A shale capillary suction time (CST) ratio calculation method

Abstract

A shale capillary absorption time CST ratio calculation method belongs to the technical field of shale oil and gas reservoir reconstruction and fracturing effect evaluation, and comprises the following steps: step 1: a capillary absorption time determination experiment is carried out on a shale sample, and a capillary absorption time CST ratio is calculated; step 2: a total organic carbon determination experiment is carried out on the shale sample, and the TOC content of the shale sample is obtained; step 3: a mineral analysis experiment is carried out on the shale sample, and the quartz and clay mineral content of the sample is obtained; step 4: taking the capillary absorption time as the dependent variable, taking the TOC content, the quartz and clay mineral content as the independent variable, adopting a multiple linear regression method, a shale capillary absorption time CST ratio calculation model is established. The present application has the advantages of simple method, economic practicality, scientific effectiveness, and the like by optimizing a plurality of capillary absorption time sensitive parameters, adopting a multiple linear regression method, and establishing a shale CST ratio calculation model, thereby guiding shale anti-swelling agent types and fracturing fluid proportioning schemes.

Description

Technical Field

[0001] The present invention belongs to the technical field of shale oil and gas reservoir transformation and fracturing effect evaluation, and particularly relates to a shale capillary absorption time (CST) ratio calculation method. Background Art

[0002] my country's shale oil and gas resources hold enormous potential. The low permeability of shale reservoirs makes it difficult to form an effective seepage system, resulting in low natural production capacity and difficulty in commercial development. Large-scale hydraulic fracturing is required to increase production and meet economic targets.

[0003] Shale reservoirs contain high levels of clay minerals. During large-scale hydraulic fracturing, the fracturing fluid undergoes a series of hydration reactions with the clay minerals, causing them to absorb water and swell. This leads to pore blockage, poor connectivity, and reduced physical properties in the shale reservoir, ultimately compromising development effectiveness. Therefore, during hydraulic fracturing, anti-swelling agents are added to the fracturing fluid to mitigate the hydration and swelling of clay minerals in the shale reservoir, reduce reservoir damage, and improve shale oil and gas recovery. Because the types and content of clay minerals in shale reservoirs vary from region to region, the appropriate anti-swelling agent type also varies. To select the most suitable anti-swelling agent for the target area, it is necessary to study the effectiveness of different anti-swelling agents and formulate appropriate fracturing fluids to ensure fracturing effectiveness and increase shale oil and gas production.

[0004] Capillary suction time (CST) is an instrumented measurement of the time it takes for various test fluids to permeate a specified distance through specialized filter paper. The CST ratio can be used to determine the degree of colloidal dispersion of shale in water. A smaller CST ratio indicates a greater effectiveness of the anti-swelling agent in inhibiting shale swelling. Minimal CST ratios indicate minimal shale hydration, colloidal dispersion, and shale activity. Calculating the CST ratio can provide scientific guidance for selecting fracturing fluids for shale gas development.

[0005] Chen Jia (Chen Jia. Preliminary study on the application of CST technology in the study of shale colloid dispersion [J]. Unconventional Oil and Gas, 2017, 4(1):4.) conducted a study on the dispersion of shale colloids. The results showed that samples with low clay mineral content had low dispersion, and 2% KCl solution had a better inhibitory effect on the dispersion of samples with high clay mineral content than distilled water. Sun Xiaorui (Sun Xiaorui, Rong Kesheng, Xiang Dongmei, et al. Study on hydration characteristics and classification of mud shale in the Mahu Sag, Junggar Basin [J]. Science, Technology and Engineering, 2017, 17(1):5.) conducted a whole-rock mineral composition and clay mineral analysis on rock samples from the Mahu Sag. Based on the correlation analysis, the hydration characteristics of the mud shale in this block were predicted, and the predicted hydration characteristics of the mud shale were verified through hydration expansion and hydration dispersion experiments; the application publication number is CN 114839101 A's invention patent provides a method for evaluating the effect of anti-swelling agents on the inhibition of hydration expansion of shale reservoirs. This method conducts anti-swelling agent solution displacement experiments on four shale samples with different clay mineral contents, and determines the amount of anti-swelling agent by measuring the changes in the physical properties of the shale samples before and after displacement.

[0006] The above studies have focused on quantitatively describing the colloidal dispersion of shale in water and selecting the dosage of anti-swelling agents. They have not involved the quantitative calculation of the CST ratio, which, in turn, cannot guide the selection of fracturing fluids for target shale development areas. Therefore, it is necessary to conduct research on CST ratio calculation methods to determine the optimal anti-swelling agent type and fracturing fluid ratio. Summary of the Invention

[0007] In order to solve the above problems, the present invention proposes a method for calculating the shale capillary absorption time (CST) ratio, comprising the following steps:

[0008] Step 1: Conduct a capillary absorption time measurement experiment on the shale sample and calculate the capillary absorption time CST ratio;

[0009] Step 2: Conduct a total organic carbon determination experiment on the shale sample to obtain the TOC content of the shale sample;

[0010] Step 3: Conduct mineral analysis experiments on shale samples to obtain the quartz and clay mineral content of the samples;

[0011] Step 4: Using capillary absorption time as the dependent variable and TOC content, quartz and clay mineral content as independent variables, a multivariate linear regression method was used to establish a calculation model for the capillary absorption time (CST) ratio of shale.

[0012] Furthermore, in step 1, a capillary absorption time meter is used to measure the CST ratio, where the CST ratio is the time required for a slurry prepared by various test solutions and shale powder to penetrate a special filter paper.

[0013] Furthermore, in step 1, the shale sample needs to be pretreated before conducting the capillary absorption time measurement experiment, including grinding, cleaning and drying the sample.

[0014] Furthermore, in step 1, the process of pretreatment of the shale sample is as follows: first, the shale sample is ground into 80-mesh powder, then the powdered shale sample is cleaned, and finally, the powdered shale sample is placed in a constant temperature drying oven for drying.

[0015] Furthermore, in step 1, the shale sample is ground using an agate mortar, the shale sample powder is washed using distilled water, the temperature of the constant temperature drying oven is 105° C., and the drying time is 24 hours.

[0016] Furthermore, in step 2, the shale sample needs to be pretreated before the TOC content determination experiment, and the process is as follows:

[0017] S21. Grind the shale sample into 100-mesh powder using an agate mortar;

[0018] S22, adding shale powder to dilute hydrochloric acid, reacting for 2 hours to completely remove carbonates and other inorganic minerals;

[0019] S23, rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it becomes neutral;

[0020] S24. Place the powdered shale sample in a constant temperature drying oven and dry it at 60°C for 24 hours.

[0021] Furthermore, in step 3, the sample needs to be pretreated before the mineral content determination experiment, and the process is as follows:

[0022] S31. Wash the shale sample with chloroform as the organic solvent and treat the sample until the fluorescence level is below level 4.

[0023] S32, drying the oil-washed shale sample in a constant temperature drying oven at 50°C for 24 hours;

[0024] S33. Grind the oil-washed and dried shale sample into 100-mesh powder using an agate mortar.

[0025] Furthermore, in step 4, the validity of the established shale capillary absorption time CST ratio calculation model is verified, and the calculated CST ratio and the experimentally obtained CST ratio are correlated. When the correlation coefficient R 2 When the CST ratio is >0.95, the CST ratio calculation model is valid.

[0026] The present invention has the following beneficial effects: Traditional methods for calculating shale CST ratios rely on capillary absorption time measurements, which are time-consuming and labor-intensive. The method provided by the present invention optimizes multiple capillary absorption time-sensitive parameters and employs a multivariate linear regression method to establish a shale CST ratio calculation model. This method is simple, economical, practical, and scientifically effective. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : Relationship between total organic carbon TOC content and CST ratio;

[0028] Figure 2 : Relationship between quartz mineral content and CST ratio;

[0029] Figure 3 : Relationship between clay mineral content and CST ratio;

[0030] Figure 4 : Relationship between the CST ratio calculated by the model and the CST ratio measured using a capillary absorption time meter. DETAILED DESCRIPTION

[0031] To make the technical means and objectives of the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments. A method for calculating the shale capillary absorption time (CST) ratio includes the following steps:

[0032] Step 1: Conduct a capillary absorption time measurement experiment on the shale sample and calculate the capillary absorption time CST ratio;

[0033] Step 2: Conduct a total organic carbon determination experiment on the shale sample to obtain the TOC content of the shale sample;

[0034] Step 3: Conduct mineral analysis experiments on shale samples to obtain the quartz and clay mineral content of the samples;

[0035] Step 4: Using capillary absorption time as the dependent variable and TOC content, quartz and clay mineral content as independent variables, a multivariate linear regression method was used to establish a calculation model for the capillary absorption time (CST) ratio of shale.

[0036] Reference Figures 1 to 4 This specific embodiment adopts the following technical solution: a method for calculating the shale capillary absorption time CST ratio, comprising the following steps:

[0037] Step 1: Conduct capillary absorption time measurement experiments on shale samples and calculate the capillary absorption time CST ratio

[0038] Prepare core powder for capillary absorption time measurement experiments as follows:

[0039] The samples used in this study were taken from the natural core of Well Z301 in the Zigong area of ​​the Sichuan Basin;

[0040] The capillary absorption time tester model is Fenn CST-440;

[0041] After cleaning the surface of the natural core from Well Z301, the shale sample was ground into 80-mesh powder using an agate mortar;

[0042] The powdered shale samples were washed with distilled water to remove impurities;

[0043] The shale sample after impurities were removed was placed in a watch glass and dried in a constant temperature drying oven at 105° for 6 h;

[0044] Prepare the solution for the capillary absorption time (CST) ratio test as follows:

[0045] Preparation of slippery water with an anti-swelling agent; preparation of slippery water degradation solution A; preparation of slippery water without an anti-swelling agent but containing 3% KCl; preparation of slippery water degradation solution B;

[0046] The specific operating procedures of the capillary absorption time determination experiment are as follows:

[0047] 4 g of core powder was added to 100 mL of slickwater degradation solution A and stirred at 100 r / min for 30 min. While stirring, 5 mL of the mixed sample was taken with a syringe and quickly transferred into a cone placed on filter paper (with the rapid filter port of 1 cm in diameter facing downward). The experiment was started and the time (t A1 ).

[0048] Use slickwater degradation solution B and repeatedly read the CST instrument time (t B1 ).

[0049] Use a syringe to take 5 mL of the slickwater degradation solution A and quickly transfer it into a cone placed on filter paper (with the 1 cm diameter rapid filter port facing downwards). Start the experiment and read the time (t A2 ).

[0050] Use slickwater degradation solution B and repeatedly read the CST instrument time (t B2 ).

[0051] The CST ratio calculation formula is:

[0052]

[0053] Where:

[0054] t A1 ——Determination time of the mixture of degradation solution A and core powder, in seconds (s);

[0055] t A2 ——Degradation solution A measurement time, in seconds (s);

[0056] t B1 ——Determination time of the mixture of degradation solution B and core powder, in seconds (s);

[0057] t B2 ——Degradation liquid B measurement time, in seconds (s).

[0058] Step 2: Conduct a total organic carbon determination experiment on the shale sample to obtain the TOC content of the shale sample;

[0059] The TOC determination experimental instrument model is CS744 carbon and sulfur analyzer;

[0060] Before the TOC content determination experiment, the shale sample needs to be pretreated. The specific process is as follows:

[0061] (1) Grind the shale sample into 100-mesh powder using an agate mortar;

[0062] (2) Add shale powder to dilute hydrochloric acid for 2 hours to completely remove inorganic minerals such as carbonates;

[0063] (3) Rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it becomes neutral;

[0064] (4) The powdered shale sample was placed in a constant temperature drying oven and dried at 60°C for 24 hours.

[0065] like Figure 1 As shown in Figure 2, TOC content and CST ratio have a good negative correlation (R 2 =0.658), indicating that TOC content can participate in the CST ratio calculation model.

[0066] Step 3: Conduct mineral analysis experiments on shale samples to obtain the quartz and clay mineral content of the samples;

[0067] The experimental instrument for mineral content analysis is a D8DISCOVER X-ray diffractometer;

[0068] The sample needs to be pretreated before the mineral content determination experiment. The specific process is as follows:

[0069] (1) The shale samples were washed with chloroform as an organic solvent until the fluorescence level was below level 4;

[0070] (2) The shale samples after oil washing were dried in a constant temperature drying oven at 50°C for 24 hours;

[0071] (3) The shale sample after washing and drying was ground into 100 mesh powder using an agate mortar.

[0072] like Figure 2 As shown in Figure 2, the CST ratio has a good negative correlation with the quartz mineral content (R 2 =0.7303), indicating that the quartz mineral content can participate in the calculation model of organic pore porosity;

[0073] like Figure 3 As shown in Figure 2, the CST ratio has a good positive correlation with the clay mineral content (R 2 =0.7387), indicating that clay mineral content can be involved in the CST ratio calculation model.

[0074] Step 4: Using capillary absorption time as the dependent variable and TOC content, quartz and clay mineral content as independent variables, a multivariate linear regression method was used to establish a calculation model for the capillary absorption time (CST) ratio of shale.

[0075] The CST ratio calculation model can be expressed as follows:

[0076] CST ratio = -0.1634 × TOC - 0.089 × quartz content + 0.0217 × clay content + 0.3228

[0077] like Figure 4 Shown is a graph showing the relationship between the CST ratio calculated by the model and the CST ratio measured by the capillary absorption time meter;

[0078] There is a good correlation between the two (R 2 =0.9615), R 2 >0.95, indicating that the calculation model provided by the example of the present invention is effective.

[0079] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed in the present invention, who makes equivalent replacements or changes based on the technical solutions and concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for calculating the capillary absorption time (CST) ratio of shale, characterized in that: The steps include: Step 1: Conduct a capillary absorption time measurement experiment on the shale sample and calculate the capillary absorption time CST ratio; Slippery water with an anti-swelling agent added was prepared; Slippery water degradation solution A was prepared; Slippery water without an anti-swelling agent but containing 3% KCl was prepared; Slippery water degradation solution B was prepared; The CST ratio calculation formula is: Where: t A1 ——Determination time of the mixture of degradation solution A and core powder, in seconds (s); t A2 ——Degradation solution A measurement time, in seconds (s); t B1 ——Determination time of the mixture of degradation solution B and core powder, in seconds (s); t B2 ——Degradation solution B measurement time, in seconds (s); Step 2: Conduct a total organic carbon determination experiment on the shale sample to obtain the TOC content of the shale sample; Step 3: Conduct mineral analysis experiments on shale samples to obtain the quartz and clay mineral content of the samples; Step 4: Using capillary absorption time as the dependent variable and TOC content, quartz and clay mineral content as independent variables, a multivariate linear regression method was used to establish a shale capillary absorption time CST ratio calculation model. The CST ratio calculation model is expressed as follows: CST ratio = -0.1634 × TOC - 0.089 × quartz content + 0.0217 × clay content + 0.3228.

2. The method for calculating the shale capillary absorption time (CST) ratio according to claim 1, wherein: In step 1, a capillary absorption time measuring instrument is used to measure the CST ratio, where the CST ratio is the time required for slurries prepared by various test solutions and shale powder to penetrate a special filter paper.

3. The method for calculating the shale capillary absorption time (CST) ratio according to claim 1, wherein: In step 1, the shale sample needs to be pretreated before the capillary absorption time measurement experiment is carried out, including grinding, cleaning and drying the sample.

4. The method for calculating the shale capillary absorption time (CST) ratio according to claim 3, wherein: In step 1, the shale sample pretreatment process is as follows: first, the shale sample is ground into 80-mesh powder, then the powdered shale sample is cleaned, and finally, the powdered shale sample is placed in a constant temperature drying oven for drying.

5. The method for calculating the shale capillary absorption time (CST) ratio according to claim 4, wherein: In the step 1, the shale sample is ground using an agate mortar, the shale sample powder is washed using distilled water, the temperature of the constant temperature drying oven is 105° C., and the drying time is 24 hours.

6. The method for calculating the shale capillary absorption time (CST) ratio according to claim 1, wherein: In step 2, the shale sample needs to be pretreated before the TOC content determination experiment. The process is as follows: S21. Grind the shale sample into 100-mesh powder using an agate mortar; S22, adding shale powder to dilute hydrochloric acid, reacting for 2 hours to completely remove carbonates and other inorganic minerals; S23, rinse the shale sample treated with dilute hydrochloric acid with distilled water for 10 minutes until it becomes neutral; S24. Place the powdered shale sample in a constant temperature drying oven and dry it at 60°C for 24 hours.

7. The method for calculating the shale capillary absorption time (CST) ratio according to claim 1, wherein: In step 3, the sample needs to be pretreated before the mineral content determination experiment. The process is as follows: S31. Wash the shale sample with chloroform as the organic solvent and treat the sample until the fluorescence level is below level 4. S32, drying the oil-washed shale sample in a constant temperature drying oven at 50°C for 24 hours; S33. Grind the oil-washed and dried shale sample into 100-mesh powder using an agate mortar.

8. The method for calculating the shale capillary absorption time (CST) ratio according to claim 1, wherein: In step 4, the validity of the established shale capillary absorption time CST ratio calculation model is verified, and the calculated CST ratio and the experimentally obtained CST ratio are correlated. 2 When the CST ratio is >0.95, the CST ratio calculation model is valid.

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