Wells – Processes – Chemical inter-reaction of two or more introduced materials
Reexamination Certificate
2000-02-24
2001-10-30
Suchfield, George (Department: 3672)
Wells
Processes
Chemical inter-reaction of two or more introduced materials
C166S307000, C507S272000, C507S274000, C507S275000, C507S933000
Reexamination Certificate
active
06308778
ABSTRACT:
The present application claims priority to Canadian patent application number 2,263,014 filed Feb. 25, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods and compositions for preventing precipitation of iron compounds during acid treatments of wells. In particular, this invention relates to methods and compositions for catalyzing the rate of iron reduction during acid treatment of wells. Specifically, this invention relates to a method for accelerating the reduction of ferric ions utilizing antimony ions in combination with other materials to minimize precipitation and other complications which result from iron compounds during acid treatments. Such other materials may include a source of copper ions and at least one of phosphinic acid, salt of phosphinic acid, or a mixture thereof.
2. Description of Related Art
During well treatments and related operations employing acid, contamination of acid by dissolved iron or iron compounds is a known phenomenon. Contamination of a well treating acid by dissolved iron or by iron compounds during the process of acid treating a well bore and/or subterranean formation is almost inevitable. In the treatment of sour wells ferric iron may oxidize sulfides to insoluble elemental sulfur deposits, and ferrous iron can form ferrous sulfides as the acid spends. These materials may cause well plugging. A discussion of dissolved iron problems and previous methods for addressing these problems may be found in Canadian Patent No. 1278178 and U.S. Pat. No. 5,063,997.
As described in the above-mentioned references, it has been estimated that in the absence of an acid prewash levels of 9,000 to 100,000 mg/L of dissolved iron may occur. It has been reported that a source of iron is the mill scale and rust on the steel tubulars used during stimulation in production applications. If an acid wash treatment is carried out prior to a formation treatment, it has been reported that levels of dissolved iron entering a formation will typically be in the range of 1,000 to 2,000 mg/L. Other reports have indicated that small volumes of acid wash may result in iron levels of 500 to 7,000 mg/L contacting the formation. Additional complications such as disposal problems, low reservoir pressure or the presence of a permanent packer around the tubing may make it impossible to conduct an acid wash prior to the acid treatment. Thus, it may be very hard or impossible to reduce levels of dissolved iron to acceptable levels.
As described in the above-mentioned references, many attempts have been made related to reduction of ferric hydroxide precipitation. Such attempts have included sequestering of ferric acid in acid solution using salicylic acid or sulfosalicylic acid proposed. However, sulfosalicylic acid has been found ineffective in preventing iron asphaltene sludge in 15% hydrochloric acid. Use of sequestering agents such as citric acid, ethylene diamine tetra-acetic acid (EDTA) or nitrilo triacetic acid (NTA) has been described. However, effectiveness of such materials at temperatures above 125-250° F. is poor. Other compounds which have been described include ascorbic acid, erythorbic acid and/or their salts. However, tests have shown that effectiveness of erythorbates at preventing iron precipitates drops off rapidly as hydrochloric acid strength increases to 15%. Furthermore erythorbates are unstable in hydrochloric acid and degrade fairly rapidly to solids. The rate of degradation increases dramatically at higher temperatures, raising particular problems for treatments in which acid remains at reservoir temperatures for several hours, such as staged acid treatments.
Many reducing agents such as stannous ion, hydrazine and related compounds etc. may cause asphaltic sludge even in the absence of irons. Other reducing agents such as erythorbates, and most organic compounds, are typically degraded to varying degrees in strong acid. This degradation may form carbonaceous residues which are ineffective in controlling gradual contamination by iron. Materials such as thiosulphates may degrade in acid to form elemental sulphur precipitates, and are thereof undesirable. An alternative to these reducing agents consists of phosphinic acid (hypophosphorous acid) and/or salts of phosphinic acid.
SUMMARY OF THE INVENTION
Disclosed are compositions and methods for controlling iron precipitation and additive incompatibility during conditions encountered during well operations utilizing acid. These disclosed methods and compositions include the use of antimony and other co-catalysts with a select reducing agent to obtain the reduction of ferric iron to ferrous iron and reducing or substantially preventing precipitation products during well acid treatments. Advantageously, using the disclosed antimony co-catalyst/s with one or more other catalytic agents results in maximum reduction of ferric iron by reducing agent during acid treatments. Furthermore the disclosed antimony co-catalyst/s may be used to accelerate reduction of ferric irons so as to provide an extremely effective means of addressing iron precipitation problems.
Significantly, the disclosed combination of co-catalyst offer advantages over catalytic agents which have been found ineffective alone in catalyzing the action of reducing agents in strong acid. Such catalytic agents include cobalt salts, ferrous iron, iodide salts etc. Advantageously, the disclosed antimony/copper co-catalyst may be employed with phosphinic acid-based reducing systems in strong acids or blends of strong acids including, but not limited to, hydrochloric acids blends having a strength up to about 15% in water. The disclosed antimony-based reducing systems may be formulated and used to provide a relatively fast reduction time for ferric ions, Fe(III).
Numerous advantages are offered by the disclosed methods and compositions. These include improvements in protection of tubulars, including coiled tubing, and sour and/or high temperature downhole environments. By allowing the minimization of copper amounts present in acid treatments employing phosphinic/copper based iron control systems in sour wells, depositing of copper sulfide may be reduced or substantially prevented. Furthermore, the disclosed antimony-containing phosphinic acid-based reducing systems may be used to provide effective sludge control and may serve to improve the function of corrosion inhibitors. Further advantageously, a combination of antimony, copper and iodide ions may be used in high acid concentrations to obtain effective sludge control.
In one respect, disclosed is a process of reducing sludge formation during acid treatment of subterranean formation with a treatment acid, comprising adding to the acid solution used for such treatment:
a) at least one of (i) phosphinic acid and (ii) a salt thereof which is soluble in the acid used for treating the formation which does not precipitate during the treatment, and
b) catalytic amount of antimony salts in combination with cupric or cuprous ions in a form soluble in the treatment acid, and wherein the antimony/copper are added as salt which do not form a sludge or precipitate with oil in the subterranean formation. An optional co-catalytic amount of iodide ions may be added to enhance the reduction of ferric iron to ferrous iron. Iodide ions may be added in a form soluble in the treatment acid and may comprise potassium iodide.
In another respect, disclosed is the use of trivalent and/or pentavalent antimony, cuprous and/or cupric salts combined with phosphinic acid and/or its salts to significantly improve the rate of ferric ion reduction over systems employing combinations of cuprous and/or cupric salts with phosphinic acid and/or its salts but without antimony ions. Advantageously, this improvement in ferric ion reduction rate may be used to minimize iron sludging problems. Furthermore, use of antimony materials with copper materials acts to reduce or substantially prevent copper plating which may occur under some conditions in which phosphinic/copper ion-only systems are
Delorey John R.
Girgis-Ghaly Magdy
BJ Services Company
O'Keefe Egan & Peterman, LLP
Suchfield George
LandOfFree
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