Method for co-processing fracturing waste liquid and petroleum produced water

Abstract

The invention relates to a method for co-processing fracturing waste liquid and petroleum produced water, and relates to the technical field of water treatment. The method comprises the following steps: carrying out hardness removal treatment on the fracturing waste liquid, wherein the calcium ion concentration of the treated fracturing waste liquid is 28.5-165 mg / L, and the pH value is 9.0-11.0; and uniformly mixing the fracturing waste liquid subjected to hardness removal with petroleum produced water according to a volume ratio of (1-9): (9-1), sequentially adding an inorganic flocculant and an organic flocculant, and filtering after flocculating settling to obtain reinjection water. The inorganic flocculant is at least one of polyaluminum chloride and polyferric sulfate; the organic flocculating agent is at least one of cationic polyacrylamide and poly dimethyl diallyl ammonium chloride. According to the method, the fracturing waste liquid and the petroleum produced water are used for cooperative treatment, the treatment cost is reduced, the suspended matter content and the oil content in the treated water are lower than 5.0 mg / L and 3.0 mg / L respectively, and the scaling amount is lower than 20 mg / L.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a method for the co-treatment of fracturing waste fluid and oil produced water. Background Technology

[0002] Currently, most oilfields in my country employ water injection for oil extraction, imposing strict requirements on the quality of the reinjected water, especially its scaling characteristics. Taking the Shaanxi North Oilfield as an example, this region's oilfields are low-permeability and ultra-low-permeability oilfields with small reservoir throats, making reservoir protection during water injection particularly crucial. Furthermore, the region is relatively water-scarce, and oil development requires large quantities of high-quality injection water. Treating operational waste fluids, such as fracturing waste fluids, and using them as supplementary water sources for oilfield reinjection is of great significance for improving water resource utilization and mitigating the environmental impact of operational waste fluid discharge.

[0003] Fracturing wastewater is complex in composition and characterized by high COD, high viscosity, high emulsification, high turbidity, high salt content, and poor biodegradability. In particular, it contains some hydrophilic polymers that are difficult to purify and remove from the wastewater, making COD reduction challenging. Common technologies for treating fracturing wastewater include: Fenton oxidation-flocculation, coagulation-oxidation-adsorption-photocatalytic oxidation, flocculation-oxidation, micro-electrolysis-Fenton combined process, and pre-oxidation-coagulation-catalytic oxidation-adsorption process. These methods are effective in reducing the viscosity of fracturing wastewater and improving the quality of flocculated water. However, when the water treated by these methods is reinjected into the reservoir, it often damages the reservoir due to poor compatibility with formation water (mainly manifested in high scaling levels in the mixed water, exceeding 200 mg / L). Therefore, it needs to be dehardened to achieve good compatibility with formation water. At the same time, the concentration of calcium ions in the dehardened fracturing wastewater can be reduced to below 50 mg / L and it has a high pH value (9.0-11.0), which has a positive effect on moderately increasing the pH of oilfield produced water (pH is usually 6.0-6.5) and subsequent flocculation treatment.

[0004] Produced water is a multiphase dispersed system consisting of suspended solids, oil, and dissolved substances (such as dissolved salts and dissolved organic matter) formed during the extraction process of crude oil from oil wells and after oil-water separation at a combined treatment station. It is highly corrosive and prone to scaling, and untreated reinjection can damage the reservoir. Reinjection treatment processes mainly include air flotation and flocculation sedimentation, and membrane treatment technology has been increasingly used in the production water reinjection process in recent years. Due to the high salinity of produced water (e.g., the salinity of produced water from the Chang 2 and Chang 4+5 formations in northern Shaanxi reaches over 27,000 mg / L, and the salinity of produced water from the Chang 6 formation reaches around 70,000 mg / L) and relatively low pH (6.0~6.5), the flocculation treatment process often requires pH adjustment, and scale and corrosion inhibitors are added to the effluent to ensure the stability of the reinjected water quality.

[0005] By co-treating oilfield produced water and fracturing wastewater to obtain a type of oilfield reinjection water that is less prone to scaling and has high stability, not only can the technical challenges of wastewater reuse be solved, but water resource utilization can also be effectively improved. Summary of the Invention

[0006] In order to solve one or more of the above-mentioned technical problems, the present invention provides a method for the co-treatment of fracturing waste fluid and oil produced water.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: This invention provides a method for the co-treatment of fracturing waste fluid and oil produced water, comprising the following steps: S1. Add a hardness-removing agent to the fracturing waste liquid to remove hardness. The hardness-removing agent is a composite agent comprising NaCO3 and NaOH, wherein the mass ratio of NaCO3 to NaOH in the composite agent is 3:1~2. After the hardness removal treatment, the calcium ion concentration in the fracturing waste liquid is 28.5~165 mg / L, and the pH is 9.0~11.0. S2. Mix the fracturing waste fluid after hardening removal in step S1 with oil produced water at a volume ratio of 1~9:9~1 for a preset time, then add inorganic flocculant and organic flocculant, and obtain reinjection water after flocculation, sedimentation and filtration.

[0008] The beneficial effects of this invention are: by using fracturing waste liquid and oil produced water for synergistic treatment, this invention not only reduces the calcium ion content of the produced water, but also avoids the addition of pH reagents, thus reducing treatment costs.

[0009] Based on the above technical solution, the present invention can be further improved as follows.

[0010] Furthermore, in S1, the mineralization of the fracturing waste liquid before hardness removal treatment is 80,000~90,000 mg / L, and the calcium ion concentration is 6,500~7,000 mg / L.

[0011] Furthermore, in S2, the mineralization of the oil produced water is 20,000~90,000 mg / L, the calcium ion concentration is 800~1300 mg / L, and the pH value is 6.3~6.5.

[0012] Furthermore, the preset time is 0.5~1h.

[0013] Furthermore, the inorganic flocculant is at least one of polyaluminum chloride and polyferric sulfate.

[0014] Furthermore, the organic flocculant is at least one of cationic polyacrylamide and polydimethyldiallyl ammonium chloride.

[0015] Furthermore, the cationic polyacrylamide has a molecular weight of 8 million to 12 million and a cationicity of 15% to 30%.

[0016] Furthermore, the molecular weight of the polydimethyldiallylammonium chloride is 50,000 to 200,000.

[0017] Furthermore, the amount of inorganic flocculant added is 50~150mg / L, the amount of organic flocculant added is 2.0~5.0mg / L, the interval between the addition of inorganic flocculant and organic flocculant is 20~40 seconds, and the flocculation and sedimentation time is 20~40min.

[0018] Furthermore, the suspended solids content in the reinjected water is less than 5.0 mg / L, the oil content in the reinjected water is less than 3.0 mg / L, and the scaling content in the reinjected water is less than 20 mg / L.

[0019] The treatment method of this invention is simple, and the content of suspended solids and oil in the reinjection water after treatment is less than 5.0 and 3.0 mg / L, respectively, and the amount of scale is less than 20 mg / L. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the preferred embodiments of this invention will be described in further detail below with reference to the examples. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0021] Example 1 S1. The fracturing waste liquid with a mineralization of 81000 mg / L and a calcium ion concentration of 6500 mg / L was treated with a NaCO3-NaOH composite agent to remove hardness. The mass ratio of NaCO3 to NaOH added was 3:1. After treatment, the calcium ion concentration of the fracturing waste liquid was 160.5 mg / L and the pH was 10.5. S2. The fracturing waste fluid (after hardening removal in step S1) and the produced water (mineralization 27933.4 mg / L, calcium ion concentration 876 mg / L, pH 6.5) from the oil-water mixture extracted from the Chang 2 oil well (after oil-water separation) were mixed at a volume ratio of 1:9 and allowed to stand for 0.5 h. Then, polyaluminum chloride (150 mg / L) was added, followed by cationic polyacrylamide (average molecular weight 12 million, cationicity 15%, 2.0 mg / L). The addition interval between polyaluminum chloride and cationic polyacrylamide was 30 seconds. After flocculation and sedimentation for 30 min, the water was filtered to obtain reinjection water. The suspended solids content and oil content in the treated water were 4.7 mg / L and 2.9 mg / L, respectively, and the scale content was 19 mg / L.

[0022] Examples 2-5 Following the method of Example 1, the volume ratio of the de-hardened fracturing wastewater to the produced water, the amount of polyaluminum chloride added, and the amount of cationic polyacrylamide added were adjusted to obtain reinjection water. The suspended solids content, oil content, and scaling amount of the reinjection water prepared in Examples 1 to 5 were tested, as shown in Table 1.

[0023] Table 1. Relevant parameters and water quality analysis results of Examples 1-5. (Note: The reinjected water is water filtered through 0.3mm quartz sand, and the same applies below.) As shown in Table 1, when fracturing flowback fluid after hardening treatment is mixed with produced water with a salinity of 27933.4 mg / L and a calcium ion concentration of 876 mg / L in different proportions and then subjected to flocculation treatment, the suspended solids content, oil content, and scaling content in the treated water are lower than 5.0, 3.0, and 20 mg / L, respectively, which fully meets the water quality standards for oilfield reinjection water ("Requirements and Analysis Methods for Water Quality Injection in Clastic Rock Reservoirs", SY / T5329-2022).

[0024] Example 6 S1. The fracturing waste liquid with a mineralization of 86000 mg / L and a calcium ion concentration of 6750 mg / L was treated with a combination of NaCO3-NaOH composite agent to remove hardness. The mass ratio of NaCO3 to NaOH added was 3:2. After treatment, the calcium ion concentration of the fracturing waste liquid was 106 mg / L and the pH was 9.5. S2. The fracturing waste fluid (after hardening removal in step S1) and the oil-water mixture produced from well 4+5 (mineralization 37287.6 mg / L, calcium ion concentration 3098.1 mg / L, pH 6.3) obtained after oil-water separation were mixed at a volume ratio of 1:9 and allowed to stand for 1 hour. Then, polyaluminum chloride (150 mg / L) and cationic polyacrylamide (average molecular weight 800, cationicity 20%, 3.0 mg / L) were added. After flocculation and sedimentation for 30 minutes, the mixture was filtered to obtain reinjection water. The suspended solids content and oil content in the treated water were 3.7 mg / L and 1.9 mg / L, respectively, and the scale content was 21 mg / L.

[0025] Examples 7-10 Referring to the method in Example 6, the volume ratio of the de-hardened fracturing waste fluid to the produced water, the amount of polyaluminum chloride added, and the amount of cationic polyacrylamide added were adjusted to obtain reinjection water. The suspended solids content, oil content, and scaling amount of the reinjection water prepared in Examples 6 to 10 were tested, as shown in Table 2.

[0026] Table 2. Relevant parameters and water quality analysis results of Examples 6-10. As shown in Table 2, when fracturing flowback fluid after hardening treatment is mixed with produced water with a salinity of 37287.6 mg / L, a calcium ion concentration of 3098.1 mg / L, and a pH of 6.3 in different proportions and then subjected to flocculation treatment, the suspended solids content, oil content, and scaling content in the treated water are lower than 4.0, 2.0, and 25 mg / L, respectively, which fully meets the water quality standards for oilfield reinjection water ("Requirements and Analysis Methods for Water Quality Injection in Clastic Rock Reservoirs", SY / T5329-2022).

[0027] Example 11 S1. The fracturing waste liquid with a mineralization of 89000 mg / L and a calcium ion concentration of 6800 mg / L was treated with a combination of NaCO3-NaOH composite agents to remove hardness. The mass ratio of NaCO3 to NaOH was 3:1.5. After treatment, the calcium ion concentration of the fracturing waste liquid was 30.5 mg / L and the pH was 11.0. S2. The fracturing waste fluid (after hardening removal in step S1) and the oil-water mixture produced from the Chang 6 oil well, after oil-water separation, are mixed at a volume ratio of 1:9 and allowed to stand for 1 hour. Then, polyaluminum chloride (150 mg / L) and polydimethyldiallylammonium chloride (3.0 mg / L, average molecular weight 200,000) are added. After flocculation and sedimentation for 30 minutes, the mixture is filtered to obtain reinjection water. The suspended solids content and oil content in the treated water are 4.5 mg / L and 3.9 mg / L, respectively, and the scale content is 23 mg / L.

[0028] Examples 12-15 Referring to the method of Example 11, the volume ratio of the de-hardened fracturing waste fluid to the oil produced water, the amount of polyaluminum chloride added, and the amount of polydimethyldiallylammonium chloride added were adjusted to obtain reinjection water. The suspended solids content, oil content, and scaling amount of the reinjection water prepared in Examples 11-15 were tested, as shown in Table 3.

[0029] Table 3. Relevant parameters and water quality analysis results of Examples 11-15. As shown in Table 3, when fracturing flowback fluid after hardening treatment is mixed with produced water with a salinity of 80252.6 mg / L, a calcium ion concentration of 12268.4 mg / L, and a pH of 6.3 in different proportions and then subjected to flocculation treatment, the suspended solids content, oil content, and scaling content in the treated water are lower than 5.0, 4.0, and 25 mg / L, respectively, which fully meets the water quality standards for oilfield reinjection water ("Requirements and Analysis Methods for Water Quality Injection Indicators in Clastic Rock Reservoirs", SY / T5329-2022).

[0030] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0031] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0032] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for the co-treatment of fracturing waste fluid and produced water, characterized in that, Includes the following steps: S1. Add a hardness-removing agent to the fracturing waste liquid to remove hardness. The hardness-removing agent is a composite agent comprising NaCO3 and NaOH, wherein the mass ratio of NaCO3 to NaOH in the composite agent is 3:1~2. After the hardness removal treatment, the calcium ion concentration in the fracturing waste liquid is 28.5~165 mg / L, and the pH is 9.0~11.

0. S2. Mix the fracturing waste fluid after hardening removal in step S1 with oil produced water at a volume ratio of 1~9:9~1 for a preset time, then add inorganic flocculant and organic flocculant, and obtain reinjection water after flocculation, sedimentation and filtration.

2. The method for co-treating fracturing waste fluid and produced water according to claim 1, characterized in that, In S1, the mineralization of the fracturing waste liquid before hardness removal treatment is 80,000~90,000 mg / L, and the calcium ion concentration is 6,500~7,000 mg / L.

3. The method for co-treatment of fracturing waste fluid and produced water according to claim 1, characterized in that, In S2, the mineralization of the produced water is 20,000~90,000 mg / L, the calcium ion concentration is 800~1300 mg / L, and the pH value is 6.3~6.

5.

4. The method for co-treating fracturing waste fluid and produced water according to claim 1, characterized in that, The preset time is 0.5~1h.

5. The method for co-treatment of fracturing waste fluid and produced water according to claim 1, characterized in that, The inorganic flocculant is at least one of polyaluminum chloride and polyferric sulfate.

6. The method for co-treatment of fracturing waste fluid and produced water according to claim 1, characterized in that, The organic flocculant is at least one of cationic polyacrylamide and polydimethyldiallyl ammonium chloride.

7. The method for co-treatment of fracturing waste fluid and produced water according to claim 6, characterized in that, The cationic polyacrylamide has a molecular weight of 8 million to 12 million and a cationicity of 15% to 30%.

8. The method for co-treating fracturing waste fluid and produced water according to claim 6, characterized in that, The molecular weight of the polydimethyldiallyl ammonium chloride is 50,000 to 200,000.

9. The method for co-treatment of fracturing waste fluid and produced water according to claim 1, characterized in that, The inorganic flocculant is added at a rate of 50-150 mg / L, the organic flocculant is added at a rate of 2.0-5.0 mg / L, the interval between the addition of the inorganic and organic flocculants is 20-40 seconds, and the flocculation and sedimentation time is 20-40 minutes.

10. The method for co-treatment of fracturing waste fluid and produced water according to claim 1, characterized in that, The suspended solids content in the reinjection water is less than 5.0 mg / L, the oil content in the reinjection water is less than 3.0 mg / L, and the scale content in the reinjection water is less than 20 mg / L.

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