Liquid aluminum phosphate salt gelling agent

A liquid aluminum phosphate salt gelling agent comprising the reaction product of: a dialkyl phosphate formed from the reaction product of (1) a polyphosphate intermediate produced by reacting triethyl phosphate and phosphorous pentoxide and (2) a mixture of aliphatic alcohols having 6 to 10 carbons in their alkyl groups; an aluminum sulfate; and a solvent.

The present invention relates to a novel liquid aluminum phosphate salt 
gelling agent comprising the reaction product of: a dialkyl phosphate 
formed from the reaction product of (1) a polyphosphate intermediate 
produced by reacting triethyl phosphate and phosphorous pentoxide and (2) 
a mixture of aliphatic alcohols having 6 to 10 carbons in their alkyl 
group; an aluminum sulfate; and a solvent. This unique gelling agent 
permits "on the fly" gelling of hydrocarbons, especially those used in 
hydraulic fracturing of subterranean formations to enhance oil and gas 
production. 
BACKGROUND OF THE INVENTION 
Hydraulic fracturing is a widely used method for stimulating oil and/or gas 
production. In performing a fracturing operation, a hydraulic fluid, 
usually a liquid hydrocarbon, is pumped into the well bore at sufficiently 
high pressure to fracture the surrounding rock formation to open cracks in 
the formation through which oil and/or gas can flow into the well bore. 
Since the cracks which are opened by the fracturing fluid tend to close 
once the pressure on the fluid is released, it is customary to inject into 
the well along with the fracturing fluid a suitable particulate proppant 
material such as sand. The small proppant particles flow into the 
fractures created in the formation along with the fracturing fluid and 
serve to prop the fracture open after the fluid pressure is released. 
Proppant materials may be either lighter or heavier than the hydraulic 
fracturing fluid and thus may tend to float or settle out of the fluid 
prematurely, or otherwise be unevenly distributed in the fracturing fluid. 
To overcome this problem, it is customary practice to use gelled 
fracturing fluids which will hold the proppant material in suspension as 
the fluid flows down the well bore and out into the formation fractures 
This requires that the gelled fracturing fluid be of sufficient viscosity 
to hold the proppant material suspended in a slurry or matrix. At the same 
time, the fluid must not be so viscous that it cannot be readily pumped 
into the well bore and out into the formation fractures. 
Various materials are known which, when admixed with hydrocarbons, will 
create hydrocarbon gels of various viscosities. However, many of these 
materials are not suitable for use as hydrocarbon fracturing fluids 
because of the particular requirements imposed by the environment in which 
they are used. The gels must be formed at or near the wellhead at ambient 
temperature Generally, several thousand gallons of normally liquid 
hydrocarbon such as crude or refined oil, a gelling agent and an activator 
are blended to form a gel. This mixture then is stored in frac tanks until 
used. 
An ideal gelling agent for forming a gelled hydrocarbon fracturing fluid 
would be one which, when mixed with the normally liquid hydrocarbon and an 
activator, forms a gel of sufficient viscosity to hold the proppant in 
suspension relatively quickly and then retains its desired range of 
viscosity for at least several hours at ambient temperatures. At the same 
time, the gel should, when injected into downhole formations at 
temperatures of 200.degree.-250.degree. C., retain sufficient viscosity to 
keep the proppant in suspension for the period of time required for the 
fracturing operation, which may be up to eight hours. 
Even more preferable would be a gelling agent and activator which can be 
mixed with a liquid hydrocarbon "on the fly", i.e., as the constituents 
are being pumped into the well bore, wherein the hydrocarbon is gelled 
almost immediately. Such a gelling agent and activator would eliminate 
premixing and storage of the gel in a frac tank prior to use, as well as 
significantly reduce the need to maintain the viscosity of the gel at 
ambient temperature for any prolonged period. The present inventor 
undertook the task of developing just such a gelling agent capable of "on 
the fly" gelling of hydrocarbons. 
Historically, the art of gelling organic liquids, e.g., hydrocarbons, for 
oil field fracturing purposes has involved introducing a phosphate ester 
and an aluminum source into the organic liquid. The in situ reaction 
between the phosphate ester and the aluminum source forms an aluminum 
phosphate ester which, in turn, gels the hydrocarbon. 
Early phosphate esters were made by reacting a mixture of alcohols, such as 
ethyl, octyl, and decyl alcohols, with P.sub.2 O.sub.5 (phosphorous 
pentoxide). The resulting product was a mixture of the corresponding mono- 
and di- phosphate esters. These and similar phosphate esters were termed 
"gelling agent" by the oil field industry. 
Various conventional gelling agents are set forth in the following patents 
and application: U.S. Pat. No. 4,007,128 (Poklacki), issued Feb. 8, 1977; 
U.S. Pat. No. 3,575,859 (Monroe), issued Apr. 20, 1971; U.S. Pat. No. 
4,877,894 (Huddleston), issued Oct. 31, 1989; U.S. Pat. No. 4,200,539 
(Burnham et al.), issued Apr. 29, 1980; U.S. Pat. No. 3,494,949 (Monroe), 
issued Feb. 10, 1970; U.S. Pat. No. 4,104,173 (Gay et al.), issued Aug. 1, 
1978; U.S. Pat. No. 3,757,864 (Crawford et al.), issued Sept. 11, 1973; 
and European Patent Application Publication No. 0 225 661, published Jun. 
16, 1987. 
U.S. Pat. Nos. 4,007,128, 3,575,859, 3,494,949, 4,104,173, 4,200,539 and 
3,757,864 all disclose various gelling agents which include salts of alkyl 
orthophosphates. In particular, U.S. Pat. No. 4,007,128 provides a partial 
salt of aluminum alkyl orthophosphates (gelling agent) and a neutralizing 
amount of polyamine (activator) which retain gel character in the presence 
of epoxy resins and aromatic diamines. The gelling agent according to this 
patent is formed from the reaction product of (A) an alkyl acid 
orthophosphate which is produced from alcohols and phosphorous pentoxide, 
and (B) a basic aluminum compound, e.g., hydrated alumina or aluminum 
isopropoxide. 
U.S. Pat. No. 3,575,859 discloses the gelling of hydrocarbons with small 
amounts of metal alkyl oleyl orthophosphates (gelling agent) and amines 
(activator). The gelling agent is formed from the reaction product of (A) 
ethyl oleyl orthophosphoric mono acid, i.e., a dialkyl phosphate mono 
acid, and (B) a metal base, e.g., aluminum, gallium or lanthanum 
hydroxide. Oleyl is a C.sub.18 alkenyl radical. 
U.S. Pat. No. 3,494,949 relates to the improvement of the viscosity of 
motor oils via the addition of aluminum salts of alkyl orthophosphates. A 
precipitate of aluminum ethyl oleyl orthophosphate is formed from the 
reaction product of (A) ethyl oleyl orthophosphate with water and ethanol, 
(B) sodium hydroxide, and (C) aluminum sulfate. 
U.S. Pat. No. 4,104,173 is directed to a gelling agent of pseudo double 
salts of alkyl orthophosphates. These gelling agents are formed from the 
reaction product of (A) a mixture of alkanol and/or alkenols and 
phosphorous pentoxide, (B) a first base, i.e., sodium aluminate or 
hydrated aluminum oxide, and (C) a second base, i.e., sodium hydroxide. 
U.S. Pat. No. 4,200,539 discloses a gelling agent formed from the reaction 
product of (A) phosphorous pentoxide and an aliphatic alcohol, and (B) an 
aluminum compound selected from the group consisting of alkali metal 
aluminate, aluminum isopropoxide, and aluminum hydroxide. 
U.S. Pat. No. 3,757,864 discloses a gelling agent of aluminum salts of 
aliphatic orthophosphate ester formed from the reaction product of (A) 
orthophosphoric acid ester, (B) phosphorous pentoxide, and (C) a basic 
aluminum compound, e.g., sodium aluminate, aluminum isopropoxide or 
hydrated alumina. 
European Patent Publication No. 0 225 661 is directed to raising the 
viscosity of a hydrocarbon by the addition of a phosphate ester and 
metallic salts which are substantially completely free of water and pH 
affecting substances. The phosphate ester gelling agent is formed from the 
reaction product of (A) a phosphate triester and phosphorous pentoxide, 
and (B) an alcohol. The metal salt activator is typically metal alkoxide 
or aluminum isopropoxide. 
Well operators have been seeking a gelling agent product that is easily 
pumpable, could be diluted if necessary, and would gel rapidly "on the 
fly". The aforementioned conventional gelling agents are unable to meet 
those requirements. Aluminum complexes or salts from aluminum isopropoxide 
or alumina are not satisfactory because they result in a precipitate, not 
a liquid product that could gel "on the fly". 
The present inventor has discovered through extensive experimentation that 
the reaction product of selected dialkyl phosphates, an aluminum sulfate 
and a solvent results in a liquid gelling agent which may be mixed "on the 
fly" with hydrocarbon and an appropriate activator at or near the wellhead 
such that a suitable gel forms almost immediately. This unique gelling 
agent overcomes the disadvantages of conventional gelling agents, i.e., 
premixing of the fracturing fluid and storage of the gelled fluid in frac 
tanks. 
The gelling agents of the present invention also provide the following 
economic benefits: (1) no residual gelled fracturing fluid, (2) no 
disposal of residual gelled fracturing fluid, (3) requires smaller dosages 
than conventional gelling agents resulting in reduced pumping friction, 
and (4) power consumption is substantially reduced by the lack of a 
premixing step and since pumping of gelled fracturing fluid from a frac 
tank to the wellhead is avoided. 
The present invention therefore overcomes the abovementioned deficiencies, 
as well as provides additional advantages which shall become apparent as 
described below. 
SUMMARY OF THE INVENTION 
The present invention provides a novel liquid aluminum phosphate salt 
gelling agent formed from the reaction product of: a dialkyl phosphate 
which is formed from the reaction product of (1) a polyphosphate 
intermediate produced by reacting triethyl phosphate and phosphorous 
pentoxide and (2) a mixture of aliphatic alcohols having 6 to 10 carbons 
in their alkyl groups; an aluminum sulfate; and a solvent. 
The aluminum sulfate is preferably aluminum sulfate hydrate and the solvent 
is preferably toluene, xylene, aromatic naphtha or blends thereof. The 
molar ratio of phosphates to aluminum is preferably in the range between 
about 6:1 to 3.2:1. 
It is also an object of the present invention to provide a method for 
treating a liquid hydrocarbon which comprises adding: a liquid aluminum 
phosphate salt gelling agent comprising the reaction product of (a) 
dialkyl phosphate formed from the reaction product of (1) a polyphosphate 
intermediate produced by reacting triethyl phosphate and phosphorous 
pentoxide and (2) a mixture of aliphatic alcohols having 6 to 10 carbons 
in their alkyl groups, (b) an aluminum sulfate, and (c) a solvent; and an 
activator, e.g., triethanolamine. 
An additional object is a method of fracturing an oil well which comprises 
pumping (A) a liquid hydrocarbon; (B) a liquid aluminum phosphate salt 
gelling agent comprising the reaction product of: dialkyl phosphate formed 
from the reaction product of (1) a polyphosphate intermediate produced by 
reacting triethyl phosphate and phosphorous pentoxide and (2) a mixture of 
aliphatic alcohols having 6 to 10 carbons in their alkyl groups, an 
aluminum sulfate, and a solvent; (C) an activator; and (D) a proppant 
material, into a well bore such that the gelling agent, activator and 
proppant are mixed with the hydrocarbon as they are pumped downhole and 
wherein a gelled hydrocarbon forms almost immediately; whereby premixing 
of the hydrocarbon, gelling agent and activator is eliminated. 
The present invention may also include many additional features which shall 
be further described below. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention employs a liquid oil soluble aluminum phosphate that 
can be activated with an oil soluble activator to gel hydrocarbons, e.g., 
diesel, kerosene, condensates, and crude oil. The gelling agent and 
activator are readily admixed with the hydrocarbon as they are pumped down 
the well bore. A suitable gel forms almost immediately, and pre-mixing and 
storage are eliminated. This concentrated liquid gelling agent can be 
mixed with hydrocarbon in smaller dosages so as to reduce pumping 
friction. 
The liquid aluminum phosphate salt gelling agent of the present invention 
includes the reaction product of a dialkyl phosphate, an aluminum sulfate 
and a solvent, e.g., toluene, xylene, aromatic naphtha or blends thereof. 
The ratio of phosphates to aluminum is in the range between about 6:1 to 
3.2:1. 
The dialkyl phosphate is formed from the reaction product of (1) a 
polyphosphate intermediate produced by reacting triethyl phosphate and 
phosphorous pentoxide and (2) a mixture of aliphatic alcohols having 6 to 
10 carbons in their alkyl groups. These and other dialkyl phosphates are 
set forth in detail throughout U.S. Pat. No. 4,877,894 (Huddleston), which 
is incorporated herein by reference. The dialkyl phosphate is present 
within the gelling agent in an amount between about 75-85% by molar 
weight. 
In producing the polyphosphate intermediate, it is preferred to use from 
about 1.0 to about 1.3 moles of triethyl phosphate for each mole of 
phosphorous pentoxide, with 1.3 moles of triethyl phosphate being most 
preferred. Approximately three moles of mixed aliphatic alcohols for each 
mole of phosphorous pentoxide used are then blended with the polyphosphate 
intermediate. 
The alcohol comprises a mixture of aliphatic alcohols having from 6 to 10 
carbons in their alkyl groups. The mixed alcohol has an increased hexanol 
content of from about 13% to about 92% by weight of hexanol, with the 
remainder being divided principally between C.sub.8 and C.sub.10 alcohols. 
Most preferably, the mixed alcohol comprises approximately 45% by weight 
of hexanol, 30% by weight of octanol and 25% by weight of decanol. 
The aluminum sulfate is preferably aluminum sulfate hydrate. The aluminum 
sulfate is present within the gelling agent in an amount between about 
5-35% by weight. The water of hydration from aluminum sulfate needs to be 
azeotroped out with a solvent , The solvent is preferably toluene, xylene, 
aromatic naphtha or a similar solvent. The solvent is present within the 
gelling agent in an amount between about 30-90% by weight. 
The dialkyl phosphates (80% yield) are typically synthesized from linear 
6-10 carbon alcohols, phosphorous pentoxide, and triethyl phosphate. It is 
believed that this reaction results in an ethyl and fatty (C.sub.6 
-C.sub.10) mixed diester. These acidic phosphate diesters are converted to 
aluminum complexes with aluminum sulfate. It was discovered that the 
resultant aluminum phosphate salt remained in solution due to the acidic 
residue (sulfuric acid) from the aluminum sulfate. Aluminum chloride 
accomplishes the same liquid aluminum phosphate salt but hydrogen chloride 
gas is liberated and the composition changes with time. Low viscosity 
solutions of about 50% aluminum phosphate salt in toluene or a similar 
solvent were obtained. 
These liquid aluminum phosphate salts gelled kerosene and similar 
hydrocarbons rapidly when partially neutralized with an amine activator. 
Triethanolamine is a particularly desirable activator due to its low 
volatility and availability. 
A novel "on the fly" hydrocarbon gel may be produced by blending with a 
normally liquid hydrocarbon a gelling amount of liquid aluminum phosphate 
salt gelling agent and an effective amount of an activator, e.g., 
triethanolamine. The hydrocarbon is typically a liquid medium density 
petroleum fraction such as kerosene, gas oil, crude oil, or diesel. From 
about 3 to about 15 gallons of gelling agent preferably are utilized for 
each 1,000 gallons of hydrocarbon, with approximately 10 gallons of 
gelling agent per 1,000 gallons of hydrocarbon being most preferred. 
When using the improved gelling agent to perform a well fracturing 
operation, the gelling agent, liquid hydrocarbon, activator and proppant 
material are pumped simultaneously down the well bore such that the 
gelling agent, activator and proppant are mixed with said hydrocarbon as 
they are pumped downhole and wherein the gelled hydrocarbon forms almost 
immediately. The premixing of the hydrocarbon, gelling agent and activator 
is thereby eliminated. The fracturing fluid is pumped down the well bore 
at the desired formation fracturing pressure and out into the formation 
fractures. The target formation may be kept under elevated pressure for up 
to several hours to promote further propagation of cracks. 
Once the fracturing operation is complete, the pressure on the hydraulic 
fracturing fluid is released. However, gelled hydrocarbon trapped in the 
fractures might tend to prevent production flow from the fractured 
formation back into the well bore. To avoid this, a neutralizing or 
"breaking" agent commonly is admixed with the gelled hydrocarbon as it is 
pumped into the well bore. The preferred breakers have a delayed 
neutralizing effect and thus tend to break down the hydrocarbon gel only 
after several hours. One suitable such breaking agent is sodium 
bicarbonate which may be admixed with the hydrocarbon, gelling agent, 
activator and proppant material in a finely granulated or powder form. It 
has only low solubility in the gelled hydrocarbon and therefore its 
neutralizing effect is suitably time delayed.

The following examples and experimental results will further illustrate the 
invention. 
EXAMPLE 1 
[Liquid Aluminum Phosphate Salt Gelling Agent] 
A 4-neck reaction flask was used, equipped with a thermometer, mechanical 
stirrer, condenser and gas (N.sub.2) inlet. 200 grams of toluene and 136 
grams of triethyl phosphate were added to the flask, followed by 80.8 
grams of phosphorous pentoxide under a nitrogen blanket. The reactants 
were heated to 80.degree. C. for approximately two hours. Thereafter, a 
blend of 122.8 grams of 6-10 carbon alcohol and 89.1 grams of hexanol were 
added to the flask dropwise over 45 minutes at 60.degree.-80.degree. C. 
The reactants were heated to 120.degree.-125.degree. C. for approximately 
two hours. The reaction product was then cooled to about 90.degree. C. 
161.5 grams of aluminum sulfate hydrate and 228.7 grams of toluene were 
added to the flask and the nitrogen blanket was discontinued. About 73 
grams of water were collected in azeotrope at 95 to about 
115.degree.-120.degree. C. Thereafter, the mixture was permitted to cool. 
A clear solution was produced. 
EXAMPLE 2 
[Dialkyl Phosphate] 
A 4-neck reaction flask was used, equipped with a thermometer, mechanical 
stirrer, condenser and gas (N.sub.2) inlet. 310.4 grams of triethyl 
phosphate and 183.9 grams of phosphorous pentoxide were added to the 
flask, mixed and reacted for two hours at 175.degree. F. to produce a 
polyphosphate intermediate. All additions and reactions throughout the 
experiment were conducted under a nitrogen blanket. The polyphosphate 
intermediate was cooled to approximately 140.degree. F. A mixture of 418.8 
grams of 6-10 carbon alcohol and 102.1 grams of hexanol was then added 
dropwise to the polyphosphate intermediate while maintaining a temperature 
between about 140.degree.-175.degree. F. After the alcohol blend addition, 
the mixture was heated at 250.degree.-260.degree. F. for two hours. The 
reaction resulted in a liquid alkyl phosphate diester. 
EXAMPLE 3 
[Liquid Aluminum Phosphate Salt Gelling Agent] 
A 4-neck reaction flask was used, equipped with a thermometer, mechanical 
stirrer, condenser and gas (N.sub.2) inlet. 30.58 grams of triethyl 
phosphate and 18.11 grams of phosphorous pentoxide were added to the flask 
under a nitrogen blanket. The reactants were heated to 80.degree. C. for 
approximately two hours. Thereafter, a blend of 41.25 grams of 6-10 carbon 
alcohol and 10.06 grams of hexanol were added to the flask dropwise over 
45 minutes at 60.degree.-80.degree. C. The reactants were then heated to 
120.degree.-125.degree. C. for approximately two hours. The reaction 
product was cooled to about 90.degree. C. 31.70 grams of aluminum sulfate 
hydrate and 100 grams of toluene were added to the flask and the nitrogen 
blanket was discontinued. 14 grams of water were collected in azeotrope at 
95 to about 115.degree.-20.degree. C. Thereafter, the mixture was 
permitted to cool. A clear solution was produced. 
EXAMPLE 4 
[Dialkyl Phosphate] 
A 4-neck reaction flask was used, equipped with a thermometer, mechanical 
stirrer, condenser and gas (N.sub.2) inlet. 27.96 grams of triethyl 
phosphate and 21.78 grams of phosphorous pentoxide were added to the 
flask, mixed and reacted for two hours at 175.degree. F. to produce a 
polyphosphate intermediate. All additions and reactions throughout the 
experiment were conducted under a nitrogen blanket. The polyphosphate 
intermediate was cooled to approximately 140.degree. F. A mixture of 8.22 
grams of 6-10 carbon alcohol and 42.04 grams of hexanol was then added 
dropwise to the polyphosphate intermediate while maintaining a temperature 
between about 140.degree.-175.degree. F. After the alcohol blend addition, 
the mixture was heated at 250.degree.-260.degree. F. for two hours. The 
reaction resulted in a liquid alkyl phosphate diester. 
EXAMPLE 5 
[Liquid Aluminum Phosphate Salt Gelling Agent] 
A 4-neck reaction flask was used, equipped with a thermometer, mechanical 
stirrer, condenser and gas (N.sub.2) inlet In the flask, 43.44 grams of 
aluminum sulfate hydrate and 100 grams of toluene were added to 100 grams 
of the dialkyl phosphate prepared in accordance with Example 4 above. 
Approximately 20 mL of water were collected in azeotrope at 95 to about 
115.degree.-120.degree. C. Thereafter, the mixture was permitted to cool 
and a clear solution was produced. The resultant gelling agent was clear 
and pourable after two days at -10.degree. F. The gelling agent also mixed 
well and gelled at -10.degree. F. in kerosene. 
EXAMPLE 6 
[Liquid Aluminum Phosphate Salt Gelling Agent] 
A 4-neck reaction flask was used, equipped with a thermometer, mechanical 
stirrer, condenser and gas (N.sub.2) inlet. In the flask, 139.8 grams of 
aluminum sulfate hydrate, 81.0 grams of toluene, 243.0 grams of aromatic 
naptha, and 0.14 grams of an antifoamer were added to 324.0 grams of the 
dialkyl phosphate prepared in accordance with Example 4 above. 
Approximately 40 mL of water were collected in azeotrope at about 
115.degree.-120.degree. C. Thereafter, the mixture was permitted to cool 
and a clear solution was produced. 
EXAMPLE 7 
The liquid aluminum phosphate gelling agent prepared in accordance with 
Example 5 above, was activated with a 50% (volume) IPA/triethanolamine 
solution and mixed with kerosene. The pour point of the gelling agent and 
the activator were well below 0.degree. F. The ratio of P:Al in the 
gelling agent was 3.2:1 Fourteen gallons per thousand of the gelling agent 
gave 56 centipoise viscosity initially at room temperature and about 185 
centipoise at 300.degree. F. Chilled samples of kerosene at about 
10.degree. F. or less were successfully gelled using this gelling agent. 
Furthermore, hydrocarbon gels were formed at very low stirring speeds in a 
blender. 
EXAMPLE 8 
The liquid aluminum phosphate salt gelling agent produced in accordance 
with Example 3 above was activated with triethanolamine to gel kerosene. 
The gel produced significant viscosity in 5-60 seconds after activation. 
While I have shown and described several embodiments in accordance with my 
invention, it is to be clearly understood that the same are susceptible to 
numerous changes apparent to one skilled in the art. Therefore, I do not 
wish to be limited to the details shown and described but intend to show 
all changes and modifications which come within the scope of the appended 
claims.