A method for treating oilfield polymer-containing wastewater

Abstract

The present application relates to a kind of oilfield polymer-containing sewage treatment methods, belong to oilfield sewage treatment technical field.The treatment method of the present application includes the following steps: in the polymer-containing sewage of oilfield to be treated, polyphosphorus aluminum chloride is input to stir, then micron silicon dioxide and cationic polyacrylamide are stirred.The treatment method of the present application, using the charge adsorption of micron silicon dioxide promotes the synergistic effect of polyphosphorus aluminum chloride and cationic polyacrylamide and the removal effect of polymer in sewage, improve the oil removal rate of oilfield polymer-containing sewage, suspended solid removal rate, and reduce flocculant dosage.

Description

Technical Field

[0001] This invention relates to a method for treating polymer-containing wastewater from oil fields, belonging to the field of oil field wastewater treatment technology. Background Technology

[0002] Polymer flooding is a commonly used oilfield extraction technology. This technology increases the viscosity of the aqueous phase and reduces permeability by dissolving polymers in water, thereby lowering the flow ratio, increasing the waterflood sweep efficiency, and improving oil recovery. However, the -COO- or -CONH2 hydrophilic groups on the polymer molecular branches strongly adsorb solid particles, forming a network structure that adsorbs at the oil-water interface. Simultaneously, due to the strong hydrophilicity of HPAM (polyaluminum hydroxide), it carries a large amount of bound water, adsorbing solid particles and forming a gel-like substance in the intermediate mixed emulsion layer, increasing the difficulty of destabilization. Furthermore, since most polymers used in oil production are anionic, some polymers adsorb at the oil-water interface, reducing the collision probability between oil droplets and increasing the degree of emulsification in the produced fluid. At the same time, the anionic polymers injected into the produced fluid increase the number of negative ions, correspondingly increasing the number of positive ions used for charge neutralization. All of these factors mean that when using traditional polyaluminum hydroxide + polyacrylamide flocculation technology, a significant increase in flocculant dosage is required to achieve high oil removal and suspended solids removal rates to meet wastewater treatment needs, resulting in high costs. Summary of the Invention

[0003] The purpose of this invention is to provide a method for treating oilfield polymer-containing wastewater with high oil removal rate and suspended solids removal rate.

[0004] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0005] A method for treating polymer-containing wastewater from oilfields includes the following steps: adding polyphosphoric aluminum chloride to the polymer-containing wastewater from the oilfield to be treated and stirring, then adding micron-sized silica and cationic polyacrylamide and stirring.

[0006] The present invention relates to a method for treating polymer-containing wastewater from oilfields. This method involves adding polyaluminum chloride (PAC) followed by cationic polyacrylamide and micronized silica to the wastewater. The high specific surface area and hydrophobic properties of micronized silica generate a charge adsorption-promoting effect, which enhances the synergistic effect of PAC and cationic polyacrylamide through associative adsorption, as well as their removal of polymers from the wastewater. This achieves the goals of increasing the oil removal rate and suspended solids removal rate of the polymer-containing wastewater from oilfields, reducing the amount of flocculant added, and lowering the cost of flocculants.

[0007] The method for treating oilfield wastewater containing polymers according to the present invention does not increase the dosing points or dosing process of the original wastewater treatment process using polyaluminum + polyacrylamide flocculation technology, does not have an adverse impact on subsequent wastewater processes, and is simple and easy to operate on site.

[0008] Polyphosphate aluminum chloride (PPAC) carries a higher positive charge during hydrolysis, rapidly neutralizing both positive and negative charges to quickly destabilize and aggregate emulsified oil and suspended solids into flocs. Compared to polyaluminum chloride (PAC), PPAC offers superior demulsification capabilities, higher oil removal rates, higher suspended solids removal rates, and lower treatment costs for oilfield wastewater. The PPAC can be a commercially available product or produced by introducing phosphates during the production of polyaluminum chloride, followed by a mixed polymerization reaction and aging.

[0009] Micron-sized silica has a large specific surface area, exhibiting not only strong adsorption capacity but also a certain degree of oleophilic and hydrophobic properties. This combination enhances the attraction of cationic polyacrylamide to oil droplets in wastewater, thereby improving the oil removal rate. Furthermore, it disrupts the synergistic effect between suspended solids particles and anionic polymers in wastewater, thus improving the removal rate of suspended solids. Due to the hydrophobic groups on its surface, micron-sized silica can associate with cationic polyacrylamide and polyaluminum chloride. This association reduces the hydrophilicity of the flocs, accelerates their settling speed, and increases their strength, resulting in large, dense flocs with low water content. Further, the average particle size of the micron-sized silica is 3-7 μm, and its specific surface area is 170-240 m². 2 / g. For example, the specific surface area of ​​the micron-sized silica is 200m². 2 / g.

[0010] Furthermore, the molar percentage of AlPO4 in the polyphosphoric aluminum chloride is 2-6%, for example, 6%.

[0011] Furthermore, the cationic polyacrylamide has a cationicity of 30-50% and a molecular weight of 8-20 million. For example, the cationic polyacrylamide has a cationicity of 30% and a molecular weight of 12 million.

[0012] The higher the anionic polymer content in oilfield wastewater, the more micronized silica is needed for better wastewater treatment. However, excessive use of micronized silica can lead to poorer wastewater treatment results. To control the appropriate ratio of hydrophobic to hydrophilic groups and achieve optimal wastewater treatment, the optimal flocculant concentration is achieved. Therefore, the mass ratio of micronized silica to cationic polyacrylamide is 2–10:100.

[0013] Furthermore, for every 1L of polyphosphate-containing wastewater from the oilfield to be treated, the corresponding mass of added polyphosphate aluminum chloride is 105-160mg, and the corresponding mass of added cationic polyacrylamide in the composite flocculant is 4.5-6mg.

[0014] Furthermore, before adding the micronized silica and cationic polyacrylamide to the polymer-containing wastewater from the oilfield, the micronized silica and cationic polyacrylamide are first dispersed in water to prepare a mixed dispersion, and then the mixed dispersion is added to the polymer-containing wastewater from the oilfield. Micronized silica and cationic polyacrylamide have good compatibility, and there is no precipitation or clumping when dispersed in water.

[0015] Furthermore, the settling time is 4 to 6 minutes, for example, 5 minutes. Detailed Implementation

[0016] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0017] In the following examples and comparative examples, the oil content of the polymer-containing wastewater from the oilfield was 112 mg / L, and the content of suspended solids was 74 mg / L. After treatment by the method for treating polymer-containing wastewater from the oilfield in the examples, the wastewater enters a dissolved air flotation machine for separation of flocs and water; the water enters a filter tank for filtration; the flocs float to the surface and become scum, which then enters the sludge treatment process.

[0018] Example 1

[0019] The method for treating polymer-containing wastewater from oil fields in this embodiment includes the following steps:

[0020] 1) Add polyphosphoric aluminum chloride to water and disperse evenly to obtain a polyphosphoric aluminum chloride solution with a mass fraction of 4%; the molar percentage of AlPO4 in the polyphosphoric aluminum chloride used is 6%;

[0021] Cationic polyacrylamide and micronized silica were added to water at a mass ratio of 100:5 and dispersed evenly to obtain a mixed dispersion with a cationic polyacrylamide mass fraction of 0.1%. The cationic polyacrylamide used had a cationicity of 30% and a molecular weight of 12 million. The micronized silica used had an average particle size of 5 μm and a specific surface area of ​​200 m². 2 / g.

[0022] 2) First, add the prepared polyphosphoric aluminum chloride solution (the mass of polyphosphoric aluminum chloride in the polyphosphoric aluminum chloride solution added for every 1L of polyphosphoric wastewater is 105mg) and stir slowly and uniformly with a glass rod for 30s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide in the mixed dispersion added for every 1L of polyphosphoric wastewater is 4.5mg), stir slowly and uniformly with a glass rod for 30s, and then let it stand for 5 minutes.

[0023] Example 2

[0024] The method for treating polymer-containing wastewater from oil fields in this embodiment includes the following steps:

[0025] 1) Polyphosphorus aluminum chloride was added to water and dispersed evenly to obtain a polyphosphorus aluminum chloride solution with a mass fraction of 4%; the molar percentage of AlPO4 in the polyphosphorus aluminum chloride used was 2%;

[0026] Cationic polyacrylamide and micronized silica were added to water at a mass ratio of 100:2 and dispersed evenly to obtain a mixed dispersion with a mass fraction of 0.1% cationic polyacrylamide. The cationic polyacrylamide used had a cationicity of 50% and a molecular weight of 8 million. The micronized silica used had an average particle size of 3 μm and a specific surface area of ​​240 m². 2 / g.

[0027] 2) First, add the prepared polyphosphoric aluminum chloride solution (the mass of polyphosphoric aluminum chloride in the polyphosphoric aluminum chloride solution added per 1L of polyphosphoric wastewater is 160mg) and stir slowly and uniformly with a glass rod for 30s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide in the mixed dispersion added per 1L of polyphosphoric wastewater is 6.0mg), stir slowly and uniformly with a glass rod for 30s, and then let it stand for 5 minutes.

[0028] Example 3

[0029] The method for treating polymer-containing wastewater from oil fields in this embodiment includes the following steps:

[0030] 1) Add polyphosphoric aluminum chloride to water and disperse evenly to obtain a polyphosphoric aluminum chloride solution with a mass fraction of 4%; the molar percentage of AlPO4 in the polyphosphoric aluminum chloride used is 4%;

[0031] Cationic polyacrylamide and micronized silica were added to water at a mass ratio of 100:10 and dispersed evenly to obtain a mixed dispersion with a cationic polyacrylamide mass fraction of 0.1%. The cationic polyacrylamide used had a cationicity of 30% and a molecular weight of 20 million. The micronized silica used had an average particle size of 7 μm and a specific surface area of ​​170 m². 2 / g.

[0032] 2) First, add the prepared polyphosphoric aluminum chloride solution (the mass of polyphosphoric aluminum chloride in the polyphosphoric aluminum chloride solution added per 1L of polyphosphoric wastewater is 130mg) and stir slowly and uniformly with a glass rod for 30s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide in the mixed dispersion added per 1L of polyphosphoric wastewater is 4.9mg), stir slowly and uniformly with a glass rod for 30s, and then let it stand for 5 minutes.

[0033] Example 4

[0034] The method for treating polymer-containing wastewater from oil fields in this embodiment includes the following steps:

[0035] 1) Add polyphosphoric aluminum chloride to water and disperse evenly to obtain a polyphosphoric aluminum chloride solution with a mass fraction of 4%; the molar percentage of AlPO4 in the polyphosphoric aluminum chloride used is 6%;

[0036] Cationic polyacrylamide and micronized silica were added to water at a mass ratio of 100:10 and dispersed evenly to obtain a mixed dispersion with a cationic polyacrylamide mass fraction of 0.1%. The cationic polyacrylamide used had a cationicity of 30% and a molecular weight of 12 million. The micronized silica used had an average particle size of 5 μm and a specific surface area of ​​200 m². 2 / g.

[0037] 2) First, add the prepared polyphosphoric aluminum chloride solution (the mass of polyphosphoric aluminum chloride in the polyphosphoric aluminum chloride solution added for every 1L of polyphosphoric wastewater is 160mg) to the polyphosphoric wastewater, and stir slowly and uniformly with a glass rod for 30s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide in the mixed dispersion added for every 1L of polyphosphoric wastewater is 6mg), stir slowly and uniformly with a glass rod for 30s, and then let it stand for 5 minutes.

[0038] Example 5

[0039] The method for treating polymer-containing wastewater from oil fields in this embodiment includes the following steps:

[0040] 1) Add polyphosphoric aluminum chloride to water and disperse evenly to obtain a polyphosphoric aluminum chloride solution with a mass fraction of 4%; the molar percentage of AlPO4 in the polyphosphoric aluminum chloride used is 6%;

[0041] Cationic polyacrylamide and micronized silica were added to water at a mass ratio of 100:2 and dispersed evenly to obtain a mixed dispersion with a mass fraction of 0.1% cationic polyacrylamide. The cationic polyacrylamide used had a cationicity of 30% and a molecular weight of 12 million. The micronized silica used had an average particle size of 5 μm and a specific surface area of ​​200 m². 2 / g.

[0042] 2) First, add the prepared polyphosphoric aluminum chloride solution (the mass of polyphosphoric aluminum chloride in the polyphosphoric aluminum chloride solution added for every 1L of polyphosphoric wastewater is 160mg) to the polyphosphoric wastewater, and stir slowly and uniformly with a glass rod for 30s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide in the mixed dispersion added for every 1L of polyphosphoric wastewater is 6mg), stir slowly and uniformly with a glass rod for 30s, and then let it stand for 5 minutes.

[0043] Comparative Example 1

[0044] The method for treating polymer-containing wastewater from oil fields in this comparative example includes the following steps:

[0045] 1) Add polyaluminum chloride to water and disperse it evenly to obtain a polyaluminum chloride solution with a mass fraction of 4%;

[0046] Cationic polyacrylamide was added to water and dispersed evenly to prepare a cationic polyacrylamide solution with a mass fraction of 0.1%; the cationic polyacrylamide used had a cationicity of 30 and a molecular weight of 12 million.

[0047] 2) First, add the prepared polyaluminum chloride solution (the mass of polyaluminum chloride in the polyaluminum chloride solution added per 1L of polyaluminum-containing wastewater) to the oilfield wastewater, and stir slowly and uniformly with a glass rod for 30s; then add the prepared cationic polyacrylamide solution (the mass of cationic polyacrylamide added per 1L of polyaluminum-containing wastewater is 4.5mg), stir slowly and uniformly with a glass rod for 30s, and then let it stand for 5 minutes.

[0048] Comparative Example 2

[0049] The treatment method for oilfield polymer-containing wastewater in this comparative example differs from that in Comparative Example 1 only in step 2):

[0050] First, add the prepared polyaluminum chloride solution (the mass of polyaluminum chloride in the polyaluminum chloride solution added per 1L of polyaluminum-containing wastewater) to the polyaluminum-containing wastewater, and stir slowly and uniformly with a glass rod for 30s; then add the prepared cationic polyacrylamide solution (the mass of cationic polyacrylamide added per 1L of polyaluminum-containing wastewater is 6.0mg), stir slowly and uniformly with a glass rod for 30s, and then let it stand for 5 minutes.

[0051] Comparative Example 3

[0052] The treatment method for oilfield polymer-containing wastewater in this comparative example differs from that in Comparative Example 1 only in step 2):

[0053] First, add the prepared polyaluminum chloride solution (the mass of polyaluminum chloride in the polyaluminum chloride solution added per 1L of polyaluminum-containing wastewater) to the polyaluminum-containing wastewater, and stir slowly and uniformly with a glass rod for 30s; then add the prepared cationic polyacrylamide solution (the mass of cationic polyacrylamide added per 1L of polyaluminum-containing wastewater is 4.9mg), stir slowly and uniformly with a glass rod for 30s, and then let it stand for 5 minutes.

[0054] Comparative Example 4

[0055] The method for treating polyphosphate-containing wastewater in this comparative example replaces the polyphosphoric aluminum chloride solution added in step 2) of the treatment method in Example 1 with a polyaluminum chloride solution, the mass concentration of which is 4%. The mass of polyaluminum chloride in the polyaluminum chloride solution added per 1L of polyphosphate-containing wastewater is 105mg. The contents not mentioned are exactly the same as in Example 1.

[0056] Comparative Example 5

[0057] The method for treating polymer-containing wastewater from oil fields in this comparative example omits step 2) of adding micronized silica to the mixed dispersion in the treatment method of Example 1; the contents not mentioned are exactly the same as in Example 1.

[0058] Comparative Example 6

[0059] The treatment method for polymer-containing wastewater in this comparative example differs from the treatment method in Example 1 only in that:

[0060] 1) Polyphosphorus aluminum chloride was added to water and dispersed evenly to obtain a polyphosphorus aluminum chloride solution with a mass fraction of 4%. Then, micron-sized silica (mass ratio of silica to polyphosphorus aluminum chloride was 0.225:105) was added to obtain a mixed dispersion. The molar percentage of AlPO4 in the polyphosphorus aluminum chloride used was 6%. The average particle size of the micron-sized silica used was 5 μm, and the specific surface area was 200 m². 2 / g.

[0061] Cationic polyacrylamide was added to water and dispersed evenly to prepare a cationic polyacrylamide solution with a mass fraction of 0.1%; the cationicity of the cationic polyacrylamide used was 30% and the molecular weight was 12 million.

[0062] 2) First, add the prepared mixed dispersion (the mass of polyphosphoric aluminum chloride added per 1L of polyphosphoric wastewater is 105mg) to the polyphosphoric wastewater in the oil field, and stir slowly and uniformly with a glass rod for 30s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide added per 1L of polyphosphoric wastewater is 4.5mg), stir slowly and uniformly with a glass rod for 30s, and then let it stand for 5 minutes.

[0063] Comparative Example 7

[0064] The method for treating polymer-containing wastewater from oil fields in this comparative example includes the following steps:

[0065] 1) Add polyphosphoric aluminum chloride to water and disperse evenly to obtain a polyphosphoric aluminum chloride solution with a mass fraction of 4%; the molar percentage of AlPO4 in the polyphosphoric aluminum chloride used is 6%;

[0066] Cationic polyacrylamide was added to water and dispersed evenly to prepare a cationic polyacrylamide solution with a mass fraction of 0.1%; the cationicity of the cationic polyacrylamide used was 30% and the molecular weight was 12 million.

[0067] 2) First, add the prepared polyphosphorus aluminum chloride solution (105 mg of polyphosphorus aluminum chloride per 1 L of polyphosphorus-containing wastewater) to the polyphosphorus-containing wastewater and stir slowly and uniformly with a glass rod for 30 s; then add the prepared cationic polyacrylamide solution (4.5 mg of cationic polyacrylamide per 1 L of polyphosphorus-containing wastewater) and stir slowly and uniformly with a glass rod for 30 s; then add micronized silica (0.225 mg of micronized silica per 1 L of polyphosphorus-containing wastewater) and stir slowly and uniformly with a glass rod for 30 s, then let stand for 5 minutes; the average particle size of the micronized silica used is 5 μm, and the specific surface area is 200 m². 2 / g.

[0068] Experimental Example

[0069] Water samples from the middle section of each example and comparative example were collected using 50 mL syringes, and their oil content, suspended solids content, and polyacrylamide content were measured. The oil removal rate, suspended solids removal rate, and polyacrylamide removal rate were calculated, and the results are shown in Table 1. The oil content of the wastewater was measured using a spectrophotometer, the suspended solids content was measured by gravimetric method, and the polyacrylamide content was determined using the starch-cadmium iodide spectrophotometric method. The ultraviolet spectrophotometer used in the experiment was a Beijing Purkinje TU-1901. The scum floating on the treated water samples was taken, and the moisture content of the scum was determined by distillation. The results are also shown in Table 1.

[0070] Table 1. Results of wastewater treatment experiments in the examples and comparative examples.

[0071]

[0072] As shown in Table 1, the method for treating oilfield polymer-containing wastewater of the present invention has a higher oil removal rate and suspended solids removal rate compared with the comparative method, and the reagent cost is lower, which is economically significant.

[0073] The method for treating oilfield wastewater containing polymers according to the present invention has good effects in removing oil and suspended solids from wastewater, and significantly improves the oil removal rate and suspended solids removal rate of wastewater. It has the advantages of low dosage, low cost and outstanding wastewater treatment effect.

Claims

1. A method for treating polymer-containing wastewater from oil fields, characterized in that: Includes the following steps: Polyphosphate aluminum chloride was added to the wastewater containing polymers from the oilfield to be treated and stirred, followed by the addition of micronized silica and cationic polyacrylamide and stirring. The micronized silica had an average particle size of 3-7 µm and a specific surface area of ​​170-240 m². 2 / g.

2. The method for treating polymer-containing wastewater from oilfields according to claim 1, characterized in that: The polyphosphorus aluminum chloride contains 2-6% AlPO4 in molar percentage.

3. The method for treating polymer-containing wastewater from oil fields according to claim 1, characterized in that: The cationic polyacrylamide has a cationicity of 30-50% and a molecular weight of 8-20 million.

4. The method for treating polymer-containing wastewater from oil fields according to claim 1, characterized in that: The mass ratio of micron-sized silica to cationic polyacrylamide is 2~10:

100.

5. The method for treating oilfield polymer-containing wastewater according to any one of claims 1 to 4, characterized in that: For every 1L of polyphosphate-containing wastewater from the oilfield to be treated, the corresponding mass of added polyphosphate aluminum chloride is 105~160mg, and the corresponding mass of added cationic polyacrylamide in the composite flocculant is 4.5~6mg.

6. The method for treating oilfield polymer-containing wastewater according to any one of claims 1 to 4, characterized in that: Before adding the micron-sized silica and cationic polyacrylamide to the polymer-containing wastewater in the oilfield, the micron-sized silica and cationic polyacrylamide are first dispersed in water to form a mixed dispersion, and then the mixed dispersion is added to the polymer-containing wastewater in the oilfield.

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