Mobility control methods

It is apparent that the addition of the mobility control agent did not affect the miscibility process, as evidenced by the comparable oil recovery to that of the no mobility control case. At the same time the mobility of carbon dioxide was decreased more than twenty-fold. This important flnding demonstrates that the mobility control method produces effective mobility control without adversely affecting the miscible recovery mechanism. 

Heller, J.P. Taber, J.J. Development of Mobility Control Methods to Improve Oil Recovery by CO9 - Final Report, U.S. Dept, of Energy Report DOE/MC/10689-17, November 1983. 

Dyes (36) and Blackwell et al. (37) as a mobility-control method to be used with light hydrocarbon solvent floods. Although the original suggestions were for simultaneous injection of water and solvent, field practicalities changed this to alternation. Because of the low viscosity of C02, WAG has become the standard for use in these floods as well, with the only variables being the WAG ratio (volumetric water rate C02 rate) and the WAG cycle time. Most of the C02 floods now being operated are WAG floods, often with a cycle time of 1 year and a WAG ratio of 1 1 or 2 1. 

Water-in-oil macroemulsions have been proposed as a method for producing viscous drive fluids that can maintain effective mobility control while displacing moderately viscous oils. For example, the use of water-in-oil and oil-in-water macroemulsions have been evaluated as drive fluids to improve oil recovery of viscous oils. Such emulsions have been created by addition of sodium hydroxide to acidic crude oils from Canada and Venezuela. In this study, the emulsions were stabilized by soap films created by saponification of acidic hydrocarbon components in the crude oil by sodium hydroxide. These soap films reduced the oil/water interfacial tension, acting as surfactants to stabilize the water-in-oil emulsion. It is well known, therefore, that the stability of such emulsions substantially depends on the use of sodium hydroxide (i.e., caustic) for producing a soap film to reduce the oil/water interfacial tension. 

The effectiveness of C02 in displacing oil from reservoirs is marred, however, by its extremely low viscosity. The viscosity of dense C02 remains low (in the range from 0.03 to 0.08 cp or 0.03 to 0.08 mpa) despite its relatively high density (above 0.45 g/cm3) under reservoir conditions. This low viscosity of C02 as compared to that of crude oil (1-10 cp) results in a high mobility ratio which degrades the macroscopic efficiency of the displacement process. Therefore, some method of mobility control is required for efficient use of C02, to increase greatly the quantity of producible oil. 

Ruggedness testing evaluates how small changes in the method conditions affect the measurement result, e.g. small changes in temperature, pH, flow rate, composition of mobile phase, etc. The aim is to identify and, if necessary, better control method conditions that might otherwise lead to variation in measurement results, when measurements are carried out at different times or in different laboratories. It can also be used to improve precision and bias. 

Mobility control, issues in, 18 626 Mobility control agents polyacrylamides as, 18 625 in polymer flooding, 18 622 Mobility control surfactants, in enhanced oil recovery, 18 625-628 Mobilizable vectors, for genetic manipulation, 12 471 Mobilization, of ascorbic acid, 25 771 Modacryhc fibers, 9 192 11 188, 189, 190 dyesite content of, 11 195 flame resistance of, 11 214 flammability of, 11 194 pigmented, 11 213 U.S. production of, 11 220t Mode conversion phenomenon, 17 422 Model agreements, 24 373-374 Model-based methods, for reliability, 26 1044... 

Beyond the density changes that can be used to control method modifications in SFC, the mobile phase composition can also be adjusted. Typical LC solvents are the first choice, most likely because of their availability, but also because of their compatibility with analytical detectors. The most common mobile phase modifiers, which have been used, are methanol, acetonitrile and tetrahydrofuran (THF). Additives, defined as solutes added to the mobile phase in addition to the modifier to counteract any specific analyte-column interactions, are frequently included also to overcome the low polarity of the carbon dioxide mobile phase. Amines are among the most common additives. 

By improving "sweep" and "mobility control," surfactant-based methods offer the most promising ways to alleviate these problems. This use of surfactants appears to be just on the verge of commercialization for steam flooding. Because miscible CO2 flooding has been commercialized more recently, the use of surfactants to improve gas-flood EOR has not yet been commercialized. Conceivably, however, the long-term viability of gas flooding could prove to be dependent on the success of current research efforts in the use of surfactants to alleviate "bypass" problems. 

It can be anticipated that all gas-flood projects, as they are presently being carried out, will leave a large fraction of the reservoir oil uncontacted by the injected fluids. This bypassed oil will remain in place, undisplaced by the injected fluid. Thus, in each current field project, the amount of incremental oil produced by gas flooding could be substantially increased if the uncontacted oil could be reached. The improvement of the vertical and areal distribution of injected fluids throughout the reservoir, so that they contact substantially more oil, will require much better methods of sweep and mobility control. 

While mechanistic simulators, based on the population balance and other methods, are being developed, it is appropriate to test the abilities of conventional simulators to match data from laboratory mobility control experiments. The chapter by Claridge, Lescure, and Wang describes mobility control experiments (which use atmospheric pressure emulsions scaled to match miscible-C02 field conditions) and attempts to match the data with a widely used field simulator that does not contain specific mechanisms for surfactant-based mobility control. Chapter 21, by French, also describes experiments on emulsion flow, including experiments at elevated temperatures. 

The development of a rational strategy of surfactant design requires some way of estimating the dependence of phase parameters on surfactant structure and reservoir characteristics (e.g., salinity). Chapter 9, by Borchardt, describes a method for correlating phase and physical properties of mobility control surfactants with their molecular structures. 

The manner of injection of the C02 is often at question. When no mobility-control additive is used, the choice is usually between continuous C02 injection and the so-called WAG (water alternated with gas) method. Continuous C02 injection method is generally used only when the reservoir is very tight or water-sensitive, so that water could be injected only at an uneconomically low rate. WAG was originally suggested by Caudle and... 

This chapter reports adsorption data for a number of surfactants suitable for mobility control foams in gas-flooding enhanced oil recovery. Surfactants suitable for foam-flooding in reservoirs containing high salinity and hardness brines are identified. The results of adsorption measurements performed with these surfactants are presented surfactant adsorption mechanisms are reviewed and the dependence of surfactant adsorption on temperature, brine salinity and hardness, surfactant type, rock type, wettability and the presence of an oil phase is discussed. The importance of surfactant adsorption to foam propagation in porous media is pointed out, and methods of minimizing surfactant adsorption are discussed. 

Low tension waterflooding is a method intermediate between alkaline and micellar/polymer technology. The LTWF employs a dilute surfactant to reduce IFT and mobilize residual oil. A few field trials (26-29) of this process have been tried with mixed success. None of these trials however employed sodium silicates in any part of the flood design. Instead, other alkalis such as sodium carbonate and sodium tripoly- phosphate were used. Some of the reasons proposed for the limited success in these trials were 1) high consumption of the sacrificial agents, leaving the surfactant unprotected, 2) poor sweep of the pay zone, 3) limited mobility control and lower than expected displacement efficiency. Recent work published and obtained in our laboratories has shown that sodium silicates may help to overcome some of these problems better than other alkalis. 

Y. Kanayama, Y. Kimura, F. Miyazaki, T. Noguchi, A stable tracking control method for a non-holonomic mobile robot, in Proceedings of the lEEE/RSJ International Workshop on Intelligent Robots and Systems.(Osaka, Japan, 1991), pp 1236-1241... 

In conclusion, much has been learned since Uren, Fahmy and others started investigating the possibility of improving oil recovery by using materials to alter the surface properties of the oil-water-solid system. An ideal displacement process for displacing oil should include good mobility control and a method for keeping the oil phase continuous while low oil-water interfacial tension is maintained. 

At the present time the improvement of areal and vertical (volumetric) sweep efficiency takes a great deal of room in secondary and tertiary oil recovery. One of the widely used and perspective methods is mobility control by diluted aqueous solutions of different polyacrylamides (1,2). In the middle of the sixties some authors (3,4) proposed that the viscosity enhancement and the non-Newtonian flow behavior of the solutions were responsible for the reduction of phase mobility. Mungan (5,6), Gogarty (7), Dauben and Menzie (8) have pointed out, however, that the sorption phenomenon plays a decisive role in the flow characteristics of the polymer solutions and carrier phases. In the papers devoted to... 

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