Mobility reduction factor measurement

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-... 

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...

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

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. 

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... 

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... 

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. 

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. 

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 ... 

The polymer used in the Vernon pilot exhibits the property of unusually high resistance to flow through porous media. " A small concentration in injected water effects a mobility reduction considerably beyond that predicted from increases in bulk viscosity as measured in a capillary or rotating cup viscosimeter. Water mobility in the subject flood is reduced by a factor of 7.55 with the addition of 500 ppm Pusher chemical to... 

Consequently, mobility reduction is estimated from flow studies for a given sample of reservoir rock and is expressed in terms of a resistance factor . This parameter is defined as the ratio of brine mobility to polymer solution mobility measured at residual oil saturation ... 

Investigatorsstudying partially hydrolyzed polyacrylamide solutions observed apparent viscosities 5 to 20 times the values measured in a conventional viscometer at the shear rates believed to exist in the porous media. These viscosity increases were not anticipated from the rheological behavior of the fluids. Pye introduced the concept of the resistance factor to quantify this effect. Burcik observed a decrease in the mobility of brine in a Berea sandstone disk that had been previously contacted with partially hydrolyzed polyacrylamide. The mobility reduction persisted even after 100 PV of brine had been flushed through the disk. Burcik concluded that polymer molecules retained in the pore structure by adsorption or mechanical entrapment were hydrophillic and restricted the flow of water. 

Table 1 summarizes the results of the field sample analyses standardized for polymer concentration. The quality of the field injection sampled collected both at the well and bottom compared closely to that of a laboratory weighed and dried polymer standard prepared in the field using normal laboratory procedures. This 300 mg/l polymer solution had a measured screen factor of 12. 9 and a viscosity, measured at 115 seconds" shear rate, of 3. 93 cp. Laboratory derived correlations showed that this standard corresponded to a mobility reduction effect, expressed in terms of a resistance factor, of 32. The close comparison between this unsheared standard and field injection samples implied that neither the surface nor bottom hole sampling induced any shear degradation. 

The reduction of the long-range diffusivity, Di by a factor of four with respect to bulk water can be attributed to the random morphology of the nanoporous network (i.e., effects of connectivity and tortuosity of nanopores). For comparison, the water self-diffusion coefficient in Nafion measured by PFG-NMR is = 0.58 x 10 cm s at T = 15. Notice that PFG-NMR probes mobilities over length scales > 0.1 /rm. Comparison of QENS and PFG-NMR studies thus reveals that the local mobility of water in Nafion is almost bulk-like within the confined domains at the nanometer scale and that the effective water diffusivity decreases due to the channeling of water molecules through the network of randomly interconnected and tortuous water-filled domains. ... 

Biynda et al. (1993) measured photogeneration efficiencies of PMPS doped with acceptor molecules with different reduction potentials. Acceptor doping increased the phologeneration efficiencies by as much as a factor of 10, but decreased the mobilities. The increase in efficiency scaled with decreasing reduction potential. 

Hole mobilities were measured for DEH doped PC and PS by Yuh and Pai (1990b, 1992). Mobilities for DEH doped PS were approximately a factor of 3 higher than for DEH doped PC. The increase was attributed to a reduction in the activation energy. A similar argument was proposed (Yuh and Pai, 1990, 1990a) to describe the role of the polymer host for TPD doped polymers. 

Enokida et al. (1991) measured hole mdbilities of PMPS before and after ultraviolet exposures. The exposures were of the order of 1 erg/s-cm2. Prior to the exposures, the mobilities were approximately 10-4 cm2/Vs and weakly field dependent. Following the exposures, a decrease in the mobility was observed. Under vacuum exposure conditions, a decrease of approximately 40% was observed for a 1 h exposure. Under atmospheric conditions, however, the decrease was approximately a factor of 4. Enokida et al. attributed the decrease in mobility to the formation of Si-O-Si bonds in the Si backbone chain. A similar study of PMPS was described by Naito et al. (1991). While the field and temperature dependencies of the mobility were not affected by the ultraviolet exposures, the dispersion in transit times increased significantly. The change in dispersion could be removed by subsequent annealing. The authors attributed the increase in transit time dispersion to a reduction in the hole lifetime, induced by Si dangling bonds created by the ultraviolet radiation. 

In general, the hollow cylinder or average microenvironment model fits the NH data extraordinarily well with only minor variation in rj, the effective density of animals. The required variation in r- presumably comes about because of the uneven distribution of animals within sediment (Jumars et al., 1977) and mobility. It may also be apparent variation due to the arbitrary requirement that r, remain fixed. The variation forced into r2 by this restriction could actually reflect changing boundary conditions at r, for example, inhibition to diffusion by burrow linings or a reduction in irrigation activity. A part of the discrepancy between the model and measured profiles could also reflect changes in the production rate of NH/ because of factors other than temperature. For example, fall profiles may show a smaller maximum than predicted, due to a lower reaction rate resulting from a depletion of substrate (see Nixon et al., 1980). 

The results from a typical injectivity test are given in Figure 12 where resistance factor (RF) and residual resistance factor (RRF) are plotted versus the number of pore volumes of polymer and brine injected. Resistance factor is the mobility of brine (k/p) divided by the mobility of polymer and is a measure of the reduced Injection rate the polymer produces in a given reservoir rock. Residual resistance factor is the mobility of brine before polymer injection divided by the mobility of brine after polymer injection. Thus, a permeability reduction of 99 percent corresponds to an RRF of 100. 

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