Cross-linking agent for improving stability of guanidine gum fracturing fluid, preparation method and fracturing fluid

Abstract

The invention relates to a preparation method of a cross-linking agent for improving the stability of guanidine gum fracturing fluid, which comprises the following steps: S1, carrying out reaction on oxalyl chloride and tetraethylenepentamine to obtain A-TEPA for later use; s2, boric acid is added into the ethylene glycol and the n-butyl alcohol under stirring, a reflux condensation reaction is carried out, the reaction temperature is 100-150 DEG C, and a reaction mixture is obtained; s3, cooling the reaction mixture to room temperature, adding A-TEPA, then heating at the temperature of 100-150 DEG C, and reacting for 3-5 hours; s4, finally adding dipentaerythritol, heating at 100-150 DEG C for 1-3 hours, cooling to room temperature, and adjusting the pH value of the solution to 10-11, so as to obtain a polyamino borate cross-linking agent; the cross-linking agent obtained by the invention can be blended with a fracturing base fluid to obtain a guanidine gum fracturing fluid with good stability.

Description

Technical Field

[0001] The invention belongs to the technical field of guar gum fracturing fluid, and in particular relates to a cross-linking agent for improving the stability of guar gum fracturing fluid, a preparation method and the fracturing fluid. Background Art

[0002] With the continuous development of the oil industry, the corresponding fracturing technology is also constantly improving and perfecting. In the field of petroleum, fracturing refers to the process of artificially creating cracks in the formation by external force during oil or gas production, thereby improving the flow environment of oil underground and increasing oil well production. It plays an important role in improving the flow conditions at the bottom of the oil well, slowing down the interlayer and improving the utilization of the oil layer. Fracturing technology generally includes water-based fracturing, oil-based fracturing, foam fracturing and low-temperature fracturing, etc., and water-based fracturing is more commonly used. Water-based fracturing fluid uses water as a dispersion medium and adds various treatment agents, especially water-soluble polymers, to form a working fluid with strong comprehensive properties required by the fracturing process (Chemical Research and Applications, 1993, 15(3): 06-16). These polymers swell into sols in water and form extremely high viscosity gels after cross-linking. They have the advantages of high viscosity, strong sand suspension capacity, low filtration loss and low friction resistance. Generally, the aqueous solution of water-soluble polymers and additives is called linear gel or thickened water-based fracturing fluid. Once a cross-linking agent is added to the linear gel, it will form a cross-linked gel with viscoelasticity. Water-based fracturing fluid is widely used for its safety, cleanliness and easy control of its properties with additives. Except for a few particularly water-sensitive formations, water-based fracturing fluid can be applied to almost all oil and gas reservoirs. It is the fastest and most comprehensive system of fracturing fluid technology. There are many chemical additives in water-based fracturing fluid. Usually, fracturing fluid additives include thickeners, degelators, and cross-linking agents. In addition, in order to improve the various performance indicators of fracturing fluid, pH regulators, high-temperature stabilizers, anti-clay swelling agents, demulsifiers, bactericides, foaming agents and other chemical additives are also needed. Hydraulic fracturing technology has been developed for nearly half a century, especially since the late 1980s, it has achieved rapid development in fracturing design, fracturing fluids, additives, fracturing equipment, monitoring instruments and crack detection, making hydraulic fracturing technology have new breakthroughs in fracture height control technology, high permeability layer sand fracturing, repeated fracturing, deep penetration fracturing and large sand volume multi-stage fracturing. At present, hydraulic fracturing technology has been widely used in the development of low-permeability oil and gas fields as the main measure to increase the production and injection of oil and water wells. Through hydraulic fracturing, the seepage conditions near the bottom of the well are improved and the oil well productivity is increased. In the United States, 30% of crude oil production is obtained through fracturing. The production of low-permeability oil fields in China and the production obtained through hydraulic fracturing transformation are also gradually increasing. Especially now that the oil industry is in a recession, the wide application and in-depth research of hydraulic fracturing technology are expected to inject new vitality and vitality into the oil industry. The optimal implementation of hydraulic fracturing technology and the breakthrough of key technologies will bring immeasurable prospects to the oil industry (Drilling and Production Technology, 1998, 4 (21): 21-25). The commonly used technology in water-based fracturing is guar fracturing. Guar is a high-molecular polymer polysaccharide with good water solubility, which exhibits the characteristics of polymer curling and winding in water.On the main chain of the guar gum structure, each sugar unit has two cis hydroxyl groups. Under appropriate pH conditions, hydrogen bonds are formed by complexation with cross-linking agents to form a gel with a network structure (Polymer Testing, 2021, 97: 107155). Guar gum is a commonly used thickener in water-based fracturing fluids. Different additives need to be added during use to meet the requirements of viscosity and sand-carrying performance. Guar gum and its derivatives are more commonly used in water-based fracturing fluids due to their strong thickening ability and low price. The gel system they form is beneficial to improving the sand-carrying and fracture-forming ability of the fracturing fluid and the conductivity of the reservoir. At the same time, there are also some disadvantages, such as poor stability and high content of residue in the degelling fluid. Therefore, the development of a guar gum fracturing fluid with stable performance at low guar gum addition has become a relatively important topic. Summary of the invention

[0003] The present invention solves the technical problem by adopting the following technical solutions:

[0004] A method for preparing a cross-linking agent for improving the stability of guar gum fracturing fluid comprises the following steps:

[0005] S1, reacting oxalyl chloride and tetraethylenepentamine to obtain A-TEPA for standby use;

[0006] S2, adding boric acid to the stirred ethylene glycol and n-butanol, performing a reflux condensation reaction at a reaction temperature of 100 to 150° C., to obtain a reaction mixture;

[0007] S3, cooling the reaction mixture to room temperature, adding A-TEPA, and then heating at 100-150° C. for a reaction time of 3-5 h;

[0008] S4. Finally, dipentaerythritol is added, and the mixture is heated at 100-150° C. for 1-3 hours, cooled to room temperature, and the pH value of the solution is adjusted to 10-11 to obtain a polyamino borate crosslinking agent.

[0009] Furthermore, the molecular structure of the polyamino borate crosslinker is:

[0010]

[0011] Furthermore, the molar ratio of ethylene glycol, n-butanol, boric acid, oxalyl chloride, tetraethylene pentamine, dipentaerythritol and A-TEPA is:

[0012] (0.98~1.5):(0.54~1):(0.4~0.8):(0.06~0.10):(0.04~0.067):(0.04~0.08):(0.03~0.05).

[0013] Furthermore, in step S1, the reaction temperature of oxalyl chloride and tetraethylenepentamine is 100-150° C., and the reaction time is 4-5 hours.

[0014] Furthermore, in step S2, the reaction time is 2 to 3 hours.

[0015] The polyamino borate crosslinking agent is prepared by the above-mentioned preparation method of the crosslinking agent for improving the stability of guar gum fracturing fluid.

[0016] The guar fracturing fluid is obtained by using the polyamino borate crosslinking agent.

[0017] The above-mentioned guar gum fracturing fluid: potassium chloride, hydroxypropyl guar gum, fungicide and sodium hydroxide are added to water, and after standing for 3 to 5 hours to stabilize, a fracturing fluid base fluid is obtained; and then a polyamino borate crosslinking agent is added thereto to obtain a guar gum fracturing fluid.

[0018] Furthermore, the mass percentages of the components in the fracturing fluid base liquid are: 0.8% to 3% potassium chloride, 0.2% to 0.5% hydroxypropyl guar gum, 0.04% to 0.1% fungicide and 0.009% to 0.1% sodium hydroxide, and 0.3 to 0.5 ml of polyamino borate crosslinking agent is required for every 100 ml of fracturing fluid base liquid.

[0019] Furthermore, the fungicide is one or a mixture of at least two of dodecyldimethylbenzyl ammonium chloride or isothiazolinones.

[0020] The advantages and positive effects of the present invention are:

[0021] The purpose of the present invention is to provide a preparation method of a cross-linking agent for stabilizing guar fracturing fluid in view of the shortcomings of the current water-based fracturing fluid system, wherein the method grafts tetraethylenepentamine with oxalyl chloride to obtain an amine product A-TEPA containing a cyclic structure and multiple amino sites. The cyclic structure can improve the stability, and the amino groups it carries can provide reaction sites for the reaction product of the previous step, and the final cross-linking agent can be obtained after multiple steps of reaction and post-treatment; the cross-linking agent obtained by the present invention can be prepared with a fracturing base fluid to obtain a guar fracturing fluid with good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a test diagram of the guar gum fracturing fluid prepared with the unmodified cross-linking agent in Comparative Example 2 of the present invention;

[0023] Figure 2 This is a test diagram of the modified cross-linking agent prepared into guar gum fracturing fluid in Comparative Example 2 of the present invention; DETAILED DESCRIPTION

[0024] First, it should be noted that the specific structure, features and advantages of the present invention will be specifically described below by way of example, but all descriptions are only for illustration and should not be understood as limiting the present invention in any way. In addition, any single technical feature described or implied in the embodiments mentioned herein can still be combined or deleted between these technical features (or their equivalents) to obtain more other embodiments of the present invention that may not be directly mentioned herein.

[0025] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0026] Example 1

[0027] The method for preparing a cross-linking agent for improving the stability of guar gum fracturing fluid provided in this embodiment is characterized by comprising the following steps:

[0028] S1, reacting oxalyl chloride and tetraethylenepentamine, the reaction temperature of oxalyl chloride and tetraethylenepentamine is 100-150° C., the reaction time is 4-5 hours, and A-TEPA is obtained for standby use;

[0029] S2. Adding boric acid to the stirred ethylene glycol and n-butanol to carry out reflux condensation reaction at a reaction temperature of 100 to 150° C. for a reaction time of 2 to 3 h to obtain a reaction mixture;

[0030] S3, cooling the reaction mixture to room temperature, adding A-TEPA, and then heating at 100-150° C. for a reaction time of 3-5 h;

[0031] S4. Finally, dipentaerythritol is added, and the mixture is heated at 100-150° C. for 1-3 hours, cooled to room temperature, and the pH value of the solution is adjusted to 10-11 with sodium hydroxide solution to obtain a polyamino borate crosslinking agent.

[0032] The reaction mechanism of the polyamino borate crosslinking agent of the present invention is shown in the following reaction formula: oxalyl chloride is grafted with tetraethylene pentamine to obtain a cyclic product A-TEPA; boric acid reacts with ethylene glycol and n-butanol at 130° C. for a dehydration condensation reaction for 3 hours, and then reacts with A-TEPA at 150° C. for 3 hours to obtain a reaction mixture; then reacts with dipentaerythritol at 150° C. for 1 hour, and finally treats with 50% (mass percentage) sodium hydroxide solution to obtain the polyamino borate crosslinking agent.

[0033]

[0034] Wherein, the molar ratio of ethylene glycol, n-butanol, boric acid, oxalyl chloride, tetraethylene pentamine, dipentaerythritol and A-TEPA is:

[0035] (0.98~1.5):(0.54~1):(0.4~0.8):(0.06~0.10):(0.04~0.067):(0.04~0.08):(0.03~0.05); wherein the molar ratio of A-TEPA here refers to the amount of A-TEPA added as a reactant in step S3.

[0036] The polyamino borate crosslinking agent prepared by the preparation method of the crosslinking agent for improving the stability of guar fracturing fluid can be used to obtain guar fracturing fluid.

[0037] The method for obtaining the guar gum fracturing fluid is as follows: potassium chloride, hydroxypropyl guar gum, a fungicide and sodium hydroxide are added into water, and the water is allowed to stand for 3 to 5 hours to stabilize, thereby obtaining a fracturing fluid base fluid; and a polyamino borate crosslinking agent is added thereto, thereby obtaining the guar gum fracturing fluid; wherein the mass percentages of the components in the fracturing fluid base fluid are: 0.8% to 3% potassium chloride, 0.2% to 0.5% hydroxypropyl guar gum, 0.04% to 0.1% fungicide and 0.009% to 0.1% sodium hydroxide, and 0.3 to 0.5 ml of the polyamino borate crosslinking agent needs to be prepared in every 100 ml of the fracturing fluid base fluid.

[0038] It should be noted that the fungicide is one or a mixture of at least two of dodecyldimethylbenzyl ammonium chloride or isothiazolinones.

[0039] The main function of guar fracturing fluid in reservoir transformation is to transmit pressure and form cracks in the bottom layer, and then transport and lay additives to the designated position for hydraulic cracking; at the same time, the guar fracturing fluid should have a certain stability to prevent the stability from decreasing due to mechanical operation; the polyamino borate crosslinking agent of the present invention is prepared with a fracturing fluid base fluid containing additives such as hydroxypropyl guar gum to obtain a guar fracturing fluid with good stability.

[0040] Example 2

[0041] The preparation method of the guar gum fracturing fluid with good stability in this embodiment comprises the following steps:

[0042] A magnetic particle was placed in a reaction tube, 7.5 g (0.06 mol) of oxalyl chloride and 7.5 g (0.04 mol) of tetraethylenepentamine were added thereto, and the reaction was controlled at 100°C for 4 h under magnetic stirring to obtain A-TEPA; another reaction tube was placed in a magnetic particle, 60 g (0.98 mol) of ethylene glycol and 40 g (0.54 mol) of n-butanol were added thereto, and 25 g (0.4 mol) of boric acid was added to the reaction tube under magnetic stirring; a reflux condenser with a water separator was installed, and the reaction was heated to 130°C under reflux. ℃, the reaction time is 3h; the reaction mixture is cooled to room temperature, and 15g (0.03mol) of A-TEPA is added, and then the reaction mixture is heated at 150℃ for 3h; 10.2g (0.04mol) of dipentaerythritol is added to the reaction mixture, heated at 150℃ for 1 hour, cooled to room temperature, and finally the pH value of the solution is adjusted to 10-11 with 50% (mass percentage) of sodium hydroxide solution to obtain a yellow liquid as the final solution, and 0.3ml of the solution is taken and mixed with 100ml of fracturing fluid base fluid to prepare guar gum.

[0043] The composition of the fracturing fluid base fluid is 100 ml of water, 1 g of potassium chloride, 0.3 g of hydroxypropyl guar gum, 0.05 g of fungicide (isothiazolinone) and 0.01 g of sodium hydroxide.

[0044] Example 3

[0045] The other steps are the same as those of Example 2, except that the mass of ethylene glycol is changed from 60 g (0.98 mol) to 74.4 g (1.2 mol), the mass of n-butanol is changed from 40 g (0.54 mol) to 59.2 g (0.8 mol), the mass of boric acid is changed from 25 g (0.4 mol) to 37.2 g (0.6 mol), the mass of A-TEPA is changed from 15 g (0.03 mol) to 20 g (0.04 mol), and the mass of dipentaerythritol is changed from 10.2 g (0.04 mol) to 15.24 g (0.06 mol);

[0046] Example 4

[0047] The other steps are the same as those of Example 2, except that the mass of ethylene glycol is changed from 60 g (0.98 mol) to 93 g (1.5 mol), the mass of n-butanol is changed from 40 g (0.54 mol) to 74 g (1 mol), the mass of boric acid is changed from 25 g (0.4 mol) to 49.6 g (0.8 mol), the mass of A-TEPA is changed from 15 g (0.03 mol) to 25 g (0.05 mol), and the mass of dipentaerythritol is changed from 10.2 g (0.04 mol) to 20.32 g (0.08 mol);

[0048] Comparative Example 1

[0049] This embodiment provides a guar gum fracturing fluid prepared with an unmodified crosslinking agent. First, a fracturing fluid base liquid needs to be prepared. Take 1000 ml of tap water, add 1% (mass percentage) of potassium chloride and start stirring until it is completely dissolved, then add 0.3% (mass percentage) of hydroxypropyl guar gum and stir at high speed for 5 to 10 minutes. Then add 0.05% (mass percentage) of fungicide and 0.01% (mass percentage) of sodium hydroxide pH regulator, and stand for 3 to 5 hours to stabilize to obtain a fracturing fluid base liquid; take 100 ml of fracturing fluid base liquid, add 0.3 ml of unmodified crosslinking agent (SPE Journal, 2014, 19 (04): 737-743), and a jelly-like guar gum fracturing fluid will be formed under stirring;

[0050] A small amount of the above guar gum fracturing fluid was taken for modulus test using a HAAKE rheometer, wherein the model of the HAAKE rheometer was HAAKE MARS60. Test conditions: oscillation angular frequency was 1 Hz, stress value was 5%, and scanning time was 3 min.

[0051] Comparative Example 2

[0052] This embodiment provides a guar fracturing fluid prepared with a modified crosslinking agent. Take 100 ml of the fracturing fluid base fluid, add 0.3 ml of the polyamino borate crosslinking agent obtained in Example 2, and a jelly-like guar fracturing fluid will be formed under stirring. Take a small amount of guar fracturing fluid and use a Haake rheometer to perform a modulus test. The model of the Haake rheometer is HAAKE MARS60. Test conditions: oscillation angular frequency of 1 Hz, stress value of 5%, and scanning time of 3 min.

[0053] As attached Figure 1 As shown, it can be seen from the modulus curve of the Haake rheometer that the storage modulus (Storage modulus) of the guar fracturing fluid prepared with the unmodified cross-linking agent in Comparative Example 1 is about 0.8-0.85 Pa, and the loss modulus (Loss modulus) is about 0.4 Pa. The storage modulus and the loss modulus are not much different, indicating that the stability of the guar fracturing fluid is poor;

[0054] As attached Figure 2As shown, the storage modulus (Storage modulus) of the guar fracturing fluid prepared with the modified crosslinking agent in this embodiment is about 3.5Pa, and the loss modulus (Loss modulus) is about 0.25Pa; the storage modulus of the guar fracturing fluid prepared with the modified crosslinking agent is much higher than the loss modulus, and the two remain basically unchanged over time, indicating that the internal network structure of the guar fracturing fluid has good stability and the internal intermolecular force can maintain balance. At the same time, it shows that the guar fracturing fluid tends to show strong elastic behavior, so that the friction between it and the pipeline is effectively reduced in construction applications.

[0055] The above embodiments describe the present invention in detail, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A method for preparing a cross-linking agent for improving the stability of guar gum fracturing fluid, characterized in that: The steps include: S1, reacting oxalyl chloride and tetraethylenepentamine to obtain A-TEPA for standby use; S2. Adding boric acid to the stirred ethylene glycol and n-butanol to carry out reflux condensation reaction at a reaction temperature of 100 to 150° C. to obtain a reaction mixture; S3, cooling the reaction mixture to room temperature, adding A-TEPA, and then heating at 100-150° C. for a reaction time of 3-5 h; S4. Finally, dipentaerythritol is added, and the mixture is heated at 100-150° C. for 1-3 hours, cooled to room temperature, and the pH value of the solution is adjusted to 10-11 to obtain a polyamino borate crosslinking agent.

2. The cross-linking agent for improving the stability of guar gum fracturing fluid according to claim 1, characterized in that: The molecular structure of the polyamino borate crosslinking agent is:

3. The method for preparing a cross-linking agent for improving the stability of guar gum fracturing fluid according to claim 1, characterized in that: The molar ratio of ethylene glycol, n-butanol, boric acid, oxalyl chloride, tetraethylene pentamine, dipentaerythritol and A-TEPA is: (0.98～1.5)：(0.54～1)：(0.4～0.8)：(0.06～0.10)：(0.04～0.067)：(0.04～0.08)：(0.03～0.05)。 4. The method for preparing a cross-linking agent for improving the stability of guar gum fracturing fluid according to claim 1, characterized in that: In step S1, the reaction temperature of oxalyl chloride and tetraethylenepentamine is 100-150° C., and the reaction time is 4-5 hours.

5. The method for preparing a cross-linking agent for improving the stability of guar gum fracturing fluid according to claim 1, characterized in that: In step S2, the reaction time is 2 to 3 hours.

6. A polyamino borate crosslinking agent obtained according to the method for preparing a crosslinking agent for improving the stability of guar gum fracturing fluid according to any one of claims 1 to 5.

7. Guar fracturing fluid obtained from the polyamino borate crosslinker according to claim 6.

8. The guar gum fracturing fluid according to claim 7, characterized in that: Potassium chloride, hydroxypropyl guar gum, fungicide and sodium hydroxide are added to water, and after standing for 3 to 5 hours to stabilize, a fracturing fluid base fluid is obtained; and then a polyamino borate cross-linking agent is added thereto to obtain a guar gum fracturing fluid.

9. The guar gum fracturing fluid according to claim 7, characterized in that: The mass percentages of the components in the fracturing fluid base liquid are: 0.8% to 3% potassium chloride, 0.2% to 0.5% hydroxypropyl guar gum, 0.04% to 0.1% fungicide and 0.009% to 0.1% sodium hydroxide. 0.3 to 0.5 ml of polyamino borate crosslinking agent is required for every 100 ml of fracturing fluid base liquid.

10. The guar gum fracturing fluid according to claim 7, characterized in that: The bactericide is one or a mixture of at least two of dodecyl dimethyl benzyl ammonium chloride or isothiazolinones.

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