Mobility control discussion

New section on the role of perilipin phosphorylation in the control of fat mobilization New discussion of the role of acetyl-CoA in the integration of fatty acid oxidation and synthesis... 

This book focuses on chemical EOR processes, including alkaline (A), surfactant (S), polymer (P), and any combination of these processes. We discuss emulsion whenever it relates to any chemical processes. In addition, we briefly describe foam when presenting an application of ASP with foam. Emulsion and foam are more related to mobility control. These two processes are not discussed in detail because they are thermodynamically unstable processes quite different from the stable processes we deal with here. Rather, we discuss the general mobility control requirement in EOR processes in Chapter 4. 

Mobility control is one of the most important concepts in any enhanced oil recovery process. It can be achieved throngh injection of chemicals to change displacing fluid viscosity or to preferentially rednce specific flnid relative permeability through injection of foams, or even through injection of chemicals, to modify wettability. This chapter does not address a specific mobility control process. Instead, it discusses the general concept of the mobility control requirement in enhanced oil recovery (EOR). 

Discussion of the CONCEPT OF TEHE Mobility Control Requirement... 

After a discussion of the mobility control requirement using the simplified flow model, this section moves to a model with realistic water and oil relative permeability curves. Now the interstitial (connate) water saturation and residual oil saturation are 0.2. The endpoint relative permeabilities of oil and water are 0.85 and 0.3, respectively. The Corey exponents of relative permeabilities for oil and water are 2. Others are the same as those in the simplified model discussed earlier particularly, the initial water saturation is 0.5. Again, capillary and gravity are not included. 

Polymers that have been suggested for mobility control in oil reservoirs include polyacrylamides, hydroxy ethyl cellulose, and modified polysaccharides which are produced either by fermentation or by more conventional chemical processes. In this paper the solution properties of these polymers are presented and compared for tertiary oil recovery applications. Among the properties discussed are non-Newtonian character for different environmental conditions (electrolytes and temperature), filterability, and long term stability. The behavior of these water soluble polymers in solution can be correlated with the effective molecular size which can be measured by the intrinsic viscosity technique. A low-shear capillary viscometer with a high precision and a capability of covering low shear rates (such as 10 sec - - for a 10 cp fluid) has been designed to measure the viscosities. The measurement of viscosities at such slow flow conditions is necessitated... 

The purpose of this discussion is to acquaint the reader with the constraints of C02 flooding and the requirements for mobility control. The major requirements are (1) that the thickening that is produced in the displacing fluid should extend back from the displacement front by a dis-... 

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. 

In general, trends in MRF with surfactant concentration and foam quality are consistent for all surfactants, but the effects of brine salinity (Figure 4) and temperature (3) vary from surfactant to surfactant. Different surfactants are also affected to different degrees by the presence of an oil phase, as discussed in Chapter 4 of this book. The MRF increases with increasing permeability (Figure 5), as also noted by Lee and Heller (4) and described earlier in Chapter 5. This effect could be very beneficial to foam performance, because it leads to better mobility control in high-permeability zones. 

This section has demonstrated that some commercially available surfactants are soluble in brines of extreme salinity and hardness and also form effective mobility control foams under these conditions. The remainder of this chapter is devoted to the development of a better understanding of the adsorption properties of foam-forming surfactants, mainly those for high-salinity conditions. It is hoped that this discussion will contribute to the development of a systematic approach for selecting or formulating surfactants with minimal adsorption levels. 

Other techniques such as the mobility controlled caustic flooding process by Saram (20, 21, 22) and combinations of polymer and alkali have been investig ated, but these have not been widely used as yet and are currently perceived as extensions of the three processes discussed above. 

Recently, Wellington and Richardson [J5] presented an interesting paper discussing the mechanism of low surfactant concentration enhanced water flood. The surfactant system consisted of alkyl-PO-EO glyceryl sulfonate with small amounts of an ethoxylated cationic surfactant to control phase behavior, interfacial activity, and surfactant loss. The surfactant systems had the ability to reduce their cloud point and interfacial tension when diluted, which was regarded as very useful for an effective flood performance. A surfactant concentration of about 0.4% removed essentially all the residual oil from sand packs in just over f PV with a surfactant loss of less than O.f PV. Mobility control by polymer was strongly required for good displacement and sweep efficiency and to reduce surfactant loss. 

Partially hydrolysed PAM solutions have been shown to suffer mechanical degradation during injection into and flow within porous media (Maerker [1975] and other references in Chapter 4, Section 4.4). This is a major problem in oil recovery, as this will reduce the polymer s ability to provide mobility control in a reservoir. The stretching of the flexible coils of the PAM molecule can break it into smaller molecular weight fragments, thus reducing the polymer viscosity. This issue is discussed in more detail in Chapter 4 above however, the point is reiterated here in order to stress the connection between the viscoelastic behaviour and the mechanical degradation phenomenon. 

Mobility control is a generic term describing any process where an attempt is made to alter the relative rates at which injected and displaced fluids move through a reservoir. The objective of mobility control is to improve the volumetric sweep efficiency of a displacement process. In some processes, there is also an improvement in microscopic displacement efficiency at a specified volume of fluid injected. Mobility control is usually discussed in terms of the mobility ratio, M, and a displacement process is considered to have mobility control if 1.0. Volumetric sweep efficiency generally increases as M is reduced, and it is sometimes advantageous to operate at a mobility ratio considerably less than unity, especially in reservoirs with substantial variation in the vertical or areal permeability. 

The testing methods discussed above may be used to determine-the effectiveness of polymer upon injection through perforations into a formation. The following may be concluded- under the specific field conditions at C-H Minnelusa Unit related to the use of partially hydrolyzed polyacrylamides as mobility control agents. ... 

Retention is controlled by solute interactions with both the mobile phase and the stationary phase and each will be discussed in this chapter. Interactions in the mobile... 

If the mixture to be separated contains fairly polar materials, the silica may need to be deactivated by a more polar solvent such as ethyl acetate, propanol or even methanol. As already discussed, polar solutes are avidly adsorbed by silica gel and thus the optimum concentration is likely to be low, e.g. l-4%v/v and consequently, a little difficult to control in a reproducible manner. Ethyl acetate is the most useful moderator as it is significantly less polar than propanol or methanol and thus, more controllable, but unfortunately adsorbs in the UV range and can only be used in the mobile phase at concentrations up to about 5%v/v. Above this concentration the mobile phase may be opaque to the detector and thus, the solutes will not be discernible against the background adsorption of the mobile phase. If a detector such as the refractive index detector is employed then there is no restriction on the concentration of the moderator. Propanol and methanol are transparent in the UV so their presence does not effect the performance of a UV detector. However, their polarity is much greater than that of ethyl acetate and thus, the adjustment of the optimum moderator concentration is more difficult and not easy to reproduce accurately. For more polar mixtures it is better to explore the possibility of a reverse phase (which will be discussed shortly) than attempt to utilize silica gel out of the range of solutes for which it is appropriate. 

The hydrolysis of acetals and ortho esters is governed hy the stereoelectronic control factor previously discussed (see A and B on p. 427) though the effect can generally be seen only in systems where conformational mobility is limited, especially in cyclic systems. There is evidence for synplanar stereoselection in the... 

The behaviour, which is not controlled by the topochemical rule but is greatly influenced by non-topochemical factors, is discussed in Section 2 in terms of molecular mobility, stabilization energy by orbital interaction and energy transfer in the crystals. 

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