Authigenic surfactant fracturing fluid for tight oil reservoir

Abstract

The invention discloses an authigenic surfactant fracturing fluid for a tight oil reservoir. The authigenic surfactant fracturing fluid consists of a surface active authigenic agent and a basic fracturing fluid in a volume ratio of (1: 1)-(1: 99), wherein the basic fracturing fluid is prepared from the following raw materials in percentage by mass: 0.2 to 0.6 percent of guanidine gum, 0.03 to 0.15 percent of demulsifying agent, 0.5 to 2.0 percent of potassium chloride and the balance of water according to 100 percent of mass; the surface activity authigenic agent is composed of a hydrogen bond complexing ligand, an auxiliary solubilizing stabilizer and an auxiliary synergist according to the mass ratio of (1.3-12): (1.5-25): (0.01-1). The surface active authigenic agent in the fracturing fluid can excite an authigenic surfactant in a reservoir, and is used in the fracturing fluid, so that the addition of a discharge aiding agent is omitted, the cost of the fracturing fluid is reduced, a newly generated hydrogen bond complex can be quickly enriched on an oil-water interface, and the interfacial tension and surface tension are remarkably reduced.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration and development, and specifically relates to a fracturing fluid with self-generated surfactant in tight oil reservoirs. Background Technology

[0002] Currently, with the expansion of unconventional oil and gas resource development (especially tight oil), fracturing operations are developing towards large-scale, high-flow-rate operations. Against this backdrop, slickwater and linear gel have become the mainstream fracturing fluid systems for reservoir stimulation. To ensure efficient flowback of the broken gel fluid after fracturing, thereby reducing secondary damage to the reservoir and increasing oil and gas production, the industry generally adds a flowback aid (a surfactant) during fracturing fluid preparation. This aims to reduce the surface tension of the broken gel fluid to below 30.0 mN / m and the interfacial tension to below 3.0 mN / m.

[0003] However, this traditional technical approach faces severe challenges in practice, especially in sandstone reservoirs, specifically: Severe adsorption loss: Domestic and international research shows that sandstone reservoir surfaces are typically negatively charged, exhibiting strong physicochemical adsorption of conventional cations, zwitterions, and even some nonionic surfactants. This "adsorption phenomenon" causes large amounts of added flowback aids to be captured and rendered ineffective by the rock surface as the fracturing fluid flows deeper into the formation, failing to reduce interfacial tension during the critical stage of fracturing and flowback. This not only significantly reduces the flowback effect but also results in serious waste of chemical agents and increased costs.

[0004] To address the adsorption problem, current technological improvements mainly focus on two aspects: Developing novel drainage aids: For example, developing nano-drainage aids that utilize the unique size effect and permeability of nanomaterials to reduce their retention on rock surfaces. However, these novel agents are expensive, and their long-term formation compatibility and environmental safety still require further evaluation. Optimizing the solution preparation process focuses on reducing the labor intensity and complexity of on-site solution preparation by improving ground equipment and automating processes, such as promoting liquid concentrate additives or integrated mixing technologies. However, this does not fundamentally solve the core problem of drainage aids failing in formations.

[0005] In summary, the existing technology system is caught in a dilemma: to meet flowback requirements, flowback aids must be added, but these aids often become ineffective due to formation adsorption, leading to an imbalance between cost and effectiveness. This inherent flaw in the "external addition" model restricts further cost reduction and efficiency improvement in fracturing fluid technology. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a fracturing fluid for tight oil reservoirs that generates its own surfactants. The fracturing fluid does not contain any drainage aids. Instead, it incorporates a surfactant-generating agent to "transform" the components of crude oil into highly efficient surfactants. This is equivalent to adding the surfactants naturally present in the tight oil and gas reservoir itself in situ, achieving a technological paradigm shift from "external addition" to "internal activation".

[0007] A tight oil reservoir self-generated surfactant fracturing fluid is composed of a surface-active self-generated agent and a base fracturing fluid in a volume ratio of 1:1 to 1:99. The base fracturing fluid, by weight, comprises the following raw materials: guar gum 0.2-0.6%, demulsifier 0.03-0.15%, potassium chloride 0.5-2.0%, and the remainder is water; The surface-active autogenous agent is composed of hydrogen-bonded complex ligands, auxiliary solubilizers and auxiliary synergists in a mass ratio of (1.3-12):(1.5-25):(0.01-1).

[0008] Preferably, the hydrogen-bonded complex ligand is composed of the following raw materials in 100% by mass: 0.5-3% triethanolamine, 0.3-2% tetraethylenepentamine, 0.1-5% isopropanol, 0.3-5% ethylene glycol, 0.1-2% glycerol, and the balance being water.

[0009] Preferably, the auxiliary solubilizing stabilizer, by weight (100%), is composed of the following raw materials in the following mass percentages: 0.5-10% potassium chloride, 0.5-5% potassium sulfate, 0.5-10% sodium chloride, and the balance being water.

[0010] Preferably, the auxiliary synergist is an aqueous solution of a demulsifier.

[0011] Preferably, the concentration of the demulsifier in the auxiliary synergist is 0.1-1 wt%.

[0012] Preferably, the demulsifier is a polyether-based demulsifier.

[0013] More preferably, the base fracturing fluid, by weight, comprises the following raw materials in the following proportions: guar gum 0.2%, demulsifier 0.03%, potassium chloride 0.5%, and the remainder being water.

[0014] More preferably, the base fracturing fluid, by weight, comprises the following raw materials in the following proportions: guar gum 0.6%, demulsifier 0.15%, potassium chloride 2.0%, and the remainder being water.

[0015] More preferably, the base fracturing fluid, by weight, comprises the following raw materials in the following proportions: guar gum 0.4%, demulsifier 0.1%, potassium chloride 1.0%, and the remainder being water.

[0016] Preferably, the base fracturing fluid also contains a low-temperature activator, a temperature stabilizer, a pH adjuster, or a bactericide.

[0017] Preferably, the mass contents of the low-temperature activator, temperature stabilizer, pH adjuster, or bactericide in the basic fracturing fluid are 0.01-0.08%, 0.01-0.1%, 0.1-0.8%, and 0.1-0.6%, respectively; the low-temperature activator is sodium sulfite, the temperature stabilizer is sodium thiosulfate, the pH adjuster is sodium carbonate or sodium hydroxide, and the bactericide is glutaraldehyde.

[0018] The tight oil reservoir self-generated surfactant fracturing fluid of the present invention can be prepared by stirring and mixing the raw materials.

[0019] This invention is based on the discovery that tight oil / shale oil from Shaanxi and other regions commonly contains polar components such as carboxylic acid groups and sulfonic acid groups. Through specific hydrogen-bonded ligands in a surfactant-derived agent, it enables molecular recognition and binding with elements such as O, N, and S in the crude oil, forming structurally stable hydrogen-bonded complexes. These complexes reduce surface tension, significantly decreasing the surface tension between water and crude oil, and lowering the viscosity of the crude oil. This enhances the flow of crude oil within the reservoir pores, improving oil recovery. Essentially, it "transforms" the crude oil's own components into highly efficient surfactants, equivalent to adding surfactants already present in the tight oil and gas reservoir itself. This represents a paradigm shift from "external addition" to "internal activation," reducing the introduction of chemical additives and minimizing potential formation contamination from external fluids. This aligns with the concept of green oil and gas field development. This "self-generating" mechanism reduces the amount of chemicals used, contributing to lower carbon emissions and environmental impact.

[0020] Advantages of this invention: (1) The surface-active self-generating agent in the fracturing fluid of the present invention can activate the self-generated surfactant in the reservoir. When used in the fracturing fluid, it eliminates the need for the addition of drainage aid, reduces the cost of fracturing fluid, and improves the economics of tight oil reservoir development. (2) When the surface-active self-generating agent is used in fracturing fluid, the newly generated hydrogen-bonded complex can be rapidly enriched at the oil-water interface, significantly reducing interfacial tension and surface tension. The surface tension of the flowback fluid after rupture is less than 30.0 mN / m and the interfacial tension is less than 3.0 mN / m. This low tension characteristic helps to reduce capillary resistance and promotes efficient flowback of the ruptured fluid from the reservoir, thereby reducing water lock effect and formation damage. The increase in flowback rate also indirectly reduces the environmental protection cost of treating flowback fluid. In addition, the fracturing fluid can also improve oil production yield, thus achieving the dual goals of "increasing production" and "reducing cost". (3) For different reservoir temperatures, low-temperature activators, temperature stabilizers or pH adjusters can be added to the basic fracturing fluid to ensure that the fracturing fluid maintains stable performance in a wide temperature range and under different pH conditions, making it suitable for various geological conditions; adding bactericides can prevent the liquid from spoiling and deteriorating, extend the preparation and storage time, and reduce the risk of on-site operation. (4) By utilizing the surfactants contained in the tight oil reservoir itself, the introduction of chemical additives is reduced, and the potential pollution of the formation by external fluids is reduced, which is in line with the concept of green oil and gas field development. This "self-generating" mechanism reduces the amount of chemicals used, which helps to reduce carbon emissions and environmental impact. Moreover, the dosage added to the formula is reduced, the liquid preparation process is simplified, the operation steps and human error are reduced, and the on-site construction efficiency is improved. Detailed Implementation

[0021] Example 1 A surface-active autogenous agent for tight oil shale oil reservoirs is prepared by mixing hydrogen-bonded complex ligands, auxiliary solubilizers and stabilizers in a mass ratio of 12:25:1. The hydrogen-bonded complex ligand, by mass percentage, is composed of the following raw materials in the following mass percentages: 0.5% triethanolamine, 0.3% tetraethylenepentamine, 0.1% isopropanol, 0.3% ethylene glycol, 0.1% glycerol, and the balance being water. The auxiliary solubilizing and stabilizing agent, by weight (100%), is composed of the following raw materials in the indicated weight percentages: 0.5% potassium chloride, 0.5% potassium sulfate, 0.5% sodium chloride, and the balance being water. The auxiliary synergist is an aqueous solution of a 0.01 wt% demulsifier, which is a polyether demulsifier 330N purchased from Shandong Hongquan Chemical Technology Co., Ltd.

[0022] Example 2 A surface-active autogenous agent for tight oil shale oil reservoirs is prepared by mixing hydrogen-bonded complex ligands, auxiliary solubilizers and stabilizers in a mass ratio of 1.3:1.5:0.01. The hydrogen-bonded complex ligand, by mass percentage, is composed of the following raw materials in the following mass percentages: 3% triethanolamine, 2% tetraethylenepentamine, 5% isopropanol, 5% ethylene glycol, 2% glycerol, and the balance being water. The auxiliary solubilizing and stabilizing agent, by weight (100%), is composed of the following raw materials in the following proportions: 10% potassium chloride, 5% potassium sulfate, 10% sodium chloride, and the balance being water. The auxiliary synergist is an aqueous solution of 1 wt% demulsifier, which is polyether demulsifier 330N, purchased from Shandong Hongquan Chemical Technology Co., Ltd.

[0023] Example 3 A surface-active autogenous agent for tight oil shale oil reservoirs is prepared by mixing hydrogen-bonded complex ligands, auxiliary solubilizers and stabilizers in a mass ratio of 5:10:0.5. The hydrogen-bonded complex ligand, by mass percentage, is composed of the following raw materials in the following mass percentages: 1% triethanolamine, 1% tetraethylenepentamine, 2% isopropanol, 2% ethylene glycol, 1% glycerol, and the balance being water. The auxiliary solubilizing and stabilizing agent, by weight (100%), is composed of the following raw materials in the following mass percentages: 5% potassium chloride, 3% potassium sulfate, 5% sodium chloride, and the balance being water. The auxiliary synergist is an aqueous solution of a 0.05 wt% demulsifier, which is a polyether demulsifier 330N purchased from Shandong Hongquan Chemical Technology Co., Ltd.

[0024] Example 4 A tight oil reservoir self-generated surfactant fracturing fluid is prepared by mixing a surface-active self-generated agent with a base fracturing fluid at a volume ratio of 1:1. The base fracturing fluid, by weight (100%), is composed of the following raw materials in the indicated mass percentages: guar gum 0.2%, demulsifier 0.03%, potassium chloride 0.5%, and the remainder being water. The surface-active self-generated agent is the surface-active self-generated agent described in Example 1 above.

[0025] Example 5 A tight oil reservoir self-generated surfactant fracturing fluid is prepared by mixing a surface-active self-generated agent with a volume ratio of 1:99 and a base fracturing fluid. The base fracturing fluid, by weight (100%), is composed of the following raw materials in the indicated mass percentages: guar gum 0.6%, demulsifier 0.15%, potassium chloride 2.0%, and the remainder being water. The surface-active self-generated agent is the surface-active self-generated agent described in Example 2 above.

[0026] Example 6 A tight oil reservoir self-generated surfactant fracturing fluid is prepared by mixing a surface-active self-generated agent with a volume ratio of 1:50 and a base fracturing fluid. The base fracturing fluid, by weight (100%), is composed of the following raw materials in the indicated mass percentages: guar gum 0.4%, demulsifier 0.1%, potassium chloride 1.0%, and the remainder being water. The surface-active self-generated agent is the surface-active self-generated agent described in Example 3 above.

[0027] Example 7 A tight oil reservoir self-generated surfactant fracturing fluid is prepared by mixing a surface-active self-generating agent with a base fracturing fluid at a volume ratio of 1:10. The base fracturing fluid, by weight (100%), is composed of the following raw materials in the indicated mass percentages: guar gum 0.3%, demulsifier 0.1%, potassium chloride 1.0%, sodium sulfite 0.03%, sodium thiosulfate 0.01%, sodium carbonate 0.2%, glutaraldehyde 0.1%, with the remainder being water. The surface-active self-generating agent is the surface-active self-generating agent described in Example 1 above.

[0028] Performance testing 1. The fracturing fluid described in Example 4 was used in a field application test in 5 wells at the Yanchang Oilfield. The reservoirs were Chang 1 to Chang 6 in the Yanchang area (Erdos Basin in northern Shaanxi). The crude oil in these 6 reservoirs was tight oil. The fracturing operations of the 5 oil wells were carried out from September to October 2023. The average flowback rate was 79.4%. The specific statistics are shown in Table 1 below. The surface tension and interfacial tension of the flowback fluid are shown in Table 2. Table 1. Statistics on the post-pressure conditions of 5 wells In terms of flowback rate, all wells had a flowback rate exceeding 50%. In terms of production, three wells were high-yield wells, accounting for 60% of the total.

[0029] Table 2 Surface tension and interfacial tension of the backflow fluid As shown in Table 2, after fracturing, the surface tension of the fracturing fluid is less than 30.0 mN / m and the interfacial tension is less than 3.0 mN / m. This invention utilizes the fact that tight oil and gas reservoirs themselves contain chemical substances (surfactants) that can reduce surface and interfacial tension. Through specific hydrogen-bonded ligands in the surfactant, it enables molecular recognition and binding with elements such as O, N, and S in crude oil, forming structurally stable hydrogen-bonded complexes. These hydrogen-bonded complexes have the effect of reducing surface and interfacial tension, significantly reducing the surface tension between water and crude oil, and lowering the viscosity of crude oil. Therefore, it can enhance the flow of crude oil in the pores of the oil reservoir, improve crude oil recovery, eliminate the need for additional flow aids, and reduce the cost of fracturing fluid.

Claims

1. A fracturing fluid with self-generated surfactant in tight oil reservoirs, characterized in that: It consists of a surface-active autogenous agent and a basic fracturing fluid in a volume ratio of 1:1 to 1:

99. The base fracturing fluid, by weight, comprises the following raw materials: guar gum 0.2-0.6%, demulsifier 0.03-0.15%, potassium chloride 0.5-2.0%, and the remainder is water; The surface-active autogenous agent is composed of hydrogen-bonded complex ligands, auxiliary solubilizers and auxiliary synergists in a mass ratio of (1.3-12):(1.5-25):(0.01-1).

2. The tight oil reservoir self-generated surfactant fracturing fluid according to claim 1, characterized in that: The hydrogen-bonded complex ligand, by mass percentage, is composed of the following raw materials in the following mass percentages: 0.5-3% triethanolamine, 0.3-2% tetraethylenepentamine, 0.1-5% isopropanol, 0.3-5% ethylene glycol, 0.1-2% glycerol, and the balance being water.

3. The tight oil reservoir self-generated surfactant fracturing fluid according to claim 1, characterized in that: The auxiliary solubilizing and stabilizing agent, by weight (100%), is composed of the following raw materials in the following mass percentages: 0.5-10% potassium chloride, 0.5-5% potassium sulfate, 0.5-10% sodium chloride, and the balance being water.

4. The tight oil reservoir self-generated surfactant fracturing fluid according to claim 1, characterized in that: The auxiliary synergist is an aqueous solution of a demulsifier.

5. The tight oil reservoir self-generated surfactant fracturing fluid according to claim 1, characterized in that: The concentration of the demulsifier in the auxiliary synergist is 0.1-1 wt%.

6. The tight oil reservoir self-generated surfactant fracturing fluid according to claim 1 or 5, characterized in that: The demulsifier is a polyether-based demulsifier.

7. The tight oil reservoir self-generated surfactant fracturing fluid according to claim 1, characterized in that: The basic fracturing fluid also contains a low-temperature activator, a temperature stabilizer, a pH adjuster, or a bactericide.

8. The tight oil reservoir self-generated surfactant fracturing fluid according to claim 7, characterized in that: The mass contents of the low-temperature activator, temperature stabilizer, pH adjuster, or bactericide in the basic fracturing fluid are 0.01-0.08%, 0.01-0.1%, 0.1-0.8%, and 0.1-0.6%, respectively.

9. The tight oil reservoir self-generated surfactant fracturing fluid according to claim 7, characterized in that: The low-temperature activator is sodium sulfite, the temperature stabilizer is sodium thiosulfate, the pH adjuster is sodium carbonate or sodium hydroxide, and the bactericide is glutaraldehyde.

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