A study was made of the specific effects of oxygen, oxygen inhibitors, temperature, and water salinity on a commercially available polyacrylamide used in oil recovery. Because oxygen greatly effects solution stability, particular attention was given to oxygen inhibitors, with emphasis on particular attention was given to oxygen inhibitors, with emphasis on sodium hydrosulfite and formaldehyde. For a number of reasons, the latter is found to be more desirable for the purpose. Introduction Adequate mobility control between fluid banks is a significant factor in the successful application of secondary and tertiary oil recovery processes. Reservoir flooding when the mobility of displacing fluids equals or is lower than the mobility of displaced fluids increases recovery efficiency by virtue of improved pattern conformance. pattern conformance. The popularity of water-soluble polymers as mobility-control agents in oil recovery processes has increased significantly in recent years. Polymers are applicable to several recovery processes. In addition, because large quantities of chemical are required to flood developed fields, many polymer manufacturers have directed their efforts toward this substantial potential market. Several chemical companies have acquired extensive technology in the manufacture of water-soluble polymers, but most of them lack expertise in the polymers, but most of them lack expertise in the oil-recovery applications of such products. High-molecular-weight polyacrylamides are widely used in secondary and tertiary recovery. The material used in this study was a partially hydrolyzed polyacrylamide marketed by The Dow Chemical Co. as 700 polyacrylamide marketed by The Dow Chemical Co. as 700 series Pusher. Other companies also are developing or marketing polyacrylamides. Polyacrylamides control mobility in reservoirs by increasing the viscosity of injection water and, more importantly, by reducing the formation permeability. Reservoir residence times are long for polymer solutions, since mobility control must be maintained essentially throughout the flood life of these solutions. Therefore, polymer stability under field conditions becomes important. Specifically, conditions that may degrade polymer solutions injected into a reservoir must be determined and evaluated. This paper describes the results of a laboratory study conducted to determine factors affecting the stability of Dow 700 series Pusher. The paper quantitatively describes the effects of several field conditions on the mobility control capability of this polymer, from the standpoint of both viscosity and polymer, from the standpoint of both viscosity and permeability reduction. Guidelines are developed for permeability reduction. Guidelines are developed for handling solutions of this material, including the proper use of treating agents, so as to enhance performance. Dow 500 series Pusher was evaluated in a manner similar to that described here. This polymer, which is also used in oil-recovery applications, is lower in molecular weight than Pusher 700. The behavior of Pusher 500 was very similar to that of Pusher 700 in laboratory experiments, so specific data Pusher 700 in laboratory experiments, so specific data discussed here are limited to the material having a higher molecular weight. In addition to obtaining bench measurements of solution properties, we also measured the effects of polymer degradation on flow behavior by flooding polymer degradation on flow behavior by flooding reservoir cores. Flow studies verified that the effectiveness of polymer solutions in providing mobility control in reservoir rock may be impaired under conditions encountered in the field. JPT P. 618
High-molecular-weight, water-soluble polyacrylamides were evaluated for use in the recovery of low-gravity crude oil by polymer flooding. Performance comparisons were made between a high-molecular-weight commercial polymer and two developmental materials higher in molecular weight than any commercial product. Sandpack floods using viscous (220 cp and 1140 cp) oils indicated that the highest-molecular-weight material was superior for oil recovery by polymer flooding. Based on these data improved recovery performance should be possible with the introduction of higher-molecular-weight products into the marketplace. In comparable flooding experiments, mobility -ratios using the highest-molecular-weight polymer were much lower than those of the other two polymers. Complete polymer retention or denudation of the leading edge of the injected polymer bank was observed with this material; this effect was not observed with other polymers. Denudation provides insight into the mobility reduction mechanism and, depending on flood design, it may either improve or reduce oil recovery. Forward loading of the polymer slug is discussed as a means to reduce denudation. Denudation is useful in explaining differences in polymer characteristics. The highest-molecular-weight material apparently exhibits a -narrower molecular-weight distribution than the other polymers. All molecules from this product were effective in the reduction of sandpack permeability, whereas only a small fraction of the molecules from the other polymers were useful in this regard. Introduction SUBSTANTIAL RESERVES of low-gravity crudes with relatively high viscosity are known to exist throughout the world. Of particular interest are North American reserves because of proximity to refineries, strong demand and a desire to improve self-sufficiency in petroleum. The U.S. Bureau of Mines places domestic low-gravity, in-place crude reserves at over 100 billion stock tank barrels(2,3). This estimate represents oil with gravity less than 25 °API which is mobile at reservoir conditions as evidenced by some commercial production. Less than 5% of this oil is classified as recoverable using current technology. Extensive low-gravity crude reserves are found in Canada, particularly in Alberta and Saskatchewan. Distribution of such reservoirs in the United States is fairly broad, but many fields are concentrated in Texas, California, Kansas and Wyoming. Most efforts directed toward recovery of low-gravity crude involve production stimulation via thermal processes. However, polymer flooding may have economic potential in this regard. Husky Oil, Ltd. has included flooding with a polymer among several programs for heavy crude recovery from reservoirs in the Lloydminster area of Saskatchewan.(3,4) Standard Oil Company of California has reported that polymer flooding has proved effective in substantially increasing oil recovery (13.2 °API crud) in the Huntington Beach field near Los Angeles.(3) High-molecular-weight, water-soluble polymers manufactured by various chemical companies have been evaluated for many years at Marathon Oil Company's Denver Research Center. The goal of polymer evaluation has been to find better and more economical chemicals for use in enhanced recovery processes. High-molecular-weight polyacrylamides appear more attractive than other polymers for recovery of heavy oil by polymer flooding. Reduction of water mobility with polyacrylainides is attained primarily by permeability reduction.
Measurements of H2 production from pure water vapour as a function of dose indicate that, like liquid water, it is essentially stable to y radiation. The net yield of H2 is very low leading to a mean integral value of G(H+0007 but the amount of H2 obtained depends critically on the care taken in cleaning the cells and admitting the water, and it is concluded that previously-published yields are all integral values obtained under a variety of conditions. Measurement of the primary yields in the presence of N H 3 and of NH3fO2 gives g(0H) = 6.650.2, g(H) = 5-7f0.2, g(H2) = 047f0.01, but no distinction can be made between yields of electrons and H atoms in this work.Primary processes of ionization and charge recombination are considered in view of earlier postulates, together with physical evidence which demonstrates the stability of ion clusters in water vapour even at low pressures. It is suggested that, under certain conditions in the vapour phase, charge neutralization of the H3Of ion leads to the same yield of radicals as in liquid water.Published data on the radiolysis of water vapour are sparse and contradictory, both in the absence and presence of added scavengers. Values for G(H2) from the radiolysis of pure water vapour vary from 0.014 to 5.9,1-5 while the value for the radical pair yield g(H)* = 11.7, obtained by Firestone 3 in studies of the Dz/H20 exchange reaction, has been challenged by Baxendale and Gilbert,4 who report g(HJ = 8 k0.7 from measurements in the presence of organic scavengers. These values are of prime importance in understanding the radiolysis of water vapour, and we have extended the previous work by measurements both in pure water vapour and on the addition of NH3 and 0 2 . EXPERIMENTAL PREPARATIONSamples were irradiated in Pyrex cells ; the cell volumes varied from 100 to 1000 ml. The cells carried a B10 glass joint with a fragile tip for reopening under vacuum. Water samples were prepared in separate tubes containing a septum break seal, which were joined to the cell by fusion. Water was admitted to the main irradiation cell by breaking the septum with a glass rod before irradiation. These water tubes were filled on an all-glass mercury-free vacuum line in which the water vapour was not allowed to come into contact with any greased stopcocks during addition or transfer. An all-glass valve was designed for use with this system. The amount of water distilled into each water tube was monitored by measuring the difference in height of water in a precision-bore capillary after filling and sealing each tube. The metering tube was filled with water, which was first boiled to remove most of the dissolved gases, and then subjected to several cycles of freezing at -78"C, pumping to 10-6 mm Hg and thawing. Water tubes were evacuated to 10-6 mm Hg before distilling water into them and again before they were sealed. This technique of admitting water separately was developed because of difficulty experienced in adding 0 2 * Primary yields are written as g(x) and experimental yields as G(x).
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