Earth boring – well treating – and oil field chemistry – Preventing contaminant deposits in petroleum oil conduits
Reexamination Certificate
1992-05-27
2001-10-23
Nazario-Gonzalez, Porfirio (Department: 1621)
Earth boring, well treating, and oil field chemistry
Preventing contaminant deposits in petroleum oil conduits
C507S267000, C507S272000, C507S277000, C507S923000, C507S932000, C166S308400, C166S311000, C166S312000
Reexamination Certificate
active
06306799
ABSTRACT:
The present invention relates to the technical field of acid treatments designed to stimulate the production of oil, gas, water, geothermal and analogous wells, as well as to that of industrial cleaning.
The objectives and techniques of acid well treatment are very familiar to a man of the art and it is quite unnecessary to reiterate them here. It will simply be recalled that the acid fluids pumped into the well and into the adjacent formations are of a very special nature in that they are of extremely high acidity.
Acid treatments are accompanied by very familiar problems linked with the presence of iron in the acid that is pumped into the formations, essentially as a result of the acid dissolving the rust in the casings during pumping, and possibly the dissolving of iron-containing minerals in formation.
The presence of iron (III) in the injected acid causes, in contact with certain crude oils, the precipitation of the asphaltic products contained in the oil in the form of deposits of a vitreous aspect known as “sludges”, which leads to practically irreversible damage to the zone treated; the scale of precipitation generally increases with the strength and concentration of the acid.
The dispersibility of customary additives, such as surfactants, is also affected by the presence of iron (III) through the formation of complexes.
When the injected acid is consumed by the dissolution of the minerals of the formation, the presence of iron (III) leads to the precipitation of a colloidal precipitate of ferric hydroxide which damages the formation.
In the particular case of wells containing hydrogen sulphide, the ferric hydroxide precipitate does not occur as a reducing medium is involved, but other damaging precipitations, such as that of colloidal sulphur, can also occur in the absence of iron control agents.
The use of iron control additives is thus necessary in most acid treatments, with a view to removing the majority of the free iron (III) in the treatment acid.
The conventional complexing agents of the soluble forms of iron, such as the aminopolycarboxylic acid derivatives, citric acid, acetic acid or salicylic acid only lead to the formation of stable complexes in a medium that is not very acid, and can only serve, therefore, to mask the iron in the spent acid, and they are ineffectual in preventing the formation of sludges induced by contact with certain crude oils and the pumped acid that still has a concentration close to initial concentration.
As a variant, liquid-liquid extraction of iron (III) in the organic phase, in processes including the injection of suitable solvents, has also been proposed after complexing with certain of these complexing products, but the efficiency of the process is only proven in a spent acid medium and is limited to low dissolved iron (III) contents.
The usual reducing agents for iron (III) are also generally more efficient in partially spent acids than in acids that have not reacted; in a highly acid medium, we often observe reduction kinetics that are too slow for thermodynamically possible reactions to enable sludge formation to be efficiently prevented under acid treatment conditions. Furthermore, the chemical and/or thermal stability of the reducing agents considerably limits their use in a very acid medium. Thus, sulphur base mineral reducing agents (sulphites, hydrosulphites, etc.) are unstable in an acid medium.
Organic reducers are often limited by the kinetics of their reactions, and by their limited chemical stability in a highly acid medium and in terms of temperature. Thus, the erythorbic or ascorbic acid, frequently used in acid treatments, can forestall the precipitation of ferric hydroxide in the spent acid, but they can sometimes present serious shortcomings as regards quickly reducing the iron in a highly acid medium, and thus forestalling sludge formation.
Similarly, the nitrogen or phosphorous base reducing systems have slow reduction kinetics in an acid medium. The use of oxidation reduction catalysts can permit a considerable acceleration of the reduction kinetics; the process is well known, for example, in the field of nickel plating, in which metallic salts are added to baths of hypophosphorous acid. The catalysing electrochemical couple must possess fast kinetics and an intermediate potential between those of Fe (III)/Fe (II) and of the reducing system selected.
The present invention represents a decisive improvement in the control of precipitations due to iron in the acid treatments and of the incompatibilities observed simultaneously. It comprises the use of a selected catalytic system combined with that of a selection of reducing products with the aim of removing the ferric ions of the acid solution practically instantaneously during pumping, thus avoiding the formation of sludges in contact with certain crude oils owing to the presence of iron (III) in the acid, opening up, moreover, new applications, some of which will be mentioned hereinafter, and the poor dispersibility of certain additives of acid solutions, as well as the subsequent formation of mineral precipitates in the course of neutralization of the acid following its coming into contact with the minerals.
It has been discovered, according to the invention, that the mercaptan function, i.e. HS- bonded to an aliphatic group with a straight or branched chain, possibly cyclic, and having sufficient hydrophilic groups to ensure solubility, would enable the above objectives to be attained with a degree of efficiency never hitherto achieved.
The examples given below show that the mercaptan function HS- in itself appears to be responsible for the decisive progress achieved.
This progress appears to be essentially linked to the far swifter reduction of far larger quantities of Fe (3+) by comparison with prior art. Furthermore, this property is not affected by the presence on the aliphatic chain of the usual hydrophilic group(s) such as —OH, —NH
2
,
(acid or salt, particularly of Na, Ca, NH
4
and the like),
(ester) which are naturally desirable since the acid fluid pumped is an aqueous medium.
The advantages of the mercaptan function used for iron control in an extremely acid medium, and most especially in an acid medium containing HCl, in the petroleum and associated fields, as well as in industrial cleaning, are numerous and form a group of properties never before obtained in this industry.
These properties will be quite especially appreciated in the acid treatment of oil and analogous wells where, in particular, the precipitation of “sludges” (precipitation of asphaltic products) has been of serious concern to operators for very many years.
On one hand, the reaction is quantitative. The compositions according to the invention are thus efficient up to Fe (3+) concentrations that were found absolutely impossible to treat hitherto.
Thus, certain prior art techniques can act more or less efficiently upon Fe (3+) concentrations not exceeding approximately 15 000 ppm in an acid medium. On the other hand, in an aqueous solution of 15% hydrochloric acid, the compositions according to the invention efficiently control Fe (3+) up to concentrations in the order of 100 g/l, or 100 000 ppm. This leads, among other advantages (notably the absence of “sludges”), to that of being able, in acid treatment operations, to dispense with the prior, extremely costly stage of well cleaning.
Indeed, controlling such concentrations means that even Fe (3+) from rust deposits, etc. will be controlled efficiently, for the first time.
Secondly, the compositions according to the invention remain efficient even in the presence of H
2
S (no sulphur precipitate).
They further have the advantage of being extremely stable in the highly acid medium under consideration, even under hot conditions, which is also an important parameter for operators in the field.
The mercaptan function is, of course, known for its reducing properties, but only in a basic medium, as well as in a very slightly acid or neutral medium, and in a completely different application, the object bei
Dejeux Philippe
Feraud Jean Pierre
Perthuis Herve
Nava Robin C.
Nazario-Gonzalez Porfirio
Ryberg John J.
Schlumberger Technology Corporation
Y'Barbo Doug
LandOfFree
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