Method for determining residual guanidium content in guanidium gel breaking solution

Abstract

The application provides a method for determining residual guanidium gel content in guanidium gel breaking fluid. The method comprises the following steps: sample pretreatment; preparation of guanidium gel breaking fluid series samples with different guanidium gel contents; taking the content of guanidium gel standard in the guanidium gel breaking fluid series samples with different guanidium gel contents as a response value, taking the characteristic fluorescence peak intensity and viscosity of the guanidium gel breaking fluid series samples with different guanidium gel contents after blank deduction as variables, performing regression analysis to obtain a standard curve equation of residual guanidium gel; and substituting the characteristic fluorescence peak intensity and viscosity of the pretreated guanidium gel breaking fluid sample after blank deduction into the standard curve equation of residual guanidium gel to obtain the content of residual guanidium gel in the guanidium gel breaking fluid sample to be determined. The determination method is scientific and reasonable, has high repeatability and accuracy, realizes qualitative and quantitative analysis of residual guanidium gel in guanidium gel breaking fluid, and can support efficient resource treatment of oil and gas field fracturing flowback fluid.

Description

Technical Field

[0001] This invention relates to a method for determining the residual guar gum content in guar gum breaking solution, belonging to the field of oil and gas extraction technology. Background Technology

[0002] In oil and gas field development, guar gum fracturing fluid is commonly used for enhanced production. However, the composition of guar gum fracturing flowback fluid is complex, and incompletely broken guar gum residue remains, increasing the difficulty of flowback fluid treatment. Therefore, it is urgent to conduct enhanced destabilization and resource utilization studies on the flowback fluid. Consequently, it is necessary to investigate the properties and concentration of residual guar gum in the flowback fluid.

[0003] Guar gum breaker fluid (i.e., flowback fluid) is the waste liquid returned to the surface after guar gum fracturing fluid has been broken down underground during oil and gas field development. Its viscosity is approximately 1.2–10 mPa·s, mainly due to incomplete guar gum breakdown, especially in flowback fluid with a viscosity >5 mPa·s, where the molecular weight of residual organic matter is relatively large. Currently, there is a lack of methods for determining the residual guar gum in the breaker fluid. Some industry or enterprise standards list methods for determining the residue in the breaker fluid, such as SY / T5107-2005 "Performance Evaluation Method of Water-Based Fracturing Fluid" and SY / T 6376-2008 "General Technical Conditions for Fracturing Fluid", which clearly define the determination process for the residue after fracturing fluid breakdown. However, unlike residue, the breaker fluid is an aqueous phase that is difficult to separate by centrifugation. CN105156087A proposes adjusting the guar gum content in the guar gum fracturing flowback fluid to a mass concentration of 1.0–1.5%, followed by a series of treatments before reinjection underground to improve oil recovery. However, it does not specify the residual guar gum concentration in the breaker fluid or how to adjust the total amount of guar gum. CN108435215A uses COD concentration to represent the residual guar gum concentration in the breaker fluid, but cannot clearly define the residual guar gum content. Many researchers characterize guar gum breaker fluids using viscosity and molecular weight (Huang Feifei et al., Research on High-Efficiency Breaker and Degrader System of Guar Gum Fracturing Fluid, Applied Chemical Industry, 2021). Some researchers also use the hydroxyl functional groups of guar gum for indirect quantitative analysis. Yin Zichen et al. (Study on the Adsorption Properties of Hydroxypropyl Guar Gum on Kaolin, Analytical Chemistry, 2019) utilized the structural similarity between guar gum and cellulose, prepared an acidified guar gum solution, reacted it with an ethyl acetate solution containing anthrone in a 90℃ water bath, and then measured the absorbance of the resulting solution at a wavelength of 620 nm. This colorimetric reaction method uses guar gum as a standard sample to prepare a standard curve with a concentration range of 20–100 mg / L. However, it does not take into account the changes in structure, viscosity, and molecular weight of guar gum after oxidation and breakage. Therefore, the results can only represent the amount of hydroxyl functional groups that can react with the colorimetric reagent.

[0004] Establishing a highly adaptable method for determining the residual guar gum content in guar gum breaking solution, based on the structural and property changes during the breaking process of guar gum, has become one of the urgent problems to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a method for determining the residual guar gum content in guar gum breaking solution. The determination method of the present invention is scientific, reasonable, and has high repeatability and accuracy.

[0006] To achieve the above objectives, the present invention provides a method for determining the residual guar gum content in guar gum breaking solution, comprising the following steps:

[0007] (1) Sample pretreatment: The guar gum rupture liquid sample to be tested was filtered by a filter column filled with calcium alginate-based composite material to obtain the pretreated guar gum rupture liquid sample.

[0008] (2) Preparation of a series of guar gum breaking fluid samples with different guar gum contents: According to the actual guar gum fracturing fluid formula corresponding to the guar gum breaking fluid sample to be tested, guar gum standard is used to prepare guar gum fracturing fluid with added breaking agent, and the fluid is reacted at a suitable temperature for a period of time to break the gum, thereby obtaining guar gum breaking fluid; after solid-liquid separation of the guar gum breaking fluid, the liquid phase is taken to obtain the breaking fluid with residual guar gum; using different amounts of guar gum standard and the breaking fluid with residual guar gum as solvent, a series of guar gum breaking fluid samples with different guar gum contents are prepared.

[0009] (3) Constructing a standard curve equation: Fluorescence spectroscopy and viscosity were performed on the residual guar gum breaking solution and the series of guar gum breaking solutions with different guar gum contents to obtain their characteristic fluorescence peak intensity and viscosity. Using the characteristic fluorescence peak intensity and viscosity of the residual guar gum breaking solution as a blank, the characteristic fluorescence peak intensity and viscosity of the series of guar gum breaking solutions with different guar gum contents were subtracted from the blank to obtain the characteristic fluorescence peak intensity and viscosity of the series of guar gum breaking solutions with different guar gum contents after subtracting the blank. Using the content of guar gum standard in the series of guar gum breaking solutions with different guar gum contents as the response value, and using the characteristic fluorescence peak intensity and viscosity of the series of guar gum breaking solutions with different guar gum contents after subtracting the blank as variables, regression analysis was performed to obtain the standard curve equation for the residual guar gum.

[0010] (4) Sample detection: Fluorescence spectroscopy and viscosity detection were performed on the pretreated guar gum fracturing fluid sample to obtain the characteristic fluorescence peak intensity and viscosity of the pretreated guar gum fracturing fluid sample; Fluorescence spectroscopy and viscosity detection were performed on the water used in the actual guar gum fracturing fluid corresponding to the pretreated guar gum fracturing fluid sample to obtain the characteristic fluorescence peak intensity and viscosity of the water, and used as a blank; The characteristic fluorescence peak intensity and viscosity of the pretreated guar gum fracturing fluid sample after subtracting the blank were obtained from the characteristic fluorescence peak intensity and viscosity of the pretreated guar gum fracturing fluid sample after subtracting the blank, and substituted into the standard curve equation of the residual guar gum to obtain the content of residual guar gum in the guar gum fracturing fluid sample to be measured.

[0011] In the above-mentioned method for determining the residual guar gum content in the guar gum breaking solution, preferably, in step (1), the calcium alginate-based composite material filler includes calcium alginate-MgO composite material and calcium alginate-bentonite composite material. More preferably, the calcium alginate-MgO composite material is prepared by the following steps: 0.5-3% sodium alginate, 0.2-2% calcium chloride, 1-5% magnesium oxide, and the balance water are mixed by weight percentage to obtain calcium alginate-MgO composite material gel; the calcium alginate-MgO composite material gel is dried at 20-50°C to constant weight to obtain the calcium alginate-MgO composite material. Further preferably, the particle size of the calcium alginate-MgO composite material is 0.5-2 mm. More preferably, the calcium alginate-bentonite composite material is prepared by the following steps: 0.5-3% sodium alginate, 0.2-2% calcium chloride, 1-5% bentonite, and the balance water are mixed by weight percentage to obtain a calcium alginate-bentonite composite material gel; the calcium alginate-bentonite composite material gel is dried at 20-50°C to constant weight to obtain the calcium alginate-bentonite composite material. Further preferably, the particle size of the calcium alginate-bentonite composite material is 0.5-2 mm. More preferably, the weight ratio of the calcium alginate-MgO composite material to the calcium alginate-bentonite composite material is 1:5 to 4:1.

[0012] In the above method for determining the residual guar gum content in the guar gum breaking solution, preferably, in step (1), when filtering the guar gum breaking solution sample, the volume ratio of the filler to the guar gum breaking solution sample is 1:2 to 1:20.

[0013] In the above-mentioned method for determining the residual guar gum content in the guar gum breaking solution, preferably, in step (1), the petroleum content in the pretreated guar gum breaking solution sample is less than 15 mg / L and the suspended solids content is less than 30 mg / L.

[0014] The determination method of the present invention performs special pretreatment on the guar gum breaking solution sample, which can remove oils, suspended solids, metal ion contaminants and other pollutants that affect the detection of residual guar gum in the sample, thereby reducing interference.

[0015] In the above-mentioned method for determining the residual guar gum content in guar gum fracturing fluid, in step (2), the guar gum standard used can be a product that is the same as or similar to the guar gum in the actual guar gum fracturing fluid in the oil and gas field. The same or similar generally refers to the same or similar molecular structure, molecular weight, etc., and can specifically include hydroxypropyl guar gum and its modified products. The formulation of the actual guar gum fracturing fluid generally mainly includes guar gum, pH adjuster, crosslinking agent, water, etc., and may further include bactericide, drainage aid, demulsifier, clay stabilizer, etc. The water in the fracturing fluid formulation is generally pure water, or it can be formation water.

[0016] In the above-described method for determining the residual guar gum content in the guar gum fracturing fluid, preferably, in step (2), based on the total weight of the guar gum fracturing fluid with added breaker as 100%, the amount of breaker added is 0.005% to 1%, the reaction temperature for breakering is 80 to 100°C, and the reaction time is 0.5 to 12 hours. More specifically, the reaction can be carried out in a water bath.

[0017] In the above method for determining the residual guar gum content in the guar gum breaking solution, preferably, in step (2), the viscosity of the guar gum breaking solution is ≤12 mPa·s.

[0018] In the above-mentioned method for determining the residual guar gum content in the guar gum breaking solution, preferably, in step (2), the solid-liquid separation may include centrifugal separation, etc.

[0019] In the above-described method for determining the residual guar gum content in the guar gum breaking solution, preferably, in step (2), the content of guar gum standard in the series of guar gum breaking solution samples with different guar gum contents is 100–4000 mg / L. More specifically, the series of guar gum breaking solution samples with different guar gum contents includes a series of samples with guar gum standard contents of 100 mg / L, 500 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 2500 mg / L, 3000 mg / L, 3500 mg / L, and 4000 mg / L.

[0020] In the above method for determining the residual guar gum content in the guar gum breaking solution, preferably, in steps (3) and (4), the characteristic fluorescence peak position of the fluorescence spectroscopy detection is excitation wavelength Ex / emission wavelength Em = 260~280nm / 320~340nm.

[0021] In the above method for determining the residual guar gum content in the guar gum breaking solution, in steps (3) and (4), the viscosity can be detected using a conventional viscometer, and the viscosity obtained is the apparent viscosity.

[0022] In the above method for determining the residual guar gum content in the guar gum breaking solution, preferably, in step (3), the standard curve equation of the residual guar gum is a polynomial equation based on the characteristic fluorescence peak intensity and viscosity. More specifically, the standard curve equation of the residual guar gum is: C = -14.1 + 0.11 × ΔF + 84.3 × Δη, with a correction coefficient R 2 =0.99, where C is the content of guar gum (mg / L), ΔF is the intensity of the characteristic fluorescence peak of the sample after subtracting the blank (au), and Δη is the viscosity of the sample after subtracting the blank (mpa·s).

[0023] After the guar gum polymer is broken down, if the breakdown is complete, the organic matter is essentially converted into small-molecule acids and other substances. If the breakdown is incomplete, organic matter with a higher carbon number and molecular weight remains. After the guar gum is broken down, the total organic matter concentration (COD) does not change significantly compared to before the breakdown, with residual guar gum being a component of COD. Some existing methods equate residual guar gum with COD, making it difficult to distinguish and accurately quantify residual guar gum in the broken solution.

[0024] The inventors of this case discovered through extensive research that, after guar gum is broken up, even in cases of incomplete breakup, the basic functional group structure of the organic matter in the broken-up solution is similar to that of the guar gum before breakup, exhibiting similar spectral characteristics, particularly the fluorescence spectral properties caused by conjugated functional groups. Viscosity can indirectly represent the molecular weight of guar gum.

[0025] The technical solution of this invention uses a solvent prepared from residual guar gum to break up the gum, combining guar gum standards with the residual guar gum. A standard curve equation is constructed using characteristic fluorescence peak intensity and viscosity as dual variables. The fluorescence spectrum reflects the incompletely broken residual guar gum in the breaking up solution. Combined with viscosity indicators characterizing molecular weight, the residual guar gum can be qualitatively identified from aspects such as functional groups and polymer structure, overcoming the shortcomings of analytical methods such as COD concentration and the amount of simple hydroxyl functional groups, and achieving accurate determination of the residual guar gum content in the breaking up solution. Although existing technologies utilize gel chromatography (i.e., size exclusion chromatography) to determine the relative molecular weight of guar gum, gel chromatography requires the preparation of standard samples, with an average measurement time of approximately 1 hour per sample, while viscosity measurement time is generally ≤10 seconds. Therefore, this invention uses viscosity as one of the variables, achieving quantitative analysis through the simplest in-situ determination method. The method for determining the residual guar gum content in the breaking up solution of this invention is more scientific and reasonable than existing methods, with repeatability and accuracy deviations both ≤5%.

[0026] Therefore, this invention establishes a highly adaptable method for determining the residual guar gum content in guar gum breaking solution, targeting the structural and property changes during the guar gum breaking process. This method enables qualitative and quantitative analysis of residual guar gum in guar gum breaking solution. Furthermore, this method is scientific, reasonable, and highly repeatable and accurate, filling a gap in existing analytical methods and supporting the efficient resource utilization of fracturing flowback fluid from oil and gas fields. Attached Figure Description

[0027] Figure 1 A flowchart illustrating a method for determining the residual guar gum content in guar gum breaking solution, provided as a specific embodiment of the present invention.

[0028] Figure 2 Optical images of the calcium alginate-MgO composite material and the calcium alginate-bentonite composite material in Example 1.

[0029] Figures 3a to 3i The image shows the three-dimensional fluorescence spectra of the guar gum breaking solution series samples with different guar gum contents in Example 1. Detailed Implementation

[0030] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0031] According to a specific embodiment of the present invention, preferably, such as Figure 1 As shown, the method for determining the residual guar gum content in the guar gum breaking solution provided by the present invention includes the following steps:

[0032] (1) Sample pretreatment: calcium alginate-MgO composite material and calcium alginate-bentonite composite material were mixed in a weight ratio of 1:5 to 4:1 to obtain calcium alginate-based composite material filler, and then filled into a filter column. The guar gum rupture liquid sample to be tested was filtered using a filter column filled with calcium alginate-based composite material filler. The volume ratio of filler to guar gum rupture liquid sample was 1:2 to 1:20 to obtain the pretreated guar gum rupture liquid sample.

[0033] The calcium alginate-MgO composite material is prepared by the following steps: 0.5–3% sodium alginate, 0.2–2% calcium chloride, 1–5% magnesium oxide, and the balance water are mixed by weight percentage to obtain a calcium alginate-MgO composite material gel. The calcium alginate-MgO composite material gel is dried at 20–50°C to constant weight to obtain the calcium alginate-MgO composite material. The particle size of the calcium alginate-MgO composite material is 0.5–2 mm.

[0034] The calcium alginate-bentonite composite material is prepared by the following steps: 0.5–3% sodium alginate, 0.2–2% calcium chloride, 1–5% bentonite, and the balance water are mixed by weight percentage to obtain a calcium alginate-bentonite composite material gel. The calcium alginate-bentonite composite material gel is dried at 20–50°C to constant weight to obtain the calcium alginate-bentonite composite material. The particle size of the calcium alginate-bentonite composite material is 0.5–2 mm.

[0035] (2) Preparation of a series of guar gum breaker samples with different guar gum contents: According to the actual guar gum fracturing fluid formula corresponding to the guar gum breaker sample to be tested, guar gum standard is used to prepare guar gum fracturing fluid with added breaker. The total weight of the guar gum fracturing fluid with added breaker is 100%, and the amount of added breaker is 0.005% to 1%. The breaker is reacted in a water bath at 80 to 100°C for 0.5 to 12 hours to obtain guar gum breaker. The viscosity of the guar gum breaker is ≤12 mPa·s. The guar gum breaker is centrifuged to remove the residue, and the stable liquid phase is taken to obtain the breaker with residual guar gum. Different amounts of guar gum standard are weighed, and the breaker with residual guar gum is used as a solvent to prepare a series of guar gum breaker samples with different guar gum contents.

[0036] The guar gum standard in the series of guar gum breaking solutions with different guar gum contents ranges from 100 to 4000 mg / L; more specifically, the series of guar gum breaking solutions with different guar gum contents includes samples with guar gum standard contents of 100 mg / L, 500 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 2500 mg / L, 3000 mg / L, 3500 mg / L, and 4000 mg / L.

[0037] (3) Constructing a standard curve equation: Fluorescence spectroscopy and viscosity measurements were performed on the residual guar gum breaking solution and the series of guar gum breaking solutions with different guar gum contents to obtain their characteristic fluorescence peak intensity (F) and viscosity (η). Using the characteristic fluorescence peak intensity and viscosity of the residual guar gum breaking solution (i.e., the guar gum standard content is 0 mg / L) as a blank, the characteristic fluorescence peak intensity and viscosity of the series of guar gum breaking solutions with different guar gum contents were subtracted from the blank to obtain the blank-subtracted guar gum breaking solution with different guar gum contents. The characteristic fluorescence peak intensity (ΔF) and viscosity (Δη) of the guar gum breaking liquid series samples were analyzed. Using the content (C) of guar gum standard in the guar gum breaking liquid series samples with different guar gum contents as the response value, and the characteristic fluorescence peak intensity (ΔF) and viscosity (Δη) of the guar gum breaking liquid series samples with different guar gum contents after blank subtraction as variables, regression analysis was performed to obtain the standard curve equation for residual guar gum. More specifically, the standard curve equation for the residual guar gum breaking liquid is: C = -14.1 + 0.11 × ΔF + 84.3 × Δη, with a correction coefficient R... 2 =0.99;

[0038] The characteristic fluorescence peak positions detected by the fluorescence spectroscopy are excitation wavelength Ex / emission wavelength / Em = 260~280nm / 320~340nm;

[0039] (4) Sample detection: The pretreated guar gum rupture fluid sample was subjected to fluorescence spectroscopy and viscosity detection to obtain the characteristic fluorescence peak intensity (F) and viscosity (η) of the pretreated guar gum rupture fluid sample; the water used in the actual guar gum fracturing fluid corresponding to the pretreated guar gum rupture fluid sample was subjected to fluorescence spectroscopy and viscosity detection to obtain the characteristic fluorescence peak intensity and viscosity of water, and used as a blank; the characteristic fluorescence peak intensity (ΔF) and viscosity (Δη) of the pretreated guar gum rupture fluid sample after subtracting the blank were obtained from the characteristic fluorescence peak intensity and viscosity of the pretreated guar gum rupture fluid sample after subtracting the blank, and substituted into the standard curve equation of the residual guar gum rupture fluid to obtain the residual guar gum content (C) in the guar gum rupture fluid sample to be measured.

[0040] The characteristic fluorescence peak positions detected by the fluorescence spectroscopy are excitation wavelength Ex / emission wavelength / Em = 260~280nm / 320~340nm.

[0041] Example 1

[0042] This embodiment provides a method for determining the residual guar gum content in guar gum breaking solution, which includes the following steps:

[0043] (1) Sample pretreatment: calcium alginate-MgO composite material and calcium alginate-bentonite composite material were mixed at a weight ratio of 1.5:1 to obtain calcium alginate-based composite material filler, and then filled into a filter column. The guar gum rupture liquid sample to be tested was filtered using a filter column filled with calcium alginate-based composite material filler. The volume ratio of filler to guar gum rupture liquid sample was 1:10 to obtain the pretreated guar gum rupture liquid sample.

[0044] The calcium alginate-MgO composite material is prepared by the following steps: 2.5% sodium alginate, 0.8% calcium chloride, 3% magnesium oxide, and the balance water are mixed by weight percentage to obtain a calcium alginate-MgO composite material gel. The calcium alginate-MgO composite material gel is dried at 20–50°C to constant weight to obtain the calcium alginate-MgO composite material. The particle size of the calcium alginate-MgO composite material is 1–1.2 mm.

[0045] The calcium alginate-bentonite composite material is prepared by the following steps: 3% sodium alginate, 2% calcium chloride, 1.8% bentonite, and the balance water are mixed by weight percentage to obtain a calcium alginate-bentonite composite material gel. The calcium alginate-bentonite composite material gel is dried at 20–50°C to constant weight to obtain the calcium alginate-bentonite composite material. The particle size of the calcium alginate-bentonite composite material is 1.2–1.4 mm.

[0046] Optical images of the calcium alginate-MgO composite material and the calcium alginate-bentonite composite material are shown below. Figure 2 As shown;

[0047] The petroleum and suspended solids contents of the pretreated guar gum breaking solution sample and the untreated guar gum breaking solution sample to be tested are shown in Table 1.

[0048] Table 1

[0049]

[0050] (2) Prepare a series of guar gum breaking solutions with different guar gum contents:

[0051] According to the formulation of the actual guar gum fracturing fluid corresponding to the guar gum rupture fluid sample to be tested, guar gum standard was used to prepare the guar gum fracturing fluid: under high-speed stirring conditions of 1500-3000 r / min, hydroxypropyl guar gum powder (i.e., guar gum standard) used in the oilfield was slowly added to pure water to prepare a 0.2-0.5% transparent guar gum solution; after complete dissolution, a pH adjuster was added to adjust the system to alkaline, and after standing for 5-15 minutes, clay stabilizer was added in proportion. Bactericide, drainage aid, demulsifier, and breaker are continuously stirred for 5-15 minutes to form a homogeneous solution. After stirring, the solution is allowed to stand for 20-40 minutes to allow the viscosity to stabilize, resulting in a guar gum base solution. The guar gum base solution is then stirred with a glass rod while adding an organoboron crosslinking agent at a crosslinking ratio of 100:0.4. The mixture is stirred until a uniform, solid gel that can be picked up is formed, preventing the formation of air bubbles. The reaction is stopped when the vortex disappears and the liquid surface bulges, from the time the crosslinking agent is added until the vortex disappears. This results in a guar gum gel fracturing fluid.

[0052] Preparation of residual guar gum breaker solution: The guar gum gel fracturing fluid was placed in a constant temperature water bath and reacted in a water bath at 80-100℃ for 0.5-12h to break the gel, thereby obtaining the guar gum breaker solution. The viscosity of the guar gum breaker solution was ≤12mpa·s. The reaction conditions, the amount of breaker added to the guar gum gel fracturing fluid, and the viscosity of the guar gum breaker solution are shown in Table 2.

[0053] Table 2. Conditions for Guar Gum Breaking

[0054]

[0055]

[0056] In this embodiment, the guar gum breaking solution (No. 6) with a viscosity of 2.5 mpa·s in Table 2 above was used. After centrifugation to remove the residue, the stable liquid phase was taken to obtain the breaking solution of residual guar gum.

[0057] Different amounts of hydroxypropyl guar gum powder (i.e., guar gum standard) used in the oilfield were weighed out, and the guar gum breaking solution with the residual guar gum was used as a solvent to prepare a series of guar gum breaking solution samples with different guar gum contents. The series of guar gum breaking solution samples with different guar gum contents included a series of samples with guar gum standard contents of 100 mg / L, 500 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 2500 mg / L, 3000 mg / L, 3500 mg / L, and 4000 mg / L.

[0058] (3) Constructing a standard curve equation: Fluorescence spectroscopy and viscosity measurements were performed on the series of samples of guar gum breaking solution with residual guar gum and guar gum breaking solution with different guar gum contents, respectively. The three-dimensional fluorescence spectra of the series of samples of guar gum breaking solution with different guar gum contents are shown below. Figure 3a , Figure 3b , Figure 3c , Figure 3d , Figure 3e , Figure 3f , Figure 3g , Figure 3h , Figure 3i As shown, the characteristic fluorescence peak positions are excitation wavelength Ex / emission wavelength Em = 275nm / 332nm, and their characteristic fluorescence peak intensities (F) and viscosities (η) are obtained. Using the characteristic fluorescence peak intensities and viscosities of the residual guar gum breaking solution (i.e., the guar gum standard content is 0 mg / L) as blanks, the characteristic fluorescence peak intensities and viscosities of the guar gum breaking solution series samples with different guar gum contents are subtracted from the blanks to obtain the characteristic fluorescence peak intensities (ΔF) and viscosities (Δη) of the guar gum breaking solution series samples with different guar gum contents after blank subtraction. Using the content (C) of the guar gum standard in the guar gum breaking solution series samples with different guar gum contents as the response value, and using the characteristic fluorescence peak intensities (ΔF) and viscosities (Δη) of the guar gum breaking solution series samples with different guar gum contents after blank subtraction as variables, regression analysis is performed, and the standard curve equation for the residual guar gum is obtained as: C = -14.1 + 0.11 × ΔF + 84.3 × Δη, with a correction coefficient R. 2 =0.99;

[0059] (4) Sample testing: The pretreated guar gum fracturing fluid sample was subjected to fluorescence spectroscopy and viscosity testing. The characteristic fluorescence peak intensity (F) at Ex / Em = 275nm / 332nm was 18002au, and the viscosity (η) was 5.15mpa·s. The pure water used in the actual guar gum fracturing fluid corresponding to the pretreated guar gum fracturing fluid sample was subjected to fluorescence spectroscopy and viscosity testing. The characteristic fluorescence peak intensity of pure water at Ex / Em = 275nm / 332nm was 900a. u, with a viscosity of 1.1 mPa·s, was used as a blank. After subtracting the blank from the characteristic fluorescence peak intensity and viscosity of the pretreated guar gum lysate sample, the characteristic fluorescence peak intensity (ΔF) and viscosity (Δη) of the pretreated guar gum lysate sample after subtracting the blank were obtained. These values ​​were then substituted into the standard curve equation of the residual guar gum lysate C = -14.1 + 0.11 × ΔF + 84.3 × Δη to obtain the residual guar gum content (C) in the guar gum lysate sample to be tested, which was found to be 2208 mg / L.

[0060] The repeatability and accuracy of the measurement method in this embodiment are described below.

[0061] The pretreated guar gum lysate samples described in this embodiment were diluted with different amounts of pure water, and the guar gum content was calculated based on the dilution volume as the actual value. Then, the samples diluted with different amounts of pure water were subjected to fluorescence spectroscopy and viscosity measurements using the method of this embodiment to obtain the characteristic fluorescence peak intensity and viscosity. These values ​​were then substituted into the standard curve equation to obtain the calculated guar gum content. The calculated value was compared with the actual value to obtain accuracy data, as shown in Table 3.

[0062] Table 3

[0063]

[0064] As can be seen from Table 3, the measurement method in this embodiment has high accuracy.

[0065] Five replicate experiments were conducted on the samples diluted 20% in Table 3. The calculated concentration values ​​were 431.5, 432.3, 434.2, 432.5, and 435.3, with a deviation of 1.38 and an average value of 433.16. The ratio of deviation to average value was 0.3%. It can be seen that the determination method in this embodiment has good repeatability.

[0066] Comparative Example 1

[0067] To compare the pretreatment method of this invention, conventional centrifugation was used to pretreat the guar gum lysate sample. A standard guar gum concentration of 200 mg / L was prepared, and oil and diatomaceous earth were added to obtain a simulated waste liquid containing oil and suspended solids, which was used as the guar gum lysate sample to be tested. The contents of petroleum and suspended solids were 195 mg / L and 150 mg / L, respectively. The properties of the samples after pretreatment by the two methods are shown in Table 4. The conventional centrifugation method involved centrifuging the guar gum lysate sample to be tested. The upper layer was an oil-like substance, the bottom layer was a solid residue, and the stable liquid phase in the middle was taken as the pretreated guar gum lysate sample.

[0068] This comparative example provides a method for determining the residual guar gum content in guar gum breaking solution. This method is essentially the same as that in Example 1, except that the pretreatment of the guar gum breaking solution sample to be tested is not performed using the method in Example 1, but rather using the conventional centrifugation method described above. The remaining steps are the same as in Example 1.

[0069] The residual guar gum content in this comparative example was 125, 100, 85, 60, and 75 mg / L. Due to interference from coexisting contaminants, the accuracy and repeatability of fluorescence detection were poor. However, using the pretreatment method of this invention, the residual guar gum content was 201, 198, 200.5, 196.5, and 201.5 mg / L, with an accuracy range of -1.7% to 0.75%, a deviation-to-mean ratio of 0.96%, and good repeatability.

[0070] Table 4

[0071]

[0072] As can be seen from Example 1 and Comparative Example 1, the determination method of the present invention performs special pretreatment on the guar gum breaking liquid sample, which can remove oils, suspended matter, metal ion contaminants and other pollutants that affect the detection of residual guar gum in the sample, thereby reducing interference.

[0073] Comparative Example 2

[0074] Using the residual guar gum breaking solution from Example 1 as a solvent, a series of guar gum breaking solutions with different guar gum contents were prepared. The correlation values ​​between fluorescence intensity and viscosity are shown in Table 5.

[0075] Table 5

[0076]

[0077] To compare the bivariate fluorescence intensity and viscosity determination model of the present invention, the fluorescence intensity of the guar gum breaking solution series samples with different guar gum contents in Table 5 was used as a univariate to perform regression analysis and obtain the guar gum content determination model (i.e., the standard curve equation of residual guar gum), which is C = 30.9 + 0.2 × ΔF, with a correction coefficient R. 2 =0.96. Compared to the bivariate model for determining guar gum content based on fluorescence intensity and viscosity in Example 1, the correlation coefficient R0.96 2 It decreased from 0.99 to 0.96.

[0078] The concentration of sample 1 (10% dilution volume) in Table 3 was calculated using a univariate model and was 208.3 mg / L. Compared with the actual value of 220.8 mg / L, the accuracy was -5.7%, which is significantly different from the -1.22% in Example 1 of this invention.

Claims

1. A method for determining the residual guar gum content in guar gum breaking solution, comprising the following steps: (1) Sample pretreatment: The guar gum rupture liquid sample to be tested was filtered using a filter column filled with calcium alginate-based composite material to obtain the pretreated guar gum rupture liquid sample. (2) Preparation of a series of guar gum breaking fluid samples with different guar gum contents: According to the actual guar gum fracturing fluid formula corresponding to the guar gum breaking fluid sample to be tested, guar gum standard is used to prepare guar gum fracturing fluid with added breaking agent, and the fluid is reacted at a suitable temperature for a period of time to break the gum, so as to obtain guar gum breaking fluid; after solid-liquid separation of the guar gum breaking fluid, the liquid phase is taken to obtain the breaking fluid with residual guar gum; using different amounts of guar gum standard, and using the breaking fluid with residual guar gum as solvent, a series of guar gum breaking fluid samples with different guar gum contents are prepared. (3) Constructing a standard curve equation: Fluorescence spectroscopy and viscosity detection were performed on the residual guar gum breaking solution and the series of guar gum breaking solutions with different guar gum contents, respectively, to obtain their characteristic fluorescence peak intensity and viscosity; using the characteristic fluorescence peak intensity and viscosity of the residual guar gum breaking solution as a blank, the characteristic fluorescence peak intensity and viscosity of the series of guar gum breaking solutions with different guar gum contents after deducting the blank were obtained; using the content of guar gum standard in the series of guar gum breaking solutions with different guar gum contents as the response value, and using the characteristic fluorescence peak intensity and viscosity of the series of guar gum breaking solutions with different guar gum contents after deducting the blank as variables, regression analysis was performed to obtain the standard curve equation of the residual guar gum; (4) Sample detection: The pretreated guar gum rupture fluid sample was subjected to fluorescence spectroscopy and viscosity detection to obtain the characteristic fluorescence peak intensity and viscosity of the pretreated guar gum rupture fluid sample; the water used in the actual guar gum fracturing fluid corresponding to the pretreated guar gum rupture fluid sample was subjected to fluorescence spectroscopy and viscosity detection to obtain the characteristic fluorescence peak intensity and viscosity of the water, and used as a blank; the characteristic fluorescence peak intensity and viscosity of the pretreated guar gum rupture fluid sample after deducting the blank were obtained by subtracting the blank from the characteristic fluorescence peak intensity and viscosity, and substituted into the standard curve equation of the residual guar gum to obtain the content of residual guar gum in the guar gum rupture fluid sample to be measured. The standard curve equation for the residual guar gum is a polynomial equation based on the characteristic fluorescence peak intensity and viscosity. The standard curve equation for the residual guar gum is: C = -14.1 + 0.11 × ΔF + 84.3 × Δη, where C is the content of guar gum, ΔF is the characteristic fluorescence peak intensity of the sample after subtracting the blank, and Δη is the viscosity of the sample after subtracting the blank.

2. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 1, wherein, In step (1), the calcium alginate-based composite filler includes calcium alginate-MgO composite material and calcium alginate-bentonite composite material.

3. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 2, wherein, The calcium alginate-MgO composite material is prepared by the following steps: 0.5-3% sodium alginate, 0.2-2% calcium chloride, 1-5% magnesium oxide and the balance water are mixed by weight percentage to obtain calcium alginate-MgO composite material gel. The calcium alginate-MgO composite material gel is dried at 20-50 °C to constant weight to obtain the calcium alginate-MgO composite material.

4. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 2 or 3, wherein, The particle size of the calcium alginate-MgO composite material is 0.5~2mm.

5. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 2, wherein, The calcium alginate-bentonite composite material is prepared by the following steps: 0.5-3% sodium alginate, 0.2-2% calcium chloride, 1-5% bentonite, and the balance water are mixed by weight percentage to obtain a calcium alginate-bentonite composite material gel. The calcium alginate-bentonite composite material gel is dried at 20-50 °C to constant weight to obtain the calcium alginate-bentonite composite material.

6. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 2 or 5, wherein, The particle size of the calcium alginate-bentonite composite material is 0.5~2mm.

7. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 2, wherein, The weight ratio of the calcium alginate-MgO composite material to the calcium alginate-bentonite composite material is 1:5 to 4:

1.

8. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 1, wherein, In step (1), when filtering the guar gum rupture sample, the volume ratio of the filler to the guar gum rupture sample is 1:2 to 1:

20.

9. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 1, wherein, In step (1), the petroleum content in the pretreated guar gum breaking solution sample is less than 15 mg / L and the suspended matter content is less than 30 mg / L.

10. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 1, wherein, In step (2), based on the total weight of the guar gum fracturing fluid with added breaker as 100%, the amount of added breaker is 0.005%~1%, the reaction temperature for breakering is 80~100℃, and the reaction time is 0.5~12h.

11. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 1, wherein, In step (2), the viscosity of the guar gum breaking solution is ≤12 mpa·s.

12. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 1, wherein, In step (2), the content of guar gum standard in the series of guar gum breaking solutions with different guar gum contents is 100~4000 mg / L.

13. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 12, wherein, In step (2), the series of guar gum breaking solutions with different guar gum contents includes a series of samples with guar gum standard contents of 100 mg / L, 500 mg / L, 1000 mg / L, 1500 mg / L, 2000 mg / L, 2500 mg / L, 3000 mg / L, 3500 mg / L, and 4000 mg / L.

14. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 1, wherein, In steps (3) and (4), the characteristic fluorescence peak position detected by the fluorescence spectrum is excitation wavelength Ex / emission wavelength Em = 260~280nm / 320~340nm.

15. The method for determining the residual guar gum content in the guar gum breaking solution according to claim 1, wherein, In step (3), the correction coefficient R of the standard curve equation of the residual guar gum is... 2 =0.99.

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