CN113804248A - Nondestructive ground stress testing device and method using digital speckle and finite element technology - Google Patents
Nondestructive ground stress testing device and method using digital speckle and finite element technology Download PDFInfo
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Abstract
本发明涉及一利用数字散斑和有限元技术的无损地应力测试装置及方法。其技术方案是：全直径岩芯夹持器的正面安设有高速摄像机或者相机，夹持器的上侧通过数据线连接伺服控制系统，伺服控制系统向夹持器注入环压，所述的高速摄像机或者相机将收集的形变和位移导入有限元模型进行地应力反演。有益效果是：本发明不破坏岩石的内部结构，试验过程中可以方便地观察到岩样表面挤压变形情况，便于记录整个加载过程中岩样位移场和应变场信息，并将其作为初始和边界条件建立有限元模型进行地应力反演，可以同时获取地应力的大小和方向，同时还可以根据深度和岩性的不同调整全直径测试岩心，从而获得更多岩样变化信息，实现多层位的地应力刻画与计算。
The invention relates to a non-destructive in-situ stress testing device and method using digital speckle and finite element technology. The technical scheme is as follows: a high-speed camera or a camera is installed on the front of the full-diameter core holder, the upper side of the holder is connected to a servo control system through a data line, and the servo control system injects ring pressure into the holder. High-speed cameras or cameras import the collected deformations and displacements into the finite element model for in-situ stress inversion. The beneficial effects are: the present invention does not destroy the internal structure of the rock, and the compression deformation of the rock sample surface can be easily observed during the test, and it is convenient to record the displacement field and strain field information of the rock sample during the whole loading process, and use them as the initial and Boundary conditions establish a finite element model for in-situ stress inversion, which can simultaneously obtain the magnitude and direction of in-situ stress, and at the same time adjust the full-diameter test core according to the depth and lithology, so as to obtain more rock sample change information and realize multi-layered Characterization and calculation of in-situ stress.
Description
Technical Field
The invention relates to a testing device and a testing method for formation ground stress in the field of oil and gas drilling and production, in particular to a nondestructive ground stress testing device and a nondestructive ground stress testing method using digital speckle and finite element technologies, which can simultaneously obtain the magnitude and the direction of the ground stress.
Background
At present, in oil and gas field development, hydraulic fracturing measures, deployment and injection-production well patterns optimization, horizontal well azimuth and hydraulic fracturing all need to consider the direction, the size and the distribution rule of the stress of the current earth. However, in the existing methods for testing the rock ground stress direction in the laboratory, for example, a rock acoustic emission method combined with paleogeomagnetism orientation, a differential strain method combined with paleogeomagnetism orientation, an acoustic velocity anisotropy method combined with paleogeomagnetism orientation and the like, cutting processing needs to be performed on a core during the testing process, the core is damaged, subsequent tests can be influenced after the core is damaged, meanwhile, the testing data is difficult to repeat, particularly, the existing ground stress magnitude and direction testing methods usually need to be coupled with a plurality of tests to be jointly completed, and the selected core is difficult to guarantee parallel tests, so that the testing result uncertainty is high, and the error is sometimes large; secondly, the traditional sound wave method requires that the rock has no obvious cracks, and the uniform texture brings great limitation to the selection of the rock.
The research on the ground stress is widely paid attention by oil and gas exploration and development personnel, and the ground stress belongs to the internal force of the rock in the natural state and reflects the stress state of the rock underground. At present, ground stress measurement work is carried out in a plurality of countries, more than ten types of measurement methods exist, and nearly hundreds of measurement instruments exist. The various measurement methods that occur in succession are broadly classified into two main categories: direct measurements and indirect measurements. The direct method comprises the following steps: flat jack method, rigid inclusion stressometer method, hydraulic fracturing method, acoustic emission method; indirect measurements include: a trepanning stress relieving method, a local stress relieving method, a strain relaxation measuring method and a geophysical detection method. At present, two stress measurement methods are mainly adopted at home and abroad: stress (strain) relief methods and hydraulic fracturing methods. The resolution method is divided into three types: strain gauges, strain gauges and stress gauges, among which strain gauges and strain gauges are widely used. The existing strain gauge method for measuring three-dimensional stress by single drilling hole has the defects of low precision and reliability and troublesome operation.
With the rapid development of the petroleum industry, more and more unconventional oil and gas resources such as shale gas, shale oil, glutenite and the like are found everywhere in China, and because the geological characteristics of reservoirs are complex, the traditional differential strain or Kaiser acoustic emission ground stress experimental test method cannot meet the requirement of test precision, so that the research and development of novel ground stress test equipment and method are necessary. The two ground stress experimental test methods cannot meet the test requirements.
Disclosure of Invention
The invention aims to provide a nondestructive ground stress testing device and method by utilizing a digital speckle and finite element technology, aiming at the defects in the prior art.
The invention provides a nondestructive ground stress testing device by using digital speckle and finite element technology, which adopts the technical scheme that:
the high-speed camera or the camera (b) is installed on one side of the front face of the full-diameter core holder (a), the servo control system (c) is connected to the upper side of the full-diameter core holder (a) through a data line, the power supply (d) is connected to the front face of the full-diameter core holder (a) through a lead, the servo control system (c) is connected to the computer (e) through the data line and used for injecting ring pressure into the full-diameter core holder (a), and the high-speed camera or the camera (b) is connected to the computer (e) through the data line.
Preferably, the full-diameter rock core holder (a) comprises a holder outer cylinder (1), a rear end plug (2), a front stop ring (3), a ring pressing capsule (4), a ring pressing injection nozzle (5) and an optical lamp strip (6), wherein the ring pressing capsule (4) is arranged in an inner cavity of the holder outer cylinder (1), a full-diameter rock core (7) is arranged in the ring pressing capsule (4), the rear side of the holder outer cylinder (1) is provided with the rear end plug (2), the inner end face of the rear end plug (2) is in contact with the full-diameter rock core (7), and the outer end face of the rear end plug is positioned on the outer side of the holder outer cylinder (1); a front retaining ring (3) is arranged on the front side of the outer cylinder (1) of the gripper, and an optical lamp strip (6) is arranged on the inner side of the front retaining ring (3); and the upper side of the outer cylinder (1) of the clamp holder is provided with an annular pressure liquid injection nozzle (5).
Preferably, the holder outer cylinder (1) comprises an outer cylinder body (1.1), a ring pressure liquid injection hole (1.2), a stop ring limit step (1.3), a capsule limit step (1.4), a rear thread (1.5) and a front thread (1.6), wherein the outer cylinder body (1.1) is of a cylindrical structure, and the upper end of the outer cylinder body (1.1) is provided with the ring pressure liquid injection hole (1.2) for installing a ring pressure liquid injection nozzle (5); the inner wall of the outer barrel body (1.1) is provided with a retainer ring limiting step (1.3) and a capsule limiting step (1.4) which respectively form a retainer ring cavity and a capsule cavity, the inner diameter of the retainer ring cavity is larger than that of the capsule cavity, the outer wall of the retainer ring cavity is provided with a front thread (1.6), and the inner wall of the rear end of the outer barrel body (1.1) is provided with a rear thread (1.5).
Preferably, the rear end plug (2) comprises an end plug main body (2.1), an end plug external thread (2.2) and a rotating body (2.3), the front end of the end plug main body (2.1) is in contact with the full-diameter core (7), and the middle part of the end plug main body (2.1) is provided with a raised end plug external thread (2.2) which is movably connected with a rear thread (1.5) of the outer cylinder (1) of the gripper; the rear end of end plug main part (2.1) is equipped with rotor (2.3) for it is rotatory to drive end plug main part (2.1), and end plug main part (2.1) and rotor (2.3) adopt 316 grades of high strength steel to make, through connecting the heating equipment, can realize the effect of heating of full diameter rock core (7), is used for simulating formation temperature.
Preferably, the aforementioned front retainer ring (3) includes a retainer ring main body (3.1), an inner retainer ring (3.2), a retainer ring external thread (3.3), and a retainer ring external step (3.4), the inner wall of the front end of the retainer ring main body (3.1) is provided with the inner retainer ring (3.2), the inner cavity of the rear end of the retainer ring main body (3.1) is of a tapered structure, the outer wall of the rear end of the retainer ring main body (3.1) is provided with the retainer ring external step (3.4), and the outer wall of the middle part of the retainer ring main body (3.1) is provided with the retainer ring external thread (3.3).
Preferably, the ring-pressing capsule (4) is made of annular silica gel.
The invention provides a using method of a nondestructive ground stress testing device by using digital speckle and finite element technology, which adopts the technical scheme that the using method comprises the following steps:
(1) putting the processed full-diameter rock core into an inner cavity of the outer cylinder (1) of the holder, screwing in a rear end plug (2) and screwing tightly; (2) the front end of the outer cylinder (1) of the gripper is provided with a front baffle ring (3), and an optical lamp strip (6) is arranged in the middle of the front baffle ring (3) and used for supplementing light to a full-diameter core; (3) at the moment, hydraulic oil is injected into the annular pressure capsule (4) through a servo control system (c) to be loaded at a certain speed in an isobaric manner, and simultaneously, a high-speed video camera or a camera (b) is used for recording the deformation condition of the full-diameter core; (4) after the experiment is finished, analyzing data to find out the maximum horizontal stress azimuth of the full-diameter rock core; (5) processing and analyzing the acquired and stored digital image, and then comparing and analyzing the gray level of the image before and after deformation of the full-diameter core to obtain the correlation coefficient of the digital image; and recording deformation and displacement parameters of the rock in the loading process to obtain a strain value of the rock, and simultaneously, deriving the strain value for subsequent finite element numerical simulation.
Preferably, finite element geometric modeling is carried out according to specific core size, after a rock strain field is obtained, strain field variable data are led into a finite element model, in actual leading, relevant unit data can also be interpolated according to an interpolation method to obtain unit integral points, initial mechanical parameters and the like are brought in according to actual rock mechanical parameters of the core, then a stress condition is loaded to solve a numerical simulation displacement field and a numerical simulation strain field, a least square objective function is constructed simultaneously, repeated comparison and correction are carried out on the actually measured displacement field and the actually measured strain field and the displacement field and the strain field obtained by digital speckles, and a particle swarm algorithm is used for optimization processing to obtain a minimum differential stress comparison result; at the moment, the calculation result of the magnitude and the direction of the crustal stress of the rock can be completely obtained; if the ground stress actual measurement data exists on site, such as a small pressure test, a well wall collapse analysis result, microseism monitoring and imaging logging, the obtained ground stress numerical simulation result can be corrected and quality controlled.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, in the process that the full-diameter rock sample is compressed, the stress-strain curve of the full-diameter rock sample in the loading direction can be recorded, and meanwhile, the deformation process of the surface of the rock sample can be recorded through a high-speed camera or a camera; the invention does not destroy the internal structure of the rock, can conveniently observe the extrusion deformation condition of the rock sample surface in the test process, is convenient for recording the displacement field and the strain field information of the rock sample in the whole loading process, establishes a finite element model as the initial and boundary conditions to carry out ground stress inversion, can simultaneously obtain the magnitude and the direction of the ground stress, and can simultaneously adjust the full-diameter test rock core according to the difference of the depth and the lithology, thereby obtaining more rock sample change information and realizing the multi-layer ground stress carving and calculation.
Drawings
FIG. 1 is a schematic view of the overall connection of the present invention;
FIG. 2 is a schematic view of a full diameter core holder configuration;
FIG. 3 is a schematic structural view of the outer cylinder of the gripper;
figure 4 is a schematic structural view of a rear end plug;
FIG. 5 is a schematic view of a front check ring;
FIG. 6 is a schematic structural diagram of a ring-pressure capsule and a ring-pressure liquid injection nozzle;
FIG. 7 is a schematic view of the forced deformation of a full diameter core tested;
FIG. 8 is a schematic view of a digital speckle reference and target image subregion;
in the upper diagram: the device comprises a full-diameter rock core holder a, a high-speed video camera or digital camera b, a servo control system c, a power supply d, a computer e, a holder outer cylinder 1, a rear end plug 2, a front retainer ring 3, a ring pressing capsule 4, a ring pressing liquid injection nozzle 5, an optical lamp strip 6 and a full-diameter rock core 7;
the outer cylinder body 1.1, the ring pressure liquid injection hole 1.2, the stop ring limit step 1.3, the capsule limit step 1.4, the back thread 1.5, the front thread 1.6, the end plug main body 2.1, the end plug external thread 2.2, the rotor 2.3, the stop ring main body 3.1, the inner stop ring 3.2, the stop ring external thread 3.3, and the stop ring external step 3.4.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
Embodiment 1, referring to fig. 1, the nondestructive ground stress testing device using digital speckle and finite element technology according to the present invention includes a full diameter core holder a, a high speed video camera or camera b, a servo control system c and a power supply d, the high speed video camera or camera b is installed on one side of the front surface of the full diameter core holder a, the upper side of the full diameter core holder a is connected to the servo control system c through a data line, the front surface of the full diameter core holder a is connected to the power supply d through a wire, the servo control system c is connected to a computer e through a data line for injecting hydraulic pressure into the full diameter core holder a to simulate formation pressure, and the high speed video camera or camera b is connected to the computer e through a data line.
Referring to fig. 2, the full-diameter core gripper a of the invention comprises a gripper outer cylinder 1, a rear end plug 2, a front stop ring 3, a ring-pressing capsule 4, a ring-pressing injection nozzle 5 and an optical lamp strip 6, wherein the ring-pressing capsule 4 is arranged in the inner cavity of the gripper outer cylinder 1, a full-diameter core 7 is arranged in the ring-pressing capsule 4, the rear end plug 2 is arranged at the rear side of the gripper outer cylinder 1, the inner end face of the rear end plug 2 is in contact with the full-diameter core 7, and the outer end face is positioned at the outer side of the gripper outer cylinder 1; a front retaining ring 3 is arranged on the front side of the outer cylinder 1 of the gripper, and an optical lamp strip 6 is arranged on the inner side of the front retaining ring 3; and the upper side of the outer cylinder 1 of the clamp holder is provided with an annular pressure liquid injection nozzle 5.
Referring to fig. 3, the outer cylinder 1 of the holder comprises an outer cylinder 1.1, a ring pressure liquid injection hole 1.2, a stop ring limit step 1.3, a capsule limit step 1.4, a rear thread 1.5 and a front thread 1.6, wherein the outer cylinder 1.1 is of a cylindrical structure, and the upper end of the outer cylinder 1.1 is provided with the ring pressure liquid injection hole 1.2 for installing a ring pressure liquid injection nozzle 5; the inner wall of the outer barrel body 1.1 is provided with a baffle ring limiting step 1.3 and a capsule limiting step 1.4 which respectively form a baffle ring cavity and a capsule cavity, the inner diameter of the baffle ring cavity is larger than that of the capsule cavity, the outer wall of the baffle ring cavity is provided with a front thread 1.6, and the inner wall of the rear end of the outer barrel body 1.1 is provided with a rear thread 1.5.
Referring to fig. 4, the rear end plug 2 of the present invention includes a main body 2.1, an external thread 2.2, and a rotor 2.3, wherein the front end of the main body 2.1 contacts with a full-diameter core 7, and the middle of the main body 2.1 is provided with a raised external thread 2.2 for movably connecting with a rear thread 1.5 of the outer cylinder 1 of the holder; the rear end of end plug main part 2.1 is equipped with rotor 2.3 for it is rotatory to drive end plug main part 2.1, and end plug main part 2.1 and rotor 2.3 adopt 316 grades of high strength steel to make, through connecting the heating equipment, can realize the effect of heating of full diameter rock core 7, is used for simulating formation temperature.
Referring to fig. 5, the front retainer 3 of the present invention includes a retainer main body 3.1, an inner retainer 3.2, a retainer external thread 3.3, and a retainer external step 3.4, wherein the inner wall of the front end of the retainer main body 3.1 is provided with the inner retainer 3.2, the inner cavity of the rear end of the retainer main body 3.1 is a tapered structure, the outer wall of the rear end of the retainer main body 3.1 is provided with the retainer external step 3.4, and the outer wall of the middle portion of the retainer main body 3.1 is provided with the retainer external thread 3.3.
Referring to fig. 6, the ring-pressing capsule 4 of the present invention is made of annular silica gel.
The invention relates to a using method of a nondestructive ground stress testing device by using digital speckle and finite element technology, which comprises the following steps:
(1) putting the processed full-diameter rock core into an inner cavity of the outer cylinder 1 of the holder, screwing in the rear end plug 2 and screwing tightly; (2) the front end of the outer cylinder 1 of the holder is provided with a front retaining ring 3, and an optical lamp strip 6 is arranged in the middle of the front retaining ring 3 and used for supplementing light to a full-diameter rock core; (3) at the moment, hydraulic oil is injected into the annular pressure capsule 4 through a servo control system c to be loaded at a certain speed in an isobaric mode, and meanwhile, a high-speed video camera or a camera b is used for recording the deformation condition of the full-diameter core; (4) after the experiment is finished, analyzing data to find out the maximum horizontal stress azimuth of the full-diameter rock core; (5) processing and analyzing the acquired and stored digital image, and then comparing and analyzing the gray level of the image before and after deformation of the full-diameter core to obtain the correlation coefficient of the digital image; and recording deformation and displacement parameters of the rock in the loading process to obtain a strain value of the rock, and simultaneously, deriving the strain value for subsequent finite element numerical simulation.
Preferably, finite element geometric modeling is carried out according to specific core size, after a rock strain field is obtained, strain field variable data are led into a finite element model, in actual leading, relevant unit data can also be interpolated according to an interpolation method to obtain unit integral points, initial mechanical parameters and the like are brought in according to actual rock mechanical parameters of the core, then a stress condition is loaded to solve a numerical simulation displacement field and a numerical simulation strain field, a least square objective function is constructed simultaneously, repeated comparison and correction are carried out on the actually measured displacement field and the actually measured strain field and the displacement field and the strain field obtained by digital speckles, and a particle swarm algorithm is used for optimization processing to obtain a minimum differential stress comparison result; at the moment, the calculation result of the magnitude and the direction of the crustal stress of the rock can be completely obtained; if the ground stress actual measurement data exists on site, such as a small pressure test, a well wall collapse analysis result, microseism monitoring and imaging logging, the obtained ground stress numerical simulation result can be corrected and quality controlled.
In addition, the processed full diameter core means: and (4) finishing the end face of the full-diameter rock core to be flat and smooth by using a diamond lathe tool, and spraying speckles on the end face of the rock.
And then putting the full-diameter rock core into a lateral holder to laterally load equal pressure on the rock, simultaneously carrying out high-speed photographing on the end face of the rock by using a high-speed camera, and analyzing the photograph by using digital speckle software after the experiment is finished. And (4) releasing the main stress after drilling the core due to different stresses of the rock in the stratum. The stress is different, the strain released by the rock is different, the greater the stress is, the greater the strain released is, and vice versa. So that the rock is laterally loaded with the same stress and the rock faces will exhibit different strains. Therefore, the speckle analysis software can see that the rock has a strain field changing with the lateral pressure, the direction with larger strain is the maximum horizontal stress, and the direction vertical to the maximum horizontal stress is the minimum horizontal stress.
In addition, in a computer in which images measured by the digital speckle correlation method exist in a matrix form, and then motion information of a measured object point is estimated from an image matrix, an assumption is needed when: the same point keeps the same gray level during the movement, i.e. the "gray level invariant assumption", the specific calculation expression can be expressed as:
in the formula:ffor the purpose of a reference picture,gis the target image.w(x;a)=x+d(x;a)Is a coordinate function.u，vAre respectively asx，yDisplacement in direction. To solveuAndvfirstly, the point to be measured is used in the reference image (x 0 ,y 0 ) Selecting a certain area as a reference image subregion for the center, and then finding the target image with the maximum correlation with the reference image subregion by a certain search method (x’, y’) Point target image sub-regions, refer specifically to fig. 8;
after the correlation function is selected, a correlation search is started, as shown in the figure. First, a sub-area of a reference image is selected, a deformation parameter is assigned to an initial value and then is substituted into a shape function, and (under the initial value), (A)x’,y’) And (4) point. During the deformation of the object, the displacement is not generally a whole pixel, so (1)x’,y’) The grey value of the point must be obtained by sub-pixel interpolation. When all points in the sub-area of the reference image correspond to (x’,y’) After the gray values of the points are all obtained, the correlation function value is calculated according to the normalized covariance correlation functionAnd comparing, and if a preset threshold value is reached, considering the deformation parameter as the required value. If not, the deformation parameters are re-assigned for calculation until the requirements are met. Similarity function for representing similarity degree of reference image and target image subareaC. The digital speckle takes the correlation function as a judgment basis, searches in the reference image and the target image and finds a sub-area with the correlation function as an extreme value. The cross correlation coefficient is adopted to measure the similarity of the reference area, and the definition formula is as follows:
(x, y) and (x ', y') respectively represent an arbitrary point before the deformation of the sub-region and the coordinates of the point after the deformation corresponding thereto. When the similarity function C value =1, it is indicated that the two sub-regions are completely correlated. When the similarity function C value =0, it is indicated that the two sub-regions are completely uncorrelated.
After acquiring digital speckle strain field data, carrying out numerical simulation on a strain field by establishing a finite element calculation model to form a parameter identification error function of the finite element strain field and the digital speckle strain field, wherein the calculation formula is expressed as follows:
in the formula:ε xn 、ε yn 、τ xyn respectively for finite element numerical calculation xDirection strain,yDirection strain, shear strain;ε xs 、ε ys 、τxysrespectively obtained by calculation in full-diameter core loading deformation experiment through digital speckle correlation methodxDirection strain,yDirection strain, shear strain; in addition, the first and second substrates are,nfor the number of integration points in the finite element model,m = n。
when the analysis of the digital speckle output strain field and the finite element numerical simulation strain field is carried out, optimization algorithm is required to be adopted to carry out function calculation precision and calculation speed optimization, such as particle swarm optimization algorithm, genetic algorithm and the like, when the strain field inversion optimization algorithm is selected, the algorithm is required to be considered, the space can be fully searched in a calculation group, and high calculation efficiency and calculation precision are realized. When the calculation accuracy does not meet the standard, the initial parameters need to be further adjusted, and trial calculation is performed again until the calculation result of the whole model is completely converged.
The above description is only a few of the preferred embodiments of the present invention, and any person skilled in the art may modify the above-described embodiments or modify them into equivalent ones. Therefore, the technical solution according to the present invention is subject to corresponding simple modifications or equivalent changes, as far as the scope of the present invention is claimed.
Claims (8)
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| Application Number | Priority Date | Filing Date | Title |
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| CN202110973452.8A CN113804248B (en) | 2021-08-24 | 2021-08-24 | Non-destructive geostress testing device and method using digital speckle and finite element technology |
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| CN202110973452.8A CN113804248B (en) | 2021-08-24 | 2021-08-24 | Non-destructive geostress testing device and method using digital speckle and finite element technology |
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