A method for testing the thermal shock resistance of oil well cement stone

Abstract

The present application provides a method for testing the thermal shock resistance of oil well cement stone. The method comprises the following steps: obtaining a cement stone sample; applying a preset temperature gradient to the cement stone sample; monitoring the stress change of the cement stone sample under the temperature gradient; and calculating the thermal shock resistance index of the cement stone sample according to the stress change of the cement stone sample; wherein the thermal shock resistance index is used to characterize the stress change of the cement stone sample under different temperature gradients and its resistance to thermal shock. The technical solution provided by the present application can improve the accuracy of testing the thermal shock resistance of oil well cement stone.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of performance testing, and in particular to a method for testing the thermal shock resistance of oil well cement stone. Background Art

[0002] In the oil extraction industry, oil well cement is one of the important materials used for cementing. It not only needs to withstand the harsh environment of high temperature and high pressure, but also needs to have good thermal shock resistance to ensure the safe and stable operation of the oil well. With the increasing development of deep wells, ultra-deep wells, and high temperature and high pressure wells, higher requirements are placed on the thermal shock resistance of oil well cement.

[0003] Currently, the method for evaluating the thermal shock resistance of cement paste mainly relies on simple temperature cycle tests, such as heating and cooling cement paste samples at different temperatures, and then evaluating their thermal shock resistance by observing the crack development of the samples.

[0004] However, the current scheme lacks accurate monitoring means for the dynamic stress changes of cement stone samples under the action of temperature gradient, which makes it difficult to capture the subtle changes in cement stone during thermal shock, resulting in low accuracy in detecting the thermal shock resistance of oil well cement stone. Summary of the invention

[0005] The embodiment of the present application provides a method for detecting the thermal shock resistance of oil well cement stone, which is used to solve the problem of low accuracy in detecting the thermal shock resistance of oil well cement stone in the prior art.

[0006] In a first aspect, the present application provides a method for detecting the thermal shock resistance of oil well cement stone, comprising:

[0007] Obtain cement paste samples;

[0008] Applying a preset temperature gradient to the cement stone sample;

[0009] Monitoring stress changes of the cement paste sample under the temperature gradient;

[0010] Calculating the thermal shock resistance index of the cement paste sample according to the stress change of the cement paste sample;

[0011] The thermal shock resistance index is used to characterize the stress change of the cement stone sample under different temperature gradients and its resistance to thermal shock;

[0012] The step of monitoring the stress change of the cement stone sample under the temperature gradient comprises:

[0013] Using a strain gauge or a pressure sensor to measure the stress change of the cement stone sample during heating and cooling;

[0014] The stress change data is collected and recorded.

[0015] Optionally, applying a preset temperature gradient to the cement stone sample comprises:

[0016] heating the cement stone sample to a first set temperature;

[0017] Maintaining the first set temperature for a preset time and then rapidly cooling to a second set temperature;

[0018] The difference between the first set temperature and the second set temperature is taken as the temperature gradient.

[0019] Optionally, the calculating the thermal shock resistance index of the cement stone sample comprises:

[0020] Calculating the stress variation of the cement paste sample under different temperature gradients;

[0021] Measuring the elastic modulus of the cement stone sample;

[0022] Calculating the cooling time of the cement paste sample under the temperature gradient;

[0023] Measuring the recovery time required for the cement stone sample to recover to the initial state after the temperature gradient is applied;

[0024] measuring the pressure change of the cement stone sample;

[0025] By formula: Calculating the thermal shock resistance index of the cement paste sample;

[0026] in, Expressed as thermal shock resistance index, It is expressed as the maximum stress change of the cement paste sample under the action of temperature gradient, represents the initial stress of cement paste sample, Expressed as the temperature gradient, represents the initial temperature of the cement paste sample, Expressed as the elastic modulus of the cement paste sample, Expressed as the thermal diffusion coefficient, Represents the cooling time, Represented as recovery time, It is expressed as the pressure change of the cement stone sample, is the initial pressure, It is expressed as an environmental factor coefficient, which is determined according to the actual working conditions of the cement stone sample. It is expressed as the damage accumulation coefficient, which represents the damage accumulation degree of the cement paste sample under the action of temperature gradient. Expressed as a pressure sensitivity index;

[0027] in, , It is expressed as the maximum time experienced by the cement paste sample, Expressed as the stress change over time, It is expressed as a material damage index, usually ranging from 1 to 3. It is expressed as the humidity change to which the cement paste sample is subjected, Expressed as initial humidity;

[0028] in, , Expressed as the temperature gradient, It is expressed as the pressure change of the cement stone sample. It is expressed as the humidity change to which the cement paste sample is subjected, It is expressed as the salinity change to which the cement stone sample is subjected, represents the initial salinity of the cement paste sample, and a, b, c, d and e represent the constant of the temperature gradient, the constant of the pressure change to which the cement paste sample is subjected, the constant of the humidity change to which the cement paste sample is subjected, and the constant of the salinity change to which the cement paste sample is subjected, respectively.

[0029] Optionally, applying a preset temperature gradient to the cement stone sample further comprises:

[0030] The rate of change of the temperature gradient is controlled to simulate the temperature change under actual working conditions.

[0031] Optionally, monitoring the stress change of the cement stone sample further includes:

[0032] Recording the deformation process of the cement stone sample under the action of temperature gradient;

[0033] The development of microcracks during the deformation process is analyzed to determine the stress change of the cement paste sample.

[0034] Optionally, the method further comprises:

[0035] Based on the thermal shock resistance index, the damage accumulation coefficient and the environmental factor coefficient, predicting the service life of the cement paste sample under specific working conditions;

[0036] The predicting of the service life of the cement stone sample under specific working conditions includes:

[0037] By formula: , predicting the service life of the cement stone sample under specific working conditions;

[0038] in, Expressed as service life, Expressed as a constant related to material properties, It is expressed as an environmental factor coefficient, which is determined according to the actual working conditions of the cement stone sample. Expressed as the damage accumulation factor, Expressed as thermal shock resistance index.

[0039] In an embodiment of the present application, a cement stone sample is obtained; a preset temperature gradient is applied to the cement stone sample; stress changes of the cement stone sample are monitored under the temperature gradient; and a thermal shock resistance index of the cement stone sample is calculated based on the stress changes of the cement stone sample; wherein the thermal shock resistance index is used to characterize the stress changes of the cement stone sample under different temperature gradients and its resistance to thermal shock, thereby improving the safety and reliability of the cement stone material when facing thermal shock.

[0040] These and other aspects of the present application will become more clearly understood in the description of the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 A flow chart of a method for detecting the thermal shock resistance of oil well cement stone provided in an embodiment of the present application. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0044] In some of the processes described in the specification and claims of this application and the above-mentioned figures, multiple operations that appear in a specific order are included, but it should be clearly understood that these operations may not be executed in the order in which they appear in this article or executed in parallel. The serial numbers of the operations, such as 101, 102, etc., are only used to distinguish between different operations, and the serial numbers themselves do not represent any execution order. In addition, these processes may include more or fewer operations, and these operations may be executed in sequence or in parallel. It should be noted that the descriptions of "first", "second", etc. in this article are used to distinguish different messages, devices, modules, etc., do not represent the order of precedence, and do not limit the "first" and "second" to be different types.

[0045] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0046] Figure 1 A flow chart of a method for detecting the thermal shock resistance of oil well cement stone is provided for the embodiment of the present application, as shown in FIG. Figure 1 As shown, the method includes:

[0047] 101. Obtain cement stone samples;

[0048] In this step, cement stone is a product composed of the main minerals formed after cement undergoes hydration reaction, which is the basic component in concrete structure. Cement stone samples are small pieces cut or drilled from the actual concrete structure for laboratory testing.

[0049] In the examples of this application, in order to ensure the representativeness and reliability of the test results, it is necessary to obtain cement stone samples from concrete structures used in actual projects. The specific examples are as follows:

[0050] Sample source: A section of solidified concrete structure is selected from an actual engineering project, such as a cement stone test block in an oil well. The age of the structure is at least 28 days to ensure that the cement is fully hydrated. It should also be noted that in actual applications, the sample can also be determined according to actual working conditions, such as selecting samples according to industry standards, and the embodiments of the present invention do not make specific limitations on this.

[0051] Sample preparation: Use professional cutting tools, such as a diamond saw blade cutter, to cut the concrete in the selected area into standard size specimens. For example, cut the concrete into cylindrical specimens with a diameter of 100 mm and a height of 100 mm. In order to ensure the uniformity and representativeness of the sample, try to avoid introducing additional stress during cutting.

[0052] Sample labeling: number each sample and record the specific location information of the sample for subsequent tracking and comparison. For example, the samples are numbered S01, S02, etc., and the specific location and date of each sample are recorded. It should also be noted that in actual applications, the samples can also be determined according to actual working conditions, such as selecting samples according to industry standards, and the embodiments of the present invention do not specifically limit this.

[0053] Sample processing: Perform necessary processing on the cut samples, such as removing the loose layer on the surface to ensure a smooth surface.

[0054] Here is a specific example:

[0055] Sample source: A section of concrete structure was selected from the pier part of an oil well site. The concrete age was 28 days.

[0056] Sample preparation: Use a DSC-1000 diamond saw blade cutting machine to cut the concrete in the selected area into standard cylindrical specimens with a diameter of 100 mm and a height of 100 mm.

[0057] Sample marking: Number the cut specimens, such as S01, S02, etc., and record the specific location information of the samples, such as the specific location coordinates of the pier and the cutting date.

[0058] Sample processing: Grind the cut samples to ensure a smooth surface for subsequent testing.

[0059] Formula Example

[0060] Although this step does not directly involve mathematical formulas, some calculations related to sample size may be used in subsequent steps. For example, if you need to calculate the volume of the sample, you can use the following formula:

[0061] Where V is the volume (unit: m 3 ); r is the radius (unit: m); h is the height (unit: m).

[0062] Assuming that the diameter of the sample is 100 mm (i.e., radius r = 50 mm = 0.05 m) and the height h = 100 mm = 0.1 m, the volume of the sample is:

[0063] V=π(0.05) 2(0.1)=π(0.0025)(0.1)=0.000785m 3

[0064] 102. Applying a preset temperature gradient to the cement stone sample;

[0065] In this step, cement stone samples: refer to small pieces of samples cut or drilled from cement products for laboratory testing.

[0066] Preset temperature gradient: refers to a temperature distribution state artificially created inside the sample. Usually one end is heated to a higher temperature while the other end is kept at a lower temperature, thus forming a temperature difference inside the sample.

[0067] In the embodiments of the present application, in order to study the behavior characteristics of cement stone samples under different temperature gradients, it is necessary to apply a preset temperature gradient to the samples under laboratory conditions. The specific embodiments are as follows:

[0068] Sample preparation: Use the cement stone sample obtained in step 101. Assume that the sample size is a standard cylindrical specimen with a diameter of 100 mm and a height of 100 mm.

[0069] Temperature gradient device: Use a heat treatment device (e.g., a heat treatment furnace) that can precisely control the temperature. This device can reach and maintain a set temperature and can simulate different temperature gradient environments.

[0070] Temperature gradient setting: Set a temperature gradient from room temperature (20°C) to a higher temperature (e.g. 100°C). This means that one end of the sample will be heated to 100°C while the other end is kept at room temperature 20°C.

[0071] Temperature gradient implementation: Place the cement stone sample in the heat treatment device so that one end of the sample is in the heated area and the other end is in the unheated area. Use a thermocouple or other temperature sensor to monitor the temperature at both ends of the sample to ensure that the temperature gradient is stable at the set value.

[0072] Here is a specific example:

[0073] Sample number: The sample number is S01.

[0074] Temperature gradient: Set the temperature gradient from 20℃ (room temperature) to 100℃, and the gradient direction is the length direction of the sample.

[0075] Heating device: Use heat treatment furnace, model HTL-1000.

[0076] Temperature monitoring: Use a thermocouple for temperature monitoring to ensure that the temperature of the heated end is stable at 100°C and the temperature of the unheated end is stable at 20°C.

[0077] Duration: Maintain this temperature gradient for 3 hours to ensure that the temperature gradient is stable and long enough for the sample to reach temperature equilibrium.

[0078] To understand the temperature gradient setting more intuitively, the following formula can be used to calculate the average value of the temperature gradient:

[0079] Temperature gradient

[0080] Where ΔT is the temperature difference (unit: °C); L is the length of the sample (unit: m).

[0081] Assuming the sample length L = 0.1m (100mm), the temperature difference ΔT = 80℃ (from 20℃ to 100℃), the temperature gradient is:

[0082] Through the above steps, we can effectively apply a preset temperature gradient to the cement stone sample, providing the necessary conditions for subsequent experimental analysis.

[0083] 103. Monitoring stress changes of the cement stone sample under the temperature gradient;

[0084] The main concepts involved in this step are "temperature gradient", "cement stone sample" and "stress change". Among them, the temperature gradient refers to the state of uneven temperature distribution formed inside the sample, that is, one end of the sample is heated to a higher temperature, while the other end is kept at a lower temperature. The cement stone sample refers to the sample obtained in step 101 for testing. Stress change refers to the change in internal stress generated by the sample under the action of temperature gradient. This stress change can be indirectly obtained through strain measurement.

[0085] In order to accurately measure the stress changes of cement stone samples under the action of temperature gradient, we need to use high-precision strain measurement equipment and combine it with a temperature control device. The specific implementation example is as follows:

[0086] Sample preparation: Use the cement stone sample obtained in step 101, assuming that the sample size is a standard cylindrical specimen with a diameter of 100 mm and a height of 100 mm.

[0087] Temperature gradient device: Use the temperature gradient device set in step 102, assuming that the temperature gradient is from room temperature (20°C) to 100°C.

[0088] Strain measurement: A high-precision resistance strain gauge (RSG) is installed on the sample and connected to a computer through a data acquisition system to monitor the changes in the sample in real time.

[0089] Data recording: Under the action of temperature gradient, record the temperature change and corresponding strain change data at both ends of the sample.

[0090] Stress calculation: Based on the strain change data and the elastic modulus of the sample, the stress change of the sample under different temperature gradients is calculated.

[0091] Here is a specific example:

[0092] Sample number: Use the sample obtained in step 101, numbered S01.

[0093] Temperature gradient: Set the temperature gradient from 20℃ (room temperature) to 100℃, and the gradient direction is the length direction of the sample.

[0094] Strain measurement: Resistance strain gauges, model RSG-1234, are mounted on the surface of the sample, two on each side, to ensure the accuracy and reliability of the data.

[0095] Data acquisition system: Use a DAQ-5600 data acquisition system to connect the strain gauges and transmit the data to the computer in real time.

[0096] Duration: Maintain this temperature gradient for 3 hours to ensure that the temperature gradient is stable and long enough for the sample to reach temperature equilibrium.

[0097] Data recording: Record the temperature changes and corresponding strain changes at both ends of the sample, and record the data once every minute.

[0098] Stress calculation: Assuming the elastic modulus of the sample is 30 GPa, the stress change is calculated based on the strain change data.

[0099] To calculate the stress change, the following formula can be used:

[0100] in, is stress (unit: Pa); E is elastic modulus (unit: Pa); is the strain (unitless). Assume that at a certain point in time, the change in strain is , elastic modulus E = 30GPa, then the stress change is:

[0101] 104. Calculate the thermal shock resistance index of the cement paste sample according to the stress change of the cement paste sample;

[0102] In this step, the concept involved is mainly "thermal shock resistance index", which is a quantitative indicator used to evaluate the ability of cement stone samples to resist stress changes caused by temperature gradient.

[0103] Thermal shock resistance index: This is a quantitative index used to characterize the stress change of cement stone samples under different temperature gradients and their resistance to thermal shock. The higher the index, the better the thermal shock resistance of the sample.

[0104] In the embodiment of the present application, in order to calculate the thermal shock resistance index, we need to base it on the stress change data obtained in step 103. The specific embodiment is as follows:

[0105] Data preparation: Use the stress variation data of the cement stone sample obtained in step 103.

[0106] Calculation method: The thermal shock resistance index P is defined as the ratio of the maximum stress change of the sample to the temperature change under a given temperature gradient. It can be expressed by the following formula:

[0107] in, is the maximum stress change, is the temperature change.

[0108] Calculation example: Assume that under the above temperature gradient, the maximum stress change is , the temperature change is (from 20℃ to 100℃), the thermal shock resistance index P is:

[0109] Here is a specific example:

[0110] Sample number: Use the sample obtained in step 101, numbered S01.

[0111] Temperature gradient: Set the temperature gradient from 20℃ (room temperature) to 100℃, and the gradient direction is the length direction of the sample.

[0112] Stress change data: Use the maximum stress change recorded in step 103 .

[0113] Temperature change: Set the temperature gradient change (from -20℃ to 100℃).

[0114] Calculation of thermal shock resistance index: Calculate the thermal shock resistance index P according to the above formula.

[0115] Formula example:

[0116] To calculate the thermal shock resistance index P, the following formula can be used:

[0117] in, is the maximum stress change (unit: Pa); is the temperature change (unit: °C).

[0118] Assume that the maximum stress change is , the temperature change is , then the thermal shock resistance index P is:

[0119] Through the above steps, we can accurately calculate the thermal shock resistance index of cement paste samples, which provides a quantitative basis for evaluating the heat resistance of cement paste samples.

[0120] Optionally, step 102 also includes: heating the cement stone sample to a first set temperature; maintaining the first set temperature for a preset time and then rapidly cooling it to a second set temperature; and taking the difference between the first set temperature and the second set temperature as a temperature gradient.

[0121] In this step, the concepts involved mainly include "first set temperature", "second set temperature", "preset time" and "temperature gradient".

[0122] The first set temperature refers to the temperature target value of the heating stage, that is, the highest temperature to which the sample is heated.

[0123] Second set temperature: refers to the target temperature in the cooling stage, which is usually close to room temperature or lower than the first set temperature.

[0124] Preset time: refers to the time maintained at the first set temperature to ensure that the sample reaches thermal equilibrium.

[0125] Temperature gradient: refers to the difference between the first set temperature and the second set temperature, which is used to describe the degree of temperature change during the heating-cooling process.

[0126] In the embodiments of the present application, in order to simulate the rapid temperature change that the cement stone sample may experience in actual use, a preset temperature gradient needs to be applied through a heating-cooling cycle. The specific embodiments are as follows:

[0127] Sample preparation: Use the cement stone sample obtained in step 101, assuming that the sample size is a standard cylindrical specimen with a diameter of 100 mm and a height of 100 mm.

[0128] Heating stage: Heat the sample to the first set temperature. Assume that the first set temperature is 100°C.

[0129] Maintain preset time: Maintain the preset time at the first set temperature to ensure that the sample reaches thermal equilibrium. Assume that the preset time is 30 minutes.

[0130] Cooling stage: Rapidly cool the sample to the second set temperature. Assume that the second set temperature is 20°C.

[0131] Temperature gradient calculation: Calculate the difference between the first set temperature and the second set temperature as the temperature gradient.

[0132] Here is a specific example:

[0133] Sample number: Use the sample obtained in step 101, numbered S01.

[0134] Heating stage: Heat the sample to the first set temperature of 100°C.

[0135] Maintain the preset time: maintain at 100℃ for 30 minutes.

[0136] Cooling stage: Rapidly cool to the second set temperature of 20°C.

[0137] Temperature gradient calculation: The first set temperature is 100°C, the second set temperature is 20°C, so the temperature gradient is 80°C.

[0138] To calculate the temperature gradient, the following formula can be used:

[0139] in, is the temperature gradient (unit: °C); is the first set temperature (unit: °C); is the second set temperature (unit: °C).

[0140] Assume the first set temperature , the second set temperature , then the temperature gradient for:

[0141] Through the above steps, we can effectively apply a preset temperature gradient to the cement stone sample, providing the necessary conditions for subsequent experimental analysis.

[0142] Optionally, monitoring the stress change of the cement stone sample under the temperature gradient includes: using a strain gauge or a pressure sensor to measure the stress change of the cement stone sample during heating and cooling; collecting and recording the stress change data.

[0143] In this step, the concepts involved mainly include the collection and recording of "strain gauges", "pressure sensors" and "stress change data".

[0144] Strain gauge: A sensor used to measure tiny deformations on the surface of an object, commonly used to measure stress and strain. By sticking it on the surface of a sample, it can convert tiny deformations into electrical signals, and then calculate stress changes.

[0145] Pressure sensor: used to measure pressure changes under the action of force, and can also be used to indirectly measure stress changes.

[0146] Stress change data: refers to the stress change of cement stone samples due to temperature changes during heating and cooling. These data are collected by strain gauges or pressure sensors and recorded for subsequent analysis.

[0147] In the embodiments of the present application, in order to accurately monitor the stress changes of cement stone samples under the action of temperature gradient, it is necessary to use a high-precision strain gauge or pressure sensor in combination with a temperature control device. The specific embodiments are as follows:

[0148] Sample preparation: Use the cement stone sample obtained in step 101, assuming that the sample size is a standard cylindrical specimen with a diameter of 100 mm and a height of 100 mm.

[0149] Temperature gradient device: Use the temperature gradient device set in step 102, assuming that the temperature gradient is from 20°C (room temperature) to 100°C, and then quickly cool back to 20°C.

[0150] Strain gauge or pressure sensor installation: A high-precision resistance strain gauge (RSG) is mounted on the surface of the sample and connected to a computer through a data acquisition system to monitor the strain changes of the sample in real time.

[0151] Data recording: Under the action of temperature gradient, record the temperature change and corresponding strain change data at both ends of the sample.

[0152] Stress calculation: Based on the strain change data and the elastic modulus of the sample, the stress change of the sample under different temperature gradients is calculated.

[0153] Here is a specific example:

[0154] Sample number: Use the sample obtained in step 101, numbered S01.

[0155] Temperature gradient: Set the temperature gradient from 20℃ (room temperature) to 100℃, and then quickly cool back to 20℃.

[0156] Strain gauge installation: Resistance strain gauges, model RSG-1234, are mounted on the surface of the sample, two on each side to ensure the accuracy and reliability of the data.

[0157] Data acquisition system: Use a DAQ-5600 data acquisition system to connect the strain gauges and transmit the data to the computer in real time.

[0158] Duration: Maintain this temperature gradient for 3 hours to ensure that the temperature gradient is stable and long enough for the sample to reach temperature equilibrium.

[0159] Data recording: Record the temperature changes and corresponding strain changes at both ends of the sample, and record the data once every minute.

[0160] Stress calculation: Assuming the elastic modulus of the sample is 30 GPa, the stress change is calculated based on the strain change data.

[0161] To calculate the stress change, the following formula can be used:

[0162] in, is stress (unit: Pa); E is elastic modulus (unit: Pa); is the strain (unitless).

[0163] Assume that at a certain point in time, the strain change is , elastic modulus , then the stress change is:

[0164] Through the above steps, we can accurately monitor the stress changes of cement stone samples under the action of temperature gradient and provide necessary data support for the subsequent calculation of thermal shock resistance index.

[0165] Optionally, the calculating the thermal shock resistance index of the cement stone sample comprises:

[0166] Calculating the stress variation of the cement paste sample under different temperature gradients;

[0167] Measuring the elastic modulus of the cement stone sample;

[0168] Calculating the cooling time of the cement paste sample under the temperature gradient;

[0169] Measuring the recovery time required for the cement stone sample to recover to the initial state after the temperature gradient is applied;

[0170] measuring the pressure change of the cement stone sample;

[0171] By formula: Calculating the thermal shock resistance index of the cement paste sample;

[0172] in, Expressed as thermal shock resistance index, It is expressed as the maximum stress change of the cement paste sample under the action of temperature gradient, represents the initial stress of cement paste sample, Expressed as the temperature gradient, represents the initial temperature of the cement paste sample, Expressed as the elastic modulus of the cement paste sample, Expressed as the thermal diffusion coefficient, Represents the cooling time, Represented as recovery time, It is expressed as the pressure change of the cement stone sample. Expressed as initial pressure, It is expressed as an environmental factor coefficient, which is determined according to the actual working conditions of the cement stone sample. It is expressed as the damage accumulation coefficient, which represents the damage accumulation degree of the cement paste sample under the action of temperature gradient. Expressed as a pressure sensitivity index;

[0173] in, , It is expressed as the maximum time experienced by the cement paste sample, Expressed as the stress change over time, It is expressed as a material damage index, usually ranging from 1 to 3. It is expressed as the humidity change to which the cement paste sample is subjected, Expressed as initial humidity;

[0174] in, , Expressed as the temperature gradient, It is expressed as the pressure change of the cement stone sample. It is expressed as the humidity change to which the cement paste sample is subjected, It is expressed as the salinity change to which the cement stone sample is subjected, represents the initial salinity of the cement paste sample, and a, b, c, d and e represent the constant of the temperature gradient, the constant of the pressure change to which the cement paste sample is subjected, the constant of the humidity change to which the cement paste sample is subjected, and the constant of the salinity change to which the cement paste sample is subjected, respectively.

[0175] In the above steps, the step of "calculating the stress change of cement paste samples under different temperature gradients" involves measuring the stress change of cement paste samples when they are subjected to temperature changes. Generally, when the temperature changes, the material will generate internal stress due to thermal expansion and contraction. The stress change can be measured experimentally, such as using strain gauges or other sensors for monitoring.

[0176] In the present embodiment, the cement stone sample is placed in a high temperature furnace and heated to 300°C at room temperature, and then quickly cooled to room temperature. A strain gauge is used to monitor the stress change on the sample surface. For example, the measured stress change is .

[0177] In the step of "measuring the elastic modulus of cement paste samples", a physical quantity is used to measure the material's ability to resist deformation within the elastic deformation range. For cement paste, it is a measure of the material's rigidity when subjected to stress.

[0178] In the present embodiment, the elastic modulus E of the cement stone sample is measured by static compression method. For example, after testing, .

[0179] In the step "Calculate the cooling time of cement paste samples under temperature gradient", the cooling time refers to the time it takes for the sample to cool from a high temperature to a specific temperature. This step helps to evaluate the thermal stability of the material during temperature changes.

[0180] In the present embodiment, the cement stone sample is cooled from 300°C to room temperature (assuming 20°C), and the time required is recorded. For example, the experiment shows =10 minutes.

[0181] In the step of "measuring the recovery time required for cement paste samples to return to their initial state after the temperature gradient", the recovery time refers to the time required for the sample to return to its initial state after the temperature change. This indicator helps to understand the recovery ability and durability of the material.

[0182] In the present embodiment, the time from the end of cooling of the sample to the recovery of its physical properties to the initial state is continuously monitored. For example, the experiment shows =20 minutes.

[0183] In the step of "measuring the pressure change of cement paste sample", the pressure change refers to the pressure change of cement paste sample when it is subjected to external pressure. This step takes into account the influence of pressure on material properties.

[0184] In the embodiment of the present application, during the temperature change process, the pressure change of the cement stone sample is measured by the pressure sensor. For example, the experiment shows .

[0185] "Calculate the thermal shock resistance index Q of the cement paste sample through the formula". This last step is to calculate the thermal shock resistance index Q of the cement paste sample through all the above data. This is a comprehensive evaluation index used to quantify the performance of the material under thermal shock.

[0186] In the embodiment of the present application, it is assumed that the parameter data obtained is as follows:

[0187] ;

[0188] (initial stress);

[0189] (initial temperature);

[0190] (temperature gradient);

[0191] (Step 2);

[0192] (thermal diffusivity);

[0193] (Step 3);

[0194] (Step 4);

[0195] (Step 5);

[0196] (initial pressure);

[0197] n=2 (pressure sensitivity index);

[0198] (Environmental factor coefficient);

[0199] (damage accumulation factor);

[0200] Calculate Q using the given formula:

[0201] Substitute the above known values ​​into the formula: The calculation results are:

[0202] In summary, through the above steps and calculations, we obtained that the thermal shock resistance index Q of the cement paste sample is about 0.15. This indicates that under a specific temperature gradient and pressure change, the cement paste sample has a certain thermal shock resistance.

[0203] Optionally, applying a preset temperature gradient to the cement stone sample further comprises:

[0204] The rate of change of the temperature gradient is controlled to simulate the temperature change under actual working conditions.

[0205] In this step, the concepts involved mainly include "the rate of change of temperature gradient" and "actual working conditions".

[0206] The rate of change of temperature gradient refers to the speed at which the temperature gradient changes over time. The temperature changes under actual working conditions can be simulated by controlling the heating and cooling processes.

[0207] Actual working conditions: refers to the various temperature changes that cement stone samples may encounter during actual use, such as temperature fluctuations caused by sunlight, seasonal changes and other factors.

[0208] In the embodiments of the present application, in order to more realistically simulate the temperature changes that cement stone samples may encounter during actual use, it is necessary to control the rate of change of the temperature gradient. The specific embodiments are as follows:

[0209] Sample preparation: Use the cement stone sample obtained in step 101, assuming that the sample size is a standard cylindrical specimen with a diameter of 100 mm and a height of 100 mm.

[0210] Temperature gradient device: Use the temperature gradient device set in step 102, assuming that the temperature gradient is from 20°C (room temperature) to 100°C, and then quickly cool back to 20°C.

[0211] Temperature change rate control: Control the temperature change rate during heating and cooling to simulate the temperature change under actual working conditions. For example, the heating rate is 5℃ / min and the cooling rate is 10℃ / min.

[0212] Duration: Maintain this temperature gradient for 3 hours to ensure that the temperature gradient is stable and long enough for the sample to reach temperature equilibrium.

[0213] Temperature gradient calculation: Calculate the difference between the first set temperature and the second set temperature as the temperature gradient.

[0214] Here is a specific example:

[0215] Sample number: Use the sample obtained in step 101, numbered S01.

[0216] Temperature gradient: Set the temperature gradient from 20℃ (room temperature) to 100℃, and then quickly cool back to 20℃.

[0217] Heating stage: Heat the sample to the first set temperature of 100°C at a heating rate of 5°C / min.

[0218] Maintain the preset time: maintain at 100℃ for 30 minutes.

[0219] Cooling stage: Rapidly cool to the second set temperature of 20°C, with a cooling rate of 10°C / min.

[0220] Temperature gradient calculation: The first set temperature is 100°C, the second set temperature is 20°C, so the temperature gradient is 80°C.

[0221] To calculate the rate of change of the temperature gradient, the following formula can be used: in, is the temperature change (unit: °C); is the time change (unit: min).

[0222] Assume the first set temperature , the second set temperature , the heating rate is 5℃ / min, then the heating time It can be calculated by the following formula: Assuming the heating rate is 5°C / min, the heating time is: Similarly, assuming the cooling rate is 10℃ / min, the cooling time is: Through the above steps, we can effectively apply a preset temperature gradient to the cement stone sample and control the rate of change of the temperature gradient to be closer to the temperature change under actual working conditions.

[0223] Optionally, monitoring the stress change of the cement stone sample further includes:

[0224] Recording the deformation process of the cement stone sample under the action of temperature gradient;

[0225] The development of microcracks during the deformation process is analyzed to determine the stress change of the cement paste sample.

[0226] In this step, the concepts involved mainly include "deformation process" and "microcrack development".

[0227] Deformation process: refers to the change in size or shape of cement paste samples under the influence of temperature gradient. This is usually monitored by strain gauges or optical measurement techniques.

[0228] Microcrack development: refers to the development process of small cracks that may be generated inside cement paste samples under the action of temperature gradient. The development of these microcracks can reflect the stress changes of the samples.

[0229] In the embodiments of the present application, in order to accurately record the deformation process of cement stone samples under the action of temperature gradient and analyze the development of microcracks, it is necessary to use high-precision strain measurement equipment in combination with tools such as optical microscopes. The specific embodiments are as follows:

[0230] Sample preparation: Use the cement stone sample obtained in step 101, assuming that the sample size is a standard cylindrical specimen with a diameter of 100 mm and a height of 100 mm.

[0231] Temperature gradient device: Use the temperature gradient device set in step 102, assuming that the temperature gradient is from 20°C (room temperature) to 100°C, and then quickly cool back to 20°C.

[0232] Strain gauge installation: A high-precision resistance strain gauge (RSG) is mounted on the surface of the sample and connected to a computer through a data acquisition system to monitor the strain changes of the sample in real time.

[0233] Optical microscopy observation: Use optical microscopy or digital image correlation (DIC) technology to monitor the deformation and microcrack development of the sample surface.

[0234] Data recording and analysis: Record the temperature changes at both ends of the sample, the corresponding strain change data and the development of microcracks, and record the data once every minute.

[0235] Here is a specific example:

[0236] Sample number: Use the sample obtained in step 101, numbered S01.

[0237] Temperature gradient: Set the temperature gradient from 20℃ (room temperature) to 100℃, and then quickly cool back to 20℃.

[0238] Strain gauge installation: Resistance strain gauges, model RSG-1234, are mounted on the surface of the sample, two on each side to ensure the accuracy and reliability of the data.

[0239] Data acquisition system: Use a DAQ-5600 data acquisition system to connect the strain gauges and transmit the data to the computer in real time.

[0240] Optical microscope: An optical microscope model OM-9000 equipped with a high-resolution camera was used to observe and record the deformation and microcrack development on the sample surface.

[0241] Duration: Maintain this temperature gradient for 3 hours to ensure that the temperature gradient is stable and long enough for the sample to reach temperature equilibrium.

[0242] Data recording and analysis: Record the temperature changes at both ends of the sample, the corresponding strain change data and the development of microcracks, and record the data once every minute.

[0243] Through optical microscope observation, the development of microcracks on the sample surface can be recorded, and combined with the stress change data, the relationship between the development of microcracks and stress changes can be analyzed.

[0244] Analysis of microcrack development:

[0245] Initial state: At room temperature, there are no obvious cracks on the sample surface.

[0246] Heating stage: As the temperature rises to 100°C, the strain value recorded by the strain gauge gradually increases, indicating that the sample undergoes expansion deformation. At the same time, an optical microscope observes tiny cracks on the surface of the sample.

[0247] Cooling stage: When the temperature is rapidly reduced back to 20°C, the strain value recorded by the strain gauge decreases, indicating that the sample shrinks. At this time, the microcracks become more obvious, and some cracks expand and connect to each other.

[0248] Through the above steps, we can accurately record the deformation process of cement stone samples under the action of temperature gradient and analyze the development of microcracks, providing necessary data support for the subsequent calculation of thermal shock resistance index.

[0249] Optionally, the method further comprises:

[0250] Based on the thermal shock resistance index, the damage accumulation coefficient and the environmental factor coefficient, the prediction concept is explained:

[0251] Thermal shock resistance index (Q): reflects the stress change characteristics and thermal shock resistance of cement paste samples when they experience temperature gradient changes.

[0252] Damage accumulation coefficient (γ): reflects the degree of damage accumulated by cement paste samples after experiencing multiple temperature gradients.

[0253] Environmental factor coefficient (β): Consider the influence of various environmental factors (temperature, pressure, humidity, salinity, etc.) on the thermal shock resistance of cement stone samples under actual working conditions.

[0254] Service life (L): The expected time that a cement stone sample can work normally under specific working conditions.

[0255] By obtaining the values ​​of Q, γ and β in the above embodiment, and k=0.001, an approximate value of the service life L is calculated.

[0256] The service life prediction formula is:

[0257] in, Expressed as service life, Expressed as a constant related to material properties, It is expressed as an environmental factor coefficient, which is determined according to the actual working conditions of the cement stone sample. Expressed as the damage accumulation factor, Expressed as thermal shock resistance index.

[0258] Specific numerical examples:

[0259] Assume that after the above calculation, we get , then the service life It can be calculated by the following formula: By substituting specific numerical values ​​for calculation, we can get the approximate value of L.

[0260] Through the above steps, we can obtain a more complex thermal shock resistance test method, which not only takes into account the basic physical quantities, but also comprehensively considers complex factors such as environmental factors and damage accumulation, thereby improving the creativity and practicality of the scheme. At the same time, by predicting the service life, it can help evaluate the reliability of cement stone samples under specific working conditions.

[0261] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for detecting the thermal shock resistance of oil well cement stone, characterized in that: include: Obtain cement paste samples; Applying a preset temperature gradient to the cement stone sample; Monitoring stress changes of the cement paste sample under the temperature gradient; Calculating the thermal shock resistance index of the cement paste sample according to the stress change of the cement paste sample; The thermal shock resistance index is used to characterize the stress change of the cement stone sample under different temperature gradients and its resistance to thermal shock; The step of monitoring the stress change of the cement stone sample under the temperature gradient comprises: Using a strain gauge or a pressure sensor to measure the stress change of the cement stone sample during heating and cooling; Collecting and recording the stress change data; The calculation of the thermal shock resistance index of the cement stone sample comprises: Calculating the stress variation of the cement paste sample under different temperature gradients; Measuring the elastic modulus of the cement stone sample; Calculating the cooling time of the cement paste sample under the temperature gradient; Measuring the recovery time required for the cement stone sample to recover to the initial state after the temperature gradient is applied; measuring the pressure change of the cement stone sample; By formula: Calculating the thermal shock resistance index of the cement paste sample; Wherein, Q represents the thermal shock resistance index, Δσ represents the maximum stress change of the cement paste sample under the temperature gradient, σ0 represents the initial stress of the cement paste sample, ΔT represents the temperature gradient, T0 represents the initial temperature of the cement paste sample, E represents the elastic modulus of the cement paste sample, α represents the thermal diffusion coefficient, t c Expressed as cooling time, t r is represented by the recovery time, ΔP is represented by the pressure change of the cement paste sample, P0 is represented by the initial pressure, β is represented by the environmental factor coefficient, and the environmental factor coefficient is determined according to the actual working condition of the cement paste sample, γ is represented by the damage accumulation coefficient, and the damage accumulation coefficient represents the damage accumulation degree of the cement paste sample under the action of the temperature gradient, and n is represented by the pressure sensitivity index; in, t max is represented by the maximum time experienced by the cement paste sample, Δσ(t) is represented by the stress change over time, m is represented by the material damage index, ΔH(t) is represented by the humidity change experienced by the cement paste sample, and H0 is represented by the initial humidity; in, ΔT represents the temperature gradient, ΔP represents the pressure change of the cement paste sample, ΔH represents the humidity change of the cement paste sample, ΔS represents the salinity change of the cement paste sample, S0 represents the initial salinity of the cement paste sample, a, b, c, d and e represent the constant of the temperature gradient, the constant of the pressure change of the cement paste sample, the constant of the humidity change of the cement paste sample, and the constant of the salinity change of the cement paste sample, respectively.

2. The method according to claim 1, characterized in that: The applying a preset temperature gradient to the cement stone sample comprises: heating the cement stone sample to a first set temperature; Maintaining the first set temperature for a preset time and then rapidly cooling to a second set temperature; The difference between the first set temperature and the second set temperature is taken as the temperature gradient.

3. The method according to claim 1, characterized in that The applying a preset temperature gradient to the cement stone sample further comprises: The rate of change of the temperature gradient is controlled to simulate the temperature change under actual working conditions.

4. The method according to claim 1, characterized in that: The monitoring of the stress change of the cement stone sample also includes: Recording the deformation process of the cement stone sample under the action of temperature gradient; The development of microcracks during the deformation process is analyzed to determine the stress change of the cement paste sample.

5. The method according to claim 1, characterized in that: The method further comprises: Based on the thermal shock resistance index, the damage accumulation coefficient and the environmental factor coefficient, predicting the service life of the cement paste sample under specific working conditions; The predicting of the service life of the cement stone sample under specific working conditions includes: By formula: Predicting the service life of the cement paste sample under specific working conditions; Wherein, L represents the service life, k represents a constant related to the material properties, β represents the environmental factor coefficient, and the environmental factor coefficient is determined according to the actual working conditions of the cement stone sample, γ represents the damage accumulation coefficient, and Q represents the thermal shock resistance index.

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