Shale capillary absorption 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 transformation fracturing effect evaluation, and comprises the following steps: 1, carrying out a capillary absorption time determination experiment on a shale sample, and calculating a capillary absorption time CST ratio; 2, carrying out a total organic carbon determination experiment on the shale sample to obtain the TOC content of the shale sample; 3, carrying out a mineral analysis experiment on the shale sample to obtain the mineral content of quartz and clay in the sample; and 4, establishing a shale capillary absorption time CST ratio calculation model by taking the capillary absorption time as a dependent variable, taking the TOC content and the quartz and clay mineral content as independent variables and adopting a multiple linear regression method. According to the method, the shale CST ratio calculation model is established by preferably selecting various capillary absorption time sensitive parameters and adopting a multiple linear regression method, so that the method has the advantages of simplicity, economy, practicability, scientificity and effectiveness, and the shale anti-swelling agent type and the fracturing fluid proportioning scheme are guided.

Description

Technical Field

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

[0002] my country's shale oil and gas resources have great potential. The low permeability of shale reservoir matrix 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 in order to meet economic benefits.

[0003] The clay mineral content in shale reservoirs is very high. During large-scale hydraulic fracturing, the fracturing fluid will undergo a series of hydration reactions with clay minerals, causing the clay minerals to absorb water and swell, resulting in pore blockage, poor connectivity, and reduced physical properties in the shale reservoir, which ultimately affects the development effect. Therefore, during hydraulic fracturing, it is necessary to add an anti-swelling agent to the fracturing fluid to reduce the hydration and swelling of clay minerals in the shale reservoir, reduce the fracturing damage to the reservoir, and improve the shale oil and gas recovery rate. Due to the different types and contents of clay minerals in shale reservoirs in different regions, the types of anti-swelling agents suitable for the region are also different. In order to select the anti-swelling agent with the best adaptability to the target block, it is necessary to study the effectiveness of different types of anti-swelling agents, configure the corresponding fracturing fluid, ensure the fracturing effect, and increase the shale oil and gas production.

[0004] Capillary suction time (CST) refers to the time required for various test fluids to penetrate a certain distance of special filter paper, measured by an instrument. The CST ratio can be used to determine the degree of colloidal dispersion of shale in water. The smaller the CST ratio, the better the effect of the anti-swelling agent in inhibiting shale water absorption and swelling. Its minimum value indicates the minimum shale hydration effect, the minimum colloidal dispersion and shale activity. Calculating the CST ratio can provide scientific guidance for the selection of 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 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 in 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 swelling of shale reservoirs. This method conducts anti-swelling agent solution displacement experiments on 4 shale samples with different clay mineral contents, and determines the amount of anti-swelling agent by measuring the changes in the physical properties of shale samples before and after displacement.

[0006] The above studies all focus on the quantitative description of the colloidal dispersion of shale in water and the selection of the dosage of anti-swelling agent, but do not involve the quantitative calculation of the CST ratio, which is unable to guide the optimization of fracturing fluid in the target shale development area. Therefore, it is necessary to conduct research on the CST ratio calculation method to determine the best anti-swelling agent type and fracturing fluid ratio scheme. 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: Carry out 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 contents of the samples;

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

[0012] Furthermore, in step 1, a capillary absorption time measuring instrument is used to measure the CST ratio, and the CST ratio is the time required for a slurry made of 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, washing and drying the sample.

[0014] Furthermore, in step 1, the process of shale sample pretreatment is: 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 for 2 hours to completely remove carbonates and other inorganic minerals;

[0019] S23, washing 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, washing the shale sample with chloroform as the organic solvent, and treating the sample to a fluorescence level below level 4;

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

[0024] S33. Grind the shale sample after washing and drying into 100 mesh powder using an agate mortar.

[0025] Furthermore, in step 4, the effectiveness of the established shale capillary absorption time CST ratio calculation model is verified, and a correlation analysis is performed on the calculated CST ratio and the experimentally obtained CST ratio. 2 When >0.95, the CST ratio calculation model is valid.

[0026] The beneficial effects of the present invention are as follows: the traditional method for calculating the shale CST ratio needs to rely on the capillary absorption time measurement experiment, which has the disadvantages of being time-consuming and laborious. The method provided by the present invention optimizes a variety of capillary absorption time sensitive parameters, adopts a multivariate linear regression method, and establishes a shale CST ratio calculation model, which has the advantages of being simple, economical, practical, scientific and 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] In order to make the technical means and objectives of the present invention easy to understand, the present invention is further described below in combination with a specific implementation method. A method for calculating the shale capillary absorption time CST ratio includes the following steps:

[0032] Step 1: Carry out 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 contents of the samples;

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

[0036] Reference Figures 1 to 4 , this specific implementation 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 experiment 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 samples were 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] Prepare slippery water with anti-swelling agent added; prepare slippery water degradation liquid A; prepare slippery water without anti-swelling agent but containing 3% KCl; prepare slippery water degradation liquid B;

[0046] The specific operation process of the capillary absorption time measurement experiment is 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 a 1 cm diameter rapid filter port facing downward) to start the experiment. The time (t A1 ).

[0048] Use the slickwater degradation solution B and repeat reading 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 the cone placed on the filter paper (with the 1 cm diameter rapid filter port facing downward) to start the experiment. Read the time (t A2 ).

[0050] Use the slickwater degradation solution B and repeat reading 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 liquid 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 samples need 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) adding 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 be involved in the CST ratio calculation model.

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

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

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

[0069] (1) Wash the shale sample with chloroform as the organic solvent and treat it to a fluorescence level 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) Use an agate mortar to grind the shale sample after washing and drying into a 100-mesh powder.

[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 surface ratio;

[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: Taking capillary absorption time as the dependent variable and TOC content, quartz and clay mineral content as independent variables, the multivariate linear regression method was used to establish a shale capillary absorption time CST ratio calculation model.

[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 implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for calculating the shale capillary absorption time CST ratio, characterized in that: The steps include: Step 1: Carry out a capillary absorption time measurement experiment on the shale sample and calculate the capillary absorption time CST ratio; 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 contents of the samples; Step 4: Taking capillary absorption time as the dependent variable and TOC content, quartz and clay mineral content as independent variables, the multivariate linear regression method was used to establish a shale capillary absorption time CST ratio calculation model.

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

3. The shale capillary absorption time CST ratio calculation method according to claim 1, characterized in that: 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, characterized in that: In step 1, the process of shale sample pretreatment is: firstly, 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, characterized in that: 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 shale capillary absorption time CST ratio calculation method according to claim 1, characterized in that: In step 2, the shale sample needs to be pretreated before the TOC content determination experiment, and 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 for 2 hours to completely remove carbonates and other inorganic minerals; S23, washing 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, characterized in that: In step 3, the sample needs to be pre-treated before the mineral content determination experiment, and the process is as follows: S31, washing the shale sample with chloroform as the organic solvent, and treating the sample to a fluorescence level below level 4; S32, drying the shale sample after oil washing in a constant temperature drying oven at a temperature of 50°C for 24 hours; S33. Grind the shale sample after washing and drying into 100 mesh powder using an agate mortar.

8. The method for calculating the shale capillary absorption time CST ratio according to claim 1, characterized in that: 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 >0.95, the CST ratio calculation model is valid.

Images