No abstract

The continuous increase of petroleum production under adverse subsea conditions and the preeminent need for adequate operational conditions and efficient use of additives to warrant flow assurance makes it interesting to set up experimental procedures to carry out n-alkane precipitation studies under high-pressure (p) and high-temperature (T) conditions. In this contribution, some preliminary experimental studies developed to characterize asphaltene precipitation in model systems consisting of asphaltene solutions in toluene or mixtures of hydrocarbons by the addition of propane, n-heptane, or other alkanes at various pressures and temperatures, using a commercial compact equipment, are reported. In general terms, it was established that these tests follow the same pattern described at ambient p and T conditions and the one single study reported in the literature for a stock tank oil sample at 3000 psi and room T. Four crude oils of different characteristics were tested, using diluted or undiluted samples, and it was possible to detect the asphaltene precipitation onset. However, these results cannot be used to infer the stability of the crude oils because results correlating onset and stability at high p and T are not yet available. The effect of pressure at high pressures was not entirely resolved because argon, used as an assumed inert gas to pressurize the system, dissolves in the hydrocarbons and displaces the precipitation onset toward lower values. The need to develop compact equipment to assess the effect of solvents, inhibitors, and other additives on the phase behavior of crude oil at high pressure and temperature and in the presence of CO2 and other gases, representing a valuable contribution to the petroleum industry in the area of flow assurance, still persists.

Abstract:In this work, a new flocculant agent was developed based on a non-ionic and water-soluble polymer, poly-(vinyl alcohol) (PVA), in order to treat oily waters from peteroleum production. Changes on its HLB were made to generate hydrophobic zones that work like flocculant agents, based on "hydrophobic bridges mechanism." Incorporation of 12 to 18 carbon atoms and carbamate groups in several concentrations were carried out. Little insertions of hydrophobic groups reduce the brine solubility, due to the inter-and intramolecular interactions; however, certain content of carbamate groups increases the resistance in a brine environment. The influence of molecular weight and the hydrolysis grade of PVA were verified as the flocculation efficiency. Their performance was verified in synthetic oily emulsion by flocculation tests. The flakes generated are different from those generated when using commercial products. High amount of additive decreases the flocculation efficiency.

Introduction Oil production is normally accompanied by a concomitant production of large amounts of water. The separation of produced water and its purification prior to discarding, represent an important technological challenge for the oil production industry. For instance a well producing, 20,000 m3/day of oil with a BSW (Basal Sediments and Water) of 50% and a TOG (Total Oil and Grease) of 300 mg/L would produce 3 tons of oil and grease per day. In order to minimize environmental impacts, these residues must be reduced to acceptable levels; this being particularly important in offshore operations where the most obvious destination of the produced waters are the oceans. The oil contained in produced oily waters often is in the form of very stable emulsions. For these systems oil/water separation by the usual physical procedures is difficult; in particular in offshore operations, where space, production facilities and residence times are limited. The use of chemicals as flocculants or flotation agents is common practice in these cases. The products generally recommended are cationic polyelectrolytes however; the field use of these polymers is limited due to the formation of solid residues that in the form of oily sludge accumulate in the treatment plant facilities reducing, after some time, the efficiency of the equipments. In this contribution, other polymers like poly(ethylene oxide) (PEO) or poly(vinyl alcohol) (PVA), that present a good performance as flocculating agents1 for other systems and fictionalized PVA containing hydrophobic alkyl chains and/or carbamate groups are assayed for oil-water separation. Furthermore some studies to identify the causes of sludge formation are also presented. Experimental Part Materials. The nonionic polymers used in this work were commercial samples kindly supplied by the manufacturers and were used without further purification. PVA1 is a poly(vinyl alcohol) (PVA) presenting a molecular weight of around 72,000, (Vetec, Qu mica Fina Ltd. Rio de Janeiro, Brazil). PVA2 and PVA3 are products manufactured by Air Products and Chemicals. Inc. (Allentown, PA. USA), commercialized as Airvol 165 and 540 respectively. Both polymers present molecular weights between 140,000 and 180,000 but PVA2 is 100% hydrolyzed and PVA3 has a hydrolysis degree between 87 and 89%. Ucarfloc 302, 304 and 309 are water-soluble poly(ethylene oxide), (PEO), polymers, presenting molecular weights of 5, 7 and 8 × 106, respectively, produced by Union Carbide (Union Carbide Corporation, Denbury, CT, USA). Two PVA samples presenting molecular weights of 72,000 (PVA1) and 140,000 (PVA2) were chemically modified by fuctionalization with carbamate groups and hydrophobic alkyl chains. The incorporation of carbamate groups (urethanes) in the structure of PVA was made by reaction of urea with PVA in the ratio of 1:1, using dimethylformamide as solvent2. The reaction temperature was fixed at 145°C and the time varied from 30 to 180 minutes. The esterification was carried out subsequently, following Schotten-Baumann reaction3 using acyl chlorides with hydrocarbon chain length varying from 12 to 18 carbon atoms. The temperature was fixed at 145°C and the reaction time was 2 hr. The solvent was also dimethylformamide for this reaction. The reaction schemes are presented in Figure 1. Three samples of crude oil, here called Crude Oil 1, 2 and 3, were used to prepare synthetic emulsions. Materials. The nonionic polymers used in this work were commercial samples kindly supplied by the manufacturers and were used without further purification. PVA1 is a poly(vinyl alcohol) (PVA) presenting a molecular weight of around 72,000, (Vetec, Qu mica Fina Ltd. Rio de Janeiro, Brazil). PVA2 and PVA3 are products manufactured by Air Products and Chemicals. Inc. (Allentown, PA. USA), commercialized as Airvol 165 and 540 respectively. Both polymers present molecular weights between 140,000 and 180,000 but PVA2 is 100% hydrolyzed and PVA3 has a hydrolysis degree between 87 and 89%. Ucarfloc 302, 304 and 309 are water-soluble poly(ethylene oxide), (PEO), polymers, presenting molecular weights of 5, 7 and 8 × 106, respectively, produced by Union Carbide (Union Carbide Corporation, Denbury, CT, USA). Two PVA samples presenting molecular weights of 72,000 (PVA1) and 140,000 (PVA2) were chemically modified by fuctionalization with carbamate groups and hydrophobic alkyl chains. The incorporation of carbamate groups (urethanes) in the structure of PVA was made by reaction of urea with PVA in the ratio of 1:1, using dimethylformamide as solvent2. The reaction temperature was fixed at 145°C and the time varied from 30 to 180 minutes. The esterification was carried out subsequently, following Schotten-Baumann reaction3 using acyl chlorides with hydrocarbon chain length varying from 12 to 18 carbon atoms. The temperature was fixed at 145°C and the reaction time was 2 hr. The solvent was also dimethylformamide for this reaction. The reaction schemes are presented in Figure 1. Three samples of crude oil, here called Crude Oil 1, 2 and 3, were used to prepare synthetic emulsions.