Treatment of subterranean formations

Abstract

A method of treating a subterranean formation by contacting the formation with the following: (a) an ammonium compound; (b) an oxidizing agent selected from a perchlorate or a nitrite or combinations thereof; and (c) one or more acids, at least one of which is a bisulfate salt.

Claims

1. A method of treating a subterranean formation, the method comprising contacting the formation with: (a) an ammonium compound; (b) an oxidizing agent selected from a perchlorate or a nitrite or combinations thereof; and (c) one or more acids, at least one of which is a bisulfate salt, wherein said bisulfate salt is treated in the method to produce gas which supplements gas produced by reaction of said ammonium compound and said oxidizing agent, and wherein, in the method, said ammonium compound and said oxidizing agent are contacted underground during passage towards or after arrival at a region of said subterranean formation it is desired to treat, wherein the gas produced includes nitrogen atoms originating in the bisulfate salt.

2. The method according to claim 1, wherein the method comprises treating the formation to create or enhance a fracture in the formation.

3. The method according to claim 1, wherein said oxidizing agent comprises a nitrite which, optionally, is sodium nitrite.

4. The method according to claim 1, wherein said ammonium compound and said oxidizing agent are contacted so they react and nitrogen and carbon dioxide are generated in the formation.

5. The method according to claim 1, wherein said oxidizing agent is a nitrite and wherein a ratio (A) defined as the number of moles of ammonium compound divided by the number of moles of nitrite contacted with the formation and/or reacted in the formation is in the range 0.05 to 2.0.

6. The method according to claim 1, wherein said ammonium compound is selected from ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, ammonium nitrate, ammonium sulfate, ammonium hydrogensulfate, ammonium carbonate, ammonium carbamate, ammonium bicarbonate, ammonium hydroxide, ammonium acetate, ammonium borates, ammonium chromate, ammonium dichromate, ammonium cyanides, ammonium glutamate, ammonium molybdate, ammonium oxalate, ammonium hydrogenoxalate, ammonium phosphate monobasic, ammonium phosphate dibasic, ammonium thiosulfate, ammonium formate, ammonium sulfamate, ammonium sulfite, ammonium persulfate, ammonium sulfide, ammonium tartrate dibasic, ammonium thiocyanate, ammonium dihydrogen phosphate and ammonium glycinate.

7. The method according to claim 1, wherein said ammonium compound includes, in addition to NH.sub.4.sup.+ moiety, a second moiety which generates a gas on reaction with said oxidizing agent and/or said bisulfate salt.

8. The method according to claim 7, wherein said second moiety comprises a sulfamate, carbonate or bicarbonate moiety.

9. The method according to claim 1, wherein a ratio (B) defined as the number of moles of ammonium compound divided by the total number of moles of acid contacted with the formation and/or reacted with the ammonium compound and oxidizing agent in the formation is greater than 0 and is 10 or less; and/or wherein a ratio (C) defined as the number of moles of ammonium compound divided by the sum of the number of moles of one or more acids which are arranged to react with other materials contacted with the formation to produce a gas is greater than 0 and is 10 or less; and/or wherein a ratio (H) defined as the number of moles of oxidizing agent divided by the total number of moles of acid contacted with the formation is in the range 0.1-10.

10. The method according to claim 1, wherein said ammonium compound is provided in water and the method comprises selecting an aqueous solution, slurry or emulsion of said ammonium compound; and wherein said oxidizing agent is provided in water and the method comprises selecting an aqueous solution, slurry or emulsion of said oxidizing agent.

11. The method according to claim 1, wherein: the sum of the total weight in grams (g) of ammonium compound, oxidizing agent and acid(s) introduced into the formation is herein referred to as SUM-W; the sum of the total volume in cm.sup.3 of gas generated by reaction of ammonium compound, oxidizing agent and said acid(s) is herein referred to as SUM-V; wherein, in the method, the Reaction Efficiency is defined as SUM-V divided by SUM-W; wherein the Reaction Efficiency is at least 100 cm.sup.3/g and is less than 300 cm.sup.3/g.

12. The method according to claim 1, wherein the method uses formulations comprising said ammonium compound, said oxidizing agent and/or said one or more acids and wherein said formulations include one or more co-solvents selected from methanol or formamide.

13. The method according to claim 1, wherein the method comprises producing pulses of pressure within the formation by controlling contact and/or amounts of said ammonium compound, said oxidizing agent and/or said acid within the formation.

14. The method according to claim 1, wherein said method includes introducing proppant and/or microproppant in one or more of formulations used in said method, so as to prop any fractures or microfractures formed as a result of the method.

15. A method of treating a subterranean formation, the method comprising contacting the formation with: (a) an ammonium compound; (b) an oxidizing agent selected from a perchlorate or a nitrite or combinations thereof; and (c) one or more acids, at least one of which is a bisulfate salt, wherein said bisulfate salt is treated in the method to produce gas which supplements gas produced by reaction of said ammonium compound and said oxidizing agent, and wherein, in the method, said ammonium compound and said oxidizing agent are contacted underground during passage towards or after arrival at a region of said subterranean formation it is desired to treat, wherein said bisulfate salt is ammonium bisulfate.

16. A method of treating a subterranean formation, the method comprising contacting the formation with: (a) an ammonium compound; (b) an oxidizing agent selected from a perchlorate or a nitrite or combinations thereof; and (c) one or more acids, at least one of which is a bisulfate salt, wherein said bisulfate salt is treated in the method to produce gas which supplements gas produced by reaction of said ammonium compound and said oxidizing agent, and wherein, in the method, said ammonium compound and said oxidizing agent are contacted underground during passage towards or after arrival at a region of said subterranean formation it is desired to treat, wherein said bisulfate salt is used in combination with an acid (2) which is sulfamic acid.

17. A method of treating a subterranean formation, the method comprising contacting the formation with: (a) an ammonium compound; (b) an oxidizing agent selected from a perchlorate or a nitrite or combinations thereof; and (c) one or more acids, at least one of which is a bisulfate salt, wherein said bisulfate salt is treated in the method to produce gas which supplements gas produced by reaction of said ammonium compound and said oxidizing agent, and wherein, in the method, said ammonium compound and said oxidizing agent are contacted underground during passage towards or after arrival at a region of said subterranean formation it is desired to treat, wherein the method comprises treating the formation to create or enhance a fracture in the formation by production of gas within the formation, wherein in the method the sum of the wt % of a formulation (F1) comprising said ammonium compound, a formulation (F2) comprising said oxidizing agent and a formulation (F3) comprising said bisulfate salt introduced into the formation is at least 98 wt % of the total weight of materials introduced into the formation as part of the fracturing of the formation, wherein said bisulfate salt is ammonium bisulfate.

18. A method of treating a subterranean formation, the method comprising contacting the formation with: (a) an ammonium compound; (b) an oxidizing agent selected from a perchlorate or a nitrite or combinations thereof; and (c) one or more acids, at least one of which is a bisulfate salt, wherein said bisulfate salt is treated in the method to produce gas which supplements gas produced by reaction of said ammonium compound and said oxidizing agent, and wherein, in the method, said ammonium compound and said oxidizing agent are contacted underground during passage towards or after arrival at a region of said subterranean formation it is desired to treat, wherein said an ammonium compound is ammonium sulfamate, said oxidizing agent is a nitrite and wherein said ammonium sulfamate and said nitrite are contacted underground during passage towards or after arrival at the region of said subterranean formation it is desired to treat.

19. The method according to claim 18, wherein: said bisulfate salt is used in combination with an acid (2) which is sulfamic acid; the method comprises treating the formation to create or enhance a fracture in the formation by production of gas within the formation; and the sum of the total weight in grams (g) of ammonium compound, oxidizing agent and acid(s) introduced into the formation is herein referred to as SUM-W; the sum of the total volume in cm.sup.3 of gas generated by reaction of ammonium compound, oxidizing agent and said acid(s) is herein referred to as SUM-V; wherein, in the method, the Reaction Efficiency is defined as SUM-V divided by SUM-W; wherein the Reaction Efficiency is at least 100 cm.sup.3/g and is less than 300 cm.sup.3/g.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Specific embodiments of the invention will now be described, by way of example, with reference to:

(2) FIG. 1, which is a graph showing gas volume generated for Examples 2 and 3.

WORKING EXAMPLES

(3) A subterranean formation may be treated with reagents which are arranged to react to produce a gas and/or heat within the formation. This may stimulate the formation by improving a fracture network within the formation, for example by creating new fractures, extending existing fractures, opening up naturally-occurring fractures or creating microfractures. The examples which follow describe reagents which may be used in a treatment.

Example 1—General Procedure for Undertaking Reactions

(4) An ammonium compound and a nitrite or perchlorate-containing compound were added to a round-bottom flask and dissolved in the minimum quantity of water. Suitable apparatus to measure gas released was arranged in position and the solution heated with stirring to 75° C. Once the solution had reached 75° C., 20 mmol of an acid was also heated to 75° C. and was injected into the reaction vessel. The quantity of gas generated was recorded.

(5) In Examples 2 and 3, reactions were undertaken using different acids.

Example 2 (Comparative)—Using Hydrochloric Acid

(6) Ammonium bicarbonate (10 mmol) and sodium nitrite (25 mmol), were added to a round-bottom flask and dissolved in the minimum quantity of water (10.5 mL). Suitable apparatus to measure gas released was arranged in position and the solution heated with stirring to 75° C. Once the solution had reached 75° C., 1.67 mL of a 12 M aqueous solution of hydrochloric acid (20 mmol) heated to 75° C. was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 3—Using Ammonium Bisulfate

(7) Example 2 was repeated using 2.4 mL of an 8.33M aqueous solution of ammonium bisulfate (20 mmol) as the acid.

(8) The results for the gas volumes generated are provided in FIGURE from which it will be noted that the volume of gas using ammonium bisulfate as the only acid is significantly greater (610 cm.sup.3) than when using hydrochloric acid (Example 2) (560 cm.sup.3).

(9) In Examples 5 to 16, the gas generated by use, as acids, of a combination of ammonium bisulfate and sulfamic acid was compared to use of hydrochloric acid.

Example 4 (Comparative)

(10) 2.9 mL of an aqueous solution of ammonium sulfamate (5 mmol) and sodium nitrite (20 mmol) was added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 0.83 mL of a 12 M aqueous solution of hydrochloric acid (10 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 5

(11) 2.9 mL of an aqueous solution of ammonium sulfamate (5 mmol) and sodium nitrite (20 mmol) was added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 4.0 mL of an aqueous solution containing sulfamic acid (7.5 mmol) and ammonium bisulfate (2.5 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 6

(12) 2.9 mL of an aqueous solution of ammonium sulfamate (5 mmol) and sodium nitrite (20 mmol) was added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 3.0 mL of an aqueous solution containing sulfamic acid (5 mmol) and ammonium bisulfate (5 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 7

(13) 2.9 mL of an aqueous solution of ammonium sulfamate (5 mmol) and sodium nitrite (20 mmol) was added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 1.95 mL of an aqueous solution containing sulfamic acid (2.5 mmol) and ammonium bisulfate (7.5 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 8

(14) 2.2 mL of an aqueous solution containing ammonium sulfamate (7 mmol), sulfamic acid (1 mmol) and ammonium bisulfate (9 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 2.2 mL of an aqueous solution containing sodium nitrite (20 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 9

(15) 2.5 mL of an aqueous solution containing ammonium sulfamate (5 mmol), sulfamic acid (2.5 mmol) and ammonium bisulfate (7.5 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 2.5 mL of an aqueous solution containing sodium nitrite (20 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 10

(16) 2.2 mL of an aqueous solution containing ammonium sulfamate (6.25 mmol), sulfamic acid (1.5 mmol) and ammonium bisulfate (8.5 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 2.2 mL of an aqueous solution containing sodium nitrite (20 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 11

(17) 2.2 mL of an aqueous solution containing ammonium sulfamate (6.25 mmol), sulfamic acid (1.75 mmol) and ammonium bisulfate (7 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 2.2 mL of an aqueous solution containing sodium nitrite (20 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 12

(18) 2.2 mL of an aqueous solution containing ammonium sulfamate (5.5 mmol), sulfamic acid (2.63 mmol) and ammonium bisulfate (4.88 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 2.2 mL of an aqueous solution containing sodium nitrite (20 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 13

(19) 2.2 mL of an aqueous solution containing ammonium sulfamate (6 mmol), sulfamic acid (2.24 mmol) and ammonium bisulfate (4.76 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 2.2 mL of an aqueous solution containing sodium nitrite (20 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 14

(20) 2.2 mL of an aqueous solution containing ammonium sulfamate (6.25 mmol), sulfamic acid (2.50 mmol) and ammonium bisulfate (4.25 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 2.2 mL of an aqueous solution containing sodium nitrite (20 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

Example 15

(21) 2.2 mL of an aqueous solution containing ammonium sulfamate (6.25 mmol), sulfamic acid (2.50 mmol) and ammonium bisulfate (3.75 mmol) were added to a round-bottom flask. Suitable apparatus to measure gas release was arranged in position and the solution heated to 75° C. Once the solution reached 75° C., 2.2 mL of an aqueous solution containing sodium nitrite (20 mmol), heated to the same temperature, was injected into the reaction vessel. The quantity of gas generated was recorded.

(22) Results for Examples 4 to 15 are provided in the table below, from which it will be noted that the combination of sulfamic acid and ammonium bisulfate is a more efficient gas generator compared to use of hydrochloric acid.

(23) TABLE-US-00001 mmol mmol mmol Gas Total Efficiency/ Example NH.sub.4NH.sub.2SO.sub.3 NaNO.sub.2 Acid acid generated/cm.sup.3 mass/g cm.sup.3 per g 4 (comparative) 5 20 Hydrochloric 10.0 460 2.95 156 5 5 20 Sulfamic/ammonium bisulfate (75:25) 10.0 740 2.97 249 6 5 20 Sulfamic/ammonium bisulfate (50:50) 10.0 700 3.01 232 7 5 20 Sulfamic/ammonium bisulfate (25:75) 10.0 660 3.06 216 8 7 20 Sulfamic/ammonium bisulfate (10:90) 10.0 630 3.31 190 9 5 20 Sulfamic/ammonium bisulfate (25:75) 10.0 660 3.06 216 10 6.25 20 Sulfamic/ammonium bisulfate (15:85) 10.0 640 3.22 199 11 6.25 20 Sulfamic/ammonium bisulfate (20:80) 8.8 660 3.07 215 12 5.5 20 Sulfamic/ammonium bisulfate (35:65) 7.5 660 2.82 234 13 6 20 Sulfamic/ammonium bisulfate (32:68) 7.0 665 2.83 235 14 6.25 20 Sulfamic/ammonium bisulfate (37:63) 6.8 670 2.83 237 15 6.25 20 Sulfamic/ammonium bisulfate (40:60) 6.3 650 2.77 235

Example 16—Comparison of Use of Acid Combination Sulfamic Acid/Ammonium Bisulfate with Hydrochloric Acid Alone and Sulfamic Acid Alone

(24) Ammonium bisulfate increases the solubility of sulfamic acid in water and, it has been found, can be used to increase the amount of gas generated by a certain volume of the composition.

(25) Comparative Example 17 was carried out in the same manner as Example 4, except 10 mmol of sulfamic acid was used instead of 10 mmol HCl.

(26) TABLE-US-00002 Total gas generated solution by 1 cm3 volume/ of solution/ Example No. Acid cm.sup.3 cm3  4 Hydrochloric 5.5  84 (comparative) 17 Sulfamic 7.5 100 (comparative)  5 Sulfamic/ammonium bisulfate 6.8 109 (75:25)  6 Sulfamic/ammonium bisulfate 6.1 115 (50:50)  7 Sulfamic/ammonium bisulfate 5.1 129 (25:75)  8 Sulfamic/ammonium bisulfate 4.4 143 (10:90)  9 Sulfamic/ammonium bisulfate 5.0 132 (25:75) 10 Sulfamic/ammonium bisulfate 4.4 145 (15:85) 11 Sulfamic/ammonium bisulfate 4.4 150 (20:80) 12 Sulfamic/ammonium bisulfate 4.4 150 (35:65) 13 Sulfamic/ammonium bisulfate 4.4 151 (32:68) 14 Sulfamic/ammonium bisulfate 4.4 152 (37:63) 15 Sulfamic/ammonium bisulfate 4.4 148 (40:60)

(27) Thus, it should be appreciated from the above that ammonium bisulfate may advantageously be used as the only acid in the reaction or may advantageously be used with sulfamic acid to improve gas generation.

(28) The reagents described herein may be used in treatment of a formation as described. Reagents may be delivered in receptacles to a well-head for subsequent injection, for example using coiled tubing as described herein, into the formation. Exemplary compositions including concentrations and amounts in pound (lb) are detailed in the table below. Pounds (lb) can be converted to kg by multiplication by 0.45.

(29) TABLE-US-00003 Amount of Amount of Acid conc/ Mass of acid NH.sub.4HCO.sub.3 NaNO.sub.2 solution/ Example No. Acid M solution/lb solution/lb* lb** 18 Ammonium bisulfate 8.33 10828 3720 9739 19 Sulfamic + 1.88 4994 2704 7079 ammonium bisulfate (75:25) 0.63 1984 20 Sulfamic + 1.67 3687 2996 7844 ammonium bisulfate (50:50) 1.67 4371 21 Sulfamic + 1.28 2072 3379 8848 ammonium bisulfate (25:75) 3.85 7388 22 Sulfamic 0.71 885 3622 9484 ammonium bisulfate (10:90) 6.43 9496 *The Ammonium Bicarbonate was made up to a 0.8M aqueous solution
** The Sodium Nitrite was made up to a 2.40M aqueous solution.

(30) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.