Solubilized and regenerating iron reducing additive

A solubilized iron reducing additive for acid solutions and method for preparing such a solubilized iron reducing additive. The additive includes an iron reducing agent reactable with ferric ions to produce therefrom ferrous ions and a spent iron reducing compound. The spent iron reducing compound is incapable of reacting with ferric ions to produce ferrous ions. So that the reducing process may continue, a regenerating agent is mixed with the iron reducing agent, the regenerating agent being reactable with the spent iron reducing compound for regenerating the spent iron reducing compound back to the iron reducing agent state. Because it has been found that the iron reducing agent and regenerating agent readily fall out of suspension as precipitates after short periods of time after mixing, a solubility facilitator is admixed thereto for facilitating establishment of the solubilized additive for acid solutions. A catalyst for catalyzing the reduction of ferric ions to ferrous ions in acid solutions may be optionally included.

TECHNICAL FIELD 
This invention relates generally to the reduction of ferric ions in aqueous 
acidic solutions. More specifically, this invention relates to a 
solubilized regenerating ferric ion reducing additive, and that additive's 
method of preparation. Through the use and employ of the additive, the 
invention also relates to the prevention of the formation of ferric 
iron-containing compounds in aqueous acidic compositions. This invention 
further relates to the treatment of a subterranean formation to stimulate 
the production of a fluid, such as a hydrocarbon, therefrom, wherein the 
treatment is conducted in the presence of iron-containing materials. This 
invention still further relates to the prevention of the formation of 
sludge in certain crude oils caused by the presence of ferric ions formed 
during the acid treatment of hydrocarbon-containing subterranean 
formations. 
BACKGROUND ART 
It is well established in the prior art that dissolved iron in the ferric 
oxidation state in aqueous acid solutions can lead to the formation of 
ferric iron-containing compounds in the bearing solution which produce 
insoluble iron solids when the pH of the acid solution increases to a 
value greater than approximately 4. In this regard, U.S. Pat. No. 
4,683,954 to Walker and U.S. Pat. No. 5,084,192 to Dill teach that ferric 
compounds such as ferric hydroxide begin to precipitate from hydrochloric 
acid solution when the pH of the acid increases to a value of about 2.5 
and greater and that precipitation is complete when the solution's pH is 
about 3.5. This precipitation phenomenon becomes a serious problem when an 
acid, such as hydrochloric acid, containing dissolved ferric iron is being 
used to react with a subsurface, acid soluble, calcareous formation, such 
as limestone, wherein the acid reaction causes the pH of the acid solution 
to typically spend to a value greater than the 4 and 5 range. 
In addition to the precipitation problem discussed above which can be 
caused by the presence of ferric ion in acid, it is taught by several 
authorities that hydrochloric acid, particularly when at high 
concentrations of about 15% and greater, can cause the development of 
sludge when the acid is placed in contact with certain types of crude oil. 
The sludge formation problem is exacerbated when the acid which is in 
contact with the crude oil also contains ferric ion. 
For purposes of this invention, sludge is defined as a solid material 
formed in crude oil containing asphaltenes and maltenes which constituents 
may, under certain conditions as pointed out above, precipitate from the 
crude oil. Sludge formed in crude oil while the crude oil is in a 
formation can render very difficult the task of recovery of the oil from 
the formation. Crude oil containing quantities of asphaltenes and maltenes 
subject to the production of sludge is referred to herein as sludging 
crude. 
Accordingly, the sludging problem specifically addressed herein is caused 
by the combination of acid, especially high concentration hydrochloric 
acid, and ferric ion in contact with a sludging crude. This problem is 
particularly severe when the sludge is produced during formation 
acidizing. 
Formation acidizing or simply, acidizing, is a well known method used to 
increase the flow of fluid from a subterranean formation. According to 
conventional practices, the underground formation is contacted with an 
acidic composition to react with and dissolve material contained therein 
for the purpose of increasing the permeability of the formation. The flow 
of fluid from the formation is therefore increased because of the increase 
in formation permeability caused by the dissolution of the material. A 
known method of acidizing comprises the steps of conducting an acid 
composition to the formation through tubing disposed in a borehole that 
penetrates the formation; forcing the acid composition into contact with 
the formation and permitting the acid to react with and dissolve certain 
materials contained therein to enlarge passages through the formation and 
thus increase the permeability of the medium so treated. 
It is apparent that the object of formation acidizing, which is to increase 
formation permeability, can be frustrated if the very acid composition 
employed in the treatment to achieve that object produces an environment 
which fosters the development of solid material which can instead fill and 
plug pore spaces intended to be enlarged in the treated formation. Instead 
of enhancing fluid production, the consequent result is a failure to 
increase production, and even possibly decrease formation permeability. 
In the context of formation acidizing, ferric ion can be introduced into 
the acid as a result of reaction between ferric compounds, such as rust 
and millscale, contacted in such locations as the tanks used to store the 
acid and/or transport it to a well that requires acidizing. Most common, 
such ferric compounds may be encountered on the interior walls of the 
conduit which conducts the acid down to the formation, reaction of the 
acid with ferrous compounds in the formation followed by oxidation of 
ferrous ion to ferric ion, and reaction between the acid and formation 
minerals that include ferric compounds, such as goethite, FeO(OH), 
magnetite, Fe.sub.3 O.sub.4, and hematite, Fe.sub.2 O.sub.3. 
Solutions to the problems of precipitation of ferric iron compounds from 
spent acid and the formation of sludge induced by the contact between 
ferric ion and acid with sludging crude revolve about the control of 
ferric ion in the acid solutions and/or the elimination of those ions from 
the solution. One suggested mitigating procedure is the removal of ferric 
compounds from the metal conduits through which the acid solutions are 
conducted down-hole, such as by a process known as pickling, prior to the 
conduit's utilization in acidizing procedures. 
Alternatively, the Dill patent ('192) discloses the use of a blend of 
formic acid and acetic acid, in combination with anti-sludge agents and 
iron control agents. U.S. Pat. No. 4,823,874 discloses the use of 
anti-sludging agents such as quaternary ammonium salts of fatty amines in 
hydrochloric acid. U.S. Pat. No. 4,574,050 to Crowe discloses the use of 
an iron control agent, such as ascorbic acid and erythorbic acid, in 
hydrochloric acid. U.S. Pat. No. 5,063,997 to Pachla appears to disclose 
the reduction of ferric ion to ferrous ion in hydrochloric acid with 
hypophosphorous acid and catalyst material selected from cupric and 
cuprous compounds. 
In U.S. Pat. No. 5,445,221 to Vinson, the reduction of ferric ion to 
ferrous ion in hydrochloric acid is disclosed with certain 
sulfur-containing, non-ionic, organic compounds in combination with a 
separate catalyst material selected from copper and vanadium compounds. 
The disclosure of the '221 patent is detailed and accurate with respect to 
the background of that invention and the needs for ferric ion reduction 
for applications in oil field settings. For these same purposes of 
background information regarding the needs and applications for ferric ion 
and iron reducing capabilities, U.S. Pat. No. 5,445,221 is expressly 
incorporated herein by reference. 
For purposes of contrast with the present invention, it should be 
appreciated that the reduction of ferric iron in the acidizing process of 
the '221 patent is accomplished through a mercaptan function wherein the 
sulfur containing, non-ionic organic compound reacts with the ferric ions 
to convert them to the more innocuous ferrous ions. Within the '221 patent 
it is specifically recognized that the mercaptan function alone (i.e. 
through the use of 2-mercaptoethanol exclusively) is only capable of 
reducing ferric ion to ferrous ion when in solution with organic acids and 
not in inorganic acids such as hydrochloric acid. Still further, it was 
appreciated in the '221 patent that utilization of the mercaptan function 
was only possible in lower concentrations of organic acids, those lower 
concentrations being at least less that 28%. The success of using the 
mercaptan function in acetic acid which is organic is demonstrated in 
EXAMPLE 8 of the '221 patent. EXAMPLE 13 of the '221 patent clearly 
indicates that the mercaptan function is ineffective for reducing ferric 
ions even in very low concentrations of inorganic acids. In that example, 
an acid mixture of 2% inorganic hydrochloric acid was prepared with a 10% 
organic acetic acid. With ferric ions present in the form of ferric 
chloride, the addition of 2-mercaptoethanol caused no color change and 
therefore no reduction of the ferric ions to the innocuous ferrous ions. 
Subsequently, cupric chloride was then added to that solution and a color 
change resulted indicative of the reduction of the ferric iron to ferrous 
iron. From this result, it was believed that the added cupric chloride 
acted as a catalyst to the sulfur containing 2-mercaptoethanol which in 
turn reduced the ferric iron to ferrous iron. 
As will be discussed in greater detail hereinbelow, however, the present 
invention demonstrates that the copper containing cupric chloride was not 
merely the catalyst, but was instead the actual reducing agent. This 
finding is consistently supported in the examples of the '221 patent where 
either a copper containing compound or a vanadium containing compound was 
always added in combination with a mercaptan functioning compound; the 
only exception being EXAMPLE 8 which was conducted exclusively with an 
organic acetic acid, and not the more common and frequently used inorganic 
acids of which hydrochloric is an example. 
In view of the obvious need developed above for ferric iron reducing 
compounds, the affected industries such as the petroleum industry and 
those providing support thereto have endeavored to develop a reducing 
agent formulation that can be readily prepared, transported, stored and 
ultimately utilized for its ferric iron reducing capabilities. During the 
development of the present invention, it has been appreciated that a 
substantial impediment to providing such a product for use at remote 
locations, such as at a well site, is the inability to prepare and 
maintain a homogenous mixture of the several components preferred in a 
ferric iron reducing additive. More specifically, it was observed that 
when the reducing agent and what had previously been believed to be a 
catalyst were mixed, constituent components precipitated from the solution 
and were difficult to redissolve. As a result, the standard practice prior 
to this invention's development has been to supply the several ingredient 
compounds unmixed to the end-user for combination at the point of 
application or use. Because the proportions of the several components can 
be critical, this was undesirable in that the ability to accurately 
measure and mix the components is difficult at best, and often not 
possible, especially on location. As a result, a primary objective of the 
present invention became the capability to prepare a ready-to-use ferric 
ion reducing additive that can be produced by the manufacturer and then 
shipped and stored for extended periods of time without separation of the 
constituent components. 
In view of these objectives and in response to the industrial requirements 
for ferric iron reducing agents, the present invention was developed and 
through its development several discoveries were made with respect to the 
function of the different constituent components ultimately incorporated 
therein and the benefits that can be potentiated and derived therefrom. 
DISCLOSURE OF THE INVENTION 
The present invention answers those needs enumerated above regarding at 
least the petroleum industry's requirements for ferric ion reducing 
agents. Through the course of researching and developing this invention, 
however, the activity and contributions of the several constituent 
compounds has been better appreciated and can therefore be better 
controlled and potentiated for end use. 
Unlike earlier known products used for ferric iron reducing purposes such 
as that disclosed in the '221 patent, it has been discovered that it is 
the copper containing compounds and those of similar activity that are in 
fact the iron reducing agents, and not the sulfurs of the mercaptan 
components. The importance of the copper to the reducing compound has been 
expressly appreciated in Canadian Patent Application No. 2,070,212 
regarding Compositions for Iron Control in Acid Treatments for Oil Wells. 
Like the reducing agents of the '221 patent, however, this Canadian 
Application promotes the copper compound as being a catalyst and not the 
actual iron reducing agent. In the present invention, it had been 
discovered that when a cuprous compound (Cu.sup.+1) is added to a solution 
containing ferric ion (Fe.sup.+3), electrons are exchanged so that the 
cuprous compound becomes cupric (Cu.sup.+2) and the ferric ion becomes 
ferrous (Fe.sup.+2). Through this reaction and changed state, the iron 
reduction process from ferric to ferrous iron is achieved. Among others, 
this reduction assists in avoiding the formation of sludge in well 
acidizing processes. 
As a complement to this discovery regarding the copper compound's action as 
a reduction agent, it has also been learned that in the presence of a 
sulfur containing compound such as those found in the mercaptan 
functioning compounds, the sulfur component reacts with the now cupric 
(Cu.sup.+2) compound to convert it back to its cuprous (Cu.sup.+1) state 
ready for a subsequent iron reducing reaction. In this way, the mercaptan 
or sulfur containing component acts not as the iron reducing agent itself, 
but instead as a regeneration agent to the copper compound that is in fact 
the iron reducing agent. In fact, the sulfur containing compound will not 
reduce ferric ion (Fe.sup.+3) in an organic acid such as hydrochloric 
acid. 
As explained above, supplying the copper compound and sulfur containing 
compound to the end user for self mixing is disadvantageous for several 
reasons, but with the most important reason being that accurate 
measurements are required for economical and proper functioning of the 
resulting iron reducing additive. 
An impediment, however, was discovered as described hereinabove with 
respect to the resistance of the copper and sulfur bearing compound to 
solubly mix together and remain in a stable combination or solution. In 
those experiments where the two components were mixed together directly or 
in water solution, precipitate solids formed thereby yielding cuprous 
salts that were difficult, if not impossible to redissolve into the 
solution. 
Through the process of experimentation, thiourea was attempted as a 
solubilizer, but it was discovered that the cuprous state element fell out 
of solution after a temperature of about 100 degrees Fahrenheit was 
reached. This was unacceptable in that such a temperature was typically 
and often reached during transportation and storage of the solution after 
its manufacture, but prior to its use. 
As a result of further experimentation, ammonia was discovered as a highly 
advantageous solubility facilitator that enabled the iron reducing agent 
and the regenerating agent to be combined into a solubilized iron reducing 
additive. When mixed together, a solution in which the iron reducing agent 
and the regenerating agent are carried is formed. The stability of such a 
solution has been tested up to temperatures well above 100 degrees 
Fahrenheit; temperatures which are typically encountered during transport 
and storage of additives used in oil field operations in such facilities 
as closed buildings exposed to direct sunlight and without cooling 
capabilities. Under these conditions, the additive solution of the present 
invention that includes the iron reducing agent, the regenerating agent 
and the solubility facilitator in the form of ammonia have remained 
soluble for periods in excess of six months. As a result, this combination 
is not only beneficial to the manufacturer because of its substantial 
shelf life, but it is likewise popular with the end user in that it may be 
stored for extended periods of time before use. Of equal importance is 
that the additive's constituent components have been accurately 
premeasured and solubilized into a single solution for easy utilization at 
a remote site such as in the oil field. 
As explained above, the cuprous compound is the one that actually combines 
with the ferric ion to reduce it to the innocuous ferrous ion. After such 
a reaction wherein the cuprous compound has been converted to a cupric 
compound, the sulfur component reacts therewith to convert that cupric 
compound back to a cuprous compound that is once again ready to react with 
ferric ions. As a result, the copper containing iron reducing agent is 
regenerated by the sulfur containing compound in a sulfur consuming 
process. Therefore, the capability of the prepared reducing additive to 
reduce ferric ion to ferrous ion is dependent to some extent on the amount 
of copper compound, but to a greater extent upon the amount of sulfur 
containing compound which is consumed and not regenerated in the reducing 
process. 
It has been discovered that the reducing reaction slows so substantially in 
higher concentrations of acid that it becomes ineffective. As a result, a 
catalyst is required that enables the iron reducing agent to continue its 
ferric ion reduction at suitable rates. As appreciated in the Canadian 
Patent Application '212, a successful catalyst is found in iodide bearing 
compounds. What was not appreciated in the '212 application is that the 
iodide is converted to iodine during the catalytic process. In the course 
of the present invention's development, it has been discovered that the 
iodine is similarly regenerated back to the iodide state by the sulfur 
containing compound much like the iron reducing agent. As a result, the 
mere presence of the iodide is initially important, but as long as the 
sulfur containing compound is also present it can be continuously 
regenerated provided sulfur containing compound is present. Still further, 
it has been discovered that iodide will itself act as a reducer, but 
because iodide is substantially more expensive than copper containing 
compounds, it is most advantageously used as a catalyst or potentiator 
instead of as the actual reducing agent. 
Though not critical, it has been found advantageous to first mix the sulfur 
containing compound together with the ammonia and then add the copper 
containing compound thereto. The benefit achieved by using such an order 
is that the copper is prevented from forming a precipitate that must then 
be redissolved, often with substantial difficulty. By utilizing this 
preferred order of add mixing, a solubilized iron reducing additive is 
immediately achieved and maintained until end use. It has also been found 
possible to first mix the ammonia and copper containing compound together 
and then add the sulfur containing compound. What is important, however, 
is that the ammonia be first mixed with either of the copper or sulfur 
containing compounds or the two together at the same time, but the latter 
two should not be initially mixed together without the ammonia. 
Other benefits are known to be derived from use of such a solution 
manufactured according to the present invention in environments other than 
acidizing subterranean formations. As an example, it has been found that 
an acid solution that is loaded with a copper bearing compound 
deteriorates metal tubing within which it is conducted at a substantially 
reduced rate when an "acid inhibitor" such as acetylenic alcohols and 
certain quaternary ammonium salts is also utilized. As a result, the 
additive of the present invention acts to potentiate or intensify the 
action of the inhibitor. It is expected that as the present invention is 
utilized more extensively, substantial and additional beneficial uses will 
be discovered that are based on the principles, features and 
characteristics disclosed herein. 
Referring now to specific embodiments of the solubilized iron reducing 
additive and methods for preparing the same, additional benefits and 
advantageous features will be appreciated. In one embodiment, the present 
invention takes the form of a solubilized iron reducing additive for acid 
solutions. The additive includes an iron reducing agent reactable with 
ferric ions to produce therefrom ferrous ions and a spent iron reducing 
compound. The spent iron reducing compound is incapable of reacting with 
ferric ions to produce ferrous ions. So that the reducing process may 
continue, a regenerating agent is mixed with the iron reducing agent, the 
regenerating agent being reactable with the spent iron reducing compound 
for regenerating that spent iron reducing compound back to the iron 
reducing agent state. Because it has been found that the iron reducing 
agent and regenerating agent readily fall out of solution as precipitates 
after short periods of time after mixing, a solubility facilitator is 
admixed thereto for facilitating establishment of the solubilized additive 
for acid solutions. 
In a preferred embodiment, the iron reducing agent is a cuprous compound 
reactable with ferric ions to produce cupric compound and ferrous ions. 
The regenerating agent is a sulfurous compound reactable with the cupric 
compound for regenerating the cupric compound back to a cuprous compound. 
The solubility facilitator is ammonia. 
Optionally, a catalyst for catalyzing the reduction of ferric ions to 
ferrous ions in acid solutions may be included. In a preferred embodiment, 
the catalyst is an iodide compound capable of being regenerated by the 
regenerating agent back from a reacted iodine state. 
As a result of this combination of components, the solubilized iron 
reducing additive is maintainable in a solubilized state for at least six 
months and constituent components are prevented from precipitating 
therefrom. Still further, the solubilized state is maintainable in 
temperatures at least as great as 130 degrees Fahrenheit. 
To achieve the most readily solubilized iron reducing additive for acid 
solutions as described herein, the order of admixing the components of the 
additive preferably begins with the regenerating agent to which the 
solubility facilitator is added and subsequently the iron reducing agent 
is combined therein. 
Among those benefits and improvements that have been disclosed, other 
objects and advantages of this invention will become apparent from the 
following description taken in conjunction with the accompanying drawings. 
The drawings constitute a part of this specification and include exemplary 
embodiments of the present invention and illustrate various objects and 
features thereof.

In each figure, sources of consumable compounds are shown in boxes bounded 
by heavy or thick lines, while boxes bounded by dashed-lines indicate 
optional additives and resulting products. 
MODE(S) FOR CARRYING OUT THE INVENTION 
As required, detailed embodiments of the present invention are disclosed 
herein. It is to be understood, however, that the disclosed embodiments 
are merely exemplary of the invention that may be embodied in various and 
alternative forms. Therefore, specifically specified compounds and 
functional details disclosed herein are not to be interpreted as limiting, 
but merely as a basis for the claims and as a representative basis for 
teaching one skilled in the art to variously employ the present invention. 
The additive compounds of the present invention consist of three basic 
components, i.e., a copper containing reducing agent, a sulfur containing 
regenerating agent, and a solubility facilitator for solubilizing the 
former two compounds stably together. It is preferred that the 
solubilizing agent be selected from the group consisting of ammonia and 
simple amines, including, but not necessarily limited to, methylamine, 
dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, 
ethanolamine, and alkyl-substituted ethanolamines, diethanolamine, and 
alkyl-substituted diethanolamines, triethanolamine, morpholine, 
isopropanolamine, and diisopropanolamine. Most preferred of these, 
however, is ammonia. 
The copper containing reducing agent is most advantageously obtained from a 
cuprous state compound (Cu.sup.+1) since that is the state from which the 
copper compound combines to reduce the ferric iron to the more innocuous 
ferrous iron. An example of such a source is cuprous chloride. 
Substantially the same benefits, however, may be enjoyed from a cupric 
state compound that is first converted to the cuprous state through a 
reaction with the sulfur containing regenerating agent. From an economic 
perspective and relatively easy solubilities of commercially available 
forms of these different components, cupric chloride is most preferred. 
A wide variety of sulfur-containing organic compounds are suitable for use 
in this invention. The requirements for such compounds are that they 
possess sufficient solubility in the acidic well-treating fluid employed 
to give a homogeneous solution when used in amounts sufficient to reduce 
an anticipated quantity of ferric ion through the regenerative process. 
Still further, those compounds' products of reaction must also be 
predominantly soluble in the treating fluid. Examples of classes of such 
sulfur-containing organic compounds include but are not limited to alkyl 
thiols, alkyl dithiols, thioalcohols, thioureas, thioamines, thioamides, 
and esters and salts of mercaptoalkanoic acids. Some specific examples of 
the classes include butanethiol, ethandithiol, 2-meracaptoethanol, 
1-mercapto-2-propanol, 1-thioglycerol, 3-mercapto-1-propanol, thiourea, 
dimethylthiourea, diethylthiourea, trimethylthiourea, ethylenethiourea, 
methylthiourea, ethylthiourea, phenylthiourea, 2-thio-1 aminoethane, 
thioacetamide, glycol dimercaptoacetate, trimethylolpropane 
tris(3-mercaptopropionate), pentaerythritol tetrathioglycolate, 
trimethylolpropane trithioglycolate, and ammonium thioglycolate. More 
preferred among these are compounds which are liquid or which are very 
soluble in inexpensive solvents; examples of the more preferred 
sulfur-containing regenerating agents are 2-mercaptoethanol, 
1-mercapto-2-propanol, and ammonium thioglycolate. Most preferred is 
2-mercaptoethanol. 
The ferric ion reducing additive of this invention can be readily prepared 
in a preformed mixture of regenerating agent with ammonia or amine that is 
then added to the copper-containing reducing agent. In any event, the 
solubility of the reducing agent and regenerating agent is promoted by the 
solubility facilitator that is usually in the form of ammonia or amine. 
The proportions of the components to be used in the combination are 
subject to considerable latitude: for each 100 parts of sulfur-containing 
regenerating agent it is preferred that from about 0.5 to about 60 parts 
ammonia or amine be used. It is also preferred that the amount of copper 
reducing agent to be used range from about 0.2 to about 40 parts. Precise 
proportions may be arrived at by one skilled in the art by considering 
among others: (1) the rapidity with which it is desired to reduce ferric 
ion to ferrous ion; (2) the amount of ferric ion anticipated to require 
reduction; (3) the conditions under which the reducing mixture is to be 
used, with those conditions including reservoir temperature and 
composition of the acidic treating fluid used; and (4) by economic 
considerations. 
The acidic well-treating fluid may be any of those commonly in use in 
acidizing including hydrochloric acid of concentrations up to about 24%, 
mixtures of hydrochloric and hydrofluoric acids, and mixtures of either of 
these with organic acids such as formic acid, acetic acid, glycolic acid, 
and citric acid. Other ingredients known to be useful in acidizing 
compositions can be included in the acidic treating fluids of this 
invention. Such other ingredients include, but are not necessarily limited 
to demulsifiers, acid inhibitors, antisludge agents, dispersants, gelling 
agents, and mutual solvents. 
Under some conditions, particularly in strong acid solutions having 28% and 
higher acid content, but also possibly ranging downward to as low as 15% 
or less, the addition of a reducing catalyst may be desirable or required. 
As was appreciated in the Canadian Patent Application '212, a suitable 
catalyst for such purposes is iodine containing compounds. Through 
experimentation, it has been discovered that iodide will react in the 
ferric iron reduction process to iodine. Through this same 
experimentation, it has also been discovered that like the reacted cupric 
iron reducing agent, iodine can be regenerated by the regenerating agent 
back to an iodide state for subsequent catalytic function. In this manner, 
a limited amount of the more expensive iodine containing compound can be 
utilized in the reducing additive when required so long as a sufficient 
amount of regenerating agent is also present for regenerating both the 
iron reducing agent and the catalyst. 
The following examples are provided to illustrate the practice of the 
invention as well as certain preferred embodiments thereof. The examples 
should not be construed as limiting in any way to the spirit or scope of 
the invention and are not provided as such a limitation. 
EXAMPLE I 
To a 50-milliliter sample of 2-mercaptoethanol was added 2 milliliters of a 
solution including 40.3% cupric chloride dihydrate in water. Upon 
stirring, the cupric chloride solution, which on initial mixing had formed 
a lumpy precipitate, dissolved to give a clear and colorless solution. 
However, within one minute of mixing, a white precipitate thought to be a 
cuprous salt formed and fell to the bottom of the reaction vessel. 
Continued stirring failed to dissolve this precipitate. This illustrates 
the difficulty encountered in attempting the directly mix the reducing 
agent and regenerating agent into a soluble solution without the benefit 
of a solubility facilitator such as ammonia. 
EXAMPLE II 
The experiment of Example I was repeated, except that 3 milliliters of 
commercial 28% aqua ammonia was dissolved in the 2-mercaptoethanol prior 
to the addition of 2 milliliters of cupric chloride. Some precipitate 
formed on initial mixing, but it redissolved within a few seconds to give 
a clear, golden-yellow solution which remained free of precipitate for a 
period of at least one month after mixing. A portion of this solution was 
also held at a temperature of 130 degrees Fahrenheit for more than a week, 
and still it remained precipitate free. 
EXAMPLE III 
A solution of an ammoniacal complex of copper was prepared from 4.5 
milliliters of water, 3.0 milliliters of aqua ammonia, and 2.5 milliliters 
of the cupric chloride solution referred to in Example I. This entire 
solution was slowly added to 50 ml of 2-mercaptoethanol. No precipitate 
formed in the resulting golden-yellow solution for a period of at least 
one month after mixing. 
EXAMPLE IV 
A sample of the solution of Example II containing 2-mercaptoethanol, aqua 
ammonia, and cupric chloride solution was tested to determine its ability 
to reduce ferric iron to the ferrous form in an acid solution. To 100 
milliliters of a 15% solution of hydrochloric acid was added sufficient 
ferric chloride to give a ferric ion concentration of 1250 parts per 
million. To this yellow solution was added 0.30 milliliter of the mixture 
of Example II. The color of the acid solution disappeared over a period of 
about ten seconds, showing the reduction of ferric iron to the ferrous 
state. 
EXAMPLE V 
A solution of 100 milliliters of 15% hydrochloric acid containing ferric 
iron at 1250 parts per million concentration was added 0.50 gram of 
cuprous chloride. The cuprous chloride slowly dissolved and the yellow 
color of ferric iron was replaced by a pale bluish color characteristic of 
cuprous chloride; thus, indicative of a reduction of the ferric ion to 
ferrous ion. 
EXAMPLE VI 
A solution of 100 milliliters of 15% hydrochloric acid containing 5000 
parts per million of ferric iron was prepared and 0.5 milliliter of the 
reducing solution of EXAMPLE II containing 28% aqua ammonia, 
2-mercaptoethanol and cupric chloride was added thereto. The dark yellow 
color of the solution lightened perceptibly, but did not disappear; thus 
illustrating incomplete reduction of ferric iron to the ferrous state. 
Upon the addition of 1.0 milliliter of 2-mercaptoethanol, the color of the 
acid solution disappeared over a period of about 20 seconds. This 
demonstrates the regeneration of the reducing agent by the addition of a 
suitable quantity of an appropriate sulfur containing compound. 
EXAMPLE VII 
A solution of 100 milliliters of 28% hydrochloric acid containing 1000 
parts per million of ferric iron was prepared. To this brownish-yellow 
solution, 0.8 milliliter of the reducing solution of EXAMPLE II containing 
28% aqua ammonia, 2-mercaptoethanol and cupric chloride was added thereto. 
No significant color change was detected. After 15 minutes, 0.01 
milliliter of a 40% solution of potassium iodide was added to the mixture. 
The brownish-yellow color almost immediately faded to a colorless and 
clear solution. 
A ferric ion reducer and its method of use has been described herein. These 
and other variations, which will be appreciated by those skilled in the 
art, are within the intended scope of this invention as claimed below. As 
previously stated, detailed embodiments of the present invention are 
disclosed herein; however, it is to be understood that the disclosed 
embodiments are merely exemplary of the invention that may be embodied in 
various forms. 
INDUSTRIAL APPLICABILITY 
The present invention finds applicability predominantly in the oil field 
services industry, and more particularly in well acidizing procedures. It 
has been discovered, however, that the additive presents utility for other 
purposes in this same industry. For example, the additive may be used as a 
potentiator or intensifier for acid inhibitors utilized in acid solutions 
to prevent deterioration of the metal conduits through which the acid 
solution is conducted. As the solubilized product is utilized and made 
available to different markets, it is anticipated that further utility 
will be appreciated and exploited.