Smackover Nacatoch Crude Oil Separation of Surfactant Precursors and Their Effect on the Crude

1981 ◽  
Vol 21 (04) ◽  
pp. 493-499 ◽  
Author(s):  
J.H. Runnels ◽  
C.J. Engel
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Sodium Hydroxide ◽  
Aqueous Phase ◽  
Oil Recovery ◽  
Crude Oils ◽  
Gel Chromatography ◽  
Active Materials ◽  
Tertiary Oil Recovery ◽  
Surface Active

Abstract An procedure is given for separating surfactant precursors that occur in some crude oils. The effect of the precursors on the properties of the oils are described also. The separations were made by silica gel chromatography on crude oil from which the asphaltenes had been removed. The effect of the precursors on the properties of the crude was evaluated by blending the surfactant precursors into the original oil, a modified oil, or a hydrocarbon solvent such as benzene. Precursors activated and converted to surface active materials by a strong base such as sodium hydroxide are effective in reducing the interfacial tension between the oil and aqueous phase. Occurrence of precursors in crude oils is essential for improved oil recovery by the causticflood process. The procedure for separating the precursors should provide a viable means for evaluating the applicability of a causticflood tertiary oil recovery process to a particular crude or reservoir. Introduction Tertiary oil recovery by the causticflood process is inherently dependent on naturally occurring surfactant precursors in the crude. The surfactant precursors react with the caustic (base) in the floodwater to form surface active compounds that reduce the interfacial tension between the crude and aqueous phase, alter the wettability of the mineral surfaces, or reduce rigid film formation at the crude/aqueous interface. In laboratory oil-recovery tests, these mechanisms stimulate oil production characterized by increased production at caustic breakthrough and a high oil/water ratio after breakthrough. An early effort to identify the surfactant precursors in a Rio Bravo (CA) crude concluded that the surfactant precursors were related closely to the asphaltene and resin fractions of the crude. Subsequent studies using an Eichlingen Niedersachen (West German) crude and a Ventura (CA) crude concluded that the surfactant precursors were acids and phenols, respectively. The extensive work of Seifert established that the surfactant precursors of a Ventura crude were carboxylic acids and that the phenolic components of the crude were interfacially inactive. The purpose of our study was to develop a simple and practical method of separating surfactant precursors from crude oil and to evaluate their effect on the interfacial tension, acid number, and other properties of the crude. The separation technique was developed using Smackover Nacatoch crude and the surfactant precursors evaluated were obtained from the same crude. Description of Smackover Nacatoch Crude The Smackover reservoir is located in southern Arkansas, and the Nacatoch pay zone is the shallowest of five pay zones. The crude has an API gravity of 21 degrees, a viscosity of 160 cp at room temperature, and is produced from an unconsolidated sand formation about 2,000 ft deep. Preliminary studies showed that the interfacial tension between the crude and an aqueous phase was reduced from about 12 to 0.02 dyne/cm when the pH of the aqueous phase was increased from 7.0 to 12.5 with sodium hydroxide. The significant reduction in interfacial tension at higher pH's indicated that the crude contained a relatively high concentration of surfactant precursors that were converted to surface active materials by sodium hydroxide. SPEJ P. 493^

Competing Roles of Interfacial Tension and Surfactant Equivalent Weight in the Development of a Chemical Flood

1982 ◽  
Vol 22 (04) ◽  
pp. 472-480 ◽  
Author(s):  
S.L. Enedy ◽  
S.M. Farouq Ali ◽  
C.D. Stahl
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Oil Recovery ◽  
Salt Concentration ◽  
Surfactant Concentration ◽  
Evolutionary Process ◽  
Chemical Flooding ◽  
Equivalent Weight ◽  
Residual Oil ◽  
Tertiary Oil Recovery

Abstract This investigation focused on developing an efficient chemical flooding process by use of dilute surfactant/polymer slugs. The competing roles of interfacial tension (IFT) and equivalent weight (EW) of the surfactant used, as well as the effect of different types of preflushes on tertiary oil recovery, were studied. Volume of residual oil recovered per gram of surfactant used was examined as a function of these variables and slug size. Tertiary oil recovery increased with an increase in the dilute surfactant slug size and buffer viscosity. However, low IFT does not ensure high oil recovery. An increase in surfactant EW used actually can lead to a decrease in oil recovery. Tertiary oil recovery was also sensitive to preflush type. Reasons for the observed behavior are examined in relation to the surfactant properties as well as to adsorption and retention. Introduction Two approaches are being used in development of surfactant /polymer-type chemical floods:a small-PV slug of high surfactant concentration, ora large-PV slug of low surfactant concentration. This study deals with the latter-i.e., dilute aqueous slugs (with polymer added in many cases) containing less than or equal 2.0 wt% sulfonates and about 0. 1 wt% crude oil. Because the dilute slug contains little of the dispersed phase, an aqueous surfactant slug usually is unable to displace the oil miscibly; however, residual brine is miscible with the slug if the inorganic salt concentration is not excessive. The dilute, aqueous petroleum sulfonate slug lowers the oil/water IFT. overcoming capillary forces. This process commonly is referred to as locally immiscible oil displacement. Objectives The objective of this work was to develop an efficient dilute surfactant/polymer slug for the Bradford crude with a variety of sulfonate combinations. Effects of varying the slug characteristics such as equivalent weight, IFT, salt concentration, etc. on tertiary oil recovery were examined. Materials and Experimental Details The petroleum sulfonates and the dilute slugs used in this study are listed in Tables 1 and 2, respectively. The crude oil tested was Bradford crude 144 degrees API (0.003 g/cm3), 4 cp (0.004 Pa.s)]. The polymer solutions were prefiltered and driven by brines of various concentrations (0.02, 1.0, and 2.0% NACl). In many cases, the polymer was added to the slug. Conventional coreflood equipment described in Ref. 3 was used. Berea sandstone cores (unfired) 2 in, (5 cm) in diameter and 4 ft (1.3 m) in length were used for all tests, with a new core for each test. Porosity ranged from 19.3 to 21.0%, permeability averaged 203 md, and the waterflood residual oil saturation averaged 33.1%. IFT's were measured by the spinning drop method. Viscosities were measured with a Brookfield viscosimeter and are reported here for 6 rpm (0.1 rev/s). The dilute slugs containing polymer exhibited non-Newtonian behavior. Without polymer the behavior was Newtonian. Sulfonate concentration in the oleic phase was determined by an infrared spectrophotometer, while the concentration in the aqueous phase was measured by ultraviolet (UV) absorbance analysis. Discussion of Results Slug development in this investigation was an evolutionary process. Dilute slugs were developed and core tested in a sequential manner (Table 2). Slugs 100 through 200 yielded insignificant ternary oil recoveries (largely because of excessive adsorption and retention), but the results helped determine improvements in slug compositions and in the overall chemical flood. This paper gives results for the more efficient slugs only. SPEJ P. 472^

Interrelation of Crude Oil and Rock Properties With the Recovery of Oil by Caustic Waterflooding

1977 ◽  
Vol 17 (04) ◽  
pp. 263-270 ◽  
Author(s):  
Robert Ehrlich ◽  
Robert J. Wygal
Keyword(s):  
Crude Oil ◽  
Reservoir Rock ◽  
Rock Properties ◽  
Core Material ◽  
Crude Oils ◽  
Active Materials ◽  
Interfacial Tensions ◽  
X Ray ◽  
Recovery Mechanisms ◽  
Surface Active

Abstract This paper describes a series of laboratory caustic (NaOH) waterfloods and related measurements using crude oils from 19 oil reservoirs. These were light (mostly,>30 degrees API) crudes mainly from South Louisiana and Texas, although crude oils from other areas also were tested. The waterfloods held core material (Berea sandstone), connate water (2-percent-NaCl brine) and other conditions (temperature, flow rate, aging time before flood) constant, and determined increased production due to NaOH injection for each crude oil. Relative permeability end-points before and after flooding were used to estimate initial and final wettabilities and, together with crude-oil acid numbers and interfacial tensions against NaOH solution, to infer the probable mechanism by which increased recovery was obtained. A series of laboratory NaOH depletion measurements by static and dynamic methods in core material from several oil-producing formations and in Berea sandstone is also described. Results are compared with those from similar measurements using pure clays and other minerals and with X-ray diffraction analysis of the core material. The following are observations from these tests.Crude oils with acid numbers greater than about 0.1 to a 0.2 mg KOH per gm of oil or interfacial tension against 0.1 percent NaOH less than about 0.5 dyne/cm gave significant caustic-waterflood increased production. There was no further correlation of increased production at higher acid numbers or lower interfacial tensions nor was there a correlation with the apparent initial rock wettability.Regardless of initial wettability or increased production, the cores are indicated to be water-wet production, the cores are indicated to be water-wet following NaOH waterflooding to a high water-oil ratio (WOR).Caustic consumption by reservoir rock is predictable from the formation mineral composition predictable from the formation mineral composition as determined by X-ray methods. Exceptions are noted where clay content is high and where trace amounts of gypsum are present. Introduction Crude oils containing naturally occurring organic acids will react with aqueous caustic solution to produce surface-active materials. These surfactants, produce surface-active materials. These surfactants, when generated during a caustic waterflood, can improve oil recovery over that of a normal waterflood by a number of mechanisms related to changes occurring at the oil-water and liquid-solid interfaces: interfacial-tension lowering, wettability change, changes in interface rheology, etc. The extent to which any of these mechanisms will be operative and the recovery improvement obtainable depends on, among other things, the amount and type of acids present, the initial formation wettability, the reservoir-rock pore geometry, and the extent to which it consumes caustic. The available literature describing mechanisms proposed for caustic-waterflooding improved recovery, proposed for caustic-waterflooding improved recovery, the conditions required for applicability, and the results of various laboratory and field studies have been surveyed most recently by Johnson. Some common currents of thought or implication in this literature and some common areas of uncertainty related to the effects of crude oil and reservoir rock properties on recovery mechanisms are listed below. properties on recovery mechanisms are listed below.The presence of acids in crude oil at some minimum level is an obvious necessary condition for improved recovery. Where emulsification is involved, minimum acid numbers ranging from 0.5 to 1.5 mg KOH per gm of oil have been suggested. No minimum has been stated for other recovery mechanisms. One might not expect such minimum requirements to be absolute since the quality of surfactants generated from these acids can vary widely among crude oils.Improved recovery by wettability alteration generally has been discussed in terms of a reversal from oil-wet to water-wet or vice versa. It has been implied that wettability reversal is required since capillary forces trapping oil are eliminated as the neutral wettability condition is traversed. SPEJ P. 263

The Static and Dynamic Interfacial Tensions Between Crude Oils and Caustic Solutions

1983 ◽  
Vol 23 (04) ◽  
pp. 645-656 ◽  
Author(s):  
Edward M. Trujillo
Keyword(s):  
Sodium Chloride ◽  
Interfacial Tension ◽  
Mathematical Models ◽  
Sodium Hydroxide ◽  
Oil Recovery ◽  
Mass Action ◽  
Wettability Alteration ◽  
Crude Oils ◽  
Alkaline Solutions ◽  
Pendant Drop

Trujillo, Edward M.; SPE; Marathon Oil Co. Abstract One method to achieve EOR is chemical alteration of the reservoir environment so that previously trapped oil cam begin to flow freely. Under certain conditions, caustic or alkaline solutions can do this. The work reported here shows that interfacial tension (IFT) between various crudes and caustics increases with time because of desorption of the surface-active species from the interface. The desorption rate is temperature-dependent. Four kinds of crude oil were used-a California crude, a Wyoming crude, an Illinois crude, and an Alaska crude. Only with crude oils with a high concentration of crude acids, such as the California crude, is the ultralow IFT maintained for any reasonable period of time, namely 24 hours. The presence of calcium ions at concentrations of 200 ppm or more destroys the capability of caustic to reduce the IFT's, even for the California crude. Mass-action relationships are presented that describe the equilibrium IFT at constant ionic strength between crude oils and sodium hydroxide solutions as a function of pH and calcium. Techniques are presented for evaluating time-dependent IFT's obtained by the spinning- drop apparatus. A transient mathematical model shows that IFT can increase by several orders of magnitude over a period of several days. Good agreement between the model and experimental data is obtained. The parameters obtained from these mathematical models describe crude parameters obtained from these mathematical models describe crude reactivity to caustic more accurately than conventional crude acid numbers. The transient effects observed in the laboratory may or may not be significant in the field. Introduction Several investigators have studied the reaction of caustic with crude oils. In one of the earliest publications, Reisberg and Doscher in 1956 measured IFT's between a California crude and various sodium hydroxide solutions by the pendant-drop method. The IFT was lowered by a factor of 1,000 with a 0.5% NaOH solution but increased at higher and lower concentrations. The pendant-drop ages were on the order of 5 seconds. They observed a change pendant-drop ages were on the order of 5 seconds. They observed a change in IFT with time, but no model for such a change was proposed. Jennings et al. determined a minimum IFT with a North American crude at about 0.1% NaOH, also with the pendant-drop technique. Several of their values were too low to be mea.sured (0.003 dyne/cm). Their data showed that only a small amount of calcium (25 ppm) increased the IFT between caustic and crude considerably. At 247 ppm calcium, sodium hydroxide was ineffective in reducing IFT at all concentrations up to 1%. Sodium chloride reduced the amount of caustic required to give maximum surface activity. All IFT measurements were made at 74F and at an interface age of 20 seconds. Jennings stated, "We selected 10 seconds because a study of the time variable showed that most of the decay of interfacial tension with time in these systems had occurred by the end of 10 seconds." Measurements were made on 164 crudes from 78 fields. An attempt to relate the interfacial properties to crude acid number was not very successful. One article stated that the "interfacial tension must fall below about 0.01 dynes/cm if oil recovery is to show a significant increase due to caustic injection." Cooke et al. proposed that wettability alteration plus IFT reduction was a factor in oil recoveries with caustic. They suggested a less restrictive criterion in IFT for oil recovery, stating that "No combination in which the interfacial tension was greater than 2 dynes/cm was ever found to be successful in an alkaline water flood." They also confirmed that sodium chloride is beneficial but calcium is detrimental. SPEJ p. 645

A Study of Caustic Solution-Crude Oil Interfacial Tensions

1975 ◽  
Vol 15 (03) ◽  
pp. 197-202 ◽  
Author(s):  
Harley Y. Jenning
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Sodium Hydroxide ◽  
Surface Activity ◽  
Acid Number ◽  
Caustic Solution ◽  
Crude Oils ◽  
Interfacial Tensions ◽  
Drop Method ◽  
Pendent Drop

Abstract This paper presents the results of a study of caustic solution-crude oil interfacial tension measurements on 164 crude oils from 78 fields. Of these crude oils 131 showed marked surface activity against caustic solutions. Surface activity of crude oil against caustic solution correlates with the acid number, gravity, and viscosity. Almost all crude oils with gravities of 20 degrees API or lower produced a caustic solution-crude oil interfacial produced a caustic solution-crude oil interfacial tension less than 0.01 dyne/cm. Of the interfacially active samples, 90 percent reached maximum measurable surface activity at a caustic concentration of close to 0.1 percent by weight. The dissolved solids content of the water bas a marked influence on the surface activity. Sodium chloride in solution reduces the caustic concentration required to give maximum surface activity. Conversely, calcium chloride in solution suppresses surface activity. Introduction The oil-production technology literature contains a number of papers that indicate that the addition of sodium hydroxide to the flood water beneficially affects oil recovery. Although the proposed recovery mechanisms differ in detail, a variable common to almost all is the interfacial tension between caustic solutions and crude oil. A study of the factors influencing caustic solution-crude oil interfacial tensions is fundamental to an understanding of the proposed mechanisms and their optimum utilization. proposed mechanisms and their optimum utilization. We have obtained interfacial tensions against caustic solutions of 164 crudes. These crudes come from all major oil-producing areas in the free world. In addition to determining the correlation of interfacial tension with crude oil properties of acid number, gravity, and viscosity, we have also determined the effect of certain dissolved solids in the water. We define acid number as the number of milligrams of potassium hydroxide required to neutralize the acid in one gram of sample. The interfacial tension data were obtained by the pendent-drop method. pendent-drop method. EXPERIMENTAL PROCEDURE The caustic solutions used in this study were prepared by adding reagent-grade sodium hydroxide prepared by adding reagent-grade sodium hydroxide to laboratory distilled water. Our standard solutions were made from a 50 percent by weight reagent-grade sodium hydroxide solution. For convenience in relating our laboratory data to possible field application, the data were recorded and plotted in terms of weight percent sodium hydroxide. The pH of the caustic solutions was determined experimentally using a Coming expanded-scale pH meter; and the densities of the caustic solutions were measured experimentally using a Chainomatic Westphal balance. CRUDE OILS The crude oils were protected from the atmosphere and were collected in carefully cleaned glass or, when practicable, in plastic-lined containers. The crude oil samples were free of chemical additives, such as emulsion breakers and corrosion inhibitors. If the oil contained suspended solid material it was dehydrated and filtered. The densities were determined by the Westphal balance; and the viscosities were determined as a function of temperature using a glass capillary viscometer. APPARATUS AND EXPERIMENTAL PROCEDURE The interfacial tension measurements described in this study were made by the pendent-drop method. The pendent-drop method is based on the formation of a drop of liquid on a tip, the drop being slightly smaller than that which will spontaneously detach itself from the tip. The profile of this drop is magnified by projection and can be recorded on a photosensitive emulsion. The interfacial tension is photosensitive emulsion. The interfacial tension is calculated from the dimensions of the drop profile, a knowledge of be densities of the liquid forming. the drop, and the bulk phase surrounding the drop. All interfacial tensions described in this paper were recorded at a temperature of 74 degrees F and at an interface age of 10 seconds. Most systems were studied as a function of temperature; but temperature was found to be a second-order effect, so we selected 74 degrees F in order that all correlations would be at constant temperature. We selected 10 seconds because a study of the time variable showed that most of the decay of interfacial tension with time in these systems had occurred by the end of 10 seconds. SPEJ P. 197

A Chemical Theory for Linear Alkaline Flooding

1982 ◽  
Vol 22 (02) ◽  
pp. 245-258 ◽  
Author(s):  
E.F. deZabala ◽  
J.M. Vislocky ◽  
E. Rubin ◽  
C.J. Radke
Keyword(s):  
Ion Exchange ◽  
Crude Oil ◽  
Oil Recovery ◽  
Acid Number ◽  
Reservoir Rock ◽  
Crude Oils ◽  
Fractional Flow ◽  
Surface Active ◽  
Displacement Model

Abstract A simple equilibrium chemical model is presented for continuous, linear, alkaline waterflooding of acid oils. The unique feature of the theory is that the chemistry of the acid hydrolysis to produce surfactants is included, but only for a single acid species. The in-situ produced surfactant is presumed to alter the oil/water fractional flow curves depending on its local concentration. Alkali adsorption lag is accounted for by base ion exchange with the reservoir rock. The effect of varying acid number, mobility ratio, and injected pH is investigated for secondary and tertiary alkaline flooding. Since the surface-active agent is produced in-situ, a continuous alkaline flood behaves similar to a displacement with a surfactant pulse. This surfactant-pulse behavior strands otherwise mobile oil. It also leads to delayed and reduced enhanced oil recovery for adverse mobility ratios, especially in the tertiary mode. Caustic ion exchange significantly delays enhanced oil production at low injected pH. New, experimental tertiary caustic displacements are presented for Ranger-zone oil in Wilmington sands. Tertiary oil recovery is observed once mobility control is established. Qualitative agreement is found between the chemical displacement model and the experimental displacement results. Introduction Use of alkaline agents to enhance oil recovery has considerable economic impetus. Hence, significant effort has been directed toward understanding and applying the process. To date, however, little progress has been made toward quantifying the alkaline flooding technique with a chemical displacement model. Part of the reason why simulation models have not been forthcoming for alkali recovery schemes is the wide divergence of opinion on the governing principles. Currently, there are at least eight postulated recovery mechanisms. As classified by Johnson and Radke and Somerton, these include emulsification with entrainment, emulsification with entrapment, emulsification (i.e., spontaneous or shear induced) with coalescence, wettability reversal (i.e., oil-wet to water-wet or water-wet to oil-wet), wettability gradients, oil-phase swelling (i.e., from water-in-oil emulsions), disruption of rigid films, and low interfacial tensions. The contradictions among these mechanisms apparently reside in the chemical sensitivity of the crude oil and the reservoir rock to reaction with hydroxide. Different crude oils in different reservoir rock can lead to widely disparate behavior upon contact with alkali under varying environments such as temperature, salinity, hardness concentration, and pH. The alkaline process remains one of the most complicated and least understood. It is not surprising that there is no consensus on how to design a high-pH flood for successful oil recovery. One theme, however, does unify all present understanding. The crude oil must contain acidic components, so that a finite acid number (i.e., the milligrams of potassium hydroxide required to neutralize 1 gram of oil) is necessary. Acid species in the oil react with hydroxide to produce salts, which must be surface active. It is not alkali per se that enhances oil recovery, but rather the hydrolyzed surfactant products. Therefore, a high acid number is not a sufficient recovery criterion, because not all the hydrolyzed acid species will be interfacially active. That acid crude oils can produce surfactants upon contact with alkali is well documented. The alkali technique must be distinguished from all others by the fundamental basis that the chemicals promoting oil recovery are generated in situ by saponification. SPEJ P. 245^

SARA-Based Correlation To Describe the Effect of Polar/Nonpolar Interaction, Salinity, and Temperature for Interfacial Tension of Low-Asphaltene Crude Oils Characteristic of Unconventional Shale Reservoirs

SPE Journal ◽  
2021 ◽  
pp. 1-13
Author(s):  
I. W. R. Saputra ◽  
D. S. Schechter
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Oil Recovery ◽  
Petroleum Engineering ◽  
Crude Oils ◽  
Oil Composition ◽  
Surface Activities ◽  
Low Salinity ◽  
Oil Water ◽  
Shale Reservoirs

Summary Oil/water interfacial tension (IFT) is an important parameter in petroleum engineering, especially for enhanced-oil-recovery (EOR) techniques. Surfactant and low-salinity EOR target IFT reduction to improve oil recovery. IFT values can be determined by empirical correlation, but widely used thermodynamic-based correlations do not account for the surface-activities characteristic of the polar/nonpolar interactions caused by naturally existing components in the crude oil. In addition, most crude oils included in these correlations come from conventional reservoirs, which are often dissimilar to the low-asphaltene crude oils produced from shale reservoirs. This study presents a novel oil-composition-based IFT correlation that can be applied to shale-crude-oil samples. The correlation is dependent on the saturates/aromatics/resins/asphaltenes (SARA) analysis of the oil samples. We show that the crude oil produced from most unconventional reservoirs contains little to no asphaltic material. In addition, a more thorough investigation of the effect of oil components, salinity, temperature, and their interactions on the oil/water IFT is provided and explained using the mutual polarity/solubility concept. Fifteen crude-oil samples from prominent US shale plays (i.e., Eagle Ford, Middle Bakken, and Wolfcamp) are included in this study. IFT was measured in systems with salinity from 0 to 24% and temperatures up to 195°F.

Observations on the Coalescence Behavior of Oil Droplets and Emulsion Stability in Enhanced Oil Recovery

1978 ◽  
Vol 18 (06) ◽  
pp. 409-417 ◽  
Author(s):  
D.T. Wasan ◽  
S.M. Shah ◽  
N. Aderangi ◽  
M.S. Chan ◽  
J.J. McNamara
Keyword(s):  
Interfacial Tension ◽  
Crude Oil ◽  
Oil Recovery ◽  
Emulsion Stability ◽  
Surfactant Solution ◽  
Chemical Additives ◽  
Oil In Water ◽  
Tertiary Oil Recovery ◽  
Oil Water ◽  
Low Tension

Original manuscript received in Society of Petroleum Engineers office Sept. 20, 1977. Paper accepted for publication June 2, 1978. Revised manuscript received Aug. 2, 1978. Paper (SPE 6846) was presented at SPE-AIME 52nd Annual Fall Technical Conference and Exhibition, held in Denver, Oct. 9-12, 1977. Abstract Results of experiments on the coalescence of crude oil drops at an oil-water interface and interdroplet coalescence in crude oil-water emulsions containing petroleum sulfonates and cosurfactant as surfactant systems with other chemical additives were analyzed in terms of interracial viscosity, interfacial tension, interfacial charge, and thickness of the films surrounding the microdroplets. A qualitative correlation was found between coalescence rates and interfacial viscosities; however, there appears to be no direct correlation with interfacial tension. New insight has been gained into the influence of emulsion stability in tertiary oil recovery by surfactant/polymer flooding in laboratory core tests. We concluded that those systems that result in relatively stable emulsions yield poor coalescence rates and, hence, poor oil recovery, Introduction The ability of the surfactant/polymer system to initiate and to propagate an oil bank is the single most important feature of a successful tertiary oil-recovery process. The mechanisms of oil-bank formation and development are yet unknown. It has been suggested that without the initiation of the oil bank, the process behaves more like the unstable injection of a surfactant solution alone, where the oil is produced by entrainment or emulsification in the flowing surfactant stream. In a laboratory study of the initial displacement of residual hydrocarbons by aqueous surfactant solutions, Childress and Schechter and Wade observed that those systems that spontaneously emulsified and coalesced rapidly yielded better oil recovery than those systems that spontaneously formed stable emulsions. Recently, Strange and Talash, Whitley and Ware, and Widmeyer et al. reported results of Salem (IL) low-tension, water-flood tests that used Witco TRS 10-80 TM petroleum sulfonate surfactant solution. They found stable oil-in-water emulsions at the observer well in addition to emulsion problems at the production well and reported that problems at the production well and reported that actual oil recovery was about one-quarter the target value. These studies clearly suggested that poor efficiency of oil recovery results from emulsion stability problems in the low-tension surfactant or micellar processes. Vinatieri presented results of experiments on the stability of crude-oil-in-water emulsions that coo be produced during a surfactant or micellar flood. More recently, we have assessed the rigidity of interfacial films and its relationship to coalescence rate through measurements of interfacial viscosities of crude oils contacted against aqueous solutions containing various concentrations of surfactants and other pertinent chemical additives. Our data clearly indicate that in the absence of a commercial surfactant, interfacial viscosity builds up rapidly, coalescence is inhibited, and the resulting emulsion is quite stable. These phenomena also have been observed by Gladden and Neustadter. Several studies were conducted on the structure of film-forming material at the crude oil/water interface, its effect on emulsion stability, and the role of such films in oil recovery by water or caustic solution displacements. Rigid films were found to reduce the amount of oil recovered. Our studies also have shown that the addition of a commercial surfactant lowered both the interfacial viscosity (ISV) and interfacial tension (IFT) of the crude oil-aqueous solution system. However, the concentration at which both the IFT and ISV are minimized cannot be identified by measuring IFT alone. We have conducted a cinephotomicrographic examination of spontaneous emulsification and a microvisual study of the displacement of residual crude oil by aqueous surfactant solutions in micromodel porous media. SPEJ P. 409

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