Weakly alkaline simulated oil extraction sewage as well as preparation and use methods thereof

Abstract

The invention discloses weakly-alkaline simulated oil extraction sewage as well as a preparation method and a use method thereof. The preparation method of the weakly-alkaline simulated oil extraction sewage comprises the following steps: determining the dosage of deionized water and the types and dosage of alkali and inorganic salt according to the pH value and mineralization degree of field oil extraction sewage; after all the inorganic salts are completely dissolved in the deionized water, adding the alkali, and after the alkali is completely dissolved, obtaining the weakly alkaline simulated oil extraction sewage; due to the feeding sequence, the precipitation reaction of HCO3 <-> and CO3 < 2-> with Ca < 2 + > and Mg < 2 + > can be effectively avoided, meanwhile, the alkalescence, the mineralization degree and the clarity of the simulated oil extraction sewage are ensured, and the mineralization degree component of the simulated oil extraction sewage is kept stable in the preparation and use process, so that the simulated oil extraction sewage is closer to the mineralization degree and the pH value of sewage in an oil field; the indoor performance evaluation experiment of the polymer is further ensured, and the performance of the polymer can be accurately evaluated.

Description

Technical Field

[0001] This disclosure relates to the field of tertiary oil recovery technology in oilfield development, specifically to a simulated oilfield wastewater and its preparation method. Background Technology

[0002] Currently, polymer flooding field tests at Daqing Oilfield utilize produced oil wastewater to prepare polymer solutions. Correspondingly, the indoor evaluation of polymer performance also needs to be conducted under produced oil wastewater conditions. Given that the quality of produced oil wastewater varies significantly with sampling time, sampling location, and storage time, to objectively evaluate the performance of polymer solutions under specific wastewater conditions, and considering the weakly alkaline nature of Daqing's produced oil wastewater, it is necessary to prepare a weakly alkaline simulated produced oil wastewater solution.

[0003] Regarding the preparation of simulated oilfield wastewater, one approach is to disregard the weak alkalinity of the wastewater during preparation. For example, the People's Republic of China Petroleum and Natural Gas Industry Standard SY / T 5862-2020 provides standard saline solution I, standard saline solution II, and standard saline solution III. Standard saline solution I is a 0.095% NaCl solution; standard saline solution II is a 0.241% NaCl solution; and standard saline solution III contains three inorganic salts: NaCl, CaCl2, and MgCl2·6H2O, with a total mineralization of 1.93%. 2+ Mg 2+ The concentration of divalent cations is 0.051%. In their article on the effects of oilfield wastewater on the properties of HPAM-organochromium gel (Hydrolyzed Poly-acrylamide, HPAM, partially hydrolyzed polyacrylamide), Wei Yajun et al. provided an indoor preparation method for K... + and Na + The mass concentrations were 10000 mg / L and Ca, respectively. 2+ and Mg 2+ The simulated wastewater had a mass concentration of 2000 mg / L. In their article exploring the influencing factors and mechanisms of viscosity in polymer solutions prepared from wastewater, Wang Zhen et al. provided a formula for simulated wastewater based on test reports. This formula dissolved 6.0104 g NaCl, 0.040 g KCl, 0.173 g CaCl2, 0.037 g Na2SO4, and 0.130 g MgCl2·6H2O in 1000 mL of pure water to form the simulated wastewater. None of the components of the simulated wastewater contained weakly alkaline substances, and the composition and pH value of the simulated wastewater differed from the actual oilfield wastewater.

[0004] Another scenario involves adding an alkaline component to simulate the weak alkalinity of produced oil wastewater. However, this addition causes the following problems: 1. When using a general preparation method, the required amounts of inorganic salts such as sodium chloride, potassium chloride, magnesium chloride hexahydrate, and calcium chloride, as well as sodium bicarbonate and deionized water, are calculated based on the mineralization composition of the produced oil wastewater. Then, following conventional techniques in the field, the inorganic salts and sodium bicarbonate are added to the deionized water and stirred for 10-20 minutes. 1. Precipitation occurs during the preparation process, resulting in turbid water. 2. When using the pre-alkali preparation method, sodium bicarbonate is first added to deionized water and stirred for 10-20 minutes to dissolve it. Then, sodium chloride, potassium chloride, magnesium chloride hexahydrate, and calcium chloride are added sequentially and stirred for 10-20 minutes to dissolve each. The resulting simulated oilfield wastewater remains turbid. 3. The weakly alkaline simulated oilfield wastewater prepared according to the above general preparation method and the pre-alkali preparation method gradually shows an increase in precipitation as the usage and storage time increases.

[0005] Obviously, the simulated oilfield wastewater prepared by the above general preparation method and the method of adding alkali first will have a lower pH value and mineralization than the actual oilfield wastewater because precipitation will occur during the preparation and use process. As a result, the simulated oilfield wastewater cannot be used to evaluate the performance of polymers and cannot obtain accurate evaluation results. Summary of the Invention

[0006] In view of this, this disclosure provides a weakly alkaline simulated oilfield wastewater and its preparation and use method, which solves the problem that precipitation occurs during the preparation and use of general and pre-addition alkali methods, resulting in the prepared weakly alkaline simulated oilfield wastewater not matching the actual wastewater in the field.

[0007] Firstly, the method for preparing weakly alkaline simulated oilfield wastewater as described in this disclosure includes:

[0008] The dosage of deionized water, as well as the types and amounts of alkali and inorganic salts, are determined based on the pH value and mineralization of the wastewater from the oilfield.

[0009] After all the inorganic salts are completely dissolved in the deionized water, the alkali is added. Once the alkali has completely dissolved, the weakly alkaline simulated oilfield wastewater is obtained.

[0010] In this disclosure and possible embodiments, the method for completely dissolving all inorganic salts in the deionized water includes:

[0011] The inorganic salts are added in one or several batches. When adding in several batches, the next batch is added only after the previous batch has completely dissolved, until all the inorganic salts are completely dissolved in the deionized water.

[0012] In this disclosure and possible embodiments, the base is sodium bicarbonate.

[0013] In this disclosure and possible embodiments, the inorganic salts include sodium chloride, potassium chloride, magnesium chloride hexahydrate, and calcium chloride.

[0014] In this disclosure and possible embodiments, the addition and dissolution of the inorganic salt and the alkali are carried out under stirring.

[0015] In this disclosure and possible embodiments, the stirring rate is 400 to 600 revolutions per minute.

[0016] In this disclosure and possible embodiments, the stirring time for completely dissolving the inorganic salt or the alkali in the deionized water is 10 to 20 minutes.

[0017] Secondly, the weakly alkaline simulated oilfield wastewater is prepared using the preparation method described in the first aspect.

[0018] In this disclosure and possible embodiments, the pH value of the wastewater is 7.1 to 9.0.

[0019] Thirdly, the method of using the weakly alkaline simulated oilfield wastewater includes:

[0020] Use within the shelf life, which is 6 hours.

[0021] This disclosure has the following beneficial effects:

[0022] The disclosed method for preparing weakly alkaline simulated oilfield wastewater avoids the presence of HCO3 by changing the order of alkali addition—specifically, by adding alkali only after all inorganic salts have been completely dissolved in deionized water. - CO3 2- Same as Ca 2+ Mg 2+ The reaction produces a large amount of precipitate, which can ensure the weak alkalinity and clarity of the simulated wastewater, and also closely resemble the salinity of actual formation oilfield wastewater. This ensures that the salinity composition of the simulated oilfield wastewater remains stable during preparation and use, further guaranteeing accurate assessment of polymer performance in indoor performance evaluation experiments. Detailed Implementation

[0023] The present disclosure is described below based on embodiments; however, it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, certain specific details are described in detail. However, those skilled in the art will fully understand the present disclosure for the parts not described in detail.

[0024] The following embodiments of this disclosure are based on simulations of actual formation produced water in Table 1:

[0025] Table 1. Actual Formation Oil Production Wastewater Quality

[0026]

[0027] Based on the ion content, mineralization, and pH value of the produced wastewater in Table 1, it can be determined that the ion content and pH value of the produced wastewater from various oilfields are not significantly different. Therefore, the ion content, mineralization, and pH value of the produced wastewater from each oilfield are averaged to simulate the produced wastewater from various oilfields in Daqing Oilfield. To this end, in accordance with the known technology in this field, the following embodiments simulate weakly alkaline produced wastewater with a mineralization of 3086 ppm and a pH value of 8.5. Based on a simulated wastewater volume of 8L, the inorganic salt and alkali components are determined to be: sodium chloride 10.928g, potassium chloride 0.72g, magnesium chloride hexahydrate 0.336g, calcium chloride 0.441g, sodium bicarbonate powder 12.12g, and deionized water 7975.455g.

[0028] Example 1

[0029] According to the method of this invention, a weakly alkaline simulated oilfield wastewater with a mineralization of 3086 ppm and a pH of 8.5 is prepared. The specific preparation process is as follows:

[0030] (1) Under the stirring state of 400-600 rpm, add 10.928 g of sodium chloride to 7975.455 g of deionized water and stir for 10-20 minutes. Continue to add and stir 0.72 g of potassium chloride, 0.336 g of magnesium chloride hexahydrate and 0.441 g of calcium chloride in the same way.

[0031] (2) After all the inorganic salts have been added and stirred, 12.12g of sodium bicarbonate is added and stirred at the same stirring rate and stirring time to obtain the weakly alkaline simulated oilfield wastewater of Example 1.

[0032] Comparative Example 1

[0033] Following a general preparation method, a weakly alkaline simulated oilfield wastewater with a mineralization of 3086 ppm and a pH of 8.5 was prepared. The specific preparation process is as follows:

[0034] Under stirring conditions of 400–600 rpm, 10.928 g of sodium chloride, 0.72 g of potassium chloride, 0.336 g of magnesium chloride hexahydrate, 0.441 g of calcium chloride, and 12.12 g of sodium bicarbonate were added to 7975.455 g of deionized water, and stirring was continued for 10–20 minutes to obtain the weakly alkaline simulated oilfield wastewater of Comparative Example 1.

[0035] The weakly alkaline simulated oilfield wastewater in Comparative Example 1 was quite turbid, and a large amount of sediment remained at the bottom of the bottle after standing.

[0036] Comparative Example 2

[0037] The order of adding materials in the preparation process of Example 1 was changed to prepare a weakly alkaline simulated oilfield wastewater with a mineralization of 3086 ppm and a pH of 8.5. The specific preparation process is as follows:

[0038] Under stirring conditions of 400–600 rpm, 12.12 g of sodium bicarbonate was added to 7975.455 g of deionized water. After stirring for 10–20 minutes, the same process was repeated to add and stir 10.928 g of sodium chloride, 0.72 g of potassium chloride, 0.336 g of magnesium chloride hexahydrate, and 0.441 g of calcium chloride to obtain the weakly alkaline simulated oilfield wastewater of Comparative Example 2.

[0039] Compared with Example 1, the feeding sequence of Comparative Example 2 is to dissolve sodium bicarbonate first, and then dissolve inorganic salt. Since sodium bicarbonate has a relatively large mass, it is dissolved first. The simulated water is already weakly alkaline. Then, inorganic salt powder is added and dissolved. During the dissolution of powder, the excessive content of calcium and magnesium ions makes it easy for calcium and magnesium ions to react with sodium bicarbonate to form precipitates. Therefore, the resulting solution is relatively turbid, and a large amount of precipitate remains at the bottom of the bottle after standing.

[0040] Example 2

[0041] According to the method of this invention, a weakly alkaline simulated oilfield wastewater with a mineralization of 3086 ppm and a pH of 8.5 is prepared. The specific preparation process is as follows:

[0042] Under stirring conditions of 400–600 rpm, 10.928 g of sodium chloride and 0.72 g of potassium chloride were added to 7975.455 g of deionized water. After stirring for 10–20 minutes, 0.336 g of magnesium chloride hexahydrate and 0.441 g of calcium chloride were added. After stirring for another 10–20 minutes, 12.12 g of sodium bicarbonate was added and stirred at the same stirring rate and time to obtain the weakly alkaline simulated oilfield wastewater of Example 2.

[0043] Compared with Example 1, Example 2 shortened the preparation time, and the resulting weakly alkaline simulated oilfield wastewater remained clear even after standing for 6 hours. This is obviously because the anions of the inorganic salts are all the same, and no precipitation reaction occurs.

[0044] Example 3

[0045] According to the method of this invention, a weakly alkaline simulated oilfield wastewater with a mineralization of 3086 ppm and a pH of 8.5 is prepared. The specific preparation process is as follows:

[0046] Under stirring conditions of 400-600 rpm, calcium chloride, magnesium chloride hexahydrate, sodium chloride, and potassium chloride were all added to deionized water. After stirring for 10-20 minutes, sodium bicarbonate was added and stirred at the same stirring rate and time to obtain the weakly alkaline simulated oilfield wastewater of Example 3.

[0047] Compared with Examples 2 and 3, Example 3 refines the preparation time, and the simulated oilfield wastewater obtained is still clear after standing for 6 hours.

[0048] Example 4

[0049] Following the same addition sequence and stirring rate as in Example 1, except that the stirring time was changed to 8 minutes before adding the next inorganic salt and sodium bicarbonate, the weakly alkaline simulated oilfield wastewater of Example 4 was obtained.

[0050] Due to the shortened stirring time, some powder that was not completely dissolved was found in the weakly alkaline simulated oilfield wastewater of Example 4.

[0051] Test Example 1

[0052] pH measurements were performed on the weakly alkaline simulated oilfield wastewater in Examples 1, 2, and 3, and Comparative Examples 1 and 2 using a pH meter. The test results are recorded in Table 2.

[0053] Table 2 pH values ​​of weakly alkaline simulated oilfield wastewater prepared by different methods

[0054] Example Example 1 Comparative Example 1 Comparative Example 2 Example 2 Example 3 pH 8.5 7.9 8.2 8.5 8.5

[0055] Based on the analysis of Table 2, the following conclusions can be drawn:

[0056] Comparative Examples 1 and 2 used a different feeding sequence than that of the present invention for wastewater preparation, Ca 2+ Mg 2+ Easily reacts with HCO3 - The reaction produces precipitates, resulting in a low pH value in the wastewater, which is significantly different from the pH value of actual formation oilfield wastewater. However, the pH values ​​of the wastewater in Examples 1, 2, and 3 are similar to those of actual formation oilfield wastewater. However, the preparation process in Examples 2 and 3 is simpler and faster.

[0057] Test Example 2

[0058] The wastewater quality of Examples 1, 2, and 3 and Comparative Examples 1 and 2 was analyzed in accordance with the standard SY / T 5523-2006 Oilfield Water Analysis Method, and the results are recorded in Table 3.

[0059] Table 3. Composition and salinity of weakly alkaline simulated oilfield wastewater prepared by different methods

[0060]

[0061]

[0062] Based on the analysis of Table 3, the following conclusions can be drawn:

[0063] Comparative Examples 1 and 2 were prepared by first preparing alkali to simulate wastewater, and it was found that Ca... 2+ Mg 2+ Easily reacts with HCO3 - The reaction produces precipitates, resulting in a difference in mineralization compared to actual formation oilfield wastewater. However, the mineralization of the preparation methods in Examples 1, 2, and 3 is similar to that of actual formation oilfield wastewater.

[0064] Test Example 3

[0065] Shelf life and pH tests were conducted on the weakly alkaline simulated oilfield wastewater from Examples 1, 2, and 3.

[0066] Table 4. pH values ​​of weakly alkaline simulated oilfield wastewater at different settling times.

[0067] Example 1 Example 2 Example 3 Standing time 0h 8.5 8.5 8.5 Settling time: 6 hours 8.5 8.5 8.5 Settling time: 12 hours 8.35 8.35 8.35

[0068] As can be seen from Table 4, the pH value of the weakly alkaline simulated oilfield wastewater in Examples 1-3 changed after being left to stand for more than 6 hours. Therefore, the shelf life of the weakly alkaline simulated oilfield wastewater in Examples 1-3 is 6 hours.

[0069] Since the prepared weakly alkaline simulated oilfield wastewater is used for indoor performance evaluation of polymers, it is required to be used within its shelf life in order to accurately test the polymers.

[0070] Test Example 4

[0071] Using weakly alkaline simulated oilfield wastewater from Examples 1, 2, and 3 and Comparative Examples 1 and 2, a polymer stock solution of 5000 ppm was prepared according to conventional techniques in the art. The polymer was CK1600 from Essen Corporation. After diluting the polymer stock solution to 800 ppm, the viscosity was measured using a Brookfield viscometer. The changes in the viscosity of the polymer solution were compared to provide an assessment of the impact of simulated oilfield wastewater on polymer performance.

[0072] Table 5. Viscosity results of polymer solutions prepared from weakly alkaline simulated oilfield wastewater using different preparation methods.

[0073]

[0074] As shown in Table 5, the impact of the proposed oilfield wastewater on polymer performance evaluation is evident. Therefore, accurate formulation is the foundation for polymer performance evaluation.

[0075] The embodiments described above are merely illustrative of implementation methods of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent disclosure. It should be noted that those skilled in the art can make various modifications, equivalent substitutions, and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent disclosure should be determined by the appended claims.

Claims

1. A method for preparing weakly alkaline simulated oilfield wastewater, characterized in that, include: The dosage of deionized water, as well as the types and amounts of alkali and inorganic salts, are determined based on the pH value and mineralization of the wastewater from the oilfield. After all the inorganic salts are completely dissolved in the deionized water, the alkali is added. Once the alkali has completely dissolved, the weakly alkaline simulated oilfield wastewater is obtained.

2. The method for preparing weakly alkaline simulated oilfield wastewater according to claim 1, characterized in that, The method for completely dissolving all inorganic salts in the deionized water includes: The inorganic salts are added in one or several batches. When adding in several batches, the next batch is added only after the previous batch has completely dissolved, until all the inorganic salts are completely dissolved in the deionized water.

3. The method for preparing weakly alkaline simulated oilfield wastewater according to claim 1 or 2, characterized in that: The alkali is sodium bicarbonate.

4. The method for preparing weakly alkaline simulated oilfield wastewater according to claim 3, characterized in that: The inorganic salts include sodium chloride, potassium chloride, magnesium chloride hexahydrate, and calcium chloride.

5. The method for preparing weakly alkaline simulated oilfield wastewater according to claim 4, characterized in that: The addition and dissolution of the inorganic salt and the alkali are carried out under stirring.

6. The method for preparing weakly alkaline simulated oilfield wastewater according to claim 5, characterized in that: The stirring rate is 400-600 rpm.

7. The method for preparing weakly alkaline simulated oilfield wastewater according to claim 6, characterized in that: The stirring time for completely dissolving the inorganic salt or the alkali in the deionized water is 10-20 minutes.

8. A weakly alkaline simulated oilfield wastewater, characterized in that, Its preparation method is as follows: The preparation method described in any one of claims 1-7 shall be used.

9. The weakly alkaline simulated oilfield wastewater according to claim 8, characterized in that: The pH value of the wastewater is 7.1~9.

0.

10. The method of using the weakly alkaline simulated oilfield wastewater as described in claim 8 or 9, characterized in that, include: Use within the shelf life, which is 6 hours.

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