Therefore, a foam surfactant reduces the gas mobility by reducing the gas relative permeability and increasing the apparent gas viscosity Friedmann et al. Gas flowing and gas trapped phenomena in porous media Kloet et al. Foam is generated by injecting gas and surfactant solution in a surfactant alternating gas SAG mode. Tsau et al. Farzaneh and Sohrabi, have observed that, the blend of anionic and nonionic surfactant showed better foaming stability, mobility reduction and less adsorption than that generated by an anionic surfactant alone.
Andrianov et al. Formulation of surfactant blend was tested in order to see the effect of generated good foam and its stability in oil. Schramm and Green have carried out MRF test at atmospheric condition. Wassmuth et al. N 2 gas was used for injection. Chevron Chaser GR with 0. They worked on modeling and MRF at different injection rates. In addition result was compared with different generated foams Wassmuth et al.
Octylphenol ethoxylate surfactant Triton X was purchased from Sigma-Aldrich. Chemicals U. Table 1 presents the composition of synthetic brine. Crude oil was collected from an oil field offshore of Malaysia. The density of oil was measured as 0. The specific gravity of crude oil is 0. The specific gravity and degree API is calculated by using following formula.
Molecular weight of crude oil is Table 2 presents the crude oil composition at atmospheric conditions. Pure CO 2 gas was selected. Berea sandstones were selected due to the hardness of its quartz grains bounded by silica. These core samples possess a chemical resistance to the erosive action of the acidic chemical.
Further, silica bond does not deteriorate with temperature change and time. These types of Berea sandstone are considered as an excellent sandstone for lab experiments, particularly in enhanced oil recovery EOR. Table 3 presents the properties of Berea core samples used in MRF experiments. For screening the surfactant blend solutions for their ability, foam stability tests were performed at atmospheric conditions.
These tests provide ideas of a possible interaction between the target crude oil and the particular blend of surfactant formulation. Figure 2 shows the schematic diagram of foam generation process.
Compact stirrer attached with Mettler Toledo 50 was used. The cup was fixed in the Mettler Toledo. After 5 min, stirrer was stopped and foam height at time equal to zero was recorded. The cup was unfixed from the system and covered with an aluminum sheet and placed on table. Liquid drainage time was noted when liquid drained out and reached 50 ml. Foam half-time of generated foam was noted Duan et al. Further, foam stability and longevity was noted above liquid level with respect to time and foam height in ml graduated cup.
The same procedure was repeated with addition of 1 ml crude oil before mixing in the solution. During the measurement process, crude oil with foam surfactant formulation was considered as Llave and Olsen MRF is the ratio of pressure drop caused by the simultaneous flow of gas and liquid through the rock core samples in presence and absence of surfactant in aqueous phase Hirasaki et al. The Mobility reduction factor may be calculated as;.
Before starting the MRF experiments, core samples were vacuumed with brine for 48 h. Figure 4 presents the schematic diagram of MRF experiments performed at reservoir conditions. Core sample was settled in the core holder.
Other required data such as weight of saturated and dry core sample were put in the software. The fluid brine, CO 2 and foam surfactant were pumped from the accumulator to the core by a syringe type pump. The effluent was collected in the graduated cylinder.
The main four slugs brine, CO 2 , surfactant, CO 2 were injected to determine the foam presence and propagation through the Berea core samples. No precipitations were seen by using these formulations. Foam stability tests were performed at room temperature and atmosphere pressure. Foam stability and longevity of foam surfactant blend formulations are presented in the Table 4. These formulations were measured in absence and presence of crude oil. Figure 5 presents the foam generated in absence and presence of crude oil by 0.
At the initial time 70 ml foam was generated from 20 ml solution of MK1. The foam height decreased slowly. After 90 min, the foam height of MK1 was recorded as 40 ml above the liquid level. In presence of crude oil, the foam height was recorded as 70 ml at the initial time. The solution showed good interaction in the presence of crude oil. The durability of this surfactant solution was recorded after 90 min as 3 ml in presence of crude oil.
Figures 6 , 7 present the foam generated in absence and presence of crude oil by using foam surfactant blend of 0. At the initial time 65 ml foam was generated from 20 ml blend solution of MK2 and 75 ml foam from blend MK3. Once the foam was generated in the ml cup, the foam volume was reduced because liquid drains through the lamellae due to the force of gravity. The lamellae in the upper layer of the foam were thinner than the lower layer of the foam due to the gravity drainage.
After 90 min the foam height of MK2 blend was noted as 30 ml above the liquid level in the cup whereas, 20 ml was noted from MK3. When these two formulations of surfactant blends were tested in presence of crude oil, the foam height was noted as 35 ml from MK2 and 75 ml from MK3 at the initial time. MK3 surfactant blend formulation generated strong foam as compared to surfactant formulation of MK2 in the presence of crude oil. The durability of these surfactant solutions was observed.
After 30 min, the foam height was noted as 3 ml from surfactant blend of MK2 whereas surfactant blend MK3 showed 20 ml in presence of crude oil. Surfactant blend of MK3 generated foam volume greater than individual surfactant of MK1. Foam stability was increased by MK3 because its hydrophobic group of a straight chain surfactant is moved to a more central position in the molecules as proved by Rossen Another reason is use of co-surfactant as an additives with 0.
Foam stability in absence and presence of crude oil by foam surfactant blend 0. The maximum foam height in presence of crude oil was recorded by surfactant blend MK3 as compared to surfactant formulations of MK1 and MK2.
Foam height generally increases with increase in surfactant concentration. The lower the surface tension of the aqueous solution the greater appears to be the foam volume. The foam volume is produced when a given amount of work is done on a surfactant aqueous solution to generate foam. Foam height increases with increase in the length of the chain, because interaction cohesion increases with increase in the length of hydrophobic group.
Further, the liquid drainage in absence and presence of crude oil by this surfactant blend of MK3 was slower as compared to surfactant formulation of MK1 and MK2. Slower liquid drainage by this surfactant blend was due to the presence of small bubbles in generated foam. Something went wrong. Try again? Cited by. Download options Please wait Supplementary information PDF K.
Article type Communication. Submitted 24 Mar Accepted 08 Apr First published 08 Apr Download Citation. Request permissions. Stable liquid foams from a new polyfluorinated surfactant M.
Social activity. Search articles by author Maria Russo. Zacharias Amara. So what things are required? The first reason surfactants help create foams is that the surface becomes elastic. This means that the bubbles can withstand being bumped, squeezed and deformed. A pure water surface has no such elasticity and the bubbles break quickly. It also means that those systems which produce more elasticity see the Elasticity section will, other things being equal, produce more stable foams.
As discussed in the Rheology section, in general a wall which is both stiff and elastic provides a foam with a greater ability to resist a pushing force and therefore a higher yield stress. Smaller bubbles also give a higher yield stress Disjoining pressure.
The second reason that surfactants help create foam is that the liquid in the foam walls is naturally sucked out of the walls into the edges. This is nothing to do with drainage as explained in Drainage, the walls contain an irrelevant fraction of the liquid , it is just simple capillarity. The capillary pressure will keep pulling liquid out unless a counter pressure "disjoining pressure" acts against it. These effects are discussed in DLVO, but because the charge effect operates over large distances 50nm compared to the small distances 5nm of steric effects, in general ionic surfactants are much better at creating stable foams.
Resistance to ripening. The Ostwald ripening effect means that small bubbles shrink and large ones grow. Resistance to drainage. The more water around the foam the less risk in general of it becoming damaged. So a foam that drains quickly is more likely to become damaged. As we will see, to resist drainage you need high viscosity and small bubbles, though the surfactant wall has some effect on the drainage process with stiffer walls giving usually slower drainage.
Resistance to defects. If oil or a hydrophobic particle can penetrate the foam wall it can cause the wall and therefore the foam to break.
Although there are plausible and simple theories discussed in AntiFoams of Entry, Bridging and Spreading coefficients they turn out to be of limited predictive value.
Once again they are necessary but not sufficient. The key issue is the Entry Barrier. When this is high the foam is resistant to defects. These principles are so easy, yet creating foams efficiently is surprisingly hard. The key issue is timescales. On the other hand, a surfactant that quickly reaches the surface to create an adequate elasticity and disjoing pressure will produce large volumes of foam - though the foam will collapse quickly, especially in the presence of oily impurities such as grease being washed from one's hands.
This leads us to the issue of Dynamic Surface Tensions. It would be wonderful to provide an app that fully described the complexities of DST and which therefore allowed you to produce a mixture with very rapid decrease of ST to give the fastest possible foaming behaviour. But my reading of the literature is that it is quicker to measure the DST behaviour using most usually a Maximum Bubble Pressure device which creates bubbles over different timescales and therefore gives the surface tension at each of those timescales than it is to attempt to describe the behaviour via theories.
Of course one can find real cases of entry barriers and real cases of micelle-limited diffusion. But it is even more complicated. An extensive analysis from U. Sofia shows that there are 4 possible outcomes in systems containing micelles, two of which are indistinguishable to the casual observer from simple diffusion kinetics and two of which might be confused with barrier kinetics.
Finally, distinguishing entry-barrier and micellar effects from the effects of small amounts of impurities in the surfactants is surprisingly difficult and for the practical formulator using commercial, unpurified surfactants there is little hope of understanding the subtleties of DST curves.
The take-home message is "Don't formulate foams without measuring DST, but don't spend too much time theorising about why you get great results for some specific surfactant combination. However, the review paper, discussed below, contains a master-class on the relevant theory and concludes "The theory doesn't really help - just measure the DSTs".
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