Mobility reduction

For the wet case, the foam enters and achieves steady state after several pore volumes. A mobility reduction compared to water of about 90% ensues. However, for the dry case, there is about a one pore-volume time lag before the pressure responds. During this time, visual observations into the micromodel indicate a catas-tropic collapse of the foam at the inlet face. The liquid surfactant solution released upon collapse imbibes into the smaller pores of the medium. Once the water saturation rises to slightly above connate (ca 30%), foam enters and eventually achieves the same mobility as that injected into the wet medium. 

Transport of O2 away from a root and its consumption in microbial processes—in addition to nitrification—and oxidation of mobile reductants such as Fe +. Microbial O2 consumption is described with Michaelis-Menten kinetics and Fe + oxidation with first-order kinetics with respect to both... 

Maini, B. Laboratory Evaluation of Foaming Agents for High Temperature Applications -III. Effect of Residual Oil on Mobility Reduction Performance in Proc. 37th Ann. Tech. Meeting CIM, The Petroleum Society Calgary, AB, 1986, paper CIM 86-37-01. 

Displacement of the discrete CO2 segments results in a much larger apparent viscosity inside porous media than the viscosity of any of the constituents. Small amounts of surfactant give large CO2 mobility reductions even at low saturation and fractional flow of brine. The mobility level can be adjusted through surfactant concentration, structure and gas/liquid ratio. 

Varion CAS foams well but the foam also dies out rather quickly. It must be a fast draining foam. In general, the critical concentration (above which no further mobility reduction takes place) is well above the CMC range of the surfactant solution. 

These mobility reductions decreased the WOR in nearby wells to 12, during the period in which the WOR increased to 28 in the rest of the field. 

These studies revealed that, at least when the dopant (A ) is small and mobile, reduction of the polymer decreases the anion exchange capacity of the polymer and increases the hydrophobicity of the polymer backbone. These changes inevitably affect how the polymer interacts with the immediate environment. 

In UTCHEM, the viscosity of the aqueous phase that contains the polymer is multiplied by the value of the polymer permeability reduction factor, F r, to account for the mobility reduction. In other words, water relative permeability, km, is reduced, whereas oil relative permeability, k , is sometimes considered almost unchanged. The reason is that polymer is not soluble in oU, so it will not reduce effective oil permeability. The mechanism of disproportionate permeability reduction is widely used in gel treatment for water shut-off. Many polymers and gels can reduce permeability to water more than to oil or gas. 

Because of its long hydrocarbon "tail" of isoprene units, CoQ is soluble in the hydrophobic core of phospholipid bilayers and is very mobile. Reduction of CoQ to the fully reduced form, QH2, occurs in two steps with a half-reduced free-radical intermediate, called semiquinone. 

Ample evidence suggests that crude oil can have an effect on foams applied to enhanced oil recovery. Rendall et al. (21) investigated the behavior of several commercial surfactant-stabilized foams in the presence of crude oils. On the basis of dynamic bulk foaming tests, gas mobility reduction factors measured in reservoir cores, and observations in a micro-... 

Figure 10. Mobility reduction factors for foams flowing in Berea sandstone at residual oil saturation versus the breakage frequencies of foam lamellae flowing in a microvisual cell when in contact with the same oil (Reproduced with permission from reference 40. Copyright 1990 Society of Petroleum Engineers.)...

Figure 11 shows all of these core-flood foam performance results plotted versus the logarithm of the lamella number. A strong correspondence is obtained with the logarithm of lamella number. That the trend between mobility reduction and lamella number is so consistent among the different systems is remarkable considering that the core-flood results... 

Often the best solution is to present a dimensionless number that indicates the effectiveness of the surfactant. Such an index is the mobility-reduction factor, mrf, which is the ratio of the mobility of the COz foam, Aco foam to total mobility of the mixture of surfactant-free brine, brine an< dense C02, Aco, at the same gas—liquid volumetric flow ratio. 

C02-foam mobility was reduced with all of these surfactants, although there were significant differences in the degree of mobility reduction. In particular, both anionic and nonionic surfactants were effective, as were the amphoteric surfactants. The major differences became evident when the amount of their adsorption on rock and their chemical stabilities were tested. 

However, the most exciting result of these experiments came when the effect of foam in different rock samples was investigated. The measured mobilities did not vary over nearly as wide a range as the permeabilities of these rocks. However, when the variation of relative mobilities were examined on a log—log plot against the permeabilities, an important trend could be discerned. The reciprocal of relative mobility can be called the effective viscosity of the C02 foam. This parameter varies, at least for these conditions, as shown in Figure 7 (33). Apparently, the C02 foam under these conditions acts like a more viscous fluid in high-permeability rock than in low-permeability rock. This selective mobility reduction (SMR) is the type of behavior that is needed for C02 foam to perform, as had been optimistically assumed in early foam literature. 

The kinds of different surfactants that are, or have been, of interest for use in C02 foams have also been referred to with special emphasis on the problems of measurement of foamability and of the property by which surfactants adsorb onto reservoir rock. A current research question concerns the apparent ability of certain surfactants to generate C02 foams that exhibit selective mobility reduction (SMR). The mobility is reduced by a greater fraction in high than in low permeability rocks by such a foam. This property thereby promises to compensate, at least partially, for the natural heterogeneity of reservoirs. 

An alternative approach to minimizing the effect of residual oil is the injection of air with steam ahead of the foam front. Air converts the residual oil to coke the result is improved mobility reduction behavior of the ensuing steam-foam (33). 

Surfactant propagation in the reservoirs has been modeled (44, 45) by allowing for surfactant adsorption, oil partitioning, and first-order surfactant decomposition all of these variables are functions of temperature. The foam mobility reduction is taken into account by reducing the gas relative permeability as follows ... 

Mobility reduction factor (MRF) in porous media Foam generated by... 

Foam Effectiveness in Porous Media. No generally accepted correlations exist between foam characteristics measured outside the porous medium and foam effectiveness as a gas mobility-reducing agent in porous media. The performance of the nine surfactants that passed the solubility criteria was therefore evaluated in porous media under typical reservoir conditions. The results of such an evaluation can be expressed in several ways. One of the simplest measures of foam effectiveness, and arguably the most straightforward one, is the mobility-reduction factor (MRF). The MRF is defined as the ratio of pressure gradients across a... 

Figures 2 to 5 show examples of mobility reduction factors measured in oil-free Berea cores containing high-salinity, high-hardness brines under reservoir conditions. (An explanation of surfactant names used in these figures appears in the Appendix.) Nitrogen was used as the gas phase. MRF values presented in these figures were obtained from pressure gradients measured after pseudosteady-state flow through the linear cores had...

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