NL8301828A - VERY DENSITIVE FLUID COMPOSITIONS INHIBITED AGAINST CORROSION. - Google Patents

Description

? * * 8

Corrosion-inhibited sheer dense fluid compositions.

The invention relates to fluids serving wells and more particularly to a corrosion-inhibited very dense fluid which can be used under rigorous service conditions.

Drilling fluids have hitherto been used to maintain control during perforation, completion or surfacing operations in oil and gas wells.

Drilling fluids heretofore used for such purposes include mud, salt water, water or oil. The use of these fluids during drilling operations has generally been sufficient per se and has in fact increased drilling efficiency. However, the same materials have been used during completion and reprocessing operations with undesired consequences.

For example, the use of drilling muds during well perforation has often led to the clogging of the perforations. Solids contained in such drilling fluids have caused clogging and have made the completion process unnecessarily complex, expensive and unreliable. Likewise, the use of drilling mud and other drilling fluids as packing fluids has led to unwanted solids deposition. In addition, drilling media can be somewhat corrosive under prolonged static machining conditions, further rendering them unsuitable for use other than as transition drilling aids.

Attempts made to overcome the above-mentioned problems include the use of very dense clear saline solutions. Clear fluids consisting of solutions of zinc bromide / calcium bromide and optionally calcium chloride with densities in the range of 15.0-20.0 [mu] s 2 ppg are disclosed in U.S. Pat. Nos. 4,292,183 and 4,304,677. Although such solutions are very sufficient materials for use in the completion, packing and perforation of oil and gas wells, such solutions have not hitherto been useful where temperatures down the hole exceed 149 ° C due to the high corrosion rate of the iron steel under such conditions. Under high temperature conditions it is therefore hitherto only possible to use less desirable fluids, such as modified rudders and the like. At high temperatures, the solids contained in the drilling mud deposit on the bottom of the wellbore, solidify and make the operation of the well much more costly and difficult to achieve.

The zinc ion in a 19.2 ppg clear fluid can only be maintained in solution by maintaining a pH in the range of 1.0-1.3, usually by adding excess hydrobromic acid. Although the pHs in this range achieve the desired solubility of the weighing salt, the resulting liquid is highly corrosive.

Even when a 19.2 ppg zinc bromide / calcium bromide solution is mixed with calcium bromide / calcium chloride solution to ultimately obtain lower density fluids, the pH remains in the highly acidic range, never rising above about 5.5. The liquids thus obtained remain highly acidic and highly corrosive at temperatures above 149 ° C.

U.S. Patent 4,292,183 describes the use of an amine-based film-forming corrosion inhibitor. However, the corrosion inhibition system disclosed in that patent is only useful in the range of up to about 149 ° C and cannot be used at the higher temperatures to which the present invention is directed.

In the prior art, 8301828 φ, 3 separate corrosion inhibition systems have been proposed for use in highly acidic environments. However, only a few have proved sufficient and even fewer have been used in practice.

For example, arsenic and / or arsenic compounds have been proposed to provide corrosion protection in highly acidic solutions used to make new and producing wells acidic.

The toxic nature of arsenic compounds to humans and the (poisoning) of the catalysts used in the refineries have made arsenic compounds undesirable.

A strong acid inhibitor is described in U.S. Pat. No. 3,077,454. The inhibitor contains an organic ketone, an aliphatic aldehyde and a fatty acid. Protection up to 177 ° C is suggested, but only for short periods of time (i.e. no longer than 15-16 hours).

Such a composition is described in U.S. Pat. No. 3,634,270. A synergistic mixture of organic nitrogen and sulfur compounds is claimed which prevents attack of the corrosive ingredient of the solution on metal. Application on industrial boiling kettle and heat exchanger cleaning is suggested. Sulfur compounds selected from the group of thiourea, allyl thiourea, sodium capaptobenzothiazole, mercaptothioazoline, sodium thiocyanate and mixtures are disclosed to be particularly effective. However, the disclosed operating range for the inhibitor systems includes low temperatures of no more than 149 ° C and short times of no more than 16 hours.

The literature contains references to the corrosion of acid corrosion of steel by thiourea and its derivatives. J. Appl. Chem. 3 (11): 502-13 (1953); Corrosion Science, 14: 597-606 (1974); British Corrosion J., 11: 208-11 (1976) and Corrosion, 36: 493-7 (1980) are representative examples of the extensive literature.

US Patent 4,100,100 8301823 4 describes the use of the combination of a quaternary pyridinium salt and an organic thiamide or water-soluble thiocyanate to reduce the corrosion of iron and steel by an aqueous acidic gas conditioning solution.

The same mixture is described in British Patent Specification 2,027,686 as a corrosion inhibitor for aqueous brines in a wellbore.

US Patents 4,100,100 and British Patent 2,027,686 report that the addition of a small amount of a water-soluble cobalt salt to the inhibitor combination improves its effectiveness. The sulfur compound of the mixture is preferably ammonium thiocyanate or thiourea. The corrosion tests described in the patents are for moderately high temperatures (ie 177 ° C) at short periods of time (ie no more than 118 hours).

A corrosion inhibitor mixture suitable for use in calcium chloride and sodium chloride brine is described in U.S. Patent 3,215,637. The mixture consists of sodium silicate, zinc chloride and sodium chromate. A mixture of inhibitors is required because no single formulation has been found to be effective in preventing general and localized corrosion. The effectiveness of the inhibitor composition is rated for longer periods, 10 days, but at a lower temperature (20 ° C).

A method of corrosion inhibition in wellbore operations is described in U.S. Patent 4,250,042. The aqueous drilling fluid is treated with at least one water-soluble ammonium carboxylate salt. The described corrosion tests are performed in an atmosphere of air and oxygen at 85 ° C for 20 hours.

The crust low temperature protection 35 of the above prior art is of little value in an oil well completion, finish, or packing fluid.

Japanese Patent 7503741 describes an oxide film remover and corrosion inhibitor for copper 5 and copper alloys with 2-20% by volume of an aqueous solution of sodium or ammonium thioglycolate, containing benzotriazole, sodium capaptohenzothiazole and / or imidiazole derivatives. Japanese Patent 7692735 describes metal coil compositions for cleaning air conditioner pipes or internal combustion radiators in shorter periods of time without corrosion of the pipes using water-soluble thioglycolate, halogenated alkyl metal or halogenated ammonium thioglycolate. Japanese Patent 79120007 describes compositions of colorants, wetting agents, amino acid derivatives and ammonium thioglycolate as jet printing inks with good shelf life and corrosion inhibition.

Thus, nowhere in the prior art is a suitable corrosion inhibition system for very dense fluids disclosed that allows its use under high downhole temperature processing conditions.

It is therefore an object of the invention to provide a corrosion inhibition system for zinc bromide / calcium bromide solutions, optionally containing calcium chloride, which can be used in oil and gas wells as well as fluids serving wells at temperatures as high as 204 ° C.

A further object is to provide a composition of the character described which is successfully used in solutions having densities in the range of about 15.0-20.0 ppg.

Yet another object is to provide corrosion protection in such systems for extended periods of up to 90 days or more.

8301828 <* ^ 6

Yet another object is to provide a corrosion inhibitor which is sufficiently soluble in very thick fluids and which can provide a base solution which can be mixed to lower densities for field use.

The above and other objects, advantages and features of this invention can be achieved with a corrosion inhibited, clear, very dense composition that can be used for a long time as a fluid at the service of a wellbore under conditions of high temperature. high temperature, and which consists of a solution of zinc bromide and calcium bromide, and optionally calcium chloride in water with a density in the range of 15.0-20.0 ppg and a corrosion inhibiting amount of a member selected from the group consisting of ammonium thioglycolate , calcium thioglycolate, thioglycerol and mixtures thereof. Desirably, the corrosion inhibitor is provided in an amount of about 0.01-5.00 wt% of the clear solution.

The invention also encompasses new methods for formulating such corrosion inhibited clear solutions as well as for their use in well service operations.

As noted, those skilled in the art have long but unsuccessfully searched for a corrosion inhibited zinc bromide / calcium bromide solution that would allow it to be used at downhole processing temperatures of up to 205 ° C. By using a corrosion inhibitor of the invention, it is possible to obtain very dense aqueous brines for use as completion, overtime or packing fluids in deep oil, gas or high pressure, high temperature geothermal wells. The objects of this invention are achieved with a corrosion inhibitor which is completely soluble in aqueous solutions of zinc bromide, calcium bromide and calcium chloride in the density range of about 8301828 * 7 15.0-20.0 ppg.

In addition to the desired solubility, the corrosion inhibitor must be capable of providing significant corrosion initiation at temperatures up to 205 ° C. The corrosion protection must be maintained for extended periods of at least 30 days and preferably up to 90 days or more. It is also important that the corrosion inhibition minimize pitting corrosion so that the small amount of corrosion that occurs is of a general rather than a very specific nature. In addition, the corrosion inhibitor must be compatible with other chemical additives commonly used with very dense aqueous brine, such as viscous, suspending and defoaming agents.

According to the invention, it has been found that ammonium thioglycolate, calcium thioglycolate, thioglycerol or mixtures thereof make it possible to achieve these objectives when provided with corrosion inhibiting amounts. Corrosion inhibited clear fluids of this invention can not only be sufficiently used at high ambient temperatures to serve the well, but have also been found to be useful for relatively long periods of time up to 90 days or more.

The preparation of zinc bromide / calcium bromide solutions, which may optionally contain calcium chloride, is not in itself part of the invention. Adequate methods of directing and mixing such solutions with densities in the range of 15.0-20.0 ppg are described in U.S. Patent Nos. 4,292,183 and 4,304,677.

Typically, such very dense fluids are formulated with a relatively high density base fluid (i.e., a zinc bromide / calcium bromide solution at a density of 19.2 ppg, which is about 54.7

__M

8301828 contains 8 wt% zinc bromide and about 20.6 wt% calcium bromide). Such a base solution can be mixed with calcium bromide or calcium bromide and calcium chloride solutions in the field to the desired density required for a given application.

The corrosion inhibitor of the invention can be added to the obtained clear fluid at virtually any point in the preparation cycle. Thus, it can be provided in the base solution and in one or more of the auxiliary solutions of calcium bromide or calcium bromide and calcium chloride, or the corrosion inhibitor can be added separately to the mixed solution at the well site.

Preferably, however, the corrosion inhibitor provides the base solution (for example, 19.2 ppg zinc bromide / calcium bromide solution) in sufficient amount to provide the final level desired under all achievable conditions of use. Thus, sufficient inhibition is provided to ensure adequate protection when the 19.2 ppg base solution 20 is mixed to a final density of about 1.50 ppg.

Generally, the solution used in a well service operation should contain about 0.01-5.0% of one or more of the corrosion inhibitors of the invention, preferably about 0.1-3.0%.

Hair in the corrosion inhibitors is provided in the very dense base solution (eg, 19.2 ppg zinc bromide / calcium bromide solution), the amount of corrosion inhibitor used is preferably about 0.1-3.0 wt% of the base solution.

As indicated, the desired degree of corrosion inhibition can be obtained according to this invention using ammonium thioglycolate, calcium thioglycolate, thioglycerol or mixtures of these agents. The correct amount of the agent to be used depends on the specific material used. So when to use ammonium thioglycolate? the preferred range is about 0.1-1.0 wt% of the base solution; for calcium thioglycolate, the preferred range is about 0.3-3.0% by weight of the base solution; and for thioglycerol, the desired amount is about 0.1-0.5 wt% of the base solution.

It is particularly preferred to use ammonium thioglycolate as the corrosion inhibitor of the invention.

The corrosion inhibitors of the invention can be added in any suitable form. Calcium thioglycolate can be provided in solid or solution form. Thioglycerol is a liquid at room temperature and is usually used in that form. Ammonium thioglycolate 15 is desirably used as a 60% aqueous solution.

When used herein, the amounts of inhibitor are reported as amounts of the active agent.

Examples of corrosion inhibiting very dense fluids are disclosed in the following examples.

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Example I

A 19.2 ppg zinc bromide, calcium bromide solution is prepared in the following manner: The pH of an uninhibited 19.2 ppg zinc bromide / calcium bromide base solution is adjusted using a slurry of zinc oxide, calcium bromide and water or 54% hydrogen bromide at 1.2 + 0.1. The density is adjusted to 19.20 + 0.05 ppg with 14.2 ppg calcium bromide. The solution is filtered through a medium sintered glass funnel coated with filter aid. The filtered fluid adjusted for density and pH is heated to 95 _ + 5 ° C.

The desired amount of corrosion inhibitor is added to the hot fluid. After stirring for 30 minutes, the solution is filtered hot through a medium sintered glass funnel coated with filter aid. Let the solution cool to room temperature.

5 Example XX

An 18.0 ppg uninhibited zinc bromide / calcium bromide base solution is prepared by dissolving 254.9 kg of zinc bromide and 306.1 kg of calcium bromide in 226.0 kg of water. One vessel of 18.0 ppg zinc-10 bromide / calcium bromide fluid is thus prepared. The pH is adjusted to 2.3 + 0.1 with a slurry of zinc oxide, calcium oxide and water or with 54% hydrogen bromide. The density is adjusted to 18.0 ± 0.05 with 14.2 ppg calcium bromide or with solid zinc bromide. The solution is filtered through a medium-sintered glass funnel coated with filter aid.

The filtered density adjusted fluid is heated to 95 + 5 ° C. The desired amount of corrosion inhibitor is added to the hot fluid. After stirring for 30 minutes, the solution is filtered hot through a medium sintered glass funnel coated with filter aid. The solution is allowed to cool to room temperature.

Example III

A 14.5 ppg uninhibited zinc bromide / calcium bromide base solution is prepared by dissolving 29.4 kg of zinc bromide and 298.9 kg of calcium bromide in 280.7 kg of water. A vessel of 14.5 ppg zinc-30 bromide / calcium bromide base solution is thus prepared. The pH is adjusted with a slurry of zinc oxide, calcium oxide and water to 6.0 ± 0.1. The density is adjusted to 14.50 ± 0.05 with 14.2 ppg calcium bromide or solid zinc bromide. The solution is filtered through a medium sintered glass funnel, lined with filter aid. The filtered fluid set at 8301828% 11 density is heated to 95 ° C.

The desired amount of corrosion inhibitor is added to the hot fluid. After stirring for 30 minutes, the solution is filtered hot through a medium sintered glass funnel, coated with filter aid. The solution is allowed to cool to room temperature.

Example IV

A 19.2 ppg zinc bromide / calcium bromide solution containing 1.0 wt.% Ammonium thioglycolate is prepared according to the procedure of Example 1. One vessel of a 17.5 ppg mixture of uninhibited 19.2 ppg is thus obtained zinc bromide / calcium bromide by mixing 532.2 kg 15 uninhibited 19.2 ppg zinc bromide / calcium bromide and 202.8 kg 14.2 ppg calcium bromide. After stirring for 30 minutes, the fluid is filtered through a medium sintered glass funnel coated with filter aid.

20

Example V

A 19.2 ppg zinc bromide / calcium bromide solution containing 1.0 wt% calcium thioglycolate is prepared according to the procedure of Example 1. 1 vessel of a 15.5 ppg zinc bromide / calcium bromide, calcium chloride solution is prepared by mixing 96 kg uninhibited 19.2 ppg zinc bromide / calcium bromide solution with 555.0 kg 15.0 ppg calcium bromide, calcium chloride solution. After stirring for 30 minutes, the fluid is filtered through a medium sintered glass funnel, coated with filter aid.

35 8301828 β 12

Example VI

A 19.2 ppg zinc bromide / calcium bromide solution containing 2.0 wt% tbioglycerol is prepared according to the procedure of Example 1. 1 vessel of 16.5 ppg zinc bromide / calcium bromide is prepared by mixing 370.9 kg uninhibited 19.2 ppg zinc bromide / calcium bromide solution with 322.1 kg 14.2 ppg calcium bromide solution.

After stirring for 30 minutes, the fluid is filtered through a medium sintered glass funnel coated with filter aid.

Example VII

A 19.2 ppg zinc bromide / calcium-15 bromide solution containing 0.5 wt% ammonium thioglycolate and 0.5 wt% tbioglycerol is prepared using the procedure of Example 1. 1 barrel of 18.5 ppg is prepared zinc bromide / calcium bromide / calcium chloride fluid by mixing 671.7 kg inhibited 19.2 ppg zinc bromide, calcium bromide and 105.2 kg 15.0 ppg calcium bromide, calcium chloride solution. After stirring for 30 minutes, the fluid is filtered and a medium sintered glass funnel coated with filter aid.

The effectiveness of the corrosion inhibitors according to the invention is demonstrated experimentally using the following test procedure. The density of a non-inhibited base fluid set is first determined. The solution is then heated to 95 + 5 ° C and the desired amount of corrosion inhibitor is added to the hot uninhibited base fluid. The solution is filtered hot through a medium sintered glass funnel, lined with filter aid, and allowed to cool to room temperature. The base fluid is then mixed to the desired density according to mixing tables, and the mixed fluid is filtered through a medium sintered glass funnel coated with filter aid. The fluid density is determined at 15 ° C and the pH of the fluid is measured with a pH meter.

The test fluid is then added to a high temperature aging cell to obtain a test sample. The test sets are pressurized with nitrogen and placed in an oven for the desired time and temperature. At the end. of the test, the test cells are removed from the oven and allowed to cool for at least 2 hours. The samples are weighed before and after the test, the weight loss being an indication of the corrosion.

The corrosion rate in mils per year is calculated using the formula: 15 mpy * (534) _ (WL) (MD) (SA) (T) where 20 E a weight loss in mg 3 MD 38 metal density in g / cm SA = specific surface area of the sample. 2 m T time in hours.

25

To provide baseline data, 7 day mild steel corrosion rates of mixtures of uninhibited zinc bromide and calcium bromide solutions with densities in the range 15.5-18.5 ppg are determined and are included in Table 1. These data demonstrate that corrosion rates range from a relatively low speed at low temperatures and densities to extraordinarily high speeds at high temperatures and densities.

35 __ 8301828 14

Table 1

Seven-day mild steel corrosion rates. Uninhibited mixtures of 19.2 ppg Znifr ^ / CaBr ^ and 1.4.2 5 ppg CaBr2

Corrosion Rate (ppy) Density

Fluid

(ppg) 121 ° C 149 ° C 177 ° C 204 ° C

15.5 1.0 1.7 4.1 13.3 10 16.5 4.4 7.6 17.6 28.3 17.5 22.3 24.8 40.4 65.6 18.5 55.5 85.4 94 .7 90.3. The seven-day corrosion rates are obtained at 204 ° C for 17.5 ppg zinc bromide / calcium bromide mixture (39.6% zinc bromide, 29.5% calcium bromide) containing 0.3% by weight of the inhibitors according to the invention. These data are recorded in Table 2.

20

Table 2

Seven-day corrosion rates 17.5 ppg mixture of zinc bromide /

^ calcium bromide 168 hours, 204 ° C

Inhibitor Corrosion Rate (MPY)

Ammonium thioglycolate 11.1 30 Calciurathioglycolate 10.7

Thioglycerol 17.3

Seven-day mild steel corrosion rates are measured for various solution mixtures containing 0.6 wt% ammonium thioglycolate and 1.0% calcium thioglycolate 8301828 «15, and these are shown in Tables 3 and 4. These data demonstrate significant reductions in corrosion rates in comparison with the uninhibited solutions, shown in Table I.

5

Table 3

Seven-day mild steel corrosion rates. Mixtures of 19.2 ppg ZnBr ^ / CaBr ^ (with 0.6 wt% ammonium thioglycolate) and 14.2 ppg CaB ^

Fluid density Corro.i «n.lhaid (npy)

(ppg) 121 ° C 149 ° C 177 ° C 204 ° C

15.5 3.1 3.5 3.4 6.6 16.5 6.6 5.2 7.1 19.8 17.5 16.3 21.1 13.0 23.3 18.5 28.9 32.7 40.6 68.7 20

Table 4

Seven-day mild steel corrosion rates. Mixtures of 19.2 ppg ^ ZnBr „/ CaBr„ (with 1.0 wt% calcium thioglycolate) and 14.2 ppg CaBr ^

Fluid density Corrosion rate (mpy)

^ PPS) 121 ° C 149 ° C 177 ° C 204 ° C

30 - - 15.5 - - - 3.1 16.5 - - - 6.2 17.5 - 26.0 18.5 - 95.3 35 830132a 16

Thirty-day corrosion tests demonstrate even better results. Tables 5 and 6 report thirty-day corrosion rates for mixtures of 19.2 ppg zinc bromide and calcium bromide (containing 0.6 wt% of ammonium thioglycolate and calcium thioglycolate, respectively) with 14.2 ppg calcium bromide. In all cases, corrosion rates of less than 10 mil per year are observed for solutions with densities less than about 18.0 ppg. The 10 mil per year corrosion rate at a thirty day trial period is generally accepted as an industrial standard for use in determining the acceptability of corrosion inhibition.

15 Table 5

Thirty-day mild steel corrosion rates. Mixtures of 19.2 ppg ZnBr ^ / CaBr ^ (with 0.6 wt% ammonium thioglycolate) and 14.2 ppg CaBr ^ 20

Fluid density Corrosion rate (mpy)

(ppg) _ 121 ° C_ 149 ° C 177 ° C 204 ° C

15.5 1.9 3.7 7.1 1.6 16.5 1.2 2.8 7.6 2.3 25 17.5 5.3 3.5 7.9 6.7 18.5 42.4 33.0 9 , 9 46.2

Table 6 30

Thirty-day mild steel corrosion rates. Mixtures of 19.2 ppg ZnB ^ / CaB ^ (with 1.0 wt% calcium thioglycolate) and 14.2 ppg CaBr2 35 8301828% 17

Fluid density Corrosion rate (mpy)

(ppg) 121 ° C 149 ° C 177 C 204 ° C

15.5 0.5 - - 2.9 16.5 1.0 - - 2.5 5 17.5 5.8 - 18.5 15.3 - - 111.1

Although the corrosion levels at a thirty day standard at 18.5 ppg are slightly above the desired level 10, they are nevertheless a significant improvement over the uninhibited solution (see Table 1). In addition, high density solutions ranging from 18.5 ppg and above are typically diluted to lower densities in actual use. Thus, the corrosion inhibitors 15 of the invention are effective in practically all technically useful conditions.

Table 7 shows seven-day and thirty-day mild steel corrosion rates for various high density fluid mixtures at different densities between 18.0 and 18.5 ppg showing the rapid increase in corrosion observed as the densities increase above 18.0 ppg · 25 Table 7

Seven-day and thirty-day mild steel corrosion rates. 18.1-18.5 mixtures of

19.2 ppg ZnBr ^ / CaBr ^ (with 0.6 wt% ammonium thioglycolate) and 14.2 ppg CaBr ^ at 204 C

30

Fluid density 7 days 30 days (ppg) _ (mpy) _ (mpy) 18.10 60.8 12.7 18.25 23.4 31.8 18.40 36.0 35.4 35 18.50 66.7 46.2 __ 8301828 ι 18

The effect of changing the inhibition level is demonstrated with. the data in Table 8, which shows thirty-day mild steel corrosion rates for 17.5 ppg mixtures inhibited with ammonium thio-5 glycolate, calcium thioglycolate and thioglycerol.

Table 8 10 Thirty-day mild steel corrosion rates »17.5 ppg ZnB ^ fluid at different inhibitor levels in the 19.2 ppg ZnBr2 / CaBr2

Corrosion rates (mpy) at different inhibitor levels in the 19.2 ppg ZnBr_ / 15 CaBr2 1 0.3 0.5 0.6 1.0 1.5 2.0 2.5 3.0

Inhibitor wt% wt% wt% wt% wt% wt% wt% wt%

Ammonium thi o-glycolate 5.2 - 6.7 - 16.1 - - -

Calcium thio glycolate - 9.3 - 3.5 - 7.0 - 5.2

Thioglycerol - 50.7 - 44.3 - 35.3

These data demonstrate the preferred and effective ranges for the inhibitors of the invention.

By using the inhibitors according to the invention, it is possible to achieve very low corrosion levels during long working periods. Table 9 provides nine-day mild steel corrosion data for mixtures of 19.2 ppg zinc bromide / calcium bromide (containing ammonium thioglycolate) with 1.42 ppg calcium bromide at four densities in the range of 15.5-18.5 ppg at 205 ° C. These data show that densities below about 18.0 ppg have extremely low corrosion rates. Only 35 above 18.0 ppg, the corrosion rate rises above the target of 10 mil a year. Although reduced levels of protection are obtained at densities above 18.0 ppg, a significant improvement is obtained compared to uninhibited 19.0 ppg fluids.

5

Table 9

Ninety-day mild steel corrosion rates. Winter mixtures of 19.2 ppg ZnB ^ / CaB ^ (with 0.6 wt% ammonium thioglycolate) and 14.2 ppg CaB ^

Fluid density Corrosion rate (mpy) (ppg) _ 204 ° C_ 15 15.5 3.9 16.5 2.1 17.5 5.0 18.5 56.7 The use of the composition according to the invention in the service of wells is shown in the following example .

Example VIII

When using a zinc bromide / calcium bromide fluid as a packing fluid in an oil well, its purpose is to minimize the pressure drop across the packing in the wellbore. The gasket serves to isolate the hydrocarbon-producing spacer from the remainder of the wellbore.

The advantage of using a clear fluid as a packing fluid is the minization of the solids in the drill ring. Solids will settle over time and build up on the gasket and make removal difficult. Therefore, cleaning of the well drill and all is 8301828. 20 surface tools of interest before the solid-free fluid is introduced into the wellbore. All equipment, pumps, pipes and storage tanks must be clean. The well drill must be scraped and rinsed with water. A fluid density is chosen to meet the requirements of the well (In many cases, a fluid density providing hydrostatic pressure in the well is applied to the packing 200 psi more than the formation pressure). The fluid is mixed with the base fluids (which preferably include a 19.2 ppg zinc bromide / calcium bromide fluid and a 15.0 ppg calcium bromide / calcium chloride or a 14.2 ppg calcium bromide fluid) containing corrosion inhibitors of the invention, and introduced into suitable storage tanks at the hearing place. At the appropriate time, the fluid 15 is introduced into the well ring by displacing the fluid in the well ring. The fluid will remain in the well until repair work is required to stimulate oil production from the well.

According to the invention, clear high density fluids are provided, which can be used safely and effectively as well completion, packing and perforation media. They are non-corrosive to equipment and personnel, remain stable and can be used sufficiently on a long-term basis. The solution fulfills a long-cherished well operating desire for clear solutions with high densities capable of being used at high well drilling operating temperatures.

30 8301828

Claims (12)

1. Corrosion inhibited clear high density compositions, capable of long-term use as a well operating fluid under elevated temperature conditions, characterized in that they consist of a solution of zinc bromide and calcium bromide in water with a density in the range 15.0-20.0 ppg and a corrosion inhibiting amount of ammonium thioglycolate, calcium thioglycolate, thioglycerol and mixtures thereof. 2. A composition according to claim 1, characterized in that the solution further contains calcium chloride. Composition according to claim 1 or 2, characterized in that the solution contains 0.01-5.0% by weight of said substance (s). Composition according to claim 1 or 2, characterized in that it contains ammonium thioglycolate. 5. Method of operating a wellbore injecting a high density fluid consisting of a solution of zinc bromide and calcium bromide in water at a density of 15.0-20.0 ppg into the well to apply sufficient hydrostatic pressure to to control the well, characterized in that a corrosion inhibiting amount of ammonium thioglycolate, calcium thioglycolate, thioglycerol and mixtures thereof is included in the high density fluid. A method according to claim 5, characterized in that the solution further contains calcium chloride. A method according to claim 5 or 6, characterized in that the solution contains about 0.01-5.0% by weight of the solution on said substance (s). 8. Process according to claim 5 or 6, characterized in that ammonium thioglycolate is used. 9. A method for inhibiting the elevated temperature corrosion potential of a clear high density solution of zinc bromide and calcium bromide in water having a density in the range of 15.0-20.0 ppg, characterized in that incorporates a corrosion inhibiting amount of ammonium thioglycolate, calcium thioglycolate, thioglycerol or mixtures thereof. Process according to claim 9, characterized in that the solution further contains calcium chloride. Process according to claim 9 or 10, characterized in that the solution contains 0.01-5.0% by weight of the solution of said substance (s). 12. Process according to claim 9 or 10, characterized in that ammonium thioglycolate is used. 15 8301828