Mobility control characteristics

In addition to the mobility control characteristics of the surfactants, critical issues in gas mobility control processes are surfactant salinity tolerance, hydrolytic stability under reservoir conditions, and surfactant propagation. Lignosulfonate has been reported to increase foam stability and function as a sacrificial adsorption agent (392). The addition of sodium carbonate or sodium bicarbonate to the surfactant solution reduces surfactant adsorption by increasing the aqueous phase pH (393). 

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 surfactant systems used for mobility control in miscible flooding do not form a surfactant rich third phase, and lack its buffering action against surfactant adsorption. Furthermore, for obvious economic reasons, it is desirable to keep the surfactant concentration as low as possible, which increases the sensitivity of the dispersion stability to surfactant loss. Hence, surfactant adsorption is necessarily an even greater concern in the use of foams, emulsions, and dispersions for mobility control in miscible-flood EOR. The importance of surfactant adsorption in surfactant-based mobility control is widely recognized by researchers. A decision tree has even been published for selection of a mobility-control surfactant based on adsorption characteristics (12). 

The block of data concerned with this area generally does not consider the developments concerning the solution behavior of nonmobility control polymers which has been reported in the polymer literature. Implicitly, one is led to believe that the mobility control polymer solutions are unique and have little in common with more conventional polymer solutions. This study will show that there is a direct qualitative correlation between the behavior of mobility control polymer solutions and other solutions of macromolecules. In particular, it is demonstrated that the viscous properties are directly related to the hydrodynamic size of the polymer chain and the influence of system characteristics such as salt concentration, shear rate, etc., can be correlated with the effective size of the polymer molecule in solution. Consequently, this study suggests that more emphasis should be placed on the measurement of the molecular size of mobility control polymers in solution if a fundamental understanding of these solutions is to be developed. 

In this paper the solution properties of a spectrum of mobility control polymers have been compared. Polysaccharides, polyacrylamides, and hydroxy ethyl cellulose show vastly different solution behavior. Despite this, the properties investigated can be correlated by noting one molecular characteristic of these polymers, namely molecular size. 

Flow resistance of foams is much higher than that of the liquid or gas phases alone. This characteristic is utilized for foam-based mobility control in enhanced oil recovery (41—46). The gas mobility in porous medium and the dilatational modulus of a-olefin sulfonates are plotted in Figure 12 (22). The displacement efficiency of the foam in the porous medium is higher if the blocking efficiency of the foam is higher. In the systems... 

Polymers are used for mobility control in chemical flooding processes such as micellar-polymer and caustic-polymer flooding and in polymer augmented waterflooding. Selection of a polymer for mobility control is a complex process because it is not possible to predict the behavior of a polymer in porous rock from rheological measurements such as viscosity/ shear rate curves. Polymers used for mobility control are non-Newtonian fluids. Flow characteristics are controlled by the shear field to which the polymer is subjected. Properties of polymers can be measured under steady shear in rheometers. However, in porous rock, it is difficult to define the shear environment a polymer experiences as it flows through tortuous pores. 

Considerable research has been conducted to identify water soluble polymers which can efficiently control the flow properties of displacement fluids for enhanced oil recovery.Two main types of polymeric viscosifiers have emerged from this research which rely mainly on ultra high molecular weight for thickening efficiency natural biopolymers such as Xanthan or Scleroglucain and synthetic acrylamide based polymers. Although these polymers possess many useful characteristics, the reservoir conditions in which they can provide adequate mobility control are limited. For example, the biopolymers provide excellent mechanical stability and salt tolerance, however, further improvement in high temperature stability would be desirable. 

Copolymer structure has a marked effect on solution properties and thus behavioral characteristics of water-soluble copolymers utilized in enhanced oil recovery. Perhaps the most critical property of a candidate polymer for mobility control is its ability to maintain a large hydrodynamic volume (HDV) in the presence of mono- and divalent electrolytes. Additionally the structure and HDV of the polymer must be tailored to allow permeation through the reservoir rock without entrapment, adsorption, or shear degradation. 

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... 

A xanthan biopolymer (C= 1,500 ppm) is to be used for mobility control in a waterflood in a sandstone reservoir. Flow characteristics of the biopolymer are given by the correlations developed by Willhite and Uhl in Eqs. 5.23e through 5.23g Table 5.66 gives properties of the reservoir. An injectivity test is planned in a watered-out five-spot pattern with a pattern area of 5 acres. Predict the pressure drop between the injection well and the effective radius of the pattern as a function of volume of polymer injected when 5,000 bbl of polymer is injected at a constant rate of 10 B/D-ft. Plot pressure drop as a function of volume of polymer injected (barrels). Assume that the region around the wellbore is at ROS and the permeability to water at ROS is 50 md. The polymer is shear thinning until the Darcy velocity is less than 0.1 ft/D. Polymer retention is 40 Ibm/ acre-ft. The density of the water is 62.4 Ibm/ft at reservoir temperature. Find the fraction of polymer retained. Determine the time required for the injectivity test. 

Pesticides vary widely in their chemical and physical characteristics and it is their solubility, mobility and rate of degradation which govern their potential to contaminate Controlled Waters. This, however, is not easy to predict under differing environmental conditions. Many modern pesticides are known to break down quickly in sunlight or in soil, but are more likely to persist if they reach groundwater because of reduced microbial activity, absence of light, and lower temperatures in the sub-surface zone. 

The concept of a characteristic reaction temperature must, therefore, be accepted with considerable reservation and as being of doubtful value since the reactivity of a crystalline material cannot readily be related to other properties of the solid. Such behaviour may at best point towards the possible occurrence of common controlling factors in the reaction, perhaps related to the onset of mobility, e.g. melting of one component or eutectic formation, onset of surface migration or commencement of bulk migration in a barrier phase. These possibilities should be investigated in detail before a mechanism can be formulated for any particular chemical change. 

The maintenance of product formation, after loss of direct contact between reactants by the interposition of a layer of product, requires the mobility of at least one component and rates are often controlled by diffusion of one or more reactant across the barrier constituted by the product layer. Reaction rates of such processes are characteristically strongly deceleratory since nucleation is effectively instantaneous and the rate of product formation is determined by bulk diffusion from one interface to another across a product zone of progressively increasing thickness. Rate measurements can be simplified by preparation of the reactant in a controlled geometric shape, such as pressing together flat discs at a common planar surface that then constitutes the initial reaction interface. Control by diffusion in one dimension results in obedience to the... 

As with solid phase decompositions (Sect. 1), the kinetic characteristics of solid—solid interactions are controlled by the properties of lattice imperfections, though here many systems of interest involve the migration, in a crystal bulk of a mobile participant, from one interface to another. Kinetic measurements have been determined for reactions in a number of favourable systems, but there remain many possibilities for development in a field that is at present so largely unexplored. 

As a result of its highly polar character, silica gel is particularly useful in the separation of polarizable materials such as the aromatic hydrocarbons and polynuclear aromatics. It is also useful in the separation of weakly polar solute mixtures such as ethers, esters and in some cases, ketones. The mobile phases that are commonly employed with silica gel are the n-paraffins and mixtures of the n-paraffins with methylene dichloride or chloroform. It should be borne in mind that chloroform is opaque to UV light at 254 nm and thus, if a fixed wavelength UV detector is being used, methylene dichloride might be a better choice. Furthermore, chloroform is considered toxic and requires special methods of waste disposal. Silica gel is strongly deactivated with water and thus, to ensure stable retentive characteristics, the solvent used for the mobile phase should either be completely dry or have a controlled amount of water present. The level of water in the solvent that will have significant effect on solute retention is extremely small. The solubility of water in n-heptane is... 

---