Note: Descriptions are shown in the official language in which they were submitted.
CA 02742256 2011-09-09
Environmentally Friendly Fracturing and Stimulation Composition and Method of
Using the Same
Background of the Invention
This invention involves compositions and a process for drilling or stimulating
of
subterranean reservoirs including but not restricted to shale, tight gas,
coal,
conventional and non- conventional reservoirs. The composition of this
invention is
composed of ingredients that are considered to be non-toxic, biodegradable and
derived
from"green" or renewable resources.
1o The growing need for oil coupled with the decline in primary production of
oil has
required the need for more novel and efficient methods of recovering residual
oil. These
methods are generally referred to as improved oil recovery (IOR) or well
stimulation.
Many flow back aids have been developed and discussed in the prior art to help
recover
injected fluids after fracturing. The flow back aids benefits the production
by reducing
damage due to phase trapping, enhance mobilization of the oil and gas, help to
increase the regained permeability and improve the oil/gas recovery. Flow back
aid
formulations generally include one or more anionic, nonionic or amphoterics
surfactants,
along with solvents and co-surfactant that are in the solution or
microemulsion form.
The various flowback aids are discussed by Howard et al. in SPE paper
122307.Also
Panga, et al. discusses the wettability alteration in SPE 100182. Pursley et
al. US
Patent 7,380,606 discloses a microemulsion well treatment formed by combining
a
solvent-surfactant blend with a carrier fluid. In the preferred embodiments,
the solvent-
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surfactant blend includes a surfactant and a solvent selected from the group
consisting
of terpenes and alkyl or aryl esters of short chain alcohols. Surfactants
include
ethoxylated castor oil, polyoxyethylene sorbitan monopalmitate and
polyethylene glycol.
Additionally, Isopropyl alcohol and triethylene glycol are used in some cases.
Penny
and Pursley in SPE 107844 give field and laboratory data supporting the
effectiveness
of microemulsions in low perm shales, coalbed methane and tight sandstone
reservoirs.
Brief Summary of the Invention
The primary object of the invention is to provide a flowback aid formulation
based
entirely on non-toxic, readily available, biodegradable, green ingredients
having
1o performance of superior performance to the formulations disclosed in the
prior art.
Another object of the present invention is to provide a flowback formulation
suitable for
application under conditions of extremely low temperatures that are sometimes
encountered during the fracturing of reservoirs.
Other objects and advantages of the present invention will become apparent
from the
following descriptions, wherein, by way of illustration and example, an
embodiment of
the present invention is disclosed.
Detailed Description of the Preferred Embodiments
Detailed descriptions of the preferred embodiment are provided herein. It is
to be
understood, however, that the present invention may be embodied in various
forms.
Therefore, specific details disclosed herein are not to be interpreted as
limiting, but
rather as a basis for the claims and as a representative basis for teaching
one skilled in
the art to employ the present invention in virtually any appropriately
detailed system,
structure or manner.
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The environmentally safe, green, non-toxic flowback aid composition of the
present
invention derived from renewable resources includes:
a. one or more water soluble esters of a low molecular weight alcohol and a
low
molecular weight organic acid,,
b. One or more oil soluble esters of a low molecular weight alcohol and a high
molecular weight fatty acid,
c. one or more water soluble or dispersible nonionic surfactant(s) derived
from
vegetable or animal sources ,
d. one or more anionic or amphoteric surfactant(s) derived from animal or
vegetable based sources, and,
e. water.
Examples of the water soluble esters derived from low molecular weight alcohol
and
low molecular weight organic acid include but are not restricted to ethyl
acetate, propyl
acetate, butyl acetate, ethyl lactate, methyl lactate, propyl lactate, methyl
succinate,
ethyl succinate.
Examples of the oil soluble esters of low molecular weight alcohols and high
molecular
weight fatty acids include but are not restricted to, methyl laurate, ethyl
laurate, methyl
laurate, propyl laurate, methyl oleate, ethyl oleate, propyl oleate, methyl
racinoleate,
ethyl racinoleate, propyl racinoleate, methyl soyate, ethyl soyate, propyl
soyate, methyl
cocoate, ethyl cocoate, propyl cocoate, methyl erucate, ethyl erucate, propyl
erucate.
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Examples of water soluble or dispersible nonionic surfactants derived from
vegetable or
animal sources include but are not restricted to oxirane or methyl oxirane or
mixtures of
oxirane and methyl oxirane derivatives of lauryl alcohol, myristyl alcohol,
palmityl
alcohol, stearyl, oleyl alcohol, erucyl alcohol, polyglucosides.
Examples of anionic or amphoteric surfactants derived from animal or vegetable
sources include but are not restricted to sodium lauryl sulfate, sodium lauryl
ether
sulfates, sodium octyl sulfosuccinate, di sodium octyl sulfosuccinates, sodium
oleyl
ether carboxylates, sodium lauryl carboxylates, cocoamidopropyl betaine,
cocodimethyl
betaine, oleylamidopropyl betaine, oleyl dimethyl betaine, erucylamidopropyl
betaine,
erucyldimethyl betaine, lauryl amine oxide, myristyl amine oxide, oleyl amine
oxide,
erucyl amine oxide.
The composition of the present invention is prepared by combining 5 - 25 wt%
of the
water soluble ester, 5 - 25 wt% of the oil soluble ester, 5 - 25 wt% of the
water soluble
or dispersible nonionic surfactant, 5 - 25 wt% of the anionic or amphoteric
surfactant
with the remainder being water. Glycerin and other environmentally friendly,
green
compounds including but not limited to polyglycerin, inorganic salts,
polyglycerol esters
may be added to lower the freezing point of the composition when necessary.
The
composition is added to a fracturing formulation at concentrations of 0.1 to 5
gallons per
1000 gallons of injection fluid depending on reservoir conditions to obtain
the desired
flowback performance.
The present invention also involves a process for conventional and non -
conventional
applications using the compositions above including but are not limited to
drilling or
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stimulation of subterranean reservoirs including but not restricted to shale,
tight gas, or
coal. The composition of the present invention is used at 0.1 to 5 gallons per
thousand
gallons of injected waterl. The injected water may be fresh water, produced
water, KCI
solution, NaCl solution, Acid Solution or the combination of two or more of
these. In
general any aqueous liquid used for fracturing may be employed. The
composition of
this invention is added to the water or injection brine and injected into the
formation to
reduce surface tension and/or increase contact angle allowing enhanced fluid
recovery
during fracturing or stimulation processes. The injection fluid may contain,
in addition to
the composition of the instantaneous invention, other ingredients known to
those
familiar with the art including but not restricted to corrosion inhibitors,
acids, dispersants,
viscosifiers, lubricity agents.
Employing the composition of the instantaneous invention improves penetration
into the
reservoir, allows better flow-back and drainage, improves load recovery,
reduces
damage due to phase trapping, in addition to providing a safe, environmentally
friendly
alternative to existing flowback aids. Other applications of the formulation
of the
instantaneous invention include Enhanced Oil Recovery (EOR), wettability
alteration,
well cleanout and work-over.
List of Figures
Figure 1 Effect of the flowback aid on regained permeability at various
residual fluid
saturation.
Figure 2 Effect of the flowback aid on regained permeability at various gas
drive
pressure
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The following examples serve to demonstrate the effectiveness of the invention
over the
prior art.
Example 1: Preparation of the flow-back aid (sample 12-8816)
An environmentally safe, green, non-toxic flowback aid was prepared by first
dissolving
15 parts of ethyl lactate in 15 parts of methyl tallate. A second solution was
prepared by
mixing 12.5 parts of lauryl alcohol containing 6 moles of ethylene oxide with
a 12.5 parts
of a 70% aqueous solution of mono-sodium dodecyl sulfosuccinate. The two
solutions
were combined with stirring and 55 parts of water was slowly added to form a
clear low
viscosity stable solution.
so Example 2: Performance Test
This test was performed to compare the ability of various flowback aids to not
form
stable emulsions when contacted with residual oil. Various flowback aids were
mixed at
a dosage of one gallon per 1000 gallons of injection brine. 50 ml of brine
containing the
flowback aid was mixed with 50 ml of oil and blended at high speed in a Waring
Blender
to emulsify the two liquids. After 5 minutes of mixing the liquid was poured
into a 500 ml
cylinder to observe the water break out from the emulsion. The API standard
for this test
is for 95% of the water to breakout in 30 minutes. Table 1 shows the results
using
sample currently used by three different treating companies along with the
results using
the sample 12-8816 from Example 1.
Table 1 Percent Breakout of Fracturing Fluid with Time
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1 min 3 min 4 min 5 min 10 min
Supplier A 60 80 85 90 100
Supplier B 80 80 85 90 100
Supplier C 92 100
Sample 12-8816 100
The result demonstrate that the formulation of the present invention is
superior to those
currently employed by three treating companies in addition to being
environmentally
safe, green and biodegradable.
Example 3: Effect of the flowback aid on regained permeability at various
residual fluid
saturation.
Figure 1 demonstrates the relative permeability at various residual fluid
saturation with
and without sample 12-8816. 0.1 % by weight of the sample 12-8816 was added in
2%
KCI and test against 2% KCI by itself. The data showed that the regained
permeability is
doubled using the small amount of sample 12-8816.
Example 4: Effect of the flowback aid on regained permeability at various gas
drive
pressure
Figure 2 demonstrates the regained permeability at various gas drive pressure.
Again,
0.1 weight % of the sample 12-8816 was added to 2% KCI and tested against 2%
KCI
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by itself. The data showed much higher regained permeability using 0.1 %
sample 12-
8816.
Example 5: Low freeze formulation
A low temperature version of Example 1 was prepared by replacing 50% of the
water
with glycerin as a pour point depressant. This formulation was found to have
the same
performance characteristics as samples formulated without glycerin but
remained fluid
down to -41 F.
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