design a strategy to maximize oil recovery with the least amount of surfactant and to inject polymer with the surfactant without phase separation. An additional benefit of the presence of the soap component is that it generates an oil-rich colloidal dispersion that produces ultralow IFT over a much wider range of salinity than in its absence. It was once thought that a cosolvent such as alcohol was necessary to make a microemulsion without gel-like phases or a polymer-rich phase separating from the surfactant solution. An example of an alternative to the use of alcohol is to blend two dissimilar surfactants: a branched alkoxylated sulfate and a double-tailed, internal olefin sulfonate. The single-phase region with NaCl or CaCl2 is greater for the blend than for either surfactant alone. It is also possible to incorporate polymer into such aqueous surfactant solutions without phase separation under some conditions. The injected surfactant solution has underoptimum phase behavior with the crude oil. It becomes optimum only as it mixes with the in-situ-generated soap, which is generally more hydrophobic than the injected surfactant. However, some crude oils do not have a sufficiently high acid number for this approach to work. Foam can be used for mobility control by alternating slugs of gas with slugs of surfactant solution. Besides effective oil displacement in a homogeneous sandpack, it demonstrated greatly improved sweep in a layered sandpack.

Controlled Release of Metformin Hydrochloride I. In vitro Release from Physical Mixture Containing Xanthan Gum as Hydrophilic Rate Retarding Polymer

1970 ◽  
Vol 4 (1) ◽  
Author(s):  
Mashkura Ashrafi ◽  
Jakir Ahmed Chowdhury ◽  
Md Selim Reza
Keyword(s):  
Controlled Release ◽  
Xanthan Gum ◽  
In Vitro Release ◽  
Correlation Coefficients ◽  
High Ratio ◽  
Water Soluble ◽  
Metformin Hydrochloride ◽  
Model Drug ◽  
Very High

Capsules of different formulations were prepared by using a hydrophilic polymer, xanthan gum and a filler Ludipress. Metformin hydrochloride, which is an anti-diabetic agent, was used as a model drug here with the aim to formulate sustained release capsules. In the first 6 formulations, metformin hydrochloride and xanthan gum were used in different ratio. Later, Ludipress was added to the formulations in a percentage of 8% to 41%. The total procedure was carried out by physical mixing of the ingredients and filling in capsule shells of size ‘1’. As metformin hydrochloride is a highly water soluble drug, the dissolution test was done in 250 ml distilled water in a thermal shaker (Memmert) with a shaking speed of 50 rpm at 370C &plusmn 0.50C for 6 hours. After the dissolution, the data were treated with different kinetic models. The results found from the graphs and data show that the formulations follow the Higuchian release pattern as they showed correlation coefficients greater than 0.99 and the sustaining effect of the formulations was very high when the xanthan gum was used in a very high ratio with the drug. It was also investigated that the Ludipress extended the sustaining effect of the formulation to some extent. But after a certain period, Ludipress did not show any significant effect as the pores made by the xanthan gum network were already blocked. It is found here that when the metformin hydrochloride and the xanthan gum ratio was 1:1, showed a high percentage of drug release, i.e. 91.80% of drug was released after 6 hours. But With a xanthan gum and metformin hydrochloride ratio of 6:1, a very slow release of the drug was obtained. Only 66.68% of the drug was released after 6 hours. The percent loading in this case was 14%. Again, when Ludipress was used in high ratio, it was found to retard the release rate more prominently. Key words: Metformin Hydrochloride, Xanthan Gum, Controlled release capsule Dhaka Univ. J. Pharm. Sci. Vol.4(1) 2005 The full text is of this article is available at the Dhaka Univ. J. Pharm. Sci. website

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