|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
Starch-acrylamide, graft copolymers are effective but shear-sensitive viscosifiers which, when synthesized with 18 or less grafts per starch molecule, duplicate the rheology of acrylamide homopolymer of 1 to 3 times higher molecular weight. Solutions of copolymer must be prepared at shear rates below 100 sec(-1) and lose up to 40 percent of their viscosity when filtered through 0.45 mu pores. Copolymers with 18 or less grafts per starch molecule have higher intrinsic viscosities, higher solution viscosities, and higher solution screen factors than equal molecular weight homopolymers and all three properties of the copolymer increase with increasing molecular weight or decreasing number of grafts. The viscosity of copolymer solutions drops by less than 3 percent when sodium chloride concentration varies from 0 to 10,000 ppm or calcium ion concentration varies from 0 to 1,000 ppm.
Solutions of copolymer may lose up to 60 percent of original viscosity from 100 shearings at a rate of 4,300 sec(-1). Sensitivity to shear increases with increasing molecular weight and, at constant molecular weight, increases with decreasing number of grafts. Loss of solution viscosity under successive shearings can be expressed with a modified Williams-Watts equation.
Most of the polymers currently used in oil reservoirs are linear, synthetic copolymers* prepared for other markets but applied to oil recovery. This paper is the first in a series of studies of the paper is the first in a series of studies of the rheology of polymers designed and synthesized to meet the requirements of enhanced oil recovery. The tested material is a graft copolymer prepared by polymerizing acrylamide side chains on a starch backbone. The starch is a series of dehydroglucose units -linked at the positions and yields, when reacted with acrylamide, a bonding structure based on the formula of Figure 1.
A distinct bond between backbone (anhydroglucose) and side chain (acrylamide) is not shown in Figure 1 because there are three possible sites of attachment.
The copolymers were tested for applicability to oil recovery by measuring intrinsic viscosity, solution viscosity after low- or high-shear mixing, viscosity after filtration, variation of viscosity and screen factor as a function of copolymer concentration, Huggins constant, Schulz-Balishka constant, Kraemer constant, variation of viscosity as a function of sodium chloride or calcium ion concentration, loss of viscosity when the solution is sheared at a rate of 4,300 sec(-1), shear decay constants, solution viscosity loss with time, and Ostwald-deWaele exponent.
Most viscosities were measured with Cannon-Fenske viscometers at a shear rate of 53 sec(-1). The viscosities used in the calculation of the Ostwald-deWaele exponent were measured in a low-shear, capillary viscometer with a variable pressure head. All viscosity tests were performed at 30 degrees C. Solutions were gravity filtered through Millipore filters under a maximum pressure head of 5 kilopascals. The orifice mixer is described in Appendix A.
SYNTHESIS AND PROPERTIES OF THE COPOLYMERS
Starch-acrylamide graft copolymers are formed in aqueous solution by ceric ion initiated, radical polymerization of acrylamide on starch. Polymerization polymerization of acrylamide on starch. Polymerization is conducted under an inert atmosphere.
The average number of chains, Ng, of acrylamide added to each starch molecule is calculated from Equation 1,
Moles of Ceric Ion Initiator Added To The Reaciton Mixture N = ..........(1) g Moles of Starch Placed in The Reaction Mixture
The calculated degree of polymerization, Dp, is the average number of monomer units contained in each grafted chain on the starch molecule.
Abstract Oil well cementing uses a variety of organic additives such as dispersing agents, retarders or fluid loss control additives. The later, which prevent interstitial water from filtering into the formation during cement placement, are generally polymer based. A widely used class of fluid loss control additive are the high molecular weight Sulfonated copolymers, generally comprising AMPS (2-Acrylamido-2-methylpropane sulfonic acid) copolymerized with Acrylamide (Am) or N, N′ Dimethylacrylamide (DMA). The mechanism of action of these polymers has been studied recently and it was demonstrated that adsorption onto the cement surface is crucial to achieve the required product performance. It was also shown that other solutes and admixtures present in the cement interstitial solution can hinder adsorption resulting in performance losses. Thus it has been recommended to incorporate an additional monomer containing strongly adsorbing units in the copolymer to enhance the interaction with the cement surfaces hence limiting competitive adsorption issues. In this study we investigated the use of diblock copolymers comprising a short but strongly adsorbing block and a long second block of DMA-AMPS as a potential new class of filtration control agent. We showed that diblock copolymers with much lower molecular weights than statistical polymers can provide satisfactory fluid loss control performance. Furthermore, it was demonstrated that these structured polymers show good formulation flexibility and deliver more robust performance in the presence of a wide range of admixtures and solutes. Finally we focused on the analysis of the adsorption on cement of various formulation admixtures and how it affected the adsorption of our diblock copolymers. With the aid of an analytical method utilising size exclusion chromatography of collected filtrate from HPHT filtration cells, it was possible to have a direct access to a fluid loss polymer concentration in the filtrate even in the case of complex formulations. Based on these studies, the mechanism of action of the diblock copolymers as fluid loss control agents is discussed with reference to that evoked for statistical polymers.
Nghia, Tu Thanh (Vietsovpetro JV, the Socialist Republic of Vietnam, Vung Tau) | Veliev, M. M. (Vietsovpetro JV, the Socialist Republic of Vietnam, Vung Tau) | Khoi, Tran Quoc (Vietsovpetro JV, the Socialist Republic of Vietnam, Vung Tau) | Ivanov, A. N. (Vietsovpetro JV, the Socialist Republic of Vietnam, Vung Tau)
The PDF file of this paper is in Russian.
Analysis of the status of the Lower Miocene development indicates the nonuniform oil reserves recovery in various areas of the reservoir. The oil recovery factor remains low, while the water-cut of the produced products increases. By means of increasing the displacing factor and areal sweep efficiency, the reservoir flooding technology based on polymer solutions allows significantly improve the production and economic performance of fields. The basis for the most implemented soluble polymers is polyacrylamide, which has limits in temperature (no higher than 90 °C) and salinity (for mediums with low salinity). The indicated properties prevent the polyacrylamide-based polymer solutions from wide implementation in oil-field practices under conditions of Vietsovpetro JV. To improve the oil-displacing factor during Lower Miocene flooding at White Tiger field the radio irradiated polymer systems and methods for their rheological and physical properties control were developed. Using of radioactive irradiation new polymer was synthesized. Its viscosity is much higher than the viscosity of the initial polymer. Study of the temperature influence on the new polymer solution viscosity under various concentrations revealed that the polymer system viscosity has a tendency to decrease under temperature rise. In that way, the viscosity lowers 2 times under low concentration and reduces 4 times under high concentration with temperature variation from 30 to 90 °C.
Анализ текущего состояния разработки залежи нижнего миоцена свидетельствует о неравномерности выработки запасов нефти на различных участках залежи. Коэффициенты извлечения нефти остаются на низком уровне при возрастающей обводненности добываемой продукции. Полимерные системы на основе водного раствора позволяют увеличить коэффициент охвата для подключения ранее не работавших, либо слабо работавших интервалов пласта. Основой большинства применяемых растворимых полимерных композиций является полиакриламид, применение которого, как известно, ограничено температурой (не более 90 °С) и минерализацией (для сред с низкой минерализацией). Указанные свойства препятствуют широкому внедрению растворов полимеров на полиакриламидной основе в нефтепромысловую практику в условиях СП «Вьетсовпетро». С целью увеличения коэффициента охвата заводнении залежи нижнего миоцена месторождения Белый Тигр разработаны радиооблученные полимерные системы и методы регулирования их реологических и физических свойств. С помощью радиооблучения создан новый полимер, вязкость которого значительно превышает вязкость исходного полимера. Исследование влияния температуры на вязкость растворов нового полимера при различных концентрациях показало, что при увеличении температуры вязкость снижается. Так, при изменении температуры от 30 до 90 °С при низкой концентрации полимера вязкость снижается в 2 раза, апри высокой - в 4 раза.
Doe, Peter H., SPE, Phillips Petroleum Co. Phillips Petroleum Co. Moradi-Araghi, Ahmad, SPE, Phillips Petroleum Co. Phillips Petroleum Co. Shaw, James E., Phillips Petroleum Co. Phillips Petroleum Co. Stahl, G. Allan,* Phillips Petroleum Co. Phillips Petroleum Co. November 1987
Summary. This paper describes the properties of synthetic water-soluble polymers that are stable for extended periods of time in hard brines at polymers that are stable for extended periods of time in hard brines at very high temperatures. Several copolymers of vinylpyrrolidone (VP) and acrylamide (AM) were prepared and evaluated in our laboratories for EOR application in hostile environments. VP in the copolymer composition protects AM against extensive thermal hydrolysis, which otherwise will protects AM against extensive thermal hydrolysis, which otherwise will result in loss of viscosity and precipitation. A range of VP/AM copolymer compositions was found to tolerate the harsh conditions of 250F [121C] in seawater for extended periods of time and to be suitable for EOR application under these conditions. The performance of these polymers in porous media was evaluated by extensive coreflood experiments in Berea porous media was evaluated by extensive coreflood experiments in Berea sandstone at 250F [121C] with synthetic seawater. The results indicate that these copolymers can easily be injected into porous media and that they can be effective polymers for EOR application in hostile environments.
In recent years, oil production has been moving toward deeper, and consequently hotter, reservoirs. This trend has produced a challenge for manufacturers of water-soluble polymers. Polyacrylamides, the most widely used products for mobility Polyacrylamides, the most widely used products for mobility control, suffer extensive thermal hydrolysis at high temperatures and, as a result, may precipitate in the presence of divalent cations. A recent study indicates a "safe" temperature limit of only 167F [75C] for typical oilfield brines. Somewhat lower limits of 154F [68C] have been observed for a brine with 3,604 ppm Ca2+ ions. Polysaccharidese.g., xanthan gums-have acquired some popularity, but are also sensitive to high temperatures and are probably not suitable for EOR application in reservoirs hotter than 200F [93C]. The use of stabilizing packages might raise this limit somewhat. Other synthetic polymers such as polyethylene oxide, polyvinyl alcohol, and cellulose derivatives suffer thermal degradation, precipitation, and substantial viscosity losses as a result of aging in seawater at elevated temperatures. An extensive investigation of the thermal stability of commercially available water-soluble polymers was conducted to determine the suitability of these products for EOR application in seawater at 250F [121C]. The objective of this study was to identify products that can tolerate this harsh combination of temperature, salinity, and hardness (Table 1) for a period of at least 3 years without a substantial loss in viscosity. Almost all but scleroglucan and polyvinylpyrrolidone (PVP) failed this test by precipitating within a few weeks. A similar conclusion was reached by Davison and Mentzer, who tested some 140 polymers for EOR application in sea-water at 194F [90C]. Although scleroglucan passed initial screening at 250F [121C], it failed to survive a passed initial screening at 250F [121C], it failed to survive a few months of aging at this temperature. PVP is not a good viscosifier, and high concentrations are needed to produce viscosities comparable to polyacrylamides. The need for 8 to 10 times higher concentrations of this polymer, coupled with a price about three times that of polyacrylamide, makes PVP unsuitable for EOR applications. polyacrylamide, makes PVP unsuitable for EOR applications. We found that copolymers of N-VP and AM have unusual thermal stability. These systems demonstrate stabilities beyond what would be expected from a simple dilution of AM with VP molecules. This paper reports the properties of poly(N-VP/co-AM) produced in our laboratories.
Polymer Preparation. VP/AM copolymers used in this study were Polymer Preparation. VP/AM copolymers used in this study were prepared by polymerization as 10 to 20 wt% solutions in distilled prepared by polymerization as 10 to 20 wt% solutions in distilled water or synthetic seawater. The polymerization was initiated by free-radical initiators under an oxygen-free atmosphere. Reagent-grade commercial monomers were used in all copolymer preparations. Details regarding the polymerization process are preparations. Details regarding the polymerization process are given elsewhere.
Sample Preparation and Aging. To avoid polymer degradation, all the sample preparation and aging tests were carried out under an oxygen-free atmosphere. Samples (25 mL) prepared for monitoring the extent of hydrolysis or cloud points were placed in 50-mL Pyrex TM ampules and torch-sealed under a vacuum. Procedures for Pyrex TM ampules and torch-sealed under a vacuum. Procedures for determining the cloud point and extent of hydrolysis are reported in Ref. 1. To evaluate the effects of aging on the viscosity of polymer solutions, stainless-steel pressure bombs equipped with Pyrex polymer solutions, stainless-steel pressure bombs equipped with Pyrex glass liners were charged with about 260 to 280 mL of polymer solution, covered with a watch glass, sealed with a stainless-steel cap, and pressurized to 100 psi [690 kPa] of N2. The bombs were then aged in ovens for the appropriate times.
Capillary Viscometer. A homemade capillary viscometer was used to scan viscosity/temperature relationships in the range of 100 to 300F [38 to 149C] for each solution. The viscometer consists of a 20-ft [6.1-m] "preheating" coil and a 40-ft [12.2-m] stainless- steel measuring coil with an ID of 0.069 in. [0.175 cm]. Both coils are immersed in a silicone oil bath and heated with a temperature programmer set at 3.6F [2C]/min. The polymer solution is driven programmer set at 3.6F [2C]/min. The polymer solution is driven through the coil by N2 pressure. The pressure drop across the measuring coil is monitored by a differential-pressure transducer. After the solution passes through the measuring coil, it goes through the flow-control section of the apparatus, which is equipped with a valve to maintain 90-psi [620-kPa] backpressure on the system. This is enough to keep the polymer solution liquid at 300F [149C].