Method for determining content of emulsified oil in oilfield produced water

Abstract

The invention belongs to the technical field of measurement of emulsified oil in oilfield produced water, and discloses a method for measuring the content of emulsified oil in oilfield produced water. According to the determination method provided by the invention, floating oil and dispersed oil in the oilfield produced water are firstly separated by adopting a static buoyancy lift method, and residual emulsified oil in a water sample is detected by adopting an oil content analysis method, namely a visible light spectrophotometric method, in oilfield produced water reinjection water. The operation is simple and convenient, and the practicability is high. The detection time is greatly shortened, the content of a detected sample is greatly reduced, and operation is easy and more accurate.

Description

Technical Field

[0001] The invention belongs to the technical field of measuring emulsified oil in produced water of oil fields, and relates to a method for measuring the emulsified oil content in produced water of oil fields. Background Art

[0002] The oil contained in the produced water of the oil field is generally divided into floating oil, dispersed oil, emulsified oil and dissolved oil according to the particle size. The diameter of floating oil droplets is greater than 100μm, the diameter of dispersed oil droplets is 10-100μm, and the diameter of emulsified oil droplets is 10 -3 -10μm, the diameter of dissolved oil droplets is less than 10 -3 μm.

[0003] The analysis method for the oil content required in the quality of produced water for reinjection in oilfields currently implements Section 5.4 of "Recommended Indicators and Analysis Methods for Water Quality in Clastic Reservoirs" (SY / T 5329-2012) and "Spectrophotometric Method for Determination of Oil Content in Produced Water in Oilfields" (SY / T 0530-2011). The analysis methods in the two standards are the same in principle, and the detection wavelength is selected at 410nm~430nm. Since dissolved oil in produced water will not cause damage to the reservoir, the wavelength of 410nm~430nm is selected as the detection band (visible light band), which only detects floating oil, dispersed oil and emulsified oil in water, but not dissolved oil.

[0004] The floating oil and dispersed oil particles in the produced water of the oil field are relatively large. According to the Stokes equation, the floating time is short and easy to remove. However, the emulsified oil in the water has a small particle size and is an oil-in-water emulsion (O / W). Conventional separation is difficult. Generally, it needs to be demulsified and aggregated into larger oil droplets before it is easier to remove. Demulsification is generally carried out by chemical demulsification and physical demulsification. Therefore, in the treatment of produced water from the oil field, mastering the distribution of oil content in the raw water, especially the proportion of emulsified oil in the water, has become the key to the selection and evaluation of produced water treatment process equipment in the oil field. The research and test project of the closed dehydration of heavy oil and the non-drug treatment process of sewage adopts the non-drug sewage treatment process and equipment. How to evaluate the adaptability of the process to the emulsified oil content in the raw water and the degree of segmented water quality treatment, and the detection method of emulsified oil in water have become the core key technologies.

[0005] Currently, there is the "Determination of Emulsified Oil and Dissolved Oil in Produced Water" (SY / T 0601-2016). The principle of this detection method is to first use infrared spectrophotometry to detect the total amount of emulsified oil and dissolved oil, and then use infrared-silica gel method to detect the dissolved oil content, and subtract the dissolved oil content from the total content of emulsified oil and dissolved oil to obtain the emulsified oil content.

[0006] This method is cumbersome and inconvenient to operate, has errors, and is not conducive to the popularization and application of working conditions. It is not very practical. Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a method for determining the emulsified oil content in oilfield produced water. The method provided by the present invention uses a static buoyancy method to first separate the floating oil and dispersed oil in the oilfield produced water, and uses a visible light spectrophotometry method, which is an analysis method for the oil content in the water quality of oilfield produced water for reinjection, to detect the remaining emulsified oil in the water sample. The method has the characteristics of simple operation and strong practicality.

[0008] The above object of the present invention is achieved through the following technical solutions:

[0009] A method for determining the emulsified oil content in oilfield produced water uses a static buoyancy method to first separate floating oil and dispersed oil in the oilfield produced water, and uses a visible light spectrophotometry method, a method for analyzing the oil content in the water quality of oilfield produced water for reinjection, to detect the remaining emulsified oil in the water sample.

[0010] The specific steps are as follows:

[0011] S1. According to the existence state of crude oil in oilfield produced water and the definition of emulsified oil and the buoyancy law it follows, the produced water sample collected on site is left to stand for 2 hours to allow floating oil and dispersed oil to float up in advance; the water sample is siphoned from the middle of the sampling device into a 250mL cylindrical separatory funnel to the 200mL mark using a latex tube, and the upper opening of the separatory funnel is plugged tightly with a stopper;

[0012] S2. Detect the density of water samples and crude oil, and determine the dynamic viscosity of water at the on-site water temperature.

[0013] S3. Calculate the time required for an oil droplet with the largest particle size of 10 μm in the emulsified oil to rise 10 cm based on the dynamic viscosity of the water sample and the density of the crude oil and water;

[0014] S4. Place the separatory funnel filled with 200 mL of water sample in a constant temperature oven with the same water temperature as the site. After floating for t0 time, drain 20 mL from the bottom of the separatory funnel and then drain 100 mL of water sample into a clean dry measuring cylinder for the next step of analysis.

[0015] S5. According to the "Spectrophotometric Method for Determination of Oil Content in Produced Water from Oilfields" (SY / T 0530-2011), the wavelength is selected at 410nm~430nm to detect the oil content in the water sample in the previous step, that is, the emulsified oil in the water sample.

[0016] Further, in step S3, the time required for an oil droplet with a maximum particle size of 10 μm in the emulsified oil to rise 10 cm is calculated by formula 2;

[0017]

[0018] Where:

[0019] t: time required for oil with diameter d0 to rise to height H0, s;

[0020] μ: dynamic viscosity of produced water, kg / (sm);

[0021] H0: oil droplet rising height, 10cm;

[0022] g: acceleration due to gravity, 9.81 m / s -2 ;

[0023] ρ w : Density of water, kg / m 3 ;

[0024] ρ0: oil density, kg / m 3 ;

[0025] d0: oil droplet diameter, m.

[0026] Furthermore, the definition of the existence state of crude oil and emulsified oil in the produced water of the oil field in step S1 is specifically as follows: the crude oil in the produced water of the oil field generally exists in four states according to the size of the oil droplets, which are classified as follows: floating oil, dispersed oil, emulsified oil, and dissolved oil.

[0027] Furthermore, the floating oil is oil with oil droplet diameter greater than 100 μm. The dispersed oil is oil with oil droplet diameter of 10-100 μm. The emulsified oil is oil with oil droplet diameter of 10 -3 -10μm oil. Dissolved oil means oil droplets with a diameter less than 10 -3 μm and has polarity and can be adsorbed by silica gel.

[0028] Furthermore, the buoyancy law in step S1 is specifically: the buoyancy of oil droplets in the produced water of the oil field conforms to the Stokes settling law (Stokes); its formula is shown below:

[0029]

[0030] Where:

[0031] V: oil droplet floating speed;

[0032] ρ w : produced water density;

[0033] ρ0: oil density;

[0034] μ: dynamic viscosity of produced water;

[0035] g: acceleration due to gravity;

[0036] d: Oil droplet diameter.

[0037] The determination of emulsified oil in oilfield produced water plays an important role in the evaluation of the adaptability of oilfield produced water reinjection treatment process equipment and the evaluation of the effects of various demulsification methods (physical demulsification, chemical demulsification). The method for determining the emulsified oil content in oilfield produced water provided by the present invention provides an important practical basis for the specific practical application and the evaluation of the adaptability of oilfield produced water reinjection treatment process equipment, as well as the evaluation of the effects of various demulsification methods (physical demulsification, chemical demulsification).

[0038] The beneficial effects of the present invention compared with the prior art are:

[0039] The present invention provides a method for determining the emulsified oil content in oilfield produced water. The present invention uses a static buoyancy method to first separate the floating oil and dispersed oil in the oilfield produced water, and uses the oil content analysis method in the oilfield produced water reinjection water quality - visible light spectrophotometry - to detect the remaining emulsified oil (excluding dissolved oil) in the water sample. Compared with the usual method of first using infrared spectrophotometry to detect the sum of emulsified oil and dissolved oil, and then using infrared-silica gel method to detect the dissolved oil content, and subtracting the dissolved oil content from the total content of emulsified oil and dissolved oil to obtain the emulsified oil content, the present invention has the characteristics of simple operation and strong practicality. The present invention greatly shortens the detection time and the detection sample content, and is easy to operate and more accurate. DETAILED DESCRIPTION

[0040] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0041] Example 1

[0042] A method for determining the emulsified oil content in oilfield produced water, the specific steps are as follows:

[0043] S1. According to the existence state of crude oil in oilfield produced water and the definition of emulsified oil and the buoyancy law it follows, the produced water sample collected on site is left to stand for 2 hours to allow floating oil and dispersed oil to float up in advance; the water sample is siphoned from the middle of the sampling device into a 250mL cylindrical separatory funnel to the 200mL mark using a latex tube, and the upper opening of the separatory funnel is plugged tightly with a stopper;

[0044] S2. Detect the density of water samples and crude oil, and determine the dynamic viscosity of water at the on-site water temperature.

[0045] S3. Calculate the time required for an oil droplet with the largest particle size of 10 μm in the emulsified oil to rise 10 cm based on the dynamic viscosity of the water sample and the density of the crude oil and water;

[0046] S4. Place the separatory funnel filled with 200 mL of water sample in a constant temperature oven with the same water temperature as the site. After floating for t0 time, drain 20 mL from the bottom of the separatory funnel and then drain 100 mL of water sample into a clean dry measuring cylinder for the next step of analysis.

[0047] S5. According to the "Spectrophotometric Method for Determination of Oil Content in Produced Water from Oilfields" (SY / T 0530-2011), the wavelength is selected at 410nm~430nm to detect the oil content in the water sample in the previous step, that is, the emulsified oil in the water sample.

[0048] Further, in step S3, the time required for an oil droplet with a maximum particle size of 10 μm in the emulsified oil to rise 10 cm is calculated by formula 2;

[0049]

[0050] Where:

[0051] t: time required for oil with diameter d0 to rise to height H0, s;

[0052] μ: dynamic viscosity of produced water, Pa·s;

[0053] H0: oil droplet rising height, cm;

[0054] g: acceleration due to gravity, 9.81 m / s -2 ;

[0055] ρ w : Density of water, kg / m 3 ;

[0056] ρ0: oil density, kg / m 3 ;

[0057] d0: oil droplet diameter, m.

[0058] Furthermore, the definition of the existence state of crude oil and emulsified oil in the produced water of the oil field in step S1 is specifically as follows: the crude oil in the produced water of the oil field generally exists in four states according to the size of the oil droplets, which are classified as follows: floating oil, dispersed oil, emulsified oil, and dissolved oil.

[0059] Furthermore, the floating oil is oil with oil droplet diameter greater than 100 μm. The dispersed oil is oil with oil droplet diameter of 10-100 μm. The emulsified oil is oil with oil droplet diameter of 10 -3 -10μm oil. Dissolved oil means oil droplets with a diameter less than 10 -3 μm and has polarity and can be adsorbed by silica gel.

[0060] Furthermore, the buoyancy law in step S1 is specifically: the buoyancy of oil droplets in the produced water of the oil field conforms to the Stokes settling law (Stokes); its formula is shown below:

[0061]

[0062] Where:

[0063] V: oil droplet floating speed;

[0064] ρ w : produced water density;

[0065] ρ0: oil density;

[0066] μ: dynamic viscosity of produced water;

[0067] g: acceleration due to gravity;

[0068] d: Oil droplet diameter.

[0069] Example 2

[0070] A method for determining the emulsified oil content in oilfield produced water is specifically applied in Liaohe Oilfield. The specific steps are as follows:

[0071] 1. Take 300mL of water sample from Huansanlian crude oil, and test the water temperature on site to 54℃;

[0072] 2. Take 100mL of qualified crude oil sample from Huan Sanlian;

[0073] 3. Preparation before testing

[0074] 1) According to SY / T 5523, the density of the water sample at the on-site water temperature is 985kg / m 3 ;

[0075] 2) According to GB / T 1884, the density of the oil sample at the on-site water temperature was measured to be 932 kg / m 3 .

[0076] 3) The dynamic viscosity of the water sample can be obtained from the data in Table 1 below

[0077] Table 1 Dynamic viscosity of water at different temperatures

[0078]

[0079]

[0080] 4. According to Formula 2, calculate the time required for an oil droplet of d0 = 10 μm to rise to H0 = 10 cm, which is 292 minutes.

[0081]

[0082] Where:

[0083] t: time required for oil with diameter d0 to rise to height H0, s;

[0084] μ: dynamic viscosity of produced water, Pa·s;

[0085] H0: oil droplet rising height, cm;

[0086] g: acceleration due to gravity, 9.81 m / s -2 ;

[0087] ρ w : Density of water, kg / m 3 ;

[0088] ρ0: oil density, kg / m 3 ;

[0089] d0: oil droplet diameter, m.

[0090] 5. Place the separatory funnel filled with 200mL of water sample in a constant temperature oven with the same water temperature as on-site. After static floating for t0 time, first release 20mL from the bottom of the separatory funnel, and then release 100mL of water sample into a clean and dry measuring cylinder for the next step of analysis.

[0091] 6. According to the "Spectrophotometric Method for Determination of Oil Content in Oilfield Produced Water" (SY / T 0530-2011), the wavelength is selected at 420nm, and the oil content in the water sample in the previous step is detected to be 120mg / L, which is the emulsified oil content in the water sample.

[0092] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for determining the emulsified oil content in oilfield produced water, characterized in that: The static buoyancy method is used to first separate the floating oil and dispersed oil in the oilfield produced water, and the remaining emulsified oil in the water sample is detected using the oil content analysis method for oilfield produced water reinjection water quality - visible light spectrophotometry.

2. A method for determining the emulsified oil content in oilfield produced water as claimed in claim 1, characterized in that: The specific steps are as follows: S1. According to the existence state of crude oil in oilfield produced water and the definition of emulsified oil and the buoyancy law it follows, the produced water sample collected on site is left to stand for 2 hours to allow floating oil and dispersed oil to float up in advance; the water sample is siphoned from the middle of the sampling device into a 250mL cylindrical separatory funnel to the 200mL mark using a latex tube, and the upper opening of the separatory funnel is plugged tightly with a stopper; S2. Detect the density of water samples and crude oil, and determine the dynamic viscosity of water at the on-site water temperature. S3. Calculate the time required for an oil droplet with the largest particle size of 10 μm in the emulsified oil to rise 10 cm based on the dynamic viscosity of the water sample and the density of the crude oil and water; S4. Place the separatory funnel filled with 200 mL of water sample in a constant temperature oven with the same water temperature as the site. After floating for t0 time, drain 20 mL from the bottom of the separatory funnel and then drain 100 mL of water sample into a clean dry measuring cylinder for the next step of analysis. S5. According to the "Spectrophotometric Method for Determination of Oil Content in Oilfield Produced Water", the wavelength is selected between 410nm and 430nm to detect the oil content in the water sample in the previous step, which is the emulsified oil in the water sample.

3. A method for determining the emulsified oil content in oilfield produced water as claimed in claim 2, characterized in that: In step S3, the time required for an oil droplet with a maximum particle size of 10 μm in the emulsified oil to rise 10 cm is calculated by formula 2; Where: t: time required for oil with diameter d0 to rise to height H0, s; μ: dynamic viscosity of produced water, kg / (sm); H0: oil droplet rising height, cm; g: acceleration due to gravity, 9.81 m / s -2 ; ρ w : Density of water, kg / m 3 ; ρ0: oil density, kg / m 3 ; d0: oil droplet diameter, m.

4. A method for determining the emulsified oil content in oilfield produced water as claimed in claim 2, characterized in that the steps The definitions of the existence states of crude oil and emulsified oil in oilfield produced water in S1 are as follows: Crude oil in oilfield produced water generally exists in four states according to the size of oil droplets, which are classified as follows: floating oil, dispersed oil, emulsified oil, and dissolved oil.

5. A method for determining the emulsified oil content in oilfield produced water as claimed in claim 4, characterized in that: The floating oil is oil with oil droplet diameter greater than 100 μm; the dispersed oil is oil with oil droplet diameter of 10-100 μm.

6. A method for determining the emulsified oil content in oilfield produced water as claimed in claim 5, characterized in that: The diameter of the emulsified oil droplets is 10 -3 -10μm oil. Dissolved oil means oil droplets with a diameter less than 10 -3 μm and has polarity and can be adsorbed by silica gel.

7. A method for determining the emulsified oil content in oilfield produced water as claimed in claim 6, characterized in that: The specific buoyancy law in step S1 is: the buoyancy of oil droplets in the produced water of the oil field conforms to the Stokes settling law (Stokes); its formula is shown below: Where: V: oil droplet floating speed; ρ w : produced water density; ρ0: oil density; μ: dynamic viscosity of produced water; g: acceleration due to gravity; d: Oil droplet diameter.

8. Application of the method for determining the emulsified oil content in oilfield produced water as claimed in any one of claims 1 to 7 in determining the emulsified oil content in Liaohe Oilfield produced water.

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