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The addition of CO2-soluble, brine-soluble surfactants to the high pressure CO2 can facilitate the in-situ generation of CO2-in-brine foams for conformance and/or mobility control. These non-ionic surfactants dissolve in CO2 to concentrations of roughly 0.02–0.10 wt% at typical CO2 enhanced oil recovery (EOR) conditions and, upon mixing with brine in a closed, agitated, windowed vessel, stabilize CO2-in-brine foams. Branched nonylphenol ethoxylates containing an average of 12 (Huntsman SURFONIC® N-120) or 15 (Huntsman SURFONIC® N-150) ethylene oxide (EO) repeat units, and a branched tridecyl alcohol ethoxylate with 9 EO repeat units (Huntsman SURFONIC® TDA-9) are selected for the mobility and computed tomography (CT) studies detailed in this paper. These foam-stabilizing surfactants are much more brine-soluble than CO2-soluble, in accordance with the Bancroft rule for generating CO2-in-brine foam. Transient mobility measurements are conducted using several mixed wettability SACROC carbonate cores of low permeability (13–16 mD), and a high permeability water-wet Bentheimer sandstone core (1550 mD). The CO2 is injected into a brine-saturated core at a constant rate, yielding superficial velocities of 60.96 cm/day or 304.8 cm/day. Surfactant was either not used, dissolved only in CO2, only in brine, or in both brine and CO2. The surfactant concentration is ~0.07 wt% in the CO2 (the maximum concentration capable of dissolving in CO2) or in the brine. The transient differential pressure drop during the injection of three pore volumes of CO2 into the core indicate that the average total pressure drop across the core during the experiment increases by an average of 25–120% when the surfactant is dissolved in the CO2, 79–300% when the surfactant is dissolved in the brine, and 220–330% if surfactant is present in both the brine and CO2. These results indicate that the greatest mobility reduction is achieved with the surfactant in both brine and CO2, and the foams that are generated with surfactant dissolved in the brine alone tend to provide greater mobility reduction than when the surfactant is dissolved only in CO2. CT scanning of in-situ foam generation is conducted by injecting high pressure CO2 into a 5 wt% KI brine-saturated water-wet Berea sandstone (4–8 mD). Tests are performed with no surfactant, surfactant dissolved in brine at 0.03 wt%, in CO2 at 0.07 wt%, or in both brine and CO2. CT images indicate that in the absence of surfactant, sweep efficiency is very low primarily because CO2 tends to flow through high permeability bedding planes. The use of CO2-soluble surfactants to form CO2-in-brine foam within a sandstone core is verified via CT imaging. At low and high superficial velocity values of 14.33–143.3 cm/day, in-situ foam generation and propagation, as indicated by piston-like flow of the CO2 through the core, is most evident when surfactant was dissolved in the brine. While there is some evidence of foam formation when Huntsman SURFONIC® N-120 or Huntsman SURFONIC® N-150 is present in the CO2, very distinct foam formation and propagation occurs when Huntsman SURFONIC® TDA-9 is dissolved in CO2.

Growing interest in Enhanced Oil Recovery (EOR) has generated renewed interest in surfactants for Chemical EOR (CEOR). While new developments typically build on past experiences of surfactant injections, academic and research institutes continue to propose new high-performance surfactant structures. Although these new molecules can easily be provided in sufficient quantities for laboratory tests and limited field trials, scale up to large commercial application could prove challenging. Moving to production on a large commercial scale will require the availability of raw materials and suitable production assets. In addition, regulatory compliance issues must be addressed, as must future supply chain efficiency. This paper describes the development process for surfactants capable of attaining low interfacial tensions. It specifically addresses the impact of raw material availability and quality, production assets and regulatory compliance on a global basis. Surfactant performance envelope data is presented as the first step to enable selection of potential candidate structures for given field conditions. The influence of the selected production assets for scale up to commercial quantities on the molecular composition of the final product is also illustrated. As will be seen, changes in the raw material feed and feed processes determine the poly dispersion of the resulting product. The impact of variations in chemical structure and total product composition manifest themselves in the product performance envelope. We show how small changes in composition not only impact performance, but also affect regulatory compliance and the corresponding supply chain processes. A holistic approach to surfactant development, which considers the full process from product concept to commercial large-scale production, is essential to make CEOR successful. The development process must consider the sustainability of the proposed structures and processes required to make them. Here we will demonstrate why design for future growth in demand must be built in from day one of the product concept.

The addition of CO2-soluble, brine-soluble, surfactants to the high pressure CO2 may facilitate the in-situ generation of CO2-in-brine foams for conformance and/or mobility control. Most of these non-ionic surfactants dissolve in CO2 to concentrations of roughly 0.05–0.10wt% at CO2 EOR conditions and stabilize CO2-in-brine foams in high pressure windowed cells. Huntsman SURFONIC® N series surfactants, branched nonylphenol ethoxylates, containing an average of 12 (N-120) or 15 (N-150) ethylene oxide repeat units were selected for mobility and CT studies detailed in this paper. Transient mobility measurements were conducted using a water-wet Berea core (104 mD), a water-wet Bentheimer sandstone core (∼1500 mD), and several mixed wettability SACROC carbonate cores (3.6 and 8.9 mD). The CO2 was injected into a brine-saturated core at a superficial velocity of 10 ft/day, and the surfactant was either not used, dissolved only in the brine at 0.06wt%, dissolved only in the CO2 at 0.06wt%, or dissolved in both the brine and the CO2 at 0.06wt. Regardless of what phase the surfactant was dissolved in, in-situ foam generation in the relatively high permeability sandstone was evidenced by total pressure drop values that were 2–3 times greater than the test with no surfactant. The mobility reduction was more modest (20–50% increases in pressure drop) in the lower permeability SACROC cores (3.6 and 8.9 mD) when the surfactant was dissolved in the CO2. When the surfactant was dissolved in the brine, the pressure drops increased by a factor of 1.5–3 for the 8.9 mD core. CT scanning of in-situ foam generation was then conducted by injecting high pressure CO2 into a 5wt% KI brine-saturated water-wet Berea sandstone (3–8 mD). Tests were done with no surfactant or with the surfactant dissolved either in the brine at 0.03wt% or in the CO2 at 0.06wt%. At a low and high superficial velocity values of 0.47 ft/day and 4.7 ft/day, in-situ foam generation occurred when surfactant was dissolved in the brine or the CO2, but the core was swept more effectively by the foam generated with the surfactant present in the brine.

Water-soluble polyampholytes based on acrylamide (AM), sodium 2-acrylamido-2-methyl-propanesulfonate (NaAMPS), (2-acrylamido-2-methylpropyl) timethylammonium chloride (AMPTAC), sodium 3-acrylamido-3-methylbutanoate (NaAMB), and 30((2-acrylamido-2-methylpropyl)dimethylammonio)-1-propanesulfonate (AMPDAPS) have been synthesized and characterized. The molecular weights of the polymers range from 1.4 [times] 10[sup 6] to 21.5 [times] 10[sup 6]. Almost all the polyampholytes showed higher intrinsic viscosities at higher solvent ionic strength. The drag reduction behavior of high and low charge density polyampholytes and polybetaines was examined with a rotating-disk rheometer. All the polymers exhibited higher drag reduction at increased solvent ionic strength. The poly(sulfobetaines) (copolymers of AM and AMPDAPS) were found to be the most efficient drag reducers, and the high charge density polyampholyte (copolymer containing 50 mol % each of AMPTAC and NaAMPS) was the least efficient. Experimental data indicate that theoretical models of drag reduction should include parameters for polymer-solvent interactions and molecular associations.

Water-soluble, low charge density polyampholytes have been synthesized by free-radical terpolymerization of acrylamide (AM) with sodium 3-acrylamide-3-methylbutanoate (NaAMB) and 2-acrylamido-2-methylpropanetrimethylammonium chloride (AMPTAC). Terpolymer compositions obtained by [sup 13]C0NMR reflect monomer feed concentrations. Molecular weights and second virial coefficients range from 3.43 to 19.4 [times] 10[sup 6] g/mol and from 1.63 to 3.61 mL mol/g[sup [minus]2], respectively, as determined by low-angle laser light scattering. Ionic associations were explored by investigating the dilute solution properties as a function of terpolymer concentration, terpolymer charge density, and added electrolytes. Terpolymers with 0.5, 2.5, and 5.0 mol% of both of the cationic (AMTAC) and anionic (NaAMB) monomers were soluble in deionized water, whereas those with 10 and 15 mol% of each monomer required electrolyte addition. The higher-density terpolymers undergo a 700% increase in intrinsic viscosity upon changing NaCl concentration from 0.05 to 1M. Polyelectrolyte behavior could be induced by decreasing solution pH below the pK[sub a] of the NaAMB mer. Intermolecular ionic associations resulting in gel networks were studied utilizing dynamic mechanical analysis.

The new monomer 2-acrylamido-2-methylpropanetrimethylammonium chloride (AMP-TAC, M2) has been synthesized. Free radical copolymerization with acrylamide (AM, M1) in feed ratios varying from 10 to 50 mol % AMPTAC gave the cationic ATAM series. Copolymer compositions were determined from 13C-NMR. The reactivity ratio product r1r2 was found to be 0.62. Molecular weights varied from 1.4 to 16.5 × 106 g/mol for the copolymers. Turbidimetric studies showed aqueous solutions of the copolymers to be phase stable in the presence of CaCl2 and Na2CO3 up to 100°C. Solution behavior was independent of pH in the range of 3 to 11, and temperature in the range of 25 to 60°C. Intrinsic viscosities of the cationic copolymers decreased with the addition of electrolytes; however, some samples showed curvature in plots of intrinsic viscosity versus the inverse square root of ionic strength. © 1993 John Wiley & Sons, Inc.

Alternating copolymers were prepared by free radical copolymerization of both comonomers in a 0.5 M NaCl aqueous solution using K 2 S 2 O 8 as the initiator. Molecular weights, second virial coefficients, diffusion coefficients and average diameters were found using classical and quasielastic LLALS. As the composition of the copolymers approach equal molar concentrations of comonomers, polyampholyte behavior is observed. The second virial coefficients can be used to distinguish the polyelectrolyte/polyampholyte transition as a function of copolymer composition

Copolymers of acrylamide (AM, M 1) with sodium 3-acrylamido-3-methylbutanoate (NaAMB, M 2) synthesized in 1 M NaCl (the ABAM2 series) are compared to those synthesized in deionized water (the ABAM1 series). At fixed feed ratios, higher incorporation rates were found for NaAMB with increasing ionic strength of the polymerization solvent. Reactivity ratios calculated by the methods of Kelen-Tudos changed from r 1 = 1.23 and r 2 = 0.50 in deionized water to r 1 = 1.00 and r 2 = 0.64 in 1 M NaCl. This change is in accord with a decrease in electrostatic repulsion between the macroradical and unreacted NaAMB. Dilute solution properties, examined as a function of composition and added electrolytes, indicate differences in microstructure for the ABAM1 and ABAM2 copolymers.

Low charge density ampholytic terpolymers of acrylamide with random distributions of sodium 2-acrylamido-2-methylpropanesulphonate and 2-acrylamido-2-methylpropanetrimethylammonium chloride have been synthesized by free radical polymerization in 0.5 M NaCl aqueous solutions. Terpolymer compositions were obtained by 13C n.m.r. Low angle laser light scattering provided molecular weights and second virial coefficients which varied from 2.78 × 106 to 6.77 × 106 g mol−1 and 1.31 to 2.95 ml mol g−2, respectively. Dilute solution properties of the terpolymers were measured with respect to composition, concentration and added electrolytes. Polyampholyte behaviour was observed for the polymer with as little as 0.5 mol% of each charged group and became significant when 7 mol% of each charged monomer was incorporated. At 12 and 15 mol% incorporation of each charged monomer, solution behaviour becomes complex consistent with the existence of intermolecular interactions at low ionic strengths and intramolecular associations at medium salt concentrations.

The free radical copolymerization of acrylamide (AM) with 3-(2-acrylamido-2-methylpropanedimethylammonio)-1-propanesulphonate (AMPDAPS) has been studied in the range from 99 to 25% AM in the feed. Copolymer compositions obtained by elemental analysis and 13C n.m.r. reflect the monomer feed concentrations. The value of r1r2 has been determined to be 0.60 for the AM-AMPDAPS pair. Copolymer microstructures, including run numbers and sequence distributions, were calculated from the reactivity ratios. Molecular weights for the series range from 3.0 × 106 to 21.5 × 106 g mol−1. Second virial coefficients decrease from 2.67 to 0.21 ml mol g−2 as charge density increases. Intrinsic viscosities decrease with increasing AMPDAPS content, but increase with increasing temperature (in the range of 25–60°C) and added electrolytes (NaCl and/or CaCl2). The solution behaviour of the homopolymer of AMPDAPS is independent of pH. The observed properties are consistent with the charge density of the polymers and the sulphobetaine structure of the AMPDAPS monomer.

Greenhouse studies were conducted using bentgrass (Agrostis tenuisSibth. ‘Highland′) as a bioassay species to measure herbicidal activity of 3.4 kg/ha of the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] when applied directly to the soil surface prior to bentgrass emergence. Activity of glyphosate also was examined by applying glyphosate to a moist soil surface and placing alfalfa (Medicago sativaL. ‘Vernal′) and red clover (Trifolium pratenseL. ‘Kenstar′) seeds on the sprayed surface 3, 6, 9, and 24 h later. In two high-organic soils, glyphosate reduced bentgrass growth in each of four experiments, even when applied up to 5 days before bentgrass emergence. Significant glyphosate activity was measured in one of the experiments in another organic soil and in three of the experiments in a Chehalis sandy loam soil. Germination and growth of alfalfa and red clover were reduced when seeds were distributed on a sprayed soil surface up to 24 h after glyphosate application. These results show that glyphosate, at least under certain conditions, can cause significant crop injury when used prior to planting or emergence of some species.

In greenhouse studies, glyphosate (N- (phosphono- methyl)glycinel at 1.0 and 3.0 kg/ha and paraquat (1,1'- dimethyl-4,4-bipyridinium ion) at 0.6 kg/ha were applied to exposed seeds of six grasses and two legume species on con- tinuously wet soil. Glyphosate reduced germination of both legumes and three grasses and reduced seedling growth of all species. Paraquat was toxic only to the grasses. Glyphosate mainly affected germination and growth of legumes when applied directly to their seeds. Reductions also were measured, however, when untreated legume seeds were transferred to glyphosate- treated soil. Additional index words. Germination, stale seedbed, soil herbicide activity.