GB2121397A

GB2121397A - Corrosion inhibited high density fluid compositions

Info

Publication number: GB2121397A
Application number: GB08310518A
Authority: GB
Inventors: Russell F Handy
Original assignee: Great Lakes Chemical Corp
Current assignee: Great Lakes Chemical Corp
Priority date: 1982-06-08
Filing date: 1983-04-19
Publication date: 1983-12-21
Also published as: DE3316677A1; GB8310518D0; NL8301828A; NO831363L; GB2121397B; CA1197673A; FR2528061A1; IL68362A0; DE3316677C2; FR2528061B1

Abstract

A corrosion inhibited, clear, high- density composition capable of long term use as a well servicing fluid under conditions of elevated temperature comprises a solution of zinc bromide, calcium bromide, and, optionally, calcium chloride in water having a density in the range of 15.0 to 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.

Description

SPECIFICATION Corrosion inhibited high density fluid compositions Background of the invention Field of the invention This invention relates to well bore servicing fluids and more particularly to a corrosion inhibited high density fluid that may be employed under rigorous service conditions.

Description of the prior art Drilling fluids have conventionally been used to maintain control during perforation, completion, or workover operations in oil and gas wells. Drilling fluids that have heretofore been employed for such purposes include mud, saltwater, water, or oil. The use of these fluids during drilling operations has per se been generally satisfactory and has actually enhanced drilling efficacy. However, the same materials have been employed during completion and workover operations with undesirable consequences.

For example, use of drilling muds during well perforation has frequentiy resulted in plugging of the perforations. Solids present in such drilling fluids have caused plugging and have made the completion process unduly complex, expensive and unreliable. Similarly, use of drilling muds and other drilling fluids as packer fluids has resulted in unwanted settling of solids. Moreover, drilling media may be somewhat corrosive under long-term, static operating conditions thereby further rendering them unsuitable for use other than as transitory drilling aids.

Among the efforts that have been made to overcome the foregoing problems has been the utilization of high density clear salt solutions. Clear fluids comprising solutions of zinc bromide/calcium bromide, and, optionally, calcium chloride having densities in the range of about 15.0 up to about 20.0 ppg are disclosed in U.S. Patents 4,292,1 83 and 4,304,677. While such solutions are highly satisfactory materials for use in the completion, packing and perforation of oil and gas wells, these solutions have not heretofore been usable where down-hole temperatures exceed about 3000F (1 49 OC) because of the high rate of corrosion of the iron and steel under such conditions. Thus, under high temperature conditions, it heretofore has only been possible to employ less desirable fluids such as modified drilling muds and the like.However, at high temperature, the solids contained in the drilling mud settle to the bottom of the well bore, solidify and make workover of the well far more costly and difficult to achieve.

The zinc ion in a 1 9.2 ppg clear fluid may only be maintained in solution by maintaining a pH in the range of about 1.0 to about 1.3, normally by the addition of excess hydrobromic acid. While pH's in this range achieve the desired solubility of the weighting salt, the resulting fluid is highly corrosive.

Even where a 1 9.2 ppg zinc bromide/calcium bromide solution is blended with calcium bromide/calcium chloride solution to produce ultimate fluids of lower density, the pH remains in the highly acidic area, never rising above about 5.5. The resulting fluids thus remain strongly acidic and very corrosive at temperatures exceeding 3000F.

U.S. Patent No.4,292,183 describes the use of a film-forming amine-based corrosion inhibitor.

However, the corrosion inhibition system disclosed in that patent is useful in the range only of up to about 3000F and cannot be used at the higher temperatures to which the subject invention is directed.

The prior art has suggested several corrosion inhibition systems for use in strong acid environments. However, only a few have proved to be satisfactory and fewer still have even been commercially employed. Thus, arsenic and/or arsenic compounds have been suggested to provide corrosion protection in strong acid solutions used to acidize new and producing wells. However, the toxic nature of arsenic compounds to humans and the "poisoning" of the catalysts used in refineries have made arsenic compounds undesirable.

A strong acid inhibitor is described in U.S. Patent No. 3,077,454. The inhibitor contains an organic ketone, an aliphatic aldehyde, and a fatty acid. Protection up to 3500F (1 770C) is suggested, but only for short periods of time (i.e., no longer than 1 6 hours).

A similar composition is described in U.S. Patent No. 3,634,270. A synergistic mixture of organic nitrogen and sulfur compounds that prevents the attack of the corrosive ingredient of the solution on metal is claimed. Application to industrial boiler and heat exchanger cleaning is suggested. Sulfur compounds selected from the group thiourea, allyl thiourea, sodium mercaptobenzothiazole, mercaptothioazoline, sodium thiocyanate and mixtures are disclosed to be particularly effective.

However, the disclosed operating range for the inhibitor systems included low temperatures no greater than 3000F and short time periods, no longer than 16 hours.

The literature contains references to the inhibition of acid corrosion of steel by thiourea and its derivatives. T. P. Hoar and R. D. Holliday in J. Appl. Chem. 3 (1 1): 502-13 (1953); B. Donnelly, T. C.

Downie, G. Grzeskowiak, H. R. Hamburg and D. Short in Corrosion Science, 14: 597-606 (1974); E.

Jackson and M. J. Wilkinson in British Corrosion J., 11: 208-11(1976); and M. B. Lawson in Corrosion, 36:493-7 (1980) are representative examples of the extensive literature.

U.S. Patent No. 4,100,100 describes the use of the combination of a quaternary pyridinium salt and an organic thiamide or water soluble thiocyanate to reduce the corrosion or iron and steel by an aqueous sour gas conditioning solution. The same mixture is described in U.K. Patent 2,027,686 as a corrosion inhibitor for aqueous brines in a well bore.

U.S. Patent 4,100,100 and U.K. 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 (i.e., 3500F (1 770C)) and short time periods (i.e., no more than 11 8 hours).

A corrosion inhibitor mixture suitable for use in calcium chloride and sodium chloride brines is described in U.S. Patent 3,215,637. The mixture is composed of sodium silicate, zinc chloride and sodium chromate. A mixture of inhibitors is required because no single composition proved effective in preventing general and localized corrosion. The effectiveness of the inhibitor composition was evaluated for longer time periods, 10 days, but at a low temperature, 680F (200 C).

A method of corrosion inhibition in well drilling 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 corrosion tests described are carried out in an atmosphere of air and oxygen at 1 850F for 20 hours.

The short term, low temperature protection of the foregoing prior art is of little value in an oil well completion, workover, or packer fluid.

Japan 75 03,741 describes an oxide film remover and corrosion inhibitor for copper and copper alloys comprising 2-20 volume percent of an aqueous solution of sodium or ammonium thioglycolate containing benzotriazole, sodium mercaptobenzothiazole and/or imidazole derivatives. Japan Kokai 76 92,735 describes metal rinsing compositions for cleaning air conditioner pipes or internal combustion radiators in shorter periods of time without corroding the piping by using water soluble thioglycolate, halogenated alkyl metal or halogenated ammonium thioglycolate. Japan Kokai Tokkyo Koho 79 120,007 describes compositions of coloring agents, wetting agents, amino acid derivatives and ammonium thioglycolate as jet printing inks having good storageability and corrosion inhibition.

None of the prior art has thus described a suitable corrosion inhibition system for high density fluids that permits their application under high temperature down-hole operating conditions.

Accordingly, a primary object of this invention is to provide a corrosion inhibition system for zinc bromide/calcium bromide solutions optionally containing calcium chloride permitting their use in oil and gas wells as a well-servicing fluids at temperatures as high as 4000F (2040 C).

A further object is to provide a composition of the character described that is successfully usable with solutions having densities in the range of about 15.0 up to about 20.0 ppg.

A still further object is to provide corrosion protection in such systems for extended periods of time up to 90 days or more.

A still further object is to provide a corrosion inhibitor that is sufficiently soluble in high density fluids that it can be'provided in a base solution which can be blended down to lower densities for field use.

Summary of invention The foregoing and other objects, advantages, and features of this invention may be achieved with a corrosion inhibited, clear, high density composition capable of long term use as a well servicing fluid under conditions of elevated temperature comprising a solution of zinc bromide and calcium bromide, and, optionally, calcium chloride in water having a density in the range of about 15.0 to about 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 at a level of about 0.01--5.00 percent by weight of the clear solution.

The present invention also includes novel methods for formulating such corrosion inhibited clear solutions as well as for their use in well servicing operations.

Description of the preferred embodiments As noted, those skilled in the art have long but unsuccessfully sought a corrosion inhibited zinc bromide/calcium bromide solution that would permit its use in down-hole operating temperatures as high as 4000 F. By employing a corrosion inhibitor in accordance with this invention, it is possible to achieve high density aqueous brines for use as completion, workover or packer fluids in deep, high pressure, high temperature oil, gas, or geothermal wells. The objectives of this invention are achieved with a corrosion inhibitor that is completely soluble in aqueous solutions of zinc bromide, calcium bromide and calcium chloride in the density range of about 15.0 ppg to 20.0 ppg.

In addition to having the desired solubility, the corrosion inhibitor must be able to provide significant corrosion inhibition at temperatures up to and including 4000 F. The corrosion protection must be maintained for extended periods of time of at least 30 days and preferably as much as 90 days or more. It is also important that the corrosion inhibition minimize pitting corrosion so that the small amount of corrosion that does occur is of a generalized rather than a highly specific nature. In addition, the corrosion inhibitor must be compatible with other chemical additives commonly employed with high density aqueous brine such as viscosifiers, suspending agents, and defoamers.

In accordance with this invention it has been found that ammonium thioglycolate, calcium thioglycolate, thioglycerol, or mixtures thereof permit these objectives to be achieved when provided in corrosion inhibiting amounts. Corrosion inhibited clear fluids in accordance with this invention not only may be satisfactorily employed at high temperatures in the well-servicing environment, but it has also been demonstrated that they may be used over relatively long periods of time of up to 90 days or more.

The formulation of zinc bromide/calcium bromide solutions, which may optionally contain calcium chloride as well, is not per se a part of the present invention. Satisfactory methods of preparing and blending such solutions with densities lying in the range of about 1 5.0 up to about 20.0 ppg are described in U.S. Patent 4,292,183 and U.S. Patent 4,304,677.

Typically such high density fluids are formulated with a base fluid of relatively high density (e.g., a zinc bromide/calcium bromide solution having a density of about 1 9.2 ppg containing about 54.7 weight percent zinc bromide and about 20.6 percent calcium bromide). Such a base solution may then be blended 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 in accordance with this invention may be added to the resulting clear fluid at substantially any point in the preparation cycle. Thus, it may 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 may be separately added to the blended solution at the well location.

Preferably, however, the corrosion inhibitor is provided in the base solution (e.g., 19.2 ppg zinc bromide/calcium bromide solution) in sufficient quantity to provide the ultimate level desired under all feasible conditions of use. Thus, sufficient inhibition is supplied to ensure adequate protection where the 1 9.2 ppg base solution is blended down to an ultimate density of about 15.0 ppg.

In general, the solution to be employed in a well-servicing operation should contain about 0.01- 5.0 percent of one or more of the corrosion inhibitors of this invention, preferably about 0.1-3.0 percent.

Where the corrosion inhibitors are provided in the high density base solution (e.g., 1 9.2 ppg zinc bromide/calcium bromide solution), the amount of corrosion inhibitor employed is preferably about 0.1-3.0 percent by weight of the base solution.

As indicated, the desired degree of corrosion inhibition may be obtained in accordance with this invention through the use of ammonium thioglycolate, calcium thioglycolate, thioglycerol or mixtures of these agents. The exact amount of agent to be employed is dependent upon the specific material that is used. Thus, where ammonium thioglycolate is employed, the preferred range is about 0.1-1.0 percent by weight of the base solution; for calcium thioglycolate, the preferred range is about 0.3-3.0 percent by weight of the base solution; and where thioglycerol is employed, the desired amount is about 0.1-0.5 percent by weight of the base solution.

It is especially preferred to employ ammonium thioglycolate as the corrosion inhibitor in accordance with this invention.

The corrosion inhibitors in accordance with this invention may be added in any convenient form.

Calcium thioglycolate may be supplied in solid or solution form. Thioglycerol is a liquid at room temperature and is normally used in that form. Ammonium thioglycolate is desirably employed as a 60% aqueous solution. Where used herein, the amounts of inhibitor are stated as amounts of active agent.

Exemplary corrosion inhibited high density fluids are disclosed in the following examples.

Example I A 19.2 ppg zinc bromide, calcium bromide solution was prepared in the following manner: The pH of an uninhibited 1 9.2 ppg zinc bromide/calcium bromide base solution was adjusted using a slurry of zinc oxide, calcium bromide and water or with 54% hydrogen bromide to 1.2+0.1. The density was adjusted to 1 9.20+0.05 ppg with 14.2 ppg calcium bromide. The solution was filtered through a medium sintered glass funnel coated with filter aid. The filtered, density- and pH-adjusted fluid was heated to 95+50C (2030F). The desired amount of corrosion inhibitor was added to the hot fluid. After stirring for 30 minutes, the solution was filtered hot through a medium sintered glass funnel coated with filter aid. The solution was allowed to cool to room temperature.

Example II An 18.0 ppg uninhibited zinc bromide/calcium bromide base solution was prepared by dissolving 224.9 pounds of zinc bromide and 306.1 pounds calcium bromide in 226.0 pounds of water. This prepared one barrel of 18.0 ppg zinc bromide/calcium bromide fluid. The pH was adjusted with a slurry of zinc oxide, calcium oxide and water or with 54% hydrogen bromide to 2.3+0.1. The density was adjusted to 1 8.0+0.05 with 1 4.2 ppg calcium bromide or with solid zinc bromide. The solution was filtered through a medium sintered glass funnel coated with filter aid. The filtered, density-adjusted fluid was heated to 95i50C (2030F). The desired amount of corrosion inhibitor was added to the hot fluid.After stirring for 30 minutes, the solution was filtered hot through a medium sintered glass funnel coated with filter aid. The solution was allowed to cool to room temperature.

Example Ill A 14.5 ppg uninhibited zinc bromide/calcium bromide base solution was prepared by dissolving 29.4 pounds of zinc bromide and 298.9 pounds of calcium bromide in 280.7 pounds of water. This prepared one barrel of 14.5 ppg zinc bromide/calcium bromide base solution. The pH was adjusted with a slurry of zinc oxide, calcium oxide and water to 6.0+0.1. The density was adjusted to 14.50+0.05 with 14.2 ppg calcium bromide or solid zinc bromide. The solution was filtered through a medium sintered glass funnel coated with filter aid. The filtered, density adjusted fluid was heated to 95+50C (2030F). The desired amount of corrosion inhibitor was added to the hot fluid. After stirring for 30 minutes, the solution was filtered hot through a medium sintered glass funnel coated with filter aid. The solution was allowed to cool to room temperature.

Example IV A 1 9.2 ppg zinc bromide/calcium bromide solution was prepared containing 1.0 weight percent ammonium thioglycolate by the procedure of Example I. One barrel of a 17.5 ppg blend of uninhibited 19.2 ppg zinc bromide/calcium bromide was prepared by mixing 0.660 barrels (532.2 pounds) of inhibited 19.2 ppg zinc bromide, calcium bromide and 0.340 barrels (202.8 pounds) of 14.2 ppg calcium bromide. After stirring for 30 minutes, the fluid was filtered through a medium sintered glass funnel coated with filter aid.

Example V A 19.2 ppg zinc bromide/calcium bromide solution was prepared containing 1.0 weight percent calcium thioglycolate by the procedure of Example I. One barrel of a 1 5.5 ppg zinc bromide/calcium bromide, calcium chloride solution was prepared by mixing 0.119 barrels (96 pounds) of inhibited 19.2 ppg zinc bromide/calcium bromide solution with 0.881 barrels (555.0 pounds) of 15.0 ppg calcium bromide, calcium chloride solution. After stirring for 30 minutes, the fluid was filtered through a medium sintered glass funnel coated with filter aid.

Example VI A 1 9.2 ppg zinc bromide/calcium bromide solution was prepared containing 2.0 weight percent thioglycerol by the procedure of Example I. One barrel of 16.5 ppg zinc bromide/calcium bromide was prepared by mixing 0.460 barrels (370.9 pounds) of inhibited 19.2 ppg zinc bromide/calcium bromide solution with 0.540 barrels (322.1 pounds) of 14.2 ppg calcium bromide solution. After stirring for 30 minutes, the fluid was filtered through a medium sintered glass funnel coated with filter aid.

Example VII A 1 9.2 ppg zinc bromide/calcium bromide solution was prepared containing 0.5 weight percent ammonium thioglycolate and 0.5 weight percent thioglycerol using the procedure of Example I. One barrel of 18.5 ppg zinc bromide/calcium bromide/calcium chloride fluid was prepared by blending 0.833 barrels (671:7 pounds) of inhibited 19.2 ppg zinc bromide, calcium bromide and 0.167 barrels (105.2 pounds) of 15.0 ppg calcium bromide, calcium chloride solution. After stirring for 30 minutes, the fluid was filtered through a medium sintered glass funnel coated with filter aid.

The effectiveness of the corrosion inhibitors of this invention has been demonstrated experimentally using the following test procedure. The density of a pH adjusted uninhibited base fluid was first determined. The solution was then heated to 95+50C, and the desired amount of corrosion inhibitor added to the hot uninhibited base fluid. The solution was filtered hot through a medium sintered glass funnel coated with filter aid, and the solution allowed to cool to room temperature. The base fluid was then blended to the desired density according to blending tables, and the blended fluid was filtered through a medium sintered glass funnel coated with filter aid. The fluid density at 600F was determined, and the pH of the fluid measured using a pH meter.

The test fluid was then added to a high temperature aging cell so as to cover a test coupon. The test cells were pressurized with nitrogen and placed in an oven for the desired time and temperature.

At the end of the test, the test cells were removed from the oven and allowed to cool for at least two hours. The coupons were weighed before and after the test, with the weight loss being an indication of corrosion.

The corrosion rate in mils per year was calculated using the formula: (534) (WL) mpy= (MD) (SA) (T) where WL=weight loss in mg MD=metal density in g/cm3 SA=coupon surface area in in2 T=time in hours To provide base line data, seven day mild steel corrosion rates of blends of uninhibited zinc bromide and calcium bromide solutions having densities in the range of 1 5.5 ppg up to 1 8.5 ppg were determined and are given in Table I. These data demonstrate that corrosion rates vary from a relatively low rate at low temperatures and densities to extremely high rates at high temperatures and densities.

Table I Seven day mild steel corrosion rates uninhibited blends of 19.2 ppg ZnBr2/CaBr2 and 14.2 ppg CaBr2 Fluid Corrosion rate (mpy) density (ppg) 2500F 3000F 350do 4000F 15.5 1.0 1.7 4.1 13.3 16.5 4.4 7.6 17.6 28.3 17.5 22.3 24.8 40.4 56.6 18.5 55.5 85.4 94.7 90.3 Seven day corrosion rates were obtained at 4000F for 17.5 ppg zinc bromide/calcium bromide blend (39.6 percent zinc bromide, 29.5 percent calcium bromide) containing 0.3 weight percent of the inhibitors of this invention. These data are reported in Table II.

Table II Seven day corrosion rates 17.5 ppg blend of zinc bromide/calcium bromide 168 hours, 4000F Inhibitor Corrosion rate (mpyJ Ammonium Thioglycolate 11.1 Calcium Thioglycolate 10.7 Thioglycerol 17.3 Seven day mild steel corrosion rates were measured for various solution blends containing 0.6 percent ammonium thioglycolate and 1.0 percent calcium thioglycolate are given in Tables Ill and IV.

These data demonstrated significant reductions in corrosion rates in comparison to the uninhibited solutions reported in Table I.

Table Ill Seven day mild steel corrosion rates blends of 19.2 ppg ZnBr2/CaBr2 (containing 0.6 wt.% ammonium thioglycolate and 14.2 ppg CaBr2 Fluid density Corrosion rate (mpy) (ppg) 250 OF 300 OF 350 OF 400 OF 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 Table IV Seven day mild steel corrosion rates blends of 19.2 ppg ZnBr2/CaBr2 (containing 1.0 wt.% calcium thioglycolate) and 14.2 ppg CaBr2 Fluid density Corrosion rate (mpyJ (ppgJ 250 OF 300 OF 350 OF 400 OF 15.5 - - - 3.1 16.5 - - - 6.2 17.5 - - - 26.0 18.5 - - - 95.3 Thirty day corrosion tests demonstrate even better results.Tables V and VI report respectively thirty day corrosion rates for blends of 1 9.2 ppg zinc bromide and calcium bromide (containing 0.6 weight percent respectively of ammonium thioglycolate and calcium thioglycolate) with 14.2 ppg calcium bromide. In all cases, corrosion rates of less than 10 mil per year were observed for solutions having densities less than about 18.0 ppg. The 10 mil per year corrosion rate on a thirty day test period is generally accepted as an industry standard for use in determining the acceptability of corrosion inhibition.

Table V Thirty day mild steel corrosion rates blends of 19.2 ppg ZnBr2/CaBr2 (containing 0.6 wt.% ammonium thioglycolate) and 14.2 ppg CaBr2 Fluid density Corrosion rate (mpy) (ppg) 250 OF 300 OF 350 OF 400 OF 15.5 1.9 3.7 7.1 1.6 16.5 1.2 2.8 7.6 2.3 17.5 5.3 3.5 7.9 6.7 18.5 42.4 33.0 9.9 46.2 Table VI Thirty day mild steel corrosion rates blends of 19.2 ppg ZnBr2/CaBr2 (containing 1.0 wt.% calcium thioglycolate) and 14.2 ppg CaBr2 Fluid density Corrosion rate (mpy) (ppg) 250 OF 300 OF 350 OF 400 OF 15.5 0.5 - - 2.9 16.5 1.0 - - 2.5 17.5 5.8 - - 18.5 15.3 - - 111.1 While the corrosion levels on a 30 day standard at 18.5 ppg fall somewhat above the desired level, they nevertheless are a significant improvement in comparison with the unhibited solution. (See Table I). Moreover, high density solutions ranging at the 18.5 ppg level and above are typically blended down to lower density ranges in actual use. Thus, the corrosion inhibitors of this invention are effective at virtually all commercially useful conditions.

Table VII gives seven and 30 day mild corrosion rates for various high density fluid blends at various densities between 18.0 and 1 8.5 ppg demonstrating the rapid increase in corrosion experienced as densities increase above 18.0 ppg.

Table VII Seven and thirty day mild steel corrosion rates 18.1 to 18.5 blends of 19.2 ppg ZnBr2/CaBr2 (containing 0.6 wt.% ammonium thioglycolate) and 14.2 ppg CaBr2at4000F Fluid density 7 Day 30 Day (ppg) (mpy) (mpy) 18.10 60.8 12.7 18.25 23.4 31.8 18.40 36.0 35.4 18.50 68.7 46.2 The effect of altering the inhibitor level is demonstrated by the data in Table VIII which shows thirty day mild steel corrosion rates for 17.5 ppg blends inhibited with ammonium thioglycolate, calcium thioglycolate and thioglycerol.

Table VIII Thirty day mild steel corrosion rates. 17.5 ppg ZnBr2 fluid, at various inhibitor levels in the 19.2 ppg ZnBrJCaBr2 Corrosion rates (mpy) at various inhibitor levels in the 19.2 ppg ZnBr2/CaBr2 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 thioglycolate 5.2 - 6.7 - 16.1 - - Calcium thioglycolate - 9.3 - 3.5 - 7.0 - 5.2 Thioglycerol - 50.7 - 44.3 - 35.3 - These data demonstrate the preferred and operative ranges for the inhibitors of this invention.

By using the inhibitors of this invention, it is possible to achieve very low levels of corrosion throughout long periods of operation. Table IX gives ninety day corrosion dates on mild steel for blends of 1 9.2 ppg zinc bromide/calcium bromide (containing ammonium thioglycolate) with 14.2 ppg calcium bromide at four densities in the range of 15.5 to 18.5 ppg at 4000 F. These data show that, at densities below about 1 8.0 ppg, extremely low corrosion rates are experienced. Only above 18.0 ppg does the corrosion rate rise above the 10 mil per year objective. Although reduced levels of protection are obtained at densities above 18.0 ppg, substantial improvement is obtained as compared to uninhibited 19.0 ppg fluids.

Table IX Ninety day mild steel corrosion rates winter blends of 19.2 ppg ZnBr2/CaBr2 (containing 0.6 wt.% ammonium thioglycolate) and 14.2 ppg CaBr2 Fluid density Corrosion rate (mpy) (ppg) 400"F 15.5 3.9 16.5 2.1 17.5 5.0 18.5 56.7 Utilization of the composition of the present invention in servicing well bores is shown in the following example.

Example VIII When a zinc bromide/calcium bromide fluid is used as a packer fluid in an oil well, its purpose is to minimize the pressure drop across the packer in the wellbore. The packer serves to isolate the hydrocarbon producing interval from the remainder of the wellbore. The advantage of using a clear fluid as a packer fluid is the minimization of solids in the well annulus. Solids will settle out over time and build up on the packer making removal of the packer difficult. Therefore, cleanup of the wellbore and all surface equipment before the solids free fluid is placed in the wellbore is important. All equipment, pumps, lines and storage tanks must be clean. The wellbore must be scraped and flushed with water.A fluid density is chosen to meet the requirements of the weil. (In many cases, a fluid density providing a hydrostatic pressure in the wellbore at the packer 200 psi greater than the formation pressure is employed). The fluid is blended from the base fluids (which, preferably, include a 1 9.2 ppg zinc bromide/calcium bromide fluid and a 1 5.0 ppg calcium bromide/calcium chloride or a 1 4.2 ppg calcium bromide fluid) containing corrosion inhibitors in accordance with this invention, and placed in appropriate storage tanks at the rig site. At the proper time, the fluid is placed in the well annulus by displacement of the fluid in the well annulus. The fluid will remain in the well until remedial work is required to stimulate oil production from the well.

In accordance with this invention there are provided clear high density fluids which may be safely and effectively employed as well-completion, packing and perforating media. They are non-corrosive to equipment and personnel, remain stable and may be satisfactorily used on a long term basis. The solution should fulfill a long felt want in the well service field for clear solutions having high densities that are capable of being employed at high well bore operating temperatures.

Claims

1. A corrosion inhibited, clear, high density composition capable of long term use as a well servicing fluid under conditions of elevated temperature comprising: a solution of zinc bromide and calcium bromide in water having a density in the range of about 15.0 to about 20.0 pounds per gallon; and a corrosion inhibiting amount of a member selected from the group consisting of ammonium thioglycolate, calcium thioglycolate, thioglycerol, and mixtures thereof.

2. A composition, as claimed in claim 1, wherein the solution further comprises calcium chloride.

3. A composition, as claimed in claims 1 or 2, wherein the solution comprises about 0.01--5.0 percent of the member by weight of the solution.

4. A composition, as claimed in claims 1 or 2, wherein the member is ammonium thioglycolate.

5. In a method for servicing a well bore wherein a high density fluid comprising a solution of zinc bromide and calcium bromide in water having a density of about 15.0 up to 20.0 pounds per gallon is injected into the well to exert sufficient hydrostatic pressure to control the well, the improvement comprising incorporating in the high density fluid a corrosion inhibiting amount of a member selected from the group consisting of ammonium thioglycolate, calcium thioglycolate, thioglycerol, and mixtures thereof.

6. A method, as claimed in claim 5, wherein the solution further comprises calcium chloride.

7. A method, as claimed in claims 5 or 6, wherein the solution comprises about 0.01--5.0 percent of the member by weight of the solution.

8. A method, as claimed in claims 5 or 6, wherein the member is ammonium thioglycolate.

9. A method of 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 about 15.0 to about 20.0 pounds per gallon comprising the step of incorporating therein a corrosion inhibiting amount of a member selected from the group consisting of ammonium thioglycolate, calcium thioglycolate, thioglycerol, and mixtures thereof.

10. A method, as claimed in claim 9, wherein the solution of further comprises calcium chloride

11. A method, as claimed in claims 9 or 10, wherein the solution comprises about 0.01--5.0 percent of the member of weight of the solution.

12. A method, as claimed in claim 9 or 10, wherein the member is ammonium thioglycolate.