Weakly adsorbable and low-damage fracturing fluid and preparation method thereof

Abstract

The present invention discloses a weak adsorption low-damage fracturing fluid, which is composed of the following components by mass percentage: 0.3-0.6% thickener, 0-0.6% crosslinker, 0.01-0.1% gel breaker, 0.3-0.6% drainage agent, 0.3-0.6% sacrificial agent, 0.3-0.6% clay stabilizer, and the balance being water. The present invention also discloses a method for preparing the weak adsorption low-damage fracturing fluid system, which comprises first dissolving the thickener in water, then adding the gel breaker, drainage agent, sacrificial agent, and clay stabilizer to form a base fluid. If the desired fracturing fluid is a cross-linked guar gum fracturing fluid, the crosslinker is added to the base fluid. If the desired fracturing fluid is not a cross-linked guar gum fracturing fluid, the base fluid is directly stirred to obtain the weak adsorption low-damage fracturing fluid. The fracturing fluid of the present invention can eliminate the interaction between the thickener and the rock from the root, effectively reduce the permeability damage caused by the adsorption and retention of the thickener in cracks and pores, and ultimately increase oil and gas production.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas reservoir exploitation, and relates to a weak-adsorption and low-damage fracturing fluid and a preparation method thereof. Background Art

[0002] Unconventional oil and gas reservoirs are an important energy replacement field, with low porosity and low permeability characteristics. Hydraulic fracturing is a key technology to increase the oil and gas production of tight reservoirs. Fracturing fluid is an important medium for transmitting pressure and carrying proppant. Under normal circumstances, only 5-55% of the liquid can be discharged back to the surface after fracturing. Based on the research of Guo Jianchun et al. in the articles "Adsorption Damage and Control Measures of Slippery Water in Shale Reservoirs" and "Reducing Adsorption of hydroxypropyl guar gum on sandstone by silicon nanoparticles", fracturing fluid thickeners can be adsorbed by hydrogen bonds with rocks and retained in large quantities. Take a 3000m 3 For example, a well hydraulically fractured with guar gum fracturing fluid had an initial guar gum concentration of 4000 mg / L, with 12 tons of guar gum entering the well. The average flowback rate, as measured by field statistics, was approximately 55.3%, with the remaining guar gum concentration in the flowback fluid at 2300 mg / L, and a total of 8.3 tons of guar gum remaining in the reservoir. With the widespread application of horizontal well and staged fracturing in tight sandstone reservoirs, the residence time of the fracturing fluid at the horizontal toe has increased, resulting in a stronger adsorption and retention capacity. Thickener adsorption can disrupt oil and gas flow pathways and increase resistance to oil and gas flow. Therefore, the key to reservoir reconstruction lies in developing new, low-damage fracturing fluid systems to improve reservoir permeability.

[0003] There are currently three common solutions to the reservoir damage caused by the use of plant gums and polymers to prepare fracturing fluids. Patents CN105154057A, CN110437816A, and CN109652053B invented high-efficiency thickeners and high-efficiency cross-linkers, and used methods to reduce the molecular weight and dosage of the thickeners to formulate low-damage fracturing fluid systems. Patent CN101993688B combines peroxide breakers, capsule breakers, and organic peroxides, using a high-efficiency breaking method to reduce the core damage rate to 19.8%. Patent CN111040752A uses glutamic acid / glycine as damage control agents to prepare a low-adsorption fracturing fluid system. The permeability after core displacement is significantly higher than that of conventional guar gum fracturing fluid systems.

[0004] Fracturing fluids produced using high-efficiency thickeners, crosslinkers, and breakers can promote fluid flowback to a certain extent and reduce adsorption damage to reservoirs. However, the short-chain thickener molecules retain their original structural characteristics after breaking. The sugar chains of broken plant gums contain numerous hydroxyl groups, while synthetic polymer chains contain numerous amide groups. These interactions remain unchanged and fail to effectively reduce adsorption damage. Using amino acids as damage control agents to reduce adsorption readily dissociates into zwitterions in aqueous solution, and the acidity of the system may affect fracturing fluid performance.

[0005] In combination with the adsorption effect of existing plant gums and polymers on the rock surface, it is necessary to develop a new weak adsorption and low-damage fracturing fluid system to reduce the adsorption capacity of the thickener from the source, effectively improve the oil and gas seepage channels of the reservoir, and increase oil and gas production. Summary of the Invention

[0006] One purpose of the present invention is to provide a weakly adsorbed and low-damage fracturing fluid, which solves the problem that the existing fracturing fluid system has great adsorption damage to oil and gas reservoirs, thereby affecting oil and gas production.

[0007] One object of the present invention is to provide a method for preparing a weakly adsorbing and low-damage fracturing fluid.

[0008] The first technical solution adopted by the present invention is that the weakly adsorbed and low-damage fracturing fluid is composed of the following components in percentage by mass: 0.3-0.6% thickener, 0-0.6% cross-linking agent, 0.01-0.1% breaker, 0.3-0.6% drainage agent, 0.3-0.6% sacrificial agent, 0.3-0.6% clay stabilizer, and the balance is water.

[0009] The thickener is one or a combination of natural plant gum, modified derivatives of natural plant gum, and synthetic polymers of natural plant gum.

[0010] The cross-linking agent is one or a combination of boron, zirconium and titanium cross-linking agents.

[0011] The gel breaker is one or a combination of ammonium persulfate, sodium persulfate or potassium persulfate.

[0012] The drainage aid is one or a combination of sodium lauryl sulfate, sodium fatty acid methyl ester sulfonate, sodium lauryl sulfonate, sodium petroleum sulfonate, dodecyl dimethyl amine oxide, and fatty alcohol polyoxyethylene ether.

[0013] The sacrificial agent includes environmentally friendly and degradable agent A and agent B, the ratio of agent A to agent B is 1:1 to 7:3, agent A is a small molecule substance with super strong hydrogen bond forming ability, and agent B is a non-ionic surfactant containing a large number of -NH- or -OH- groups.

[0014] Agent A is a combination of one or more of carbonamide, formamide, oxalamide, guanidine hydrochloride, and tris(hydroxymethyl)aminomethane, and agent B is a combination of one or more of sophorolipids, rhamnolipids, octyl glucoside APG0810, decyl glucoside APG10, and lauryl glucoside (APG1214).

[0015] The clay stabilizer is potassium chloride, ammonium chloride or a combination of the two.

[0016] A method for preparing a weakly adsorbable and low-damage fracturing fluid comprises dissolving a thickener in water according to the mass percentage of each component, adding a gel breaker, a drainage agent, a sacrificial agent, and a clay stabilizer after the thickener is fully swollen, and preparing a base fluid. If the desired fracturing fluid is a cross-linked guar gum fracturing fluid, then adding a cross-linking agent to the base fluid and stirring to fully cross-link the components. If the desired fracturing fluid is not a cross-linked guar gum fracturing fluid, then directly stirring the base fluid to uniformly mix the components to prepare the weakly adsorbable and low-damage fracturing fluid.

[0017] When the required fracturing fluid is a cross-linked guar gum fracturing fluid, the pH value of the base fluid is adjusted to 9-11 before adding the cross-linking agent to the base fluid, and then the cross-linking agent is added.

[0018] The beneficial effect of the present invention is that, based on the hydrogen bond adsorption between the thickener molecules and the rock surface, environmentally friendly and degradable agent A and agent B are used as sacrificial agents to prepare the fracturing fluid. On the one hand, they can be adsorbed with the rock. Agent A has a super strong hydrogen bond forming ability and can form intramolecular hydrogen bonds by itself and spread on the rock surface. The hydrophilic head group in agent B can form a hydrophobic layer after being adsorbed on the rock surface, thereby reducing the free energy of the rock surface. The combination of agent A and agent B can effectively reduce the contact area between the residual small molecule thickener and the rock, and destroy the hydrogen bonds formed between the thickener and the rock surface. , making it difficult to adsorb to the rock surface, eliminating the interaction between the thickener and the rock from the root; on the other hand, the sacrificial agent can interact with the thickener molecules. Both agent A and agent B can combine with the residual small molecule thickener to reduce its adsorption sites on the rock surface. The combination of the two effects can disperse the small molecule polymers in the gel breaking liquid in the water and return to the ground, effectively reducing the adsorption damage caused on the rock surface, effectively reducing the permeability damage caused by the adsorption and retention of the thickener in cracks and pores, restoring the oil and gas flow channel, and ultimately increasing oil and gas production. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to specific embodiments.

[0020] Example 1

[0021] A weak adsorption and low-damage fracturing fluid was prepared by adding 0.3 g of xanthan gum thickener to 98.27 g of water at a stirrer speed of 400 r / min and stirring for 10 minutes to allow the thickener to fully swell. Then, 0.4 g of sodium dodecyl sulfate drainage agent, 0.5 g of sacrificial agent (0.3 g formamide + 0.2 g rhamnolipid), and 0.5 g of clay stabilizer ammonium chloride were added. After they were fully dissolved, 0.03 g of ammonium persulfate as a gel breaker was finally added and stirred evenly to obtain a weak adsorption and low-damage fracturing fluid.

[0022] Comparative Example 1

[0023] The method of Example 1 was followed, except that no sacrificial agent was added, to finally produce a conventional linear gel fracturing fluid 1'.

[0024] Example 2

[0025] A weak adsorption and low-damage fracturing fluid was prepared. 0.33 g of a hydroxypropyl guar gum thickener was added to 98.18 g of water at a stirrer speed of 400 r / min. The mixture was stirred for 10 minutes to allow the thickener to fully swell. 0.3 g of a drainage aid, fatty alcohol polyoxyethylene ether, 0.35 g of a sacrificial agent (0.2 g of guanidine hydrochloride + 0.15 g of octyl glucoside (APG0810)), 0.4 g of a clay stabilizer, potassium chloride, and 0.04 g of a gel breaker, sodium persulfate, were then added. The mixture was stirred evenly until all substances were fully dissolved to obtain a base fluid. A 5% sodium hydroxide solution was prepared and added dropwise to the base fluid sample. When the pH value was approximately 9.5 as measured by precision pH test paper, 0.4 g of an organic boron crosslinker was finally added. The mixture was stirred to allow the components to fully crosslink, thereby obtaining a weak adsorption and low-damage fracturing fluid.

[0026] Comparative Example 2

[0027] The method of Example 2 was followed, except that no sacrificial agent was added, to finally produce a conventional cross-linked guar gum fracturing fluid 2'.

[0028] Example 3

[0029] A weak adsorption and low-damage fracturing fluid was prepared by adding 0.3 g of dry powder polyacrylamide thickener to 98.17 g of water at a stirrer speed of 400 r / min. After continuous stirring for 10 minutes to allow the thickener to fully swell, 0.5 g of drainage agent (0.3 g of sodium petroleum sulfonate + 0.2 g of dodecyl dimethylamine oxide), 0.6 g of sacrificial agent (0.4 g of formamide + 0.2 g of sophora biosurfactant), and 0.4 g of clay stabilizer ammonium chloride were added. After sufficient dissolution, 0.03 g of gel breaker potassium persulfate was finally added to obtain a weak adsorption and low-damage fracturing fluid.

[0030] Comparative Example 3

[0031] The method of Example 3 was followed, except that no sacrificial agent was added, to finally produce a conventional polymer fracturing fluid 3'.

[0032] Example 4

[0033] A weak adsorption and low-damage fracturing fluid is prepared. At a stirrer speed of 400 r / min, 0.1 g of emulsion polyacrylamide and 0.2 g of hydroxypropyl guar gum are added to 98.12 g of water. Stirring is continued for 10 minutes to fully swell the thickener. Then, 0.35 g of sodium fatty acid methyl ester sulfonate as a drainage aid, 0.4 g of a sacrificial agent (0.2 g of lauryl glucoside (APG1214) + 0.2 g of tris(hydroxymethylaminomethane)), and 0.5 g of potassium chloride as a clay stabilizer are added. After sufficient dissolution, 0.035 g of sodium persulfate is added and mixed to obtain a base fluid. A 5% sodium hydroxide solution is prepared and added dropwise to the base fluid sample. The pH value is adjusted to 9-11. 0.2 g of potassium tetraborate is added for cross-linking to obtain a weak adsorption and low-damage fracturing fluid.

[0034] Comparative Example 4

[0035] The method of Example 4 was followed, except that no sacrificial agent was added, to finally produce a mixed fracturing fluid 4'.

[0036] The damage rate of the fracturing fluids prepared in Examples 1-4 and Comparative Examples 1-4 was determined. The fracturing fluids were heated in a water bath at 90°C for 4 hours to break the gel, and the resulting gel-breaking solutions were filtered. Dry core samples were weighed, saturated with 2% KCl brine, and injected with water to measure the initial permeability (K0). A 5PV gel-breaking solution was injected, and the cores were aged for 24 hours. The permeability (K1) of the cores after being damaged by the fracturing fluids was then measured by further injection of brine. The degree of damage to the cores from the different fracturing fluids was calculated, as shown in Table 1.

[0037] Table 1

[0038]

[0039] It can be seen from Table 1 that the weakly adsorbed and low-damage fracturing fluid prepared in the present invention causes significantly less damage to the core after injection than conventional fracturing fluid without a sacrificial agent.

Claims

1. Weak adsorption and low damage fracturing fluid, characterized by: The composition is as follows according to mass percentage: thickener 0.3-0.6%, cross-linking agent 0-0.6%, breaker 0.01-0.1%, drainage agent 0.3-0.6%, sacrificial agent 0.3-0.6%, clay stabilizer 0.3-1%, and the balance is water; The sacrificial agent includes environmentally friendly and degradable agent A and agent B, wherein the agent A is one or more of carbonamide, formamide, oxalamide, guanidine hydrochloride, and trishydroxymethylaminomethane, and the agent B is one or more of sophorolipids, rhamnolipids, octyl glucoside APG0810, decyl glucoside APG10, and lauryl glucoside APG1214.

2. The weakly adsorbed and low-damage fracturing fluid according to claim 1, characterized in that: The thickener is one or a combination of natural plant gum, modified derivatives of natural plant gum, and synthetic polymers of natural plant gum.

3. The weakly adsorbable and low-damage fracturing fluid according to claim 1, characterized in that: The cross-linking agent is one or a combination of boron, zirconium and titanium cross-linking agents.

4. The weakly adsorbable and low-damage fracturing fluid according to claim 1, characterized in that: The gel breaker is one or a combination of ammonium persulfate, sodium persulfate or potassium persulfate.

5. The weakly adsorbable and low-damage fracturing fluid according to claim 1, characterized in that: The drainage aid is one or a combination of sodium lauryl sulfate, sodium fatty acid methyl ester sulfonate, sodium lauryl sulfonate, sodium petroleum sulfonate, dodecyl dimethyl amine oxide, and fatty alcohol polyoxyethylene ether.

6. The weakly adsorbable and low-damage fracturing fluid according to claim 1, characterized in that: The clay stabilizer is potassium chloride, ammonium chloride or a combination of the two.

7. The method for preparing the weakly adsorbing and low-damage fracturing fluid according to any one of claims 1 to 6, characterized in that: The method includes dissolving a thickener in water according to the mass percentage of each component, adding a breaker, a drainage agent, a sacrificial agent and a clay stabilizer to prepare a base fluid after the thickener is fully swollen, and adding a cross-linking agent to the base fluid if the desired fracturing fluid is a cross-linked guar gum fracturing fluid, stirring to fully cross-link the components; if the desired fracturing fluid is not a cross-linked guar gum fracturing fluid, stirring the base fluid directly to evenly mix the components to obtain a weakly adsorbed and low-damage fracturing fluid.

8. The method for preparing a weakly adsorbed and low-damage fracturing fluid according to claim 7, characterized in that: When the required fracturing fluid is a cross-linked guar gum fracturing fluid, the pH value of the base fluid is adjusted to 9-11 before adding the cross-linking agent to the base fluid, and then the cross-linking agent is added.

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