A method for analyzing the microstructure evolution of coal and rock before and after fracturing

Abstract

The present invention is a method for analyzing the microstructure evolution of coal rock before and after fracturing, which belongs to the technical field of coal rock microstructure testing, and specifically relates to an inventive method for analyzing the microstructure evolution characteristics of coal rock before and after fracturing agent treatment. The devices required for the method of the present invention include a constant temperature drying oven, a deionized water vacuum saturation device, a centrifuge, and a high-precision electronic balance. The present invention can analyze the changes in the microscopic components and moisture content of coal rock by measuring the mass changes of coal rock in the natural state and dry state before and after fracturing agent treatment, analyze the changes in its porosity by the mass changes of coal rock in the dry state and saturated state, and analyze the changes in its pore connectivity by the mass changes of coal rock in the saturated state and centrifugal state. The method of the present invention can more efficiently and accurately quantitatively characterize the microstructure evolution characteristics of coal rock before and after fracturing agent treatment, and make up for the defects of qualitative analysis, complex operation, and high cost of existing devices and methods for analyzing the microstructure evolution characteristics of coal rock.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal rock microstructure testing, and in particular, relates to an inventive method for analyzing the microstructure evolution of coal rock before and after fracturing. Background Art

[0002] In the context of "carbon peak and carbon neutrality", gas extraction and utilization in my country are becoming increasingly important. In order to efficiently extract gas from deep coal and rock formations, various coal rock fracturing and permeability enhancement technologies and methods have emerged, and corresponding methods for exploring the effects of various fracturing technologies on coal rock permeability enhancement and microstructure transformation have also emerged. Such common methods include low-temperature nitrogen adsorption and desorption experiments, high-pressure mercury injection experiments, CO2 adsorption and desorption experiments, low-field nuclear magnetic resonance experiments, etc., and these test methods are relatively expensive, and their respective test ranges are single and limited. Therefore, in order to make up for the defects of existing technologies and methods for analyzing the evolution characteristics of coal rock microstructures, the present invention proposes a new method for analyzing the evolution characteristics of coal rock microstructures.

[0003] Coal rock is composed of a variety of organic compounds and minerals. Due to the natural pores and cracks inside it, formation gas and groundwater can be absorbed into it. Because the mass of formation gas is almost zero, the mass of coal rock is generally composed of the superposition of the contents of organic compounds, mineral components and groundwater. The change in coal rock mass caused by fracturing agents can be regarded as the change in the organic compounds, mineral components and water content in coal rock.

[0004] According to the internal composition of the above-mentioned coal rock, and combined with the fracturing, drying, saturation and centrifugal treatment of the coal rock, four states of the coal rock are proposed: natural state, dry state, saturated state and centrifugal state. Then, by simple electronic balance weighing, drying oven drying, vacuum saturation device saturation and centrifuge centrifugation, the changes in microscopic components and moisture content, porosity and pore connectivity in the coal rock can be quantitatively analyzed. The method of the present invention can effectively save costs and quantitatively and accurately characterize the influence of the fracturing agent on the microstructural characteristics of the coal rock. Summary of the invention

[0005] The object of the present invention is to provide an inventive method for analyzing the microstructural evolution of coal rock before and after fracturing, so as to efficiently and quantitatively characterize the influence of fracturing agents on the microstructural characteristics of coal rock.

[0006] To achieve the above objectives, the present invention combines the four states of coal rock: natural, dry, saturated and centrifuged, and quantitatively analyzes the changes in the microscopic component content, moisture content, porosity and pore connectivity of the coal rock through electronic balance weighing, drying in a drying oven, saturation with a vacuum saturation device and centrifuge centrifugation.

[0007] The method for analyzing the microstructure evolution of coal rock before and after fracturing comprises the following steps:

[0008] S1: Sample drying. Place the sample in a constant temperature drying oven for drying. When the sample is dried in the constant temperature drying oven until the difference between two consecutive weighings is less than 0.1%, it is considered completely dry. Then use a precision electronic balance to weigh the sample to obtain the mass of the sample in the dry state before the first treatment.

[0009] S2: Sample saturation. The dried sample is placed in a vacuum saturation device filled with deionized water for saturation. When no obvious bubbles appear in the sample in the vacuum saturation device, it is considered to be fully saturated. Then, it is weighed using a precision electronic balance to obtain the mass of the sample in the saturated state before the first treatment.

[0010] S3: Sample centrifugation. Place the saturated sample in a centrifuge and centrifuge for 1 hour. After centrifugation, weigh it with a precision electronic balance to obtain the mass of the sample in the centrifugal state before the first treatment. This mass is also the natural mass of the sample before the first treatment with the fracturing agent.

[0011] S4: Fracturing agent treatment. The centrifuged sample is treated with a fracturing agent once, and after the treatment, it is weighed using a precision electronic balance to obtain the mass of the sample in its natural state after the treatment;

[0012] S5: The sample after the first treatment with the fracturing agent is subjected to S1 to S3 in sequence, and the mass of the sample in the dry state after the first treatment, the mass of the sample in the saturated state after the first treatment, and the mass of the sample in the centrifuged state after the first treatment are measured respectively, and the mass of the sample in the centrifuged state after the first treatment at this time is the mass of the sample in the natural state before the second treatment with the fracturing agent;

[0013] S6: Samples treated with fracturing agent circulation. Treat the sample centrifuged once twice with the fracturing agent, and weigh it with a precision electronic balance after the treatment to obtain the mass of the sample in the natural state after the second treatment. Perform S1 to S3 on the sample treated with the fracturing agent twice, and use a precision electronic balance to measure the mass of the sample in the dry state after the second treatment, the mass of the sample in the saturated state after the second treatment, and the mass of the sample in the centrifuged state after the second treatment, respectively. The mass of the sample in the centrifuged state after the second treatment is the mass of the sample in the natural state before the third treatment with the fracturing agent. Repeat the above steps to gradually obtain the mass in four states: 3 treatments, 4 treatments, and n treatments.

[0014] S7: Analyze the changes in the microscopic components and moisture content of the samples by combining the changes in the mass of the samples in the natural state and dry state before and after the treatment with the fracturing agent; analyze the changes in the porosity of the samples by combining the changes in the mass of the samples in the dry state and saturated state before and after the treatment with the fracturing agent; analyze the changes in the pore connectivity of the samples by combining the changes in the mass of the samples in the saturated state and centrifuged state before and after the treatment with the fracturing agent.

[0015] In the above technical solution, the method for analyzing the changes in the sample micro-component content, moisture content, porosity and pore connectivity in step S7 comprises the following steps:

[0016] S71: The dry state mass of the sample before and after the fracturing agent treatment is subtracted, and the difference is the microscopic component change, so as to analyze the change in the content of the microscopic components of the sample after the fracturing agent treatment, as shown in Formula 1:

[0017]

[0018] Where, ΔM mic is the change in the microscopic components of the sample, in g. A positive value means that the content of the microscopic components of the sample increases after the fracturing agent treatment, and vice versa. The dry mass of the sample after fracturing agent treatment, unit: g; It is the dry mass of the sample before fracturing agent treatment, in g.

[0019] The sample in the dry state does not contain water, so the mass of the sample in the dry state is the sum of the mass of the organic compounds and the mass of the mineral components it contains, and the sum of the masses is defined as the mass of the microscopic components of the sample, as shown in Formula 2. Therefore, the change in the content of the microscopic components in the sample can be analyzed by the change in the mass of the sample in the dry state.

[0020] M dry =M oc +M min =M mic (2)

[0021] Where M oc is the mass of the sample organic compound, in g; M min is the mass of the mineral components of the sample, in g; M mic is the mass of the sample's microscopic components, in g.

[0022] S72: Subtract the mass of the sample in its natural state from the mass in its dry state to obtain the moisture content in the sample, as shown in Formula 3. Subtract the moisture content of the sample before and after the fracturing agent treatment to analyze the change in moisture content of the sample after the fracturing agent treatment, as shown in Formula 4.

[0023] M nat -M dry =M wat (3)

[0024]

[0025] Where M nat is the mass of the sample in its natural state, in g; M wat is the moisture content of the sample, in g; ΔM watis the change in sample moisture content, in g. If the value is positive, it means that the moisture content of the sample increases after the fracturing agent treatment, otherwise it decreases. is the moisture content of the sample after fracturing agent treatment, unit: g; It is the moisture content of the sample before fracturing agent treatment, unit is g.

[0026] The mass of the sample in its natural state is the sum of the contents of organic compounds, mineral components and groundwater, that is, Formula 5. Combined with Formula 2, it can be seen that the mass of the sample in its natural state is the sum of the mass in its dry state and the water content, as shown in Formula 6.

[0027] M nat =M oc +M min +M wat (5)

[0028] M nat =M dry +M wat (6)

[0029] S73: Subtract the mass of the sample in a saturated state from the mass in a dry state to obtain the saturable water volume of the sample, as shown in Formula 7. The saturable water volume can characterize the pore volume of the sample, that is, the porosity of the sample. Subtract the saturable water volume of the sample before and after the fracturing agent treatment to analyze the change in the porosity of the sample after the fracturing agent treatment, as shown in Formula 8.

[0030] M sat -M dry =M abs (7)

[0031]

[0032] Where M sat M is the mass of the sample in a saturated state, in g; abs is the water saturation capacity of the sample, in g; ΔM abs is the change in the sample's saturable water content, in g. If its value is positive, it means that the sample's saturable water content increases and the sample's porosity increases after the fracturing agent treatment, and vice versa. The water saturation capacity of the sample after fracturing agent treatment, unit: g; It is the amount of water that the sample can be saturated with before fracturing agent treatment, in g.

[0033] S74: Subtract the mass of the sample in the saturated state from the mass in the centrifugal state to obtain the centrifugal water loss of the sample, as shown in Formula 9. The centrifugal water loss can characterize the pore connectivity of the sample, that is, the fluid seepage capacity of the sample. Subtract the centrifugal water loss of the sample before and after the fracturing agent treatment to analyze the change in pore connectivity of the sample after the fracturing agent treatment, as shown in Formula 10.

[0034] M sat -M cen =M los (9)

[0035]

[0036] Where M cen M is the mass of the sample in centrifugal state, in g; los is the water loss of the sample by centrifugation, unit: g; ΔM los is the change in centrifugal water loss of the sample, in g. A positive value means that the centrifugal water loss of the sample increases after the fracturing agent treatment, and the pore connectivity of the sample is enhanced, otherwise it decreases. The centrifugal water loss of the sample after fracturing agent treatment, unit: g; It is the centrifugal water loss of the sample before fracturing agent treatment, unit is g.

[0037] In the above technical solution, the centrifugation time described in S3 can be changed according to the mechanical strength of the sample, but the centrifugation time of the sample before and after the fracturing agent treatment needs to be fixed.

[0038] Compared with the prior art and methods, the present invention has the following advantages:

[0039] 1. The method of the present invention has low cost, and the required experimental device is simple and easy to obtain.

[0040] 2. The method of the present invention can safely and efficiently quantitatively analyze the changes in microscopic components and moisture content, porosity and pore connectivity in coal rocks, with multiple test parameters and a short experimental cycle.

[0041] 3. The method of the present invention is suitable for exploring the effects of various fracturing technologies on coal rock masses and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is an experimental analysis flow chart of the method of the present invention.

[0043] Figure 2 It is a diagram of the experimental device required for the method of the present invention.

[0044] Figure 3 It is a schematic diagram of the quality changes of the samples in four states before and after fracturing agent treatment.

[0045] Figure 4 It is a schematic diagram of the difference in mass of the four states of the sample before and after fracturing agent treatment.

[0046] Figure 5 It is a schematic diagram of the changes in sample parameters before and after fracturing agent treatment.

[0047] In the figure: 1. Constant temperature drying oven; 2. Vacuum water saturation device; 3. Centrifuge; 4. Precision electronic balance; 5. Instrument switch; 6. Control panel; 7. Pressure gauge; 8. Vacuum pump; 9. Sealed glass cover; 10. Display screen. DETAILED DESCRIPTION

[0048] The method of the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation schemes.

[0049] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, carry out the following steps:

[0050] S1: Sample drying. Place the sample in a constant temperature drying oven (1) for drying. When the sample is dried in the constant temperature drying oven (1) until the difference between two consecutive weighings is less than 0.1%, it is considered completely dry. Then, the sample is weighed using a precision electronic balance (4) to obtain the mass of the sample in the dry state before the first treatment (B1).

[0051] S2: Sample saturation. The dried sample is placed in a vacuum saturation device (2) filled with deionized water for saturation. When no obvious bubbles appear in the sample in the vacuum saturation device (2), it is considered to be fully saturated. Then, it is weighed using a precision electronic balance (4) to obtain the mass of the sample in the saturated state before the first treatment (C1);

[0052] S3: Sample centrifugation. Place the saturated sample in a centrifuge (3) and centrifuge for 1 hour. After centrifugation, weigh it using a precision electronic balance (4) to obtain the mass of the sample in the centrifuged state before the first treatment (D1), which is also the mass of the sample in the natural state before the first treatment with the fracturing agent (A1).

[0053] S4: Fracturing agent treatment. The centrifuged sample is treated with a fracturing agent once, and after the treatment, it is weighed using a precision electronic balance (4) to obtain the mass of the sample in its natural state after the treatment (A2);

[0054] S5: The sample after the first treatment with the fracturing agent is subjected to S1 to S3 in sequence, and the mass of the sample in the dry state after the first treatment (B2), the mass of the sample in the saturated state after the first treatment (C2), and the mass of the sample in the centrifuged state after the first treatment (D2) are measured respectively, and the mass of the sample in the centrifuged state after the first treatment at this time is the mass of the sample in the natural state before the second treatment with the fracturing agent;

[0055] S6: Samples treated with fracturing agent circulation. The sample treated with fracturing agent twice after centrifugation is weighed with a precision electronic balance (4) after treatment to obtain the mass of the sample in the natural state after the second treatment. The sample treated with the fracturing agent twice is subjected to S1 to S3 in sequence, and the mass of the sample in the dry state after the second treatment, the mass of the sample in the saturated state after the second treatment, and the mass of the sample in the centrifuged state after the second treatment are measured with a precision electronic balance respectively. The mass of the sample in the centrifuged state after the second treatment is the mass of the sample in the natural state before the third treatment with the fracturing agent. Repeat the above steps to gradually obtain the mass in the four states of 3 treatments, 4 treatments, ... n treatments.

[0056] S7: Analyze the changes in the microscopic components and moisture content of the samples by combining the changes in the mass of the samples in the natural state and dry state before and after the treatment with the fracturing agent; analyze the changes in the porosity of the samples by combining the changes in the mass of the samples in the dry state and saturated state before and after the treatment with the fracturing agent; analyze the changes in the pore connectivity of the samples by combining the changes in the mass of the samples in the saturated state and centrifuged state before and after the treatment with the fracturing agent.

[0057] In the above technical solution, the method for analyzing the changes in the sample micro-component content, moisture content, porosity and pore connectivity in step S7 comprises the following steps:

[0058] S71: The dry state mass of the sample before and after the fracturing agent treatment is subtracted (B2-B1), and the difference is the change in microscopic components to analyze the change in the content of microscopic components of the sample after the fracturing agent treatment, as shown in Formula 1:

[0059]

[0060] Where, ΔM mic is the change in the microscopic components of the sample, in g. A positive value means that the content of the microscopic components of the sample increases after the fracturing agent treatment, and vice versa. is the dry mass of the sample after fracturing agent treatment (B2), unit: g; is the dry mass of the sample before fracturing agent treatment (B1), unit: g.

[0061] The sample in the dry state does not contain water, so the mass of the sample in the dry state is the sum of the mass of the organic compounds and the mass of the mineral components it contains, and the sum of the masses is defined as the mass of the microscopic components of the sample, as shown in Formula 2. Therefore, the change in the content of the microscopic components in the sample can be analyzed by the change in the mass of the sample in the dry state.

[0062] M dry =M oc +M min =M mic (2)

[0063] Where Moc is the mass of the sample organic compound, in g; M min is the mass of the mineral components of the sample, in g; M mic is the mass of the sample's microscopic components, in g.

[0064] S72: Subtract the mass of the sample in its natural state from the mass in its dry state (A1-B1, A2-B2) to obtain the moisture content in the sample, as shown in Formula 3, and subtract the moisture content of the sample before and after the fracturing agent treatment ((A2-B2)-(A1-B1)) to analyze the change in moisture content of the sample after the fracturing agent treatment, as shown in Formula 4.

[0065] M nat -M dry =M wat (3)

[0066]

[0067] Where M nat is the mass of the sample in its natural state, in g; M wat is the moisture content of the sample, in g; ΔM wat is the change in sample moisture content, in g. If the value is positive, it means that the moisture content of the sample increases after the fracturing agent treatment, otherwise it decreases. is the moisture content of the sample after fracturing agent treatment (A2-B2), unit: g; It is the moisture content of the sample before fracturing agent treatment (A1-B1), unit is g.

[0068] The mass of the sample in its natural state is the sum of the contents of organic compounds, mineral components and groundwater, that is, Formula 5. Combined with Formula 2, it can be seen that the mass of the sample in its natural state is the sum of the mass in its dry state and the water content, as shown in Formula 6.

[0069] M nat =M oc +M min +M wat (5)

[0070] M nat =M dry +M wat (6)

[0071] S73: Subtract the mass of the sample in the saturated state from the mass in the dry state (C1-B1, C2-B2) to obtain the saturable water volume of the sample, as shown in Formula 7. The saturable water volume can characterize the pore volume of the sample, that is, the porosity of the sample. Subtract the saturable water volume of the sample before and after the fracturing agent treatment ((C2-B2)-(C1-B1)) to analyze the change in the porosity of the sample after the fracturing agent treatment, as shown in Formula 8.

[0072] M sat -M dry =M abs (7)

[0073]

[0074] Where M sat M is the mass of the sample in a saturated state, in g; abs is the water saturation capacity of the sample, in g; ΔM abs is the change in the sample's saturable water content, in g. If its value is positive, it means that the sample's saturable water content increases and the sample's porosity increases after the fracturing agent treatment, and vice versa. is the saturated water content of the sample after fracturing agent treatment (C2-B2), unit: g; It is the saturated water content of the sample before fracturing agent treatment (C1-B1), unit: g.

[0075] S74: Subtract the mass of the sample in the saturated state from the mass in the centrifugal state (C1-D1, C2-D2) to obtain the centrifugal water loss of the sample, as shown in Formula 9. The centrifugal water loss can characterize the pore connectivity of the sample, that is, the fluid seepage capacity of the sample. Subtract the centrifugal water loss of the sample before and after the fracturing agent treatment ((C2-D2)-(C1-D1)) to analyze the change in pore connectivity of the sample after the fracturing agent treatment, as shown in Formula 10.

[0076] M sat -M cen =M los (9)

[0077]

[0078] Where M cen M is the mass of the sample in centrifugal state, in g; los is the water loss of the sample by centrifugation, unit: g; ΔM los is the change in centrifugal water loss of the sample, in g. A positive value means that the centrifugal water loss of the sample increases after the fracturing agent treatment, and the pore connectivity of the sample is enhanced, otherwise it decreases. is the centrifugal water loss of the sample after fracturing agent treatment (C2-D2), unit: g; It is the centrifugal water loss of the sample before fracturing agent treatment (C1-D1), unit is g.

[0079] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for analyzing the microstructure evolution of coal and rock before and after fracturing, characterized in that: The following steps are involved: S1: Sample drying: Place the sample in a constant temperature drying oven for drying. When the sample is dried in the constant temperature drying oven until the difference between two consecutive weighings is less than 0.1%, it is considered completely dry. Then, a precision electronic balance is used to weigh the sample to obtain the mass of the sample in the dry state before the first treatment. S2: Sample saturation: Place the dried sample in a vacuum saturation device filled with deionized water for saturation. When no obvious bubbles appear in the sample in the vacuum saturation device, it is considered to be fully saturated. Then, weigh it with a precision electronic balance to obtain the mass of the sample in the saturated state before the first treatment. S3: Sample centrifugation: Place the saturated sample in a centrifuge for 1 hour of centrifugation. After centrifugation, weigh it with a precision electronic balance to obtain the mass of the sample in the centrifugal state before the first treatment. This mass is also the mass of the sample in the natural state before the first treatment with the fracturing agent. The centrifugation time can be changed according to the mechanical strength of the sample, but the centrifugation time of the sample before and after the fracturing agent treatment needs to be fixed. S4: fracturing agent treatment: the centrifuged sample is treated with the fracturing agent once, and after the treatment, it is weighed with a precision electronic balance to obtain the mass of the sample in its natural state after the treatment; S5: The sample after the first treatment with the fracturing agent is subjected to S1 to S3 in sequence, and the mass of the sample in the dry state after the first treatment, the mass of the sample in the saturated state after the first treatment, and the mass of the sample in the centrifuged state after the first treatment are measured respectively, and the mass of the sample in the centrifuged state after the first treatment at this time is the mass of the sample in the natural state before the second treatment with the fracturing agent; S6: fracturing agent cyclic treatment sample, use fracturing agent to treat the sample after centrifugation for 2 times, weigh it with precision electronic balance after treatment, get the mass of the sample in natural state after 2 treatments, and perform S1 to S3 on the sample after 2 treatments of fracturing agent, respectively measure the mass of the sample in dry state after 2 treatments, the mass of the sample in saturated state after 2 treatments, and the mass of the sample in centrifuged state after 2 treatments with precision electronic balance, and the mass of the sample in centrifuged state after 2 treatments is the mass of the sample in natural state before 3 treatments of fracturing agent; repeat the above steps, and gradually get the mass in four states of 3 treatments, 4 treatments...n treatments; S7: Analyze the changes in the microscopic components and moisture content of the samples by combining the changes in the mass of the samples in the natural state and dry state before and after the treatment with the fracturing agent; analyze the changes in the porosity of the samples by combining the changes in the mass of the samples in the dry state and saturated state before and after the treatment with the fracturing agent; analyze the changes in the pore connectivity of the samples by combining the changes in the mass of the samples in the saturated state and centrifuged state before and after the treatment with the fracturing agent; The specific steps of the method for analyzing the changes in the sample micro-component content, moisture content, porosity and pore connectivity in step S7 are described as follows: S71: The dry state mass of the sample before and after the fracturing agent treatment is subtracted, and the difference is the microscopic component change, so as to analyze the change in the content of the microscopic components of the sample after the fracturing agent treatment, as shown in Formula 1: In the formula, ΔM mic is the change in the microscopic components of the sample, in g. A positive value means that the content of the microscopic components of the sample increases after the fracturing agent treatment, and vice versa. The dry mass of the sample after fracturing agent treatment, unit: g; The dry mass of the sample before fracturing agent treatment, unit: g; The sample in the dry state does not contain water, so the mass of the sample in the dry state is the sum of the mass of the organic compounds and the mass of the mineral components contained therein, and the sum of the masses is defined as the mass of the microscopic components of the sample, as shown in Formula 2. Therefore, the change in the content of the microscopic components in the sample can be analyzed by the change in the mass of the sample in the dry state; M dry =M oc +M min =M mic (2) Where M oc is the mass of the sample organic compound, in g; M min is the mass of the mineral components of the sample, in g; M mic is the mass of the sample's microscopic components, in g; S72: Subtract the mass of the sample in its natural state from the mass in its dry state to obtain the moisture content in the sample, as shown in Formula 3, and subtract the moisture content of the sample before and after the fracturing agent treatment to analyze the change in the moisture content of the sample after the fracturing agent treatment, as shown in Formula 4: M nat -M dry =M wat (3) Where M nat is the mass of the sample in its natural state, in g; M wat is the moisture content of the sample, in g; ΔM wat is the change in sample moisture content, in g. If the value is positive, it means that the moisture content of the sample increases after the fracturing agent treatment, otherwise it decreases. is the moisture content of the sample after fracturing agent treatment, unit: g; is the moisture content of the sample before fracturing agent treatment, unit: g; The mass of the sample in its natural state is the sum of the mass in its dry state and the water content, as shown in Formula 6: M nat =M oc +M min +M wat (5) M nat =M dry +M wat (6) S73: Subtract the mass of the sample in the saturated state from the mass in the dry state to obtain the saturable water volume of the sample, as shown in Formula 7. The saturable water volume can characterize the pore volume of the sample, that is, the porosity of the sample. Subtract the saturable water volume of the sample before and after the fracturing agent treatment to analyze the change in the porosity of the sample after the fracturing agent treatment, as shown in Formula 8: M sat -M dry =M abs (7) Where M sat M is the mass of the sample in a saturated state, in g; abs is the water saturation capacity of the sample, in g; ΔM abs is the change in the sample's saturable water content, in g. If its value is positive, it means that the sample's saturable water content increases and the sample's porosity increases after the fracturing agent treatment, and vice versa. The water saturation capacity of the sample after fracturing agent treatment, unit: g; The water saturation capacity of the sample before fracturing agent treatment, unit: g; S74: Subtract the mass of the sample in a saturated state from the mass of the sample in a centrifugal state to obtain the centrifugal water loss of the sample, as shown in Formula 9. The centrifugal water loss can characterize the pore connectivity of the sample, that is, the fluid seepage capacity of the sample. Subtract the centrifugal water loss of the sample before and after the fracturing agent treatment to analyze the change in pore connectivity of the sample after the fracturing agent treatment, as shown in Formula 10: M sat -M cen =M los (9) Where M cen is the mass of the sample in centrifugal state, unit: g; M los is the water loss of the sample by centrifugation, unit: g; ΔM los is the change in centrifugal water loss of the sample, in g. A positive value means that the centrifugal water loss of the sample increases after the fracturing agent treatment, and the pore connectivity of the sample is enhanced, otherwise it decreases. The centrifugal water loss of the sample after fracturing agent treatment, unit: g; It is the centrifugal water loss of the sample before fracturing agent treatment, unit is g.

Images