CN110437818B - Gel breaking activator suitable for reservoir fracturing at 20-50 ℃ and preparation method thereof - Google Patents
Gel breaking activator suitable for reservoir fracturing at 20-50 ℃ and preparation method thereof Download PDFInfo
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- CN110437818B CN110437818B CN201910781885.6A CN201910781885A CN110437818B CN 110437818 B CN110437818 B CN 110437818B CN 201910781885 A CN201910781885 A CN 201910781885A CN 110437818 B CN110437818 B CN 110437818B
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- C07C233/00—Carboxylic acid amides
- C07C233/01—Carboxylic acid amides having carbon atoms of carboxamide groups bound to hydrogen atoms or to acyclic carbon atoms
- C07C233/30—Carboxylic acid amides having carbon atoms of carboxamide groups bound to hydrogen atoms or to acyclic carbon atoms having the nitrogen atom of at least one of the carboxamide groups bound to a carbon atom of a hydrocarbon radical substituted by doubly-bound oxygen atoms
- C07C233/33—Carboxylic acid amides having carbon atoms of carboxamide groups bound to hydrogen atoms or to acyclic carbon atoms having the nitrogen atom of at least one of the carboxamide groups bound to a carbon atom of a hydrocarbon radical substituted by doubly-bound oxygen atoms with the substituted hydrocarbon radical bound to the nitrogen atom of the carboxamide group by a carbon atom of a six-membered aromatic ring
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- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/60—Compositions for stimulating production by acting on the underground formation
- C09K8/62—Compositions for forming crevices or fractures
- C09K8/66—Compositions based on water or polar solvents
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- C09K8/685—Compositions based on water or polar solvents containing organic compounds containing cross-linking agents
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- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/60—Compositions for stimulating production by acting on the underground formation
- C09K8/84—Compositions based on water or polar solvents
- C09K8/86—Compositions based on water or polar solvents containing organic compounds
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K2208/00—Aspects relating to compositions of drilling or well treatment fluids
- C09K2208/26—Gel breakers other than bacteria or enzymes
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Abstract
The invention discloses a gel breaking activator suitable for reservoir fracturing at 20-50 ℃, and the activator is a soluble Ag ion complex. The activator is a complex formed by silver nitrate and a ligand A with a structure shown in a formula I or a ligand B with a structure shown in a formula II; the mass ratio of the silver nitrate to the ligand A or the ligand B is 3-5: 20-35. The preparation method of the activator comprises the following steps: dissolving ligand A or B in methanol water solution containing methanol 60-75%, heating to 50-70 deg.C, adjusting pH to 4-5, adding AgNO3Stirring uniformly, and adjusting the pH value to 7-8 by using ammonia water to obtain the activator. The mass percentage of the ligand A or B in the methanol water solution is 20-35%. AgNO3The mass percentage of the methanol aqueous solution is 3-5%. The invention provides a low-temperature gel-breaking activator which can activate gel-breaking agent (NH) in a low-temperature reservoir at 20-50 DEG C4)2S2O8And (5) gel breaking reaction.
Description
Technical Field
The invention relates to the technical field of oil and gas exploitation, in particular to a gel breaking activator suitable for reservoir fracturing at 20-50 ℃ and a preparation method thereof.
Background
With the development of exploration and development technology, low-permeability oil and gas reservoirs with permeability lower than 50mD gradually become the main body of increasing oil reserves. A large number of low-permeability oil and gas reservoirs are distributed all over the world, and the resource amount of the low-permeability oil and gas reservoirs accounts for about 20% -60% of the basin resources, such as Pabina oil fields in Canada, extended oil fields in China, Changqing oil fields and the like.
The main transformation means of the development of the low-permeability oil and gas field is a hydraulic fracturing process, the technology accumulates over 60 years of experience, and the technology is widely applied to the exploration and development of the oil field. Specific embodiments of the hydraulic fracturing process are: high-pressure viscous fluid (fracturing fluid) carrying a propping agent is injected into a shaft to prop and enter a cracked oil storage stratum, then the fracturing fluid is broken and drained back to the ground, and the propping agent is retained in the middle of the stratum and is accumulated to form an excellent communicating gap, so that a long-lasting high-conductivity fracture is artificially manufactured to improve the permeability of oil gas and finally achieve the purpose of increasing the yield.
In low-permeability oil reservoirs discovered in China at present, low-temperature oil reservoirs with the burial depth of less than 1000m account for about 5.2%. For the low-temperature low-permeability shallow oil reservoir, the biggest difficulty for implementing fracturing construction is that the temperature of the reservoir is too low (generally, the well temperature is 30-50 ℃, and the well temperature of part of wells is even as low as 25-30 ℃). The lower the reservoir temperature is, the slower the gel breaking rate of the fracturing fluid is, the smaller the flowback speed is, the lower the flowback degree is, and finally, the reservoir is damaged.
Ammonium persulfate is generally used as a breaker for fracturing fluids in conventional fracturing operations. But at low temperature, (NH)4)2S2O8Decomposition is difficult and sufficient radicals cannot be generated. The fracturing fluid gel breaking effect is directly influenced, and the fracturing fluid gel breaking effect cannot be fully degraded, so that the diversion capacity of a proppant filling layer and the original permeability of a stratum are damaged, and the productivity of a treated well is greatly reduced.
In view of the defects of slow gel breaking speed and overlong gel breaking time of the conventional oxidation gel breaker for the guar fracturing fluid at low temperature, experts at home and abroad develop various novel low-temperature gel breaking technologies which can be applied to low-temperature environments so as to improve the gel breaking efficiency at low temperature. Currently, there are mainly three new low-temperature gel breaking technologies: low temperature activated gel breaker, enzyme gel breaker and capsule gel breaker. Wherein the applicable temperature of the enzyme gel breaker is between 20 and 90 ℃, the cost is high, and the field operation is complex; the capsule gel breaker has low chemical reaction rate and large dosage under the condition of low temperature, so that the fracturing cost is high. Therefore, of the three low-temperature gel breaking technologies, the most widely applied field is the low-temperature activated gel breaking system. However, the low-temperature gel breaking activation system developed and used in production at present requires a large amount of ammonium persulfate and a large amount of low-temperature activator, and the capability of improving the gel breaking rate of the fracturing fluid and shortening the gel breaking time cannot completely meet the requirements of site construction. Therefore, a low-temperature activation system with higher efficiency needs to be developed, so that the consumption of ammonium persulfate can be reduced, the gel breaking rate of the fracturing fluid of the low-temperature well can be improved to a greater extent, the gel breaking time is shortened, and the damage of the gel breaking fluid to the stratum of the oil field is reduced.
Disclosure of Invention
The invention aims to provide a low-temperature gel breaking activator suitable for fracturing a reservoir stratum at 20-50 ℃ aiming at the technical defects that the existing low-temperature gel breaking activation system needs larger ammonium persulfate dosage and lower-temperature activator dosage, improves the gel breaking rate of a fracturing fluid, and cannot completely meet the requirements of field construction due to the capacity of shortening the gel breaking time.
The invention also aims to provide a preparation method of the low-temperature gel breaking activator suitable for fracturing the reservoir at the temperature of 20-50 ℃.
The low-temperature gel breaking activator suitable for the reservoir fracturing at the temperature of 20-50 ℃ provided by the invention is a soluble Ag ion complex. The activator is a complex formed by silver nitrate and a ligand A with a structure shown in a formula I or a ligand B with a structure shown in a formula II and stably exists under an alkaline condition:
in the formula, R is H or CH3。8,11-tetraazacylotetradeca-7,11-diene
Preferably, the mass ratio of the silver nitrate to the ligand A or the ligand B is 3-5: 20-35.
The molecular structural formula of the complex formed by silver nitrate and ligand A is shown as formula III:
the molecular structural formula of the complex formed by silver nitrate and ligand B is shown as formula IV:
in the formula, R is H or CH3。
The preparation method of the gel breaking activator suitable for reservoir fracturing at 20-50 ℃ comprises the following specific steps: dissolving ligand A or B in methanol water solution containing methanol 60-75%, heating to 50-70 deg.C, adjusting pH to 4-5 with citric acid, and adding AgNO 3Stirring uniformly, and adjusting the pH value to 7-8 by using ammonia water to obtain the activator.
Preferably, the mass percentage of the ligand A or the ligand B in the methanol aqueous solution is 20-35%. AgNO3The mass percentage of the methanol aqueous solution is 3-5%. The heating temperature is preferably 60 ℃.
Compared with the prior art, the invention has the advantages that:
the low-temperature gel breaking activator is Ag+Complexes with ligands, metal Ag+The outermost d-level electron has higher energy and is unpaired electron, so the structure is unstable and has stronger reducibility. Ag+Can reduce (NH)4)2S2O8Activation energy of reaction, Ag+Activation of S2O8 2-Generating free radicals SO4·-And OH. to increase (NH)4)2S2O8The reaction rate at low temperature, so that the gel breaking reaction at low temperature can be smoothly carried out. Furthermore, low temperature activator activation (NH)4)2S2O8High valence transition metal cation Ag generated after the reaction2+Can also perform oxidation-reduction reaction with organic free radicals, thereby reducing metal cations.
Ag+Although capable of accelerating (NH)4)2S2O8Decomposition at low temperature, but it reacts with OH in an alkaline environment-The reaction takes place to form a precipitate of AgOH which is extremely unstable and decomposes to give a brown silver oxide solid. This not only results in AgNO 3While the resulting silver oxide solids also contribute to contamination of the fracturing fluid. Thus, the present invention uses ligand A or ligand B with Ag+Forming a complex as an activator; the complex is a water-soluble substance and can stably exist under an alkaline condition, AgOH precipitation is avoided, and the application range of the low-temperature gel breaking activator is expanded.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Detailed Description
The following description of the preferred embodiments of the present invention is provided for the purpose of illustration and description, and is in no way intended to limit the invention.
First, preparation example
Example 1
A preparation method of a gel breaking activator suitable for reservoir fracturing at 20-50 ℃ comprises the following specific steps: dissolving ligand A in methanol water solution containing methanol 60-75% (20% by weight of ligand A in methanol water solution), heating to 60 deg.C, adjusting pH to 4-5 with citric acid, and adding AgNO3，AgNO3The mass percent of the catalyst in methanol aqueous solution is 3 percent, the catalyst is evenly stirred, and the pH value is adjusted to 7-8 by ammonia water, thus obtaining the complex activator A which stably exists under the alkaline condition. Ligand A has the following structural formula:
Example 2bis (benzaidehyde) (L)
A preparation method of a gel breaking activator suitable for reservoir fracturing at 20-50 ℃ comprises the following specific steps: dissolving ligand B in methanol water solution containing methanol 60-75 wt%, heating to 60 deg.C,adjusting pH to 4-5 with citric acid, adding AgNO3，AgNO3The mass percent of the catalyst in methanol aqueous solution is 5 percent, the catalyst is evenly stirred, and the pH value is adjusted to 7-8 by ammonia water, thus obtaining the complex activator B which stably exists under the alkaline condition. Ligand B has the following structural formula:
second, activator performance test 8,11-tetraazacylotetradeca-7,11-diene
The performance of activator a and activator B prepared in examples 1 and 2 was tested. The experimental method mainly comprises the following two steps:
(1) preparation of jelly
Base liquid: 0.4% of hydroxypropyl guar gum plus (0.02% -0.032%) of NaOH (the pH value is adjusted to be 11) + 0.1% of HCHO plus 0.3% of demulsification and cleanup additive plus 1% of KCl plus low-temperature activators (activator A or activator B) with different concentrations.
A crosslinking agent: 1% of borax;
a gel breaker: 200ppm (NH)4)2S2O8；
Crosslinking ratio: 100: 5;
(2) determination of static gel breaking time
And (3) filling the prepared gel into a closed container, and placing the closed container into an electric thermostat with constant temperature of 20 ℃, 40 ℃ and 50 ℃ respectively for constant temperature heating to ensure that the fracturing fluid breaks gel at the constant temperature (the apparent viscosity of the gel breaking liquid is less than 5 mPa.s). And recording the time from the beginning of gel breaking to the end of gel breaking, wherein the time is the static gel breaking time of the fracturing fluid. Each test is repeated at least once, and the average gel breaking time is taken as the standard. The test results are shown in tables 1 and 2.
TABLE 1 static gel breaking time of fracturing fluids containing different concentrations of activator A at different temperatures
TABLE 2 static gel breaking time of fracturing fluids containing different concentrations of activator B at different temperatures
As can be seen from tables 1 and 2, the static gel breaking time of the low temperature activated system with the addition of the activator A or B is much lower than that of the non-activated gel breaking system, which shows that the activator of the present invention can accelerate (NH)4)2S2O8Decomposing and increasing gel breaking speed of the jelly. For the jelly containing the same concentration of the activator, the lower the gel breaking temperature is, the longer the static gel breaking time is. At the same gel breaking temperature, the smaller the concentration of the activator contained in the gel is, the longer the static gel breaking time is. At 50 ℃, 5ppm of the activator A can shorten the gel breaking time of the jelly to 300min, and 5ppm of the activator B can shorten the gel breaking time of the jelly to 296 min. The 20ppm of the activator A can shorten the gel breaking time of the jelly to 140min, and the 20ppm of the activator B can shorten the gel breaking time of the jelly to 142min, so that the requirement of the conventional fracturing scale on the gel breaking time can be met. In addition, it was found that only 10ppm of activator and No (NH) were present4)2S2O8The blank system of (2) can not break the gel, which shows that the activator can not degrade the gel and can not be independently used.
Table 3 shows the compositions containing different concentrations of AgNO3The static gel breaking time of the fracturing fluid at different temperatures. The experimental test methods are the same as in tables 1 and 2. As can be seen from Table 3, AgNO alone3To (NH)4)2S2O8Has activating effect and can raise gel breaking rate of jelly. But when AgNO3When the concentration of (A) exceeds 10ppm, even if AgNO is continuously increased3To a concentration of 20ppm, AgNO3To (NH)4)2S2O8The activation effect is not obviously improved, and AgNO3The gel breaking time of the fracturing fluid has little difference between the concentration of 10ppm and the concentration of 20 ppm. This is because: when Ag is in solution+At lower concentrations, less AgOH is formed and less brown silver oxide solid is formed by decomposition, all Ag+Can exert activating effect. But when Ag+When the concentration of (B) exceeds 10ppm, Ag+AgOH precipitate is easily generated in alkaline environment, and the AgOH precipitate is further decomposed into silver oxide solid, and the part of Ag which becomes silver oxide+It cannot exert an activating effect. Thus, if AgNO is used alone3In a low temperature activation system AgNO3Must be less than or equal to 10 ppm. But 10ppm of AgNO at 20 deg.C3The gel breaking time of the gel cannot meet the requirements of certain fracturing scales on the gel breaking time, so that the gel breaking time needs to be further shortened, but the single AgNO is used 3As an activator, the object of further shortening the gel breaking time has not been achieved. Only using AgNO3And a complex is formed with the ligand to avoid the precipitation of Ag ions, so that the effective use concentration of the Ag ions in the fracturing fluid can be increased. Comparing Table 3 with tables 1 and 2, respectively, it can be seen that AgNO is used in the present invention3React with ligand to form soluble complex, avoiding Ag+Generating AgOH precipitate under the alkaline condition; and the same concentration of AgNO3And a complex, both of which have substantially the same activating effect.
Table 3 illustrates AgNO alone3As activators, i.e. without addition of ligands, when AgNO3After the concentration is increased to a certain degree of 10ppm, the concentration is continuously increased, and the gel breaking effect is not obviously increased. The reason is that when the concentration of Ag ions is increased to a certain degree, precipitates are generated, redundant Ag becomes precipitates when the concentration is increased continuously, and 10ppm of Ag ions in the oil act all the time in the fracturing fluid. Compared with tables 1 and 2, the gel breaking effect of the Ag complex with the concentration of 20ppm is obviously better than that of the 20ppm Ag ion in the table 3.
TABLE 3 AgNO concentrations3The static gel breaking time of the fracturing fluid at different temperatures
In conclusion, the invention adopts Ag+Complex formed by complex reaction with ligand is used as low temperature breaker A glue activator; the complex is a water-soluble substance and can stably exist in a fracturing fluid system for a long time; at 50 ℃, 5ppm of the activator can shorten the gel breaking time of the gel, meet the requirement of conventional fracturing scale on the gel breaking time, and have the advantages of small using amount of the activator and remarkable effect.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (9)
1. The gel breaking activator is suitable for reservoir fracturing at the temperature of 20-50 ℃, and is characterized in that the activator is a water-soluble complex which is formed by silver ions and a ligand A with a structure shown in a formula I or a ligand B with a structure shown in a formula II and stably exists under an alkaline condition;
Formula I:
formula II:
in the formula II, R is H or CH3。
2. The gel-breaking activator suitable for use in reservoir fracturing at 20-50 ℃ as claimed in claim 1, wherein the activator is a complex of silver nitrate and a ligand a having a structure represented by formula i or a ligand B having a structure represented by formula ii.
3. The gel-breaking activator suitable for reservoir fracturing at 20-50 ℃ according to claim 2, wherein the mass ratio of the silver nitrate to the ligand A or the ligand B is 3-5: 20-35.
4. The gel-breaking activator suitable for use in reservoir fracturing at 20-50 ℃ according to claim 2, wherein the silver nitrate forms a complex with ligand a and ligand B of the molecular structure shown in formula iii and formula iv:
in the formula, R is H or CH3。
5. A method for preparing a gel-breaking activator suitable for use in reservoir fracturing at 20-50 ℃ as claimed in any one of claims 1-4, wherein the ligand A or B is dissolved in an aqueous solution of methanol containing 60-75% by mass of methanol, heated to 50-70 ℃, adjusted to pH 4-5, and AgNO is added3Stirring uniformly, and adjusting the pH value to 7-8 by using ammonia water to obtain the activator.
6. The preparation method of the gel breaking activator suitable for the reservoir fracturing at the temperature of 20-50 ℃ according to claim 5, wherein the mass percentage of the ligand A or the ligand B in the methanol aqueous solution is 20-35%.
7. The method for preparing the gel breaking activator suitable for the reservoir fracturing at 20-50 ℃ according to claim 6, wherein AgNO3The mass percentage of the methanol aqueous solution is 3-5%.
8. The method of claim 7, wherein the heating temperature is 60 ℃.
9. The method of claim 7, wherein the pH is adjusted to 4-5 with citric acid.
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