GB1588566A - Method of scavenging sulphide - Google Patents

Description

(54) A METHOD OF SCAVENGING SULPHIDE (71) We, HALLIBURTON COMPANY, a corporation organized under the laws of the State of Delaware, United States of America, of 1015 Bois d'Arc Street, P.O. Drawer 1431, Duncan, Oklahoma 73533, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: .The present invention is concerned with the scavenging of sulphide from liquids.

Liquids used in wells penetrating subterranean formations (for example, drilling, completing or servicing liquids used in oil wells or gas wells), liquids produced from and make-up liquids used in such wells, and liquids in sewerage systems frequently contain sulphides, such as hydrogen sulphide.

Hydrogen sulphide is poisonous and promotes corrosion of steel pipes and tubes which come into contact with liquids containing it. It has therefore been proposed to remove hydrogen sulphide from such liquids either as it is formed or after the liquid has been contaminated by hydrogen sulphide. This process is known as "scavenging".

It has been proposed in U.S. Patent 3928211 to use zinc hydroxide, zinc carbonate or basic zinc carbonate as the scavenging agent. We have found that these compounds tends to form an insoluble precipitate in which the zinc is unavailable for reaction with hydrogen sulphide, and tend to adversely affect the rheological properties of some liquids, particularly where the liquid contains a clay. Typical adverse effects on the rheological properties include undesired thickening or gelling of the liquid and increased liquid loss.

We have now developed an improved class of scavenging agents for this purpose.

According to the invention, there is provided a method of scavenging sulphide from a liquid having a pH of 5 to 12, in which there is used as the scavenging agent a complex formed between at least one zinc compound and an organic chelating agent, the complex having a stability constant of 10 to 16.

The scavenging agents used in the method according to the invention have little or no adverse effect on the rheology of the liquid, for example, they do not cause flocculation of clays in the liquid, and the stability constant is such that insoluble zinc hydroxide or zinc oxide is not formed to any appreciable extent.

The complex has a stability constant of 10 to 16, as mentioned above. The term "stability constant" is defined in 'Organic Sequestering Agents" by S. Chaber and A.E. Martell; John Wiley and Sons, Inc., New York, and in "Stability Constants of Metal-Ion Complexes" by L.G. Sillen and A.E. Martell; Metcalf and Cooper Limited, London (1964).

The scavenging agent used in the method according to the invention may be added to the liquid as a previously prepared complex (either in liquid concentrate, or dry powder form or pre-mixed with water) or. preferably, the complex may be formed in situ by reaction of the zinc compound with the chelating agent in the desired ratio in the liquid to be treated. In the latter case, when the liquid to be treated is oil-based (or a dispersion, such as an emulsion, of an oil), it is sometimes desirable to add the zinc compound in the form of a solution or dispersion in oil.

When the complex is formed in situ, the chelating agent is preferably present in excess of the amount needed to completely chelate the available.zinc, whereby precipitation of any clays in the liquid being treated and adsorption of the zinc compound on solids in the liquid being treated, which take place when an ionic zinc compound is used, are avoided. when the liquid being treated is a drilling fluid of high solids content, the zinc compound and the chelating agent should be added slowly and thoroughly mixed with the fluid before it is circulated in the well.

The zinc compound, which preferably contains no anions capable of causing flocculation of any clays in the liquid, may be, for example, a formate, acetate, chloride, bromide, iodide, chlorate, bromate, nitrate, sulphate, sulphoxylate, hydrosulphite or silicofluoride salt. The salt may be water-soluble, for example, zinc sulphate or zinc chloride, although it is possible to use less soluble compounds such as zinc carbonate or basic zinc carbonate, even though these involve longer reaction times. It is therefore preferred that when these less soluble compounds are used, the complex is formed before adding it to the liquid.

When a zinc carbonate is used, the carbonate ions may be removed from the complex in order to avoid flocculation of clays encountered in the liquid to be treated.

Particularly when hydrogen sulphide and oxygen are both present in the liquid (such as a drilling fluid), the zinc compound is preferably zinc hydrosulphite, which is preferably added to the liquid in the form of a suspension or slurry in an organic carrier liquid, which carrier-liquid should be substantially unreactive with the zinc compound, oxygen, hydrogen sulphide and additives to the liquid (such as conventional well fluid additives). Preferred carrier liquids include aliphatic hydrocarbons, aromatic hydrocarbons, substituted hydrocarbons or mixtures thereof, such as mineral oils, diesel oils and kerosene, which should have a viscosity sufficient to suspend the zinc hydrosulphite (and any other additives). A preferred viscosity is at least five centipoise; it may be necessary to add unreactive thickeners, such as silica or polymers.Other optional additives include emulsifiers, surfactants, dispersing agents and modifiers for the pour point, flammability, volatility and colour.

The abovementioned zinc hydrosulphite preferably has a fine particle size (for easier suspension and faster reaction) and is preferably pure (e.g. at least 80% pure). The zinc hydrosulphite, which may be used together with other zinc compounds and/or hydrosulphites, is preferably present in the carrier liquid in a concentration of from 10 to 90% (more preferably 15 to 75% by weight).

For scavenging sulphides from oil based liquids (that is a liquid containing at least one oil or organic liquid phase such as a normally liquid hydrocarbon) or from oil-external emulsion fluids, a preferred scavenger is basic zinc carbonate. This scavenger can be added directly to the liquid as a finely divided particulate material or suspended in a slurry using an organic carrier liquid as described above. For the treatment of oil-external emulsion liquids, the scavenger can be suspended in an aqueous or an organic carrier liquid. The basic zinc carbonate is preferably suspended in the carrier liquid in concentrations of from 10 to 90% by weight more preferably 15 to 75%. Other additives can be used to modify the properties of the carrier liquid, for example, to modify the viscosity, flammability, volatility of colour, as referred to above.

When using zinc hydrosulphite or basic zinc carbonate, as described above, it is not necessary that the zinc compound be chelated with an organic chelating agent.

The chelating agent is preferably a low molecular weight compound having carboxylic acid and/or amino functional groups, for example, a compound having at least one tertiary amine group and at least two carboxyl groups, or a salt thereof, a polyfunctional amine or a hydroxycarboxylic acid.

The following are examples of such chelating agents, the stability constant of the corresponding complex being in parenthesis: dithiotartaric acid (15.85); triethylene tetramine (12.1); ethylene-bis-alpha,alpha'-(2-amino-methyl)-pyridine (11.5); ss, p', ss", triaminotriethylamine (14.65); tetrakis (2-amino-ethyl)-ethylene diamine; a,ss-diamino propionic acid (11.5); p-mercaptoethyliminodiacetic acid (15.92); ethylene diamine-N, N'-diacetic acid (11.1); ethylene diamine-N, N-diacetic acid (11.93); ethylene-bis-N, N'-2 (aminomethyl)-pyridine N-N'-diacetic acid (15.2); N-hydroxy ethylethylene diamine tetraacetic acid (HEDTA) (14.5); ethylene diamine N-N' dipropionic N-N'diacetic acid (14.5); hydroxy acetic acid; and nitrilotriacetic acid (NTA) (11.0). The preferred chelating agent is the NTA which is especially effective for reacting with or absorbing high ratios of hydrogen sulphide with little or no adverse effect on the drilling fluid rheology. Other chelating agents with structures similar to NTA and a stability constant near that of NTA are also effective under typical drilling conditions. The zinc NTA complex is also preferred because it is effective over a wide pH range and reacts practically instantaneously on addition to a drilling fluid to effectively inactivate hydrogen sulphide to prevent stress cracking of metals and liberation of hydrogen sulphide at the surface.

When the complex is formed in situ, the organic chelating agent should be combined with the soluble zinc compound in a certain weight ratio depending on its sequestering ability.

For NTA and similar chelants the preferred range is about 4:1 to 99:1, more preferably from about 4:1 to 9:1.

In the scavenging agent according to the invention, zinc effectively stops stress cracking of ferrous metals without plating out on the metal and causing galvanic corrosion.

Furthermore, zinc does not cause stress cracking through secondary oxygen reactions. Zinc sulphide precipitates out when the liquid contains sulphides. This precipitate does not adversely affect the well fluid rheology and can be readily removed by conventional methods such as centrifuging, filtering or settling in mud pits.

The scavenging agents according to the invention are effective over a wide pH range (from 5 to 12), but they are preferably used in the pH range of about 6 to 11. The scavenging agents can be used alone or in conjunction with conventional well fluid additives, even other sulphide scavenging agents. The scavenging agents of this invention can effectively remove hydrogen sulphide concentrations from only trace amounts like one ppm up to large amounts such as thousands of ppm or more by simply adding the amount of chelate needed to stoichiometrically react with the sulphide.

In a preferred method according to the invention, the complex is added to a drilling fluid which is preferably an aqueous dispersed or nondispersed fluid. The drilling fluid can also be an oil-based or emulsion fluid. The oil can be any normally liquid hydrocarbon such as aliphatic hydrocarbon, an aromatic hydrocarbon or mixtures thereof. The fluid is typically circulated in the well during drilling and other operations so that the concentration of complex should be monitored to maintain a certain concentration, preferably from about several parts per million (ppm) to several percent, depending on the likely amount of hydrogen sulphide present. Normally, a concentration of up to about five pounds per barrel (ppb) of fluid will be sufficient.The fluis should also be monitored to indicate the presence of any hydrogen sulphide or sulphide ions which would indicate that more complex should be added or that the concentration of the complex in the liquid should be increased. As a safeguard where hydrogen sulphide is not likely to be a severe problem, chelate' concentrations of about 0.25 to 0.5 ppb (1.258 to 2.516 grams per litre) should be used to scavenge out trace amounts of sulphides that may not be detected by tests on the surface.

In order that the invention may be more fully understood, that following Examples are given by way of illustration only.

EXAMPLES Thirty three 350 ml. samples of a water-based drilling fluid were formulated using water containing the following additives: 0.9 ppb NaCI. 1.75 ppb CaCO3. 16 ppb Wyoming bentonite. 28 ppb Southern bentonite. 4 ppb chrome lignosulphonate dispersant and a fluid loss additive. The pH was adjusted to 9.0 with NaOH. Various sulphide scavenging agents were added in the quantities indicated in the following Table 1. (One ppb is one pound per 42-gallon barrel of total fluid and is equal to one gram per 350 millilitres of fluid or about 3 grams per litre of fluid).

When the fluid contained a zinc-containing scavenging agent, the amount of the latter was such that each fluid contained the same molar concentration of zinc metal.

The effect of some additives on stress cracking was evaluated using prestressed steel bearings in some of the drilling fluids at 1500F with rolling; i.e.. ageing or hot rolling the sample for the time indicated in the folloiwng Table 1.

The majoritv of the scavenging agents were synthesized by the following steps: 1. Equimolar quantities of the chelating agent and zinc salt were stirred in a minimum amount of water for 30 minutes.

2. The solution was basified (pH 8-9) with KOH.

3. Absolute ethanol was added to precipitate the chelates. which were filtered and dried.

Zinc NTA complexes were prepared by reacting sodium NTA (NTANa3) with each of the following: ZnCl2 and ZnSO4. These complexes were tested both as slurries and as oven-dried solids.

Some of the fluids were treated with H2S. as shown in Table 1. When hydrogen sulphide treatment was used. the H2S was generated from 0.1 M sodium sulphide (Na2S) with sulphuric acid and the H2S was bubbled into the drilling fluid sample in a Waring blender.

For each 100 ml of 0.1 M Na,S used. 970 ppm of H.S was generated for reaction in the drilling fluid. Hydrogen sulphide was bubbled through the sample until H.S emission was detected by lead acetate paper indicating saturation of the mud with H,S.

The stability of complexes of lead. zinc. and copper vary according to the metal. chelating agent. pH. etc. With the zinc metal ion chelated by nitrilotriacetic acid (NTA). the compounds had little detrimental effect on the drilling fluid properties. Hydrogen sulphide reacts readily with the Cu, Pb, and Zn chelates of NTA, precipitating the sulphide ion as insoluble CuS, PbS, ZnS. Although these compounds are very effective H2S scavengers, the following results show that only the ZnNTA also prevented sulphide stress cracking of prestressed steel bearings and has no detrimental effects on the drilling mud. In fact, the bearings placed in mud treated with PbNTA and CuNTA often crack before bearings in untreated mud.

The zinc lignosulphonates containing zinc are effective in preventing stress cracking in bearings. However, foaming is a severe problem and the zinc concentration is very low in this complex.

Inorganic compounds of zinc (sodium zincate) and lead (sodium plumbite) are effective H2S scavengers. However, these compounds fail to prevent sulphide stress cracking of bearings in treated mud.

Rheology, fluid loss and pH for each sample was measured using a Fann type direct reading viscometer, fluid loss cell or pH meter according to API method 13B. The tests indicated that zinc NTA complexes gave acceptable results in preventing stress cracking of steel bearings; however, preblended and purified ZnNTA gave the best results.

TABLE 1 Identification of Samples Sample No. Treatment or Additive 1,3,6,8,10,12 Base Fluid without treatment or additive 2,5,9,11,13 2.86 ppb ZnNTA 4 24 ppb of 15% zinc lignosulphonate solution 5 3.98 ppb zinc ethylene diamine tetraacetic acid salt (ZnEDTA) 7 1.12 ppb basic zinc carbonate (ZnC03) 14,19 2 ppb ZnNTA 15 Base Fluid with H2S treatment.

no additive.

16 2 ppb ZnCO3 17 Base Fluid without treatment or additive 18 Base Fluid with H25 treatment, no additive 20 2 ppb copper carbonate (CuC03) 21 2 ppb ZnEDTA 22 2 ppb ZnDET (diethylene triamine) 23 2 ppb Zn TETA (Triethylene tetra amine) TABLE 1 (Continued) Sample No. Treatment or Additive 24 Base Fluid with 1 ppb sulphides or 2,494 ppm sulphides. Ageing by hot rolling at 1500F for 16 hours. This base mud contains 4.5 ppb VC-10 chrome ligno sulphonate dispersant.

25 Same as Sample 24 with 2.08 ppb basic Zn carbonate containing 45% zinc.

26 Same as Sample 24 with 8.66 ppb ZnNTA containing 21% zinc.

27 Base fluid without treatment or additive.

28 Same as Sample 24 with 8.6 ppb ZnSO4 and Na3NTA mixture containing 21% zinc.

29 Standard base fluid (as Sample 24 without sulphides).

30 Same as Sample 29 with 5 ppb of a mixture of 35:65 weight ratio of ZnSO4:Na3NTA.

31 Same as Sample 30 with the ratio of 40:60 32 Same as Sample 30 with the ratio of 45:55 33 Same as Sample 30 with the ratio of 50:50.

Various properties of the above Samples are indicated in the following Tables 2 to 11. TABLE 2 Effect of additive on rheology and reaction with hydrogen sulfide Initial rheology and H2S uptake Set 1 Set 2 Set 3 Sample No. 1 2 3 4 5 6 7 Apparent Viscosity 19.5 16.5 19.5 47.5 28.5 21.5 21.0 600 Reading 39 33 39 95 57 43 42 300 Reading 24 20 26 72 40 28 27 Plastic Viscosity (PV) 15 13 13 23 17 15 15 Yield Point (YP) 9 7 13 49 23 13 12 Gel Strength (10 sec.) 3 3 - - - 5 4 Gel Strength (10 min.) - - - - - 23 27 Vol. of 0.1 M Na2S (ml) absorbed 15 217 12 * 52** 14 24 Final Temp. F 80 102 86 - - 80 90 Final pH - - 8.1 6.5 8.1 - *Foamed **Gelled Samples 3,4 and 5 show that zinc lignosulfonate and zinc ethylene diamine tetraacetic acid salt (ZnEDTA) caused excess foaming and gelation of the drilling fluid.

Samples 6 and 7 show that basic zinc carbonate has a very low reactive capacity for H2S.

TABLE 3 Rheology after reaction with H2S Set 1 Sample No. 1 2 Apparent Viscosity 18.5 17.5 600 Reading 37 35.

300 Reading 22 21 Plastic Viscosity (PV) 15 14 Yield Point (YP) 7 7 Gel Strength (10 sec.) 4 4 Gel Strength (10 min.) 12 25 API Filtrate (ml/30 min.) 8 8 These tests show that the ZnNTA chelate had a high reactive capacity for H2S with good rheology and fluid loss.

TABLE 4 Initial rheology and fluid loss Set 1 Sample No. 8 9 Apparent Viscosity 18 16.5 600 Reading 36 33 300 Reading 23 20 Plastic Viscosity (PV) 13 13 Yield Point (YP) 10 7 Gel Strength 10 sec.) 3 6 Gel Strength 10 min.) 14 38 API Filtrate (ml/30 min.) 7.1 6.4 TABLE 5 Rheology and fluid loss after hotrolling 16 hours at 1500F.

Set 1 Sample No. 8 9 Apparent Viscosity 18.5 19.5 600 Reading 37 39 300 Reading 22 22 Plastic Viscosity (PV) 15 17 Yield Point (YP) 7 5 Gel Strength (10 sec.) 3 3 Gel Strength (10 min.) 9 3 API Filtrate (ml/30 min.) 6.6 7.6 These tests show that drilling fluid with ZnNTA has good rheology and fluid loss after aging or hotrolling.

TABLE 6 Initial rheology Set 2 Set 4 Sample No. 10 11 12 13 Apparent Viscosity 22 22.5 18 19 600 Reading 44 45 36 38 300 Reading 37 39 22 25 Plastic Viscosity 7 6 14 13 Yield Point (YP) 30 33 8 12 Gel Strength (10 sec.) 5 17 6 13 Gel Strength (10 min.) 14 82 27 58 TABLE 7 Rheology, fluid loss, and H2S uptake after hotrolling 16 hours at 3250F Set 2 Sample No. 10 11 Apparent Viscosity 46.5 38 600 Reading 93 76 300 Reading 62 59 Plastic Viscosity (PV) 31 - 17 Yield Point (YP) 31 42 Gel Strength (10 sec.) 14 4 Gel Strength 10 min.) 244 45 API Filtrate (ml/30 min.) 12.7 13.5 Vol. of 0.1 M Na2S (ml) absorbed 19 116 These tests show that drilling mud with ZnNTA has good rheology and fluid loss after reacting with H2S and aging.

TABLE 8 Rheology and H2S uptake after aging for 8 days at 780F Set 4 Sample No. 12 13 Apparent Viscosity 19 23.5 600 Reading 38 47 300 Reading 24 29 Plastic Viscosity (PV) 14 18 Yield Point 10 11 Gel Strength (10 sec.) 4 5 Gel Strength (10 min.) 21 26 Vol. of 0.1 M Na2S (ml) absorbed 22 60 These tests show that drilling mud with ZnNTA has good rheology after heat aging for extended periods with H2S reaction.

TABLE 9 Set I - Rolled 16 hours Sample No. Description of Bearing 14 Medium dark; rough surface. no cracks 15 Dark; smooth surface; cracked 16 Dark; smooth surface; cracked Set 2 - Rolled 5 hours with 2 Bearings 20 Dark color; one cracked 21 Black; no cracks 22 Black; no cracks 23 Dark; no cracks Set 2 -- Rolled 22 Hours 17 Both black and cracked 18 Both black and cracked 19 Both dark; no cracks 20 Copper coated; cracked 21 Both black; one cracked 22 Both black; one cracked 23 Both black; one cracked TABLE 10 Sulfide Scavengers Effectiveness Comparison In Situ Formation Initial Aging Initial Aging Initial Aging Initial Aging Initial Aging Sample No. 24 25 26 27 28 Apparent Viscosity 8 11 12 10 18 15 13 - 22 15 600 RPM 15 22 21 20 33 30 26 44 29 300 RPM 8 11 12 12 25 16 18 - 30 17 Plastic Viscosity 7 11 9 8 8 14 8 - 14 12 Yield Point (&num;100 ft.2) 1 0 3 4 17 2 10 - 16 5 Initial Gel 1 1 1 1 3 1 8 - 7 2 10 Min.Gel 4 3 20 4 65 15 31 - 82 50 pH 12.4 11.2 12.3 11.0 12.2 10.8 - - 12.0 H2S Remaining 1800 1080 1800 < 1.0 15 - - - - Sulfides Remaining - - - - - - - - 10 3-4 TABLE 11 Ratio of Zinc to Chelant Initial Aging Initial Aging Initial Aging Initial Aging Initial Aging Sample No. 29 30 31 32 33 Apparent Viscosity 16 12 16 15 20 15 23 16 31 16 600 RPM 32 24 33 30 40 30 47 32 62 33 300 RPM 20 14 21 16 25 17 32 19 49 20 Plastic Viscosity 13 10 12 14 15 13 15 13 13 13 Yield Point (&num;100 ft.2) 7 4 9 2 10 4 17 6 36 17 Initial Gel 4 1 2 1 8 1 13 1 22 2 10 Min. Gel 90 3 109 5 144 10 187 20 239 28 pH - 8.9 - 8.5 - 8.5 - 8.6 - 8.6 Table 10, Samples 24 to 26, show that ZnNTA effectively removes H2S from the drilling fluid quickly and for an extended period of time with good rheology of the fluid.ZnNTA reduces the sulphide ion concentration practically instantaneously as compared to basic ZnC03.

Samples 27 and 28 of Table 10 show that ZnNTA can be formed in situ and react practically instantaneously to remove sulphide ions, reducing the sulphide ion concentration to only trace amounts.

Table 11, Samples 29 to 33, show that high ratios of zinc: NTA produces higher gel strength or higher viscosity and yield point at the high additive concentration of 5 ppb. The weight ratio of zinc ion to NTA should be such that NTA is in a molecular excess relative to the zinc ion.

EXAMPLE (Samples 34-40) A base mud was prepared using 350 milliliters (ml).deionized water, 88 gm salt, 10 gm attapulgite clay, 5 gm starch and 0.25 gm sodium hydroxide caustic for each sample. To three samples, portions of ammonium bisulfite (NH4HSO3), as a 60% solution in water, was added and recorded as pounds per 42 gallons per barrel (ppb) or gm per 350 ml sample.

To three other samples portions of zinc hydrosulfite, as a 30% slurry in white oil was added and recorded ppb which is equivalent to gm per 350 ml sample. The pH of several samples was measured and adjusted using caustic. Fourteen ml of sodium sulfide solution was added to each sample at a concentration of 187.5 gm Na2S.8H2O per 1000 ml of solution in deionized water. Fourteen milliliters were equivalent to 1000 ppm H2S in 350 milliliters of mud. The resulting pH and H2S present was measured. The H2S concentration was measured in API filtrate using a Garrett gas train. After hot rolling the samples in an oven at 1500F for 16 hours with the pH and H2S concentration were again measured.

Measured properties of the samples are tabulated as Table 12: TABLE 12 Sample 34 35 36 37 38 39 40 NH4 HSO3 (gm or ppb) Base Mud 1 2 4 - - Zn hydrosulfite (gm or ppb) - - - - 1 2 4 pH (before NaOH) - - 6.0 5.6 - - Caustic (gm or ppb) - - 0.25 0.75 - - pH (after NaOH) - - 7.4 7.6 - - pH (after Na2S) 11.6 10.4 9.6 9.3 11.4 11.1 7.7 H2S (ppm) 960 550 400 250 400 640 100 After Hot Rolling pH 11.1 10.3 9.7 9.1 11.1 10.9 9.2 H2S (ppm) 480 300 175 25 340 120 trace TABLE 13 (Samples 41-43) Sample 41 Sample 42 Sample 43 Initial After Test Initial After Test Initial After Test Scavenger NH4HSO3 Zn Hydrosulfite Na2SO3 Fann Viscosity 600 RPM 26 16 22 18 25 28 300 RPM 16 10 14 11 15 19 Apparent Viscosity (AV) 13 8 11 9 12.5 14 Plastic Viscosity (PV) 10 6 8 7 10 9 Yield Point (YP) 6 4 6 4 5 10 Gel Strength, Initial 3 1 2 1 2 6 Gel strength, 10 min. 22 1 19 2 22 31 pH 11.6 6.5 11.3 7.5 11.3 10.5 Temp. C 24 24 24.5 24.5 23 23 O2 Conc. (ppm) 7.8 - 8.2 - 8.3 - EXAMPLE Sample 41) A polymer type aqueous base mud was prepared using the following recipe based on grams (gm) per a 350 milliliter (ml) sample which is proportional to pounds per 42-gallon barrel (ppb): 350 ml - deionized water 12 gm - bentonite clay 0.05 gm - polyvinyl acetate-maleic anhydride copolymer bentonite extender 0.5 gm - AMOCO Drillaid 425 poly acrylamide polymer 0.25 gm - NaOH caustic The properties of this mud Sample 41 were measured before aerating using air passed through a Garrett gas train dispersion tube and adding ammonium bisulfite (60% in water) dropwise to the mud. The measured and calculated properties are tabulated in Table 13.

After measuring the initial properties the ammonium solution was added dropwise to Sample 41 at 3 drops per 60 seconds with stirring (one drop = 0.027933 gm of NH4HSO3) and the oxygen concentration in ppm was recorded. After twenty minutes, addition of the NH4HSO3 solution resumed. Recorded values for drops of solution added, oxygen concentration as measured by a YSI oxygen meter in parts per million (ppm) and time in minutes are as follows: TABLE 14 Time Drops 2 ppm Time Drops O2ppm 0 0 7.8 19:00 57 0.07 1:00 3 7.5 20:00 60 0.07 2:00 6 7.0 21:00* -- 0.70 3:00 9 6.4 22:00* -- 0.80 4:00 12 5.8 23:00* -- 2.00 5:00 15 5.0 24:00* -- 1.85 6:00 18 3.7 25:00* -- 1.75 7:00 21 0.9 26:00 -- 1.60 8:00 24 0.45 27:00 63 1.40 9:00 27 0.33 28:00 66 0.55 10:00 30 0.25 29:00 69 0.43 11:00 33 0.20 30:00 72 0.37 12:00 36 0.15 31:00 75 0.32 13:00 39 0.10 32::00 78 0.26 14:00 42 0.09 33:00 81 0.23 15:00 45 0.07 34:00 84 0.18 16:00 48 0.07 35:00 87 0.15 17:00 51 0.07 36:00 90 0.14 18:00 54 0.07 Aerating sample EXAMPLE (Sample 42) Another portion of the polymer base mud (Sample 42) was tested, aerated and treated with a 30% slurry of zinc hydrosulfite in white oil. The properties of Sample 42 are shown in Table 13. The zinc hydrosulfite was added dropwise at 3 drops per minute (one drop being 0.018484 gm of zinc hydrosulfite).The times in minutes, drops of slurry and oxygen concentration in ppm are tabulated as follows: TABLE 15 Time Drops O2ppm Time Drops 2 ppm 0 0 8.20 18:00 54 0.11 1:00 3 8.20 19:00 57 0.10 2:00 6 8.07 20:00 60 0.10 3:00 9 7.80 21:00* -- 2.00 4:00 12 7.48 22:00* -- 3.85 5:00 15 7.03 23:00* - 5.20 6:00 18 6.45 24:00* -- 4.70 7:00 21 5.78 25:00* -- 4.30 8:00 24 5.00 26:00 -- 4.00 9:00 27 4.20 27:00 -- 1.40 10:00 30 3.35 28:00 -- 0.90 11:00 33 2.55 29:00 -- 0.57 12:00 36 1.65 30:00 -- 0.46 13:00 39 0.75 31:00 -- 0.43 14:00 42 0.30 32:00 63 0.37 15:00 45 0.20 33:00 66 0.35 16:00 48 0.15 34:00 69 0.31 17:00 51 0.14 35::00 72 0.38 * Aerating Sample EXAMPLE (Sample 43) A third portion of polymer base mud (Sample 43) was tested, aerated and treated with a solution of 20 grams of sodium sulfite anhydrous, Na2SO3, per 100 ml of solution with deionized water. The properties of Sample 43 are in Table 13. The sodium sulfite solution was added at 3 and 5 drops per minutes with stirring as for the previous samples (one drop equals 0.0262415 gm of Na2SO3).The time in minutes, drops of solution and oxygen concentration in ppm are tabulated as follows: TABLE 16 Time Drops 2 ppm Time Drops 2 ppm 0 0 8.30 22:00 90 6.00 1:00 3 8.28 23:00 95 5.70 2:00 6 8.28 24:00 100 5.20 3:00 9 8.28 25:00 105 4.85 4:00 12 8.20 26:00 110 4.50 5:00 15 8.10 27:00 115 4.15 6:00 18 8.18 28:00 120 3.80 7:00 21 8.11 29:00 125 3.50 8:00 24 8.10 30:00 130 3.15 9:00 27 8.05 31:00 135 2.73 10:00 30 8;0 32:00 140 2.34 9:00 35 7.98 33:00 145 1.90 12:00 40 7.9 34:00 150 1.40 13:00 45 7.8 35:00 155 1.00 14:00 50 7.71 36:00 160 0.65 15:00 55 7.51 37:00 165 0.42 16:00 60 7.35 38:00 170 0.31 17:00 65 7.12 39:00 175 0.25 18:00 70 6.92 40:00 180 0.21 19:00 75 6.80 41:00 185 0.20 20:00 80 6.52 42:00 190 0.18 21:00 85 6.30 43:00 195 0.15 44:00 200 0.15 61:00 245 0.45 45: :00 205 0.13 62:00 250 0.41 46:00 210 0.11 63:00 255 0.37 47:00 215 0.10 64:00 260 0.34 48:00 220 0.10 65:00 265 0.31 49:00 225 0.10 66:00 270 0.28 50:00 230 0.10 67:00 275 0.25 51:00* -- 0.75 68:00 280 0.23 52:00* -- 1.62 69:00 285 0.20 53:00* -- 2.30 70:00 290 0.19 54:00* -- 2.55 71:00 295 0.16 55:00* -- 2.85 72:00 300 0.15 56:00 -- 0.30 73:00 305 0.14 57:00 -- 0.70 74:00 310 0.13 58:00 -- 0.65 75:00 315 0.11 59:00 235 0.55 76:00 320 0.10 60:00 240 0.50 *Aerating Sample From Samples 34-43 it is readily apparent that zinc hydrosulfite effectively removes both oxygen and hydrogen sulfide from drilling fluids without adversely affecting the rheology of the drilling fluid.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (15)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   EXAMPLE (Sample 43) A third portion of polymer base mud (Sample 43) was tested, aerated and treated with a solution of 20 grams of sodium sulfite anhydrous, Na2SO3, per 100 ml of solution with deionized water. The properties of Sample 43 are in Table 13. The sodium sulfite solution was added at 3 and 5 drops per minutes with stirring as for the previous samples (one drop equals 0.0262415 gm of Na2SO3).The time in minutes, drops of solution and oxygen concentration in ppm are tabulated as follows: TABLE 16 Time Drops 2 ppm Time Drops 2 ppm 0 0 8.30 22:00 90 6.00 1:00 3 8.28 23:00 95 5.70 2:00 6 8.28 24:00 100 5.20 3:00 9 8.28 25:00 105 4.85 4:00 12 8.20 26:00 110 4.50 5:00 15 8.10 27:00 115 4.15 6:00 18 8.18 28:00 120 3.80 7:00 21 8.11 29:00 125 3.50 8:00 24 8.10 30:00 130 3.15 9:00 27 8.05 31:00 135 2.73 10:00 30 8;0 32:00 140 2.34 9:00 35 7.98 33:00 145 1.90 12:00 40 7.9 34:00 150 1.40 13:00 45 7.8 35:00 155 1.00 14:00 50 7.71 36:00 160 0.65 15:00 55 7.51 37:00 165 0.42 16:00 60 7.35 38:00 170 0.31 17:00 65 7.12 39:00 175 0.25 18:00 70 6.92 40:00 180 0.21 19:00 75 6.80 41:00 185 0.20 20:00 80 6.52 42:00 190 0.18 21:00 85 6.30 43:00 195 0.15 44:00 200 0.15 61:00 245 0.45 45: :00 205 0.13 62:00 250 0.41 46:00 210 0.11 63:00 255 0.37 47:00 215 0.10 64:00 260 0.34 48:00 220 0.10 65:00 265 0.31 49:00 225 0.10 66:00 270 0.28 50:00 230 0.10 67:00 275 0.25 51:00* -- 0.75 68:00 280 0.23 52:00* -- 1.62 69:00 285 0.20 53:00* -- 2.30 70:00 290 0.19 54:00* -- 2.55 71:00 295 0.16 55:00* -- 2.85 72:00 300 0.15 56:00 -- 0.30 73:00 305 0.14 57:00 -- 0.70 74:00 310 0.13 58:00 -- 0.65 75:00 315 0.11 59:00 235 0.55 76:00 320 0.10 60:00 240 0.50 *Aerating Sample From Samples 34-43 it is readily apparent that zinc hydrosulfite effectively removes both oxygen and hydrogen sulfide from drilling fluids without adversely affecting the rheology of the drilling fluid.

   WHAT WE CLAIM IS: 1. A method of scavenging sulphide from a liquid having a pH of 5 to 12, in which there is used as the scavenging agent a complex formed between at least one zinc compound and an organic chelating agent, the complex having a stability constant of 10 to 16.
2. 2. A method according to claim 1, in which the complex is formed in situ in the liquid.
3. 3. A method according to claim 2, in which the liquid is oil-based and the zinc compound is added in the form of a solution or dispersion in oil.
4. 4. A method according to claim 2 or 3, in which the chelating agent is present in excess of the amount needed to chelate all the available zinc.
5. 5. A method according to any of claims 1 to 4, in which the zinc compound contains no anions capable of causing flocculation of any clays in the liquid.
6. 6. A method according to claim 5, in which the zinc compound is a formate, acetate, chloride, bromide, iodide, chlorate, bromate, nitrate, sulphate, sulphoxylate, hydrosulphite or silicofluoride salt.
7. 7. A method according to any of claims 1 to 6, in which the chelating agent is a compound having at least one tertiary amine group and at least two carboxyl groups, or a salt thereof.
8. 8. A method according to claim 7, in which the chelating agent is ethylenediamine tetra-acetic acid, ss-mercaptoethyliminodiacetic acid, ethylene-bis-N,N'-2(aminomethyl)pyridine-N,N'-diacetic acid, N-hydroxyethyl ethylene diamine tetra-acetic acid, ethylene diamine-N,N' dipropionic acid-N,N' di-acetic acid, ethylene diamine-N,N' di-acetic acid or ethylene diamine-N,N di-acetic acid.
9. 9. A method according to claim 7. in which the chelating agent is nitrilotri-acetic acid and/or a salt thereof.
10. 10. A method according to claim 7, in which the chelating agent is a polyfunctional amine or a hydroxy-carboxylic acid.
11. 11. A method according to claim 10, in which the polyfunctional amine is triethylene tetramine, ethylene-bis-a, a'-2(aminomethyl) pyridine, (3, (3', (3"tri-aminotriethylamine or a, (3-diamino propionic acid.
12. 12. A method according to claim 10, in which the hydroxy-carboxylic acid is dithiotartaric acid.
13. 13. A method according to any of claims 1 to 12, in which the complex contains at least 10% by weight of zinc.
14. 14. A method according to any of claims 1 to 13, in which the amount of the complex is

    controlled such that the concentration of sulphide ions in the liquid is maintained below a predetermined amount.
15. 15. A method of scavenging sulphide from a liquid having a pH of 5 to 12, in which there is used as the scavenging agent a complex substantially as herein described in any of Samples 2, 5, 9, 11, 13, 14, 19, 21, 22, 23, 26, 28, 30 to 33, or 41 to 54.