Treatment method for polymer-containing sewage of oil field

Abstract

The invention relates to a method for treating polymer-containing sewage of an oil field, and belongs to the technical field of oil field sewage treatment. The treatment method comprises the following steps: adding polymeric phosphorus aluminum chloride into the polymer-containing sewage of the oil field to be treated, stirring, then adding micron silicon dioxide and cationic polyacrylamide, and stirring. According to the treatment method disclosed by the invention, the synergistic effect of polymeric phosphate aluminum chloride and cationic polyacrylamide and the removal effect on polymers in the sewage are enhanced by utilizing the charge adsorption coagulation promoting effect of the micron silicon dioxide, the oil removal rate of the polymer-containing sewage of the oil field and the removal rate of suspended solids are improved, and the dosage of a flocculating agent is reduced.

Description

Technical Field

[0001] The present invention relates to a method for treating polymer-containing sewage in oil fields, belonging to the technical field of oil field sewage treatment. Background Art

[0002] Polymer flooding is a commonly used oil field exploitation technology. This technology increases the viscosity of the aqueous phase and reduces the permeability by dissolving polymers in water, thereby reducing the mobility ratio, increasing the water flooding sweep efficiency, and improving the recovery rate. However, the hydrophilic groups -COO- or -CONH2 on the polymer molecular branches have strong adsorption on solid particles, forming a certain network structure and co-adsorbing on the oil-water interface. At the same time, due to the strong hydrophilicity of HPAM, it carries a large amount of bound water, adsorbs solid particles, and forms a gel-like substance in the intermediate mixed emulsion layer, increasing the difficulty of destabilization. And because most of the polymers used for oil production are anionic, some polymers adsorb on the oil-water interface, reducing the collision probability between oil droplets and increasing the emulsification degree of the produced liquid. At the same time, the anionic polymers injected for oil production increase the negative ions carried by the produced liquid, and correspondingly increase the positive ions used for electrical neutralization. All of these make it necessary to greatly increase the dosage of flocculants when using the traditional polyaluminum chloride + polyacrylamide flocculation technology to achieve a high oil removal rate and suspended solid removal rate to meet the requirements of sewage treatment, resulting in high costs. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for treating polymer-containing sewage in oil fields with high oil removal rate and suspended solid removal rate.

[0004] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A method for treating polymer-containing sewage in oil fields includes the following steps: adding polyaluminum chlorophosphate to the polymer-containing sewage in the oil field to be treated and stirring, and then adding micron silica and cationic polyacrylamide and stirring.

[0006] In the method for treating polymer-containing sewage in oil fields of the present invention, after adding polyaluminum chlorophosphate to the polymer-containing sewage, cationic polyacrylamide and micron silica are added. The high specific surface area of micron silica and the charge adsorption coagulation promoting effect generated by the characteristics of having hydrophobic groups enhance the synergistic effect of polyaluminum chlorophosphate and cationic polyacrylamide and the removal effect on polymers in the sewage through the association adsorption method, so as to achieve the purpose of improving the oil removal rate, suspended solid removal rate of polymer-containing sewage in oil fields, reducing the dosage of flocculants, and reducing the flocculant cost.

[0007] The method for treating polymer-containing sewage in oil fields of the present invention does not increase the chemical dosing points and chemical dosing process flow of the original sewage treatment process using polyaluminum chloride + polyacrylamide flocculation technology, does not have an adverse impact on the subsequent process of sewage, and is simple and easy to operate on site.

[0008] When polyaluminum chloride phosphate (PPAC) hydrolyzes, it carries more positive charges. By quickly neutralizing positive and negative charges, it can rapidly destabilize and aggregate emulsified oil and suspended solid particles into flocs. Compared with polyaluminum chloride (PAC), polyaluminum chloride phosphate has the characteristics of strong demulsification ability, high oil removal rate, high suspended solid removal rate, and low treatment cost for oilfield sewage. The polyaluminum chloride phosphate can be an existing commercially available product, or can be made by introducing phosphate during the production process of polyaluminum chloride, followed by mixing and polymerization reaction, and aging.

[0009] Micron-sized silica has a large specific surface area. It not only has strong adsorption, but also has certain lipophilic and hydrophobic properties. Its strong adsorption and lipophilic and hydrophobic properties can enhance the attraction of cationic polyacrylamide to oil droplets in sewage, thereby increasing the oil removal rate, and can disrupt the synergistic effect between suspended solid particles in sewage and anionic polymers in sewage, thereby increasing the suspended solid removal rate; due to the hydrophobic groups on the surface of micron-sized silica, it can form an association with cationic polyacrylamide and polyaluminum chloride phosphate. This association can reduce the hydrophilic property of the flocs, accelerate the sedimentation speed of the flocs, and increase the floc strength, making the formed flocs large, dense, and with low water content. Further, the average particle size of the micron-sized silica is 3 - 7 μm, and the specific surface area is 170 - 240 m 2 / g. For example, the specific surface area of the micron-sized silica is 200 m 2 / g.

[0010] Further, the molar percentage content of AlPO4 in the polyaluminum chloride phosphate is 2 - 6%, for example, 6%.

[0011] Further, the cationicity of the cationic polyacrylamide is 30 - 50%, and the molecular weight is 800 - 20 million. For example, the cationicity of the cationic polyacrylamide is 30%, and the molecular weight is 12 million.

[0012] The higher the content of anionic polymers in the polymer-containing oilfield sewage, the more micron-sized silica is used, and the better the sewage treatment effect. However, if the amount of micron-sized silica used is too high, the sewage treatment effect will become worse. In order to control the ratio of hydrophobic groups to hydrophilic groups appropriately to achieve the best sewage treatment effect and the best flocculant dosing concentration, further, the mass ratio of micron-sized silica to cationic polyacrylamide is 2 - 10:100.

[0013] Further, the mass of polyaluminum chloride phosphate added per 1 L of polymer-containing oilfield sewage to be treated is 105 - 160 mg, and the mass of cationic polyacrylamide in the composite flocculant added is 4.5 - 6 mg.

[0014] Further, before adding the micron silica and cationic polyacrylamide to the polymer-containing oilfield wastewater, the micron silica and cationic polyacrylamide are first dispersed in water to form a mixed dispersion liquid, and then the mixed dispersion liquid is added to the polymer-containing oilfield wastewater. The micron silica and cationic polyacrylamide have good compatibility, and there is no precipitation or caking phenomenon during water dispersion.

[0015] Further, the standing time is 4 - 6 min, for example, 5 min. Specific embodiments

[0016] The technical solutions of the present invention will be further described below in conjunction with specific embodiments.

[0017] In the following examples and comparative examples, the oil content of the polymer-containing oilfield wastewater is 112 mg / L, and the content of solid suspended matter is 74 mg / L. The wastewater treated by the polymer-containing oilfield wastewater treatment method in the examples enters a dissolved air flotation machine for separation of flocs and water; the water enters a filter tank for filtration; the flocs float up to become scum and enter the sludge treatment process.

[0018] Example 1

[0019] The treatment method of the polymer-containing oilfield wastewater in this example includes the following steps:

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

[0021] Add cationic polyacrylamide and micron silica to water in a mass ratio of 100:5 and disperse evenly to prepare a mixed dispersion liquid with a mass fraction of cationic polyacrylamide of 0.1%; the cationic degree of the cationic polyacrylamide used is 30%, and the molecular weight is 12 million; the average particle size of the micron silica used is 5 μm, and the specific surface area is 200 m 2 / g.

[0022] 2) First, add the prepared polyaluminum chlorophosphate solution (the mass of polyaluminum chlorophosphate in the polyaluminum chlorophosphate solution added per 1 L of polymer-containing wastewater is 105 mg) to the polymer-containing oilfield wastewater, and slowly stir evenly with a glass rod for 30 s; then add the prepared mixed dispersion liquid (the mass of cationic polyacrylamide in the mixed dispersion liquid added per 1 L of polymer-containing wastewater is 4.5 mg), and then slowly stir evenly with a glass rod for 30 s, and then stand for 5 minutes.

[0023] Example 2

[0024] The treatment method of the polymer-containing oilfield wastewater in this example includes the following steps:

[0025] 1) Add polyaluminum chloride with phosphorus into water and disperse it evenly to obtain a polyaluminum chloride solution with a mass fraction of polyaluminum chloride of 4%; the molar percentage content of AlPO4 in the polyaluminum chloride used is 2%;

[0026] Add cationic polyacrylamide and micron-sized silica into water in a mass ratio of 100:2 and disperse it evenly to prepare a mixed dispersion with a mass fraction of cationic polyacrylamide of 0.1%; the cationic degree of the cationic polyacrylamide used is 50%, and the molecular weight is 8 million; the average particle size of the micron-sized silica used is 3 μm, and the specific surface area is 240 m 2 / g.

[0027] 2) First, add the prepared polyaluminum chloride solution into the oily sewage containing polymer in oilfield (the mass of polyaluminum chloride in the polyaluminum chloride solution added per 1 L of oily sewage containing polymer is 160 mg), and stir it slowly and evenly with a glass rod for 30 s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide in the mixed dispersion added per 1 L of oily sewage containing polymer is 6.0 mg), stir it slowly and evenly with a glass rod for another 30 s, and then let it stand for 5 minutes.

[0028] Example 3

[0029] The treatment method of oily sewage containing polymer in oilfield in this example includes the following steps:

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

[0031] Add cationic polyacrylamide and micron-sized silica into water in a mass ratio of 100:10 and disperse it evenly to prepare a mixed dispersion with a mass fraction of cationic polyacrylamide of 0.1%; the cationic degree of the cationic polyacrylamide used is 30%, and the molecular weight is 20 million; the average particle size of the micron-sized silica used is 7 μm, and the specific surface area is 170 m 2 / g.

[0032] 2) First, add the prepared polyaluminum chloride solution into the oily sewage containing polymer in oilfield (the mass of polyaluminum chloride in the polyaluminum chloride solution added per 1 L of oily sewage containing polymer is 130 mg), and stir it slowly and evenly with a glass rod for 30 s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide in the mixed dispersion added per 1 L of oily sewage containing polymer is 4.9 mg), stir it slowly and evenly with a glass rod for another 30 s, and then let it stand for 5 minutes.

[0033] Example 4

[0034] The treatment method of polymer-containing oily sewage in this embodiment includes the following steps:

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

[0036] Add cationic polyacrylamide and micron-sized silica to water in a mass ratio of 100:10 and disperse evenly to prepare a mixed dispersion with a mass fraction of cationic polyacrylamide of 0.1%; the cationicity of the cationic polyacrylamide used is 30%, and the molecular weight is 12 million; the average particle size of the micron-sized silica used is 5 μm, and the specific surface area is 200 m 2 / g.

[0037] 2) First, add the prepared polyaluminum chlorophosphate solution to the polymer-containing oily sewage (the mass of polyaluminum chlorophosphate in the polyaluminum chlorophosphate solution added per 1 L of polymer-containing sewage is 160 mg), and stir slowly and evenly with a glass rod for 30 s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide in the mixed dispersion added per 1 L of polymer-containing sewage is 6 mg), stir slowly and evenly with a glass rod for another 30 s, and then let it stand for 5 minutes.

[0038] Example 5

[0039] The treatment method of polymer-containing oily sewage in this embodiment includes the following steps:

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

[0041] Add cationic polyacrylamide and micron-sized silica to water in a mass ratio of 100:2 and disperse evenly to prepare a mixed dispersion with a mass fraction of cationic polyacrylamide of 0.1%; the cationicity of the cationic polyacrylamide used is 30%, and the molecular weight is 12 million; the average particle size of the micron-sized silica used is 5 μm, and the specific surface area is 200 m 2 / g.

[0042] 2) First, add the prepared polyaluminum chlorophosphate solution to the polymer-containing oily sewage (the mass of polyaluminum chlorophosphate in the polyaluminum chlorophosphate solution added per 1 L of polymer-containing sewage is 160 mg), and stir slowly and evenly with a glass rod for 30 s; then add the prepared mixed dispersion (the mass of cationic polyacrylamide in the mixed dispersion added per 1 L of polymer-containing sewage is 6 mg), stir slowly and evenly with a glass rod for another 30 s, and then let it stand for 5 minutes.

[0043] Comparative Example 1

[0044] The treatment method for polymer-containing oily sewage in this comparative example includes the following steps:

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

[0046] Add cationic polyacrylamide into water and disperse it evenly to prepare a solution with a mass fraction of cationic polyacrylamide of 0.1%; the cationicity of the cationic polyacrylamide used is 30, and the molecular weight is 12 million.

[0047] 2) First, add the prepared polyaluminum chloride solution into the polymer-containing oily sewage (the mass of polyaluminum chloride in the polyaluminum chloride solution added per 1 L of polymer-containing oily sewage is 105 mg), and slowly stir it evenly with a glass rod for 30 s; then add the prepared cationic polyacrylamide solution (the mass of cationic polyacrylamide added per 1 L of polymer-containing oily sewage is 4.5 mg), then slowly stir it evenly with a glass rod for 30 s, and then let it stand for 5 minutes.

[0048] Comparative Example 2

[0049] The treatment method for polymer-containing oily sewage in this comparative example is only different from the treatment method of Comparative Example 1 in that in step 2) of this comparative example:

[0050] First, add the prepared polyaluminum chloride solution into the polymer-containing oily sewage (the mass of polyaluminum chloride in the polyaluminum chloride solution added per 1 L of polymer-containing oily sewage is 160 mg), and slowly stir it evenly with a glass rod for 30 s; then add the prepared cationic polyacrylamide solution (the mass of cationic polyacrylamide added per 1 L of polymer-containing oily sewage is 6.0 mg), then slowly stir it evenly with a glass rod for 30 s, and then let it stand for 5 minutes.

[0051] Comparative Example 3

[0052] The treatment method for polymer-containing oily sewage in this comparative example is only different from the treatment method of Comparative Example 1 in that in step 2) of this comparative example:

[0053] First, add the prepared polyaluminum chloride solution into the polymer-containing oily sewage (the mass of polyaluminum chloride in the polyaluminum chloride solution added per 1 L of polymer-containing oily sewage is 130 mg), and slowly stir it evenly with a glass rod for 30 s; then add the prepared cationic polyacrylamide solution (the mass of cationic polyacrylamide added per 1 L of polymer-containing oily sewage is 4.9 mg), then slowly stir it evenly with a glass rod for 30 s, and then let it stand for 5 minutes.

[0054] Comparative Example 4

[0055] For the treatment method of oily polymer-containing sewage in this comparative example, the polyaluminum phosphochloride solution added in step 2) of the treatment method in Example 1 was replaced with a polyaluminum chloride solution. The mass concentration of the polyaluminum chloride solution was 4%; the mass of polyaluminum chloride in the polyaluminum chloride solution added per 1 L of polymer-containing sewage was 105 mg; the content not described was exactly the same as that in Example 1.

[0056] Comparative Example 5

[0057] For the treatment method of oily polymer-containing sewage in this comparative example, the micron-sized silica in the mixed dispersion added in step 2) of the treatment method in Example 1 was omitted; the content not described was exactly the same as that in Example 1.

[0058] Comparative Example 6

[0059] The treatment method of oily polymer-containing sewage in this comparative example is only different from the treatment method in Example 1 in that:

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

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

[0062] 2) First, the prepared mixed dispersion (the mass of polyaluminum phosphochloride added per 1 L of polymer-containing sewage was 105 mg) was added to the oily polymer-containing sewage, and stirred slowly and evenly with a glass rod for 30 s; then, the prepared mixed dispersion (the mass of cationic polyacrylamide added per 1 L of polymer-containing sewage was 4.5 mg) was added, and then stirred slowly and evenly with a glass rod for 30 s, and then left to stand for 5 minutes.

[0063] Comparative Example 7

[0064] The treatment method of oily polymer-containing sewage in this comparative example includes the following steps:

[0065] 1) Polyaluminum phosphochloride was added to water and dispersed evenly to obtain a polyaluminum phosphochloride solution with a mass fraction of polyaluminum phosphochloride of 4%; the molar percentage content of AlPO4 in the polyaluminum phosphochloride used was 6%;

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

[0067] 2) First, the prepared polyaluminum chlorophosphate solution was added to the oily polymer-containing produced water in oilfields (the mass of polyaluminum chlorophosphate added corresponding to each 1 L of oily polymer-containing produced water was 105 mg), and it was slowly and evenly stirred with a glass rod for 30 s. Then, the prepared cationic polyacrylamide solution was added (the mass of cationic polyacrylamide added corresponding to each 1 L of oily polymer-containing produced water was 4.5 mg), and it was slowly and evenly stirred with a glass rod for another 30 s. Then, micron-sized silica was added (the mass of micron-sized silica added corresponding to each 1 L of oily polymer-containing produced water was 0.225 mg), and it was slowly and evenly stirred with a glass rod for another 30 s. Then, it was left standing for 5 minutes. The average particle size of the micron-sized silica used was 5 μm, and the specific surface area was 200 m 2 / g.

[0068] Experimental example

[0069] 50 mL syringes were used to suck the middle water samples after treatment in each example and comparative example respectively, and their oil content, suspended solid content and polyacrylamide content were measured. The oil removal rate, suspended solid removal rate and polyacrylamide removal rate of the sewage were calculated. The results are shown in Table 1. The oil content in the sewage was measured by the spectrophotometer method, the suspended solid content was measured by the gravimetric method, and the polyacrylamide content was determined by the starch-cadmium iodide spectrophotometry method; the ultraviolet spectrophotometer used in the experiment was TU-1901 produced by Purkinje General Instrument Co., Ltd. in Beijing. The floating scum on the treated water sample was taken, and the moisture content of the floating scum was measured by the distillation method. The results are also shown in Table 1.

[0070] Table 1 Experimental results of sewage treatment in examples and comparative examples

[0071]

[0072] As can be seen from Table 1, the method for treating oily polymer-containing produced water in oilfields of the present invention has a higher oil removal rate and suspended solid removal rate compared with the treatment method of the comparative example, and the chemical agent cost is lower, with significant economy.

[0073] The method for treating oily polymer-containing produced water in oilfields of the present invention has good effects of removing oil and suspended solids from sewage. The oil removal rate and suspended solid removal rate of the sewage are greatly improved, and it has the advantages of less dosage, low cost and outstanding sewage treatment effect.

Claims

1. A treatment method for polymer-containing oily sewage in oil fields, characterized in that: It includes the following steps: Add polyaluminum phosphochloride to the oily wastewater containing polymer in the oilfield to be treated and stir, and then add micron-sized silica and cationic polyacrylamide and stir.

2. The treatment method of polymer-containing oily sewage according to claim 1, wherein: The average particle size of the micron silica is 3 to 7 μm, and the specific surface area is 170 to 240 m 2 / g.

3. The treatment method of polymer-containing oily sewage according to claim 1, characterized in that: The molar percentage content of AlPO4 in the polyaluminum phosphochloride is 2-6%.

4. The treatment method of polymer-containing oily sewage according to claim 1, wherein: The cationic degree of the cationic polyacrylamide is 30-50%, and the molecular weight is 8 million - 20 million.

5. The treatment method for polymer-containing oily sewage in an oilfield according to claim 1, characterized in that: The mass ratio of micron-sized silica to cationic polyacrylamide is 2-10:

100.

6. The method for treating oily polymer-containing sewage according to any one of claims 1 to 5, characterized in that: For every 1 L of the oily wastewater containing polymer in the oilfield to be treated, the mass of polyaluminum phosphochloride added is 105-160 mg, and the mass of cationic polyacrylamide in the composite flocculant added is 4.5-6 mg.

7. The treatment method for oily polymer-containing sewage in oil fields according to any one of claims 1 to 5, characterized in that: Before adding the micron-sized silica and cationic polyacrylamide to the oily wastewater containing polymer in the oilfield, first disperse the micron-sized silica and cationic polyacrylamide in water to make a mixed dispersion liquid, and then add the mixed dispersion liquid to the oily wastewater containing polymer in the oilfield.

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