Rock core deformation optical monitoring system and method

Abstract

The invention discloses a rock core deformation optical monitoring system and method, and aims to solve the problems that in the prior art, early-stage key deformation of rock core sampling cannot be captured, the measurement precision is insufficient, and the field adaptability is poor. The micro optical projection unit, the high-speed imaging unit and the environment compensation unit are integrated on the inner wall of the coring cylinder, and the optical lever amplification effect is achieved through the 40-50-degree projection imaging angle design; double-frequency grating monitoring is adopted, a low-frequency grating is used for large-range deformation monitoring, a high-frequency grating is used for capturing tiny deformation, and by combining an improved multi-frequency heterodyne phase demodulation algorithm, the radial and axial tiny deformation of a rock core can be converted into phase change capable of being accurately measured. The system is automatically started when a rock core enters a coring cylinder, the whole stress release deformation process is captured in stages, the system can be integrated in a standard coring process without additional operation, and the system is suitable for the fields of geological exploration, oil exploitation, mine engineering and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of rock mechanics testing and optical measurement technology, and particularly relates to a core sampling process stress release deformation monitoring system and method based on dual-frequency grating projection. BACKGROUND

[0002] Underground surrounding rock is in a complex confining pressure environment for a long time. When the core is taken out from the underground, stress release deformation will immediately occur due to the sudden decrease of confining pressure. The deformation process mainly includes axial deformation and radial deformation. These small deformations (usually several microns to tens of microns) are completed within a few minutes after the core is taken out. Traditional measurement methods cannot capture the key process and measure the accurate deformation due to slow response speed and low precision. The data of this stage is the core basis for analyzing the distribution of in-situ stress field, and is crucial for the safety design of underground engineering such as oil and gas exploitation and mine engineering.

[0003] The traditional methods such as relaxation strain measurement method and flat jack method in the prior art need to be tested offline after the core is completely taken out. The interval from the completion of coring to the installation of equipment has missed the early key deformation, resulting in the loss of data integrity and the difficulty in reflecting the initial dynamic characteristics of stress release. Although the existing technologies such as digital image correlation (DIC) and optical fiber sensing can measure small deformations, they are expensive and complex to operate, and are sensitive to environmental disturbances such as underground temperature and humidity fluctuations, vibration and mud coverage. They are prone to failure in high humidity and high dust environments, and have poor adaptability. Other patent technologies are related to core measurement, but they are all aimed at the core after taking, and do not cover the key early stage of stress release during the coring process. In addition, the existing technical methods mostly rely on manual operation, and professional personnel are needed to debug the equipment and collect data on the coring site. The standardization of the coring process is complicated and has low integration, which not only prolongs the operation time, but also may affect the data precision due to operation errors, and it is difficult to meet the needs of fast and automatic monitoring on site. SUMMARY

[0004] In view of the problems of existing core stress release deformation monitoring technology such as late monitoring opportunity, insufficient measurement precision, complicated process and low integration, the present application provides a core deformation optical monitoring system and method. Through the cooperative design of dual-frequency grating projection and high-speed imaging, the present application realizes the high-precision capture of micron-level deformation during the core sampling process, and aims to realize the real-time, high-precision and full-cycle monitoring of stress release deformation during the core sampling process.

[0005] The purpose of the present application is mainly achieved by the following technical solutions:

[0006] One aspect of the present application provides a core deformation optical monitoring method, and the specific steps are as follows:

[0007] Step 1. A dedicated coring barrel integrated with a miniature optical monitoring module is installed on the drilling equipment. When the front end of the core enters the coring barrel and triggers the pressure sensor, the system automatically starts. The miniature projection unit projects a dynamically encoded dual-frequency grating (low-frequency grating for large-scale deformation monitoring, high-frequency grating for small deformation capture) onto the core surface; the high-speed imaging unit enters the synchronous acquisition mode. The environmental compensation unit starts simultaneously, recording temperature, humidity, and pressure parameters in real time, establishing an environmental benchmark for subsequent data correction. The data processing unit adjusts the grating contrast adaptively according to the initial image characteristics of the core surface to adapt to different lithology and downhole environmental conditions.

[0008] Step 2. The miniature projection unit projects a sequence of low, medium, and high frequency sinusoidal gratings in turn; the high-speed imaging unit synchronously acquires the corresponding four-step phase shift images (phase shift amounts are 0, π / 2, π, 3π / 2 in turn), and improves the phase calculation accuracy through the four-step phase shift method. Through the design of a 40°-50° projection-imaging angle, an optical leverage effect is formed, which converts radial / axial small deformation into observable phase shift. The collected image data is synchronously associated with the environmental benchmark established in step 1 for subsequent compensation and correction.

[0009] Step 3. For the whole process of core stress release, a phased sampling strategy is adopted to record strain value, strain rate, and time sequence, forming a complete dynamic curve of the stress release process. The data processing unit uses an improved multi-frequency heterodyne phase demodulation algorithm for processing: first, determine the large-scale deformation interval with the low-frequency grating phase to avoid phase ambiguity, then correct the low-frequency result error with the medium-frequency grating phase, and establish a mapping relationship with the high-frequency phase, finally realize fine measurement with the high-frequency grating phase, and complete phase unwrapping combined with environmental adaptive threshold. Combined with the reference region stabilization technology, the influence of downhole vibration and global drift is offset, and according to the phase-optical path change-deformation conversion model, the known optical path change calculation formula is: wherein represents the vertical displacement of the core surface monitoring point, i.e., the deformation, with units of microns ( ); represents the grating period, with units of microns ( ); represents the phase shift, with units of radians (rad); represents the included angle between the projection light and the core surface normal, i.e., the projection angle, with units of degrees (°); represents the included angle between the imaging light and the core surface normal, i.e., the imaging angle, with units of degrees (°). When a symmetric optical path design is used, i.e., θ = φ, the above formula can be simplified as . Through this formula, radial and axial deformation can be calculated with high precision.

[0010] Step 4. The core circumference is divided into multiple sector monitoring units, and the radial / axial phase data of each sector is obtained, and the strain value is calculated by demodulation algorithm. The data processing unit fuses the sector results to generate a non-uniform shrinkage feature map of the core surface, and intuitively presents the anisotropy and spatial distribution law in the stress release process.

[0011] Another aspect of the present application also provides a core deformation optical monitoring system, characterized in that it comprises the following parts:

[0012] The optical monitoring module is embedded in the inner wall of the coring barrel and does not occupy the coring channel space. At least two sets of optical detection units are arranged along the circumference of the core, preferably three to four sets of symmetrical ring-shaped arrangements to realize multi-sector synchronous monitoring. Each set of optical detection unit includes three sub-units: a miniature projection unit, a high-speed imaging unit and an environmental compensation unit. The miniature projection unit is used to project a dynamically coded low / middle / high frequency sinusoidal grating to the corresponding sector core surface, realizing large-scale and fine measurement coordination. Combined with the preset projection angle and imaging angle, the optical lever effect is formed, which converts the small deformation of the core into significant grating phase change. The high-speed imaging unit is time-synchronous with the miniature projection unit, and uses the four-step phase shift method to synchronously collect grating images, ensuring that the image acquisition accuracy and the projection unit are completely synchronized, and ensuring the high accuracy of phase calculation. The environmental compensation unit is equipped with temperature, humidity and pressure sensors to monitor the downhole environmental parameters in real time, establish an environmental benchmark, and ensure the accuracy of subsequent calculation.

[0013] Data processing unit: The unit is installed at the end of the coring barrel and connected with each optical detection unit through cable, including embedded processor, storage module, algorithm module and synchronous control module. The embedded processor is used to process the phase shift images collected by multiple imaging units in parallel, quickly calculate and output the radial and axial deformation values; the storage module is used to store the original images, phase data and deformation calculation results, to ensure the retention and backtracking analysis of full-cycle data; the algorithm module has improved multi-frequency heterodyne phase demodulation algorithm and phase-optical path-deformation conversion model, and introduces environmental adaptive threshold and reference region stability technology, to realize phase unwrapping and environmental compensation of multiple optical monitoring unit data, and ensure the monitoring accuracy in complex downhole environment; the synchronous control module sends and receives trigger signals to all projection units, imaging units and environmental compensation units, to ensure the timing consistency of multiple sectors and multiple units.

[0014] Coring barrel adaptive structure: The inner and outer barrels are designed as an integrated structure, and optical windows are arranged on the inner barrel wall corresponding to each set of projection and imaging units. The optical windows are preferably made of high-strength transparent material, and the surface is coated with an antireflection film to reduce light loss and improve imaging effect. This structure is compatible with standard cores of different diameters and can be directly used with conventional drilling equipment without modifying the coring process.

[0015] The present application converts the micro-deformation of the core into phase change by the projection-imaging light path of a specific angle, and has the following beneficial effects compared with the prior art:

[0016] 1) The present application discards the scheme of monitoring the surface deformation of the object by the projection of the light spot, and instead adopts the projection of the grating, which breaks through the pixel-level limitation of the displacement of the projection point of the measurement light spot, effectively overcomes the inherent defects such as the insufficient pixel point accuracy of the object surface with rough texture and complex non-ideal surface conditions, speckle noise, light spot centroid drift and image matching error. As a full-field, non-contact optical interference measurement method, the method converts the measured physical quantity from geometric spatial displacement to optical phase field change, realizes the technical optimization from discrete pixel point tracking to continuous field phase demodulation, significantly improves the recognition ability and measurement accuracy of the micro-deformation, effectively solves the signal distortion problem in the monitoring of the rough surface of the core, and meets the needs of early key deformation capture.

[0017] 2) The present application provides a projection-imaging light path design based on a specific angle (40°-50°), which fully utilizes the optical lever amplification principle and the phase-optical path-deformation conversion formula derived based on the geometric optical model: , wherein represents the vertical displacement of the monitoring point on the core surface, i.e. the deformation, with the unit of microns ( ); represents the grating period, with the unit of microns ( ); represents the phase shift, with the unit of radian (rad); represents the included angle between the projection light and the normal of the core surface, i.e. the projection angle, with the unit of degree (°); represents the included angle between the imaging light and the normal of the core surface, i.e. the imaging angle, with the unit of degree (°). When the symmetric light path design is adopted, i.e. θ=φ, the above formula can be simplified as . Through the formula, the micro-deformation of the core surface is converted into quantifiable high-sensitivity phase change, and the high-precision calculation of the deformation is realized by combining the phase distribution characteristics of the double-frequency grating fringe and the improved multi-frequency heterodyne phase demodulation algorithm.

[0018] 3) The present application innovatively adopts the composite projection of the low-frequency grating and the high-frequency grating to construct a collaborative measurement system covering large-range deformation monitoring and micro-deformation capture. The low-frequency grating effectively avoids phase ambiguity and expands the measurement range; the high-frequency grating improves the resolution to realize fine measurement. The combination of the two can complete the full-range phase unwrapping without manual intervention. The design effectively breaks through the contradiction between the measurement range and the accuracy of a single grating, is suitable for dynamic monitoring of the whole process of stress release of the core, and ensures the accurate capture of the radial and axial micro-deformation.

[0019] 4) This invention deeply integrates an optical monitoring module (including a micro-optical projection unit, a high-speed imaging unit, and an environmental compensation unit) into the inner wall of the core tube. Through a staged sampling strategy, it achieves zero-delay monitoring of the core sampling process, accurately capturing key data on early rapid deformation. This design eliminates the monitoring blind spots of traditional offline testing, ensuring complete recording of the initial dynamic characteristics of stress release, providing reliable initial conditions for in-situ stress inversion. Furthermore, it can be seamlessly integrated into standard core sampling procedures without additional operations, improving on-site adaptability and operational convenience.

[0020] 5) This invention employs a symmetrical optical path structure, combined with reference area stabilization technology and real-time environmental parameter compensation, effectively resisting complex environmental interferences such as downhole vibration, temperature and humidity fluctuations, and mud coverage. Even when space constraints necessitate the use of asymmetrical optical paths, algorithmic correction maintains high accuracy and ensures measurement stability. The modular integrated design eliminates the need for professional optical path debugging, directly compatibility with standardized coring procedures, significantly reducing on-site deployment difficulty and maintenance costs, and balancing the cost-effectiveness of high-precision monitoring systems with engineering applications.

[0021] 6) This invention employs a low-power hardware architecture and efficient energy management design, reducing reliance on external power supplies and lowering long-term maintenance costs. Modular component design optimizes manufacturing costs, while integrated design enhances system reliability and resistance to environmental interference. It demonstrates economic efficiency and practicality in complex geological exploration, oil extraction, and mining engineering scenarios. This design is not only suitable for traditional oil extraction and mining engineering but can also be extended to fields such as deep geological disaster early warning. The low-power architecture significantly reduces system maintenance costs in various application scenarios, improving the economics of large-scale deployment.

[0022] Other features and advantages of the present invention will be further set forth in the following description, and some of these will be learned through practice of the invention. The objectives and advantages of the present invention are realized and manifested through the structures described in the specification and claims. Attached Figure Description

[0023] The accompanying drawings are for illustrative purposes only and do not constitute a limitation of the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0024] Figure 1 This is a schematic diagram of the optical lever amplification principle;

[0025] Figure 2 The flowchart of the improved multi-frequency heterodyne phase demodulation algorithm proposed in this invention is shown below.

[0026] Figure 3 This is a schematic diagram of the workflow of a rock core stress release deformation monitoring system.

[0027] Reference numerals: 1-Miniature projection unit; 2-High-speed imaging unit.

[0028] The accompanying drawings are provided to further understand the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. Detailed Implementation

[0029] The following describes in further detail a rock core deformation optical monitoring system and method of the present invention with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate and explain the present invention, and the scope of protection of the present invention is not limited thereto.

[0030] Example 1 (Explanation of the principle of optical lever amplification deformation monitoring)

[0031] This embodiment provides a simple explanation of the monitoring principle of optically magnified deformation, which is the core of this invention. Taking radial shrinkage of a rock core as an example, the following optical path model is established based on the geometric relationship between projection and imaging of the optical monitoring module: [Example follows] Figure 1 As shown in the figure, point O is the projection point. Point is the observation point. The initial position of the monitoring point on the rock core surface is shown. After stress release and deformation, the point is displaced to [location missing]. past the point Draw a perpendicular line pay At point ,extend The core surface after cross-deformation at point ; in the picture The projection angle is the angle between the projected ray and the normal to the core surface. The imaging angle is the angle between the light received by the camera and the normal to the core surface. The change in the optical path length illuminating the same point on the core surface before and after stress release and deformation is the sum of the changes in the incident light's optical path length and the reflected light's optical path length, where the change in the incident light's optical path length is... (Due to the deformation of the rock core surface) It is a very small quantity, approximately taken Then there is Similarly, the change in optical path of the reflected light can be obtained. Therefore, the change in optical path length is According to the phase shift-optical path change conversion relationship, , The change in optical path length, or optical path difference, is expressed in micrometers (μm). Combining these equations, we can obtain the formula for calculating the deformation of monitoring points on the rock core surface: ,in This represents the vertical displacement, or deformation, of the monitoring points on the rock core surface, expressed in micrometers (µm). ); Optical path difference represents the change in optical path length, expressed in millimeters (mm). The grating period is expressed in micrometers. ); Indicates phase offset, in radians (rad); The projection angle is the angle between the projected ray and the normal to the rock core surface, expressed in degrees (°). The imaging angle, expressed in degrees (°), represents the angle between the imaging ray and the normal to the core surface. In practical applications, for ease of arrangement and calculation, this invention employs a symmetrical arrangement of the projection angle and the observation angle, with dual-frequency grating control for monitoring. The specific angle is designed to be 40°~50°. The above design elements are primarily based on the following considerations:

[0032] 1) Because the core is cylindrical, its surface curvature causes deviations in the projection and imaging angles from their nominal values ​​in local areas. The symmetrical angle design ensures good symmetry and consistency of the incident points of the projection and imaging optical axes on the core circumference, effectively reducing systematic errors caused by the core's curved surface geometry. This symmetry can partially offset local cosine value variations caused by surface effects, thus ensuring consistent minute surface deformations at different locations on the core circumference. It can produce the most consistent phase shift possible, improving the spatial consistency and accuracy of the measurement.

[0033] 2) This angle design helps maintain the high signal-to-noise ratio required for phase calculation. When the projected light is incident on the rough surface of the rock core at an angle of 40°~50°, the best diffuse reflection effect can be obtained, ensuring that the grating fringe image acquired by the high-speed imaging unit has a clear and stable sinusoidal intensity distribution. This is crucial for subsequent high-precision phase calculation using the four-step phase-shifting method. If the angle is too small (close to perpendicular), the reflected light may be too concentrated, forming specular reflection, resulting in overexposure of the image or low fringe contrast; if the angle is too large (close to grazing), the intensity of the reflected light will decrease sharply, the image signal-to-noise ratio will deteriorate, and the phase calculation error will increase.

[0034] 3) From the perspective of magnification calculation, based on the principle of optical lever, the minute deformations on the surface of the rock core... This translates into an observable phase shift, the magnification of which is directly related to the cosine of the projection angle and the imaging angle. When a symmetrical optical path design is used, i.e., the projection angle equals the imaging angle (…),… When the magnification factor is taken as... (dimensionless) (wherein) This represents the vertical displacement of the projection point, i.e., the deformation. Indicates the grating period. Indicates phase shift, Indicates the projection angle. (This indicates the imaging angle). The range of 40° to 50° was chosen because within this range... A value of approximately 0.64 to 0.77 provides a suitable magnification. If the angle is too small (e.g., less than 40°), the magnification will increase sharply. Although the sensitivity will be improved, it is very easy to exceed the measurement range, resulting in phase ambiguity. If the angle is too large (e.g., greater than 50°), the magnification will decrease significantly, and it will be unable to effectively amplify micron-level deformations, thereby reducing the measurement sensitivity.

[0035] 4) The considerations for replacing single-frequency monitoring with dual-frequency grating projection monitoring are as follows: Since the deformation of stress release in rock cores is usually on the order of a few micrometers to tens of micrometers, the deformation generated on the rock core surface... Smaller deformation and Taking a large deformation as an example for analysis, we will choose a phase change that is easy to analyze and ensures accurate monitoring. and (To allow for a safety margin and avoid phase ambiguity), for ease of calculation, this invention takes... For example (the same applies to the analysis below), the following can be calculated respectively. The magnification under smaller deformation is The corresponding grating projection period is calculated. ; The magnification under larger deformation is The corresponding grating period is calculated. Given a fixed projection angle and imaging angle, the magnification and grating period... Inversely proportional; however, the above examples only apply to calculations of a single deformation. When using single-frequency monitoring, if only one high-frequency, short-period grating (such as...) is used... Although it can accurately capture minute deformations, in the early stages of core sampling, when the deformation rapidly reaches a certain level... At this rate, the phase shift can reach 8.88 rad, or even exceed 2π (≈6.28 rad), making phase ambiguity highly likely and leading to measurement failure. Conversely, if only a low-frequency, large-period grating (e.g., 400 μm) is used, although it can easily handle the situation... Larger deformation, but for Even minute deformations, with phase changes of only 0.22 radians, result in weak signals and significantly reduced measurement accuracy, failing to meet the high-precision requirements for residual deformation. In practical terms, core stress release is a continuous dynamic process from rapid, large deformation to slow, minute deformation. Single-frequency gratings, regardless of whether a large or small period is selected, can only optimize one stage of the measurement process, sacrificing performance in another. Therefore, this invention employs a dual-frequency grating strategy, using a collaborative mechanism of "low frequency preserving range, high frequency improving accuracy," successfully covering the entire process from early rapid deformation to later residual deformation, achieving truly high-precision, full-cycle, and blind-spot-free monitoring.

[0036] Example 2 (Implementation of Dynamic Dual-Frequency Grating Projection Phase Demodulation Algorithm)

[0037] This embodiment will describe in detail the implementation process of the improved multi-frequency heterodyne phase demodulation algorithm used in this invention. This algorithm is the core link connecting the optical measurement signal and the final deformation data. Its goal is to accurately and stably convert the grating image sequence acquired by the high-speed imaging unit into the radial and axial deformation of the rock core surface. To accurately calculate the phase shift caused by deformation on the rock core surface, this invention employs a four-step phase-shifting method for image acquisition. The choice of four steps instead of N steps represents the optimal engineering trade-off between accuracy and speed. While increasing the number of phase shift steps (e.g., 8 or 16 steps) theoretically further suppresses random noise and improves the accuracy of single phase calculations, in the application scenario of this invention, the system's monitoring requirements for micron-level relative deformation are fully met by the phase calculation accuracy (typically better than 0.01 radians) provided by the four-step phase shift method. The monitoring rate is extremely high during the core stress release cycle, especially during rapid deformation, allowing a complete "projection-acquisition-resolution" cycle to be completed in a very short time (e.g., only 40ms at 100fps), ensuring the capture of instantaneous deformation dynamics. If a 16-step phase shift method were used, the single measurement cycle would extend to over 160ms, potentially resulting in the loss of critical data. Sacrificing time for higher monitoring accuracy and resolution would be counterproductive. Furthermore, more steps mean higher data throughput, computational load, and power consumption, which is unacceptable in downhole battery-powered, embedded processing environments.

[0038] The following will elaborate on the implementation process of the algorithm according to the logical closed loop of "obtaining the initial phase reference and the deformed phase by the four-step phase shift method → ​​obtaining the offset wrapped phase by phase difference → unwrapping by multi-frequency heterodyne method → ​​phase-optical path-deformation conversion".

[0039] Step 1: The core of this invention lies in capturing the relative surface deformation of the rock core caused by stress release, rather than its absolute three-dimensional shape. Therefore, the algorithm employs a four-step phase-shift differential method, the fundamental purpose of which is to eliminate the interference of static features such as inherent texture, color, and roughness of the rock core surface on the measurement results. When the front end of the rock core just enters the coring cylinder, the system is triggered by the pressure sensor of the environmental compensation unit. At this time, stress release has not yet begun or is extremely weak, and can be considered the initial reference state. For each frequency (low frequency, medium frequency, high frequency) grating, the micro-projection unit sequentially projects the first set of four sinusoidal grating fringes with a phase difference of π / 2 onto the rock core surface, i.e., phase shifts of 0, π / 2, π, and 3π / 2, respectively. The high-speed imaging unit simultaneously acquires these four images, which are denoted as... At this point, the light intensity of each pixel (x, y) in the image is not only modulated by the projection grating, but also includes the initial phase shift introduced by the inherent morphology of the core surface. For any pixel in the image, the intensity distribution of the light reference interference fringes... ,in Background light intensity, For modulation intensity, This represents the total phase. Its intensity values ​​in the four images can be expressed as follows:

[0040]

[0041]

[0042]

[0043]

[0044] Subsequently, at any later time t during the core stress release process, the system projects another set of identical four-step phase-shifting gratings and acquires four corresponding images. At this point, due to core deformation and changes in surface shape, the phase shifts, and the images acquired by the imaging unit will have an additional phase shift added to the initial reference state. ,Right now The corresponding image sequences are denoted as follows: Its light intensity values ​​in the four images can be expressed as follows:

[0045]

[0046]

[0047]

[0048]

[0049] Step 2: Solve for the initial phase separately and the phase after deformation The offset phase can then be obtained. Therefore, here we will analyze the two image sequences respectively. , , , }and{ , , , The unwrapped phase is determined based on the standard four-step phase shift solution formula: This allows us to calculate the wrapped phase diagrams in the range [-π, π) or [0, 2π) respectively. and Then, through phase difference operation, static interference is eliminated to obtain... This refers to the dynamic phase change caused by stress release.

[0050] Step 3: Due to the wrapping phase The value range is limited to within 2π. When the core deformation is large, using a single projection period will result in a true phase shift exceeding 2π, leading to phase ambiguity, or phase wrapping problem. To solve this problem, this invention employs an improved multi-frequency heterodyne phase demodulation algorithm. Its core idea is to utilize the complementarity of grating phase information at different frequencies (high, medium, and low frequencies; the specific projection grating period data is determined based on the actual engineering application) to superimpose multiple fringe images of different frequencies. By solving for the wrapped phase of the superimposed images, the absolute phase is gradually calculated.

[0051] Firstly, consider low-frequency gratings (with large periods, such as...) ) Monitored phase offset For rough reference. Due to its large period and small phase response to the same physical displacement, phase ambiguity is almost non-existent throughout the entire measurement range. It provides a global, unambiguous, coarse deformation distribution map to determine a wide range of deformation intervals.

[0052] Then, a medium-frequency grating (with a medium period, such as...) is used. ) Monitored phase offset Error correction and mapping are performed using an algorithm module. Reference benchmark, for Phase unwrapping is based on difference frequency calculation to generate a lower frequency, easier-to-process phase diagram, thereby correcting the systematic error of the low-frequency result and establishing a precise mapping relationship between the low-frequency and high-frequency phases.

[0053] Finally, using the phase diagram after intermediate frequency correction as a reference, the high-frequency grating (with a small period, such as...) is processed. The corresponding phase offset The high-frequency phase is then unwrapped to achieve precise measurement. The absolute phase offset after unwrapping contains the finest deformation information, which is used for the final high-precision deformation calculation.

[0054] Step 4: After obtaining the absolute phase of the high-frequency grating, the phase shift caused by core deformation can be calculated. That is, the phase value at the current moment minus the phase value at the initial moment (when the core just entered the core tube). This yields the final phase offset. Then, it needs to be converted into real physical form variables. (x, y, t). This process deeply integrates an environmental compensation mechanism to ensure measurement accuracy and stability in complex downhole environments and to counteract the interference of complex downhole environments.

[0055] Since this mechanism needs to be relevant to actual application scenarios, only examples of intervention points are provided here. The following points can be considered in detail.

[0056] Environmental compensation intervention point 1: Since the temperature, humidity and other data collected in real time by the environmental compensation unit will directly affect the optical parameters such as reflectivity and air refractive index of the rock core surface, and thus change the unknown parameters A and B in the light intensity distribution of the image, adaptive threshold modulation environmental compensation is introduced in step 1. The algorithm module can dynamically adjust the numerical stability threshold used to calculate the function according to the current environmental parameters to avoid division by zero error or phase jump caused by drastic environmental fluctuations.

[0057] Environmental compensation intervention point 2: Since the overall vibration or temperature drift of the coring cylinder in the downhole environment can cause a global shift in the entire phase field, which may be mistaken for core deformation, a reference area stabilization technique is introduced in steps 2 and 3. The algorithm delineates a "reference area" (such as a fixed point on the inner wall of the coring cylinder) in the image and dynamically calibrates the expected phase of the area based on the pressure and temperature data provided by the environmental compensation unit. The algorithm module can calculate the actual phase shift of the reference area in real time and use it as a global compensation amount. Then, the compensation amount is subtracted from the entire phase field, which helps to offset environmental interference and separate the real core deformation signal.

[0058] Environmental compensation intervention point 3: Similar to intervention point 1, ambient temperature and pressure affect the air refractive index, and in precise calculations, the optical path... It should be the geometric path length. With refractive index The product of Therefore, the algorithm module should be able to dynamically correct the equivalent grating period or phase-optical path conversion coefficient in the phase-optical path conversion formula based on real-time temperature and pressure data to ensure... The calculation results accurately reflect the actual physical optical path changes, rather than environmental disturbances.

[0059] Considering the environmental compensation mechanism, and based on the geometric optical model derived in Example 1, the phase shift amount is... Converted into optical path change Finally, it is converted into the true deformation of the rock core surface. In a symmetrical optical path (θ=φ), the conversion formula is: ,in This represents the vertical displacement of the projection point, i.e., the deformation. Indicates the change in optical path length. Indicates the grating period. Indicates phase shift, Indicates the projection angle. This indicates the imaging angle. This formula establishes a direct relationship between phase shift and surface deformation, forming the theoretical basis for the high-precision measurement achieved in this invention. The intensity of the light after interference changes due to the phase change. If this phase change is caused by the optical path difference, the length change in units of light wavelength can be calculated from the change in light intensity.

[0060] Through the above four steps, this algorithm transforms the original raster image data into accurate core stress release deformation curves, providing a reliable foundation for subsequent data analysis and engineering applications.

[0061] Example 3 (Overall Application Workflow of the Monitoring System)

[0062] This embodiment uses a 30-minute core sampling monitoring cycle as an example to illustrate in detail the complete workflow of the monitoring system of this invention, from hardware integration and deployment, automatic triggering, phased data acquisition to final deformation data output. The entire process is highly automated, integrated into standard core sampling operations, and requires no manual intervention, ensuring accurate capture of the entire process of core stress release, especially early critical deformations.

[0063] Phase 1: Before the rock core enters the coring tube, the special coring tube of this invention is installed to the end of the drill pipe of the drilling equipment. The inner wall of the coring tube has pre-integrated an optical detection module (including three to four sets of optical detection units arranged symmetrically along the circumference) and a data processing unit at the end. The high-strength transparent optical window on the coring tube adapter structure has been cleaned and inspected in advance. Subsequently, the data processing unit is powered on, the built-in processor is started, and the synchronous control module sends a self-test command to all optical detection units to confirm that the micro projection unit, high-speed imaging unit, and environmental compensation unit are all in normal working condition. The storage module is initialized to prepare for recording monitoring data. The algorithm module loads preset measurement parameters, mainly including projection / imaging angle, low, medium and high frequency grating period, stage sampling frequency and duration (sampling frequency of rapid deformation period, main deformation period, and residual deformation period), and setting the initial environmental compensation amount, etc.

[0064] Phase Two: As the core sampler begins to enter the core barrel, the system automatically triggers when the built-in sensor of the environmental compensation unit detects a pressure change, and monitoring and recording officially begin. The environmental compensation unit collects real-time data on current ambient temperature, humidity, and pressure to establish an environmental baseline for subsequent dynamic data compensation. The projection unit begins to project the first set of low-frequency gratings onto the core surface, and the imaging unit simultaneously acquires the grating images. Based on the four-step phase-shifting method, the initial phase is calculated. The data processing unit adaptively adjusts the grating projection intensity and camera exposure parameters according to the contrast and brightness of the image at this time to adapt to the reflective characteristics of the downhole core and ambient lighting conditions.

[0065] Phase Three: Based on the preset phased sampling strategy, the system automatically and dynamically adjusts the monitoring frequency and generates corresponding deformed images. Data from the environmental compensation unit is used in real time for reference area stabilization and optical path parameter correction, ensuring data accuracy under drastically changing environments. An example is a 30-minute monitoring cycle. 0–5 minutes (rapid deformation period): During this period, the deformation rate is relatively fast. The highest sampling frequency is used (e.g., a projection-acquisition-resolution process is completed every 5 seconds). The projection unit sequentially and rapidly projects low-frequency, medium-frequency, and high-frequency grating sequences, while the imaging unit simultaneously and at high speed acquires the corresponding four-step phase-shift images. The high-frequency grating data is processed in a focused manner to accurately capture the initial rapid deformation. An improved multi-frequency heterodyne algorithm is used to quickly calculate the phase shift, accurately capturing the initial rate and peak value of stress release, and generating a high-temporal-resolution initial deformation curve. 5–15 minutes (main deformation period): During this period, core deformation slows down, but significant deformation still exists. A medium-frequency sampling frequency is used (e.g., a projection-acquisition-resolution process is completed every 15 seconds). Low-frequency and high-frequency data are fused to monitor the deformation rate and peak value. At this time, the projection and acquisition of three-frequency grating images continue to record the main deformation process completely, determining the overall magnitude and trend of deformation as the monitoring focus. 15–30 minutes Minutes (Residual Deformation Period): During this period, the core deformation has stabilized, with only slow residual deformation remaining. Low-frequency sampling is used (e.g., a projection-acquisition-resolution process is completed every 30 seconds). At this time, projection and acquisition mainly use low-frequency raster images, supplemented by high-frequency raster sampling for verification at regular intervals. The algorithm module focuses on using low-frequency data to track minute residual changes, determine whether the deformation has completely converged, and confirm the final converged and stable deformation, providing complete endpoint data for subsequent analysis.

[0066] Phase Four: Based on the radial or axial deformation data of each two-dimensional plane point independently calculated by all sector monitoring units on the circumference and ends, the data processing unit performs temporal and spatial data alignment and fusion of these deformation data, and outputs visualization results, including a visual display of the time-deformation process of each sector's dynamic deformation over 30 minutes. The system generates curves and circumferential strain distribution maps that map the final stable deformation of each sector to the circumference of the core, reflecting the non-uniform deformation characteristics of the core. After core sampling and monitoring, the system records all raw image data, intermediate phase data, and final deformation results completely in the local storage module. The data can be uploaded and backed up via wired or wireless transmission for later analysis and research.

[0067] This system activates as soon as the core enters the coring cylinder, capturing the entire process of stress release deformation in stages. It can be integrated into the standard coring procedure without additional operation. Through this complete monitoring system workflow, this invention proposes a full-process monitoring method for stress release deformation during core sampling based on dual-frequency grating projection. This effectively solves the technical challenge of traditional methods failing to obtain early-stage stress release deformation monitoring data, providing relevant data support for geological exploration and engineering safety.

[0068] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A rock core deformation optical monitoring system, characterized in that, include: The core sampling tube integrates an optical monitoring module, which is set on the inner wall of the core sampling tube. It is used to project a dual-frequency grating onto the surface of the rock core and acquire grating images carrying deformation information. A data processing unit, connected to the optical monitoring module, is installed at the end of the core sampling cylinder and is used to perform phase calculation on the acquired grating image and output the deformation result. The core sampling tube adapter structure includes an optical window opened on the inner wall of the core sampling tube to support and protect the optical monitoring module and ensure the stability of the optical path channel.

2. The core deformation optical monitoring system according to claim 1, characterized in that, The optical monitoring module includes multiple optical detection units arranged along the circumference of the rock core. Each optical detection unit includes three sub-units: a micro-projection unit, a high-speed imaging unit, and an environmental compensation unit.

3. The core deformation optical monitoring system according to claim 2, characterized in that, The dual-frequency grating projected by the micro-projection unit includes a low-frequency grating and a high-frequency grating. The period of the low-frequency grating is used for large-scale deformation monitoring, and the period of the high-frequency grating is used for high-precision micro-deformation capture.

4. The core deformation optical monitoring system according to claim 2, characterized in that, The high-speed imaging unit uses a four-step phase-shifting method to acquire grating images. By acquiring four images with phase shifts of 0, π / 2, π, and 3π / 2, the phase calculation accuracy is improved.

5. The core deformation optical monitoring system according to claim 2, characterized in that, The environmental compensation unit includes a temperature sensor, a humidity sensor, and a pressure sensor, which can collect environmental parameters in real time and correct the optical path parameters.

6. The core deformation optical monitoring system according to claim 1, characterized in that, The data processing unit includes an embedded processor, a storage module, an algorithm module, and a synchronization control module; wherein, the embedded processor is used to control the operation of the system, the storage module is used to store the original image data and processing results, the algorithm module is used to perform phase demodulation and deformation calculation, and the synchronization control module is used to coordinate the working timing of the optical monitoring module and the data processing unit.

7. The core deformation optical monitoring system according to claim 6, characterized in that, The algorithm module employs an improved multi-frequency heterodyne phase demodulation method, which sequentially uses the low-frequency phase as a coarse reference, the mid-frequency phase for correction, and the high-frequency phase for fine measurement, thereby realizing phase unwrapping and calculation of radial and axial deformation of the core.

8. The core deformation optical monitoring system according to claim 1, characterized in that, The optical window of the core tube adapter structure is made of high-strength transparent material and coated with an anti-reflection film to reduce light loss and improve imaging quality.

9. A monitoring method for a core deformation optical monitoring system as described in any one of claims 1-8, characterized in that, Includes the following steps: Installation and startup steps: Install the core barrel with integrated optical monitoring module into the drilling equipment. When the front end of the rock core enters the core barrel, the system will automatically trigger and project a dual-frequency grating. Image acquisition steps: Based on a preset projection-imaging angle of 40°~50°, the projection unit projects a multi-frequency grating, and the imaging unit simultaneously acquires phase-shifted images, converting the small deformation of the rock core into phase changes through the optical lever effect; Deformation calculation steps: Implement a phased monitoring strategy based on the time characteristics of stress release, and use different sampling frequencies for each period of rapid deformation, main deformation and residual deformation; The data processing unit performs phase demodulation and unwrapping, and calculates the deformation by combining environmental compensation parameters; The multi-frequency heterodyne phase demodulation algorithm is used to calculate the deformation of the core surface. Data fusion steps: Based on deformation data from multiple sectors in the circumferential direction, generate deformation curves and circumferential strain distribution maps that characterize the entire stress release process.

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