Mobility reduction factor

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.)...

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. 

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...

Figure 2. The dependence of mobility-reduction factor on surfactant concentration in Berea sandstone at 80 °C and 98% foam quality in 210,000 ppm (21 mass %) reservoir brine.

Table IV. Comparison of Mobility-Reduction Factors Measured with Nitrogen and with Light Hydrocarbon Solvent Mixtures...

Measurements of mobility-reduction factors showed that the surfactants for which adsorption levels are shown in Figure 15 are equally effective in generating mobility-control foams in porous media. Selection of... 

Many hydrocarbon-miscible floods are run in reservoirs containing brines of extremely high salinity and hardness. Surfactants that may be used for mobility control foams at such conditions are commercially available. The effectiveness of foams generated with these surfactants was illustrated by way of representative mobility reductions factors measured in oil-free porous media. 

Mobility Reduction Factor (MRF) A dimensionless measure of the effectiveness of a foam at reducing gas mobility when flowing in porous media. The mobility reduction factor is equal to the mobility (or pressure drop) measured for foam flowing through porous media, divided by the mobility (or pressure drop) measured for surfactant-free solution and gas flowing at the same volumetric flow rates. 

Meso-scale experiments involve conducting foam floods in samples of porous rock, which may be reservoir core samples or quarried sandstones and carbonates, the quarried samples being more reproducible. The overall rock dimension here is of the order of 10 cm. These meso-scale foam floods allow the determination of gas mobility reduction by foams under widely varying conditions [J]. The mobility reduction factor (MRF) is the ratio of pressure drops across a core resulting from the simultaneous flow of gas and liquid in the presence and absence of surfactant in the liquid phase. Mobility reduction factors achieved depend on many factors [82, 83, 88, 89] including ... 

Foam experiments were duplicated in both short (20 cm) and long (2 m) Berea cores to ascertain how to scale-up foam performance. Gas mobility reduction factors were measured at pseudo-steady state as a function of foam quality, and foam velocity in oil free cores and at residual oil saturation, at room temperature and at 7000 kPa system pressure. 

The experimental results indicate that different water fractional flows, for particular frontal advance rates, are needed to generate strong foams. This effect is much more pronounced in the presence of oil, i.e. higher fractional flow of water was needed to establish significant mobility reduction factors when residual oil was present. Foams generated in the presence of residual oil produced consistently lower mobility reduction factors than foams generated in cores without oil. 

Foam Flooding in Oil Free Cores. Short Core Experiments. The bulk of the short core experiments consist of measurements of pressure drops and mobility reduction factors (MRFs) generated by foams in porous media. The MRF is determined by comparing the pressure drop across a core during simultaneous injection of surfactant solution and gas with that during injection of brine (without surfactant) and gas at the same experimental conditions. The MRF is defined as follows ... 

Calculated mobility reduction factors are also shown in Figure 6. For the 60% foam quality case an experimental baseline pressure drop was not available, so we used the results of the modelling work described in a later section to estimate the pressure drop expected for gas/brine flow at the appropriate fractional flow. Since the 95% quality foam flood did not reach steady state foam flow conditions, and since the pressure drops in individual sections of the long core were influenced by the pressure drops due to foam flowing in downstream sections of the core, we cannot make exact comparison between the MRFs generated in the long core with... 

Figure 6. Mobility reduction factors from long core experiment (no oil).

The foam factor FFmax is a scaling factor that weighs the overall foam effects. FFmax is related to the foam mobility reduction factor MRF , but there exists no straightforward correlation between the two factors. In the STARS formulation, the single capillary number Nep is based on the local pressure drop, and the length over which the pressure drop is effective ... 

APf/AP , mobility reduction factor monolayer coverage of surfactant monolayer coverage of solvent K APIctL, capillary number based on pressure reference capillary number for shear thinning p v /a, water capillary number PgVg/a, gas capillary number lamellae number per unit volume pressure... 

Once the foam flows into a specific zone, the mobility of the fluid in this zone will decrease. This is referred to as the mobility reduction factor, MRF. 

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