Note: Descriptions are shown in the official language in which they were submitted.
CA 02620538 2008-02-06
METHOD AND APPARATUS FOR REMOVING SUSPENDED SOLIDS AND
TURBIDITY FROM ALKALI METAL FORMATE BRINE FLUIDS
FIELD OF THE INVENTION
This invention relates to a method and apparatus for quickly and economically
removirig suspended
solids from used alkali metal formate brine fluids to allow for their re-use
rather than disposal. The
invention is particularly useful for cleaning and recycling of high density
brine drilling fluids such
as potassium, caesium and sodium formate brines which have been contaminated
with excess
amounts of suspended solids and colloidal matter during use.
BACKGROUND AND PRIOR ART
Alkali metal formate brine fluids have been used in industry for a number of
years, with one of the
largest users being the oil industry, where they are commonly used as drilling
or completion fluids.
One common property of these brines which makes them valuable in such
applications is their
ability to produce a clear high density liquid which doesn't contain solids.
This is particularly useful
in the oil drilling and production industry where high density fluids are
commonly used for a variety
of purposes including displacing lighter weight fluids in drill holes during
drilling and completion
operations.
When brine fluids are used in these applications they often pick up undesired
contaminants from the
drill hole such as very fine solids which subsequently become suspended in the
brine water. When
the total suspended solids (TSS) concentration in the brine fluid reaches a
specified threshold, the
used brine is typically disposed and replaced with new brine, since excess
solids in the water can
have negative effects on the drilling operations. Due to the high cost of
producing some of these
brine fluids, as well as concerns over disposing such products into the
environment, companies
using these brine fluids would prefer to be able to clean and re-use them if
it was economically
feasible, rather than disposing of them when they become contaminated.
Various inventions have been developed over the years to address this problem
including filtration
technologies, use of organic chelants to remove metal impurities, and addition
of various chemicals
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to try to precipitate out various contaminants. All of these have offered
varying degrees of success
in achieving this objective, but retain a number of limitations and
disadvantages.
With filtration technologies, many brine fluids used in the oil industry
typically become
contaminated with extremely small clay type particles commonly referred to as
`colloidal' solids.
These solids are so small that they fall into the sub-micron and nano size
ranges and can't typically
be removed economically with common filtration technologies due to their small
size.
Other inventions have employed the use of multi-parameter chemical adjustments
or adding
chemicals aimed at precipitating out metal ions from the fluid. This is
typically carried out in
conjunction with various other process stages such as filtration to remove
resulting precipitates from
the fluid. One limitation of these processes is that they generally target
metal contaminants in the
water and don't address the issue of clay type colloidal particles which can
comprise the majority of
the solids suspended in the water.
One disadvantage common to almost all options is their cost. When the cost of
cleaning the used
fluid exceeds the cost of producing new fluids, then the recycling process
normally won't be used.
Prior patents of background relevance to the current invention include the
following;
US PAT. #7172703 - 02/06/2007 - Method of Reclaiming a Well Completion Brine
Solution
using an Organic Chelant
US PAT. #4465598 - 08/14/1984 - Method of Treating Well Servicing Fluids
US PAT. #4303624 - 12/01/1981 - Purification of Alkali Metal Chloride Brines
US PAT. #4207152 - 06/10/1980 - Process for the Purification of Alkali Metal
Chloride Brines
METHOD BY WHICH THE PRESENT INVENTION OVERCOMES PRIOR
ART PROBLEMS
It is an object of this invention to provide a method and apparatus for
removing suspended solids
from alkali metal formate brines which is simpler, more economical, and
effective in removing
colloidal clay particles from the fluid. This is accomplished by adjusting the
fluid environment to
promote the flocculation and removal of these particles in one simple step.
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It has long been known in other fields of industry that extremely small solids
suspended in water
will not settle out of solution through normal gravity forces, or float to the
surface through normal
buoyancy forces. This occurs when the particles involved are in the sub-micron
and nano size
ranges, at which point they are typically referred to as `colloidal' solids.
In the case of colloidal clay
particles in water, it has also been known that these particles tend to carry
a small negative electrical
charge around their perimeter which repels other similarly charged particles
suspended in the fluid,
keeping them separate from each other. This property prevents the particles
from coniing together
as a larger group, which would then be dense enough to settle out. This
property of colloidal clay
particles is one which `flocculation' technologies have been designed to
overcome in the past by
encouraging the particles to coagulate and settle out. These processes
typically work by injecting
one or more chemicals into the fluid which are designed to introduce a
propensity of strongly
charged ions in the fluid which have an opposite charge to that of the clay
particles. These strongly
charged ions attract the oppositely charged clay particles in the water,
causing them to `attach' to
the flocculant ion in sufficient numbers to cause an increase in the density
of the combined group,
such that they eventually settle out of solution together as a group.
In conventional flocculation processes, a chemical compound known as
a`flocculant' is typically
added to the water to begin this process, along with various water
conditioning chemicals designed
to adjust the chemical environment of the water to one in which the flocculant
will work best. This
flocculant, when dissolved in water, releases strongly charged ions which
carry an opposite charge
to that of the target contaminant. One such product commonly used for this
purpose is aluminum
sulfate (A12012S3). When aluminum sulfate is dissolved in water it releases
strongly charged
positive ions (Al 3+), which attract negatively charged clay particles in the
water to promote the
flocculation process. Other chemicals and polymers have been developed for
this purpose as well,
but all generally seek to provide strongly charged ions in the water which are
opposite in charge to
that of the target contaminant.
Unfortunately, typical flocculation processes are relatively complicated, are
capital intensive, are
costly to operate, and consequently are not well suited for economically
processing potentially low
quantities of brine fluids. Costs of the process typically include the
purchase, storage and handling
of various flocculant and conditioning chemicals, determining optimal chemical
balances required
to achieve desired reactions, and attempting to ensure that the flocculant
selected doesn't introduce
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new chemical species into the brine fluid which could result in the creation
of by-product
compounds which could negatively affect the physical properties of the brine.
To overcome these issues, the current invention has developed a method of
removing solids from
brine fluids without incurring the disadvantages noted above. This process
involves greatly
simplifying the flocculation process by activating existing elements already
in the brine fluid to act
as flocculating agents, thereby eliminating the need to add any new chemicals
for this purpose. The
process and methodology by which this is accomplished, and which comprises the
embodiment of
the present invention, is described below:
1) All alkali metal formate brine fluids which comprise the subject of this
invention naturally
contain one or more alkali metal atoms such as potassium, sodium, calcium or
caesium.
Each of these, when dissolved in water, release metal ions into solution which
carry a small
positive charge (eg. Na+, K+, Ca+);
2) While these ions are not typically used as flocculants because of the small
charge they
carry, it has been found in the case of brine fluids that by adding a strong
base to the brine
fluid, such as sodium hydroxide (NaOH), and raising the pH of the brine flui(i
to 12.80 or
higher, the fluid environment is adjusted in a manner which promotes a cascade
reaction in
the fluid whereby positive ions already in solution begin acting as natural
flocculants, and a
strong floc begins forming in the liquid to remove the suspended solids.
3) This process happens immediately upon reaching the necessary pH threshold,
and floc
containing suspended solid particles quickly begins to settle to the bottom of
the container,
leaving only clarified water at the top. This clarified water is easily de-
canted to provide a
clean brine fluid which is free of most or all previously suspended solids,
making it
immediately suitable for re-use;
4) Because the resultant fluid has a high ph, however, and a high pH fluid may
be undesirable
for handling or corrosion reasons, an acid such as Hydrochloric Acid (HCL) can
be added
to the clarified fluid to easily adjust the pH to whatever final pH is
desired.
This process improves on the prior art by eliminating one of the major steps
in the flocculation
process - that of having to purchase, store and add flocculant compounds to
the water to achieve
the desired treatment. This greatly reduces complexity of the operation,
reduces capital and
operating costs to much more competitive levels, and eliminates concerns
regarding any by-
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products that could otherwise be formed by the introduction of new chemical
species from use of
the flocculant. The treatment process described herein is therefore reduced to
the simple addition of
a strong base material such as NaOH to the used brine fluid in sufficient
quantities to initiate the
flocculation process, and then decanting the clean water for re-use. The
quantity of base material
required for this purpose can be calculated arithmetically or done visually
whereby the base
compound is added until flocs beginning appearing in the water.
When the flocculated solids settle to the bottom of the container, and the
clean water has been
removed from the top, neutralizing acid can be added to both the clean and
waste waters to bring
the pH of the fluids back to a desired operating range.
Tests were carried out to confirm the efficiency of the described process.
These tests utilized a used
potassium formate brine solution (KCOOH) as the raw material. This product had
been returned
from an actual oil well completion project, and was contaminated with
suspended colloidal solids
and a small amount of residual hydrocarbons. The used fluid was allowed to
settle for a period of
two weeks prior to conducting the tests described below to ensure that the
settleable solids in the
water had been removed, and any remaining solids being extracted by the new
process would be
primarily colloidal in nature.
Test Result:
= Raw Test fluid - Used potassium formate brine (KCOOH)
= Brine Density - 1120 gms/L
= Total Suspended Solids - 153 ppm
= Turbidity - 100 NTU
= pH of brine - 9.94
Solid sodium hydroxide (NaOH) was added to six separate test containers in
varying concentrations
representing 0.1%, 0.2%, 0.25%, 0.3%, 0.4% and 0.5% NaOH by weight. After
dissolution of the
NaOH in the brine water, the fluid in each test container was stirred to
ensure mixing of the two
compounds. Each sample was then observed for a period of time, and the
reactions recorded.
Sample #1 (0.10%) - no flocculation occurred.
Sample #2 (0.20%) - flocculation commenced immediately upon being stirred.
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Sample #3 (0.25%) - flocculation commenced immediately upon being stirred.
Sample #4 (0.30%) - flocculation commenced immediately upon being stirred.
Sample #5 (0.40%) - flocculation commenced immediately upon being stirred.
Sample #6 (0.50%) - flocculation commenced immediately upon being stirred.
At lower NaOH concentrations (#2 and #3), the flocculation process proceeded
more slowly and
less thoroughly than at higher concentrations.
At the three higher concentrations, all samples showed greatly increased water
clarity within 10
minutes of mixing, but small floc particles remained in suspension for up to 6
hours. After settling
for 6 hours, most of the floc had settled to the bottom of the container, and
the clarified water on top
(representing 85% of the water in the containers) was ready for decanting as
clean water. The
remaining 15% of water and floc at the bottom of the test containers was then
added together and
allowed to settle for a further 6 hours, following which a further 8% of the
original brine was able to
be removed as clarified water, resulting in an overall recovery rate of 93% in
12 hours.
The pH of each test sample resulting from addition of the NaOH was;
Sample #1: pH = 10.99
Sample #2: pH = 12.80
Sample #3: pH = 12.95
Sample #4: pH = 13.28
Sample #5: pH = 13.43
Sample #6: pH = 13.50
The clean water decanted from sample #6 was tested to determine the level of
treatment which had
been achieved, with the following results:
Clarified Water Quality (Sample #6):
= Fluid Density - 1120 gms/L (no change)
= Suspended Solids Content- 6 ppm (96% reduction from original)
= Water Turbidity - 5.4 NTU (94.6% reduction from original)
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It was noted during testing that gentle stirring of the water to achieve water
mixing with the NaOH
resulted in all of the floc particles settling to the bottom of the treatment
container after the required
settling time, whereas mixing the water with air (which happens when a test
container is shook
vigorously) results in bubbles being entrained in the floc particles, causing
many of them to initially
float to the top of the container instead, making it more difficult to decant
clarified water than if the
flocs reside at the bottom.
The present treatment process improves on the prior art by:
= Providing a much faster and simpler treatment process which requires only
one step to achieve
clarified water;
= Eliminating concerns over possible addition of new chemical species to the
brine which could
produce compounds which impart negative fluid properties to the brine;
= Making the treatment process much more economical by eliminating the cost of
significant
amounts of chemicals, time and equipment that would otherwise be needed using
alternate
options.
LIST OF FIGURES AND DESCRIPTION OF THE INVENTION
In drawings which illustrate embodiments of the invention, Figure 1 is an
elevation view as it would
apply to one preferred embodiment.
The invention as illustrated consists of a process and apparatus for quickly
and economically
removing suspended solids from used alkali metal formate brine fluids which
involves the following
steps:
1) Addition of a strong base material (preferably NaOH) to the brine fluid to
raise its pH to
a level where existing positively charged ions in the fluid will begin acting
as
flocculants;
2) Storage of the brine fluid in a container for a period of time as required
to allow the
majority of floc created in the flocculation process to settle to the bottom
of the
container;
3) De-canting the clarified water from the top of the container;
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4) Addition of acid to the brine to return the pH to a final desired level.
In one preferred embodiment of the invention as shown in figure 1, the
contaminated brine fluid is
placed in a primary treatment tank (1) constructed of a material resistant to
high pH fluids. The
treatment tank (1) may be at atmospheric pressure, with an open top or access
openings in the top to
permit easy access. A water sample is drawn from the tank to check its pH. A
calculation is made to
determine the amount of base material required to raise the pH of the brine
liquid to a level
sufficient to initiate the flocculation process. In tests carried out on the
brine described herein, this
level needed to be 12.8 or greater. However, this may vary somewhat depending
on the: liquid being
treated, and a bench test is recommended each time a new fluid is to be
treated by adding increasing
amounts of NaOH to a measured amount of brine until the level at which the
flocculation process
begins can be identified. A strong base, preferably sodium oxide (NaOH), is
then addeci to the brine
by injecting it into the treatment tank (1) under pressure, or adding it by
gravity through the top (2).
A means of mixing the brine fluid and base material in the treatment tank (1)
is provided by use of a
re-circulating pump (7) or a mechanical mixer located in the tank. Following
mixing, the brine is
allowed to sit for a period of 6 hours or more, or as otherwise needed to
achieve a desired level of
clarification. Sample and drain ports (5) can be installed at different
elevations on the tank (1) to
permit monitoring of the clarification process and removal of clarified water
(3) when it has reached
a desired clarity. Clarified water (3) from the primary treatment tank (1) is
then decanted by means
of a pump (6), or any other fluid movement equipment, to a final storage tank
(8) for storage and
subsequent reuse. Residual water and floc (4) remaining in the primary
treatment tank (1) is left
there until it builds up to a level where it needs to be removed and disposed.
An acid solution,
preferably hydrochloric acid, can be added to the clarified water in the final
storage tank (8) to
adjust the pH to its final desired level. A means of mixing the clarified
brine fluid and the acid
material in the final storage treatment tank (8) is needed, and can be
provided by means of a re-
circulating pump (9) or a mechanical mixer located in the tank
In another embodiment of the invention, the primary treatment and final
storage tanks (1) & (8) can
be any size or shape capable of holding the water to be treated, or a
plurality of containers as
appropriate to permit higher flows or better management of the product;
In another embodiment of the invention, the primary treatment and final
storage tanks (1) & (8) can
be pressurized vessels not open to the atmosphere, wherein all products to be
added tc- or removed
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from the vessels can be accomplished through use of pressure injection
systems, pumps or other
commonly available fluid movement equipment;
In another embodiment of the invention, the means of mixing the brine fluids
in the tanks can be by
any common means of mixing fluids in an enclosed chamber including use of air
injection systems;
In another embodiment of the invention, the material to be used for raising
the pH of the brine water
can be any chemical base capable of raising the pH of the brine to a level at
which flocculation will
begin;
In another embodiment of the invention, the acid to be used for adjusting the
pH of the final treated
product can be any acid capable of reducing the pH to the desired level. In
this regard, it may be
preferred in some cases to use acids which do not introduce new chemical
species to the brine
water, such as formic acid when dealing with formate brines, as this material
is an existing
component of formate brines;
In another embodiment of the invention, a floc concentrating tank may be added
to the system to
provide a repository in which the waste floc and water from the treatment
process can be deposited
for further concentration prior to disposal. One preferred method of doing
this would be through the
use of a tall slender tank in which the depth of floc in the tank can be
increased by the shape of the
tank so the self-weight of the floc can be used to compress the floc towards
the bottom of the
container, expelling clean water to the top which can then be decanted as
additional treated fluid;
In another embodiment of the invention, concentration of waste floc material
may be accomplished
by means of conventional filters, screens or filter presses to reduce the
water content of the floc
prior to disposal;
In another embodiment of the invention, filter systems can be used to remove
the eiitrained floc
particles from the water after the flocculation process has taken place, for
the purpose of speeding
up the decanting process and minimizing storage requirements.
In another embodiment of the invention, the treatment system may be a closed
system in which
brine water enters one end of the process, base and acid products are injected
into the system where
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required, and a treated product exits the discharge end of the process without
operators having to
handle the product along the process.
In another embodiment of the invention, more than one treatment tank can be
placed in series
between the primary treatment tank (1) and the final storage tank (8) to
permit better control of the
decanting process, and reduce the likelihood of floc particles escaping into
to the final clarified
brine product. Under this arrangement, one or more additional treatment tanks
would. be installed
between primary treatment tank (1) and the final storage tank (8). Clarified
water decarited from the
primary treatment tank (1) under this arrangement could accommodate small
amounts of floc
particles in the decant product, as such solids could settle out in the next
stage of the treatment
process. This would permit decanting from the primary treatment tank (1) to be
less sensitive to
whether some floc was entering the decant water, and allow operators to more
quickly and easily
decant the primary treatment tank (1) down to a level closer to the top of the
main floc layer without
concern. Any floc decanted in this manner would settle to the bottom of the
new treatment tank,
following which clarified water from there would be decanted to the final
storage tank (8) as before.
Under this arrangement, residual water and floc settling to the bottom of the
new treatment tank
would be redirected back to the primary treatment tank (1) for further
treatment after each decanting
procedure.
ONE INTENDED USE OF THE INVENTION
One preferred use of the invention is to enable used alkali metal formate
brine fluids from the
drilling industry to be cleaned of suspended solids so they can be reused
rather than disposed into
the environment.
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