Note: Descriptions are shown in the official language in which they were submitted.
"COMPOSITIONS ~ ~ C~G SLUDGING
DURING WELL ACIDIZING"
Backqround Of The Invention
1. Field Of The Invention
The present invention relates to a method and composition
for reducing the production of sludge upon acid contact with
sludging crude oil, more particularly to an impxoved sludge
inhibiting acidizing composition and method of use.
2. De c ~ on Of The Prior Art
The treatment of a hydrocarbon-containing formation with
an aqueous acid solution is a commonly used technique for
stimulating the production of hydrocarbons from the
subterranean formation. Such a treatment generally includes
the pumping of an aqueous acid solution into the formation to
dissolve acid soluble materials and produce enlarged flow
channels. The enlarged channels result in an increase in the
quantity of hydrocarbons recovered as a result of flow through
the formation into the channels and then into the wellbore.
Certain crude oils contained in subterranean formations
produce sludge upon contact with aqueous acid solutions during
the performance of the treatments. The sludge that is formed
is an asphalt-like material which precipitates in the
formation and thereafter plugs or clogs the enlarged flow
channels. The potential for sludge to form has been found to
be significantly increased by the presence of ferric iron in
the aqueous acid solution which contacts the hydrocarbons in
the formation. There are examples of crude oils which do not
form a sludge upon contact with a simple acid, whereas the
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presence of ferric iron in the acid induces sludge formation.
Ferric iron can be naturally present in a subterranean
formation; however, the initial portion of acid introduced
into the formation often is likely to contain dissolved ferric
iron irrespective of any iron in the formation. This commonly
results from the dissolution of rust or corrosion products
from iron-containing containers or conduits for conveying the
acid into the formation.
Methods for preventing or reducing sludge formation upon
contact between sludging oils and an aqueous acid in the
presence or absence of dissolved ferric iron in the acid have
been developed and used heretofore. Such methods include
combining certain anti-sludging agents or other additives with
the aqueous acid solution, whereby the formation of sludge is
inhibited when the acid solution contacts the oil in the
formation. While such techniques have achieved varying
degrees of success, the anti-sludging agents and other
additives often separate and permit sludge to form in the
subterranean formation.
By the present invention, an improved acidizing method
and composition to reduce sludge formation are provided.
Summary Of The_Invention
The present invention relates to a well treating process
in which an aqueous acid solution that is capable of
dissolving a portion of a subterranean formation to increase
its permeability is brought into successive contact with an
iron-containing source and an asphaltenic crude oil. The
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process comprises including within at least the first injected
portion of the aqueous acid solution an effective amount of at
least one member selected from the group of thiourea,
dimethylthiourea, diethylthiourea, diisopropylthiourea,
imidazolidine-2-thione, hexahydropyrimidine-2~thione,
monomethylthiourea, monoethylthiourea and
monoisopropylthiourea together with an effective amount of a
compound capable of providing cuprous ions in solution,
whereby a substantial portion of any iron present in the
ferric state is reduced to the ferrous oxidation state.
DesoriptionQf ?he Preferred Embodiment
In accordance with the present invention, a method and
composition is provided to reduce the production of sludge
upon acid contact with sludging crude oil.
In general, the aqueous acid used in the present
invention can be substantially any acid which is capable of
dissolving solid materials located in a permeable subterranean
formation in a manner to increase the permeability of such
formation. Commonly used acids include hydrofluoric acid,
hydrochloric acid, organic acids such as formic or acetic
acids and mixtures of such acids. Aqueous solutions of the
acids generally are used at a concentration in the range of
from about 5% to about 28-32% by weight. An aqueous 15%
hydrochloric acid solution is particularly suita~le for u~e in
accordance with ths present invention.
Included within at least a portion of the initial aqueous
acid introduced into the subterranean formation is a sludge
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inhibiting effective amount of an additive comprising at least
one member selected from the group of thiourea,
dimethylthiourea, diethylthiourea, diisopropylthiourea,
imidazolidine-2-thione, hexahydropyrimidine-2-thione,
monomethylthiourea, monoethylthiourea and
monoisopropylthiourea together with an effective amount of a
compound capable of providing cuprous ions in the aqueous acid
solution whereby a substantial portion of any iron present in
the acidic solution or dissolved by the acidic solution is
reduced to the ferrous oxidation state. The first member of
the additive generally is present in the aqueous acid solution
in an amount of from about 0.5% to about 10% by weight.
Preferably, the first member is present in an amount of from
about 0.75% to about 5~ by weight. The copper containing
compound is present in the additive in an amount sufficient to
provide a soluble cuprous ion concentration in an amount of at
least about 0.005% by weight. Generally, the concentrations
can be in the range of from about 0.005% to about 0.1% by
weight or greater. Preferably, the cuprous ion concentration
is in a range of from about 0.005 to about 0.05% by weight of
the aqueous acidic solution. The cuprous ions can be provided
by compounds such as, for example, cuprous chloride, cuprous
oxide, cuprous sulfite, cuprous sulfate, cuprous carbonate and
the like. While the specific reaction mechanism is not known
it is believed that the ferric iron in solution is reduced to
ferrous iron by the following reaction sequence:
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Fe+3 + Cu (Tu)4 +~ ~ Fe+2 + Cu (Tu)4+2 (labile)
Cu (Tu)4+2 ~ Cu (TU)3+l + oxidation product
Cu (Tu)3+l + Tu ' Cu (Tu) 4+1
The reaction then would continue until the thiourea
compound is reduced in concentration to a level below the
reaction threshold or until all Fe+3 is consumed. D~pending
upon the particular hydrocarbon and the quantities of sludging
agents present, the composition and method of the present
invention can substantially reduce the amount of sludge
produced and in some instances substantially eliminate any
sludge formation during the acidizing treatment.
In accordance with the present invention, the aqueous
acidic solution also can contain one or more other additives
such as a corrosion inhibitor, a non-emulsifying surfactant,
an anti-sludging agent, a dispersing agent and substantially
any other conventionally known additive used in acidizing
treatments that does not adversely react with the other
1 additives present to detrimentally effect the present
;~1 invention. The corrosion inhibitor generally maybe present in
an amount of from about 0.1 to about 2.0 percent by weight of
the acidic solution. The non-emulsifying surfactant generally
may be present in an amount of from about 0.1 to about 2.0
percent by weight of the acidizing solution. The anti-
sludging agent generally may be present in an amount of from
about 0.5 to about 10 percent by weight of the acidic
solution. The dispersing agent generally may be present in an
amount of from about 0.1 to about 2.0 percent by weight of the
acidic solution. Examples of such additives are set forth in
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U.S. Patents 4,096,914 and 4,823,874, the entire disclosure of
which is incorporated herein by references.
In general, the acidic solution of the present invention
is injected down a wellbore to contact a subterranean
formation. The solution may be injected into the formation
either at a rate and pressure sufficient to fracture the
formation or at a rate and pressure below that at which
fracturing can occur. Such low-pressure or ~ow-rate injection
generally is referred to as matrix acidizing. The acidic
solution generally is permitted to contact the subterranean
formation for a sufficient time to substantially spend by
dissolution of acid soluble constituents; however, no specific
contact time is required. Upon conclusion of the acidizing
treatment, the at-least-partially spent solution generally is
withdrawn from the formation by pumping on the wellbore.
To further illustrate the utility of the present
invention, but not by way of limitation, the following
examples are provided.
EXAMP~E I
An acid composition is prepared by admixing 900 parts by
volume 10% HCl with 100 parts glacial acetic acid. To this
composition was added the following conventional acidizing
additives : 1~ by weight 19 N surfactant, 3~ by weight AS-7
additive, 0.3% by weight Sperse-All additive, 0.8~ HAI-85
corrosion inhibitor, which are proprietary chemicals available
from Halliburton Services, Duncan, Oklahoma. Samples of the
acid solution then were admixed with an equal volume of crude
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oil in a series of tests to which different quantities of
ferric iron had been added with different additives of the
present invention. More specifically, 50 mls of the acid
solution containing the ferric iron, added by dissolution of
FeCl3^6H20 in the acid, was heated to 180F. and admixed with
a guantity of Beaver Hill Lake crude that had been strained
through a lO0 mesh screen to remove solids and heated to the
same temperature. The sample was shaken for l minute upon
mixing and placed in a controlled temperature both at 180F.to
stand for one hour. The sample then was strained through a
100 mesh screen upon mixing and placed in a controlled
temperature bath at 180F. to stand for one hour. The sample
then was strained through a 100 mesh screen, any residue on
the screen was washed with 140F. water and dried prior to
weighing of the residue (sludge). The results of the tests
are set forth below:
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Table I
1 2 0.013 none 4.06
2 2 0.0136% thiourea 0.05
3 _ 2 0.0135% thiourea 0.19
; _4 2 0.0134% thiourea 0.31
5 _ 2 _ 0.0133% thiourea 0.61
6 2 0.01~6% hexahydropyrimidine- 0.07
_ . 2-thione
: 7 2 0.0135% hexahydropyrimidine- 0.22
:, _ 2-thione
. ¦8 2 0.0134% hexahydropyrimidine- 1.11
: _ _ 2-thione _
9 2 0.0136% imidazolidine-2-thione 0.28
: 10 0.5 _ 0.013 1.5 thiourea 0.02
11 0.50.0131.25 thiourea 0.03
12 0.5 _ 0.013 1.0 thiourea 0.05
_ 13 0.50.0130.75% thiourea 0.06
¦14 0.50.0131.5% hexahydropyrimidine- o 0
_ 2-thione
: 15 0.50.0131.25% hexahydropyrimidine- 0.42
_- _ 2-thione
16 0.50.0131.5% imidazolidine- 0 04
_ 2-thione
17 0.50.0131.25% imidazolidine- 0.04
2-thione
18 0.50.0131.0% imidazolidine- 0 08
- _ ~_ _ 2-th one
To confirm the Fe+3 iron was the cause of the sludge
several tests were repeated using Fe+2 in place of Fe+3. No
sludge was formed in sny test
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EXANPLE II
The preceding test was repeated using a different crude
known as the Judy Lake crude. The results are set forth
~ I 2 1.00.013 0 0.76
,~ 3 1.0 0 4% 50/50 blend thiourea- 0.39
hexahydropyrimidine-2-thione _ _ ,
~;~ 4 l.o0.134% 50/50 blend thiourea- 0.01
I hexahydropyrimidine-2-thione
2.0 0 0 0.99
6 2.00.013 _1.01 ,
7 2.0 04% 50/50 blend thiourea- 0.62
_ _hexahydropyrimidine-2-thione
8 2.00.0134% 50/50 blend thiourea- 0.06
_ ______ _ _ hexahydropyrimidine-2-thione
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The results of the foregoing Examples clearly illustrate
the effectiveness of the present invention in substantially
reducing the guantity of sludqe formed upon contacting of an
acidizing solution with a crude formation where iron in a
ferric oxidation state is present. These results further show
that if either part of this invention is left out, the desired
result is not achieved.
While that which applicants presently consider to be the
preferred embodiments of the present invention has been
described herein, it is to be understood that changes and
modifications can be made to the method and composition by
those skilled in the art without departing from the spirit or
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scope of the invention as def ined by the appended claims .
