TREATMENT OF SUBTERRANEAN FORMATIONS

Abstract

A method of treating a subterranean formation by contacting the formation with the following (a) ammonium bicarbonate; (b) and oxidizing agent selected from a perchlorate or a nitrite or combinations thereof; and (c) an acid (AA).

Claims

1-34. (canceled)

35. A method of treating a subterranean formation, the method comprising contacting the formation with the following: (a) ammonium bicarbonate; (b) an oxidizing agent selected from a perchlorate or a nitrite or combinations thereof; and (c) an acid (AA).

36. The method according to claim 35, wherein the method comprises treating the formation to create or enhance a fracture in the formation.

37. The method according to claim 36, wherein said oxidizing agent comprises a nitrite which, optionally, is sodium nitrite.

38. The method according to claim 36, wherein said ammonium bicarbonate and said oxidizing agent are contacted so they react and nitrogen and carbon dioxide are generated in the formation.

39. The method according to claim 36, wherein a ratio (A) defined as the number of moles of ammonium bicarbonate divided by the number of moles of nitrite contacted with the formation and/or reacted in the formation is in the range 0.1 to 2.0, preferably in the range 0.3 to 0.6.

40. The method according to claim 36, wherein said acid (AA) is arranged to react to produce a gas, wherein the gas produced includes carbon and/or nitrogen atoms originating in the acid (AA).

41. The method according to claim 40, wherein said acid (AA) is treated in the method to produce gas which supplements gas produced by reaction of said ammonium bicarbonate and said oxidizing agent.

42. The method according to claim 41, wherein said acid (AA) includes a moiety ##STR00004## and includes a nitrogen-atom.

43. The method according to claim 36, wherein said acid (AA) is selected from sulfamic acid and ammonium bisulfate; and mixtures of sulfamic acid and ammonium bisulfate.

44. The method according to claim 36, wherein a ratio (B) defined as the number of moles of ammonium bicarbonate divided by the total number of moles of acid contacted with the formation and/or reacted with bicarbonate and oxidizing agent in the formation is greater than 0 and is 10 or less; and is preferably in the range 0.3 to 0.6; and/or wherein a ratio (C) defined as the number of moles of ammonium bicarbonate 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 is preferably in the range 0.3 to 0.6.

45. The method according to claim 36, wherein a ratio (E) defined as the number of moles of ammonium bicarbonate divided by the sum of the number of moles of sulfamic acid and ammonium bisulfate contacted with the formation is greater than 0 and is 10 or less; and is preferably in the range 0.3 to 0.6; and/or wherein a ratio (F) defined as the number of moles of ammonium bicarbonate divided by the number of moles of sulfamic acid contacted with the formation is greater than 0 and is 10 or less; and preferably is in the range 0.3 to 0.6; and/or wherein a ratio (G) defined as the number of moles of ammonium bicarbonate divided by the number of moles of ammonium bisulphate contacted with the formation is greater than 0 and is 10 or less; and preferably is in the range 0.3 to 0.6.

46. The method according to claim 36, wherein a ratio (H) defined as the number of moles of nitrite divided by the total number of moles of acid contacted with the formation is in the range 0.1-10; and preferably is in the range 1.3-1.7; and/or wherein a ratio (K) defined as the number of moles of nitrite divided by the sum of the number of moles of sulfamic acid and ammonium bisulfate which are arranged to react with materials contacted with the formation, to produce a gas is in the range 0.1 to 10; and preferably is in the range 1.3 to 1.7.

47. The method according to claim 36, wherein said ammonium bicarbonate is provided as an aqueous solution of ammonium bicarbonate; wherein said nitrite is provided in aqueous solution; and said acid (AA) is provided as an aqueous solution or slurry of acid (AA).

48. The method according to claim 36, wherein in the method the sum of the wt % of a formulation (F1) comprising said ammonium bicarbonate, a formulation (F2) comprising said oxidizing agent, preferably said nitrite, and a formulation (F3) comprising an or said acid (AA) introduced into the formation is at least 80 wt %, preferably at least 98 wt %, of the total weight of materials introduced into the formation as part of the fracturing of the formation by production of gas within the formation.

49. The method according to claim 35, wherein: the sum of the total weight in grams (g) of ammonium bicarbonate, oxidizing agent, preferably said nitrite, 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 bicarbonate, oxidizing agent, preferably said nitrite, 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, preferably at least 260 cm.sup.3/g.

50. The method according to claim 36, wherein formulations comprising ammonium bicarbonate, oxidizing agent and/or acid (AA) include one or more co-solvents selected from methanol or formamide.

51. The method according to claim 35, wherein the method comprises producing pulses of pressure within the formation, for example by controlling contact and/or amounts of ammonium bicarbonate, oxidizing agent and/or acid (AA) within the formation.

52. A method of treating a subterranean formation, the method comprising contacting the formation with the following: (a) ammonium bicarbonate; (b) an oxidizing agent which is sodium nitrite; (c) an acid (AA) selected from sulfamic acid and ammonium bisulfate; and mixtures of sulfamic acid and ammonium bisulfate; wherein a ratio (A) defined as the number of moles of ammonium bicarbonate divided by the number of moles of nitrite contacted with the formation and/or reacted in the formation is in the range 0.3 to 0.6; wherein a ratio (E) defined as the number of moles of ammonium bicarbonate divided by the sum of the number of moles of sulfamic acid and ammonium bisulfate contacted with the formation is greater than 0 and is 10 or less; and wherein a ratio (K) defined as the number of moles of nitrite divided by the sum of the number of moles of sulfamic acid and ammonium bisulfate which are arranged to react with materials contacted with the formation, to produce a gas is in the range 0.1 to 10.

53. The method according to claim 52, wherein in the method the sum of the wt % of a formulation (F1) comprising said ammonium bicarbonate, a formulation (F2) comprising said nitrite, and a formulation (F3) comprising an or said acid (AA) 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 by production of gas within the formation.

54. The method according to claim 53, wherein the method includes introducing proppant and/or microproppant into the formation to enter fractures formed in the method.

55. The method according to claim 36, wherein the method includes introducing proppant and/or microproppant into the formation to enter fractures formed in the method.

56. A method of treating a subterranean formation to create or enhance a fracture in the formation, the method comprising contacting the formation with the following: (a) ammonium bicarbonate; (b) an oxidizing agent which is sodium nitrite; (c) an acid (AA) selected from sulfamic acid and ammonium bisulfate; and mixtures of sulfamic acid and ammonium bisulfate; wherein a ratio (A) defined as the number of moles of ammonium bicarbonate divided by the number of moles of nitrite contacted with the formation and/or reacted in the formation is in the range 0.3 to 0.6; wherein a ratio (E) defined as the number of moles of ammonium bicarbonate divided by the sum of the number of moles of sulfamic acid and ammonium bisulfate contacted with the formation is in the range 0.3 to 0.6; wherein a ratio (K) defined as the number of moles of nitrite divided by the sum of the number of moles of sulfamic acid and ammonium bisulfate which are arranged to react with materials contacted with the formation, to produce a gas is in the range 3 to 1.7; wherein in the method the sum of the wt % of a formulation (F1) comprising said ammonium bicarbonate, a formulation (F2) comprising said nitrite, and a formulation (F3) comprising an or said acid (AA) 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 by production of gas within the formation; wherein the method includes introducing proppant and/or microproppant into the formation to enter fractures formed in the method.

Description

[0123] Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying figures, in which:

[0124] FIG. 1 is a graph showing gas volume generated for Examples 4 to 10;

[0125] FIG. 2 is a graph showing gas volume generated for Examples 11 to 15;

[0126] FIG. 3 is a graph showing gas volume generated for Examples 16 to 21;

[0127] FIG. 4 is a graph showing gas volume generated for Examples 22 to 26;

[0128] FIG. 5 is a graph showing gas volume generated for Examples 27 to 30;

[0129] FIG. 6 is a graph showing gas volume generated for Example 31; and

[0130] FIG. 7 is a graph showing gas volume generated for Examples 32.

[0131] 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

[0132] 10 mmol of ammonium bicarbonate 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., a selected amount of acid also heated to 75° C. was injected into the reaction vessel. The quantity of gas generated was recorded.

EXAMPLES 2 AND 3—COMPARISON BETWEEN AMMONIUM BICARBONATE AND OTHER AMMONIUM COMPOUNDS

[0133] In order to compare use of ammonium bicarbonate with ammonium carbonate, ammonium bicarbonate was reacted with sodium nitrite and sulfamic acid in Example 2, and the gas volume determined. From this, the gas volume (cm.sup.3) per g of reactant was calculated to determine the Reaction Efficiency. For comparison purposes, in Examples 3a and 3b, the same reaction and assessment was undertaken wherein the ammonium bicarbonate was replaced with ammonium carbonate or ammonium chloride. The unbalanced equations for the reactions are as follows:

NH.sub.4HCO.sub.3+NaNO.sub.2+H.sub.3NSO.sub.3.fwdarw.metal salt+N.sub.2+CO.sub.2+H.sub.2O

(NH.sub.4).sub.2CO.sub.3+NaNO.sub.2+H.sub.3NSO.sub.3.fwdarw.metal salt+N.sub.2+CO.sub.2+H.sub.2O

NH.sub.4Cl+NaNO.sub.2+H.sub.3NSO.sub.3.fwdarw.metal salt+N.sub.2+H.sub.2O

[0134] The table below details the results.

TABLE-US-00001 Nature of Mmol of Mmol of Mass of Reaction ammonium ammonium sodium Mmol Gas reagents Efficiency/cm.sup.3 Example No. compound compound nitrite of acid volume/cm.sup.3 (g) gas per g 2 Ammonium 10 30 20 1360 4.80 283 bicarbonate 3a Ammonium 10 30 20 1230 4.97 247 (comparative) carbonate 3b Ammonium 10 30 20 900 4.55 198 (comparative) Chloride

[0135] The table shows that use of ammonium bicarbonate (in Example 2) is advantageous, in terms of reaction efficiency as described, compared to use of carbonate (Example 3a) and ammonium chloride (Example 3b) under identical conditions.

[0136] In Examples 4 to 10, the general procedure of Example 1 was undertaken with a range of different acids.

EXAMPLE 4

[0137] 12.5 ml of an aqueous solution containing ammonium bicarbonate (10 mmol) and sodium nitrite (25 mmol), was added to a round-bottom flask. 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 5

[0138] Example 4 was repeated using 2.4 mL of an 8.33M aqueous solution of ammonium bisulfate (20 mmol) as the acid.

EXAMPLE 6

[0139] Example 5 was repeated using 30 mmol of sodium nitrite and 9.5 ml of 2.11M aqueous solution of sulfamic acid (20 mmol) as the acid.

EXAMPLE 7

[0140] Example 5 was repeated using 8.0 ml or an aqueous solution of 1.457 g (15 mmol) of sulfamic acid and 0.576 g (5 mmol) of ammonium bisulfate as the acid. The molar ratio of sulfamic acid to ammonium bisulfate was 75:25.

EXAMPLE 8

[0141] Example 5 was repeated using, 6.0 mL of an aqueous solution containing 0.971 g sulfamic acid (10 mmol) and 1.511 g ammonium bisulfate (10 mmol), as the acid. The molar ratio of sulfamic acid to ammonium bisulfate was 50:50.

EXAMPLE 9

[0142] Example 5 was repeated using, 3.9 mL of an aqueous solution containing 0.486 g sulfamic acid (5 mmol) and 1.723 g ammonium bisulfate (15 mmol), as the acid. The molar ratio of sulfamic acid to ammonium bisulfate was 25:75.

EXAMPLE 10

[0143] Example 5 was repeated using, 2.8 mL of an aqueous solution containing 0.1942 sulfamic acid (2 mmol) and 2.072 g ammonium bisulfate (18 mmol), as the acid. The molar ratio of sulfamic acid to ammonium bisulfate was 10:90.

[0144] The results for the gas volumes generated are shown in FIG. 1

EXAMPLES 11 TO 15

[0145] The reaction investigated, was the reaction between ammonium bicarbonate, sodium nitrite and HCl. The effect of varying the molar quantity of HCl was investigated using the general procedure described in Example 1.

[0146] A summary of the reagents used is provided in the table below.

TABLE-US-00002 Ammonium bicarbonate Sodium nitrite HCl Example No. mmol mmol mmol 11 10 15 5 12 10 15 10 13 10 15 20 14 10 15 30 15 10 15 40

[0147] Results are provided in FIG. 2 wherein it is clear that there is no significant difference in the gas volume observed when the amount of HCl is increased beyond 20 mmol. The preferred amount of HCl, in order to maximise the reaction efficiency, is taken to be 20 mmol which defines an ammonium bicarbonate to acid ratio of 1:2

[0148] In Examples 16 to 21, the effect of varying the molar quantity of sodium nitrite was investigated.

EXAMPLES 16 TO 21

[0149] The reaction investigated, using the general procedure described in Example 1, was repeated as described for Examples 11 to 15 except that the quantity of sodium nitrite was varied. A summary of the reagents used is provided in the table below.

TABLE-US-00003 Ammonium bicarbonate Sodium nitrite HCl Example No. mmol mmol mmol 16 10 10 20 17 10 12.5 20 18 10 15 20 19 10 20 20 20 10 25 20 21 10 30 20

[0150] Results are provided in FIG. 3 from which it is noted that there is no significant increase in gas release beyond 25 mmol NaNO.sub.2. Therefore 25 mmol was chosen as the preferred quantity of nitrite for reaction efficiency reasons. The nitrite to ammonium ratio is 2.5:1; and the nitrite to acid ratio is 1.25:1.

[0151] In Examples 22 to 26, the effect of varying the molar quantity of sulfamic acid was investigated.

EXAMPLES 22 TO 26

[0152] The reaction investigated was the reaction between ammonium bicarbonate, sodium nitrite and sulfamic acid. The effect of changing the quantities of sulfamic acid was investigated, using the general procedure described in Example 1.

[0153] A summary of reagents used is provided in the table below:

TABLE-US-00004 Ammonium bicarbonate Sodium nitrite Sulfamic acid Example No. mmol mmol mmol 22 10 10 5 23 10 10 7.5 24 10 10 10 25 10 10 20 26 10 10 25

[0154] Results are provided in FIG. 4, from which it is noted that there is no significant improvement in gas generation beyond 20 mmol sulfamic acid, implying a preferred ammonium bicarbonate to sulfamic acid ratio of 1:2.

EXAMPLES 27 TO 30

[0155] The effect of varying the molar quantity of sodium nitrite when reacted with ammonium bicarbonate and sulfamic acid was investigated using the general procedure described in Example 1 and the reagents provided in the table below.

TABLE-US-00005 Ammonium bicarbonate Sulfamic acid Sodium nitrite Example No. mmol mmol mmol 27 10 20 20 28 10 20 30 29 10 20 40 30 10 20 50

[0156] Results are provided in FIG. 5, from which it is noted that there is limited increase in gas release beyond 30 mmol NaNO.sub.2. Therefore 30 mmol was chosen as the preferred quantity of nitrite for reaction efficiency reasons, implying a preferred nitrite to ammonium bicarbonate ratio of 3:1 and a nitrite to acid ratio of 1.5:1

[0157] In Example 31, the minimum quantity of hydrochloric acid needed to cause a reaction involving ammonium bicarbonate to go to completion was investigated.

EXAMPLE 31

[0158] The general procedure of Example 1 was used to investigate the following reaction.

NH.sub.4HCO.sub.3+NaNO.sub.2+HCl.fwdarw.N.sub.2+CO.sub.2+NaCl+3H.sub.2O

10 mmol NH.sub.4HCO.sub.3 and 25 mmol NaNO.sub.2 were used with a range of acid concentrations. Gas volume was measured as a function of time and the results are provided in the table below.

TABLE-US-00006 Quantity of HCl Time/ 0 1 2.5 5 10 15 16 17.5 20 mins mmol mmol mmol mmol mmol mmol mmol mmol mmol 0 0 0 0 0 0 0 0 0 0 0.5 25 52 78 195 265 360 345 410 460 1 49 90 108 210 280 440 420 465 515 2.5 138 170 190 260 305 510 515 545 565 5 212 230 241 302 365 530 540 560 565 10 231 233 248 305 428 540 540 560 565 15 232 233 248 310 452 540 540 560 565 20 232 233 248 310 467 540 540 560 565 30 232 233 248 310 480 540 540 560 565

[0159] Results are also shown in FIG. 6.

[0160] The results show that, in the reaction, approximately 16 mmol is the lowest acid concentration at which the reaction goes to completion; and completion is within about 5 minutes.

[0161] In Example 32, the minimum quantity of sulfamic acid needed to cause a reaction involving ammonium carbonate to go to completion was investigated.

EXAMPLE 32

[0162] The general procedure of Example 1 was used to investigate the following reaction.

NH.sub.4HCO.sub.3+H.sub.3NSO.sub.3+2NaNO.sub.2.fwdarw.Na.sub.2SO.sub.4+2N.sub.2+CO.sub.2+4H.sub.2O

10 mmol NH.sub.4HCO.sub.3 and 30 mmol NaNO.sub.2 were used with a range of acid concentrations. Gas volume was measures as a function of time and the results are provided in the table below.

TABLE-US-00007 Quantity of sulfamic acid Time/mins 5 mmol 10 mmol 15 mmol 20 mmol 0 0 0 0 0 0.5 300 540 1020 1360 1 344 550 1020 1360 2.5 448 550 1020 1360 5 516 550 1020 1360 10 524 550 1020 1360 15 524 550 1020 1360 20 524 550 1020 1360 30 524 550 1020 1360

[0163] Results are shown in FIG. 7.

[0164] The results show that, using sulfamic acid, reactions involving ammonium carbonate and sulfamic acid are complete within seconds.

[0165] 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 (Ib) are detailed in the table below. Pounds (Ib) can be converted to kg by multiplication by 0.45.

TABLE-US-00008 Acid Amount of Amount NaNO.sub.2 Composition Acid conc/M Mass of acid/lb NH.sub.4HCO.sub.3/lb solution/lb A HCl 12.00 9915 lb 37% HCl 3911 8534 B Sulfamic 2.11 6202 2519 6596 C Ammonium bisulfate 8.33 10828 3720 9739 D Sulfamic + 1.88 H.sub.3NSO.sub.3 = 4994 2704 7079 ammonium bisulfate 0.63 NH.sub.4HSO.sub.4 = 1984 (75:25) E Sulfamic + 1.67 H.sub.3NSO.sub.3 = 3687 2996 7844 ammonium bisulfate 1.67 NH.sub.4HSO.sub.4 = 4371 (50:50) F Sulfamic + 1.28 H.sub.3NSO.sub.3 = 2072 3379 8848 ammonium bisulfate 3.85 NH.sub.4HSO.sub.4 = 7388 (25:75) G Sulfamic 0.71 H.sub.3NSO.sub.3 = 885 3622 9484 ammonium bisulfate 6.43 NH.sub.4HSO.sub.4 = 9496 (10:90) * The Ammonium Bicarbonate was made up to a 0.8M aqueous solution ** The Sodium Nitrite was made up to a 2.40M aqueous solution

[0166] 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.