Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYNTHETIC ACID COMPOSITIONS ALTERNATIVES
TO CONVENTIONAL ACIDS FOR USE IN THE OIL AND GAS INDUSTRY
FIELD OF THE INVENTION
This invention relates to compositions for use in performing various
applications in the oil &
gas industry, more specifically to synthetic acid compositions as alternatives
to conventional acids.
BACKGROUND OF THE INVENTION
In the oil & gas industry, stimulation with an acid is performed on a well to
increase or
restore production. In some instances, a well initially exhibits low
permeability, and stimulation is
employed to commence production from the reservoir. In other instances,
stimulation is used to
further encourage permeability and flow from an already existing well that has
become under-
productive.
Acidizing is a type of stimulation treatment which is performed above or below
the reservoir
fracture pressure in an effort to restore or increase the natural permeability
of the reservoir rock.
Acidizing is achieved by pumping acid into the well to dissolve limestone,
dolomite and calcite
cement between the sediment grains of the reservoir rocks.
There are three major types of acid applications: matrix acidizing, fracture
acidizing, and
spearhead breakdown acidizing (pumped prior to a fracturing pad in order to
assist with formation
breakdown (reduce fracture pressures), or to clean up left over cement in the
well bore. A matrix
acid treatment is performed when acid is pumped into the well and into the
pores of the reservoir
rocks. In this form of acidization, the acids dissolve the sediments and mud
solids that are inhibiting
the permeability of the rock, enlarging the natural pores of the reservoir and
stimulating flow of
hydrocarbons. While matrix acidizing is done at a low enough pressure to keep
from fracturing the
reservoir rock, fracture acidizing involves pumping highly pressurized acid
into the well, physically
fracturing the reservoir rock and etching the permeability inhibitive
sediments. This type of acid
treatment forms channels or fractures through which the hydrocarbons can flow.
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There are many different mineral and organic acids used to perform an acid
treatment on
wells. The most common type of acid employed on wells to stimulate production
is hydrochloric
acid (HCI), which is useful in stimulating carbonate reservoirs.
Some of the major challenges faced in the oil & gas industry from using
hydrochloric acid
include the following: extremely high levels of corrosion (which is countered
by the addition of
'filming' corrosion inhibitors that are typically themselves toxic and harmful
to humans, the
environment and equipment) reactions between acids and various types of metals
can vary greatly
but softer metals, such as aluminum, are very susceptible to major effects
causing immediate
damage. Hydrochloric acid produces Hydrogen chloride gas which is toxic and
corrosive to skin,
eyes and metals. At levels above 50 PPM (parts per million) it can be
Immediately Dangerous to
Life and Health (IDHL). At levels from 1300-2000 PPM death can occur in 2-3
minutes.
The inherent environmental effects (organic sterility, poisoning of wildlife
etc.) of acids in
the event of an unintended/accidental release on surface or downhole into
water aquifers or sources
of water are devastating which can cause significant pH reduction of such and
can substantially
increase the toxicity and could potentially cause a mass culling of aquatic
species and potential
poisoning of humans/livestock and wildlife exposed to/or drinking the water.
An unintended release
at surface can also cause a hydrogen chloride gas cloud to be released,
potentially endangering
human and animal health. This is a common event at large storage sites when
tanks split or leak.
Typically if near the public, large areas need to be evacuated post event.
Because of its acidic
nature, hydrogen chloride gas is also corrosive, particularly in the presence
of moisture.
The inability for acids and blends of such to biodegrade naturally without
neutralizing the
soil results in expensive cleanup-reclamation costs for the operator should an
unintended release
occur. Moreover, the toxic fumes produced by mineral & organic acids are
harmful to
humans/animals and are highly corrosive and/or explosive potentially,
transportation and storage
requirements for acids are restrictive and taxing in such that you must
typically haul the products in
acid tankers or intermediate bulk containers (IBC) that are rated to handle
such corrosive-regulated
products, blending exposure dangers for personnel exposed to handling.
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Another concern is the potential for spills on locations due to high corrosion
levels of acids
causing storage container failures and/or deployment equipment failures i.e.
coiled tubing/tubing
failures caused by high corrosion rates (pitting, cracks, major failures).
Other concerns include:
downhole equipment corrosion causing the operator to execute a work-over and
replace down hole
pumps, tubing, cables, packers etc.; inconsistent strength or quality level of
mineral & organic
acids; potential supply issues based on industrial output levels; high levels
of corrosion on surface
pumping equipment resulting in expensive repair and maintenance levels for
operators and service
companies; the requirement of specialized equipment that is purpose built to
pump acids greatly
increasing the capital expenditures of operators and service companies; and
the inability to source a
finished product locally or very near its end use.
Typically, acids are produced in industrial areas of countries located far
from oil & gas
applications, up to= 10 additives can be required to control various aspects
of the acids performance
adding to complications in the handling and shipping logistics.
Large price fluctuations with typical mineral and organic acids based on
industrial output
causing end users an inability to establish long term costs in their
respective budgets; severe
reaction with dermal/eye tissue; major PPE requirements (personal protective
equipment) for
handling, such as on site shower units; extremely high corrosion rates and
reaction rates as
temperature increases causing the product to "spend/react or become neutral"
prior to achieving its
desired effect such as penetrating an oil or gas fonnation to increase the
wormhole "pathway"
effectively to allow the petroleum product to flow freely to the surface. As
an example,
hydrochloric acid or mud acid is utilized in an attempt to free stuck drill
pipe in some situations.
Prior to getting to the required depth to solubilize the formation that has
caused the pipe/tubing to
become stuck many acids spend or neutralize due to increased bottom hole
temperatures and
increased reaction rate, so it is advantageous to have an alternative that
spends or reacts more
methodically allowing the slough to be treated with a solution that is still
active, allowing the
= pipe/tubing to be pulled free.
When used to treat scaling issues on surface due to water/fluid precipitation,
acids are
exposed to humans and mechanical devices as well as expensive pumping
equipment causing
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increased risk for the operator and corrosion effects that damage equipment
and create hazardous
fumes. When mixed with bases or higher pH fluids, acids will create a large
amount of thermal
energy (exothermic reaction) causing potential safety concerns and equipment
damage, acids
typically need to be blended with fresh water to the desired concentration
requiring companies to
pre-blend off-site as opposed to blending on-site with water thereby
increasing costs associated with
transportation.
Typical mineral acids used in a pH control situation can cause degradation of
certain
polymers/additives/systems requiring further chemicals to be added to counter
these potentially
negative effects, many offshore areas of operations have very strict
regulatory rules regarding the
transportation/handling and deployment of acids causing increased liability
and costs for the
operator. When using an acid to pickle tubing or pipe, very careful attention
must be paid to the
process due to high levels of corrosion, as temperatures increase, the typical
additives used to
control corrosion levels in acid systems begin to degrade very quickly (due to
the inhibitors "plating
out" on the steel) causing the acids to become very corrosive and resulting in
damage to
equipment/wells. Acids are very destructive to most typical elastomers found
in the oil & gas
industry such as blow out preventers (BOP's) /downhole
tools/packers/submersible pumps/seals etc.
Having to deal with spent acid during the back flush process is also very
expensive as acids
typically are still a low pH and toxic. It is advantageous to have an acid
blend that can be exported
to production facilities through pipelines that once spent or applied, is
commonly a neutral pH
greatly reducing disposal costs/fees.
Acids perform many actions in the oil & gas industry and are considered
necessary to
achieve the desired production of various petroleum wells, maintain their
respective systems and aid
in certain functions (i.e. freeing stuck pipe). The associated dangers that
come with using acids are
expansive and tasking to mitigate through controls whether they are chemically
or mechanically
engineered.
Eliminating or even simply reducing the negative effects of acids while
maintaining their
usefulness is a struggle for the industry. As the public demand for the use of
cleaner/safer/greener
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products increases, companies are looking for alternatives that perform the
required function
without all or most of the drawbacks associated with the use of acids.
US patent no. 4,40,852 discloses compositions containing 5 to 75% of urea, 5
to 85% of
sulfuric acid and from 5 to 75% of water. These compositions are said to have
reduced corrosivity
to carbon steels.
US patent no. 6,147,042 discloses compositions comprising a polyphosphoric
acid- urea
condensate or polymer which results from the reaction of orthophosphoric acid
and urea used in the
removal of etching residue containing organometal residues.
US patent no. 7,938,912 discloses compositions containing hydrochloric acid,
urea, a
complex substituted keto-amine-hydrochloride, an alcohol, an ethoxylate and a
ketone for use to
clean surfaces having cementitious compositions. US patent no. 8,430,971 and
8,580,047 disclose
and claim compositions containing specific amounts of hydrochloric acid (55%
by wt); urea (42%
by wt), a complex substituted keto-amine-hydrochloride (0.067% by wt);
propargyl alcohol
" (0.067% by wt); an ethoxylated nonylphenyl (0.022% by wt); methyl vinyl
ketone (0.022% by wt);
acetone (0.0022% by wt); and acetophenone (0.0022% by wt) for use in specific
oil industry
applications, namely oil drilling and hydraulic fracturing.
US patent no. 5,672,279 discloses a composition containing urea hydrochloride
prepared by
mixing urea and hydrochloric acid. Urea hydrochloride is used to remove scale
in hot water boilers
and other industrial equipment such as papermaking equipment. Scale is caused
by the presence of
calcium carbonate which is poorly soluble in water and tends to accumulate on
surfaces and affect
equipment exposed to it.
Consequently, there is still a need for compositions for use in the oil
industry which can be
used over a range of applications which can decrease a number of the
associated dangers/issues
= typically associated with acid applications to the extent that these acid
compositions are considered
much safer for handling on worksites.
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SUMMARY OF THE INVENTION
Compositions according to the present invention have been developed for the
oil & gas
industry and its associated applications, by specifically targeting the
problems of corrosion,
logistics/handling, human/environmental exposure and formation/fluid
compatibilities.
It is an object of the present invention to provide a synthetic acid
composition which can be
used over a broad range of applications in the oil and gas industry and which
exhibit advantageous
properties over known compositions.
According to one aspect of the present invention, there is provided a
synthetic acid
composition which, upon proper use, results in a very low corrosion rate of
oil and gas industry
activities equipment.
According to another aspect of the present invention, there is provided a
synthetic acid
composition for use in the oil industry which is biodegradable.
According to another aspect of the present invention, there is provided a
synthetic acid
composition for use in the oil industry which has a methodically spending
(reacting) nature that is
linear as temperature increases, non-fuming, non-toxic, and highly controlled
manufacturing
process.
According to another aspect of the present invention, there is provided a
synthetic acid
composition for use in the oil industry which has a pH below 1.
According to another aspect of the present invention, there is provided a
synthetic acid
composition for use in the oil industry which has minimal exothermic
reactivity.
According to another aspect of the present invention, there is provided a
synthetic acid
composition for use in the oil industry which is compatible with most existing
industry additives.
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According to another aspect of the present invention, there is provided a
synthetic acid
composition for use in the oil industry which has high salinity tolerance. A
tolerance for high
salinity fluids, or brines, is desirable for onshore and offshore acid
applications. Typical acids are
blended with fresh water and additives, typically far offsite, and then
transported to the area of
treatment as a finished blend. It is advantageous to have an alternative that
can be transported as a
concentrate safely to the treatment area, then blended with a high salinity
produced water or sea
water greatly reducing the logistics requirement typical with conventional
acid systems. A typical
acid system could precipitate salts heavily if blended with fluids of an
excessive salinity level.
Brines are also typically present in formations thus having an acid system
that has a high tolerance
for brines greatly reduces the potential for formation damage or emulsions.
According to another aspect of the present invention, there is provided a
synthetic acid
composition for use in the oil industry which is immediately reactive upon
contact/application.
1 5 According to another aspect of the present invention, there is provided
a synthetic acid
composition for use in the oil industry which results in less unintended near
wellbore erosion due to
the slower reaction rate. This, in turn, results in deeper formation
penetration and reduces the
potential for zonal communication during a typical 'open hole' isolation
application treatment. As a
highly reactive acid, such as hydrochloric acid, is deployed into a well that
has open hole packers or
isolation (without casing) there is a potential to cause a loss of near-
wellbore compressive strength
resulting in a potential for communication between zones or formations
sections of interest as well
as potential sand production, fines migration. Excessive reaction may also
remove the natural
cementation holding quartz grains together. It is advantageous to have an
alternative that will react
with a much more methodical rate or speed, thus greatly reducing the potential
for zonal
communication and the above potential negative side effects of traditional
acid systems.
According to another aspect of the present invention, there is provided a
synthetic acid
composition for use in the oil industry which provides a methodical and
comprehensive reaction
rate.
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Accordingly, the product would overcome many of the drawbacks found in the use
of
compositions of the prior art related to the oil & gas industry.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
It will be appreciated that, numerous specific details have provided for a
thorough
understanding of the exemplary embodiments described herein. However, it will
be understood by
those of ordinary skill in the art that the embodiments described herein may
be practiced without
these specific details. In other instances, well-known methods, procedures and
components have not
been described in detail so as not to obscure the embodiments described
herein. Furthermore, this
description is not to be considered so that it may limit the scope of the
embodiments described
herein in any way, but rather as merely describing the implementation of the
various embodiments
described herein.
The description that follows, and the embodiments described therein, are
provided by way of
illustration of an example, or examples, of particular embodiments of the
principles of the present
invention. These examples are provided for the purposes of explanation, and
not limitation, of those
principles and of the invention.
According to an aspect of the invention, there is provided a synthetic acid
composition
comprising:
-
Urea & Hydrogen Chloride in a molar ratio of not less than 0.1:1; preferably
in a molar
ratio not less than 0.5:1, more preferably in a molar ratio not less than
0.8:1;
- optionally, a phosphonic acid or derivatives, preferably alkylphosphonic
acid or
derivatives thereof and more preferably amino tris methylene phosphonic acid
and
derivatives thereof
- Metal iodide or iodates, preferably cupric iodide, potassium iodide, or
sodium iodide;
and
- an alcohol or derivatives thereof preferably alkynyl alcohol or
derivatives thereof, more
preferably propargyl alcohol (or a derivative of).
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Urea-HC1 Acid
Urea is the main component in terms of volume and weight percent of the
composition of
= the present invention, and consists basically of a carbonyl group
connecting with nitrogen and
hydrogen. When added to hydrochloric acid, there is a reaction that results in
urea hydrochloride,
which basically traps the chloride ion within the molecular structure. This
reaction greatly reduces
the hazardous effects of the hydrochloric acid on its own, such as the fuming
effects, the
hygroscopic effects, and the highly corrosive nature (the CF ion will not
readily bond with the Fe
ion). The excess nitrogen can also act as a corrosion inhibitor at higher
temperatures. Urea &
Hydrogen Chloride in a molar ratio of not less than 0.1:1; preferably in a
molar ratio not less than
0.5:1, and more preferably in a molar ratio not less than 0.8:1. However, this
ratio can be increased
depending on the application.
The urea (hydrochloride) also allows for a reduced rate of reaction when in
the presence of
carbonate-based materials. This again due to the stronger molecular bonds
associated over what
hydrochloric acid traditionally displays. Further, since the composition
according to the present
invention is mainly comprised of urea (which is naturally biodegradable), the
product testing has
shown that the urea hydrochloride will maintain the same biodegradability
function, something that
hydrochloric acid will not.
Phosphonic acids and derivatives such as amino tris methylene phosphonic acid
(ATMP)
have some value as scale inhibitors. In fact, ATMP is a chemical traditionally
used as an oilfield
scale inhibitor, it has been found, when used in combination with urea/HC1, to
increase the
corrosion inhibition. It has a good environmental profile, is readily
available and reasonably priced.
Amino tris (methylenephosphonic acid) (ATMP) and its sodium salts are
typically used in
water treatment operations as scale inhibitors. They also find use as
detergents and in cleaning
applications, in paper, textile and photographic industries and in off-shore
oil applications. Pure
ATMP presents itself as a solid but it is generally obtained through process
steps leading to a
solution ranging from being colourless to having a pale yellow colour. ATMP
acid and some of its
sodium salts may cause corrosion to metals and may cause serious eye
irritation to a varying degree
dependent upon the pH/degree of neutralization.
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ATMP must be handled with care when in its pure form or not in combination
with certain
other products. Typically, ATMP present in products intended for industrial
use must be maintained
in appropriate conditions in order to limit the exposure at a safe level to
ensure human health and
environment.
Amino tris (methylenephosphonic acid) and its sodium salts belong to the ATMP
category
in that all category members are various ionized forms of the acid. This
category includes potassium
and ammonium salts of that acid. The properties of the members of a category
are usually
consistent. Moreover, certain properties for a salt, in ecotoxicity studies,
for example, can be
directly appreciated by analogy to the properties of the parent acid. Amino
tris
(methylenephosphonic acid) may specifically be used as an intermediate for
producing the
phosphonates salts. The salt is used in situ (usually the case) or stored
separately for further
neutralization. One of the common uses of phosphonates is as scale inhibitors
in the treatment of
cooling and boiler water systems. In particular, for ATMP and its sodium salts
are used in to
prevent the formation of calcium carbonate scale.
Alcohols and derivatives thereof, such as alkyne alcohols and derivatives and
preferably
propargyl alcohol and derivatives thereof can be used as corrosion inhibitors.
Propargyl alcohol
itself is traditionally used as a corrosion inhibitor which works extremely
well at low
concentrations. It is a toxic/flammable chemical to handle as a concentrate,
so care must be taken
during handling the concentrate. In the composition according to the present
invention, the toxic
effect does not negatively impact the safety of the composition.
Metal iodides or iodates such= as potassium iodide, sodium iodide and cuprous
iodide can
potentially be used as corrosion inhibitor intensifier. In fact, potassium
iodide is a metal iodide
traditionally used as corrosion inhibitor intensifier, however it is
expensive, but works extremely
well. It is non-regulated and friendly to handle.
Process to prepare a composition according to a preferred embodiment of the
invention
Start with a 50% by weight solution of pure urea liquor. Add a 36% by weight
solution of
hydrogen chloride while circulating until all reactions have completely
ceased. The ATMP is then
added followed by propargyl alcohol, and potassium iodide. Circulation is
maintained until all
products have been solubilized. Additional products can then be added as
required.
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Example 1: Composition of a preferred embodiment of the present invention
Chemical % Wt Composition CAS#
Water 60.315% 7732-18-5
Urea Hydrochloride 39.0% 506-89-8
Amino tris methylene phosphonic acid 0.576% 6419-19-8
Propargyl Alcohol 0.087% 107-19-7
Potassium Iodide 0.022% 7681-11-0
The resulting composition of Example 1 is a clear, odourless liquid having
shelf-life of
greater than 1 year. It has a freezing point temperature of approximately
minus 30 C and a boiling
point temperature of approximately 100 C. It has a specific gravity of 1.15
0.02. It is completely
soluble in water and its pH is less than 1.
The composition is biodegradable and is classified as a mild irritant
according to the
classifications for skin and eye tests. The composition is non-fuming and has
no volatile organic
compounds nor does it have any BTEX levels above the drinking water quality
levels. BTEX refers
to the chemicals benzene, toluene, ethylbenzene and xylene. Toxicity testing
was carried out on rats
and the LD50 was determined to be not greater than 2000mg/kg.
With iespect to the corrosion impact of the composition on typical oilfield
grade steel, it was
established that it was clearly well below the acceptable corrosion limits set
by industry.
The compositions according to the present invention can be used directly
(ready-to-use) or
be diluted with water depending on their use.
The uses (or applications) of the compositions according to the present
invention upon
dilution thereof ranging from approximately 1 to 75% dilution, include, but
are not limited to:
injection/disposal in wells; squeezes and soaks or bullheads; acid fracturing,
acid washes or matrix
stimulations; fracturing spearheads (breakdowns); pipeline scale treatments,
cement breakdowns or
perforation cleaning; pH control; and de-scaling applications.
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Use of a composition according to the present invention in spearhead on multi-
well pad
An operator in Western Canada was performing horizontal multi-stage fracturing
completions on a multiple well pad, using plug and perforate technology.
Traditional methods of
formation breakdown required the use of 6-10 ni.3 of 15% HC1 acid to be pumped
down the casing
prior to each fracturing stage.
Prior to testing, multiple samples of the high salinity fracturing water
(recycled fracturing
fluid) were tested for compatibility, as this was proposed to be used as the
diluents for the
concentrated synthetic acid. By storing the concentrated synthetic acid
composition in a tank and
diluting it with the fracturing water on site, only a few storage tanks were
required for the
treatments ( 500 in3 of spearhead acid). These are intended on being refilled
periodically.
For each treatment, the tank of concentrated synthetic acid composition was
blended on site
through the fracturing blender with the fracturing water down to reach a
concentration of 33% of
the initial composition. 6-10 m3 of the synthetic acid composition was pumped
for each spearhead
stage, all other operational components and procedures remained the same as
traditional methods
using HC1 acid (15% HC1 acid was on location for a comparison well).
A total of 18 stages were treated on more than 8 wells, with 100% breakdown
success on
every stage. Breakdown pressure differentials in the range of 10-15 MPa were
observed, and were
found to be very comparable to HC1 acid.
The main advantages of the use of the synthetic acid composition included: the
reduction of
the total loads of acid, and the required number of tanks by delivering
concentrated product to
location and diluting with fluids available on location (high salinity
production water). Other
advantages of the composition according to the present invention include:
operational efficiencies
which led to the elimination of having to circulate tanks of HC1 acid; reduced
potential corrosion to
downhole tubular; and reduced HC1 acid exposure to personnel by having a non-
hazardous, non-
fuming acid on location.
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While the foregoing invention has been described in some detail for purposes
of clarity and
understanding, it will be appreciated by those skilled in the relevant arts,
once they have been made
familiar with this disclosure, that various changes in form and detail can be
made without departing
from the true scope of the invention in the appended claims.
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