Note: Descriptions are shown in the official language in which they were submitted.
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ECONOMICAL METHOD FOR SCAVENGING HYDROGEN SULFIDE IN FLUIDS
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to methods and compositions for removal or inactivation
of
hydrogen sulfide or soluble sulfide ions from various fluids used in various
hydrocarbon
recovery or mineral mining operations in subterranean formations. The
invention is also
applicable to removal of hydrogen sulfide or soluble sulfide ions from other
fluids such as fluids
produced in such operations from a subterranean formation, and to other fluids
that contain
hydrogen sulfide such as fluids in sewage systems. The advantages of the
invention are
particularly appreciated with high pH fluids.
2. Description of Relevant Art
Hydrogen sulfide in fluids is well known to be corrosive to pipes and other
containers of
the fluids and to many other surfaces in contact with the fluids. Hydrogen
sulfide is also a
known environmental pollutant and a health risk to persons exposed to it. Low
concentrations of
hydrogen sulfide irritate conjunctiva and mucous membranes and cause
headaches, dizziness,
nausea and lassitude. Exposure to high concentrations can result in death.
In drilling some subterranean formations, and often particularly those bearing
oil or gas,
hydrogen sulfide accumulations are frequently encountered. The drilling fluid
or mud brings the
hydrogen sulfide to the surface. Such sulfide in the drilling fluid is
problematic for the reasons
noted above. Generally, to protect the health of those working with the
drilling fluid and those at
the surface of the well, conditions are maintained to ensure that the
concentration of hydrogen
sulfide above the fluid, emitted due to the partial pressure of the gas, is
less than about 15 ppm.
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The partial pressure of hydrogen sulfide at ambient temperature is a function
of the concentration
of sulfide ions in the fluid and the pH of the fluid. To ensure that the limit
of 15 ppm is not
exceeded even for the maximum sulfide concentration that may be encountered in
a subterranean
formation, the pH of the drilling fluid is typically maintained at a minimum
of about 11.5. Also,
to prevent the soluble sulfide concentration in the fluid from becoming
excessive, action is
routinely taken to remove sulfide from the fluid.
Various methods, techniques and compositions have been used for removing
hydrogen
sulfide from such fluids. U.S. Patent No. 4,008,775, issued February 22, 1977,
to Fox, teaches a
method of scavenging hydrogen sulfide from drilling mud using porous iron
oxide particles
having a composition of substantially Fe304 and having a surface area at least
ten times that of
magnetite particles of equal size, the greater part of which are no longer
than 60 microns.
U.S. Patent No. 4,756,836, issued July 12, 1988, to Jeffrey et al. teaches
decreasing
hydrogen sulfide entrained in a drilling mud by adding iron chelate to the mud
at the wellhead
and circulating the mud in the well being drilling with the mud, allowing the
hydrogen sulfide in
the mud to be exposed to the iron chelate for conversion of the hydrogen
sulfide into elemental
sulfur.
The chelating agents taught are ethylenediaminetetraacetic acid (EDTA),
hydroxethylethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA),
and
diethylenetriaminepentaacetic acid (DTPA). Claimed advantages of this
invention are said to be
that the iron chelate is regenerated by oxygen at the surface and that the
iron scavenges oxygen
in the mud stream to cut down oxygen assisted corrosion of the drill stem.
This patent to Jeffrey et al. further teaches that whether the iron is
supplied in the Fe (II)
or Fe (III) form, exposure to oxygen at some point in the mud flow changes the
form to Fe (III)
to prepare the chelate for hydrogen sulfide conversion. Oxygen exposure in an
aerated mud pit or
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in the shale shaker or by another oxygen source is said to aid regeneration of
the iron chelate.
While iron (III) is known to readily chelate with EDTA, NTA and HEDTA and
DTPA, such
complexes have limited stability at high pH. Iron in these complexes is well
known to tend to
precipitate out as ferric hydroxide at a pH greater than 9. For example,
manufacturers of these
chelates typically quote stability or effectiveness as an Fe (III) chelate, of
NTA at pH 1-3, DPTA
at pH 1-7, EDTA at pH 1-6, and HEDTA at pH 1-9. At pH higher than such ranges,
these
chelating agents lack ability to stabilize the iron against precipitation as
the hydroxide. For
effective use as a scavenger according to the teachings of Jeffrey invention
of U.S. Pat. No.
4,756,836, the iron must stay in chelated form. Further, the multivalent
nature of iron III is likely
to cause crosslinking of polymers in a polymer based drilling mud, leading to
gelation and
interference with the rheology of the fluid.
U.S. Patent No. 6,365,053 BI, issued April 2, 2002 to Sunde, et al. teaches a
method of
removing hydrogen sulfide from drilling mud using a relatively sparingly
soluble divalent
environmentally acceptable iron salt in the drilling mud. The preferred such
divalent iron salt
taught is iron oxalate. The hydrogen sulfide in the mud is said to react with
the iron salt to form
iron sulfide.
U.S. Patent No. 6,746,611 B2, issued June 8, 2004 to Davidson, teaches an
environmentally friendly method of removing hydrogen sulfide or hydrogen
sulfide ions from
fluids having a pH in excess of about 9 and as high as a pH of 12 or higher
using iron chelating
agents having stability at such high pH. The preferred chelating agents taught
are ferrous
gluconates which are added to the fluid in sufficient quantities to form iron
sulfide with the
sulfide ion. The iron chelating agent is mixed with the fluid and an iron
sulfide is formed.
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Using ferrous gluconate to remove hydrogen sulfide from drilling fluids as
taught by
Davidson has become well known and accepted, as ferrous gluconate is an
effective sulfide
scavenger that does not impair the properties of the drilling fluid to which
it is added. Ferrous
gluconate is also fully biodegradable and, as a common dietary supplement, is
not considered
environmentally incompatible.
Ferrous gluconate is relatively expensive, however, and thus there is a
continuing need
for environmentally compatible alternatives.
SUMMARY OF THE INVENTION
The present invention provides an economical alternative to adding ferrous
gluconate to
fluid containing hydrogen sulfide for removal of the hydrogen sulfide, that
has the advantages of
that method but at a lower cost. The method of the invention comprises adding
a gluconate
additive to the fluid, and if the fluid does not already contain iron ions or
a source of iron, also
adding a source of iron to the fluid, both to be in sufficient quantity that
they react together, that
is, the gluconate reacts with the iron to form iron gluconate in the fluid. In
turn, the iron
gluconate will react with the hydrogen sulfide in the fluid, forming iron
sulfide, water and
gluconic acid, providing the advantages as if iron gluconate had been directly
added to the fluid,
but without the cost of iron gluconate. Also, the gluconic acid formed in the
fluid will further
react with the iron in the fluid to form more iron gluconate, which is then
available for reaction
with hydrogen sulfide for creating more iron sulfide and removing more
hydrogen sulfide from
the fluid In this manner the gluconate acts in a catalytic manner,
participating in the reaction but
reformed at the end of reaction to allow more ferrous gluconate to be formed.
The overall effect
is that an inexpensive source of iron such as the oxide is made into ferrous
gluconate in situ and
the benefits are obtained without the cost.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The present invention provides a cost effective method for rapid and complete
removal of
hydrogen sulfide from fluids such as, for example: wellbore construction and
treating fluids;
sour waters and other fluids produced from oil and gas wells, including
hydrocarbons such as
crude, bitumen and asphalt, as well as brines and other oilfield effluents;
surface treatment fluids
associated with wellbore construction and treatments; non-oilfield effluents
from mining
operations and non-oilfield industrial drilling or boring and other
construction operations; and
tank fluids from tanks, vessels, and other containers of produced waters, oil,
gas, tars, and other
petroleum hydrocarbons and treatments from such containers. The method is
particularly
suitable for scavenging hydrogen sulfide in high pH fluids such as drilling
fluids used in drilling
wells in hydrocarbon-bearing subterranean formations, but is not limited to
such an application.
The method of the invention employs a gluconate additive comprising an organic
compound from a group capable of acting as a chelating agent with iron. The
iron chelate
compounds or complexes are stable at high pH and preferably do not form gels
in polymer based
fluids, making the complexes or compounds excellent sulfide scavengers for use
in drilling
fluids, for example. Particularly, gluconic acid has been found to form stable
complexes with
iron (II) at pH above 9 and even at pH ranging from about 11 to 12 or higher,
the pH most
commonly desired for drilling fluids that are in contact with soluble sulfide
or hydrogen sulfide.
In the method of this invention, the gluconate additive (other than ferrous
gluconate) is
added to a fluid, such as a drilling fluid or mud, containing hydrogen
sulfide. When the fluid is a
drilling fluid, this gluconate additive may typically be added to the fluid in
the mud pit, before
the fluid has circulated in a subterranean well, or before the fluid contains
any detectable amount
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of sulfur or hydrogen sulfide, as a prophylactic measure against any hydrogen
sulfide the fluid
may encounter downhole. However, alternatively or additionally, the additive
may be added
after the fluid has been circulating downhole and has already encountered
sulfur or hydrogen
sulfide and contains same. The additive may also be added to fluids in tanks
that contain
hydrogen sulfide to be removed.
For the method of the invention, the fluid must also contain iron or a source
of iron or
iron ions. Such iron may already be in the fluid or may be added to the fluid
at the same time or
before or after the gluconate additive of the invention. According to the
method of the invention,
the gluconate additive and the iron or iron ions will react so that iron
gluconate is formed in situ.
In turn, this iron gluconate will react with the hydrogen sulfide in the
fluid, forming iron sulfide,
water, and gluconic acid. The gluconic acid will react with the iron to form
more iron gluconate,
which will also be available to react with any remaining hydrogen sulfide to
form iron sulfide.
The quantity of iron desired in the fluid should be sufficient to react with
or chelate with
the gluconate additive to form iron gluconate in the fluid in a quantity
sufficient to react with the
hydrogen sulfide in the fluid in the amount to remove the desired amount of
hydrogen sulfide
from the fluid. That is, the quantity of gluconate additive to be added will
generally depend on
the quantity of hydrogen sulfide desired to be removed or scavenged.
Generally, one mole of
ferrous gluconate will remove one mole of hydrogen sulfide. Stronger chelation
of the iron may
result when an excess of the gluconate is present in the fluid for the amount
of hydrogen sulfide
in the fluid.
The gluconate additive may be added in solid or liquid form. If in liquid
form, the
preferred carrier fluid is aqueous. Any other components of the additive
should not be of the
type that can interfere with the chelating action of the gluconate with the
iron or with the stability
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of the complex. Further, any such other components should preferably not be of
a type to cause
crosslinking of any polymers that may be in the fluid, particularly if the
fluid is polymer based.
Iron (II) or ferrous gluconate is commonly used as an iron supplement for
dietary purposes and
thus is considered non-toxic. Further, the gluconic moiety is derived from
glucose and thus iron
(II) gluconate is also fully biodegradable. Heptagluconate may be substituted
for gluconate in the
compounds or complexes of this invention and the term "gluconate" as used
herein shall be
understood to encompass "heptagluconate" as well.
The gluconate additive of the invention is preferably comprised of gluconic
acid, sodium
gluconate, or other gluconate salts other than ferrous gluconate which is made
in the invention,
or combinations thereof. Such gluconate salts are environmentally friendly or
environmentally
acceptable, as is iron (II) gluconate made in the invention and effective as a
sulfide scavenger.
Gluconate salts also do not impair the properties of the drilling fluid to
which it is added.
The iron source for use in the invention is preferably comprised of ferric
oxide, ferrous
oxide, ferric hydroxide, ferrous hydroxide, or combinations thereof. Such iron
may be in solid or
liquid form and if in liquid form, the preferred carrier fluid is aqueous.
The foregoing description of the invention is intended to be a description of
preferred
embodiments. Various changes in the details of the described composition and
method can be
made without departing from the intended scope of this invention as defined by
the appended
claims.
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