Low-temperature coal bed gas reservoir acid fracturing fluid and preparation method thereof

Abstract

The application provides a low-temperature coal bed gas reservoir acidic fracturing fluid and a preparation method thereof, and comprises the following components: a thickening agent, an iron ion stabilizer, a clay stabilizer, a water lock breaking agent, a corrosion inhibitor, a gel breaker, a gel breaking activator, a pH regulator and water; the thickening agent is modified hydroxypropyl guanidine gum, which is prepared from hydroxypropyl guanidine gum by modification of sodium 2-chloroethyl sulfonate and maleic anhydride, and the raw material ratio is hydroxypropyl guanidine gum, sodium 2-chloroethyl sulfonate, maleic anhydride and concentrated sulfuric acid; the pH regulator is inorganic acid or organic acid or a mixture of the two, and the pH value range of the low-temperature coal bed gas reservoir acidic fracturing fluid is adjusted to 1.0-5.0 by adding the pH regulator. The low-temperature coal bed gas reservoir acidic fracturing fluid provided by the application is suitable for low-temperature shallow coal bed gas reservoirs, gel breaking is controllable and the residual content is low in a wide pH range, and the reservoir damage is small.

Description

TECHNICAL FIELD

[0001] The present application relates to a fracturing fluid, in particular to an acid fracturing fluid applied to low-temperature shallow coalbed methane reservoirs and a preparation method thereof, and belongs to the technical field of unconventional gas reservoir reconstruction. BACKGROUND

[0002] The physical and chemical properties of low-temperature shallow coalbed methane reservoirs determine the core problems of high reservoir damage risk and difficult fracture pattern control in the reservoir reconstruction process. This is mainly because the activity of the breaker of conventional fracturing fluids (such as slickwater and guar gum) is insufficient at low temperatures (usually below 60℃), and the gel is not broken completely and is prone to residual gel, thereby plugging the pores and channels and causing a significant decrease in permeability. At the same time, the coalbed methane reservoir has a strong adsorption capacity for additives (such as surfactants) in the fracturing fluid, and the residual substances can occupy the methane adsorption space, thereby inhibiting the desorption of the gas; the differential stress of the shallow formation is small, and it is difficult for the fracturing fluid to continuously extend the fractures after entering the formation, which results in insufficient extension energy of the main fractures and the formation of "short and wide" fractures, and the formation of long-distance effective supporting fractures is difficult.

[0003] The acid fracturing fluid system developed by the prior art is not suitable for low-temperature shallow coalbed methane reservoirs, and has limited ability to inhibit formation damage, the gel breaking time cannot be controlled at low temperatures, the gel breaking is not complete at low temperatures, the residual content is high, and the pH value after crosslinking is high, which cannot efficiently form fractures, remove reservoir damage and improve the gas conductivity at low temperatures. SUMMARY

[0004] The present application provides a low-temperature coalbed methane reservoir acid fracturing fluid, which solves the problems in the background art. It is suitable for low-temperature shallow coalbed methane reservoirs, and has controllable gel breaking and low residual content in a wide pH range, which causes little damage to the reservoir.

[0005] The technical scheme adopted to achieve the above-mentioned purposes of the present application is as follows:

[0006] A low-temperature coalbed methane reservoir acid fracturing fluid, comprising the following components: a thickening agent 0.11-0.50wt%; an iron ion stabilizer 0.1-0.3wt%; a clay stabilizer 0.1-0.5wt%; a water lock remover 0.1-0.5wt%; a corrosion inhibitor 0.002-0.05wt%; a gel breaker 0.001-0.10wt%; a gel breaking activator 0.002-0.25wt%; a pH adjuster; and water in an amount of the balance.

[0007] The thickening agent is a modified hydroxypropyl guar gum, which is prepared by modifying hydroxypropyl guar gum with 2-chloroethyl sodium sulfonate and maleic anhydride. The raw material ratio is as follows: hydroxypropyl guar gum 50-70 parts, 2-chloroethyl sodium sulfonate 5-35 parts, maleic anhydride 2-6 parts, and concentrated sulfuric acid 0.02-5 parts.

[0008] The pH regulator is inorganic acid or organic acid or mixture of both, the pH value of the low-temperature coal bed gas reservoir acid fracturing fluid is adjusted to 1.0~5.0 by adding pH regulator.

[0009] Further, the modified hydroxypropyl guanidium gum is prepared by the following method: 50~80 parts of hydroxypropyl guanidium gum is dissolved in 10~20 times of its mass of anhydrous ethanol, stirred uniformly, then 2~6 parts of maleic anhydride and 5~35 parts of 2-chloroethyl sodium sulfonate and 0.02~5 parts of concentrated sulfuric acid are added, and stirred at 25~45℃ for 2~8 hours to make the components fully react; after the reaction is completed, it is cooled to room temperature, filtered, the filter cake is washed with anhydrous ethanol for three times, then dried at 80~90℃ for 1~3 hours to make the anhydrous ethanol fully volatilize, and finally ground to obtain the powder-like modified hydroxypropyl guanidium gum.

[0010] Further, the inorganic acid is hydrochloric acid, and the organic acid is formic acid or acetic acid.

[0011] Further, the iron ion stabilizer is one or a mixture of multiple of tartaric acid, citric acid, ethylenediaminetetraacetic acid, hydroxyethylidene diphosphonic acid, preferably tartaric acid and citric acid.

[0012] Further, the clay stabilizer is one or a mixture of multiple of potassium chloride, ammonium chloride, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, cationic polyacrylamide, hydroxypropyltrimethylammonium chloride cellulose, hydroxyethyl cellulose, preferably potassium chloride or dodecyltrimethylammonium chloride.

[0013] Further, the water lock breaker is a cationic fluorocarbon gemini surfactant.

[0014] Further, the corrosion inhibitor is one or a mixture of multiple of benzotriazole, dodecylamine, hexadecylamine, diethanolamine, 1-hydroxyethyl-2-heptadecyl imidazoline, preferably dodecylamine.

[0015] Further, the gel breaker is one of sodium persulfate, potassium persulfate and ammonium persulfate, preferably potassium persulfate.

[0016] Further, the gel breaking activator is one or a mixture of multiple of sodium sulfite, sodium bisulfite, triethanolamine, thiourea, preferably sodium bisulfite.

[0017] Further, the low-temperature coal bed gas reservoir acid fracturing fluid has an applicable temperature range of 15~60℃, and the gel breaking time is controllably adjustable within 3~6 hours.

[0018] Compared with the prior art, the low-temperature coal bed gas reservoir acid fracturing fluid provided by the application has the following advantages:

[0019] 1、In this application, no matter using strong acid hydrochloric acid or if organic acid formic acid or acetic acid, in a wide pH value range (1.0~5.0), lower temperature range (15~60°C) and a wide range of adhesion (5~70 mPa.s) can be achieved 3~6h controllable adjustment of the gel breaking time and lower residue content.

[0020] 2、In the acid fracturing fluid of the application, the modified hydroxypropyl guanidine gum prepared by introducing carboxyl groups through maleic anhydride makes its water solubility better, so that the thickening agent can have faster thickening rate, lower thickening agent dosage under strong acid conditions and more stable shear rheological properties. The introduction of sulfonic acid groups in the modified hydroxypropyl guanidine gum makes it have better performance in complex formula system, and it can still maintain stable viscosity and sand carrying capacity in high salinity (>20× mg / L) or high calcium and magnesium formation, its excellent performance and lower use concentration compensate for the increased cost in the modification process, and it also has a higher cost performance as a new type of thickening agent.

[0021] 3、In this application, water lock agent is introduced, so that the acid fracturing fluid not only has a lower surface tension of 19~24 mN / m, but also can reverse the wetting of coal seams and release the water lock effect. After the fracturing fluid is returned, the permeability recovery rate of the coal core can be more than 100% in a short period (such as the attached Figure 2 ), and the better wetting reversal effect can greatly extend the stable production period of coal deposits. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is the viscosity change curve of each level of fracturing fluid system prepared in this application at 20°C;

[0023] Figure 2 is the permeability recovery curve of the secondary acid fracturing fluid system in this application after injecting into coal core at 20°C;

[0024] Figure 3 is the rheological curve of the secondary acid fracturing fluid system in this application at 20°C. DETAILED DESCRIPTION

[0025] The application will be described in detail below in combination with examples.

[0026] Example 1

[0027] 78 parts of hydroxypropyl guanidine gum was dissolved in 10 times of anhydrous ethanol, stirred uniformly, then 2 parts of maleic anhydride and 20 parts of 2-chloroethyl sodium sulfonate and 0.03 parts of concentrated sulfuric acid were added, and stirred at 25°C for 4 hours to make it fully react.

[0028] After the reaction is completed, it is cooled to room temperature, filtered, the filter cake is washed with anhydrous ethanol three times, then dried at 80°C for 1.5 hours to make the anhydrous ethanol evaporate completely, and finally ground to obtain the modified hydroxypropyl guar gum in powder form.

[0029] The modified hydroxypropyl guar gum is used as a thickening agent, and the thickening agent, iron ion stabilizer, clay stabilizer, water lock breaker, corrosion inhibitor, breaker, breaker activator, and pH regulator are added to water in the proportions described in Example 1 at a concentration of 0.11-0.40 wt% under the condition of 20°C, and stirred until completely dissolved in a mixing device to obtain an acidic fracturing fluid system. By changing the amount of thickening agent, a primary (5≤μ<10 mPa.s), secondary (10≤μ<15 mPa.s), tertiary (15≤μ<20 mPa.s), medium viscosity (20≤μ<30 mPa.s), and high viscosity fracturing fluid (50 mPa.s≤μ) system that meets the requirements of fracturing fluid field construction is prepared in turn, and the viscosity of the prepared multi-stage fracturing fluid system is detected. The detection results are shown in FIG. 1. Figure 1 As can be seen from Figure 1 , the modified hydroxypropyl guar gum prepared by the method can be used as a thickening agent to prepare fracturing fluid systems with different viscosity requirements under the condition of 20°C, and all of them can be broken down within 4-6 hours.

[0030] The specific proportions of the multi-stage fracturing fluid system prepared in this example are shown in Table 1.

[0031] Table 1: Amounts of each component in each stage of the fracturing fluid system

[0032] .

[0033] Example 2

[0034] 65 parts of hydroxypropyl guar gum is dissolved in 12 times its amount of anhydrous ethanol, stirred until uniform, then 3 parts of maleic anhydride and 32 parts of 2-chloroethyl sodium sulfonate and 0.05 parts of concentrated sulfuric acid are added, and stirred at 30°C for 4 hours to make them react completely.

[0035] After the reaction is completed, it is cooled to room temperature, filtered, the filter cake is washed with anhydrous ethanol three times, then dried at 80°C for 2 hours to make the anhydrous ethanol evaporate completely, and finally ground to obtain the modified hydroxypropyl guar gum in powder form.

[0036] At 20°C, using 0.16 wt% modified hydroxypropyl guar gum, 0.1 wt% iron ion stabilizer, 0.3 wt% clay stabilizer, 0.3 wt% water-locking agent, 0.01 wt% corrosion inhibitor, 0.01 wt% breaker, 0.01 wt% breaker activator, 0.05% hydrochloric acid, and water, a secondary acidic fracturing fluid system with an initial viscosity of 14 mPa·s was obtained at pH=2.52. The surface tension of this fracturing fluid was 19.8 mN / m. After the breaker fluid was injected into the core to establish damage, the permeability recovery rate measured by gas drive was 109.89%. (See attached figure.) Figure 2 As shown.

[0037] A fracturing fluid system was prepared by adding 0.16 wt% modified hydroxypropyl guar gum, 0.1 wt% iron ion stabilizer, 0.3 wt% clay stabilizer, 0.3 wt% water-locking agent, and 0.01 wt% corrosion inhibitor. The system was analyzed using an RS-600 rheometer. At 20°C, the shear rate was 170 s⁻¹. -1 Test its rheological properties, as shown in the attached figure. Figure 3 As shown, it exhibits good shear resistance.

Claims

1. A low-temperature coalbed methane reservoir acid fracturing fluid, characterized in that: It comprises the following components: thickener 0.11~0.50wt%; iron ion stabilizer 0.1~0.3wt%; clay stabilizer 0.1~0.5wt%; water-locking agent 0.1~0.5wt%; corrosion inhibitor 0.002~0.05wt%; breaker 0.001~0.10wt%; breaker activator 0.002~0.25wt%; pH adjuster; water balance; The thickener is modified hydroxypropyl guar gum, prepared by modifying hydroxypropyl guar gum with sodium 2-chloroethyl sulfonate and maleic anhydride. The raw material ratio is: 50-70 parts hydroxypropyl guar gum, 5-35 parts sodium 2-chloroethyl sulfonate, 2-6 parts maleic anhydride, and 0.02-5 parts concentrated sulfuric acid. The modified hydroxypropyl guar gum is prepared by the following method: 50-70 parts of hydroxypropyl guar gum are dissolved in 10-20 times its weight in anhydrous ethanol, stirred evenly, and then 2-6 parts of maleic anhydride, 5-35 parts of sodium 2-chloroethyl sulfonate, and 0.02-5 parts of concentrated sulfuric acid are added. The mixture is stirred and reacted at 25-45°C for 2-8 hours to ensure complete reaction of all components. After the reaction, the mixture is cooled to room temperature, filtered, and the filter cake is washed three times with anhydrous ethanol, and then dried at 80-90°C for 1-2 hours. After 3 hours, the anhydrous ethanol was completely evaporated, and finally the modified hydroxypropyl guanidine gum was ground into powder. The clay stabilizer is one or more of the following: potassium chloride, ammonium chloride, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, cationic polyacrylamide, hydroxypropyltrimethylammonium chloride cellulose, and hydroxyethyl cellulose. The water-locking agent is a cationic fluorocarbon gemini surfactant; The corrosion inhibitor is one or a mixture of several of the following: benzotriazole, dodecaam, hexadecylamine, diethanolamine, and 1-hydroxyethyl-2-heptadecylimidazoline; The de-icing agent is one of sodium persulfate, potassium persulfate, and ammonium persulfate; The gel breaking activator is one or a mixture of several of sodium sulfite, sodium bisulfite, triethanolamine, and thiourea. The pH adjuster is an inorganic acid, an organic acid, or a mixture of both. By adding the pH adjuster, the pH range of the acidic fracturing fluid in low-temperature coalbed methane reservoirs is adjusted to 1.0 to 5.

0.

2. The acidic fracturing fluid for low-temperature coalbed methane reservoirs according to claim 1, characterized in that: The inorganic acid is hydrochloric acid, and the organic acid is formic acid or acetic acid.

3. The acidic fracturing fluid for low-temperature coalbed methane reservoirs according to claim 1, characterized in that: The iron ion stabilizer is one or more of tartaric acid, citric acid, ethylenediaminetetraacetic acid, and hydroxyethylidene diphosphonic acid.

4. The acidic fracturing fluid for low-temperature coalbed methane reservoirs according to claim 1, characterized in that: The applicable temperature range for the acid fracturing fluid used in the low-temperature coalbed methane reservoir is 15 ~ 60°C, and the gel breaking time is controllable and adjustable from 3 to 6 hours.

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