A comprehensive evaluation method for the gel breaking degree of gel fracturing fluid

Abstract

The present invention belongs to the technical field of oil and gas field development, and specifically relates to a comprehensive evaluation method for the degree of gel breaking of gel fracturing fluid. The present invention establishes a comprehensive evaluation method for the degree of gel breaking of gel fracturing fluid based on the quality of the residual colloid or the quality of the gel breaking clear liquid separated after gel breaking, combined with the viscosity of the gel breaking clear liquid. P The calculation model is used to quantify the degree of gel breaking. The present invention establishes the integrity of the gel fracturing fluid after gel breaking at different gel breaking stages by weighted calculation of the residual colloid mass or the gel breaking clear liquid mass and the gel breaking clear liquid viscosity. P The calculation model quantifies the degree of gel breaking, solving the problem that the traditional single viscosity index cannot be measured or measurement interference occurs; it also solves the problem that the amount of solid residue after drying is very small, which is extremely inconvenient to weigh and easily causes large errors; the present invention can adapt to the characteristic differences at different gel breaking stages, significantly improves the reliability of the evaluation, and provides data support for optimizing the performance of controlled-release breakers.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and particularly relates to a comprehensive evaluation method for the gel breaking degree of gel fracturing fluid. Background Art

[0002] Incomplete gel fracturing fluid breaking can cause numerous problems, such as residual debris clogging fracture pores and proppant packs, significantly reducing fracture permeability; directly impacting fracturing fluid viscosity, with high-viscosity residual fluid retention exacerbating water lock damage. Evaluating the degree of gel fracturing fluid breaking is a key step in balancing reservoir protection, project efficiency, and economic and environmental performance, directly impacting production enhancement and overall cost control. By evaluating the breaking effect, we can ensure that the breaking time and residual fluid viscosity meet operational requirements, thereby minimizing reservoir damage and improving flowback efficiency. Furthermore, evaluating the breaking effect can optimize the breaker formulation and dosage to suit different operating conditions. For example, hydrogen sulfide-containing formations require simultaneous breaking and H2S neutralization to ensure safe and environmentally friendly operation. Furthermore, gel breaking evaluation methods promote the synergistic effect of plugging agents and fracturing fluid systems, improving plugging efficiency and self-breaking flowback capabilities, providing technical support for efficient and cost-effective operations in complex formations.

[0003] At present, traditional gel breaking evaluation usually relies on the measurement of the viscosity of the gel breaking liquid and the mass of the solid residue after drying, which has the following defects: (1) When the residual colloid is excessive, the amount of gel breaking liquid is insufficient and the viscosity measurement cannot be completed; (2) The residual colloid adheres to the rotor of the rotating viscometer, resulting in a "climbing rod effect" and interfering with the accuracy of the viscosity test; (3) When performing traditional gel breaking evaluation in the laboratory, the amount of solid residue after drying is very small (measured in mg), which is extremely inconvenient to weigh and can easily cause large errors. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention proposes a comprehensive evaluation method for the degree of gel breaking of gel fracturing fluid. The present invention establishes a comprehensive evaluation method for the integrity of gel fracturing fluid after gel breaking based on the quality of residual colloid or gel breaking clear liquid separated after gel breaking and the viscosity of gel breaking clear liquid. P A computational model was developed to quantify the degree of gel breaking.

[0005] Based on the quality of the clear liquid obtained after gel breaking, combined with the viscosity and integrity of the clear liquid P The calculation model is:

[0006] ;

[0007] Where: P ——Integrity of 200g gel fracturing fluid after being coated with resin and broken, 0≤ P ≤1;

[0008] m L ——mass of gel-breaking supernatant, g;

[0009] n ——Viscosity of the gel-breaking supernatant, mPa·s.

[0010] Based on the residual colloid mass obtained after separation and the viscosity of the clear solution after gel breaking, P The calculation model is:

[0011] ;

[0012] Where: P ——Integrity of 200g gel fracturing fluid after being coated with resin and broken, 0≤ P ≤1;

[0013] m S ——Residual colloid mass, g;

[0014] n ——Viscosity of the gel-breaking supernatant, mPa·s.

[0015] The specific steps are:

[0016] (1) Separate the solid and liquid of the mixed liquid after gel breaking to obtain residual colloid and gel breaking clear liquid;

[0017] (2) Weigh the residual colloid mass m S And the mass of the gel-breaking clear liquid m L ;

[0018] (3) According to m L or m S Interval selection corresponds to P The value calculation model outputs the quantitative index of gel breaking degree.

[0019] described P The integrity of 200g of gel fracturing fluid after being coated with resin and broken. P The smaller the value, the higher the degree of hydration and gel breaking.

[0020] According to the "SY / T 7627-2021 Technical Requirements for Water-Based Fracturing Fluids" and "SY / T 6376-2008 General Technical Conditions for Fracturing Fluids", the viscosity of water-based gel fracturing fluids after gel breaking is required to be less than 5 mPa·s, and the residual colloid and solid residue filtered out after drying is required to be less than 600 mg·L -1 For 200 g of gel fracturing fluid prepared with 0.5% thickener solution, 600 mg·L -1 The standard for the residue after drying can be converted to 24 g of residual gel mass. That is, when the viscosity of 200 g of gel fracturing fluid is less than 5 mPa·s and the mass of the separated residual gel is less than 24 g, it is considered to have met the gel breaking standard. The gel integrity at this time is calculated by formula 1-2 Pis 0.106. Therefore, P 0=0.1 is used as the basis for judging whether the gel fracturing fluid is completely broken when the gel breaker is selected. P ≤0.1, to meet the gel breaking standard.

[0021] The viscosity of the gel-breaking clear liquid is the viscosity value measured by a digital viscometer with a No. 1 rotor rotating at a speed of 60 r / min.

[0022] In step (1), a filter is used for solid-liquid separation, and the filter pore size is ≤1mm.

[0023] Compared with the prior art, the present invention is based on the residual colloid mass (m S ) or the mass of the gel-breaking supernatant (m L ) and the viscosity of the gel-breaking supernatant ( n ) is calculated by weighted calculation to establish the integrity of the frozen fracturing fluid after gel breaking at different gel breaking stages. P The calculation model quantifies the degree of gel breaking, solving the problem that the traditional single viscosity index cannot be measured or measurement interference occurs; it also solves the problem that the amount of solid residue after drying is very small, which is extremely inconvenient to weigh and easily causes large errors; the present invention can adapt to the characteristic differences at different gel breaking stages, significantly improves the reliability of the evaluation, and provides data support for optimizing the performance of controlled-release breakers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 For gel integrity P 3D network diagram of residual colloid mass and viscosity of broken gel supernatant;

[0025] Figure 2 The gel-breaking effect of different oxidative breakers (ammonium persulfate and potassium persulfate) on boron cross-linked guar jelly fracturing fluid was studied.

[0026] Figure 3 For gel integrity P Curve of value changing with breaker dosage;

[0027] Figure 4 The gel-breaking effect of different acid breaker dosages on boron cross-linked guar jelly fracturing fluid;

[0028] Figure 5 For gel integrity P The value changes with the amount of acid breaker added. DETAILED DESCRIPTION

[0029] Example 1

[0030] In order to establish the integrity of the gel fracturing fluid after gel breaking P A large number of experiments were first conducted to systematically study the residual colloid mass mS and viscosity of the supernatant n Completeness P During the experiment, the residual colloid mass m after gel breaking under different conditions was accurately measured. S and viscosity of the supernatant n and through observation and evaluation, the corresponding completeness is determined P After collecting a large amount of experimental data, the data were analyzed and summarized in detail. The experiment found that P With m S and n There is an obvious piecewise linear relationship between them. Specifically, when m S In different ranges, P The changing pattern of is also different. Based on these observations, the present invention proposes a piecewise linear mathematical model to describe this relationship. The inventor found that when 0≤m S ≤50, mainly affected by m S and n The joint influence of S When ≤150, it is mainly affected by m S The influence of S When ≤200, it is still mainly affected by m S The influence of m is not significant, but the trend of change has changed. Through further mathematical analysis and parameter estimation, the coefficients and parameters in the model are finally determined, and the complete calculation model is obtained, namely formula (1-2). S +m L =200g, and we get formula (1-1).

[0031] To verify the accuracy and applicability of the model, the model was applied to experimental data that were not involved in the modeling, and further experimental verification was carried out.

[0032] Example 2

[0033] Experiments were conducted on boron-crosslinked guar jelly fracturing fluid using various breakers to identify those with excellent breaking performance and suitability for controlled-release applications. The breakers selected for optimization included oxidizing breakers (APS (ammonium persulfate), KPS (potassium persulfate)), acid breakers (oxalic acid, citric acid, AH (organic sulfonic acid), ML (organic carboxylic acid), and ammonium bisulfate), and chelating breakers (sodium citrate, sodium succinate, sodium gluconate, EDTA-2Na, sodium tartrate, sodium pyrophosphate, and sodium dihydrogen phosphate).

[0034] The gel breaking effects of the above breakers were evaluated through a systematic and quantitative experimental scheme:

[0035] (1) Several 200 g portions of frozen gel fracturing fluid were placed in a constant temperature water bath at 70 °C and broken for 2 h with different amounts of breaker (0.25-1.5 g). The broken fracturing fluid system was then subjected to solid-liquid separation to obtain the broken gel clear liquid and residual colloid.

[0036] (2) The viscosity of the supernatant was measured using an NDJ-9S digital viscometer, and the supernatant and residual colloid were weighed using an analytical balance;

[0037] (3) According to the mass of the clear liquid m L Or residual colloid mass m S Interval selection corresponds to P The value calculation model outputs a quantitative index of gel breaking degree to evaluate the gel breaking effect of the gel breaker on the frozen gel fracturing fluid. For example:

[0038] When m S =43g, n =20mPa·s, then P =0.2*43 / 50+0.2*20 / 100=0.212;

[0039] When m S =118g, then P =0.4+0.4*(118-50) / 100=0.672;

[0040] When m S =176g, then P =0.8+0.2*(176-150) / 50=0.864;

[0041] According to the above measurement and calculation results, the Figure 2-5 .

[0042] Figure 2 The viscosity of the clear solution and the residual colloid mass of boron-crosslinked guar jelly after breaking in a 70 ℃ water bath for 2 h with different amounts of oxidizing breakers (ammonium persulfate and potassium persulfate) were analyzed.

[0043] Figure 3 Is the integrity of the gel P The curve of the value changing with the amount of gel breaker. It can be seen that ammonium persulfate and potassium persulfate have a very good gel breaking effect on boron cross-linked guar gum jelly. The addition of 0.25g can reduce the integrity of 200g boron cross-linked guar gum jelly to P 0 or less.

[0044] Figure 3 The results directly show that the breaking integrity of boron cross-linked guar jelly fracturing fluid changes with the addition of oxidizing breaker. Figure 2Only the viscosity of the broken gel supernatant and the mass of the residual colloid are shown. The completeness of gel breaking is a more direct indicator of the integrity of the colloid structure and can more clearly illustrate the impact of gel breaking on the colloid structure. Figure 3 A unified breaking integrity index was used ( P ), so that the effects of different breakers (KPS and APS) can be directly compared, and Figure 2 The viscosity of the gel-breaking supernatant and the quality of the residual colloid are two different indicators, and the comparison is not direct enough. Figure 3 The completeness threshold is clearly marked in P 0=0.1), it can be intuitively judged whether the colloid has achieved the ideal breaking effect under different addition amounts. Figure 2 There is no similar threshold in . However, whether Figure 2 The viscosity of the breaking liquid and the quality of the residual glue are still Figure 3 The breaking integrity of the gel shows that with the increase of the amount of gel breaker, the breaking effect of the colloid gradually increases and the breaking integrity gradually decreases. Figure 2 and Figure 3 It can be seen that the effect comparison trends of KPS and APS are consistent. KPS can achieve better gel breaking effect at a lower dosage, while APS requires a higher dosage to achieve similar effect.

[0045] Figure 4 The viscosity and residual gel mass of boron-crosslinked guar jelly after 2 hours of gel breaking in a 70°C water bath with different acid breakers (oxalic acid, citric acid, AH, ML, ammonium bisulfate, etc.) were measured. The residual gel mass of guar jelly after treatment with AH, oxalic acid, citric acid, and ammonium bisulfate was lower, while the viscosity of the gel breaking solution after treatment with citric acid and oxalic acid was higher.

[0046] Figure 5 Is the integrity of the gel ψ The value changes with the amount of acid breaker. It can be seen that there are great differences in the breaking effect of different acid breakers on guar gum jelly. Among them, AH and ammonium bisulfate have the best breaking effect. Only 0.5 g of the addition can reduce the integrity of 200 g guar gum jelly to P 0 or less.

[0047] Figure 5 and Figure 4 Both indicate that the breaking effect will gradually increase with the increase of the amount of breaker added, and both show the difference in effect between different breakers. For example, AH and ammonium bisulfate have better breaking effects than other breakers. Figure 5 and Figure 4 compared to, Figure 5 Provides more comprehensive and intuitive information. Figure 5The effects of different acid breakers (oxalic acid, citric acid, AH, ML, ammonium bisulfate and AH+ML) on the breaking integrity of boron cross-linked guar jelly were demonstrated. Figure 4 The effects of different breakers on the viscosity of the breaking liquid and the quality of the residual colloid are respectively demonstrated. Figure 5 The advantage of is that it can directly reflect the effect of the breaker on the integrity of the gel breaking. Figure 4 It is necessary to indirectly infer the breaking effect through the changes in the viscosity of the breaking liquid and the mass of the residual colloid. Figure 5 It can also more intuitively compare the differences in the effects of different breakers. Figure 4 You need to look at the graphs for each breaker separately for comparison.

Claims

1. A comprehensive evaluation method for the gel breaking degree of gel fracturing fluid, characterized in that: The integrity of the gel fracturing fluid after gel breaking is established based on the residual colloid mass or the quality of the gel breaking clear liquid separated after gel breaking, combined with the viscosity of the gel breaking clear liquid. Ψ The calculation model is used to quantify the degree of gel breaking; Based on the quality of the clear liquid obtained after gel breaking, combined with the viscosity and integrity of the clear liquid Ψ The calculation model is: ； Based on the residual colloid mass obtained after separation, combined with the viscosity of the clear liquid after gel breaking, the integrity Ψ The calculation model is: ； Where: Ψ ——Integrity of 200g gel fracturing fluid after being coated with resin and broken, 0≤ Ψ ≤1; m L ——mass of gel-breaking supernatant, g; m S ——Residual colloid mass, g; ν ——Viscosity of the gel-breaking supernatant, mPa·s.

2. The comprehensive evaluation method for gel breaking degree of gel fracturing fluid according to claim 1, characterized in that: Ψ ≤0.1, to meet the gel breaking standard.

3. The comprehensive evaluation method for gel breaking degree of gel fracturing fluid according to claim 1, characterized in that: The specific steps are: (1) Separate the solid and liquid of the mixed liquid after gel breaking to obtain residual colloid and gel breaking clear liquid; (2) Weigh the residual colloid mass m S And the mass of the gel-breaking clear liquid m L ; (3) According to m L or m S Interval selection corresponds to Ψ The value calculation model outputs the quantitative index of gel breaking degree.

4. The comprehensive evaluation method for gel breaking degree of gel fracturing fluid according to claim 1, characterized in that: The viscosity of the gel-breaking clear liquid is the viscosity value measured by a digital viscometer with a No. 1 rotor rotating at a speed of 60 r / min.

5. The comprehensive evaluation method for gel breaking degree of gel fracturing fluid according to claim 3, characterized in that: In step (1), a filter is used for solid-liquid separation, and the filter pore size is ≤1mm.

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