CN105331351B - A kind of degradable water base clean fracturing fluid thickening agent in oil gas field - Google Patents

Abstract

The invention discloses a kind of degradable water base clean fracturing fluid thickening agents in oil gas field.The present invention is by betaine type amphoteric surfac-tant's thickening agent formula (I) with ester group and sulfo group in degradable water base clean fracturing fluid, obtained degradable water base clean fracturing fluid can break glue automatically, and the viscosity of fracturing fluid remains at 50mPas or more after shearing one hour.The main chemical compositions of the degradable water base clean fracturing fluid are betaine type amphoteric surfac-tant's thickening agent and crosslinking agent with ester group and sulfo group, and the mass percent of thickening agent is 1.5% 4.0%；The mass percent of crosslinking agent is 0.5% 1.0%.The biological degradability of the degradable water base clean fracturing fluid of the present invention is good, and effect on environment is small, temperature and shearing sustainability is good, broken glue is simple entirely without residue, preparation.

Description

A degradable water-based clean fracturing fluid thickener used in oil and gas fields

technical field

The invention belongs to the field of petroleum exploitation engineering, in particular to a degradable water-based clean fracturing fluid thickener used in oil and gas fields.

Background technique

Fracturing is widely used as the main means to increase production capacity in oil and gas fields, and the widely used fracturing fluid system is water-based fracturing fluid. At present, the thickeners used in water-based fracturing fluids are mainly vegetable gum natural polymers and synthetic polymers. The relatively large molecular weight of the polymer has the disadvantages of poor solubility and many water-insoluble substances. After the gel is broken, there are a large number of residues that can reduce the permeability of the formation, which will damage the formation and make the fracturing effect worse. Clean fracturing fluids using viscoelastic surfactants can reduce damage to reservoirs and fractures and improve fracturing effects.

A lot of work has been done on clean fracturing fluids in China, including clean fracturing fluids using cationic surfactants, anionic surfactants, amphoteric surfactants and nonionic surfactants as thickeners. Currently synthesized amphoteric surfactant thickeners for fracturing fluids such as long-chain amide betaines in CN201410276802A, erucic acid-containing betaines in CN201210290896A and amphoteric betaines with phenylene and amido groups in CN201110374771A Gemini surfactants, etc.

Although these clean fracturing fluids using surfactants as thickeners have the advantages of less damage to the formation and improved fracturing stimulation effects, there are still some problems in the current clean fracturing fluids, such as: (1) the use of cationic surface The clean fracturing fluid of active agent thickener and zwitterionic surfactant thickener is difficult to degrade, and it is easy to cause reservoir and environmental pollution. (2) Clean fracturing with anionic surfactant thickener is not suitable for salt-sensitive layers, and needs to rely on external phase gel breaking, the gel breaking performance of the fracturing fluid is restricted, making the clean fracturing fluid The preparation is complicated.

Contents of the invention

Aiming at the above defects or improvement needs of the prior art, the present invention provides a degradable water-based clean fracturing fluid thickener used in oil and gas fields and a degradable water-based clean fracturing fluid containing the thickener , the purpose of which is to use a betaine-type amphoteric surfactant thickener with ester and sulfo groups with good degradation performance to prepare clean fracturing fluid. Coating into a spherical structure enables the clean fracturing fluid to break automatically, thus solving the current technical problems of poor environmental degradation performance and complicated preparation of clean fracturing fluid.

To achieve the above object, the present invention provides a thickening agent for degradable water-based clean fracturing fluid in oil and gas fields, the molecular structural formula of the thickening agent is as shown in formula (I):

Formula (I)

Wherein R is a C ₁₃ -C ₁₉ straight-chain alkyl group, and the R carbon chain contains at most one double bond and/or one hydroxyl substituent; wherein, when the thickener encounters hydrophobic substances in oil and gas fields, it will cover the hydrophobic substances Formed into a spherical structure, the degradable water-based clean fracturing fluid containing this thickener automatically breaks the gel.

Preferably, the viscosity of the degradable water-based clean fracturing fluid remains above 50 mPa·s after shearing for one hour.

Preferably, the degradable water-based cleaning fracturing fluid further includes a cross-linking agent, wherein the mass percentage of the thickener is 1.5%-4.0%, and the mass percentage of the cross-linking agent is 0.5%-1.0%.

Preferably, the cross-linking agent is sodium salicylate and/or EDTA.

Preferably, the main chemical components of the degradable water-based clean fracturing fluid are thickeners and cross-linking agents.

Preferably, the R carbon chain in the thickener contains a double bond and/or a hydroxyl substituent. Among them, R is preferably a C ₁₅ -C ₁₇ linear alkyl group.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects due to the use of an amphoteric surfactant with good degradation performance as a water-based clean fracturing fluid thickener:

(1) The present invention adopts betaine-type amphoteric surfactants containing ester groups and sulfo groups as thickeners for oil field cleaning and fracturing fluids. When this material encounters hydrophobic substances, these molecules will be coated into a spherical structure Therefore, the clean fracturing fluid containing this thickener does not need to add a gel breaker. When encountering organic matter such as oil and gas, the worm-like network structure of the fracturing fluid is destroyed, the viscosity drops, and the gel can be broken automatically. At the same time, after the gel is broken, the fracturing fluid forms an emulsion, leaving no residue, and has little damage to the applied structures such as reservoirs and cracks; the betaine-type amphoteric surfactant containing ester groups and sulfo groups is used as a clean fracturing agent Liquid thickener, this kind of thickener can be completely hydrolyzed into single-molecule compounds, which can be quickly degraded by microorganisms to generate CO ₂ , H ₂ O and inorganic salts, so that the obtained clean fracturing fluid can be guaranteed to have a relatively high With good temperature and shear resistance, it can achieve natural degradation and will not pollute the environment.

(2) The degradable water-based clean fracturing fluid used in oil and gas fields of the present invention is applicable in various reservoirs; Inventing a specific thickener ratio for research and design, so that the obtained degradable water-based clean fracturing fluid has good cleaning and reverse flow ability, and also has excellent temperature resistance and shear resistance.

(3) Specifically, the degradable water-based clean fracturing fluid of the present invention can maintain the viscosity of all examples above 50 mPa·s after shearing for one hour, especially at 80°C and 170s ^-1 shear conditions All are better than the general technical indicators of viscoelastic surfactant fracturing fluid in SY/T6376-2008 "General Technical Specifications for Fracturing Fluids". The clean fracturing fluid of the present invention is added with 5% cyclohexane at a simulated formation temperature (60° C.), and the apparent viscosity after 6 hours is all less than 5 mPa·s, that is, the gel is completely broken without precipitation.

(4) The degradable water-based clean fracturing fluid of the present invention is simple to prepare, has no pollution to the environment, and has important strategic and practical significance for the sustainable development of oil fields.

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

The present invention provides a thickening agent for degradable water-based clean fracturing fluid used in oil and gas fields, the molecular structural formula of the thickening agent is as shown in formula (I):

Formula (I)

Wherein R is a C ₁₃ -C ₁₉ straight-chain alkyl group, and the R carbon chain contains at most one double bond and/or one hydroxyl substituent; wherein, when the thickener encounters hydrophobic substances in oil and gas fields, it will cover the hydrophobic substances Formed into a spherical structure, the degradable water-based clean fracturing fluid containing this thickener automatically breaks the gel.

Wherein, the viscosity of the degradable water-based clean fracturing fluid remains above 50 mPa·s after shearing for one hour, and the preferred shearing conditions are 80°C, 170s ^-1 .

Wherein, the R carbon chain in the thickener contains a double bond and/or a hydroxyl substituent. Among them, R is preferably a C ₁₅ -C ₁₇ linear alkyl group.

The degradable water-based cleaning fracturing fluid of the present invention also includes a cross-linking agent, and the cross-linking agent undergoes a cross-linking reaction with the thickener through electrostatic attraction to improve the temperature resistance of the fracturing fluid. Wherein, the mass percentage of the thickener is 1.5%-4.0%, and the mass percentage of the crosslinking agent is 0.5%-1.0%. Preferably, the cross-linking agent is sodium salicylate and/or EDTA.

Preferably, the main chemical components of the degradable water-based clean fracturing fluid used in oil and gas fields of the present invention are the thickener with a mass percentage of 1.5%-4.0% and the crosslinking agent with a mass percentage of 0.5%-1.0% agent;

Preferably, the main chemical components of the degradable water-based clean fracturing fluid used in oil and gas fields of the present invention are a thickener with a mass percentage of 2.0%-3.0% and a crosslinking agent with a mass percentage of 0.5%-0.8%;

Preferably, the degradable water-based clean fracturing fluid used in oil and gas fields of the present invention includes 2.5%-3.0% by mass of a thickener and 0.5%-0.8% by mass of a crosslinking agent.

The main chemical components of the degradable water-based clean fracturing fluid used in oil and gas fields of the present invention are thickeners and crosslinking agents, and do not contain gel breakers. On this basis, in order to improve various performances, various common additives can also be added to the degradable water-based clean fracturing fluid of the present invention, such as pH regulators, high-temperature stabilizers, anti-clay swelling agents, drag-reducing agents, bactericidal agent, etc., and the balance is water; the addition amount of additives is the conventional amount of cleaning fracturing fluid in this field.

In the degradable water-based clean fracturing fluid used in oil and gas fields of the present invention, the mass percentage of water is less than or equal to 98%, preferably 95%-98%.

The degradable water-based clean fracturing fluid used in oil and gas fields of the present invention can maintain the viscosity of all the examples above 50mPa·s after one hour under the shear conditions of 80°C and 170s ^-1 , and at the simulated formation temperature (60° C.) After adding 5% cyclohexane, the apparent viscosity after 6 hours is less than 5 mPa·s, that is, the gel is completely broken and there is no precipitation.

According to another aspect of the present invention, there is provided a method for preparing a degradable water-based clean fracturing fluid used in oil and gas fields, comprising dissolving the main components of the fracturing fluid of the present invention, a thickener and a crosslinking agent, in water ,well mixed.

The degradable water-based clean fracturing fluid used in oil and gas fields of the present invention is pumped into oil and gas fields according to conventional methods.

The thickener of the degradable water-based clean fracturing fluid of the present invention can be, more preferably, hexadecanoate-based sulfobetaine thickener, octadecylcarbonate-based sulfobetaine thickener, octadecyl enoate-based sultaine thickener, eicosanate-based sultaine thickener, hydroxyoctadecenoate-based sultaine thickener, myristate-based sultaine thickener Thickener.

The synthesis route of the degradable water-based clean fracturing fluid thickener in the present invention is as follows:

The specific preparation method of the degradable water-based clean fracturing fluid thickener is as follows:

Add the compound of formula II and N,N-dimethylethanolamine into the reaction kettle according to a certain molar ratio and mix evenly, add p-toluenesulfonic acid with a mass fraction of 0.5% to 1.5% of the reactant as a catalyst, and react at 170°C to 180°C After 12 hours, the compound of formula III was obtained after distillation under reduced pressure; wherein the compound of formula II is a straight-chain fatty acid of C ₁₄ -C ₂₀ containing at most one double bond and/or one hydroxyl substituent, and the compound of formula II and N,N-dimethyl The molar ratio of ethanolamine is 1:1.2～1:1.6.

Dissolve the compound of formula III in an appropriate amount of acetone and put it into a reaction kettle, take 1,3-propanesultone in a certain molar ratio, dissolve it in an appropriate amount of acetone, and place it in a high-level feeding tank. Slowly drop 1,3-propanesultone acetone solution into the reaction kettle, stir evenly, raise the temperature to 60℃～70℃ to fully react, and recrystallize with acetone-ethanol after vacuum filtration under reduced pressure to obtain white powder cleaning Fracturing fluid thickener; wherein the molar ratio of the compound of formula III to 1,3-propanesultone is 1:1.1 to 1:1.3.

The following are examples:

Example 1

Under the catalysis of p-toluenesulfonic acid, palmitic acid (16) is esterified with N,N-dimethylethanolamine, and then quaternized with 1,3-propane sultone to obtain And sulfo betaine type amphoteric surfactant cleaning fracturing fluid thickener. The molar ratio of palmitic acid to N,N-dimethylethanolamine is 1:1.2, the catalyst p-toluenesulfonic acid is 0.5%, the molar ratio of esterified product to 1,3-propane sultone is 1:1.3, and the synthesis is Cetyl sulfobetaine thickener.

According to the mass percentage, the hexadecanoate-based sultaine thickener and the cross-linking agent sodium salicylate are respectively dissolved in water, and then mixed to form a degradable water-based clean fracturing fluid with uniform viscosity. The mass percent of each component is: thickener 4.0%, crosslinking agent 1.0%, water 95%.

Example 2

Repeat Example 1 with the same procedure as described, except that stearic acid is used instead of palmitic acid. The molar ratio of stearic acid (18) to N,N-dimethylethanolamine is 1:1.5, the catalyst p-toluenesulfonic acid is 1.5%, and the molar ratio of esterified product to 1,3-propane sultone is 1:1.2 , The composition is stearic acid ester sulfobetaine thickener.

According to the mass percentage, the stearic carbonate-based sulfobetaine thickener and the cross-linking agent EDTA are respectively dissolved in water, and then mixed to form a degradable water-based clean fracturing fluid with uniform viscosity. The mass percent of each component is: thickener 3.0%, crosslinking agent 0.6%, water 96.4%.

Example 3

Repeat Example 1 with the same steps as described, the difference is that palmitic acid is replaced with arachidic acid. The molar ratio of arachidic acid (c20) to N,N-dimethylethanolamine is 1:1.6, the catalyst p-toluenesulfonic acid is 1.0%, and the molar ratio of esterified product to 1,3-propanesultone is 1:1.1, The composition is eicosanate sulfobetaine thickener.

According to the mass percentage, the eicosanate-based sultaine thickener and the cross-linking agent sodium salicylate are respectively dissolved in water, and then mixed to form a degradable water-based clean fracturing fluid with uniform viscosity. The mass percent of each component is: thickener 2.0%, crosslinking agent 0.8%, water 97.2%.

Example 4

Example 1 was repeated with the same steps as described, except that palmitic acid was replaced with oleic acid. The molar ratio of oleic acid (c18) to N,N-dimethylethanolamine is 1:1.5, the catalyst p-toluenesulfonic acid is 1.0%, and the molar ratio of esterified product to 1,3-propanesultone is 1:1.2, The composition is octadecenoate-based sultaine thickener.

According to the mass percentage, the octadecenoate-based sultaine thickener and the cross-linking agent EDTA are respectively dissolved in water, and then mixed to form a degradable water-based clean fracturing fluid with uniform viscosity. The mass percentage of each component is: 2.5% of thickener, 0.5% of crosslinking agent, and 97% of water.

Example 5

Repeat Example 1 with the same steps as described, the difference is that palmitic acid is replaced with ricinoleic acid. The molar ratio of ricinoleic acid to N,N-dimethylethanolamine is 1:1.2, the catalyst p-toluenesulfonic acid is 1.0%, and the molar ratio of esterified product to 1,3-propanesultone is 1:1.1. It is a hydroxyoctadecenoate-based sultaine thickener.

According to the mass percentage, the hydroxyoctadecenoate-based sultaine thickener and the crosslinking agent EDTA are respectively dissolved in water, and then mixed to form a degradable water-based clean fracturing fluid with uniform viscosity. The mass percent of each component is: thickener 1.5%, crosslinking agent 0.5%, water 98%.

Example 6

Example 1 was repeated with the same steps as described, except that myristic acid was used instead of palmitic acid. The molar ratio of myristic acid (14) to N,N-dimethylethanolamine is 1:1.4, the catalyst p-toluenesulfonic acid is 0.5%, and the molar ratio of esterified product to 1,3-propanesultone is 1:1.3 , The composition is myristate-based sulfobetaine thickener.

According to the mass percentage, the myristate-based sulfobetaine thickener and the cross-linking agent EDTA are respectively dissolved in water, and then mixed to form a degradable water-based clean fracturing fluid with uniform viscosity. The mass percent of each component is: thickener 4%, crosslinking agent 1.0%, water 95%.

Example 7

Performance evaluation of clean fracturing fluid

According to the clean fracturing fluid evaluation standard in SY/T6376-2008 "General Technical Conditions for Fracturing Fluids", using a Brookfield plus R/S rheometer in the United States, at 80°C, 170s ^-1 shear for 1h was used to test Examples 1 to 1. 6 viscosity performance; under simulated formation temperature (60° C.), 5% cyclohexane was added to test the gel breaking performance of Examples 1 to 6. The results are listed in Table 1 and Table 2, respectively.

Table 1 Properties of clean fracturing fluids

Table 2 Gel breaking performance of clean fracturing fluid

Under the condition of 80°C and 170s ^-1 shear, the viscosities of all the examples can be maintained above 50mPa·s after one hour, indicating that the clean fracturing fluid has excellent temperature resistance and shear resistance, which are better than SY/ T6376-2008 "General Specifications for Fracturing Fluids" general technical indicators for viscoelastic surfactant fracturing fluids. Adding 5% cyclohexane at simulated formation temperature (60°C), the apparent viscosity is less than 5mPa·s after 6 hours, that is, the gel is completely broken and there is no precipitation. Gel breaking, with good gel breaking performance.

The clean fracturing fluid is easy to prepare, because the thickener used is a long-chain quaternary ammonium salt containing a monoester group, which can be completely hydrolyzed into a single-molecule compound. These small-molecule compounds have good biodegradability and can be quickly degraded by microorganisms. Degrade to produce CO ₂ , H ₂ O and inorganic salts, which will not pollute the environment. At the same time, the thickener used is an amphoteric surfactant. When encountering hydrophobic substances such as oil and gas, these molecules will be coated to form a spherical structure. The worm-like network of the fracturing fluid will be destroyed and the viscosity will drop. Therefore, there is no need to add gel breakers. Agent, the clean fracturing fluid can automatically break the gel when it encounters organic matter such as oil and gas. After the gel is broken, the fracturing fluid will form an emulsion without residue, which will cause little damage to the reservoir and fractures.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (6)

1. an application of the betaine type amphoteric surfactant containing ester group and sulfo group, the molecular structural formula of the betaine type amphoteric surfactant containing ester group and sulfo group is as shown in formula (I): Wherein R is a straight-chain alkyl group of C ₁₃ -C ₁₉ , and the carbon chain of R contains at most one double bond and/or one hydroxyl substituent, and is characterized in that it is used for thickening of degradable water-based clean fracturing fluid in oil and gas fields When the thickener meets the hydrophobic substance in the oil and gas field, the hydrophobic substance will be coated into a spherical structure, and the degradable water-based cleaning fracturing fluid containing the thickener will automatically break the gel; the degradable water-based cleaning The viscosity of the fracturing fluid remains above 50mPa·s after shearing for one hour. 2. The application according to claim 1, wherein the degradable water-based clean fracturing fluid also includes a crosslinking agent, wherein the mass percent of the thickener is 1.5%-4.0%, and the amount of the crosslinking agent The mass percentage is 0.5%-1.0%. 3. application as claimed in claim 2, is characterized in that, described linking agent is sodium salicylate and/or EDTA. 4. The application according to claim 2 or 3, characterized in that the main chemical components of the degradable water-based clean fracturing fluid are thickeners and crosslinking agents. 5. application as claimed in claim 1, is characterized in that, comprises a double bond and/or a hydroxyl substituent on the R carbon chain in the thickening agent. 6. The application according to claim 1, wherein R is a C ₁₅ -C ₁₇ linear alkyl group.