A casing deformation and crack slip measurement method based on optical fiber, DIC and strain gauge and a casing deformation adjustment method

Abstract

The present invention discloses a casing deformation and crack slip measurement method and a casing deformation adjustment method based on optical fiber, DIC, and strain gauges, which are applied to the field of geological engineering and mechanical monitoring technology. In view of the limitations of the prior art in monitoring fault slip and casing deformation, the present invention proposes a casing deformation and crack slip simulation method based on DIC and strain gauges. Transparent soil samples are prepared with reference to the rock properties of the studied stratum, and processed to obtain standard samples; the standard samples are cut, and fault mud is laid on the cut surface. By arranging strain gauges near the fault, combined with optical fiber sensors and DIC technology on the casing surface, the casing deformation behavior during the fault slip process can be monitored in real time and accurately, and the slip amount, deformation amount and related mechanical parameters can be obtained. This multi-technology fusion monitoring method provides a high-precision and efficient solution for the dynamic monitoring and analysis of the casing mechanical behavior, which is of great significance for optimizing casing design and improving the safety of mining projects.

Description

Technical Field

[0001] The invention belongs to the technical field of geological engineering and mechanical monitoring, and in particular relates to a casing deformation and crack slip measurement technology. Background Art

[0002] With the continuous growth of global energy demand, the exploitation of oil and gas resources and geothermal resources has gradually developed towards deep and complex geological conditions, especially the development of unconventional oil and gas resources such as shale gas and tight gas has become increasingly important. In these exploitation processes, hydraulic fracturing technology is widely used to improve the permeability of reservoirs and enhance the recoverability of resources. However, the hydraulic fracturing process will cause the expansion of rock cracks and fault slip, which will have a huge impact on the casing structure around the casing, which may cause casing deformation, damage or even failure. Therefore, how to accurately monitor and analyze the casing deformation caused by fault slip has become an important issue to ensure the safety and effectiveness of deep well mining.

[0003] During the indoor experiment, traditional monitoring methods, such as acoustic emission and CT scanning technology, can effectively characterize post-compression cracks, but they often cannot provide global dynamic monitoring information of fault slip and casing deformation. Especially under complex geological conditions, the instantaneous characteristics of crack extension and fault slip are difficult to capture with a single monitoring method. In addition, the mechanical behavior of the casing is affected by many factors, including fault activity, formation pressure changes, construction technology, etc., which makes it difficult for existing technologies to fully analyze the coupling effects of these factors.

[0004] In recent years, digital image correlation (DIC) technology has been widely used in the fields of material mechanics, structural deformation, etc. as a non-contact, full-field measurement method. By analyzing the changes in the surface image of an object, DIC technology can obtain the displacement field and strain field distribution of the object under load. Its high precision and real-time performance give it unique advantages in dynamic monitoring. However, the research on the application of DIC technology in combination with other sensors in fault slip and casing deformation monitoring is still in the initial exploration stage.

[0005] Fiber optic sensing technology is also gradually being used in deep well engineering, and can achieve long-distance, continuous strain monitoring along the casing, providing important technical support for global monitoring of casing deformation. However, the synergistic application of fiber optic sensing technology with traditional sensors and DIC technology has not been fully developed, and its potential technical advantages need to be further explored and integrated. Summary of the invention

[0006] In view of the limitations of existing technologies in monitoring fault slip and casing deformation, the present invention proposes a casing deformation and crack slip measurement method and a casing deformation adjustment method based on optical fiber, DIC, and strain gauge. By simulating real underground working conditions, the dynamic process of fault slip and casing deformation is obtained, providing a reliable theoretical basis and data support for oil and gas development and other projects.

[0007] One of the technical solutions adopted by the present invention is: a method for measuring casing deformation and crack slip based on optical fiber, DIC and strain gauge, comprising:

[0008] S1. Rock sample preparation: Prepare transparent soil samples with reference to the rock properties of the studied stratum, and process them to obtain standard samples;

[0009] Drill blind holes on standard specimens;

[0010] Then the standard sample after the blind hole is drilled is cut through, and fault gouge is laid on the cutting surfaces of the upper and lower rock samples;

[0011] S2. Preparation of casing simulation device: Use a thin-walled aluminum tube to simulate the fracturing casing, spirally wind the optical fiber on the casing, and fill the bottom of the blind hole with edible salt. Insert the casing after winding the optical fiber into the blind hole, and fill the gap between the casing and the rock sample with epoxy resin; polish the surface of the sample to make it smooth; the blind hole into which the casing after winding the optical fiber is inserted passes through the fault;

[0012] In order to effectively isolate the direct effect of the fracturing fluid and obtain real fault slip data, the present invention also improves the casing simulation device; it is divided into the following two cases:

[0013] (1) Preparation for monitoring deformation of casing near the wellbore section: a thin-walled aluminum tube is used to simulate the fracturing casing, and a section of epoxy resin tape is added inside the casing to block the channel between the fracturing section and the measuring section; an optical fiber is wound around the measuring section to monitor deformation data in real time; and epoxy resin is filled in the gap between the casing and the rock sample; the surface of the sample is polished and flat; the fracturing section does not pass through the fault, and the measuring section passes through the fault;

[0014] (2) Preparation for monitoring casing deformation in near-well measurements: Preparation for monitoring casing deformation in near-well measurements is as follows: First, 5 cm blind holes are drilled symmetrically at both ends of the fault zone, and a 10 cm long casing wrapped with optical fiber is placed in it, and the gap between the casing and the rock sample is filled with epoxy resin to form a monitoring well; that is, the monitoring well passes through the fault. At the same time, a 10 cm blind hole is drilled at the left end of the sample, and a casing is placed in it, and the gap between the casing and the rock sample is also filled with epoxy resin to form a fracturing well; the fracturing well does not pass through the fault; the surface of the sample is polished and smooth;

[0015] S3. Fault slip monitoring preparation: strain gauges are arranged along the fault gap on both sides of the standard specimen after laying fault gouge;

[0016] S4, hydraulic fracturing: fix the sample processed in step S3 in a triaxial testing machine, place a piece of highly transparent tempered glass at the front end of the side parallel to the shaft axis, so that the camera can monitor the fault slip in real time through the glass; apply triaxial stress to the sample at the same time; then use hydraulic fracturing technology to pump fracturing fluid into the rock sample to generate cracks in the rock sample; the fracturing fluid is connected to the fault through the crack expansion, the fracturing fluid enters the fault and causes shear slip of the fault;

[0017] S5. When the fault slips, the casing deformation detected by the optical fiber sensor is recorded; the casing deformation is obtained through the optical fiber monitoring data;

[0018] When the fault slips, the response data of the strain gauge during the fault slip process is recorded;

[0019] The photos recorded by the camera are imported into the DIC technology software for processing to obtain the continuous fault slip field distribution;

[0020] S6. Correcting the fault slip field distribution according to the response data of the strain deviation;

[0021] S7. Constructing a stress response model of fault slip and casing deformation according to the fault slip field distribution corrected in step S6 and the casing deformation detected by the optical fiber.

[0022] The second technical solution adopted by the present invention is: a casing deformation adjustment method, which constructs a relationship between hydraulic fracturing parameters and casing deformation, and adjusts the hydraulic fracturing parameters based on the relationship to control the casing deformation.

[0023] Beneficial effects of the present invention: By arranging strain gauges near the fault, the present invention combines optical fiber sensors on the casing surface and DIC technology to monitor the casing deformation behavior during fault slip in real time and accurately, and obtain the slip amount, deformation amount and related mechanical parameters. This multi-technical fusion monitoring method provides a high-precision and efficient solution for the dynamic monitoring and analysis of casing mechanical behavior, which is of great significance for optimizing casing design and improving the safety of mining projects. Compared with the prior art, the present invention has the following advantages:

[0024] (1) Multi-technology integration: Through the comprehensive application of DIC technology, strain gauges and fiber optic sensors, global and real-time monitoring of fault slip and casing deformation is achieved, which improves the monitoring accuracy and comprehensiveness of analysis.

[0025] (2) Experimental controllability: By simulating the crack propagation and fault slip under real geological conditions through hydraulic fracturing and combining it with a true triaxial experimental device, we can ensure that the experimental results are close to the actual underground working conditions.

[0026] (3) Effectively predict failure modes and ensure mining safety: By constructing a stress response model of casing deformation and fault slip, the present invention can predict the failure mode of the casing, thereby optimizing the engineering design and enhancing the safety of the mining process.

[0027] (4) The present invention is applicable to hydraulic fracturing projects in complex geological environments, especially in deep well oil and gas production and geothermal development, and has important guiding significance for fault slip and casing deformation monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the relationship between fault slip and casing deformation based on DIC and strain gauge monitoring;

[0029] Figure 2 It is a schematic diagram of the overall structure of the pressure-fault slip measurement device of the present invention;

[0030] Figure 3 It is a schematic diagram of the overall structure of the fault slip measurement device for adjacent fracturing sections of the present invention;

[0031] Figure 4 It is a schematic diagram of the overall structure of the fault slip measurement device near the well of the present invention;

[0032] Figure 5 It is the schematic diagram of rock sample and fault after cutting;

[0033] Figure 6 is a schematic diagram of the optical fiber arrangement for monitoring the deformation of the casing;

[0034] Figure 7 This is a schematic diagram of the arrangement of strain gauges for monitoring fault slip;

[0035] Explanation of the accompanying numbers: 1 is a rock cut into two upper and lower blocks, 2 is fault mud, 3 is tempered glass, 4 is an aluminum casing, 5 is an optical fiber, 6 is a strain gauge, 7 is a high-speed camera, 8 is a generated hydraulic fracture, and 9 is an epoxy resin partition tape. DETAILED DESCRIPTION

[0036] To facilitate those skilled in the art to understand the technical content of the present invention, the present invention is further explained below with reference to the accompanying drawings.

[0037] The present invention provides a method for simulating casing deformation and crack slip based on digital image correlation (DIC) technology and strain gauges, aiming to solve the problem that the existing technology cannot accurately monitor the dynamic changes and mechanical behaviors of fault slip and casing deformation during hydraulic fracturing. The method of the present invention can effectively simulate the casing deformation and stress response caused by fault slip under complex underground geological conditions, ultimately optimize the engineering design, and ensure the stability and safety of the casing in actual engineering. Figure 1 As shown, the implementation process of the method of the present invention includes the following contents:

[0038] 1. Rock sample preparation

[0039] In order to better simulate the rock and fault environment in the stratum, a transparent soil sample with physical and mechanical properties similar to the actual stratum was prepared as the experimental material. The rock sample was processed and cut into a rock sample with a standard size of 300mm×150mm×150mm. After that, a blind hole with a diameter of 20mm and a depth of 270mm was drilled in the rock sample to simulate the position of the actual casing.

[0040] Transparent soil is a similar material used to study the mechanical properties of soil; transparent soil is transparent to the senses due to the matching refractive index of its solid and liquid phase materials. The raw materials of clay-type transparent soil are generally amorphous silica powder, # 15 White oil and n-dodecane. # 15 White oil, n-dodecane, fumed silica and quartz glass blocks can be used to prepare a transparent soil-rock mixture. The reason why transparent soil can be used to simulate real rock and soil materials is that its physical and mechanical properties are close to those of real rock and soil materials.

[0041] In order to further simulate the real characteristics of the fault, such as Figure 5 As shown, the rock sample is cut through, and fault mud is laid on the upper and lower rock samples after cutting. The role of fault mud is to simulate the sliding friction characteristics on the actual fault surface, so that the experiment can more accurately simulate the fault sliding process and its influence on the casing deformation. In the embodiment, fault mud with a large permeability is selected.

[0042] 2. Preparation for casing deformation monitoring

[0043] In order to monitor the mechanical effect of fault slip on casing, the present invention uses a thin-walled aluminum tube (diameter 18mm, length 250mm) as a casing simulation device. The size and wall thickness of the aluminum tube are experimentally designed to maximize the simulation of the stress response behavior of the downhole casing during hydraulic fracturing.

[0044] This embodiment provides the following three types of sleeves:

[0045] (1) Figure 2 As shown in the figure, the preparation for monitoring casing deformation with pressure measurement is as follows: a thin-walled aluminum tube is selected to simulate the fracturing casing, an optical fiber is spirally wound on the casing, and the bottom of the blind hole is filled with edible salt. The casing with the fiber wound is inserted into the blind hole, and the gap between the casing and the rock sample is filled with epoxy resin; the surface of the sample is polished and smooth;

[0046] (2) Figure 3 As shown in the figure, the preparation for monitoring the deformation of the casing in the adjacent well section is as follows: a thin-walled aluminum tube is used to simulate the fracturing casing, and a section of epoxy resin tape is added inside the casing to block the channel between the fracturing section and the measuring section. The optical fiber is wound around the measuring section to monitor the deformation data in real time. The gap between the casing and the rock sample is filled with epoxy resin; the surface of the sample is polished and smooth;

[0047] Figure 3 The situation shown. Fiber optic sensors are usually arranged in the unfractured section adjacent to the fractured section, and the two sections are usually separated by a bridge plug. When the fracturing fluid is injected into the fractured section, the expansion of the crack may cause the adjacent fault to slip and generate slip pressure. Since the fiber optic sensor is arranged in the section adjacent to the fault but not fractured, it can effectively isolate the direct effect of the fracturing fluid and obtain the real fault slip data. Since the fractured section does not cross the fault, the fault slip will not have a direct impact on the wellbore structure of the fractured section itself. However, the adjacent unfractured section crosses the fault, so when the fault slip occurs, the impact of the fault slip will be transmitted to the adjacent section, which may cause the casing to deform. In order to monitor this deformation, the fiber optic sensor is arranged in the wellbore adjacent to the fractured section, especially on the casing of the unfractured section that crosses the fault. The fiber optic sensor can reflect the stress change caused by the fault slip by accurately measuring the deformation of the casing. The arrangement of the fiber optic sensor can monitor the deformation of the casing in real time, thereby providing engineers with the wellbore deformation data caused by the fault slip.

[0048] (3) Figure 4 As shown, the preparation for monitoring casing deformation in the adjacent well is as follows: First, 5 cm blind holes are drilled symmetrically at both ends of the fault zone, and a 10 cm long casing wrapped with optical fiber is placed in it, and the gap between the casing and the rock sample is filled with epoxy resin to form a monitoring well. At the same time, a 10 cm blind hole is drilled at the left end of the sample, and the casing is placed in it, and the gap between the casing and the rock sample is also filled with epoxy resin to form a fracturing well; the surface of the sample is polished and smooth;

[0049] Figure 4The situation shown includes: a fracturing well that does not cross the fault, and a well adjacent to the fault. The expansion of the cracks during the fracturing process may activate the adjacent faults, but since the fracturing well does not directly cross the fault, the fault slip will not have a direct impact on the fracturing well itself. However, the well adjacent to the fault crosses the fault, and the fault slip may cause deformation or damage to the casing, which is crucial for evaluating the safety of the wellbore and the fracturing effect. In this case, the fiber optic sensor is arranged in the well adjacent to the fault, especially in the casing, to monitor the deformation of the casing in real time. The fiber optic sensor can accurately measure the deformation of the casing through the change of the reflected light signal, thereby reflecting the deformation strain caused by the fault slip. These data can provide engineers with information about the degree of influence of the fault slip on the wellbore structure, thereby providing data support for subsequent fracturing operations and helping to determine the stability and safety of the well adjacent to the fault. Through this measuring device, the casing deformation caused by fault slip in the well adjacent to the fault during the fracturing process can be effectively monitored. These data are of great significance for evaluating the bearing capacity of the wellbore, determining the possible risk of casing damage, optimizing fracturing design and ensuring the safety of downhole operations.

[0050] like Figure 6 As shown in the figure, the fiber optic sensor is spirally wound on the surface of the aluminum tube, and the fiber optic sensor is used to monitor the deformation of the casing caused by fault slip in real time. The winding method of the optical fiber is designed to ensure that the optical fiber can evenly cover the surface of the casing, so that it can accurately record the deformation when the fault slips.

[0051] In order to simulate the actual compaction state of the well bottom, the bottom of the blind hole can be filled with 20mm thick edible salt or small particles such as quartz sand. The aluminum casing is inserted into the blind hole, and epoxy resin is injected into the gap between the rock sample and the casing to fix the casing to ensure that the force transmission is not disturbed during the experiment and to prevent the epoxy resin from penetrating into the casing.

[0052] After filling the epoxy resin, in order to ensure the uniform force on the sample, the surface of the sample is polished with a grinder to make the surface flat and smooth, which is crucial to the accuracy of the experiment and the precision of the fiber optic sensor data.

[0053] Fiber Bragg Grating (FBG) technology derives strain by measuring the change in the Bragg wavelength in the optical fiber. When the optical fiber is stretched or compressed externally, the optical properties of the Bragg grating in the optical fiber will change, which manifests as a change in the Bragg wavelength.

[0054] When the optical fiber is stressed, the Bragg wavelength λ B will change, the formula is:

[0055] △λ B =λ B ·(1-pe)·εF iber

[0056] Where: △λ B is the change in Bragg wavelength; λ B is the initial Bragg wavelength; pe is the photoelastic coefficient of the optical fiber, usually 0.22 to 0.23; ε F iber is the fiber strain (dimensionless);

[0057] The strain calculation formula can be calculated by measuring the wavelength change △λ B , the strain can be calculated directly:

[0058]

[0059] This formula shows that a small change in the Bragg wavelength is proportional to the strain. After measuring the change in the Bragg wavelength, the initial wavelength △λ of the optical fiber is used to calculate the B and the photoelastic coefficient pe, we can get the strain ε of the optical fiber at that point F iber.

[0060] The relationship between the casing deformation and the measured strain value is:

[0061] △L 2 =ε F iber×L F iber

[0062] Where: L F iber is the initial length of the optical fiber along the measurement direction; △L 2 is the deformation of the casing.

[0063] 3. Fault slip monitoring preparation

[0064] Strain Gauge Monitoring Technology

[0065] In the process of monitoring fault slip, the present invention arranges strain gauges on both sides of the fault gap on the rock surface. Figure 7 As shown, strain gauges are distributed at different positions on both sides of the fault slip surface. The purpose is to measure the displacement difference of the fault slip and record the strain changes in different areas during the slip process, so as to accurately measure the fault slip amount, slip velocity and stress distribution in different parts.

[0066] These strain gauges can capture the stress and strain changes at various locations on the slip surface during the fault slip process in real time, and the data will serve as the main basis for the change in fault slip. The sensitivity of the strain gauge can reach the micro-strain level, which means that even if the fault slip is very small, it can be accurately captured, thereby providing high-precision data support for the quantitative analysis of fault slip. The data obtained through the strain gauge can establish a mechanical behavior model during the fault slip process and provide a reference for subsequent engineering optimization.

[0067] 4. Combination of DIC and strain gauge technology

[0068] During the entire process of hydraulic fracturing and fault slip, the experiment was recorded using high-speed camera technology. Through the tempered glass window, the camera can clearly capture the crack expansion and fault slip of the sample.

[0069] Strain gauges have the ability to monitor strains at local locations in real time with high precision, and are particularly suitable for accurately measuring displacement differences, strain magnitudes, and stress distributions before and after faults during fault slip. However, they also have limitations. They can only provide strain data at a limited number of arrangement points, and cannot cover the slip amount or global strain distribution of the entire fault. Therefore, DIC technology is introduced to monitor the entire fault. DIC technology uses camera data and image correlation algorithms to obtain the displacement field and strain field distribution of the specimen during the force process. After the image data recorded by the high-speed camera is processed by DIC technology, the real-time dynamic analysis results of the fault slip can be obtained, and important mechanical parameters such as the strain field and displacement field on the slip surface can be generated. This process provides important technical support for studying local mechanical behavior in slip, and can accurately reflect the entire process of crack extension and fault slip.

[0070] DIC technology can provide a global view of fault slip through image processing technology, monitor the overall deformation and slip of the fault, and is particularly suitable for capturing strain and displacement changes over a large area. However, its accuracy may not be as good as strain gauges, especially when monitoring small strains. Therefore, it is necessary to effectively combine strain gauges with DIC technology, and it is necessary to coordinate the synchronous acquisition and processing of the two types of data to give full play to their advantages. The combination can be achieved through the following steps:

[0071] Modeling local and global relationships

[0072] The present invention uses the local data of the strain gauge as the basis for correcting the global data of the DIC technology, that is, through the accurate strain gauge measurement results, the DIC image processing results are calibrated to construct a mathematical model reflecting the slip of the entire fault.

[0073] The strain gauge is arranged at different positions of the fault. Assuming that the strain gauge is arranged at a position xi, the measured strain value is εsg(t). According to the relationship between strain and slip, the slip at this position can be obtained through the strain gauge. The relationship between strain and slip at the strain gauge measurement point is:

[0074] △Lsg(xi,t)=εsg(t)×Lsg

[0075] Among them: εsg(t) is the strain value at time t measured by the strain gauge; Lsg is the initial length of the strain gauge along the measurement direction; △Lsg(xi,t) is the slip amount of the fault at a certain point calculated by the strain gauge.

[0076] DIC global measurement data:

[0077] DIC technology can monitor the displacement changes at continuous positions on the fault and obtain a continuous fault slip field distribution △L DIC (x, t), which can describe the slip at the fault front and other areas not covered by strain gauges.

[0078] Fusion strategy:

[0079] First, the DIC data is calibrated using the strain gauge data. At the point xi where the strain gauge is arranged, the slip △Lsg(xi,t) measured by the strain gauge is compared with the DIC data △L DIC (x,t), compare and construct the calibration factor λ(xi,t)

[0080]

[0081] The DIC global slip data is corrected to a more accurate slip distribution by this calibration factor λ(xi,t):

[0082] △L 1 (xi,t)=λ(xi,t)·△L DIC (x,t)

[0083] Among them, λ(xi,t) can be used to extend the strain gauge correction factor to the entire fault through interpolation or fitting methods.

[0084] 5. Hydraulic fracturing

[0085] In the present invention, hydraulic fracturing technology is used to induce the generation and expansion of rock sample cracks and simulate the actual underground fault slip conditions. The processed samples are fixed in a triaxial testing machine, and the design of the testing machine can ensure that the rock samples are subjected to triaxial stress close to the actual underground conditions during the fracturing process.

[0086] In order to monitor the whole process of crack extension and fault slip, Figure 2As shown in the figure, a piece of tempered glass is placed at the front end of the triaxial testing machine, which not only ensures the authenticity of the force applied to the specimen, but also provides a transparent window for subsequent high-speed photography and DIC technical analysis.

[0087] During the hydraulic fracturing process, by pumping high-pressure fracturing fluid into the sample, the cracks expand along the weak surface or natural cracks in the rock sample until they are connected to the fault. As the cracks are connected to the fault, the fracturing fluid continues to act on the fault, causing shear slip of the fault. This process truly reproduces the fault slip phenomenon caused by hydraulic fracturing in actual engineering.

[0088] 6. Data Analysis and Optimization

[0089] During the experiment, the collected data include strain information obtained by strain gauges, casing deformation recorded by optical fiber sensors, and displacement and strain distribution diagrams generated by DIC technology. Through comprehensive analysis of these data, an accurate stress response model of fault slip and casing deformation can be constructed.

[0090] Response Model:

[0091] Fault slip △L 1 (xi,t) will cause the casing to deform △L 2 (xi,t), the deformation can be expressed as a function of the slip:

[0092] △L 2 (xi,t)=m·△L 1 (xi,t)

[0093] Among them, m is the proportional coefficient of slip and casing deformation, which depends on the material and geometric characteristics of the casing.

[0094] The model can effectively deduce the casing deformation according to the fault slip, or inversely calculate the fault slip according to the casing deformation. Through the analysis of the model, the failure mode that may be caused by casing deformation can be predicted, providing an important basis for further casing design.

[0095] One of the optimization directions of the present invention is to adjust the hydraulic fracturing parameters, such as the injection rate of the fracturing fluid, the fluid viscosity, and the injection pressure, etc. The adjustment of these parameters can control the direction and speed of the crack expansion, thereby optimizing the coordination between the crack and the fault slip, and further providing technical support for the hydraulic fracturing process in the actual formation.

[0096] The fracture propagation velocity vf(t) varies with time and is affected by the fracturing fluid injection rate q(t), fluid viscosity μ, and injection pressure P(t). Its expression can be written as:

[0097]

[0098] Among them, k1 ,k 2 ,k 3 is an empirical constant obtained through experiments.

[0099] The direction of fracture propagation θf(t) is also affected by these parameters, especially the difference in injection pressure and ground stress. It can be expressed as:

[0100] θf(t)=g(P(t),σ)

[0101] Where σ is the distribution of geostress.

[0102] The amount of slip after the crack meets the fault:

[0103] When the crack meets the fault, the fault slip △L 1 (xi,t) is affected by the crack propagation velocity vf(t), the crack direction θf(t) and the fracturing conditions. It can be expressed as:

[0104] △L 1 (xi,t)=h(vf(t),θf(t),P(t))

[0105] Or simplified to:

[0106] △L 1 (xi,t)=c 1 ·vf(t)+c 2 ·θf(t)+c 3 ·P(t)

[0107] Among them, c 1 ,c 2 ,c 3 is the adjustment coefficient, which depends on the geometric relationship between the fault and the crack; △L 1 (xi,t) is the fault slip which can be measured by strain gauges.

[0108] Casing deformation:

[0109] Finally, the fault slip △L 1 (xi,t) will cause the casing to deform △L 2 (xj,t), the deformation can be expressed as a function of the slip:

[0110] △L 2 (xj,t)=m·△L 1 (xi,t)

[0111] Among them, m is the proportional coefficient of slip and casing deformation, which depends on the material and geometric characteristics of the casing.

[0112] By setting △L 1Substituting the expression of (t) into the equation, we can get the complete expression of casing deformation over time:

[0113] △L 2 (xj,t)=m·(c 1 ·vf(t)+c 2 ·θf(t)+c 3 ·P(t)

[0114] Substituting the expressions of vf(t) and θf(t), we finally get:

[0115]

[0116] Therefore, the magnitude of fault slip can be adjusted by changing the fracturing fluid injection rate q(t), fluid viscosity μ, and injection pressure P(t), thereby reducing the casing deformation.

[0117] In practical applications, the casing deformation safety value is determined based on the casing material; and based on the deformation safety value, the safety values ​​of the parameters such as the fracturing fluid injection rate q(t), fluid viscosity μ, and injection pressure P(t) are calculated; thereby providing safety guidance for the parameters of on-site wellbore fracturing.

[0118] As shown in Table 1, for casing with a normal inner diameter of 114.3 mm, when the inner diameter of the casing changes due to different deformation amounts, the corresponding risk level is, for example, when the risk level is A, the casing deformation amount is 29.3 mm, when the risk level is B, the casing deformation amount is 29.3 mm to 60.3 mm, and when the risk level is C, the casing deformation amount is greater than 60.3 mm; obviously, for casing with a normal inner diameter of 114.3 mm, when the casing deformation amount is greater than 60.3 mm, the well has no reconstruction value; therefore, for casing with a normal inner diameter of 114.3 mm, the safety value of its deformation amount should be controlled within 60.3 mm; in actual applications, for casings with different inner diameters, the safety value of its deformation amount is set to half of the corresponding casing inner diameter.

[0119] Table 1 Risk levels corresponding to different deformation amounts of casing with a normal inner diameter of 114.3 mm

[0120]

[0121] According to the safety value of casing deformation in actual application set above, based on the geometric similarity and deformation similarity given below, the deformation safety value corresponding to the casing in the test is obtained; thus, based on this safety value, the fracturing fluid injection rate q(t), fluid viscosity μ, and injection pressure in the test are adjusted so that the deformation of the casing in the test is within the safety value range.

[0122] The parameters of the on-site wellbore fracturing fluid are calculated based on the similarity criterion according to the parameter safety values ​​obtained in the test.

[0123] Similarity criteria

[0124] When applying indoor experimental data to field conditions, the conversion should be done according to similar principles as follows:

[0125] (1) Geometric similarity

[0126] The geometric shape of the wellbore model must follow the principle of similarity with the field wellbore, that is, the geometric proportions of the two should be consistent. Assuming that the size of the experimental model is Lmodel and the size of the field wellbore is Lfield, the geometric similarity requirements between the two are:

[0127]

[0128] This ensures that the deformation mode reflected in the experimental results is consistent with the deformation of the actual wellbore on site.

[0129] (2) Stress similarity

[0130] In the laboratory, the stress conditions of the wellbore (such as fracturing fluid injection pressure, formation stress, etc.) are different from those in the field. In order to accurately convert the experimental results into the field stress field, it is necessary to maintain stress similarity by adjusting the ratio of the injection pressure Pmodel in the experiment and the actual fracturing pressure Pfield in the field:

[0131]

[0132] This formula reflects the relationship between pressure and volume. By adjusting the experimental pressure, the stress distribution in the experimental model can be matched with the stress distribution under field conditions.

[0133] (3) Deformation similarity

[0134] Deformation similarity requires that the casing deformation measured in the experiment is in the same proportion to the actual wellbore deformation in the field. Assuming that the deformation at a certain position in the experiment is △dmodel and the deformation at the corresponding position in the field is △dfield, the two should satisfy:

[0135]

[0136] Through this ratio, the small-scale deformation in the experiment can be converted into the large-scale deformation in the field.

[0137] (4) Temporal similarity

[0138] Since the duration of experiments under laboratory conditions is different from the time scale of field fracturing operations, the time scale may be compressed in the experiment. Therefore, the time tfield in the field and the time tmodel in the laboratory should be similar:

[0139]

[0140] With this time-scale adjustment formula, the same stress / deformation development process can be simulated in the experiment and applied to the prediction of the field wellbore.

[0141] Based on the above four-point similarity criteria, in practical applications, the size of the rock sample in the test and the conventional wellbore fracturing parameters are known. Then, according to the stress similarity and time similarity, the stress that needs to be applied to the rock sample in the test, the test time, the injection rate q(t), and the fluid viscosity μ are calculated when the initial conditions are calculated; the fault slip of the rock sample in the test measured under the initial conditions and the casing deformation in the test are obtained; if the casing deformation in the test does not exceed the set safety value, the actual wellbore deformation calculated by deformation similarity can be calculated according to the risk level shown in Table 1, and the actual wellbore can be fractured; if the casing deformation in the test is greater than the safety value, the injection rate q(t), fluid viscosity μ, and injection pressure P(t) of the fracturing fluid in the test need to be adjusted so that according to the formula The calculated casing deformation is less than or equal to the safety value. Then, based on stress similarity and time similarity, the corresponding parameter values ​​of injection rate, fluid viscosity, and injection pressure in the actual wellbore fracturing are obtained. This avoids the wellbore deformation exceeding the safety value in the actual wellbore fracturing, resulting in the actual fracturing well being unable to be reformed or the reformation cost being too high.

[0142] The second optimization direction of the present invention is: based on the calculated deformation position of the casing under the initial conditions, thickening treatment is performed at the corresponding position of the new casing.

[0143] Based on similarity criteria and experimental data, the locations where casing deformation may occur in the field wellbore during fracturing can be estimated. Based on the conversion coefficient between the experiment and the field, the high-risk locations where deformation or rupture may occur in the field wellbore under the same conditions can be predicted.

[0144] The actual wellbore deformation position is predicted based on geometric similarity, and corresponding thickening measures are taken to enhance the structural strength of the wellbore and ensure the stability of the wellbore in subsequent operations. The specific thickening treatment needs to consider the actual deformation of the depth section where the casing is located, and the thickening standard is determined based on the calculated deformation range, which is generally 1 / 5 of the casing deformation. For example, when the casing deformation reaches 30-60mm, it may be necessary to increase the casing thickness by 6-12mm to ensure that the casing strength can withstand the long-term internal and external pressure difference and formation stress.

[0145] In addition, the casing material can be replaced to improve its bearing capacity. The replacement material must be an alloy material with higher pressure resistance, corrosion resistance and temperature resistance. Common replaceable materials include alloy steel, nickel-based alloy, titanium alloy, etc. Among them, alloy steel (such as J55, K55, N80, etc.) has good tolerance under conventional pressure; nickel-based alloy (such as Inconel 625) can provide stronger corrosion resistance and fatigue resistance under high temperature and high pressure environment; titanium alloy (such as Ti-6Al-4V) exhibits excellent corrosion resistance and high strength in a strong corrosive environment. According to the specific formation conditions and operating environment, selecting suitable alloy materials for replacement can significantly improve the bearing capacity and durability of the casing, and prevent the casing from excessive deformation or damage during the fracturing process.

[0146] Through the above method, it is possible to ensure that the casing maintains sufficient stability during the entire fracturing process based on real-time monitoring data and similarity criteria without changing the fracturing parameters.

[0147] Application and Effect

[0148] Through the above implementation, the experimental process of the present invention can accurately simulate the mechanical behavior of fault slip and casing deformation under complex geological conditions. Compared with the traditional single monitoring technology, the present invention combines DIC technology, optical fiber sensor and strain gauge, which can realize global and real-time monitoring of fault slip and casing deformation and obtain high-precision mechanical parameters.

[0149] The method of the present invention is not only applicable to hydraulic fracturing research under laboratory conditions, but also can provide a reference basis for actual oil and gas wells, geothermal wells and other projects. By analyzing the impact of fault slip on casing, the casing design can be optimized, the overall safety and reliability of the casing can be improved, and the engineering risk can be reduced.

[0150] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for measuring casing deformation and crack slip based on optical fiber, DIC and strain gauge, characterized in that: include: S1. Rock sample preparation: Prepare transparent soil samples with reference to the rock properties of the studied stratum, and process them to obtain standard samples; S2. Preparation of casing simulation device: Drill blind holes on standard specimens; Then the standard sample after the blind hole is drilled is cut through, and fault gouge is laid on the cutting surfaces of the upper and lower rock samples; A thin-walled aluminum tube is used to simulate a fracturing casing, an optical fiber is spirally wound on the casing, and edible salt is filled at the bottom of the blind hole. The casing wound with the optical fiber is inserted into the blind hole, and epoxy resin is filled in the gap between the casing and the rock sample. The surface of the sample is polished and flat. The blind hole into which the casing wound with the optical fiber is inserted passes through the fault. S3. Fault slip monitoring preparation: strain gauges are arranged along the fault gap on both sides of the standard specimen after laying fault gouge; S4, hydraulic fracturing: fix the sample processed in step S3 in a triaxial testing machine, place a piece of highly transparent tempered glass at the front end of the side parallel to the shaft axis, so that the camera can monitor the fault slip in real time through the glass; apply triaxial stress to the sample at the same time; then use hydraulic fracturing technology to pump fracturing fluid into the rock sample to generate cracks in the rock sample; the fracturing fluid is connected to the fault through the crack expansion, the fracturing fluid enters the fault and causes shear slip of the fault; S5. When the fault slips, the casing deformation detected by the optical fiber sensor is recorded; the casing deformation is obtained through the optical fiber monitoring data; When the fault slips, the response data of the strain gauge during the fault slip process is recorded; The photos recorded by the camera are imported into the DIC technology software for processing to obtain the continuous fault slip field distribution; S6. Correcting the fault slip field distribution according to the response data of the strain gauge; S7. Constructing a stress response model of fault slip and casing deformation according to the fault slip field distribution corrected in step S6 and the casing deformation detected by the optical fiber.

2. The method for measuring casing deformation and crack slip based on optical fiber, DIC and strain gauge according to claim 1, characterized in that: Transparent soil sample utilization # 15 white oil, n-dodecane, fumed silica and quartz glass block are prepared.

3. The method for measuring casing deformation and crack slip based on optical fiber, DIC and strain gauge according to claim 2, characterized in that: Replace step S2 with: S2. Preparation of casing simulation device: Drill blind holes on standard specimens; Then the standard sample after the blind hole is drilled is cut through, and fault gouge is laid on the cutting surfaces of the upper and lower rock samples; A thin-walled aluminum tube was used to simulate the fracturing casing, and a section of epoxy resin tape was added inside the casing to block the channel between the fracturing section and the measuring section. An optical fiber was wound around the measuring section to monitor deformation data in real time. The gap between the casing and the rock sample was filled with epoxy resin. The surface of the sample was polished and smooth. The fracturing section did not pass through the fault, but the measuring section passed through the fault.

4. The method for measuring casing deformation and crack slip based on optical fiber, DIC and strain gauge according to claim 3 is characterized in that: Replace step S2 with: S2. Preparation of casing simulation device: The standard sample is cut, and fault gouge is laid on the cutting surfaces of the upper and lower rock samples, so as to construct a fault zone in the standard sample; Two blind holes of the same length are symmetrically drilled at both ends of the fault zone to obtain a first blind hole that passes through the fault; a first sleeve wrapped with an optical fiber is placed in the first blind hole, and the gap between the first sleeve and the first blind hole is filled with epoxy resin to form a monitoring well; at the same time, a second blind hole of the same length as the first blind hole is drilled next to the monitoring well, the second blind hole does not pass through the fault, a second sleeve is placed in the second blind hole, and the second sleeve and the second blind hole are filled with epoxy resin to form a fracturing well; the surface of the sample is polished and smooth.

5. A method for measuring casing deformation and crack slip based on optical fiber, DIC and strain gauge according to any one of claims 1 to 4, characterized in that: Step S6 is specifically as follows: Assume that the position x on the fault i The strain value measured by the arranged strain gauge at time t is ε sg (t); According to the relationship between strain and slip, the slip at this position is obtained through the strain gauge: △L sg (x i ,t)=ε sg (t)×L sg Where: L sg is the initial length of the strain gauge along the measuring direction; △L sg (x i ,t) is the position x on the fault at time t i The amount of slip; The continuous fault slip field distribution obtained by DIC technology is denoted as △L DIC (x,t); Use the strain gauge data to calibrate the DIC data. Specifically: at the point x where the strain gauge is arranged i At the point where the slip measured by the strain gauge is sg (x i ,t) and DIC data △L DIC (x, t), and compare them to construct the strain gauge calibration factor λ(x i ,t) By using this calibration factor λ(x i ,t) Correction of DIC global slip data: △L1(t)=λ(x i ,t)·△L DIC (x,t) Among them, △L1(t) is the corrected fault slip distribution.

6. The method for measuring casing deformation and crack slip based on optical fiber, DIC and strain gauge according to claim 5, characterized in that: The strain gauge correction factor is extended to the entire fault by interpolation or fitting methods.

7. The method for measuring casing deformation and crack slip based on optical fiber, DIC and strain gauge according to claim 6, characterized in that: The stress response model of fault slip and casing deformation in step S7 is: △L2(t)=m·△L1(t) Among them, △L2(t) is the sleeve deformation variable measured by the optical fiber at time t, and m is the proportional coefficient between the slip amount and the sleeve deformation.

8. The method for measuring casing deformation and crack slip based on optical fiber, DIC and strain gauge according to claim 7, characterized in that: m is obtained by fitting the fault slip field distribution at each moment with the casing deformation detected by optical fiber.

9. A method for adjusting casing deformation, characterized in that: Construct a relationship between hydraulic fracturing parameters and casing deformation, and adjust the hydraulic fracturing parameters based on the relationship to control the casing deformation; the hydraulic fracturing parameters include: crack expansion speed v f (t), crack direction θ f (t) and injection pressure P(t); The process of constructing the relationship between hydraulic fracturing parameters and casing deformation is as follows: Consider that when a crack meets a fault, the fault slip △L1(t) is affected by the crack extension velocity v f (t), crack direction θ f (t) and the influence of injection pressure P(t); △L1(t) is expressed as: △L1(t)=h(v f (t),θ f (t),P(t)) Simplified to: △L1(t)=c1·v f (t)+c2·θ f (t)+c3·P(t) Among them, c1, c2, c3 are adjustment coefficients; Combining △L2(t)=m·△L1(t), we get: △L2(t)=m·(c1·v f (t)+c2·θ f (t)+c3·P(t)) The fracture propagation rate is affected by the fracturing fluid injection rate q(t), fluid viscosity μ, and injection pressure P(t); v f The expression of (t) is: Among them, k1, k2, k3 are empirical constants; The direction of crack extension θ f (t) is expressed as: i f (t)=g(P(t),σ) Where, σ is the distribution of ground stress; v f (t) and θ f Substitute the expression of (t) into △L2(t) = m·(c1·v f (t)+c2·θ f (t)+c3·P(t)), we finally get: Determine the safe value of casing deformation; Based on the safe value of casing deformation, the safe values ​​of q(t), μ, and P(t) corresponding to the casing fracturing fluid are calculated.

10. A method for adjusting casing deformation, characterized in that: According to claim 8, the deformation of the casing at different positions is measured, and the positions exceeding the safe value of the casing deformation are reinforced.

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