Perforation and fracturing whole-process cement sheath damage visualized experimental device and method

Abstract

This invention relates to the field of perforation fracturing damage testing technology, and provides a visualization experimental device and method for cement sheath damage throughout the perforation fracturing process. The device includes a vessel body, simulated surrounding rock, casing, and a perforating gun. An upper vessel cover and a lower vessel cover are installed on the upper and lower sides of the vessel body, respectively. Inside the vessel body, casing and simulated surrounding rock are sequentially spaced from the inside out, forming a cement sheath void between the casing and the simulated surrounding rock. A confining pressure cavity is formed between the simulated surrounding rock and the vessel body, and this cavity is connected to a confining pressure tank via a confining pressure pipeline. A perforating gun located within the casing cavity is installed on the lower vessel cover. This invention has a reasonable and compact structure and is easy to use. It simulates the formation environment and surrounding rock constraints outside the cement sheath through heating and confining pressure. The liquid circulation control system and different colored calcium ion fluorescent probes enable the differentiation between perforation damage sites and fracturing damage sites at the first and second interfaces of the cement sheath, facilitating damage area differentiation and quantitative analysis.

Description

Technical Field

[0001] This invention relates to the field of perforation fracturing damage testing technology, and is a visualization experimental device and method for cement sheath damage throughout the perforation fracturing process. Background Technology

[0002] In oil and gas well development, perforation is a crucial step connecting the wellbore and the reservoir. It involves using a perforating gun to penetrate the casing and cement sheath, establishing a channel for oil and gas flow. Subsequent fracturing operations, on the other hand, apply high pressure to create fractures in the reservoir, further enhancing oil and gas production. Throughout this process, the cement sheath, as the core barrier for wellbore integrity, must withstand the dual effects of perforation impact and fracturing pressure. Perforation can cause initial cracks and micro-fractures due to mechanical impact on the cement sheath itself, the cement sheath-casing interface, and the cement sheath-formation interface. The continuous pressure changes within the casing and the formation during fracturing can further extend these initial damages, even leading to interface debonding, directly threatening wellbore sealing performance and increasing oil and gas leakage and well control risks.

[0003] Regarding the monitoring of cement sheath integrity throughout the perforation-fracturing process, current technologies have limitations. Existing monitoring methods only focus on the impact of perforation on cement sheath integrity, failing to fully consider the synergistic effects of perforation and subsequent fracturing. The perforation operation itself causes initial damage to the cement sheath body, the cement sheath-casing interface, and the cement sheath-formation interface. The stress continuously applied during subsequent fracturing can further extend this initial damage. Furthermore, the downhole perforation and fracturing processes are not simply mechanical or flow-based processes, but rather occur under complex conditions involving high temperature, confining pressure, casing pressure, fluid circulation, and perforation impact. Current technologies lack systematic monitoring of the entire perforation-fracturing process. Summary of the Invention

[0004] This invention provides a visualization experimental device and method for cement sheath damage throughout the perforation-fracturing process, which overcomes the shortcomings of the prior art. It can effectively solve the problem that the lack of systematic monitoring of the entire perforation-fracturing process in the existing technology makes it difficult to evaluate the impact of fracturing operations on the integrity of the cement sheath.

[0005] One of the technical solutions of this invention is achieved through the following measures: a visualization experimental device for cement sheath damage in the entire perforation and fracturing process, comprising a vessel body, simulated surrounding rock, casing, and perforation gun. An upper vessel cover and a lower vessel cover are respectively installed on the upper and lower sides of the vessel body. The casing and simulated surrounding rock are sequentially spaced from the inside to the outside of the vessel body. A cement sheath void is formed between the casing and the simulated surrounding rock. A confining pressure cavity is formed between the simulated surrounding rock and the vessel body. The confining pressure cavity is connected to the confining pressure tank through a confining pressure pipeline. A perforation gun located in the inner cavity of the casing is installed on the lower vessel cover. The inner cavity of the casing is connected to the perforation fluid tank and the fracturing fluid tank through the casing pipeline. The perforation fluid and fracturing fluid can be visualized.

[0006] The following are further optimizations and / or improvements to the above-mentioned technical solution: Preferably, it also includes a clear water tank, the casing pipeline is connected to the clear water tank, the perforation tank is a No. 1 fluorescent perforation tank, and the fracturing fluid tank is a No. 2 fluorescent fracturing fluid tank. The No. 1 fluorescent perforation tank contains a No. 1 fluorescent perforation fluid containing a No. 1 calcium ion fluorescent probe, and the No. 2 fluorescent fracturing fluid tank contains a No. 2 fluorescent fracturing fluid containing a No. 2 calcium ion fluorescent probe. The two reagents are different colors.

[0007] Preferably, it also includes a heating rod, a temperature control system, and a temperature sensor. The heating rod is installed on the lower lid of the confining pressure chamber, and a temperature sensor is installed inside the confining pressure chamber. The temperature sensor, the heating rod, and the temperature control system are connected, and an insulation sleeve is provided on the outside of the vessel body.

[0008] Preferably, the casing pipeline is equipped with a casing internal pressure valve and a casing internal pressure gauge, both of which are connected to the liquid circulation control system. The confining pressure pipeline is equipped with a confining pressure valve and a confining pressure gauge, and the end of the confining pressure pipeline is connected to a confining pressure tank, both of which are connected to the confining pressure control system.

[0009] Preferably, the upper and lower sides of the vessel body are sealed to the upper and lower vessel covers respectively by sealing gaskets.

[0010] The second technical solution of the present invention is achieved through the following measures: an experimental method for a perforation fracturing process cement sheath damage visualization experimental device, characterized by the following steps: Step 1: First, install the simulated surrounding rock, casing, and vessel body onto the lower vessel cover in sequence, then install the perforating gun onto the lower vessel cover, while keeping the upper vessel cover open; Step 2: Prepare the cement grout according to API standards. Under conditions where no confining pressure, casing pressure, or temperature is applied, inject the cement grout into the cement annulus between the casing and the simulated surrounding rock from the top of the reactor body. The injection volume should be determined according to experimental requirements. After grouting, seal and fix the upper reactor cover to the top of the reactor body with a sealing gasket, and install the insulation sleeve on the outside of the reactor body. Cure the cement grout for the time specified in API standards until the cement annulus is formed. Step 3: After the cement ring has cured and formed, apply the required temperature, confining pressure, and casing pressure according to the experimental requirements: Turn on the heating rod and adjust it to the required temperature through the temperature control system; after the temperature stabilizes, pressurize the confining pressure chamber and observe the confining pressure gauge. When the required confining pressure is reached, close the confining pressure valve; at the same time, open the casing pressure valve, introduce the No. 1 fluorescent perforating liquid from the No. 1 fluorescent perforating liquid tank into the casing cavity and pressurize the casing cavity. Observe the casing pressure gauge. When the required casing pressure is reached, close the casing pressure valve. Step 4: Maintain stable loading temperature, casing pressure, and confining pressure. Perforate the wellbore assembly using a perforation gun to form perforation channels, simulating the downhole perforation process. At this time, the No. 1 calcium ion fluorescent probe will adhere to the damaged areas of the cement sheath caused by the perforation operation. Then, open the casing pressure valve to drain the No. 1 fluorescent perforation fluid from the casing cavity. Pour clean water from the clean water tank into the casing cavity to flush away the remaining No. 1 fluorescent perforation fluid and any unattached No. 1 calcium ion fluorescent probes. Then, drain the clean water from the casing cavity. Next, pour the No. 2 fluorescent fracturing fluid from the No. 2 fluorescent fracturing fluid tank into the casing cavity and adjust the casing pressure valve to increase the casing pressure to simulate fracturing operations. At this time, the No. 2 calcium ion fluorescent probe will adhere to the damaged areas of the cement sheath caused by the perforation and fracturing operations. Step 5: At this point, adjust the confining pressure valve to release the confining pressure, adjust the casing internal pressure valve to discharge the No. 2 fluorescent fracturing fluid and release the casing internal pressure, remove the upper reactor cover and disassemble the cement sheath from the experimental equipment, irradiate the inner and outer interfaces of the cement sheath with a fluorescent lamp and observe the fluorescence color development of the first and second interfaces of the cement sheath, and collect fluorescence images under the same light source intensity, shooting distance and exposure conditions. The areas where both No. 1 and No. 2 calcium ion fluorescent probes show color are the damaged areas of the cement sheath caused by the perforation operation, and the areas where only No. 2 calcium ion fluorescent probe shows color are the damaged areas of the cement sheath caused by the fracturing operation. The area and intensity of the fluorescence images are then quantitatively analyzed. Step Six: After completing the above fluorescence observation and quantitative analysis, clean the experimental equipment and complete the experiment.

[0011] Preferably, in step five, the acquired fluorescence image is preprocessed, including image cropping, background subtraction, brightness uniformization, and selection of effective observation area. The effective observation area includes the area within a specified radius around the first and second interfaces of the cement ring or the perforation channel, denoted as A0. Based on the color difference between the first and second calcium ion fluorescent probes, thresholds are set in the corresponding color channels to extract the color display area C1 of the first probe and the color display area C2 of the second probe. In damage assessment, the area where the first calcium ion fluorescent probe shows color or the area where the first and second calcium ion fluorescent probes show color over time is denoted as the damage area Cs formed during the perforation stage; the area where only the second calcium ion fluorescent probe shows color and there is no signal from the first probe is denoted as the newly added or extended damage area Cf during the fracturing stage; the union of Cs and Cf is denoted as the total damage area Ct, from which the perforation damage area As, the newly added fracturing damage area Af, and the total damage area At can be calculated. Calculate perforation damage coverage Increased damage coverage from fracturing and total damage coverage For fluorescence intensity information, the average value and integral value of pixel gray level or color channel intensity in each color development area are statistically analyzed to obtain the average fluorescence intensity Iavg and the integral fluorescence intensity Isum, which are used to characterize the degree of probe adhesion and damage connectivity in the damage channel. The crack morphology is described, the colored area is processed into a skeleton, the total length L of the fluorescent damage channel is extracted, and the damage length density is represented by L / A0; the equivalent damage width is represented by As / L, Af / L or At / L, which are used to compare the crack propagation degree and interface debonding scale under different casing internal pressure or different confining pressure conditions. When establishing the relationship between casing internal pressure and damage quantification index, multiple casing internal pressure levels P1, P2, P3...Pn were set, and parallel experiments were carried out under the same cement slurry formula, curing time, perforation parameters, confining pressure, temperature and liquid circulation regime. The As, Af, At, ηs, ηf, ηt, Iavg, L / A0 and other indices obtained at each pressure level were statistically analyzed to obtain a data set of damage index changes with casing internal pressure. Based on the above data set, the relationship between the damage area and the casing pressure was established by using linear fitting, quadratic polynomial fitting, exponential fitting, power function fitting or piecewise fitting. When the damage area or damage coverage rate showed a significant accelerated increase with the increase of casing pressure, the corresponding pressure range was taken as the critical pressure range for rapid expansion of cement ring interface damage. When the experiment needs to consider the effects of confining pressure and temperature simultaneously, a multi-factor relationship is established: D=f(P,σc,T,t), where D represents the damage quantification index, P represents the casing pressure, σc represents the confining pressure, T represents the experimental temperature, and t represents the cycle or loading time. By comparing the D values ​​under different parameter combinations, the effects of casing pressure, formation confining pressure, and temperature conditions on the damage evolution of the cement sheath after perforation fracturing are analyzed.

[0012] This invention has a reasonable and compact structure and is easy to use. It simulates the formation environment and surrounding rock constraints outside the cement sheath through heating and confining pressure. The liquid circulation control system and calcium ion fluorescent probes of different colors enable the differentiation of perforation damage sites and fracturing damage sites at the first and second interfaces of the cement sheath, which facilitates the differentiation and quantitative analysis of damage areas. Attached Figure Description

[0013] Appendix Figure 1 This is a schematic diagram of the front half-section structure according to an embodiment of the present invention.

[0014] The codes in the attached diagram are as follows: 1. Insulation sleeve; 2. Reactor body; 3. Confining pressure chamber; 4. Temperature sensor; 5. Heating rod; 6. Temperature control system; 7. Sealing gasket; 8. Simulated surrounding rock; 9. Confining pressure valve; 10. Confining pressure pipeline; 11. Confining pressure gauge; 12. Cement annulus; 13. Cement ring; 14. Perforation gun; 15. Perforation channel; 16. Liquid circulation control system; 17. Clear water tank; 18. No. 1 fluorescent perforation fluid tank; 19. Casing; 20. Casing internal pressure valve; 21. Casing pipeline; 22. Casing internal pressure gauge; 23. Confining pressure control system; 24. No. 2 fluorescent fracturing fluid tank; 25. Upper reactor cover; 26. Lower reactor cover; 27. Confining pressure tank; 28. Casing inner cavity. Detailed Implementation

[0015] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0016] In this invention, for ease of description, the description of the relative positions of the components is based on the appendix to the specification. Figure 1 The layout is described using a diagrammatic method, such as front, back, top, bottom, left, right, etc. The positional relationships are determined based on the layout direction of the attached diagram in the instruction manual.

[0017] The present invention will be further described below with reference to embodiments and accompanying drawings: As attached Figure 1 As shown, the perforation fracturing process cement sheath damage visualization experimental device includes a vessel body 2, simulated surrounding rock 8, casing 19, and perforation gun 14. The upper vessel cover 25 and the lower vessel cover 26 are installed on the upper and lower sides of the vessel body 2, respectively. The casing 19 and the simulated surrounding rock 8 are sequentially spaced from the inside to the outside of the vessel body 2. A cement sheath void 12 is formed between the casing 19 and the simulated surrounding rock 8. A confining pressure cavity 3 is formed between the simulated surrounding rock 8 and the vessel body 2. The confining pressure cavity 3 is connected to the confining pressure tank 27 through the confining pressure pipeline 10. The perforation gun 14 is installed on the lower vessel cover 26 and is located in the inner cavity 28 of the casing. The inner cavity 28 of the casing is connected to the perforation fluid tank and the fracturing fluid tank through the casing pipeline 21, respectively. The perforation fluid and the fracturing fluid can be visualized.

[0018] A controllable confining pressure is applied and maintained to the outside of the simulated surrounding rock 8 through the confining pressure pipeline 10. This confining pressure corresponds to the actual downhole formation stress and the constraint effect of the surrounding rock on the wellbore assembly. By adjusting the magnitude of the confining pressure, the state of the cement sheath 13 under external constraint at different burial depths and different ground stress levels can be simulated. The perforation fluid is mainly used in the perforation operation stage. Its purpose is to maintain wellbore safety, protect the reservoir, reduce contamination, and help the perforation channel form better connectivity when the perforation gun perforates the casing, cement sheath, and formation. Its color-coding ability can mark the area of ​​the perforation channel 15. The fracturing fluid is injected into the perforation channel 15 to simulate fracturing. Its color-coding ability can mark the newly damaged area of ​​the perforation channel 15 by the fracturing fluid, which is convenient for visual observation of minor damage and interface damage that is not easily visible to the naked eye. This invention couples perforation and fracturing operations, better reflecting actual working conditions. It can distinguish between damage already formed during the perforation stage and damage newly added or expanded during the fracturing stage, thereby improving the accuracy of cement sheath integrity evaluation throughout the perforation-fracturing process. By repeating experiments under different casing pressure conditions and maintaining consistent or controlled variables such as cement slurry system, curing regime, temperature, confining pressure, perforation parameters, and fracturing time, the relationship between casing pressure and damage area or damage coverage can be established. This allows for the identification of the expansion law and critical growth range of cement sheath interface damage as fracturing pressure increases. It can provide a basis for optimizing fracturing construction parameters after perforation in practical engineering, such as determining a reasonable casing pressure range under specific confining pressure, temperature, and wellbore structure conditions, evaluating the impact of fracturing on cement sheath integrity, and providing experimental support for reducing the risk of interface debonding, annular air channeling, or seal failure.

[0019] The above-mentioned visualization experimental device for cement sheath damage throughout the perforation fracturing process can be further optimized and / or improved according to actual needs: As attached Figure 1 As shown, it also includes a water tank 17, with casing line 21 connected to the water tank 17, a perforation tank 18 (a first fluorescent perforation tank), and a fracturing fluid tank 24 (a second fluorescent fracturing fluid tank). The first fluorescent perforation tank 18 contains a first fluorescent perforation fluid containing a first calcium ion fluorescent probe, and the second fluorescent fracturing fluid tank 24 contains a second fluorescent fracturing fluid containing a second calcium ion fluorescent probe. The two reagents are different colors.

[0020] After the perforation fluid circulation is completed, the clean water tank 17 performs a transitional flushing of the casing cavity 28 and the perforation channel 15. This flushing removes residual No. 1 fluorescent fracturing fluid and unattached No. 1 calcium ion fluorescent probes, reducing the possibility of residual fluorescent material entering the fracturing stage. This avoids mis-displaying of non-fracturing damage areas or overlapping of perforation and fracturing damage markers during subsequent monitoring, allowing the subsequently introduced No. 2 fluorescent fracturing fluid to perform fracturing simulation in a relatively clean fluid environment, thus improving the independence and accuracy of damage identification results during the fracturing stage.

[0021] The reason for using a calcium ion fluorescent probe is that the cement ring 13 contains a large amount of calcium-containing hydration products. After perforation impact or fracturing loading forms cracks, pore connectivity zones, and interface debonding zones, the damaged interface will expose calcium-containing components that can respond to the calcium ion fluorescent probe. After the calcium ion fluorescent probe enters the microcracks and interface gaps with the perforation fluid or fracturing fluid, it can form a clear color under fluorescent light, which facilitates the visual observation of minute damage and interface damage that is not easily visible to the naked eye.

[0022] Compared with ordinary staining agents, calcium ion fluorescent probes have the advantages of clear target response, strong fluorescence signal, low background interference, easy entry into micro-damage channels with working fluid, and intuitive observation results. By setting calcium ion fluorescent probe No. 1 and calcium ion fluorescent probe No. 2 to different colors, damage formed in the perforation stage can be distinguished from damage newly added or expanded in the fracturing stage, thereby improving the accuracy of cement sheath integrity evaluation in the entire perforation-fracturing process.

[0023] As attached Figure 1 As shown, it also includes a heating rod 5, a temperature control system 6, and a temperature sensor 4. The heating rod 5 is installed on the lower lid 26 at the position of the confining pressure cavity 3. The temperature sensor 4 is provided inside the confining pressure cavity 3. The temperature sensor 4, the heating rod 5 and the temperature control system 6 are connected. The outer side of the vessel body 2 is provided with a heat insulation sleeve 1.

[0024] Heating rod 5 is used to provide the heat required for the experiment, insulation sleeve 1 is used to reduce the heat dissipation of the vessel body 2 to the external environment, temperature sensor 4 and temperature control system 6 are used to provide real-time feedback and adjust the experimental temperature, thereby simulating the high temperature conditions in the underground well and formation environment, so that the cement sheath 13 can undergo perforation and fracturing under conditions close to the underground thermal state.

[0025] As attached Figure 1 As shown, the casing line 21 is equipped with a casing internal pressure valve 20 and a casing internal pressure gauge 22. Both the casing internal pressure valve 20 and the casing internal pressure gauge 22 are connected to the liquid circulation control system 16. The confining pressure line 10 is equipped with a confining pressure valve 9 and a confining pressure gauge 11. The end of the confining pressure line 10 is connected to a confining pressure tank 27. Both the confining pressure valve 9 and the confining pressure gauge 11 are connected to the confining pressure control system 23.

[0026] The casing inner cavity 28, casing line 21, casing inner pressure valve 20, casing inner pressure gauge 22, and liquid circulation control system 16 are used to control the injection, discharge, and pressurization process of liquid inside the casing 19. This function corresponds to the actual wellbore pressure, perforation fluid circulation, fracturing fluid circulation, and fracturing operation pressurization process. By adjusting the casing inner pressure, the loading effect of high-pressure liquid on the casing 19, cement sheath 13, and interface during fracturing operation can be simulated.

[0027] The confining pressure chamber 3, confining pressure tank 27, confining pressure pipeline 10, confining pressure valve 9, confining pressure gauge 11, and confining pressure control system 23 are used to apply and maintain a controllable confining pressure to the outside of the simulated surrounding rock 8. This confining pressure corresponds to the actual downhole formation stress and the constraint effect of the surrounding rock on the wellbore assembly. By adjusting the size of the confining pressure, the state of the cement sheath 13 under external constraint at different burial depths and different ground stress levels can be simulated.

[0028] As attached Figure 1 As shown, the upper and lower sides of the vessel body 2 are sealed to the upper vessel cover 25 and the lower vessel cover 26 respectively via sealing gaskets 7. The sealing gaskets 7 enhance the sealing performance and prevent pressure leakage.

[0029] As attached Figure 1 The experimental method of the perforation fracturing process cement sheath damage visualization experimental device, as shown, is characterized by the following steps: Step 1: First, install the simulated surrounding rock 8, casing 19 and vessel body 2 on the lower vessel cover 26 in sequence, then install the perforating gun 14 on the lower vessel cover 26, and keep the upper vessel cover 25 in the open position. Step 2: Prepare the cement grout according to API standards. Under conditions where no confining pressure, internal pressure of the casing, or temperature is applied, inject the cement grout into the cement annulus 12 between the casing 19 and the simulated surrounding rock 8 from the upper end of the reactor body 2. The injection volume should be in accordance with experimental requirements. After grouting, seal and fix the upper reactor cover 25 to the upper end of the reactor body 2 with the sealing gasket 7, and install the insulation sleeve 1 on the outside of the reactor body 2. Cure the cement grout for the time specified in API standards until the cement annulus 13 is formed. Step 3: After the cement ring 13 has cured and formed, apply the temperature, confining pressure, and inner pressure of the casing according to the experimental requirements: energize the heating rod 5 and adjust it to the required temperature through the temperature control system 6; after the temperature stabilizes, pressurize the confining pressure chamber 3 and observe the confining pressure gauge 11. When the required confining pressure is reached, close the confining pressure valve 9; at the same time, open the inner pressure valve 20 of the casing, introduce the No. 1 fluorescent perforating liquid from the No. 1 fluorescent perforating liquid tank 18 into the inner cavity 28 of the casing, and pressurize the inner cavity 28 of the casing. Observe the inner pressure gauge 22 of the casing. When the required inner pressure is reached, close the inner pressure valve 20 of the casing. Step 4: Maintain stable loading temperature, casing pressure, and confining pressure. Perforate the wellbore assembly using the perforation gun 14 to form a perforation channel 15, simulating the downhole perforation process. At this time, the No. 1 calcium ion fluorescent probe will adhere to the damaged area of ​​the cement sheath 13 caused by the perforation operation. Then, open the casing pressure valve 20 to discharge the No. 1 fluorescent perforation fluid in the casing cavity 28. Introduce clean water from the clean water tank 17 into the casing cavity 28 to flush away the residual No. 1 fluorescent perforation fluid and the unattached No. 1 calcium ion fluorescent probe. Then, discharge the clean water from the casing cavity 28. Introduce the No. 2 fluorescent fracturing fluid from the No. 2 fluorescent fracturing fluid tank 24 into the casing cavity 28 and adjust the casing pressure valve 20 to increase the casing pressure to simulate fracturing operations. At this time, the No. 2 calcium ion fluorescent probe will adhere to the damaged area of ​​the cement sheath 13 caused by the perforation and fracturing operations. Step 5: At this time, adjust the confining pressure valve 9 to release the confining pressure, adjust the casing internal pressure valve 20 to discharge the No. 2 fluorescent fracturing fluid and release the casing internal pressure, remove the upper vessel cover 25 and remove the cement ring 13 from the experimental equipment, irradiate the inner and outer interfaces of the cement ring with a fluorescent lamp and observe the fluorescence color development of the first and second interfaces of the cement ring, and collect fluorescence images under the same light source intensity, shooting distance and exposure conditions. The parts where both No. 1 and No. 2 calcium ion fluorescent probes show color are the damaged parts of the cement ring 13 caused by the perforation operation, and the parts where only No. 2 calcium ion fluorescent probe shows color are the damaged parts of the cement ring 13 caused by the fracturing operation. The area and intensity of the fluorescence images are then quantitatively analyzed. Step Six: After completing the above fluorescence observation and quantitative analysis, clean the experimental equipment and complete the experiment.

[0030] After the experiment, the fluorescence colorimetric results can be quantitatively processed. The first interface (the interface between cement ring 13 and sleeve 19) and the second interface (the interface between cement ring 13 and simulated surrounding rock 8) of the extracted cement ring 13 are placed under a stable fluorescence excitation light source for imaging. During imaging, the light source intensity, illumination angle, imaging distance, exposure time and environmental background are kept consistent. A scale is set in the field of view or the known sample size is used as a scale to establish the conversion relationship between pixel size and actual length and actual area.

[0031] As attached Figure 1 In step five, the acquired fluorescence image is preprocessed, including image cropping, background subtraction, brightness uniformization, and selection of effective observation area. The effective observation area includes the area within a specified radius around the first and second interfaces of the cement ring or the perforation channel, denoted as A0. Based on the color difference between the first and second calcium ion fluorescent probes, thresholds are set in the corresponding color channels to extract the color display area C1 of the first probe and the color display area C2 of the second probe. In damage assessment, the area where the first calcium ion fluorescent probe shows color or the area where the first and second calcium ion fluorescent probes show color over time is denoted as the damage area Cs formed during the perforation stage; the area where only the second calcium ion fluorescent probe shows color and there is no signal from the first probe is denoted as the newly added or extended damage area Cf during the fracturing stage; the union of Cs and Cf is denoted as the total damage area Ct, from which the perforation damage area As, the newly added fracturing damage area Af, and the total damage area At can be calculated. Calculate perforation damage coverage Increased damage coverage from fracturing and total damage coverage For fluorescence intensity information, the average value and integral value of pixel gray level or color channel intensity in each color development area are statistically analyzed to obtain the average fluorescence intensity Iavg and the integral fluorescence intensity Isum, which are used to characterize the degree of probe adhesion and damage connectivity in the damage channel. The crack morphology is described, the colored area is processed into a skeleton, the total length L of the fluorescent damage channel is extracted, and the damage length density is represented by L / A0; the equivalent damage width is represented by As / L, Af / L or At / L, which are used to compare the crack propagation degree and interface debonding scale under different casing internal pressure or different confining pressure conditions. When establishing the relationship between casing internal pressure and damage quantification index, multiple casing internal pressure levels P1, P2, P3...Pn were set, and parallel experiments were carried out under the same cement slurry formula, curing time, perforation parameters, confining pressure, temperature and liquid circulation regime. The As, Af, At, ηs, ηf, ηt, Iavg, L / A0 and other indices obtained at each pressure level were statistically analyzed to obtain a data set of damage index changes with casing internal pressure. Based on the above data set, the relationship between the damage area and the casing pressure was established by using linear fitting, quadratic polynomial fitting, exponential fitting, power function fitting or piecewise fitting. When the damage area or damage coverage rate showed a significant accelerated increase with the increase of casing pressure, the corresponding pressure range was taken as the critical pressure range for rapid expansion of cement ring interface damage. When the experiment needs to consider the effects of confining pressure and temperature simultaneously, a multi-factor relationship is established: D=f(P,σc,T,t), where D represents the damage quantification index, P represents the casing pressure, σc represents the confining pressure, T represents the experimental temperature, and t represents the cycle or loading time. By comparing the D values ​​under different parameter combinations, the effects of casing pressure, formation confining pressure, and temperature conditions on the damage evolution of the cement sheath after perforation fracturing are analyzed.

[0032] When the newly added damage coverage ηf or the total damage coverage ηt corresponding to a certain fracturing pressure increases significantly, it indicates that the risk of cement sheath interface integrity increases at that pressure level. Based on this, the fracturing construction pressure, pressurization rate and fluid circulation regime after perforation can be optimized to select construction parameters that can meet the reservoir stimulation requirements while reducing the risk of cement sheath interface debonding and sealing failure.

[0033] The above technical features constitute various embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A visualization experimental device for cement sheath damage throughout the entire perforation fracturing process, characterized in that... The system includes a vessel body, simulated surrounding rock, casing, and a perforating gun. An upper vessel cover and a lower vessel cover are installed on the upper and lower sides of the vessel body, respectively. Inside the vessel body, casing and simulated surrounding rock are sequentially arranged at intervals from the inside out, forming a cement annulus between the casing and the simulated surrounding rock. A confining pressure cavity is formed between the simulated surrounding rock and the vessel body, and this cavity is connected to a confining pressure tank via a confining pressure pipeline. A perforating gun located inside the casing is installed on the lower vessel cover. The casing cavity is connected to a perforation fluid tank and a fracturing fluid tank via casing pipelines. The perforation fluid and fracturing fluid are color-sensitive. The system also includes a clear water tank, connected to the clear water tank via casing pipelines. The system includes a No. 1 fluorescent perforating fluid tank and a No. 2 fluorescent fracturing fluid tank. The No. 1 fluorescent perforating fluid tank contains No. 1 fluorescent perforating fluid with a No. 1 calcium ion fluorescent probe, while the No. 2 fluorescent fracturing fluid tank contains No. 2 fluorescent fracturing fluid with a No. 2 calcium ion fluorescent probe. The two reagents are different colors. The system also includes a heating rod, a temperature control system, and a temperature sensor. A heating rod is installed on the lower lid of the confining pressure chamber, and a temperature sensor is installed inside the confining pressure chamber. The temperature sensor and heating rod are connected to the temperature control system, and an insulation sleeve is installed on the outside of the vessel.

2. The perforation fracturing process cement sheath damage visualization experimental device according to claim 1, characterized in that... The casing pipeline is equipped with a casing internal pressure valve and a casing internal pressure gauge, both of which are connected to the liquid circulation control system. The confining pressure pipeline is equipped with a confining pressure valve and a confining pressure gauge, both of which are connected to the confining pressure control system.

3. The perforation fracturing process cement sheath damage visualization experimental device according to claim 1 or 2, characterized in that... The upper and lower sides of the vessel body are sealed to the upper and lower vessel covers respectively by sealing gaskets.

4. An experimental method using the perforation fracturing full-process cement sheath damage visualization experimental device as described in claim 3, characterized in that... Follow these steps: Step 1: First, install the simulated surrounding rock, casing, and vessel body onto the lower vessel cover in sequence, then install the perforating gun onto the lower vessel cover, while keeping the upper vessel cover open; Step 2: Prepare the cement grout according to API standards. Under conditions where no confining pressure, casing pressure, or temperature is applied, inject the cement grout into the cement annulus between the casing and the simulated surrounding rock from the top of the reactor body. The injection volume should be determined according to experimental requirements. After grouting, seal and fix the upper reactor cover to the top of the reactor body with a sealing gasket, and install the insulation sleeve on the outside of the reactor body. Cure the cement grout for the time specified in API standards until the cement annulus is formed. Step 3: After the cement ring has cured and formed, apply the required temperature, confining pressure, and casing pressure according to the experimental requirements: Turn on the heating rod and adjust it to the required temperature through the temperature control system; after the temperature stabilizes, pressurize the confining pressure chamber and observe the confining pressure gauge. When the required confining pressure is reached, close the confining pressure valve; at the same time, open the casing pressure valve, introduce the No. 1 fluorescent perforating liquid from the No. 1 fluorescent perforating liquid tank into the casing cavity and pressurize the casing cavity. Observe the casing pressure gauge. When the required casing pressure is reached, close the casing pressure valve. Step 4: Maintain stable loading temperature, casing pressure, and confining pressure. Perforate the wellbore assembly using a perforation gun to form perforation channels, simulating the downhole perforation process. At this time, the No. 1 calcium ion fluorescent probe will adhere to the damaged areas of the cement sheath caused by the perforation operation. Then, open the casing pressure valve to drain the No. 1 fluorescent perforation fluid from the casing cavity. Pour clean water from the clean water tank into the casing cavity to flush away the remaining No. 1 fluorescent perforation fluid and any unattached No. 1 calcium ion fluorescent probes. Then, drain the clean water from the casing cavity. Next, pour the No. 2 fluorescent fracturing fluid from the No. 2 fluorescent fracturing fluid tank into the casing cavity and adjust the casing pressure valve to increase the casing pressure to simulate fracturing operations. At this time, the No. 2 calcium ion fluorescent probe will adhere to the damaged areas of the cement sheath caused by the perforation and fracturing operations. Step 5: At this point, adjust the confining pressure valve to release the confining pressure, adjust the casing internal pressure valve to discharge the No. 2 fluorescent fracturing fluid and release the casing internal pressure, remove the upper reactor cover and disassemble the cement sheath from the experimental equipment, irradiate the inner and outer interfaces of the cement sheath with a fluorescent lamp and observe the fluorescence color development of the first and second interfaces of the cement sheath, and collect fluorescence images under the same light source intensity, shooting distance and exposure conditions. The areas where both No. 1 and No. 2 calcium ion fluorescent probes show color are the damaged areas of the cement sheath caused by the perforation operation, and the areas where only No. 2 calcium ion fluorescent probe shows color are the damaged areas of the cement sheath caused by the fracturing operation. The area and intensity of the fluorescence images are then quantitatively analyzed. Step Six: After completing the above fluorescence observation and quantitative analysis, clean the experimental equipment and complete the experiment.

5. The experimental method according to claim 4, characterized in that... In step five, the acquired fluorescence images are preprocessed, including image cropping, background subtraction, brightness uniformization, and selection of effective observation areas. The effective observation areas include the area within a specified radius around the first and second interfaces of the cement ring or the perforation channel, denoted as A0. Based on the color difference between the first and second calcium ion fluorescent probes, thresholds are set in the corresponding color channels to extract the color development areas C1 and C2 of the first probe. In damage assessment, the area where the first calcium ion fluorescent probe shows color or the area where the first and second calcium ion fluorescent probes show color over time is denoted as the damage area Cs formed during the perforation stage; the area where only the second calcium ion fluorescent probe shows color and there is no signal from the first probe is denoted as the newly added or extended damage area Cf during the fracturing stage; the union of Cs and Cf is denoted as the total damage area Ct, from which the perforation damage area As, the newly added fracturing damage area Af, and the total damage area At can be calculated. Calculate the perforation damage coverage ηs = As / A0 × 100%, the new fracturing damage coverage ηf = Af / A0 × 100%, and the total damage coverage. For fluorescence intensity information, the average value and integral value of pixel gray level or color channel intensity in each color development area are statistically analyzed to obtain the average fluorescence intensity Iavg and the integral fluorescence intensity Isum, which are used to characterize the degree of probe adhesion and damage connectivity in the damage channel. The crack morphology is described, the colored area is processed into a skeleton, the total length L of the fluorescent damage channel is extracted, and the damage length density is expressed as L / A0. The equivalent damage width is represented by As / L, Af / L, or At / L, and is used to compare the degree of crack propagation and the scale of interface debonding under different casing internal pressures or different confining pressures. When establishing the relationship between casing internal pressure and damage quantification index, multiple casing internal pressure levels P1, P2, P3...Pn were set, and parallel experiments were carried out under the same cement slurry formula, curing time, perforation parameters, confining pressure, temperature and liquid circulation regime. The As, Af, At, ηs, ηf, ηt, Iavg, L / A0 and other indices obtained at each pressure level were statistically analyzed to obtain a data set of damage index changes with casing internal pressure. Based on the above data set, the relationship between the damage area and the casing pressure was established by using linear fitting, quadratic polynomial fitting, exponential fitting, power function fitting or piecewise fitting. When the damage area or damage coverage rate showed a significant accelerated increase with the increase of casing pressure, the corresponding pressure range was taken as the critical pressure range for rapid expansion of cement ring interface damage. When the experiment needs to consider the effects of confining pressure and temperature simultaneously, a multi-factor relationship is established: D=f(P,σc,T,t), where D represents the damage quantification index, P represents the casing pressure, σc represents the confining pressure, T represents the experimental temperature, and t represents the cycle or loading time. By comparing the D values ​​under different parameter combinations, the effects of casing pressure, formation confining pressure, and temperature conditions on the damage evolution of the cement sheath after perforation fracturing are analyzed.

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