A method for detecting the oil content rate of drilling fluid based on spectrometry

Abstract

The present invention provides a method for detecting the oil content rate of drilling fluid based on spectrometry, which solves the technical problem that when incident light hits turbidity particles during the fluorescence detection of existing drilling fluid, the turbidity particles themselves will absorb to a certain extent and scatter in all directions, resulting in the attenuation of the incident light; therefore, the light intensity irradiated onto the oil component becomes weak, thus affecting the final emitted fluorescence intensity. It can be widely applied to the field of spectral detection; specifically, it includes the following steps: mixing the drilling fluid sample with water and oscillating to obtain a solution to be measured; irradiating the solution to be measured with an ultraviolet light source, detecting the spectral image of the solution to be measured through a fluorescence spectrophotometer, and obtaining the fluorescence intensity at the corresponding wavelength according to the oil types contained in the drilling fluid; obtaining the current oil content rate according to the oil content rate - fluorescence intensity relationship model; detecting the turbidity value of the solution to be measured, and obtaining the standard oil content rate of the drilling fluid according to the turbidity compensation model.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectral detection, and particularly relates to a method for detecting the oil content rate of drilling fluid based on spectral determination. Background Art

[0002] The ultraviolet fluorescence method is based on the fluorescence effect of oil molecules. When ultraviolet incident light irradiates oil particles, it is absorbed and at the same time emits emission light of another wavelength. By detecting the emission light intensity, the oil concentration in the sample solution to be measured can be obtained. Usually, an "overflow type" or "immersion type" structure is adopted, such as Figure 1 . This method is a commonly used method for on-line measurement, has relevant standards, a wide measurement range, and its sensitivity is usually 2-3 orders of magnitude higher than that of the spectrophotometry method. Moreover, the fluorescence effects of oils with different compositions vary greatly, and the selectivity is better.

[0003] The light intensity and the peak positions in the three-dimensional fluorescence spectrum generated by the same substance in different solvents are also different. The main reason for this phenomenon is that there is a certain interaction force between the solution and the substance molecules. When the substance absorbs energy and is excited, a certain number of molecules transition from the ground state to the excited state, resulting in different electron distributions in the ground state and the excited state, thus having different effects on the fluorescence spectrum. At the same time, if there are scattering media in the solution, it will also hinder the excitation and emission of fluorescence.

[0004] When the incident light hits the turbidity particles, the turbidity particles themselves will absorb a certain amount and scatter in all directions, causing attenuation of the incident light; therefore, the light intensity hitting the oil is weakened, thus affecting the final emitted fluorescence intensity. Summary of the Invention

[0005] The purpose of the present invention is to solve the above-mentioned technical deficiencies and provide a method for detecting the oil content rate of drilling fluid based on spectral determination.

[0006] To this end, the present invention provides a method for detecting the oil content rate of drilling fluid based on spectral determination, including the following steps:

[0007] S10: Mix the drilling fluid sample with water and oscillate to obtain a solution to be measured;

[0008] S20: Use an ultraviolet light source to irradiate the solution to be measured, detect the spectral image of the solution to be measured through a fluorescence spectrophotometer, and obtain the fluorescence intensity at the corresponding wavelength according to the oil types contained in the drilling fluid;

[0009] S30: Obtain the current oil content rate according to the oil content rate - fluorescence intensity relationship model;

[0010] S40: Detect the turbidity value of the solution to be measured and obtain the standard oil content rate of the drilling fluid according to the turbidity compensation model.

[0011] Furthermore, the drilling fluid sample is mixed with water at a mass ratio of 1:100.

[0012] Furthermore, the steps for establishing the oil content-fluorescence intensity relationship model are as follows:

[0013] Select those with an absorbance within 0.1 as the standard drilling fluid samples;

[0014] Irradiate the standard drilling fluid samples with multiple oil content gradients using an ultraviolet light source, detect the spectral images of the standard drilling fluid samples through a fluorescence spectrophotometer, and obtain multiple fluorescence intensity images with oil content gradients at corresponding wavelengths according to the types of oil contained in the standard drilling fluid samples;

[0015] Establish an oil content-fluorescence intensity fitting function based on the multiple fluorescence intensity images with oil content gradients, and obtain the oil content-fluorescence intensity relationship model according to the corresponding relationship of the oil content-fluorescence intensity fitting function.

[0016] Furthermore, the steps for establishing the turbidity compensation model are as follows:

[0017] Irradiate the drilling fluid samples with the same oil content with multiple turbidity gradients using an ultraviolet light source, detect the spectral images of the drilling fluid samples with the same oil content through a fluorescence spectrophotometer, and obtain multiple fluorescence intensity images with turbidity gradients at corresponding wavelengths according to the types of oil contained in the drilling fluid samples with the same oil content;

[0018] Obtain the theoretical oil content corresponding to each turbidity gradient according to the oil content-fluorescence intensity relationship model;

[0019] Establish a turbidity compensation model based on the difference between the theoretical oil content and the actual oil content corresponding to each turbidity gradient.

[0020] Furthermore, the fluorescence intensity is selected from the spectral images in the excitation / emission wavelength range of 280 - 320 nm / 370 - 470 nm.

[0021] The present invention provides a method for detecting the oil content of drilling fluid based on spectral measurement, which has the following beneficial effects:

[0022] Through turbidity compensation, the present invention pulls back the fluorescence values measured under different turbidities to near the baseline. The fluorescence intensity values fluctuate above and below the true value, and the fluctuation range is small.

[0023] The relative error between the fluorescence intensity after compensation and the reference true value is small, and the compensation relative error is within 2%. The influence of turbidity change on the detection of oil concentration in water by fluorescence spectrometry can be well corrected through the turbidity compensation model. Description of the Drawings

[0024] Figure 1 is the schematic diagram of the fluorescence detection of the present invention;

[0025] Figure 2 is the three-dimensional fluorescence spectrum diagram of the drilling fluid of the present invention;

[0026] Figure 3 is the contour map of the drilling fluid of the present invention;

[0027] Figure 4 is the three-dimensional fluorescence spectrum diagram of the drilling fluid sample + emulsifier of the present invention;

[0028] Figure 5 is the three-dimensional fluorescence spectrum diagram of the emulsifier of the present invention;

[0029] Figure 6 is the three-dimensional fluorescence spectrum diagram of the drilling fluid sample after deducting the emulsifier background of the present invention;

[0030] Figure 7 is the three-dimensional fluorescence spectrum diagram of the drilling fluid sample of the present invention;

[0031] Figure 8 is the subtraction three-dimensional fluorescence spectrum diagram of the present invention;

[0032] Figure 9 is the fluorescence spectrum diagram of the drilling fluid sample diluted at a ratio of 1:10 of the present invention;

[0033] Figure 10 is the fluorescence spectrum diagram of the drilling fluid sample diluted at a ratio of 1:50 of the present invention;

[0034] Figure 11 is the fluorescence spectrum diagram of the drilling fluid sample diluted at a ratio of 1:100 of the present invention;

[0035] Figure 12 is the diagram of the concentration and fluorescence intensity of the drilling fluid sample of the present invention;

[0036] Figure 13 is the diagram of the concentration and fluorescence intensity of the drilling fluid sample after controlling the turbidity of the present invention;

[0037] Figure 14 is the three-dimensional fluorescence spectrum diagram of the drilling fluid sample at 0, 10, 20, 30, 40, 50 NTU of the present invention;

[0038] Figure 15 is the relationship curve of the fluorescence intensity corresponding to the turbidity at the excitation wavelength of 310 nm and the emission wavelength of 354 nm of the drilling fluid sample of the present invention;

[0039] Figure 16 is the relationship curve of the fluorescence intensity corresponding to the turbidity at the excitation wavelength of 340 nm and the emission wavelength of 412 nm of the drilling fluid sample of the present invention;

[0040] Figure 17 is the comparison diagram of the results before and after turbidity compensation of the present invention;

[0041] Figure 18 It is the relative error graph after turbidity compensation of the present invention. Specific embodiments

[0042] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments to help understand the content of the present invention. The methods used in the present invention are all conventional methods unless otherwise specified; the raw materials and devices used are all conventional commercially available products unless otherwise specified.

[0043] The present invention provides a method for detecting the oil content rate of drilling fluid based on spectral determination, including the following steps:

[0044] After stirring the drilling fluid cuttings sample evenly, take a sample and dilute it with pure water in a certain proportion to form a sample with a certain concentration gradient;

[0045] Transfer the diluted sample into a cuvette and place it in a fluorescence spectrophotometer for measurement;

[0046] Set the excitation wavelength range of the fluorescence spectrophotometer to 200 - 700 nm and the emission wavelength range to 200 - 900 nm to obtain the three-dimensional fluorescence data of the sample;

[0047] Use matlab to draw the three-dimensional fluorescence spectrum diagram and analyze the fluorescence intensity and fluorescence peak characteristics of the sample.

[0048] I. Selection of fluorescence characteristic peaks

[0049] The three-dimensional fluorescence spectrum of the drilling fluid sample is as Figure 2 , as shown in Figure 3, and its characteristic peak position is at the excitation / emission wavelength of 280 - 320 nm / 370 - 470 nm.

[0050] II. Selection of drilling fluid solvents

[0051] After stirring the drilling fluid sample evenly, take a sample and dilute it with pure water in a certain proportion to form a sample with a certain concentration; at the same time, prepare another sample with the same concentration, add an appropriate amount of emulsifier and mix evenly; prepare a sample with the same sample volume and the same amount of emulsifier added;

[0052] Transfer the three samples into cuvettes and place them in a fluorescence spectrophotometer for measurement;

[0053] Set the excitation wavelength range of the fluorescence spectrophotometer to 200 - 600 nm and the emission wavelength range to 250 - 650 nm to obtain the three-dimensional fluorescence data of the sample;

[0054] Use matlab to draw the three-dimensional fluorescence spectrum diagram and analyze the fluorescence intensity and fluorescence peak characteristics of the sample.

[0055] The fluorescence spectrum of the drilling fluid with emulsifier added and the fluorescence spectrum of the pure emulsifier aqueous solution are asFigure 4 As shown in Figure 5, the drilling fluid sample with an emulsifier added has a strong fluorescence response, and the emulsifier sample has a weak fluorescence around 300 / 350 nm. Figure 4 This is the superposition of the fluorescence of the drilling fluid sample and the fluorescence of the emulsifier. To compare with the sample directly prepared with water, the interference of the emulsifier needs to be deducted from the mixed fluorescence.

[0056] The fluorescence spectrum of the drilling fluid sample after deducting the emulsifier is as Figure 6 shown, and the fluorescence spectrum of the sample directly prepared with pure water is as Figure 7 shown. It can be seen that the spectral shapes of the two are exactly the same near the characteristic fluorescence peak of oil.

[0057] To test whether the fluorescence intensities of the two change, the fluorescence spectrum of the drilling fluid after deducting the emulsifier is subtracted from the fluorescence spectrum of the drill cuttings of the drilling fluid directly prepared with pure water. If the fluorescence intensity after subtraction is zero, it proves that the fluorescence intensities of the two are the same. The subtraction results are as Figure 8 shown. It can be seen from the figure that the fluorescence intensity near the oil fluorescence peak after subtraction is close to 0, indicating that the spectral shape and fluorescence intensity of the sample have not changed before and after adding the emulsifier, that is, the sample directly prepared with water can also reach a homogeneous and stable state after adding the emulsifier.

[0058] III. Selection of Drilling Fluid Dilution Ratio

[0059] As Figures 9 - 11 shown, when the drilling fluid sample is diluted at a mass ratio of 1:10, the drilling fluid sample is still relatively mixed, and a certain fluorescence is excited, but there is strong scattered light interference. After the drilling fluid sample is diluted at a ratio of 1:100, the transmittance of the drilling fluid sample increases, and there is a significant fluorescence peak.

[0060] IV. Establishment of Oil Content - Fluorescence Intensity Relationship Model

[0061] The drilling fluid sample is detected by a fluorescence sensor, and the results are as Figure 12 shown. The linearity is good at low concentrations, and fluorescence saturation occurs at high concentrations.

[0062] Regarding the fluorescence saturation problem of the drilling fluid sample, a feedback model is proposed to detect the turbidity of the solution using a turbidity sensor. Through experiments, when the absorbance of the drilling fluid sample is controlled within 0.1, the detection linearity is good, as Figure 13 shown. The fitting determination coefficient is 0.9889, and the detection accuracy is 5.79%.

[0063] V. Establishment of Turbidity Compensation Model

[0064] Solution samples with turbidities of 0, 10, 20, 30, 40, and 50 NTU are prepared using kaolin.

[0065] Take drilling fluid samples and sodium dodecyl sulfate and dissolve them in the prepared solution samples.

[0066] Excitation wavelength: 200 - 600 nm; excitation / emission slit: 5 / 10 nm; scanning speed: 1200 nm·min －1 ; scanning band: 250 - 650 nm; the scanning spectrum is automatically corrected by the instrument. The fluorescence spectra of the solution samples are scanned respectively in the range of turbidity from 0 to 50 (the interval unit is 5).

[0067] Using the data detected by the oil-in-water sensor, fit the fluorescence intensities at the same excitation / emission under different turbidity conditions respectively to verify the influence of different turbidities on the detection linearity of the oil-in-water sensor.

[0068] As Figure 14 shown, as the turbidity increases, the range of high-intensity fluorescence gradually shrinks, and the fluorescence intensity at the same excitation wavelength and emission wavelength also continuously decreases. To further verify the change law of the fluorescence intensity, compare the changes in the fluorescence intensities of two groups at the same excitation wavelength and emission wavelength, and fit these data. The fitting results are as Figure 15 shown, which is the fluorescence intensity at the excitation wavelength of 310 nm and the emission wavelength of 354 nm, the fitting function is y = -13.96x + 3890, and the correlation coefficient is 0.9723; as Figure 16 shown, the fluorescence intensity at the excitation wavelength of 340 nm and the emission wavelength of 412 nm, the fitting function is y = -9.754x + 2288, and the correlation coefficient is 0.9839. It can be seen that the linearity of the two fittings is good.

[0069] It can be seen from the above experiments that the intensity of the fluorescence emission spectrum is negatively correlated with the turbidity, and the influence brought by the turbidity cannot be ignored.

[0070] In order to avoid detection errors caused by turbidity interference, before substituting the fluorescence intensity of the sample into the oil content-fluorescence intensity relationship model, compensate its fluorescence intensity, that is, compensate the fluorescence intensity corresponding to different turbidities back to the value without turbidity.

[0071] Based on the linear relationship between the turbidity and the fluorescence intensity, taking the fluorescence value at 0 turbidity as the benchmark, compensate the fluorescence intensity in the range of 0 - 50 NTU. The comparison results of the true value of the fluorescence intensity of the sample before and after turbidity compensation, the predicted value before compensation and the predicted value after compensation are as Figure 17As shown, the measured value of the turbidity solution sample at 0 turbidity is the true fluorescence value without any other interference, so it can be used as a benchmark. As the turbidity increases, the fluorescence value of the sample gradually decreases and gradually deviates from the original true fluorescence value. The greater the turbidity, the stronger the influence and the greater the deviation value. After turbidity compensation, the fluorescence values measured at different turbidities are pulled back near the baseline, and their fluorescence intensity values fluctuate above and below the true value with a small fluctuation range.

[0072] Further calculate the relative error between the fluorescence intensity after compensation and the reference true value. The results are as Figure 18 shown. The compensation relative error is within 2%, which proves that the influence of turbidity change on the detection of oil concentration in water by fluorescence spectrometry can be well corrected through the turbidity compensation model.

[0073] However, the above are only specific embodiments of the present invention, and the scope of implementation of the present invention cannot be limited thereby. Therefore, the replacement of equivalent components or the equivalent changes and modifications made according to the scope of protection of the present invention shall still fall within the scope covered by the claims of the present invention.

Claims

1. A method for detecting the oil content rate of drilling fluid based on spectrometry, characterized in that, It includes the following steps: S10: Mix the drilling fluid sample with water and oscillate to obtain a solution to be measured; S20: Irradiate the solution to be measured with an ultraviolet light source, detect the spectral image of the solution to be measured through a fluorescence spectrophotometer, and obtain the fluorescence intensity at the corresponding wavelength according to the oil types contained in the drilling fluid; S30: Obtain the current oil content rate according to the oil content rate - fluorescence intensity relationship model; Among them, the steps for establishing the oil content rate - fluorescence intensity relationship model are as follows: Select those with an absorbance within 0.1 as standard drilling fluid samples; Irradiate the standard drilling fluid samples with multiple oil content rate gradients with an ultraviolet light source, detect the spectral images of the standard drilling fluid samples through a fluorescence spectrophotometer, and obtain multiple fluorescence intensity images with different oil content rate gradients at the corresponding wavelength according to the oil types contained in the standard drilling fluid samples; Establish an oil content rate - fluorescence intensity fitting function based on the multiple fluorescence intensity images with different oil content rate gradients, and obtain the oil content rate - fluorescence intensity relationship model according to the corresponding relationship of the oil content rate - fluorescence intensity fitting function; S40: Detect the turbidity value of the solution to be measured, and obtain the standard oil content rate of the drilling fluid according to the turbidity compensation model; Among them, the steps for establishing the turbidity compensation model are as follows: Irradiate the drilling fluid samples with the same oil content rate with multiple turbidity gradients with an ultraviolet light source, detect the spectral images of the drilling fluid samples with the same oil content rate through a fluorescence spectrophotometer, and obtain multiple fluorescence intensity images with different turbidity gradients at the corresponding wavelength according to the oil types contained in the drilling fluid samples with the same oil content rate; Obtain the theoretical oil content rate corresponding to each turbidity gradient according to the oil content rate - fluorescence intensity relationship model; Establish a turbidity compensation model based on the difference between the theoretical oil content rate and the actual oil content rate corresponding to each turbidity gradient.

2. The oil content detection method of drilling fluid based on spectrometry according to claim 1, wherein: The drilling fluid sample and water are mixed at a mass ratio of 1:

100.

3. The oil content detection method of drilling fluid based on spectrometry according to claim 1 or 2, characterized in that: The fluorescence intensity is selected within the range of excitation / emission wavelength 280 - 320 nm / 370 - 470 nm of the spectral image.

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