JPS62216625A - Treatment of geothermal steam - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for drilling a geothermal well, in which untreated steam generated in this case is treated with ferric chelate to remove hydrogen sulfide gas contained in the steam. substantially all removed.

Geothermal steam wells are drilled using compressed air as the motive force for the drill bit. Drilling mud cannot be used due to the high temperatures encountered and the reservoir being rich in volatile components. When the drilling point enters the steam generation area, air and steam pass through the casing into an open line (bloo
ie 1ine) and escape into the silencer. Stringent air pollution standards require the reduction of 112e in steam.

After the well is completed, flow tests are conducted. The flow test consists of fully opening the wellbore and blowing through an open line. During this time, H
Most of the 2S low frequency needs occur. These flow tests last from 30 to 90 days depending on the nature of each reservoir.

Once the well is in production, it tends to become clogged as a result of impurities present in the steam.

Eventually, production will decline and the well will need to be re-drilled. This re-excavation involves bringing in a rig to dig deeper or widen the hole into another steam generation area. Again, a reduction of 112S is required. Once the steam generation region is reached, the wellbore is flow tested again. The flow test at this point is much shorter, between 150 and 3011. In general, H
The 2S reduction requirement is approximately half that of a new well.

U.S. Pat. No. 4,151,260 discloses that during the drilling of geothermal wells, nzs gas contained in steam can be reduced by treating the steam with an alkaline solution of hydrogen peroxide. This is disclosed.

US Patent No. 4,414,817 teaches the use of iron chelates to treat exhaust geothermal steam from steam turbines.

The present invention provides for the treatment of untreated geothermal steam generated from a geothermal well during drilling, flow testing or re-drilling of a wellbore so as to reduce the amount of carbon dioxide contained in the steam prior to release to the atmosphere.
A method for reducing 12S gas, comprising the following steps: (A) The untreated steam containing entrained solids and H2S gas is reduced to 1 to 6 moles per mole of 11ls in the steam. containing ferric chelates of 7 to 11
(B) contacting the ferrous iron with an aqueous solution having a pl+ in the range of , thereby substantially completely absorbing and converting the H2S to sulfur solids and thereby producing a ferrous chelate solution; Separating the Kill-1 solution from entrained solids and sulfur solids; (C
) converting the ferrous chelate solution to a ferric chelate solution using an oxygen-containing gas stream; and <D) recycling the ferric chelate solution for reuse. and returning to the contacting step.

Optionally, step (A) also includes an effective amount of 01 or more water-soluble cationic polymeric catalysts.

The present invention provides a clear improvement over the use of conventional hydrogen peroxide solutions. The use of hydrogen peroxide was an expensive one-time use. This is because expensive chemicals, such as hydrogen peroxide, had to be transported to remote drilling sites. In contrast, the present invention
Uses ferric chelates that can be recycled, recycled and reused. Since the chelate degrades only by a small amount, the loss is compensated for by the addition of fresh ferric chelate.

Addition of this chelate is much more economical than traditional methods using hydrogen peroxide.

The accompanying drawings illustrate the trenching operation and the process in which the exhaust from the geothermal steam is directed by an open line to a separator. In the drawing, pump I2 pumps air from line 10 to line 14 and through rotary table 16 into hollow drill string 20.

Table 16 rotates drill string 20 and drill bit 22. Drill cuttings are removed from the wellbore by a combination of airflow and geothermal steam.

This combined air and steam exits into open line 24.

At injection point 54 , an aqueous solution of ferric chloride is injected into open line 24 . The injection point is located at the separator 28.
The distance from the wellbore casing 18 to the wellbore casing 18 is carefully chosen to be as large as possible.

However, this time period may be shorter as long as sufficient mixing is provided by one or more mixing devices, such as static mixers or equivalent devices. This is because the H2S is absorbed by a solution of ferric chelate and the resulting sulfide ions are oxidized by the ferric chelate. In this cyclone separator 28 the gas is discharged to the atmosphere by line 26 and the sulfur solids, rock chips and debris are removed by line 36 into a settling tank 34.

In the settling tank 34, a liquid level 40 is maintained above the outlet line 42 such that there is a constant flow of liquid chelate from the settling tank 34 into the aeration tank 48. The entrained solids settle in the form of a sludge pile 38 at the bottom of the tank 34. Entrance line 3
2 is provided for adding ferric chelate solution when necessary. If desired, this ferric chelate solution may also be added to tank 48. The same inlet line can be used to add cationic polymer catalyst as needed.

Aeration tank 48 is a spar tube supplied with air by pump 46 and air supply 44.
ger) 47. Entrance line 49 is 21-rate? It is provided for adding a basic solution, such as an aqueous sodium hydroxide solution or an aqueous sodium carbonate solution, to adjust or control the pH of the solution.

The sparge tube 47 of the tank 48 oxidizes the ferrous chelate to ferric chelate by known methods. If desired, this oxidation process can be carried out in the settling tank 3 by adding a similar sparger tube operated from the same air pump 46.
4 can also be applied.

Ferric chelate from aeration tank 48 is removed by line 50 and pump 52 and sent to line 53.
is injected into the open line 24 by.

Chelating agents useful in preparing the ferric chelates of the present invention include chelating agents or complexing agents that form water-soluble chelates. Representative of such chelating agents are aminocarboxylic acids such as nitrilotriacetic acid, N-hydroxyethyliminodiacetic acid, ethylenediaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, and cycloL1 hexane. diaminetetraacetic acid, triethylenetetraamic acid, etc., and salts thereof. Another useful chelating agent is polymer sulfonate. Among these chelating agents, ethylenediaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, and N-hydroxyethyliminodiacetic acid and their salts are used to prepare the ferric chelates used in the present invention. most conveniently used.

The concentration of chelated iron in the circulating solution is IOθ~20.0
00 ppm iron range, preferably from 1,000 to 3,0
Must be in the range 00ρρm.

Examples of useful cationic polymeric catalysts for use in the present invention include polyethylene amines, such as poly(2-hydroxypropyl-1-N-methylammonium chloride), poly(2-hydroxypropyl-1,1- N-
dimethylammonium chloride), poly(CN-(dimethylaminomethyl))acrylamide, poly(2-vinylimidazolinum bisulfate), poly(diallyldimethylammonium chloride) and poly(N-
dimethylaminopropyl) methacrylamide. These cationic polymers are well known and available commercially under various trade names. For example, “Commercial Organic Flocutank”
rcial Organic Flocculants
) J, VosLrc
Noyes Data Inc. (i#) etc.
Data Corp. (1972). Other useful cationic catalysts are GII, Macromol, and Sci-Chem.

J, Macromol, Science-Chem)
A 4.1327-14'17 (1970).

Any of the catalysts mentioned above can be used at 25 to 3,000 p in circulating solution.
pm, preferably in the range of 50 to 500 ppm, and most preferably 150 to 300 ppm. It will be appreciated that the above ranges are considered effective amounts of catalyst. Use of amounts less than the above range generally does not provide the desired effect. Use of amounts greater than the above range is uneconomical. The circulation rate of the KIRE-1 solution is dependent on the hydrogen sulfide level in the geothermal steam.

Generally, this circulation rate is determined by the reaction zone or open line 24.
It should be sufficient to provide from 1 to 6 moles, preferably from 2 to 4 moles of ferric chelate per mole of H2S entering.

The contact time of the reactants should be a minimum of 0.05 seconds or more, preferably in the range of 0.2 to 1.0 seconds.

The pH of the ferric chelate solution is in the range 7-11, preferably 9.5-t0. Must be in the range of S.

Below a pH level of 7, H2S removal is insufficient and above a pH level of 11, the solution does not retain ferric gyrate in a mono-soluble form.

Solids and debris entrained by the wellbore are separated from the ferrous clear-1 solution in a separation zone. −
Finally, a settling tank or vessel must be provided with a capacity such that a residence time of the KIL-1 solution in the range 0.1 to 5 hours, preferably 1 to 2 hours, is provided.

In the aeration or conversion zone, air or oxygen-containing gas is present at a rate of at least 0.0 ml per 11□31 moles treated.
dispersed therein at a rate giving 5 moles of oxygen. in general,
This rate is between 0.6 and 20.0 moles of oxygen per mole of H2S, preferably 1.0 mole of oxygen per mole of H2S.
~10.0 mol.

[Brief explanation of drawings]

This figure is a diagram relating to a method of reducing 112S gas in geothermal steam. 24 =...open line (blooie 1ine),
28...Separator, 32...Population line, 3
4...Settling tank, 44...Air inlet, 48.
...Aeration tank.

Claims (1)

[Claims] 1. A method for reducing H_2S gas contained in the steam by treating untreated geothermal steam generated during drilling, flow testing or re-drilling of a geothermal well. (A) converting said untreated steam containing entrained solids and H_2S gas to a mixture containing 1 to 6 moles of ferric chelate per mole of H_2S in said steam; (B) contacting with an aqueous solution having a pH in the range of ~11, thereby substantially completely absorbing and rapidly converting the H_2S to sulfur solids, and thereby producing a first chelate solution; Ferrous chelate solution, entrained solids,
and (C) converting said ferrous chelate solution to a ferric chelate solution using an oxygen-containing gas stream; and (D) said ferric chelate solution for reuse. recycling the water back to the contacting step. 2. The method of claim 1, wherein step (A) also includes an effective amount of one or more water-soluble cationic polymeric catalysts. 3. The molar ratio of ferric chelate to H_2S is 1 to 6.
3. A method according to claim 1 or 2, wherein the pH range is from 7 to 11. 4. The molar ratio of ferric chelate to H_2S is 2 to 4
4. The method of claim 3, wherein the pH range is from 9.5 to 10.5. 5. The method according to claim 1 or 2, wherein the separation step includes a residence time of the chelate solution of 0.1 to 5 hours. 6. The method of claim 1 or 2, wherein the conversion step is carried out using an oxygen-containing gas at a rate that provides at least 0.5 moles of oxygen per mole of H_2S treated. 7. The method of claim 6, wherein the conversion step is carried out using an oxygen-containing gas at a rate of 0.6 to 20.0 moles of oxygen per mole of H_2S treated. 8. The method according to claim 1, wherein the chelate is a ferric chelate of ethylenediaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, N-hydroxyethylaminodiacetic acid, or a salt thereof. 9. The polymer catalyst is poly(2-hydroxypropyl-1-N-methylammonium chloride) poly(2-hydroxypropyl-1,1-N-dimethylammonium chloride), poly[N-(dimethylaminomethyl) The method according to claim 2, wherein the acrylamide, poly(2-vinyl-imidazolinum bisulfate), poly(diallyldimethylammonium chloride) or poly(N-dimethylaminopropyl)methacrylamide is used. 10. The method of claim 1, wherein the chelate is N-hydroxyethylethylenediaminetriacetic acid and the polymeric catalyst is poly(diallyldimethylammonium chloride).