A low-crosslinking profile adjustment and displacement system for clastic rock reservoirs and its preparation method

Abstract

A low-crosslinked flooding system for clastic reservoirs and its preparation method. The system comprises the following components: 0.05-0.1 wt% of a biopolysaccharide polymer, 0.1-0.45 wt% of an organic zirconium crosslinker, and a solvent. The biopolysaccharide polymer is diutan gum, and the solvent is high-mineralization simulated oilfield water. This polymer flooding system, primarily used for flooding in high-temperature oil-salt clastic reservoirs, is resistant to temperatures up to 110°C and salts up to 220,000 mg / l. The addition of an organic zirconium crosslinker to a biopolysaccharide system with excellent heat and salt resistance effectively improves the system's heat and salt resistance while reducing the biopolysaccharide concentration and system cost.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield adjustment and displacement, and in particular to a high-temperature-resistant and high-salt-resistant biopolysaccharide low-crosslinked polymer system for clastic rock oil reservoirs and a preparation method thereof. Background Art

[0002] Some clastic oil reservoirs, such as the Tahe Oilfield, have the characteristics of ultra-deep, high-temperature, high-mineralization, high-calcium-magnesium, and strong heterogeneity. The reservoir depth is 4200-5100m, the formation temperature is 90-110℃, and the formation water mineralization is as high as 22×10 4 mg / L, of which calcium and magnesium ion content is 1.0×10 4 mg / L, permeability 56-5100mD, average permeability range 28.2. The recoverable reserves of Tahe clastic oil reservoir are 2459×10 4 The recovery rate is 33.7%, while the degree of recovery is only 24%, indicating significant potential for further development. In recent years, with the rapid increase in water cut during development, the clastic reservoirs in the Tahe Oilfield have entered a high-water-cut phase. Initially, particle and gel water plugging were primarily used to control bottom water and tap the potential for residual oil around the wellbore. However, after multiple rounds of water plugging, the effectiveness of water plugging deteriorated dramatically. Later, the recovery focus gradually shifted to tapping the potential of residual oil between wells and at the top. Polymer profile control is an effective water control technology, but due to the harsh high-temperature, high-salinity reservoir conditions, conventional polymer profile control is not applicable in high-temperature, high-salinity clastic reservoirs.

[0003] Polymer flooding technologies, currently the most widely researched and applied, primarily include polyacrylamide and xanthan gum-based deep flooding technologies. Among these, weak-gel polyacrylamide-based flooding agents are the most widely used. These flooding systems generally operate at temperatures between 20°C and 90°C, and their salt tolerance is generally less than 10,000 mg / L.

[0004] By investigating the current status of research and application of domestic profile adjustment and flooding technology, it was found that conventional polymer profile adjustment and flooding systems have problems such as poor stability, weak controllability, and high injection pressure under the high temperature and high salinity conditions of the Tahe oil reservoir, and their performance is difficult to meet the needs of oil reservoir profile adjustment and flooding. Summary of the Invention

[0005] In order to solve the problems of poor stability, weak controllability and high injection pressure of conventional polymer profile adjustment and displacement systems in clastic oil reservoirs under high temperature and high salinity conditions in the prior art, the present invention provides a low-crosslinking profile adjustment and displacement system for clastic oil reservoirs and a preparation method.

[0006] The technical solutions of the present invention are as follows:

[0007] A low-crosslinking profile adjustment and displacement system for clastic oil reservoirs, characterized by comprising the following components:

[0008] 0.05-0.1 wt% of a biopolysaccharide polymer, 0.1-0.45 wt% of an organic zirconium cross-linking agent and a solvent, wherein the biopolysaccharide polymer is diutan gum, and the solvent is simulated water with high mineralization in oil fields.

[0009] Preferably, the biopolysaccharide diutanol is a tetrasaccharide repeating unit, the main chain is composed of repeating units composed of four monosaccharides, the four monosaccharides are β-1,3-D-pyranose glucose; β-1,4-D-glucuronic acid; β-1,3-D-pyranose glucose; α-1,4-L-rhamnose, and the side chain is composed of two α-L-rhamnosyl groups connected to 4-O-substituted-β-D-glucose by β-(1-3) bonds, with a relative molecular mass of 2.88×10 6 ~5.18×10 6 g·mol -1 .

[0010] Preferably, the organic zirconium cross-linking agent is synthesized by reacting an inorganic zirconium salt with an organic ligand.

[0011] More preferably, the reaction raw materials include an inorganic zirconium salt of zirconium oxychloride, and the organic ligands are polyhydroxycarboxylic acid ligands such as lactic acid and polyol ligands such as glycerol.

[0012] More preferably, the mass ratio of the zirconium oxychloride, the polyhydroxycarboxylic acid ligand lactic acid, and the polyol ligand glycerol is 10:7-8:6-7.

[0013] The aforementioned method for preparing a low-crosslinking profile adjustment and displacement system for clastic oil reservoirs is characterized by comprising the following steps:

[0014] (1) Prepare solvent oilfield simulated oilfield water;

[0015] (2) Preparation of an organic zirconium crosslinker: Ultrapure water and zirconium oxychloride were added to a container and stirred in a water bath until completely dissolved. Lactic acid, a polyhydroxycarboxylic acid ligand, and glycerol, a polyol ligand, were weighed and added to the container in sequence. The pH was adjusted to below 5 using sodium hydroxide solution. The mixture was stirred and reacted for 2-4 hours to obtain an organic zirconium crosslinker.

[0016] (3) Preparation of the control and flooding system: Weigh the various components of the system according to the formula, put a certain amount of biopolysaccharide into the weighed solvent, stir for 1-3 hours to obtain a biopolysaccharide aqueous solution, add an organic zirconium cross-linking agent to the biopolysaccharide aqueous solution, and continue stirring for 1-3 hours to mix evenly.

[0017] Preferably, in step (1), each reagent is completely dissolved before adding another reagent, and then stirred with a magnetic stirrer for 10-20 minutes before use. The prepared brine is clear and transparent, with no sediment at the bottom of the bottle.

[0018] Preferably, in step (2), a constant temperature heating magnetic stirrer is used during preparation, and the temperature is set to 75°C. 10.0g of ultrapure water is measured in a wide-mouth bottle, 10.0g of zirconium oxychloride is weighed and added to the wide-mouth bottle, a magnetic rotor is added, and the bottle is placed in a water bath and stirred until completely dissolved. After the water bath temperature reaches 75°C, 7.5g of lactic acid, a polyhydroxycarboxylic acid ligand, and 6.0g of glycerol, a polyol ligand, are weighed and added to the wide-mouth bottle in sequence. The pH is adjusted to 4.5 using a 5mol / L sodium hydroxide solution, and the reaction is stirred for 3 hours to obtain an organic zirconium crosslinker.

[0019] The beneficial technical effects of the present invention are as follows:

[0020] To address the water control problem in existing high-temperature, high-salt clastic reservoirs with high water content, such as the Tahe Oilfield, the present invention provides a biopolysaccharide organic zirconium low-crosslinking flooding system, which is mainly used for flooding in high-temperature oil-salt clastic reservoirs. It is a polymer flooding system with a temperature resistance of 110°C and a salt resistance of 220,000 mg / l.

[0021] The present invention adds an organic zirconium cross-linking agent to a biopolysaccharide system with excellent heat and salt resistance, which can effectively improve the heat and salt resistance of the system, while reducing the concentration of the biopolysaccharide used and effectively reducing the cost of the system.

[0022] Among them, the biopolysaccharide diutan gum has good viscosity-increasing properties and can achieve high viscosity even at low concentrations under single use conditions. At 110°C and 220,000 degrees of salinity, to achieve the same viscosity as a biopolysaccharide solution (Cp = 0.1%), the mass concentration of welan gum requires 0.15%, xanthan gum requires 0.25%, and HPAM is as high as 0.5%. The viscosity-increasing properties of biopolysaccharides are superior to those of other polymers. Therefore, under high salinity conditions, aqueous solutions of biopolysaccharides maintain higher retained viscosity and viscosity residual rate than existing polymers such as acrylamide and xanthan gum. They have excellent shear resistance and viscosity-increasing properties under high temperature conditions of 110°C. This is related to their three-dimensional physical network structure. In high temperature and high salt environments, the Cp is 0.15%-0.3%, and the viscosity residual rate is greater than 65% throughout the entire temperature scan process (25-150°C). Furthermore, they have a high residual viscosity, Cp ≤ 0.1%, and the viscosity residual rate is greater than 50%. Biopolysaccharide polymers are relatively expensive, so they are weakly cross-linked in order to effectively improve the stability of the system under low concentrations (0.1%, 0.05%) and high temperature and high salt conditions.

[0023] Organic zirconium crosslinkers are synthesized by the reaction of inorganic zirconium salts and organic ligands. The addition of organic ligands forms polynuclear complex ions, enhancing the crosslinking strength per crosslink point and improving the temperature resistance of the solution. Compared to common inorganic boron, organic boron, and phenolic crosslinkers, the organic zirconium crosslinked biopolysaccharide flooding system exhibits superior temperature resistance and shear resistance. This effectively improves the temperature resistance of biopolysaccharide polymers and reduces their concentration, significantly enhancing the stability of the solution under high temperature and high salinity conditions.

[0024] The cross-linked biopolysaccharide-organic zirconium flooding system exhibited significantly better viscosity-increasing properties than the uncross-linked biopolysaccharide polymer at a biopolysaccharide concentration of 0.1% and an organic zirconium concentration of 0.05%, with a viscosity increase exceeding 100%. At 110°C, the viscosity remained unchanged for 10 days, and the system demonstrated high-temperature and high-salinity stability for up to 120 days. In a simulated reservoir environment at 110°C, the low-crosslinked biopolysaccharide-organic zirconium system increased oil recovery by 16.3% over a single waterflood.

[0025] On the one hand, this system has a certain strength that can block the high-permeability channels in the formation, allowing the subsequent injected water to bypass the medium and low permeability layers to play a role in oil displacement. On the other hand, due to the low cross-linking strength, the oil displacement system with a certain viscosity can slowly move deep into the formation under the push of subsequent injected water, producing an effect similar to polymer flooding. This dynamic sweep effect is far better than that of higher-strength gel, and can maximize the expansion of sweep and improve oil displacement efficiency. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below through specific embodiments, but this does not limit the technical solution of the present invention. All changes or equivalent substitutions based on the present invention should fall within the scope of protection of the present invention.

[0027] Examples 1-12

[0028] A biopolysaccharide low-crosslinked polymer profile control and flooding system for high-temperature, high-salt clastic reservoirs according to Example 12 comprises the following components:

[0029] Example 1: 0.05% wt% biopolysaccharide polymer, 0.10% organic zirconium cross-linking agent, and the balance is solvent;

[0030] Example 2: 0.05% wt% biopolysaccharide polymer, 0.15% organic zirconium cross-linking agent, and the balance is solvent;

[0031] Example 3: 0.05% wt% biopolysaccharide polymer, 0.4% organic zirconium cross-linking agent, and the balance is solvent;

[0032] Example 4: 0.05% wt% biopolysaccharide polymer, 0.5% organic zirconium cross-linking agent, and the balance being solvent;

[0033] Example 5: 0.06% wt% biopolysaccharide polymer, 0.15% organic zirconium cross-linking agent, and the balance being solvent;

[0034] Example 6: 0.06% wt% biopolysaccharide polymer, 0.25% organic zirconium cross-linking agent, and the balance is solvent;

[0035] Example 7: 0.06% wt% biopolysaccharide polymer, 0.35% organic zirconium cross-linking agent, and the balance being solvent;

[0036] Example 8: 0.07% wt% biopolysaccharide polymer, 0.15% organic zirconium cross-linking agent, and the balance being solvent;

[0037] Example 9: 0.07% wt% biopolysaccharide polymer, 0.20% organic zirconium cross-linking agent, and the balance being solvent;

[0038] Example 10: 0.07% wt% biopolysaccharide polymer, 0.45% organic zirconium cross-linking agent, and the balance being solvent;

[0039] Example 11: 0.1% wt% biopolysaccharide polymer, 0.20% organic zirconium cross-linking agent, and the balance being solvent;

[0040] Example 12: 0.1% wt% biopolysaccharide polymer, 0.35% organic zirconium cross-linking agent, and the balance being solvent.

[0041] Among them, the biopolysaccharide polymer is the biopolysaccharide diutan gum, which refers to a biopolymer with self-protection function secreted during biological metabolism. Diutan gum is a microbial extracellular polysaccharide aerobically fermented by Sphingomonas sp.ATCC 53159. The biopolysaccharide diutan gum is a tetrasaccharide repeating unit, and the main chain is composed of repeating units composed of 4 monosaccharides. The 4 monosaccharides are β-1,3-D-pyranose glucose, β-1,4-D-glucuronic acid, β-1,3-D-pyranose glucose and α-1,4-L-rhamnose, respectively. The side chain is composed of two α-L-rhamnosyl groups connected to 4-O-substituted-β-D-glucose with a β-(1-3) bond, as shown in the following formula, with a relative molecular mass of 2.88×10 6 ~5.18×10 6 g·mol -1 The polymer has good pseudoplasticity. The solution viscosity decreases with increasing shear rate, showing shear thinning properties and good viscosity-increasing properties. The high molecular weight of the biopolysaccharide allows for high viscosity to be achieved at lower concentrations.

[0042]

[0043] Formula (1) is the molecular structure of biopolysaccharide diutan gum, M + Represents the metal cation of polysaccharide D.

[0044] The crosslinker is an organic zirconium crosslinker, synthesized by the reaction of an inorganic zirconium salt and an organic ligand. The preparation process is detailed below. The addition of the organic ligand significantly enhances the stability of the crosslinker, forming polynuclear complexes that increase the crosslinking strength per crosslink point and improve the temperature resistance of the solution.

[0045] Wherein, the solvent is simulated oilfield water from Tahe Oilfield.

[0046] A method for preparing a biopolysaccharide oligomeric polymer flooding system is also provided. The system preparation method is simple and rapid, and the prepared system has good stability. The specific laboratory synthesis steps of the above embodiment are:

[0047] The specific steps are:

[0048] (1) The solvent used in this system is simulated oilfield water from the Tahe Oilfield. When preparing, each reagent is completely dissolved before adding another reagent. Then, stir it with a magnetic stirrer for 15 minutes before use. The prepared brine is clear and transparent, with no sediment at the bottom of the bottle.

[0049] (2) Preparation of an organic zirconium crosslinker: Using a thermostatically heated magnetic stirrer set to 75°C, 10.0 g of ultrapure water was weighed into a wide-mouth bottle. 10.0 g of zirconium oxychloride was added to the bottle. A magnetic rotor was added to the bottle, and the mixture was placed in a water bath and stirred until completely dissolved. After the water bath temperature reached 75°C, 7.5 g of lactic acid (a polyhydroxycarboxylic acid ligand) and 6.0 g of glycerol (a polyol ligand) were weighed and added to the bottle in sequence. The pH was adjusted to 4.5 using a 5 mol / L sodium hydroxide solution. The mixture was stirred for 3 h to obtain the organic zirconium crosslinker.

[0050] (3) Preparation of the control and displacement system: Weigh the various components of the system according to the formula. Place a certain amount of biopolysaccharide into the simulated saline solvent. After adding a magnetic rotor, stir with a magnetic stirrer for 2 hours to obtain a cross-linked biopolysaccharide aqueous solution. Add a certain amount of organic zirconium crosslinker to this solution and continue stirring for 2 hours to obtain a cross-linked biopolysaccharide aqueous solution. After stirring and mixing, place the solution in an oven at 110-130°C to observe its viscosity-increasing properties and temperature and salt stability.

[0051] Evaluation of viscosity-increasing properties of low-crosslinked biopolysaccharide polymer system:

[0052] The experimental instrument used is a high-temperature, high-pressure rheological test system equipped with Anton Paar's MCR302 rheometer. Viscosity test conditions: temperature sweep, 25°C (room temperature) to 150°C; shear rate, 100s-1

[0053] Experimental results show that the viscosity of low-crosslinked organic zirconium solutions containing biopolysaccharides decreases with increasing temperature. Under the same biopolysaccharide concentration conditions, the viscosity of the system gradually increases with increasing crosslinker concentration. The viscosity of underground crude oil in the 110°C target reservoir of the Tahe Oilfield is approximately 3-5 mPa·s. The viscosities of Examples 1-12 at room temperature and 110°C are shown in the table below. This experiment demonstrates that the above solutions can be used for crude oil profile management in the 110°C target reservoir.

[0054] Relationship between viscosity of aqueous solution of organozirconium cross-linked biopolysaccharide diutan gum and its concentration and temperature

[0055]

[0056] Evaluation of shear energy of low cross-linked biopolysaccharide polymer system:

[0057] The polymer solution has a strong shearing effect when injected into the ground at high speed, and the shear rate is as high as 4000-6000s during pumping. -1 This intense shearing can easily cause mechanical degradation of polymer molecules, leading to a loss of polymer solution viscosity. To ensure that the polymer maintains a good viscosity-increasing ability after injection into the formation, it must possess a certain degree of shear resistance, so its shear resistance must be evaluated. Shearing was performed using a high-speed emulsifier at a shear rate of 3000 r / min and an emulsification time of 1 to 3 minutes. The viscosity of the solution before and after shearing was measured using a rheometer.

[0058] After high-speed shearing, the viscosity of the solutions in each example increased by 35% between 1 and 6 minutes compared to the initial viscosity. One reason for the slight increase in viscosity rather than a decrease is that the high-speed shearing process essentially disrupts crosslinking, disentangling the long polymer chains, strengthening intermolecular forces, and increasing the hydrodynamic volume. However, after 7 minutes, the viscosity dropped back to the initial viscosity, likely due to the disruption of the system's molecular chains.

[0059] Evaluation of stability of biopolysaccharide low cross-linked polymer system:

[0060] The long-term viscosity retention value of the polymer solution under reservoir conditions is used to ensure that the selected polymer can retain sufficient viscosity during the displacement time, and long-term thermal stability performance evaluation is required.

[0061] Experimental instruments include an aging tank that can withstand high temperatures of 200°C and 10 MPa, a constant temperature oil bath, a glove box, and an Anton Paar MCR302 rheometer high temperature and high pressure system.

[0062] At 110° C., after aging for 110 days, the viscosity retention rate of the biopolysaccharide low-crosslinked polymer system of each embodiment is still 50%, indicating good long-term stability.

[0063] Evaluation of displacement performance of biopolysaccharide low cross-linked polymer system:

[0064] Simulate high salinity in oilfield (TDS = 10.1 × 10 4 mg·L -1 or 22.0×10 4 mg·L -1 ) environment, 110℃ of Tahe Oilfield was selected as the simulated displacement temperature, and medium permeability core was used for simulation. The core water permeability was about 300mD. The flow properties and oil displacement efficiency of the biopolysaccharide low-cross-linked polymer system were characterized through core displacement experiment simulation.

[0065] Under the simulated environment of 110℃ oil reservoir, the resistance coefficient (Rf) and residual resistance coefficient (Rff) of the biopolysaccharide low cross-linked polymer system are both greater than those of the HPAM and xanthan gum low cross-linked system.

[0066]

[0067] The low-crosslinked biopolysaccharide polymer system formed a three-dimensional network structure at 110°C, exhibiting significant viscoelasticity and stable solution properties. Once it seeped into the pores of the core, it exhibited excellent fluidity control. Therefore, the RF value of the low-crosslinked biopolysaccharide polymer system was higher than that of xanthan gum and HPAM.

[0068] In the simulated environment of a 110℃ oil reservoir, the biopolysaccharide low-crosslinked polymer system increased the crude oil recovery by 16.3% based on a single water flooding.

[0069] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that are not conceived through creative work should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined in the claims.

Claims

1. A profile control and displacement system for clastic oil reservoirs, characterized in that Includes the following ingredients: 0.05-0.1 wt% of a biopolysaccharide polymer, 0.1-0.45 wt% of an organic zirconium cross-linking agent and a solvent, wherein the biopolysaccharide polymer is diutan gum, and the solvent is simulated water with high mineralization in an oil field. The organic zirconium crosslinking agent is synthesized by the reaction of an inorganic zirconium salt and an organic ligand. The reaction raw materials include the inorganic zirconium salt being zirconium oxychloride, and the organic ligand being polyhydroxycarboxylic acid ligand lactic acid and polyol ligand glycerol.

2. The system according to claim 1, characterized in that The biopolysaccharide diutanol is a tetrasaccharide repeating unit. The main chain is composed of repeating units composed of four monosaccharides, which are β-1,3-D-pyranose glucose, β-1,4-D-glucuronic acid, β-1,3-D-pyranose glucose and α-1,4-L-rhamnose. The side chain is composed of two α-L-rhamnosyl groups connected to 4-O-substituted-β-D-glucose via a β-(1-3) bond. The relative molecular mass is 2.88×10 6 ~5.18×10 6 g·mol -1 .

3. The system according to claim 1, characterized in that The mass ratio of the zirconium oxychloride, the polyhydroxycarboxylic acid ligand lactic acid and the polyol ligand glycerol is 10:7-8:6-7.

4. The method for preparing a profile adjustment and displacement system for clastic oil reservoirs according to any one of claims 1 to 3, characterized in that The following steps are involved: (1) Prepare solvent oilfield simulated oilfield water; (2) Preparation of an organic zirconium crosslinker: Ultrapure water and zirconium oxychloride were added to a container and stirred in a water bath until completely dissolved. Lactic acid, a polyhydroxycarboxylic acid ligand, and glycerol, a polyol ligand, were weighed and added to the container in sequence. The pH was adjusted to below 5 using sodium hydroxide solution. The mixture was stirred and reacted for 2-4 hours to obtain an organic zirconium crosslinker. (3) Preparation of the control and flooding system: Weigh the various components of the system according to the formula, put a certain amount of biopolysaccharide into the weighed solvent, stir for 1-3 hours to obtain a biopolysaccharide aqueous solution, add an organic zirconium cross-linking agent to the biopolysaccharide aqueous solution, and continue stirring for 1-3 hours to mix evenly.

5. The method according to claim 4, characterized in that In step (1), each reagent is completely dissolved before adding another reagent, and then stirred with a magnetic stirrer for 10-20 minutes before use. The prepared brine is clear and transparent, with no sediment at the bottom of the bottle.

6. The method according to claim 4, characterized in that In step (2), a constant temperature heating magnetic stirrer is used during the preparation, and the temperature is set to 75°C. 10.0g of ultrapure water is measured in a wide-mouth bottle, 10.0g of zirconium oxychloride is weighed and added to the wide-mouth bottle, a magnetic rotor is added and the mixture is placed in a water bath and stirred until completely dissolved. After the water bath temperature reaches 75°C, 7.5g of polyhydroxycarboxylic acid ligand lactic acid and 6.0g of polyol ligand propylene glycol are weighed and added to the wide-mouth bottle in sequence, and the pH is adjusted to 4.5 using a sodium hydroxide solution with a concentration of 5mol / L. The reaction is stirred for 3h to obtain an organic zirconium crosslinker.

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