Polymer enhanced foam for blocking fluid flow in soil

A soil treatment process is provided utilizing a polymer enhanced foam to block the flow of a migratory fluid in a soil. Placement of the polymer enhanced foam in a desired treatment region of the soil produces a seal that substantially eliminates the permeability of the treatment region to the migratory fluid and prevents migration of fluid across the region. In each of its numerous embodiments, the process can be employed as either a remedial or a preventative treatment.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates to a process for blocking fluid flow in a 
soil, and more particularly to a process for placing a polymer enhanced 
foam in a soil to eliminate the flow capacity of a soil to a migratory 
fluid. 
2. Description of Related Art 
The utility of foams, and particularly polymer enhanced foams, has been 
demonstrated in numerous hydrocarbon recovery applications. For example, 
U.S. Pat. No. 5,129,457 discloses the utility of a polymer enhanced foam 
as a displacement fluid for recovering oil retained in vertical fractures 
of a subterranean oil-bearing formation. The same patent also discloses 
the utility of the polymer enhanced foam as a mobility control fluid in 
fractured formations ahead of a gas drive fluid. U.S. Pat. No. 4,856,588 
likewise recognizes the effectiveness of specific foam compositions as a 
mobility control fluid ahead of a drive fluid in oil recovery 
applications. U.S. Pat. No. 3,393,738 discloses the utility of a polymer 
enhanced foam generated in situ for controlling leakage of stored gas in a 
subterranean formation containing mobile water. The foam can also improve 
the displacement of the mobile water from the formation, thereby 
increasing the gas storage capacity of the formation. 
The conventional oil field foams taught by the above-disclosed prior art 
references reduce the permeability of relatively deep subterranean 
formations to certain fluids, but are not deemed useful in soil sealing 
applications near the surface because the foams retain a degree of 
mobility in contact with flowing liquids, such as liquid drive fluids or 
formation water, which is undesirable for soil sealing applications. 
Concerns regarding the mobility of conventional oil field foams in soil, 
which is generally less consolidated and more porous than the geological 
material of hydrocarbon-bearing formations, suggest the ineffectiveness of 
oil field foams in soil sealing applications. 
For example, foams utilized as water sealants for shallow subterranean 
structures and surrounding soils are commonly held to require more 
resistance to water flow and greater durability in the near-surface 
environment than provided by conventional oil field foams. As such, a need 
exists for compositions that can effectively block the flow of migratory 
fluids through soils in a wide range of near-surface applications. In 
particular, soil sealing composition are needed that are relatively 
immobile in the soil when subjected to the natural drift pressure of 
migratory liquids flowing through the soil. 
U.S. Pat. No. 3,894,131 discloses a conventional high-strength durable 
crosslinked polymer foam for near-surface water sealing applications. Such 
crosslinked polymer foams, however, present the user with another set of 
problems not encountered when using conventional oil field foams. The 
crosslinking reaction of the water sealing foam adds a higher degree of 
operational complexity to proper placement of the foam. In addition, 
referral of the foam, if subsequent removal of the foam is desired from 
the treatment region, can be very difficult. Finally, and importantly, the 
precrosslinked composition of the foam contains organic solvents posing a 
high degree of risk when introduced into the environment. The use of such 
materials in or near water lines and other water containments is often 
precluded in today's stricter environmental regulatory climate. 
Accordingly, it is an object of the present invention to provide a soil 
treatment process for blocking flow of a migratory fluid in a soil. It is 
another object of the present invention to provide such a soil treatment 
process that is economical and operationally uncomplex. It is also an 
object of the present invention to provide such a soil treatment process 
that utilizes an effective fluid blocking composition. It is further an 
object of the present invention to provide such a soil treatment process 
that utilizes an environmentally compatible fluid blocking composition. 
SUMMARY OF THE INVENTION 
The present invention is a soil treatment process utilizing a polymer 
enhanced foam to block the flow of a migratory fluid in a soil. Placement 
of the polymer enhanced foam in a desired volume of soil constituting the 
treatment region produces a seal that substantially eliminates the 
permeability of the treatment region at normal fluid drift pressures and 
prevents the migration of the fluid across the region. In each of its 
numerous embodiments set forth hereafter, the process can be employed as 
either a remedial or a preventative treatment. 
In accordance with one embodiment, the process mitigates the effect of 
surface or subsurface leaks or spills of toxic, hazardous or otherwise 
undesirable fluids into soil, preventing the migration of such fluids 
through the soil into drinking water supplies or other water sources. In 
accordance with another embodiment, the process seals soil surrounding 
building structures, preventing the invasion of rainwater or groundwater 
into the structures. In accordance with yet another embodiment, the 
process provides linings under surface liquid containments preventing 
leakage of liquids from the containment into surrounding soil or 
underlying strata. In accordance with still another embodiment, the 
process provides a fluid impermeable barrier between topsoil and 
underlying subterranean strata. The barrier prevents the downward 
percolation of contaminated surface water or leachate into the underlying 
strata, prevents the upward migration of underlying alkaline aquifer water 
into the arable topsoil, or prevents the loss of rainwater or irrigation 
water from the arable topsoil to underlying strata. 
The process, in each of its embodiments, comprises generation of the foam 
and placement of the foam in the desired treatment region. The foam is 
generated by initially forming an aqueous liquid solution of a polymer, a 
surfactant and an aqueous solvent. A gas is then added to the liquid 
solution, either before, after, or during injection of the solution into 
the soil. In any case, the resulting admixture of gas and aqueous solution 
is subjected to foaming conditions that generate the desired foam for 
placement in the treatment region. 
Addition of the gas to the solution before injection of the solution into 
the soil generates a preformed foam at the surface before the foam enters 
the soil. Placement of the preformed foam in the soil is subsequently 
effectuated by injecting the foam into the soil via injection means and 
displacing the foam into the desired treatment region of the soil. 
Addition of the gas to the solution in situ after injection of the solution 
into the soil generates the foam in situ, rendering foam placement 
substantially simultaneous with foam generation. Foam placement is 
effectuated by sequentially injecting the foam components into the soil 
via injection means, generating the foam from the foam components in situ 
upon entering the soil, and displacing the resulting foam into the desired 
treatment region of the soil. 
Addition of the gas to the solution during injection of the solution into 
the soil is achieved by coinjection of the gas and solution into the soil. 
The foam is either generated in the injection means before the foam enters 
the soil or, alternatively, in situ after the foam components enter the 
soil. In either case, placement of the resulting foam is effectuated by 
displacement into the desired treatment region.

DESCRIPTION OF PREFERRED EMBODIMENTS 
A number of specific terms are used throughout the specification to 
describe the process of the present invention and are defined as follows. 
"Fluid flow capacity" is the degree to which porous media facilitates or, 
conversely, resists fluid flow. "Soil" is near-surface earthen geological 
material that is usually unconsolidated. "Soil", as used herein, can also 
be material contained in man-made earthen formations, such as dams, dikes, 
levees, and the like. "Strata" are any substantially horizontally disposed 
geological structures beneath the soil. The "foam" of the present 
invention is a stabilized gas dispersion maintained within a liquid phase, 
wherein the dispersed gas phase constitutes at least half of the total 
volume of the foam. The foam appears as a plurality of gas bubbles 
separated from one another by stabilized films of liquid. In porous media, 
such as soil, the foam may exist as discrete gas bubbles within the pore 
bodies of the porous medium. The bubbles are separated from one another by 
lamellae of interfacially stabilized liquid films. 
Conventional foams consist of a gas dispersed in a surfactant solution made 
up of a surfactant and a solvent. The surfactant acts as a foaming agent 
to facilitate and stabilize the gas dispersion within the liquid phase. A 
"polymer enhanced foam" is a specific type of foam comprising a gas 
dispersed in an aqueous surfactant solution, wherein the aqueous 
surfactant solution further includes a polymer dissolved therein. Other 
terms used herein have the same definitions as ascribed to them in U.S. 
Pat. No. 5,129,457, incorporated herein by reference, or have definitions 
in accordance with the conventional usage of a skilled artisan, unless 
otherwise defined hereafter. 
The process of the present invention is performed by generating and placing 
a polymer enhanced foam in a soil in the specific manner described 
hereafter. The polymer enhanced foam is generated from a substantially 
uncrosslinked polymer, an aqueous solvent, a surfactant and a gas. It is 
important to note that the foam composition is substantially free of any 
polymer crosslinking agent. By themselves, conventional polymer 
crosslinking agents are often potentially toxic to the environment. 
Furthermore, the presence of crosslinking agents with the polymers 
disclosed herein can undesirably crosslink the polymer and convert the 
liquid phase of the foam to a crosslinked polymer gel at some point in the 
process. 
The polymer component of the foam is substantially any water-soluble, 
viscosity-enhancing polymer that is substantially uncrosslinked. Either a 
biopolymer or a synthetic polymer has utility herein. Examples of 
biopolymers having utility herein include polysaccharides and modified 
polysaccharides, such as xanthan gum, guar gum, succinoglycan, 
scleroglycan, polyvinylsaccharides, carboxymethylcellulose, 
o-carboxychitosans, hydroxyethylcellulose, hydroxypropylcellulose, and 
modified starches. 
Examples of synthetic polymers having utility herein include polyvinyl 
alcohol, polyethylene oxide, polyvinyl pyrrolidone, and acrylamide 
polymers. Exemplary acrylamide polymers are polyacrylamide, partially 
hydrolyzed polyacrylamide, and acrylamide copolymers, terpolymers and 
tetrapolymers, wherein acrylamide is one of the monomeric species of the 
polymer. Polyacrylamide (PA) is defined as an acrylamide homopolymer 
having substantially less than about 1% of its acrylamide groups converted 
to carboxylate groups. Partially hydrolyzed polyacrylamide (PHPA)is an 
acrylamide homopolymer having more than about 1%, but not 100%, of its 
acrylamide groups converted to carboxylate groups. Useful acrylamide 
polymers are prepared according to any conventional method, but preferably 
have the specific properties of an acrylamide polymer prepared according 
to the method disclosed in U.S. Pat. No. Re.32,114, incorporated herein by 
reference. 
The average molecular weight of an acrylamide polymer having utility herein 
is generally in a range between about 10,000 and about 50,000,000, 
preferably between about 250,000 and about 20,000,000, and most preferably 
between about 1,000,000 and about 15,000,000. The polymer concentration in 
the liquid phase of the foam is generally at least about 500 ppm, 
preferably at least about 2,000 ppm, and most preferably within a range 
between about 3,000 ppm and about 10,000 ppm. 
Polymers satisfying the criteria set forth above impart a high degree of 
stability to a polymer enhanced foam relative to conventional foams 
formulated from a gas and a liquid phase containing a surfactant, but 
lacking polymer enhancement. The polymer enhanced foam better retains its 
stability when contacted by certain migrating fluids within soil, such as 
liquid hydrocarbons, relative to conventional polymer-free foams that are 
readily destabilized by liquid hydrocarbon contact. Polymer enhancement of 
the foam also advantageously increases the structural strength and 
critical pressure gradient for flow of the foam relative to conventional 
polymer-free foams. The "critical pressure gradient for flow" is defined 
herein as the maximum pressure that can be applied to the foam without 
foam flow. 
The aqueous solvent of the present polymer enhanced foam is substantially 
any aqueous liquid capable of forming a solution with the selected 
polymer. The term "solution" as used herein, in addition to true 
solutions, is intended to broadly encompass dispersions, emulsions, or any 
other homogeneous mixture of the polymer in the aqueous solvent. The 
solvent is preferably water, including either a fresh water or a brine. 
The surfactant of the polymer enhanced foam is substantially any 
water-soluble foaming agent that is compatible with the specific polymer 
selected as will be evident to the skilled artisan. As such, the 
surfactant can be anionic, cationic or nonionic. A preferred surfactant is 
selected from the group consisting of ethoxylated alcohols, ethoxylated 
sulfates, refined sulfonates, petroleum sulfonates, and alpha olefin 
sulfonates. The concentration of surfactant in the liquid phase of the 
foam is in a range between about 20 ppm and about 50,000 ppm, preferably 
between about 50 ppm and about 20,000 ppm, and most preferably at least 
about 500 ppm. In general, the performance of the polymer enhanced foam in 
the method of the present invention is relatively insensitive to the 
particular species and concentration of the surfactant selected, subject 
to the above-recited criteria, particularly when the selected polymer is 
an acrylamide polymer. 
Virtually any gas can be employed in the present polymer enhanced foam to 
the extent the gas is substantially chemically inert with respect to the 
other foam components and with respect to the foam generation or injection 
equipment. A preferred gas is one which is readily available. Such gases 
include nitrogen, air, flue gases and carbon dioxide. The quality of the 
polymer enhanced foam product, i.e., the volume percentage of gas in the 
foam, is typically within a range from about 50% to about 99%, and 
preferably within a range from about 60% to about 98%. 
Foam generation requires mixing the liquid phase and the gas either at a 
high velocity or through a small orifice as can be provided by any 
conventional foam generator. The liquid phase is preferably preformulated 
by dissolving the surfactant and polymer in the aqueous solvent prior to 
foam generation. In one embodiment, the foam is generated at the surface 
before injection into the soil by passing the liquid phase and gas through 
a surface foam generator. The resulting preformed foam is then delivered 
to an injection means. Alternatively, the foam is generated during 
injection into the soil by coinjecting the gas and liquid phase across a 
surface injection tee acting as a foam generator, or coinjecting the gas 
and liquid phases via separate injectors into the soil, but passing them 
through a common subsurface foam generator before entering the soil. 
The pH of the liquid phase in the polymer enhanced foam is generally within 
a range of about 4 to about 10, and preferably within a nearly neutral 
range of about 6 to about 8. In most cases, the pH of the liquid phase 
inherently falls within the above-recited range without any pH adjustment 
thereof. However, should the pH of the liquid phase be outside the desired 
range, the pH can be adjusted prior to or during foam generation to 
achieve a desired pH range. The pH adjustment can be made in any manner 
known to the skilled artisan. Nevertheless, it has been found that the 
present process is relatively insensitive to the pH of the liquid phase. 
Placement of the polymer enhanced foam in a soil is preceded by injection 
of the foam components into the soil in accordance with one of the 
above-described sequences via conventional injection means penetrating the 
soil. Exemplary foam injection means is open-ended tubing having the open 
end positionable within a treatment region of the soil or capped tubing 
having perforations or slots formed in the tubing that are positionable 
across the treatment region. When the foam exits the injection means into 
the soil, placement is effectuated by displacing the foam throughout the 
desired treatment region with materials injected behind it, typically 
additional foam. 
Placement of the foam is facilitated by the relatively high shear thinning 
properties of the polymer enhanced foam. The polymer enhanced foam 
exhibits relatively high viscosities when placed substantially beyond the 
injection point, but exhibits relatively low effective viscosities under 
the high flow rate, high pressure gradient for flow and high shear rate 
conditions encountered at or near the injection point during the injection 
step due to the ability of the foam to highly shear thin. 
Thus, the high shear thinning ability of the foam results in relatively 
good injectivity of the foam into the soil with a minimum of injectivity 
reduction. Nevertheless, once the polymer enhanced foam is successfully 
placed in the soil, it beneficially shear thickens, thereby achieving a 
sufficient degree of structure. The associated relatively large critical 
pressure gradient for flow renders the polymer enhanced foam an effective 
sealant. 
The character of the soil in which it is desired to place the foam can 
influence the selection of a specific foam composition. In general, 
placement of a foam in less permeable soil preferentially dictates 
selection of a foam having relatively limited structure, whereas a foam 
having a greater degree of structure can be selected for placement in more 
permeable soil. The degree of structure of the polymer enhanced foam 
formulated in the manner of the present invention is primarily a function 
of the polymer properties and polymer concentration. 
In general, the degree of structure of a polymer enhanced foam containing 
an acrylamide polymer is increased by increasing the polymer concentration 
of the liquid phase. However, a more cost-effective and often preferred 
means for achieving the same effect is to employ a higher molecular weight 
polymer or, in some cases, a polymer having a higher degree of hydrolysis 
at a relatively fixed concentration. Conversely, a reduction in the degree 
of structure is achieved by using a lower molecular weight polymer or, in 
some cases, one having a lower degree of hydrolysis. Thus, the skilled 
practitioner can modify the degree of structure of the present polymer 
enhanced foam in the above-described manner to correspond with the 
permeability of the region of the soil in which the foam is to be placed. 
As is apparent from above, the performance of the polymer enhanced foam as 
a sealant is a function of its critical pressure gradient for flow, which 
can alternatively be termed yield pressure. When fluids migrate through 
the soil, the fluids encounter a natural drift pressure gradient for fluid 
flow. It is necessary that the foam occupying the fluid flowpaths, through 
which the fluid must pass to flow, exhibits a critical pressure gradient 
for foam flow higher than the natural drift pressure gradient for flow of 
the fluid. By satisfying this criteria, the migratory fluid is unable to 
mobilize or displace the foam from the flowpaths. Consequently, the foam 
performs as an effective sealant in accordance with the present invention. 
Relative to conventional polymer-free foams, the polymer enhanced foam is 
highly stable and resistant to flow. The polymer enhanced foam is stable 
over a wide range of temperatures, pressures, and water salinities and 
hardness. The polymer enhanced foam is also relatively stable, resisting 
foam collapse and fluid drainage in the presence of many environmental 
contaminants, including liquid hydrocarbons. The foam can be self healing 
so that if foam degradation occurs, the foam is capable of reforming 
itself as it begins to flow through the soil. Thus, placement of the foam 
in desired treatment regions of the soil provides long-term elimination of 
permeability to the natural drift of fluids, thereby substantially 
blocking the flow of migratory fluids through the treatment region when 
the foam is fully in place. The process is particularly applicable to the 
blockage of undesirable migratory liquids, such as water or liquid 
hydrocarbons. Nevertheless, the soil can be restored to its original 
condition, if desired, by injection of a conventional breaker into the 
treatment region to degrade the foam or polymer in situ. 
Embodiments of the present process have been described above wherein, the 
polymer enhanced foam is generated prior to placement of the foam in the 
soil. However, other embodiments exist within the scope of the present 
invention, wherein the polymer enhanced foam is generated in situ 
simultaneous with placement of the foam in the soil. In one such 
embodiment, the liquid phase and gas are sequentially injected into the 
soil. The liquid phase preferably precedes the gas, enabling the 
higher-mobility trailing gas slug to overtake and finger through the 
leading liquid slug as the injected fluids are displaced into the soil. 
The restricted flowpaths of the soil act as a natural foam generator. As 
the gas and liquid phases pass through the pore throats of the soil the 
foam is generated. The volume of the liquid and gas slugs injected into 
the soil can be relatively small, but repetitive, to optimize utilization 
of the surfactant and formation of the foam in situ. In another similar 
embodiment, the liquid phase and gas are coinjected into the soil and the 
foam is generated in situ as the liquid phase and gas pass through the 
pore throats of the soil. 
In the practice of the present invention, the polymer enhanced foam may be 
placed in a selected treatment region of the soil as either a remedial 
treatment after undesirable fluids have entered the soil or as a 
preventative treatment before undesirable fluids enter the soil. In 
accordance with one embodiment, the treatment region in which the foam is 
placed is a substantially vertical plane through the soil proximal to 
surface or subsurface leakage or spillage of toxic, hazardous or otherwise 
undesirable fluids. The foam occupying the treatment region forms a 
barrier to lateral fluid flow past the treatment region, thereby 
mitigating the effect of the leak or spill in adjoining soil. Thus, the 
present embodiment can be employed to prevent the migration of the 
undesirable fluids into drinking water supplies or other water sources, 
such as reservoirs, wells, rivers, lakes and the like, by placing the foam 
in a treatment region between the spill or leak site and the water source. 
In a similar embodiment, the treatment region in which the foam is placed 
is a substantially horizontal plane through the soil beneath surface or 
subsurface leakage or spillage of toxic, hazardous or otherwise desirable 
fluids. The foam occupying the treatment region forms a barrier to 
downward fluid flow past the treatment region, thereby mitigating the 
effect of the leak or spill in underlying soil or strata. This embodiment 
can be employed to prevent the migration of the undesirable fluids into 
subterranean drinking water supplies or other water sources, such as 
aquifers, by placing the foam in a treatment region between the spill or 
leak site and the water source. 
In another embodiment, the treatment region is a circumferential or 
underlying volume of soil surrounding a subterranean building structure, 
such as a basement or foundation. Placement of the foam in the treatment 
region forms a fluid impermeable barrier around the building structure 
preventing the invasion of rainwater or groundwater into the structure or 
the migration of the water into contact with the structure or adjacent 
water-sensitive soil, such as clay. 
In accordance with yet another embodiment, the treatment region is a 
circumferential or underlying volume of soil surrounding a surface or 
subsurface, open or enclosed, liquid containment, such as an open waste 
pit, an irrigation ditch or an enclosed underground storage tank. 
Placement of the foam in the treatment region forms a fluid impermeable 
lining or blanket for the containment preventing leakage of liquids from 
the containment into surrounding soil or underlying strata. 
In another embodiment, the treatment region is a substantially horizontal 
plane residing between topsoil and an underlying subterranean strata. The 
foam occupying the treatment region forms a barrier to either downward or 
upward fluid flow past the treatment region. The present embodiment can be 
employed to substantially prevent the downward percolation of contaminated 
surface water or leachate into the underlying strata. Alternatively, where 
the overlying topsoil is arable farmland, the present embodiment can be 
employed to substantially prevent the upward migration of underlying 
alkaline aquifer water into the topsoil, or to prevent the downward 
migration of rainwater or irrigation water from the arable topsoil to 
underlying strata. It is apparent to the skilled artisan from the instant 
disclosure that there are numerous other related applications within the 
scope of the present invention. 
The following examples demonstrate the practice and utility of the present 
invention, but are not to be construed as limiting the scope thereof. 
EXAMPLE 1 
A sample of a polymer enhanced foam and a sample of a conventional 
polymer-free foam that is substantially identical in composition to the 
polymer component are prepared to compare the stability, and in particular 
the resistance to physical foam collapse and water drainage, of the two 
foams. The liquid phase of both foams is made up of a fresh water solvent 
containing 1000 ppm of a C.sub.12-15 ethoxylated sulfate surfactant. The 
liquid phase of the polymer enhanced foam, however, is further enhanced 
with an unhydrolyzed polyacrylamide at a concentration of 7000 ppm. The 
molecular weight of the polymer is 11,000,000. 
The foam samples are generated by coninjecting the liquid phase and a gas 
consisting of N.sub.2 into a sandpack. The sandpack has a permeability of 
67 darcies, a length of 30 cm and a diameter of 1.1 cm. All flooding is 
conducted at 170 kPa constant differential pressure across the sandpack. 
The polymer enhanced foam propagates at a frontal advance rate of 207 
m/day and exhibits an average apparent effective viscosity within the 
sandpack of 89 cp, while the conventional foam propagates at a frontal 
advance rate of 8230 m/day and exhibits an average apparant effective 
viscosity of only 2 cp at the same differential pressure. 
A 100 cm.sup.3 sample of each foam is collected as an effluent from the 
sandpack and placed in a stoppered graduated cylinder for aging at ambient 
temperature. The position of the foam/water and foam/air interfaces in the 
graduated cylinders are measured as a function of time to determine the 
rates of water drainage and foam collapse, respectively for each of the 
samples. The results are shown in FIGS. 1a and 1b, respectively, It is 
apparent therein that the rates of water drainage and foam collapse are 
much greater for a conventional polymer-free foam than a polymer enhanced 
foam. Thus, this example shows that the polymer enhanced foam is more 
stable and more viscous than the conventional polymer-free foam. 
EXAMPLE 2 
A sandpack modeling a sandy soil is flooded with a series of polymer 
enhanced foam samples, differing only in the foam quality of each sample, 
to determine the relation between foam quality and apparent viscosity for 
the polymer enhanced foam of the present invention. The sandpack has a 
length of 30 cm and a permeability of 150 darcies. All flooding is 
conducted at 340 kPa constant differential pressure across the sandpack. 
The polymer enhanced foam propagates at a frontal advance rate of about 
150 m/day. 
The foam is formulated from N.sub.2 and a brine solvent containing a 
C.sub.14-16 alpha olefin sulfonate surfactant at a concentration of 2000 
ppm and a partially hydrolyzed polyacrylamide at a concentration of 7000 
ppm. The partially hydrolyzed polyacrylamide has a molecular weight of 
11,000,000 and is 30% hydrolyzed. The results are set forth below in Table 
1. 
TABLE 1 
______________________________________ 
FOAM QUALITY AVERAGE APENT VISCOSITY 
(%) (cp) 
______________________________________ 
0 150 
57 190 
63 200 
74 210 
80 230 
85 230 
89 240 
93 240 
______________________________________ 
The results indicate that the performance of the polymer enhanced foam is 
relatively insensitive to foam quality. 
EXAMPLE 3 
A sample of a polymer enhanced foam and a sample of a conventional 
polymer-free foam that is substantially identical in composition to the 
polymer enhanced foam except for the absence of a polymer component are 
prepared to compare the effective viscosities of the two foams as a 
function of foam quality. Both foams are formulated from N.sub.2 and a 
brine solvent having a C.sub.14-16 alpha olefin sulfonate surfactant 
dissolved therein at a concentration of 2000 ppm. The brine contains 5800 
ppm TDS and has principle constituents in the following concentrations: 
560 ppm Ca.sup.++, 160 ppm Mg.sup.++, 1500 ppm Na.sup.+, 200 ppm K.sup.+, 
2200 ppm SO.sub.4.sup.=, and 1400 Cl.sup.31 . 
The polymer enhanced foam additionally contains a partially hydrolyzed 
polyacrylamide at a concentration of 7,000 ppm. The partially hydrolyzed 
polyacrylamide has a molecular weight of 11,000,000 and is 30% hydrolyzed. 
A sandpack substantially the same as that of Example 2 is flooded with each 
foam. The polymer enhanced foam sample is flooded at a backpressure of 
3060 kPa and a differential pressure of 340 kPa. The polymer enhanced foam 
propagates at a frontal advance rate of between about 146 and 213 m/day. 
The conventional foam sample is flooded at atmospheric pressure and a 
differential pressure of 136 kPa and propagates at a frontal advance rate 
of between about 335 and 1460 m/day. 
The results are set forth in FIG. 2 and indicate that the sensitivity of 
the polymer enhanced foam viscosity to foam quality is much less than that 
for the conventional foam. Furthermore, the effective viscosity of the 
polymer enhanced foam at any given foam quality is much greater than that 
of the conventional foam. Similar floods performed over a range of 
absolute pressures show that the viscosity performances of the 
conventional foam and the polymer enhanced foam remain essentially 
invariant with absolute test pressure. 
EXAMPLE 4 
A sandpack modeling sandy soil is flooded with a fully formed polymer 
enhanced foam sample to determine the critical pressure gradient for foam 
flow. The composition of the polymer enhanced foam sample is the same as 
Example 3 and the foam quality is about 85%. The sandpack has a length of 
30 cm and a permeability of 140 darcies. The critical pressure gradient 
for foam flow is determined to be in the range of 1.34 to 1.56 kPa/cm. 
Normal natural drift pressure gradients for fluids in soils are not 
expected to approach values of 1.34 kPa/cm suggesting that the polymer 
enhanced foam is well suited for effectively blocking fluid flow through 
soil. 
EXAMPLE 5 
Two separate floods of a sandpack modeling sandy soil are conducted at room 
temperature with 0.2 pore volumes of a fully formed polymer enhanced foam 
sample followed by 0.8 pore volumes of a brine. In the first flood the 
sandpack is flushed with a brine immediately prior to foam injection and 
the sandpack is initially at 100% brine saturation. In the second flood 
the sandpack is flushed with a brine, saturated with a Wyoming crude oil, 
and then flooded with the brine to residual oil saturation immediately 
prior to foam injection to demonstrate the stability of the polymer 
enhanced foam in the presence of a hydrocarbon. 
The sandpack has a permeability of 150 darcies, a length of 6.1 m and a 
diameter of 0.46 cm. A constant differential pressure of 680 kPa is 
applied to the sandpack. The polymer enhanced foam is formulated from 
N.sub.2 and the synthetic injection water brine of Example 4, having a 
C.sub.14-16 alpha olefin sulfonate surfactant and a partially hydrolyzed 
polyacrylamide dissolved therein at concentrations of 2000 ppm and 7000 
ppm respectively. The partially hydrolyzed polyacrylamide has a molecular 
weight of 11,000,000 and is 30% hydrolyzed. The polymer enhanced foam in 
the first flood has an apparent viscosity of 43 cp after it has propagated 
almost entirely through the sandpack, while the polymer enhanced foam in 
the second flood has an apparent viscosity of 50 cp after it has 
propagated almost entirely through the sandpack. During both floods, the 
polymer enhanced foam bank was essentially intact after propagating 
through the entire length of the sandpack. These results suggest that 
polymer enhanced foam performance is relatively insensitive to liquid 
hydrocarbons. Thus, the polymer enhanced foam is capable of effectively 
blocking the undesirable flow of leaking or spilled hydrocarbons through 
soil. 
While the foregoing preferred embodiments of the invention have been 
described and shown, it is understood that alternatives and modifications, 
such as those suggested and others, may be made thereto and fall within 
the scope of the present invention.