CN115655133A - Optical fiber strain sensing pipe column and ground stress measuring method - Google Patents

Abstract

The invention belongs to the technical field of ground stress measurement, and particularly relates to an optical fiber strain sensing pipe column and a ground stress measurement method, wherein the optical fiber strain sensing pipe column comprises a pipe column body and an optical fiber sensor, the pipe column body is provided with an inlet end for connecting a liquid injection pressurizing system, and the pipe column body can generate strain according to the change of internal and external pressure; the optical fiber sensor is adhered to the outer peripheral wall of the tubular column body and can measure the strain of the tubular column body, and a plurality of sensing points which are arranged at intervals and positioning marks used for marking the spatial positions of the sensing points are arranged on the optical fiber sensor. The invention adopts the wound optical fiber strain sensing pipe column, the optical fiber sensor with high spatial resolution is installed in the stratum, different stress states of different sensing sections at positions can be calculated according to the strain measured by different sensing points on the optical fiber strain sensing pipe column, and the real-time measurement of multiple layers of the ground stress is realized. Compared with the traditional ground stress measuring method, the method is simpler and easier to operate, can measure the ground stress state of a continuous time-space domain, and greatly improves the ground stress measuring capability.

Description

Optical fiber strain sensing pipe string and ground stress measurement method

technical field

The invention belongs to the technical field of geostress measurement, in particular to an optical fiber strain sensing pipe string and a geostress measurement method.

Background technique

In-situ stress refers to the in-situ in-situ stress state of the formation. In geotechnical engineering fields such as drilling engineering, mining engineering, and road engineering, in-situ stress, as one of the key engineering parameters, has received extensive attention. Therefore, how to accurately measure and predict the ground stress has always been a research hotspot in the field of geotechnical engineering.

However, the traditional in-situ stress measurement can only perform static measurement at a single point, and the measurement results can only represent the in-situ stress state at a certain moment and at a certain location. After the oil and gas well is cemented or put into production, the in-situ stress cannot be measured again ; and the higher the spatial resolution of in-situ stress measurement, the more points need to be measured, the traditional method can only measure the in-situ stress state at a certain point or a certain depth; in addition, the traditional in-situ stress measurement method needs to take coring, A series of complex operations such as drilling, lowering sensors, hydraulic fracturing, and embedded flat jacks make measurement difficult.

Contents of the invention

The main purpose of the present invention is to propose an optical fiber strain sensing pipe string and a ground stress measurement method, aiming to solve the technical problem that the ground stress measurement method in the prior art can only perform single-point static measurement and the operation is difficult.

In order to achieve the above object, the present invention provides an optical fiber strain sensing column, wherein the optical fiber strain sensing column includes:

The main body of the pipe string is provided with an inlet port for connecting the liquid injection pressurization system, and the main body of the pipe string can generate strain according to the change of internal and external pressure;

The fiber optic sensor is bonded to the outer peripheral wall of the pipe string body and can measure the strain of the pipe string body. The fiber optic sensor is provided with a plurality of sensing points arranged at intervals and used to mark the positioning of the spatial positions of the plurality of sensing points mark.

In the embodiment of the present invention, the outer peripheral wall of the pipe string body is provided with thread-shaped shallow grooves, and the optical fiber sensor is located in the shallow grooves and helically wound on the outer peripheral side of the pipe string body along the shallow grooves.

In the embodiment of the present invention, the optical fiber strain sensing column further includes a film wrapped on the outer wall of the column body.

In the embodiment of the present invention, a ground stress measurement method is also proposed, which is applied to an optical fiber strain sensing pipe string. The ground stress measurement method includes:

Step S10: Prepare the optical fiber strain sensing string, and obtain the strain correction coefficient of the optical fiber strain sensing string;

Step S20: Embedding the optical fiber strain sensing string into the rock mass;

Step S30: applying different preset pressures to the optical fiber strain sensing string, and measuring the actual strain value of the peripheral wall of the optical fiber strain sensing string under different preset pressures according to the strain correction coefficient;

Step S40: Obtain formation elastic parameters according to the actual strain value;

Step S50: Obtain the overlying formation pressure, and calculate the static ground stress of the rock mass according to the overlying formation pressure and the formation elastic parameters.

In the embodiment of the present invention, step S10 includes:

Sealed fiber optic strain sensing string;

Apply a preset pressure to the optical fiber strain sensing string through a liquid injection pressurization system, and calculate the corrected strain actual value of the optical fiber strain sensing string according to the preset pressure;

Recording the corrected strain measurement values measured at each sensing point;

Using the analytical method or numerical simulation method, the strain correction coefficient can be obtained by linearly correcting the measured value of the corrected strain and the actual value of the corrected strain.

In the embodiment of the present invention, step S20 includes:

Drill installation holes in the rock mass;

The optical fiber strain sensing pipe string is placed in the installation hole, and cement is poured between the inner wall surface of the installation hole and the outer wall surface of the optical fiber strain sensing pipe string.

In the embodiment of the present invention, step S30 includes:

Inject high-pressure liquids of different preset pressures into the optical fiber strain sensing string through the liquid injection pressurization system, so that different internal pressures are generated inside the optical fiber strain sensing string;

The optical fiber sensor is used to sense the strain of the optical fiber strain sensing string, and the strain measurement value of the optical fiber strain sensing string under different internal pressures is obtained;

The actual strain value is obtained according to the measured strain value and the strain correction factor.

In the embodiment of the present invention, step S40 includes:

Step S41: According to the functional relationship between the preset pressure and strain actual values of the optical fiber strain sensing string and the formation elastic parameters, obtain the assumed strain value and the assumed value of the formation elastic parameters;

Step S42: Step S41 is repeated until the error between the assumed strain value and the actual strain value reaches the preset error range, and the assumed value of the formation elastic parameter is the actual formation elastic parameter of the rock mass.

In the embodiment of the present invention, step S50 includes:

The ratio between the static ground stress and the overlying formation pressure is obtained by using the linear relationship between the formation elastic parameters and the static ground stress, and the static ground stress is obtained according to the overlying formation pressure and the ratio.

In the embodiment of the present invention, the linear relationship between the elastic parameters of the formation and the static ground stress is:

Among them, E _x , E _y , E _z , υ _xy , υ _xz , and υ _yz are formation elastic parameters; σ _x , σ _y are horizontal in-situ stresses; σ _z is the overlying formation pressure.

Through the above technical solution, the optical fiber strain sensing column provided by the embodiment of the present invention has the following beneficial effects:

Compared with the traditional ground stress measurement, when the ground stress is measured using the optical fiber strain sensing pipe string of the present invention, it can continuously sense the dynamic changes of the ground stress in different time periods; and the winding optical fiber strain sensor The measuring pipe string installs the optical fiber sensor with high spatial resolution into the formation. Since the optical fiber sensor has multiple sensing points and the spatial sensing resolution is as high as 1mm, it can realize multi-point measurement of ground stress with high spatial resolution. . In addition, after the optical fiber strain sensing pipe string is buried in the formation rock mass, it can remain in the formation as a production pipe string, structural pipe string, fluid flow channel, or structural part in the rock mass, so as to realize the monitoring of the ground stress state at different times. Continuous sensing of segments without additional action.

Other features and advantages of the present invention will be described in detail in the detailed description that follows.

Description of drawings

The accompanying drawings are used to provide an understanding of the present invention, and constitute a part of the description, together with the following specific embodiments, are used to explain the present invention, but do not constitute a limitation to the present invention. In the attached picture:

Fig. 1 is a schematic flow chart of a method for measuring ground stress according to an embodiment of the present invention;

Fig. 2 is a schematic structural view of an optical fiber strain sensing column according to an embodiment of the present invention;

FIG. 3 is a graph showing a response curve of an actual strain value to a preset pressure according to an embodiment of the present invention.

Explanation of reference signs

label name label name 10 Fiber Optic Sensor 20 String body 11 Sensing point

Detailed ways

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described here are only used to illustrate and explain the present invention, not to limit the present invention.

The optical fiber strain sensing pipe string and the ground stress measurement method according to the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 2 , in an embodiment of the present invention, a fiber optic strain sensing column is provided, wherein the fiber optic strain sensing column includes a column body 20 and an optical fiber sensor 10 , and the column body 20 is provided for connecting At the inlet end of the liquid injection pressurization system, the pipe string body 20 can produce strain according to the change of internal and external pressure; the optical fiber sensor 10 is bonded on the outer peripheral wall of the pipe string body 20, and can measure the strain of the pipe string body 20. There are a plurality of sensing points 11 arranged at intervals and positioning marks for marking the spatial positions of the plurality of sensing points 11 .

When the optical fiber strain sensing pipe string of the present invention is used to measure the ground stress, it can continuously sense the dynamic changes of the ground stress in different time periods; The optical fiber sensor 10 is installed in the formation. Since the optical fiber sensor 10 has multiple sensing points 11 and the spatial sensing resolution is as high as 1mm, it can realize multi-point measurement of ground stress with high spatial resolution.

When preparing the optical fiber strain sensing column, firstly, the optical fiber sensor 10 is spirally wound on the outer peripheral wall of the column body 20, and the optical fiber sensor 10 is fixed on the column body 20 through 502 glue or phenolic resin and other adhesives. superior. At this time, the fiber optic sensor 10 is wrapped on the outer wall of the pipe string body 20 , and establishes a strain correspondence relationship with the pipe string body 20 , so that the fiber optic sensor 10 can sense the strain on the outer surface of the pipe string body 20 synchronously.

When winding the fiber optic sensor 10 , two methods can be used for winding and installing the fiber optic sensor 10 : groove positioning or winding with a fixed helix angle. The groove positioning method is as follows: through mechanical processing, a threaded shallow groove is made on the outer peripheral wall of the pipe string body 20, and the optical fiber sensor 10 is installed in the shallow groove and spirally wound on the pipe string along the shallow groove. The outer peripheral side of the main body 20, this method can realize the installation and positioning of the optical fiber sensor 10 under the condition that the strength of the pipe string main body 20 is slightly affected, and the optical fiber sensor 10 can be protected by shallow grooves so that it is not adhered to the outer interface. The impact of the contact material can be avoided, and the sensing stability of the optical fiber sensor 10 can be improved. The winding method with a fixed helix angle is: using an optical fiber winding device to stably fix the optical fiber sensor 10 on the pipe string body 20 at a preset position with a certain helix angle. The advantage of the fixed helix angle method is that it has no additional impact on the strength and stress distribution of the structural member 20 of the pipe string body, and the advantage of the groove positioning method is that it can better protect the stability of the optical fiber strain sensing.

Due to the limitation of the physical characteristics of the optical fiber sensor 10, there are a plurality of sensing points 11 arranged at equal intervals on the optical fiber sensor 10. The initial distribution positions of the measuring points 11 on the outer peripheral wall of the pipe string body 20 are marked to clarify the initial positions of the sensing points 11 , so as to obtain the strain of the pipe string body 20 during the external changes of the sensing points 11 . The specific operation is: after the fiber optic sensor 10 is bonded to the string body 20, the sensing point 11 is marked by a point pressure method or a liquid nitrogen point spray method. Among them, the point pressure method uses a sharp rigid object such as a probe to mark a certain point on the optical fiber sensor 10, so that a local strain is generated at the point to be pressed, and the next sensing point is obtained by using the distance between the sensing points 11. The specific spatial position of point 11, and then deduce the spatial position of subsequent sensing points 11; the liquid nitrogen point spray method is similar to the point pressure method, and the liquid nitrogen point spray method is used to make the optical fiber sensor 10 locally generate obvious frequency shifts, thereby realizing mark.

After the fiber optic sensor 10 is installed on the pipe string body 20 , it is necessary to wrap the pipe string body 20 with a film to shield the influence of the interface bonding substance and ensure the measurement accuracy of the fiber optic sensor 10 .

It should be noted that, in the prior art, the differential strain method, as a commonly used indoor test method, is widely used in the measurement of in-situ stress, and its theoretical basis is the memory of micro-fractures in the formation: when the well on the rock mass After the borehole is formed, the equilibrium state controlled by the far-field stress in the borehole wall and the drilled rock mass is destroyed, and the stress is released, forming a new stress equilibrium state. However, a large number of micro-cracks contained in the rock mass are affected by the release of stress and undergo displacement effects such as expansion, compression, and shearing, thereby affecting the rock elastic parameters of the well wall and rock mass. Therefore, the state of in-situ stress is contained in the rock elastic parameters. The experimental object of the traditional differential strain method is to take the underground core from the ground. Firstly, the strain gauge is applied to the surface of the core, and then the hydrostatic pressure is applied to the rock mass. The strain during the pressurization process is recorded, and the far field stress ratio is represented by calculating the principal stress ratio. , and then calculate the far-field stress.

With the development of sensing technology, key technical indicators such as measurement accuracy and spatial resolution of optical fiber sensing technology have been greatly improved. Compared with traditional strain measurement methods, optical fiber sensing technology has the advantages of high spatial resolution, high frequency, and high accuracy. Its application in the field of geotechnical engineering has become one of the new research hotspots. The invention combines the optical fiber strain sensing technology and the differential strain method to invent a brand-new ground stress measurement method, which can be applied to various measurement scenarios such as indoor test and underground measurement.

The theoretical basis of the present invention is the same as that of the traditional differential strain method, that is, the micro-cracks of the rock have memory, and the state information of the in-situ stress can be stored in the elastic parameters of the rock, and then the in-situ stress can be inverted by using the elastic-mechanical parameters of the rock . The core component of the ground stress measurement method in the present invention is the above-mentioned optical fiber strain sensing pipe string. When measuring in-situ stress, it is first necessary to open a wellhead on the formation rock mass, then bury the optical fiber strain sensing pipe string into the formation from the wellhead, and use cementing cement to bond the optical fiber strain sensing pipe string to the formation, and then form a stress transfer relationship. At this time, the strain sensed by the optical fiber sensor 10 is the strain at the interface between the pipe string body 20 and the cement. Since the ground stress state of the formation has been released before the pipe string is run in, a new equilibrium state has been formed, so the optical fiber strain sensing After the pipe string is lowered into the formation, no strain signal is generated. At this time, the internal pressure method is used to artificially inject high-pressure liquid into the interior of the pipe string body 20, so that the optical fiber sensor 10 generates a strain signal that can reflect the elastic parameters of the formation.

The strain value at the outer surface of the pipe string body 20 under different internal pressures can be obtained by using the internal pressure method. It should be noted that due to the high spatial resolution of the optical fiber sensor 10 , the sensing column can obtain a large number of strain sensing results at different times and in different spaces. At this time, inversion may be performed on the strain sensing results to obtain the change curve of the formation elastic parameters with the internal pressure of the pipe string body 20 , and then invert to obtain the ground stress in a certain period of time. In addition, the invention can obtain derived parameters such as rock anisotropic elastic parameters.

After obtaining the ground stress for a certain period of time, since the optical fiber strain sensing pipe string is buried in the formation rock mass, it can be used as a production pipe string, a structural pipe string, a fluid flow channel, or a structural part in the rock mass, etc. . When the ground stress in the formation changes with time, the outer surface of the optical fiber strain sensing string will generate strain and send out a corresponding strain signal. The continuous monitoring of the strain signal can invert the change of the ground stress, and then obtain the dynamic ground stress change results on different time axes, so as to realize the continuous sensing of the ground stress state in different time periods.

It should be noted that in order to form the internal high pressure of the pipe string body 20, it is necessary to ensure that the pipe string body 20 has a sealed structure, so that a physical seal needs to be formed at both ends of the pipe string body 20, and the seal can be selected according to different geostress measurement environments. The string body 20 is sealed by means of spacer packing or end welding.

As shown in Figure 1, in order to further understand the technical scheme of the present application, the overall working steps of the ground stress measurement method are described in detail as follows, the ground stress measurement method of the present invention includes:

Step S10: Prepare the optical fiber strain sensing string, and obtain the strain correction coefficient of the optical fiber strain sensing string;

Step S20: Embedding the optical fiber strain sensing string into the rock mass;

Step S30: Apply different preset pressures to the optical fiber strain sensing string, and measure the actual strain value of the peripheral wall of the optical fiber strain sensing string under different preset pressures according to the strain correction coefficient. The range of the preset pressure is about 0-25MPa;

Step S40: Obtain formation elastic parameters according to the actual strain value;

Step S50: Obtain the overlying formation pressure, and calculate the static ground stress of the rock mass according to the overlying formation pressure and the formation elastic parameters.

Compared with the traditional ground stress measurement method, the present invention adopts the optical fiber strain sensing pipe string as the sensing medium to sense the strain of the formation rock mass, and then inverts formation elastic parameters and ground stress. The ground stress measurement method of the present invention can continuously sense the dynamic changes of ground stress in different time periods; and the fiber optic sensor 10 with high spatial resolution is installed in the formation by using a wound optical fiber strain sensing string, because The optical fiber sensor 10 has a plurality of sensing points 11 and the spatial sensing resolution is as high as 1mm, which can realize the multi-point measurement of the high spatial resolution of the ground stress; in addition, the operation difficulty of the ground stress measurement method of the present invention is low, and the optical fiber After the strain sensing pipe string is buried in the formation rock mass, it can remain in the formation as a production pipe string, a structural pipe string, a fluid flow channel, or a structural part in the rock mass. When it is necessary to measure the dynamic value of the ground stress at different times At this time, it is only necessary to carry out a new round of inversion of the formation elastic parameters through the actual value of the re-measurement of the strain, and then the results of the dynamic stress changes on different time axes can be obtained, so as to realize the continuous sensing of the stress state in different time periods. Measurement. It effectively solves the technical problem that the ground stress measurement method in the prior art can only perform static measurement of the ground stress in a single time period without additional operations.

In the embodiment of the present invention, step S10 includes preparing the optical fiber strain sensing string and obtaining the strain correction coefficient of the optical fiber strain sensing string. Since the fiber body strain is the Rayleigh post-scattered light frequency shift value, the measured value obtained by the fiber optic sensor 10 is different from the actual strain value and there is a linear relationship between the two, so it is necessary to use the strain correction coefficient to correct the measured value to the The actual strain value of the outer surface of the body 20.

In this case, it is necessary to use the internal pressure method to obtain the strain correction coefficient. Specifically, the preset pressure is first applied to the optical fiber strain sensing string through the liquid injection pressurization system, and the analytical solution or numerical simulation method is used to calculate the spatial strain of the internal pressure string according to the preset pressure to obtain the optical fiber strain Sensing the actual value of the corrected strain of the pipe string, and then recording the measured value of the corrected strain measured by each sensing point 11, and finally performing a linear correction between the measured value of the corrected strain and the actual value of the corrected strain by using an analytical method or a numerical simulation method, that is The strain correction factor can be obtained.

After the strain correction coefficient is obtained, the strain measurement value detected by the optical fiber sensor 10 can be changed into an actual strain value, which greatly increases the detection accuracy of the optical fiber sensor 10 to the strain of the pipe string body 20, and then makes the ground stress measurement method in this application The measurement effect is better and more accurate.

In the embodiment of the present invention, step S20 includes:

An installation hole is drilled in the rock mass, and the optical fiber strain sensing pipe string is placed in the installation hole, and cement is poured between the inner wall surface of the installation hole and the outer wall surface of the optical fiber strain sensing pipe string. The optical fiber strain sensing string and the formation are bonded with cement, so that the seamless connection between the optical fiber strain sensing string and the formation is realized, and then a stress-strain transfer relationship is formed between the optical fiber strain sensing string and the formation, so that the optical fiber The strain sensing pipe string can be synchronized with the strain of the formation, so that the strain measured by the optical fiber sensor 10 can better reflect the stress state in the formation.

In the embodiment of the present invention, step S30 includes:

Inject high-pressure liquids of different preset pressures into the optical fiber strain sensing string through the liquid injection pressurization system, so that different internal pressures are generated inside the optical fiber strain sensing string; The strain is sensed, and the strain measurement value of the optical fiber strain sensing string under different internal pressures is obtained; finally, the actual strain value of the optical fiber strain sensing string is obtained according to the strain measurement value and the strain correction coefficient obtained above.

At this time, after the preset pressure is applied in the optical fiber strain sensing pipe string, the combination of the pipe string body 20-concrete bonding layer-the formation is deformed at the same time, and the formation generates strain under the preset pressure of the optical fiber strain sensing pipe string , to obtain the response curve of the actual strain value to the preset pressure as shown in Fig. 3 .

The multiple sensing points 11 on the optical fiber strain sensing column can measure multiple actual strain values, which are reflected in Figure 3. The detection of multiple sensing points 11 at different spatial positions can reflect the actual strain more accurately. The relationship between the value and the preset pressure improves the accuracy of the measurement experiment.

In the embodiment of the present invention, step S40 is the inversion process of formation elastic parameters, including:

Step S41: According to the relationship between the preset pressure and strain actual values of the optical fiber strain sensing pipe string and the elastic parameters of the formation, the assumed strain value and the assumed value of the elastic parameters of the formation can be obtained by using the finite element method;

Step S42 is: continuously repeating step S41 to obtain new assumed strain values and assumed values of formation elastic parameters until the error between the assumed strain values and the actual strain values reaches the tolerance range, it can be considered that the actual elastic parameters of the rock mass and The formation elasticity parameters assume the same values.

Among them, for the inversion process of the formation elastic parameters under different preset pressures, the inversion process of the formation elastic parameters can be carried out in two ways: numerical method and analytical method. Among them, the numerical method is to use numerical simulation software or algorithms to invert the elastic parameters of the formation; the analytical method is to use the analytical solution model to invert the elastic mechanical parameters. Since the theoretical basis for the implementation of the numerical method and the analytical method is established on the above step S40, the numerical method and the analytical method will not be described in detail here.

In addition, optimization method, machine learning method, and deep learning method can be used to perform arithmetic optimization on the inversion process of formation elastic parameters. The optimization methods include evolutionary algorithms such as particle swarm optimization, simulated annealing, snake optimization, and whale optimization. Common methods of machine learning include random forests, support vector machines, etc. Deep learning methods include BP neural networks and neural networks combined with optimization algorithms. Within the technical scope of the present invention, the inversion process of elastic mechanics can be optimized in various ways, including combining the above-mentioned specific optimization methods in any suitable way, or other conventional optimization algorithms. Possible algorithms are not described otherwise. However, these algorithms should also be regarded as the content disclosed in the present invention, and all belong to the protection scope of the present invention.

It should be noted that before the wellhead is opened in the formation and the optical fiber strain sensing string is embedded, the formation is squeezed by the stress around the wellbore, so that the formation fractures are in an over-closed state. After the optical fiber strain sensing string is buried in the formation from the wellbore, in the process of internal pressurization and expansion, the formation fractures around the wellbore are forced to reopen, resulting in the density of the formation becoming smaller during the pressurization process, as shown in Figure 3 Reflected in the increasing slope of the curve.

Specifically, the curve in Fig. 3 can be divided into the first linear zone, the nonlinear zone and the second linear zone in sequence with the increase of the preset pressure. When the preset pressure is in the first linear zone, the formation fracture is in an over-closed state, The formation elastic parameter is a constant value, the slope of the curve remains unchanged, and the formation is in an isotropic state; when the preset pressure is in the nonlinear region, the formation fractures are in a state of gradually opening, the formation elastic parameters change nonlinearly, and the slope of the curve gradually increases; When the preset pressure is in the second linear zone, the fractures in the formation are fully open, the elastic parameters of the formation are constant, the slope of the curve remains unchanged, and the formation is in an orthotropic state.

Using step S40 to invert the formation elastic parameters on the data in the first linear region, the formation elastic parameters can be obtained: E, υ, wherein, E is the elastic modulus of the isotropic formation; υ is the Poisson's ratio of the isotropic formation.

Using step S40 to invert the formation elastic parameters on the data in the second linear zone, the formation elastic parameters can be obtained: E _x , E _y , E _z , υ _xy , υ _xz , υ _yz , where E _x , E _y , E _z is the elastic modulus of orthotropic formation; υ _xy , υ _xz , υ _yz are Poisson's ratios of orthotropic formation.

In the embodiment of the present invention, step S50 includes:

Combined with the overlying formation pressure, the ratio between the static in-situ stress and the overlying formation pressure is obtained by using the linear relationship between the formation elastic parameters and the in-situ stress, and the static in-situ stress of the formation is obtained according to the overlying formation pressure and the obtained ratio.

Among them, the overlying formation pressure can be calculated by the following formula:

σ _z = Hρ _r g

Among them, _σz is the pressure of the overlying formation, H is the depth of the sensing point 11 in the formation; _ρr is the total density of the formation, and _ρr can be measured by density logging; g is the acceleration of gravity.

The linear relationship between formation elastic parameters and ground stress is:

Among them, σ _x and σ _y are horizontal in-situ stress. According to the above formula and the formation elastic parameters obtained in step S40: E _x , E _y , E _z , υ _xy , υ _{x z} , υ _yz , finally obtain the ratios of σ _x to σ _{z , σ y to} σ _z respectively, and then The specific values of horizontal ground stress σ _x and σ _y can be obtained, and the measurement of ground stress (including horizontal ground stress and overlying formation pressure) can be completed.

In general, the present invention can calculate the different ground stresses at the positions of different sensing points 11 according to the strains measured by different sensing points 11 on the optical fiber strain sensing pipe string, thereby realizing the multi-point location of ground stress Measurement, and does not require complex operations of traditional measurement methods, which greatly reduces the difficulty of measuring ground stress.

It should be noted that the ground stress and formation elastic parameters in the formation are not a constant value, but are constantly changing with time. The ground stress measurement method of the present invention can not only measure the static ground stress in a certain period of time, but also the optical fiber strain sensor The measuring tube can be left in the formation as a production string, a structural string, a fluid flow channel, or a structural member in the rock body. When the ground stress and formation elastic parameters in the formation change with time, the outer surface of the optical fiber strain sensing string will generate strain and continuously measure new actual strain values, which can re-adjust the formation elastic parameters and ground stress. A new round of inversion is used to obtain formation elastic parameters on different time axes, and to realize continuous sensing of the ground stress state in different time periods. The method effectively solves the technical problem that the ground stress measurement method in the prior art can only perform static measurement of the ground stress in a single time period.

In the description of the present invention, it should be understood that the terms "first" and "second" are used for description purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

In the present invention, unless otherwise clearly specified and limited, terms such as "installation", "connection", "connection" and "fixation" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection , or integrated; can be mechanically connected, can also be electrically connected or can communicate with each other; can be directly connected, can also be indirectly connected through an intermediary, can be the internal communication of two components or the interaction relationship between two components, Unless expressly defined otherwise. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

In the description of this specification, descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structure, material or characteristic is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention, those skilled in the art can make the above-mentioned The embodiments are subject to changes, modifications, substitutions and variations.

Claims (10)

1. An optical fiber strain sensing string, comprising:

the pipe column body (20) is provided with an inlet end used for being connected with a liquid injection pressurization system, and the pipe column body (20) can generate strain according to the change of internal pressure and external pressure; and

the optical fiber sensor (10) is bonded on the outer peripheral wall of the column body (20) and can measure the strain of the column body (20), and a plurality of sensing points (11) arranged at intervals and positioning marks for marking the spatial positions of the sensing points (11) are arranged on the optical fiber sensor (10).

2. The optical fiber strain sensing string according to claim 1, wherein the outer peripheral wall of the string body (20) is provided with a thread-like shallow groove, and the optical fiber sensor (10) is located in the shallow groove and spirally wound around the outer peripheral side of the string body (20) along the shallow groove.

3. The fiber optic strain sensing string of claim 1, further comprising a membrane wrapped around an outer wall of the string body (20).

4. A method for measuring the ground stress, which is applied to the optical fiber strain sensing pipe column according to any one of claims 1 to 3, and comprises the following steps:

step S10: preparing an optical fiber strain sensing pipe column and acquiring a strain correction coefficient of the optical fiber strain sensing pipe column;

step S20: embedding the optical fiber strain sensing pipe column into a rock body;

step S30: applying different preset pressures to the optical fiber strain sensing pipe column, and measuring strain actual values of the peripheral wall of the optical fiber strain sensing pipe column under different preset pressures according to the strain correction coefficients;

step S40: acquiring a stratum elasticity parameter according to the actual strain value;

step S50: and acquiring the pressure of the overlying strata, and calculating the static crustal stress of the rock mass according to the pressure of the overlying strata and the stratum elastic parameters.

5. The ground stress measuring method according to claim 4, wherein the step S10 comprises:

sealing the optical fiber strain sensing string;

applying preset pressure to the optical fiber strain sensing pipe column through a liquid injection pressurization system, and calculating a corrected strain actual value of the optical fiber strain sensing pipe column according to the preset pressure;

recording the corrected strain measurement value measured by each sensing point (11);

and performing linear correction on the corrected strain measurement value and the corrected strain actual value by using an analytical method or a numerical simulation method to obtain a strain correction coefficient.

6. The ground stress measuring method according to claim 4, wherein the step S20 comprises:

drilling a mounting hole on a rock mass;

and placing the optical fiber strain sensing pipe column in the mounting hole, and pouring cement between the inner wall surface of the mounting hole and the outer wall surface of the optical fiber strain sensing pipe column.

7. The ground stress measuring method according to claim 4, wherein the step S30 comprises:

injecting high-pressure liquid with different preset pressures into the optical fiber strain sensing pipe column through a liquid injection pressurization system so as to generate different internal pressures inside the optical fiber strain sensing pipe column;

sensing the strain of the optical fiber strain sensing pipe column by adopting an optical fiber sensor (10), and acquiring strain measurement values of the optical fiber strain sensing pipe column under the action of different internal pressures;

and obtaining the actual strain value according to the strain measurement value and the strain correction coefficient.

8. The ground stress measuring method according to claim 4, wherein the step S40 comprises:

step S41: acquiring a supposed value of strain and a supposed value of stratum elasticity parameter according to the functional relation between the preset pressure and the actual value of strain of the optical fiber strain sensing pipe column and the stratum elasticity parameter;

step S42: and repeating the step S41 until the error between the assumed strain value and the actual strain value reaches a preset error range, wherein the assumed stratum elasticity parameter value is the actual stratum elasticity parameter of the rock mass.

9. The ground stress measuring method according to claim 4, wherein the step S50 comprises:

and acquiring the ratio of the static ground stress to the overlying formation pressure by using the linear relation of the formation elastic parameters and the static ground stress, and acquiring the static ground stress according to the overlying formation pressure and the ratio.

10. The method of claim 9, wherein the linear relationship between the formation elastic parameter and the static ground stress is:

wherein, E _x 、E _y 、E _z 、υ _xy 、υ _xz 、υ _yz Are all formation elasticity parameters; sigma _x 、σ _y Is a horizontal ground stress; sigma _z Is overburden pressure.

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