Preparation method of chelating alkaline prepad fluid for fracture acidizing

Abstract

The invention belongs to the technical field of fracture acidizing in the field of petroleum engineering, and relates to a preparation method of a chelating alkaline prepad fluid for fracture acidizing, which comprises the following steps: firstly preparing tetrapropylamine-N, N, N ', N'-tetraacetic acid, and uniformly mixing potassium hydroxide and methanol to obtain a mixed solution I; uniformly mixing tetrapropylammonium bromide and methanol to obtain a mixed solution II; quickly adding the mixed solution I into the mixed solution II, and continuously stirring until all precipitates are separated out; filtering and precipitating under reduced pressure to obtain a faint yellow liquid which is a crude product; refining the crude product, cooling and crystallizing to obtain a tetrapropylamine-N, N, N ', N'-tetraacetic acid finished product; the preparation method comprises the following steps: preparing tetrapropylamine-N, N, N ', N'-tetraacetic acid and EDTA (Ethylene Diamine Tetraacetic Acid) disodium into an aqueous solution, namely prepad fluid; barium and strontium scales and stratum pollution and clay components can be effectively dissolved; while the fracturing acidizing effect is guaranteed, the environmental protection property and the equipment durability are greatly improved, and the fracturing acidizing agent has wide application prospects and market value.

Description

Technical Field

[0001] The invention belongs to the technical field of fracturing and acidizing in the field of petroleum engineering, in particular to a method for preparing a chelated alkaline prefluid for fracturing and acidizing. Background Art

[0002] Acid fracturing is referred to as acid fracturing. It is to use acid as fracturing fluid at a pressure higher than the formation fracture pressure, and to perform fracturing without adding proppant. During the acid fracturing process, the wall of the crack is corroded into an uneven surface by the dissolution of the acid, so that after stopping the pump and unloading the pressure, the wall of the crack will not be completely closed. Therefore, it has a higher conductivity and is effective in restoring and improving the production capacity of oil wells. This method is suitable for carbonate reservoirs.

[0003] Chinese patent CN202010819815.8 discloses an autogenous acid and pre-fluid system for high-temperature carbonate rock fracturing acidification. The autogenous acid pre-fluid system includes the following substances by mass fraction: 0.5% cationic thickener, 1% potassium chloride, 1% drainage agent, 1% clay stabilizer, 0.3% cross-linking agent, 10% autogenous acid and 86.2% water; wherein the autogenous acid includes the following substances: 45% to 50% methyl formate, 15% to 2% glycerol 0%, methanol 15% to 20%, formic acid 0.1% to 0.5%, and the balance is water; the autogenous acid prefluid system of the invention has a simple preparation process, does not generate acid at room temperature, and is convenient for on-site reservoirs. After reaching the target layer, the system begins to gradually generate acid with a high acid concentration, which can effectively increase the acid etching distance. Compared with the existing system, the deep acidizing effect is significantly enhanced. At the same time, it has good compatibility with the autogenous acid prefluid thickener, and its combined use can achieve the dual production-increasing effects of fracturing and acidizing. Chinese patent CN201610712207.0 discloses a method for the combined operation of explosive fracturing and acidizing, which includes optimizing the process parameters of the combined operation of explosive fracturing and acidizing, preparing for the operation before explosive fracturing and filling the wellbore with liquid, testing the absorption of the formation before explosive fracturing, lowering the explosive fracturing operation string to a predetermined operating depth, pressurizing and detonating the string, killing the well, detonating the explosive fracturing operation string, testing the absorption of the formation after the explosive fracturing is completed, lowering the acidizing operation string, pumping the acid liquid segment plug, and starting The steps of acidizing operation string, lowering electric pump production string and electric pump drainage and wellhead alkali neutralization, lowering electric pump production Y string without Y plug, pumping acid plug, Y plug, electric pump drainage and wellhead alkali neutralization can further enhance the effect of deflagration fracturing and acidizing, enhance the acid injection capacity, expand the acidizing radius, and further prevent the closure of cracks, and enhance the physical effect; it can enhance the effect of deflagration fracturing, flexibly select the subsequent acidizing steps, and save operation steps while ensuring the operation effect. However, in the traditional fracturing acidizing process, strong acid is used to clean and expand rock cracks, and the acid corrodes the equipment severely and the environmental pollution problem is prominent. Therefore, seeking a new type of fracturing acidizing pre-fluid that is efficient, environmentally friendly and can effectively prevent metal ion precipitation has become an urgent need in the industry. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a chelated alkaline pre-fluid for fracturing acidification. The chelated system composed of tetrapropylamine-N,N,N',N'-tetraacetic acid and disodium EDTA is used as the main component of the pre-fluid, which can effectively dissolve barium and strontium scales as well as formation pollution and clay components.

[0005] In order to achieve the above object, the present invention provides a method for preparing a chelated alkaline pre-fluid for fracturing acidification, the main steps of which are as follows: (1) Preparation of tetrapropylamine-N,N,N',N'-tetraacetic acid: 1) preparing a solution: mixing potassium hydroxide and methanol evenly, wherein the mass ratio of potassium hydroxide to methanol is 0.8-1:1, to obtain a mixed solution 1; 2) Reaction: Tetrapropylammonium bromide and solvent methanol are uniformly mixed, the mass ratio of tetrapropylammonium bromide to methanol is 1:2, to obtain mixed solution 2, the mixed solution 1 obtained in step 1) is quickly added to the mixed solution 2, and the reaction is continued under stirring for 2 hours at room temperature until all precipitates are precipitated; the volume ratio of the mixed solution 1 to the mixed solution 2 is: 0.97:2.53; 3) Filtration: Filter the precipitate under reduced pressure, and the resulting light yellow liquid is the crude product of tetrapropylamine-N,N,N',N'-tetraacetic acid; 4) Purification: add deionized water to the crude product, heat to reflux, keep the temperature at 35-50°C, react at constant temperature for 1-6 hours, cool and crystallize, and the obtained white crystals are the finished product of tetrapropylamine-N,N,N',N'-tetraacetic acid; the amount of deionized water added should be sufficient to dissolve the crude product, and the volume ratio of the crude product to deionized water is preferably 1:10 to 1:20; The tetrapropylamine-N,N,N',N'-tetraacetic acid is an amine carboxylic acid compound having a plurality of dissociable groups, including an amine group (-NH2) and a carboxylic acid group (-COOH); (2) Preparation of chelating alkaline pre-liquid: Add tetrapropylamine-N,N,N',N'-tetraacetic acid, disodium EDTA and KCl into a reaction kettle, fully blend them at room temperature and pressure, and prepare an aqueous solution, i.e., the pre-liquid. The mass concentration of tetrapropylamine-N,N,N',N'-tetraacetic acid in the pre-liquid is 25%-30%, the mass concentration of disodium EDTA is 10%-15%, and the mass concentration of KCl is 1%.

[0006] The present invention also provides a chelated alkaline prefluid for fracturing acidification prepared by the preparation method, which can effectively dissolve barium and strontium scales, formation pollution and clay components.

[0007] The chelated alkaline pre-fluid prepared by the present invention can fully dissolve mud pollution and iron and calcium scale ions in the formation; and the dissolved substances cannot decompose to form precipitation in a short period of time. Injecting the chelated alkaline pre-fluid before fracturing and acidizing operations can pre-clear metal ions in the wellbore and reservoir that may affect the effect of the acid solution, improve the effective utilization rate of the acid solution, reduce the ineffective reaction between the acid solution and the rock, and significantly reduce the degree of corrosion to the equipment, thereby realizing environmentally friendly and efficient fracturing and acidizing operations.

[0008] Compared with the prior art, the synthesized tetrapropylamine-N,N,N',N'-tetraacetic acid in the present invention has good temperature resistance and excellent calcium and magnesium ion chelating ability, and can maintain stable chelating effect under high pressure and high temperature environment; and disodium EDTA (disodium ethylenediaminetetraacetic acid), as a widely used chelating agent, can effectively form stable complexes with various metal ions, thereby preventing acid from reacting with metal ions in the wellbore and reservoir to form insoluble salts; the chelating system composed of tetrapropylamine-N,N,N',N'-tetraacetic acid and disodium EDTA is weakly alkaline with a pH value of 9-12, and can effectively dissolve barium and strontium scales as well as formation pollution and clay components; while ensuring the fracturing acidizing effect, the environmental protection and equipment durability are greatly improved, and the present invention has broad application prospects and market value. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a schematic diagram of the experimental results of dissolving barium strontium scale with chelated alkaline pre-liquid in Example 1 of the present invention, wherein A is before dissolution and B is 96 hours after dissolution.

[0010] Figure 2 This is a schematic diagram of the experimental results of the present invention involving the use of a 25% mass concentration of tetrapropylamine-N,N,N',N'-tetraacetic acid aqueous solution to dissolve barium strontium scale, wherein A is before dissolution, B is during the 96-hour constant temperature process, and C is 48 hours after dissolution.

[0011] Figure 3 This is a schematic diagram of the experimental results of the present invention for dissolving barium strontium scale using a disodium EDTA aqueous solution with a mass concentration of 10% alone, wherein A is before dissolution and B is after constant temperature for 96 hours. DETAILED DESCRIPTION

[0012] The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0013] Embodiment 1: This embodiment relates to a method for preparing a chelated alkaline pre-fluid for fracturing acidification, and its main steps are as follows: (1) Preparation of tetrapropylamine-N,N,N',N'-tetraacetic acid: 1) preparing a solution: mixing potassium hydroxide and methanol, wherein the weight ratio of potassium hydroxide to methanol is 0.8:1, to obtain a mixed solution 1; 2) Reaction: Tetrapropylammonium bromide and solvent methanol are uniformly mixed, the weight ratio of tetrapropylammonium bromide to methanol is 1:2, to obtain mixed solution 2, to which the mixed solution 1 obtained in step 1) is quickly added, and the reaction is continued with stirring for 2 hours until all precipitates are precipitated, and the volume ratio of mixed solution 1 to mixed solution 2 is 0.97:2.53; 3) Filtration: Filter the precipitate under reduced pressure, and the resulting light yellow liquid is a tetrapropylammonium hydroxide mixed solution, i.e., a crude product of tetrapropylamine-N,N,N',N'-tetraacetic acid; 4) Purification: add 1L of deionized water to 100ml of the crude product, heat to reflux, keep the temperature at 40°C, react at constant temperature for 3 hours, cool and crystallize, and the obtained white crystals are the finished product of tetrapropylamine-N,N,N',N'-tetraacetic acid; Tetrapropylamine-N,N,N',N'-tetraacetic acid is an amine carboxylic acid compound having multiple dissociable groups, including an amine group (-NH2) and a carboxylic acid group (-COOH); (2) Preparation of chelating alkaline pre-fluid: Tetrapropylamine-N,N,N',N'-tetraacetic acid, disodium EDTA and KCl are dissolved in water and fully blended at room temperature and pressure to prepare a pre-fluid, wherein the mass concentration of tetrapropylamine-N,N,N',N'-tetraacetic acid is 25%, the mass concentration of disodium EDTA is 10%, and the mass concentration of KCl is 1%. The KCl is used as a clay anti-swelling agent.

[0014] Embodiment 2: This embodiment relates to a method for preparing a chelated alkaline pre-fluid for fracturing acidification, and its main steps are as follows: (1) Preparation of tetrapropylamine-N,N,N',N'-tetraacetic acid: 1) preparing a solution: mixing potassium hydroxide and methanol, wherein the weight ratio of potassium hydroxide to methanol is 1:1, to obtain a mixed solution 1; 2) Reaction: Tetrapropylammonium bromide and solvent methanol are uniformly mixed, the weight ratio of tetrapropylammonium bromide to methanol is 1:2, to obtain mixed solution 2, to which the mixed solution 1 obtained in step 1) is quickly added, and the reaction is continued with stirring for 2 hours until all precipitates are precipitated, and the volume ratio of mixed solution 1 to mixed solution 2 is 0.97:2.53; 3) Filtration: Filter the precipitate under reduced pressure, and the resulting light yellow liquid is a tetrapropylammonium hydroxide mixed solution, i.e., a crude product of tetrapropylamine-N,N,N',N'-tetraacetic acid; 4) Purification: add 1L of deionized water to 100ml of the crude product, heat to reflux, keep the temperature at 35°C, react at constant temperature for 6 hours, cool and crystallize, and the obtained white crystals are the finished product of tetrapropylamine-N,N,N',N'-tetraacetic acid; Tetrapropylamine-N,N,N',N'-tetraacetic acid is an amine carboxylic acid compound having multiple dissociable groups, including an amine group (-NH2) and a carboxylic acid group (-COOH); (2) Preparation of chelating alkaline pre-solution: dissolve tetrapropylamine-N,N,N',N'-tetraacetic acid and disodium EDTA in water, fully blend at room temperature and pressure to prepare a pre-solution, wherein the mass concentration of tetrapropylamine-N,N,N',N'-tetraacetic acid in the pre-solution is 25%, and the mass concentration of disodium EDTA is 10%.

[0015] Embodiment 3: This embodiment relates to a method for preparing a chelated alkaline pre-fluid for fracturing acidification, and its main steps are as follows: (1) Preparation of tetrapropylamine-N,N,N',N'-tetraacetic acid: 1) preparing a solution: mixing potassium hydroxide and methanol, wherein the weight ratio of potassium hydroxide to methanol is 0.8:1, to obtain a mixed solution 1; 2) Reaction: Tetrapropylammonium bromide and solvent methanol are uniformly mixed, the weight ratio of tetrapropylammonium bromide to methanol is 1:2, to obtain mixed solution 2, to which the mixed solution 1 obtained in step 1) is quickly added, and the reaction is continued with stirring for 2 hours until all precipitates are precipitated, and the volume ratio of mixed solution 1 to mixed solution 2 is 0.97:2.53; 3) Filtration: Filter the precipitate under reduced pressure, and the resulting light yellow liquid is a tetrapropylammonium hydroxide mixed solution, i.e., a crude product of tetrapropylamine-N,N,N',N'-tetraacetic acid; 4) Purification: add 1L of deionized water to 100ml of the crude product, heat to reflux, keep the temperature at 50°C, react at constant temperature for 3 hours, cool and crystallize, and the obtained white crystals are the finished product of tetrapropylamine-N,N,N',N'-tetraacetic acid; Tetrapropylamine-N,N,N',N'-tetraacetic acid is an amine carboxylic acid compound having multiple dissociable groups, including an amine group (-NH2) and a carboxylic acid group (-COOH); (2) Preparation of chelating alkaline pre-liquid: Tetrapropylamine-N,N,N',N'-tetraacetic acid, disodium EDTA and KCl are dissolved in water and fully blended at room temperature and pressure to prepare a pre-liquid, wherein the mass concentration of tetrapropylamine-N,N,N',N'-tetraacetic acid is 30%, the mass concentration of disodium EDTA is 15%, and the mass concentration of KCl is 1%. The KCl is used as a clay anti-swelling agent.

[0016] Embodiment 4: This embodiment relates to a method for preparing a chelated alkaline pre-fluid for fracturing acidification, and its main steps are as follows: (1) Preparation of tetrapropylamine-N,N,N',N'-tetraacetic acid: 1) preparing a solution: mixing potassium hydroxide and methanol, wherein the weight ratio of potassium hydroxide to methanol is 0.9:1, to obtain a mixed solution 1; 2) Reaction: Tetrapropylammonium bromide and solvent methanol are uniformly mixed, the weight ratio of tetrapropylammonium bromide to methanol is 1:2, to obtain mixed solution 2, to which the mixed solution 1 obtained in step 1) is quickly added, and the reaction is continued with stirring for 2 hours until all precipitates are precipitated, and the volume ratio of mixed solution 1 to mixed solution 2 is 0.97:2.53; 3) Filtration: Filter the precipitate under reduced pressure, and the resulting light yellow liquid is a tetrapropylammonium hydroxide mixed solution, i.e., a crude product of tetrapropylamine-N,N,N',N'-tetraacetic acid; 4) Purification: add 1L of deionized water to 100ml of the crude product, heat to reflux, keep the temperature at 50°C, react at constant temperature for 1 hour, cool and crystallize, and the obtained white crystals are the finished product of tetrapropylamine-N,N,N',N'-tetraacetic acid; Tetrapropylamine-N,N,N',N'-tetraacetic acid is an amine carboxylic acid compound having multiple dissociable groups, including an amine group (-NH2) and a carboxylic acid group (-COOH); (2) Preparation of chelating alkaline pre-liquid: Tetrapropylamine-N,N,N',N'-tetraacetic acid, disodium EDTA and KCl are dissolved in water and fully blended at room temperature and pressure to prepare a pre-liquid, wherein the mass concentration of tetrapropylamine-N,N,N',N'-tetraacetic acid is 27%, the mass concentration of disodium EDTA is 13%, and the mass concentration of KCl is 1%. The KCl is used as a clay anti-swelling agent.

[0017] Embodiment 5: This example involves an experiment on the application effect of the chelated alkaline pre-pad liquid prepared in Example 1. The barium strontium scale retrieved from the oil well is used as the experimental object. 2.5 grams of barium strontium scale is added to 100 ml of the prepared pre-pad liquid and allowed to stand at a constant temperature of 60°C for 96 hours. The barium strontium scale is dissolved, and the liquid is clear without precipitation. The experimental results are as follows: Figure 1 shown.

[0018] In this example, the barium strontium scale was dissolved by using a 25% tetrapropylamine-N,N,N',N'-tetraacetic acid aqueous solution as control group 1. 2.5 g of barium strontium scale was added to 100 ml of a 25% tetrapropylamine-N,N,N',N'-tetraacetic acid aqueous solution and the barium strontium scale was dissolved at a constant temperature of 60°C for 96 hours. However, after being kept at this temperature for 48 hours, flocculent precipitation appeared. The experimental results are shown in FIG. Figure 2 shown.

[0019] In this example, a 10% mass concentration of disodium EDTA aqueous solution was used alone to dissolve barium strontium scale as control group 2. 2.5 g of barium strontium scale was added to 100 ml of prepared 10% EDTA and allowed to stand at a constant temperature of 60° C. for 96 hours. The barium strontium scale was not dissolved. The experimental results are as follows: Figure 3 shown.

[0020] The above experiments show that the chelating alkaline pre-fluid of the present invention can fully dissolve barium and strontium scale, and no precipitation is formed after dissolution, and its effect is better than the dissolution effect of using tetrapropylamine-N,N,N',N'-tetraacetic acid aqueous solution and disodium EDTA aqueous solution alone. It shows that the combination of tetrapropylamine-N,N,N',N'-tetraacetic acid and disodium EDTA in the chelating alkaline pre-fluid of the present invention has a synergistic effect, which enhances the dissolution effect on barium and strontium scale.

[0021] The chelated alkaline pre-fluid prepared by the present invention can fully dissolve mud pollution and barium and strontium ions in the formation; at the same time, it has a good chelating effect on ions such as iron and calcium, which not only solves the problem of mud pollution, but also has a good transformation effect on the formation. The overall property is weakly alkaline (pH 9-12), and does not affect the performance of subsequent fracturing fluid.

Claims

1. A method for preparing a chelated alkaline pre-fluid for fracturing acidification, characterized in that: The main steps are as follows: (1) Preparation of tetrapropylamine-N,N,N',N'-tetraacetic acid: 1) Liquid preparation: Mix potassium hydroxide and methanol evenly to obtain a mixed solution 1; 2) Reaction: Tetrapropylammonium bromide and methanol are mixed evenly to obtain a mixed solution 2; the mixed solution 1 obtained in step 1) is added to the mixed solution 2, and the mixture is stirred continuously until all precipitates are precipitated; 3) Filtration: Filter the precipitate under reduced pressure, and the resulting light yellow liquid is the crude product of tetrapropylamine-N,N,N',N'-tetraacetic acid; 4) Purification: Add deionized water to the crude product, heat to reflux, react at a constant temperature, and then cool and crystallize. The resulting white crystals are the finished product of tetrapropylamine-N,N,N',N'-tetraacetic acid; (2) Preparation of chelating alkaline pre-solution: Dissolve tetrapropylamine-N,N,N',N'-tetraacetic acid and disodium EDTA in water to prepare a pre-solution, wherein the mass concentration of tetrapropylamine-N,N,N',N'-tetraacetic acid in the pre-solution is 25%-30%, and the mass concentration of disodium EDTA is 10%-15%.

2. The method for preparing the chelated alkaline prefluid for fracturing acidification according to claim 1, characterized in that: The pre-flushing liquid also contains a clay anti-swelling agent; the clay anti-swelling agent is KCl, and the mass concentration of KCl is 1%.

3. The method for preparing the chelated alkaline pre-fluid for fracturing acidification according to claim 1, characterized in that: The mass ratio of potassium hydroxide to methanol in the mixed solution 1 is 0.8-1:

1.

4. The method for preparing the chelated alkaline pre-fluid for fracturing acidification according to claim 1, characterized in that: The mass ratio of tetrapropylammonium bromide to methanol in the mixed solution 2 is 1:

2.

5. The method for preparing the chelated alkaline prefluid for fracturing acidification according to claim 1, characterized in that: The volume ratio of the mixed solution 1 to the mixed solution 2 is 0.97:2.

53.

6. The method for preparing the chelated alkaline prefluid for fracturing acidification according to claim 1, characterized in that: Step 4) During the refining, the isothermal reaction temperature is maintained at 35-50°C for 1-6 hours.

7. The chelated alkaline prefluid for fracturing acidification prepared by the preparation method according to any one of claims 1 to 6.

8. The chelated alkaline pre-fluid for fracturing acidification according to claim 7, characterized in that: It can effectively dissolve barium and strontium scale as well as formation pollution and clay components.

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