CN213543861U - Underground stress measuring device based on distributed optical fiber sensing - Google Patents
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Abstract
The utility model provides an underground stress measuring device based on distributed optical fiber sensing, which comprises a metal sleeve arranged in a drill hole, wherein an armored optical cable is fixed on the inner wall of the sleeve; the armored optical cable comprises more than one high-temperature-resistant pressure-sensitive optical cable and more than two high-temperature-resistant multimode optical fibers; the underground stress measuring well also comprises two separators which are arranged underground, and a sealed ground stress measuring well section is arranged between the two separators; the underground stress measuring well also comprises a water injection pipe column for injecting high-pressure water into the underground stress measuring well section; the DPS/DTS composite modulation and demodulation instrument is respectively connected with a high-temperature-resistant pressure-sensitive optical cable and a high-temperature-resistant multimode optical fiber in the armored optical cable. The utility model discloses utilize hydraulic fracturing method to measure the two-dimensional ground stress field of the different degree of depth along the pit shaft point by point, lay pressure and temperature sensing armor optical cable from the shaft bottom to the well head, correct pressure data with temperature data, the quick accurate reliable measurement is from the shallow well to the two-dimensional ground stress field of rock around the whole well section well of ultra-deep well.
Description
Technical Field
The utility model belongs to the technical field of the ground stress measurement, concretely relates to underground stress measuring device based on distributed optical fiber sensing.
Background
The optical fiber sensing technology started in 1977 and developed rapidly along with the development of the optical fiber communication technology, and the optical fiber sensing technology is an important mark for measuring the informatization degree of a country. The optical fiber sensing technology is widely applied to the fields of military affairs, national defense, aerospace, industrial and mining enterprises, energy environmental protection, industrial control, medicine and health, metering test, building, household appliances and the like, and has a wide market. There are hundreds of fiber sensing technologies in the world, and physical quantities such as temperature, pressure, flow, displacement, vibration, rotation, bending, liquid level, speed, acceleration, sound field, current, voltage, magnetic field, radiation and the like realize sensing with different performances.
The downhole optical fiber sensing system can be used downhole to make measurements of stress, strain, pressure, temperature, noise, vibration, acoustic, seismic, flow, compositional analysis, electric and magnetic fields. The system is based on a full armored optical cable structure, and the sensor and the connecting and data transmission cable are all made of optical fibers.
At present, the measurement methods of the ground stress are more, and comprise direct measurement methods such as a hydraulic fracturing method, an acoustic emission method and a drilling collapse method, and indirect measurement methods such as a sleeve core stress relieving method and a strain recovery method.
The direct measurement method is to measure and record various stress values, such as compensating stress, restoring stress and balancing stress, directly by a measuring instrument, and obtain the stress value of the original rock through calculation according to the mutual relation between the stress values and the stress of the original rock. The calculation process does not involve the conversion of different physical quantities, and the physical mechanical property and stress-strain relation of the rock do not need to be known.
The direct measurement method mainly comprises a flat jack method, a hydraulic fracturing method, a rigid inclusion stressometer method and an acoustic emission method. The indirect measurement method is not a direct measurement of the stress amount, but measures and records some indirect physical quantity changes related to the stress in the rock mass, such as deformation or strain in the rock mass, changes in density, permeability, water absorption, resistance, capacitance of the rock mass, changes in propagation velocity of elastic waves and the like, by means of some sensing elements or some mediums, and then calculates the stress value in the rock mass by a known theoretical formula or empirical formula from the measured indirect physical quantity changes. Thus, in indirect measurement, in order to calculate the stress value, it is first necessary to determine certain physical-mechanical properties of the rock mass and the correlation of the measured physical quantity with the stress.
The hydrofracturing ground stress measurement method is used for in-situ measurement in a rock body, directly measuring the stress state in the rock body without acquiring related rock mechanical parameters, has the advantages of small disturbance on the stress field of an original rock structure, simple equipment, convenience in operation, strong measured value representativeness, good adaptability and the like, is widely applied to ground stress measurement of various geotechnical engineering, and is particularly widely applied to ground stress measurement of deep rock mass engineering.
The hydrofracturing method is an effective method for measuring the crustal deep rock crustal stress state, and the test principle of crustal deep rock crustal stress measurement is based on three basic assumptions: (1) crustal rock is a linear uniform, isotropic elastomer; (2) when the rock is a porous medium, the flow of the fluid in the pores conforms to Darcy's law; (3) one of the principal stress directions is parallel to the axial direction of the borehole. High-pressure water is injected into the closed drill hole,when the pressure reaches a maximum value PiThen, the borehole wall is broken to cause pressure reduction in the borehole, in order to maintain the crack to be kept in an open state, the pressure in the hole finally reaches a constant value, after the crack is not injected, the pressure in the hole is rapidly reduced, the crack is healed, then the pressure reduction speed is slowed down, and the critical value is instantaneous closing pressure PsReinjection is carried out after complete pressure relief to obtain the re-tensioning pressure P of the fracturerAnd instantaneous closing pressure PsFinally, the direction of the crack is recorded by an instrument and the two-dimensional ground stress field (sigma) of the ground stress measuring position of the drill hole is calculated according to a corresponding formula2,σ1)。
SUMMERY OF THE UTILITY MODEL
The utility model provides an use the metal casing that the installation finishes in the drilling, the armor optical cable that the metal casing inner wall was laid, install the divider in the pit, a water injection tubular column for filling the water under high pressure in the pit, and place in near well head distributed optical fiber pressure sensing/distributed optical fiber temperature sensing (DPS/DTS) composite modulation demodulation instrument and constitute the underground stress measuring device based on distributed optical fiber sensing, utilize the hydraulic fracturing method to measure the two-dimensional ground stress field (sigma) of the different degree of depth along the pit shaft point by point along the pit shaft2,σ1) The method can lay the pressure and temperature sensing armored optical cable from the bottom to the mouth of the well at one time, quickly, accurately and reliably measure the two-dimensional ground stress field of the rock around the whole well section from the shallow well to the ultra-deep well, and provides powerful support for the whole well section ground stress field data for the implementation scheme of the underground engineering.
The utility model aims at overcoming current underground stress measurement technique not enough, it lays the armor optical cable on the metal sleeve inner wall to have proposed, utilize hydraulic fracturing ground stress measurement method, a measurement system based on distributed optical fiber sensing's rock stratum ground stress distribution changes in the pit has been built, long-term real-time supervision and measurement ground stress are to the harm or the destruction that underground casing and various instrument and pipeline in the pit probably caused, be for guaranteeing oil and gas production well, water injection well and monitoring or observation well for a long time stable safe and reliable's work provides indispensable means, system and method.
In order to achieve the above object, the specific technical solution of the present invention is:
the underground stress measuring device based on distributed optical fiber sensing comprises a metal sleeve arranged in a drill hole, wherein an armored optical cable is distributed on the inner wall of the metal sleeve; the armored optical cable comprises more than one high-temperature-resistant pressure-sensitive optical cable and more than two high-temperature-resistant multimode optical fibers;
the underground stress measuring well also comprises at least two separators which are arranged underground, and a sealed ground stress measuring well section is arranged between the two separators; the underground stress measuring well comprises a water injection pipe column used for injecting high-pressure water into an underground stress measuring well section, and a high-pressure pump truck used for providing a high-pressure water source for the underground stress measuring well section; the water injection pipe column is connected with the high-pressure pump truck;
the high-temperature resistant and pressure sensitive optical cable is characterized by further comprising a DPS/DTS composite modulation and demodulation instrument arranged near the wellhead, wherein the DPS/DTS composite modulation and demodulation instrument is respectively connected with a high-temperature resistant pressure sensitive optical cable and a high-temperature resistant multimode optical fiber in the armored optical cable.
The DPS/DTS composite modulation and demodulation instrument is a distributed optical fiber pressure sensing and distributed optical fiber temperature sensing composite modulation and demodulation instrument and comprises a data acquisition module and a modulation and demodulation module.
The high-temperature-resistant pressure-sensitive optical cable is internally provided with a high-temperature-resistant single-mode or high-temperature-resistant special pressure-sensitive optical fiber, and the high-temperature-resistant pressure-sensitive optical cable and the high-temperature-resistant multi-mode optical fiber are respectively packaged in a continuous first metal thin tube and a continuous second metal thin tube.
The high-temperature-resistant pressure-sensitive optical cable is internally provided with a single-mode pressure-sensitive optical fiber, or a high-density continuous grating optical fiber with the space less than 1 meter, or a three-dimensional high-density array type normal poise cavity pressure sensor optical fiber with the space between 1 meter and 5 meters.
And single-layer or multi-layer armor steel wires for protection are wound outside the first metal thin tube and the second metal thin tube.
The first metal thin tube is internally provided with a high-temperature-resistant pressure-sensitive optical cable which is manufactured by tightly wrapping the optical fiber with a high-temperature-resistant high-strength composite material or wrapping the optical fiber by one-step forming through an injection molding machine, the optical cable is tightly attached to the wall and sealed in the first metal thin tube, and the tail end of the high-temperature-resistant pressure-sensitive optical cable is provided with an extinction device for eliminating strong light reflected back to the optical fiber from the tail end of the optical fiber.
And high-temperature-resistant optical fiber paste is also arranged in the second metal thin tube.
The separator arranged in the well is a pressurizing expansion type, and the pressurizing medium is liquid or gas.
The measuring method of the underground stress measuring device based on the distributed optical fiber sensing comprises the following steps:
(a) perforating operation for perforating the metal casing at all depth positions needing the ground stress measurement in the well;
(b) slowly putting the armored optical cable into the metal sleeve to enable the armored optical cable to be tightly attached to the inner wall of the metal sleeve; connecting a high-temperature-resistant pressure-sensitive optical cable in an armored optical cable to a DPS signal input end of a DPS/DTS composite modulation and demodulation instrument at a wellhead, welding two high-temperature-resistant multimode optical fibers together at the tail end of the armored optical cable to form a U-shaped structure, and connecting the two high-temperature-resistant multimode optical fibers to a TDS double-end signal input end of the DPS/DTS composite modulation and demodulation instrument at the top end of the armored optical cable;
(c) respectively arranging two separators at the upper part and the lower part of a depth position needing ground stress measurement, and filling water or inflating gas into the separators until the fluid exchange with a well section except the two separators is completely cut off;
(d) injecting high-pressure water into the ground stress measuring well section between the two separators through the water injection pipe column;
(e) continuously increasing water injection pressure until the rock outside the metal casing pipe begins to crack, demodulating the phase change of backward Rayleigh scattering light caused by pressure change on a high-temperature-resistant pressure-sensitive optical cable in an armored optical cable of the ground stress measurement well section by a DPS/DTS composite modulation and demodulation instrument to obtain the initial cracking pressure P of the rocki；
(f) Continuing to increase the water injection pressure to expand the rock fracture, stopping high-pressure water injection when the fracture is expanded to the depth of three times of the diameter of the well hole, keeping the water pressure constant, and measuring the closing pressure P by a DPS/DTS composite modulation and demodulation instrumentsThen releasing the pressure to close the crack;
(g) simultaneously recording a pressure-time curve chart and a flow-time curve chart in the whole pressurizing process to determine PiAnd PsA value;
(h) re-injecting high pressure water into the ground stress measuring well section to reopen the rock crack, and simultaneously measuring the pressure P when the crack reopens by the DPS/DTS composite modulation and demodulation instrumentrAnd a subsequent constant closing pressure Ps；
(i) Repeating the pressure relief-repressurization process for 2-3 times, and improving the accuracy of pressure measurement data;
(j) determining P by recording the pressure-time curve and the flow-time curve simultaneously during the whole process of repeatedly relieving pressure and re-pressurizingrAnd PsA value;
(j) the temperature change in the metal casing of the whole well section is monitored and measured in real time by utilizing a high-temperature-resistant multimode optical fiber and a DPS/DTS composite modulation-demodulation instrument, the temperature change data in the stress measurement well section in the metal casing is monitored and measured, the spectrum drift delta lambda similar to resonance waves or the spectrum drift delta upsilon of Bragg gratings is obtained by responding to the strain epsilon or the temperature t, and the formula is utilized:
Δλ/λ＝-Δυ/υ＝KTΔt+Kεε
wherein λ and υ are average light wavelength and frequency respectively; kTAnd KεTemperature and strain standard constants, respectively;
correcting data measured by DPS (data processing System) by using the temperature value of a specific measurement position to perform drift of a scattered light spectrum in the optical fiber caused by temperature change, and obtaining a real pressure value in the stress measurement well section in the metal casing pipe, wherein the temperature influence is eliminated;
(k) the fracture water pressure at the ground stress measurement depth separation section is P0The tensile strength of the rock is T according to the formula Pi＝3σ2-σ1+T-P0,Pr＝3σ2-σ1-P0And Ps＝σ2Calculating two-dimensional stress field (sigma) of ground stress measurement position2,σ1)。
From the aboveThe latter two formulas to find the two-dimensional ground stress sigma2And σ1The tensile strength of the rock need not be known and therefore measuring the raw rock stress by the hydrofracturing method will not involve the physico-mechanical properties of the rock but will be determined entirely by the measured and recorded pressure values.
The utility model provides an underground stress measuring device based on distributed optical fiber sensing, measurement and dynamic change monitoring method and technique for the underground stress distribution change in the whole well section rock stratum of low cost, high accuracy, high reliability. The utility model provides an use the metal casing that the installation finishes in the drilling, the armor optical cable that the metal casing inner wall was laid, install the divider in the pit, a water injection tubular column for filling the water under high pressure in the pit, and place in the underground stress measuring device based on distributed optical fiber sensing that distributed optical fiber pressure sensing/distributed optical fiber temperature sensing (DPS/DTS) composite modulation demodulation instrument constitutes jointly near the well head, utilize the hydraulic fracturing method to measure the two-dimentional ground stress field (sigma) of the different degree of depth along the pit shaft point by point along the pit shaft2,σ1) The method can lay pressure and temperature sensing armored optical cables from the well bottom to the well mouth at one time, quickly, accurately and reliably measure the two-dimensional ground stress field of rocks around the whole well section from a shallow well to an ultra-deep well, provides powerful support for the whole well section ground stress field data for the implementation scheme of underground engineering, effectively ensures the long-term stable, safe and reliable work of an oil and gas production well, a water injection well and a monitoring or observation well, and provides indispensable means, systems and methods for scientific management of oil and gas reservoirs and improvement of recovery ratio.
Drawings
Fig. 1 is a schematic diagram of the system structure of the present invention.
Fig. 2 is a schematic structural view of the metal sleeve and the armored optical cable of the present invention.
Fig. 3 is a schematic view of the internal structure (cross section) of the armored optical cable of the present invention.
Fig. 4 is the pumping pressure change and characteristic pressure diagram of the fracturing process of the present invention.
Detailed Description
The embodiments of the present invention will be described in detail with reference to the accompanying drawings, but they are not to be construed as limiting the invention, and are presented by way of example only, and the advantages of the invention will become more apparent and can be easily understood by description.
The utility model discloses a ground stress distribution monitoring system's embodiment based on distributed optical fiber sensing's rock stratum in pit, as follows:
as shown in fig. 1, the underground stress measuring device based on distributed optical fiber sensing comprises a metal casing 1 which is installed in a drill hole, an armored optical cable 2 distributed on the inner wall of the metal casing 1, and a DPS/DTS composite modem instrument 3 placed near a wellhead; a separator 6 installed in the well, a water injection string 7 for injecting high pressure water into the well, and a high pressure pump truck 9 for supplying high pressure water to the sealed section of the separator in the well. The DPS/DTS composite modulation and demodulation instrument 3 is respectively connected with a high-temperature-resistant pressure-sensitive optical cable 4 and a high-temperature-resistant multimode optical fiber 5 in the armored optical cable 2.
As shown in fig. 2, the DPS/DTS composite modem apparatus 3 includes data acquisition and modem functions of distributed fiber pressure sensing and distributed fiber temperature sensing (DPS/DTS). The armored optical cable 2 comprises at least more than one high-temperature-resistant pressure-sensitive optical cable 4 and at least more than two high-temperature-resistant multimode optical fibers 5, wherein the high-temperature-resistant pressure-sensitive optical cable 4 is internally provided with high-temperature-resistant single-mode or high-temperature-resistant special pressure-sensitive optical fibers, the high-temperature-resistant pressure-sensitive optical cable 4 and the high-temperature-resistant multimode optical fibers 5 are respectively encapsulated in a first metal thin tube 41 and a second metal thin tube 51, and the tail end of the high-temperature-resistant pressure-sensitive optical cable 4 is provided with an extinction device 8 for eliminating strong light reflected back to the optical fibers from the tail end of.
The high-temperature-resistant pressure-sensitive optical cable 4 can be a single-mode pressure-sensitive optical fiber, a high-density (the distance is less than 1 meter) continuous grating optical fiber, or a high-density array type Fabry-Perot cavity pressure sensor optical fiber with the distance between 1 meter and 5 meters.
As shown in fig. 3, the high temperature resistant pressure sensitive optical cable 4 made by tightly wrapping the optical fiber with a high temperature resistant high strength composite material or by one-step molding and wrapping the optical fiber with an injection molding machine is disposed in the first metal thin tube 41, and tightly adhered and sealed in the first metal thin tube 41. The second metal tubule 51 for packaging the high-temperature resistant multimode optical fiber 5 is also provided with high-temperature resistant optical fiber paste. The first metal tubule 41 and the second metal tubule 51 are also wound with single-layer or multi-layer armoured steel wires with protection function.
The separator 6 is of a pressure-expandable type, and the pressure can be liquid or gas.
The measuring method of the underground stress measuring device based on the distributed optical fiber sensing comprises the following steps:
(a) perforating 10 operation for perforating the metal casing 1 is carried out at all depth positions needing ground stress measurement in the underground;
(b) slowly putting the armored optical cable 2 into the metal sleeve 1 to enable the armored optical cable to be tightly attached to the inner wall of the metal sleeve 1; connecting a high-temperature-resistant pressure-sensitive optical cable 4 in an armored optical cable 2 to a DPS signal input end of a DPS/DTS composite modulation and demodulation instrument 3 at a wellhead, welding two high-temperature-resistant multimode optical fibers 5 together at the tail end of the armored optical cable 2 to form a U-shaped structure, and connecting the two high-temperature-resistant multimode optical fibers 5 to a DTS double-end signal input end of the DPS/DTS composite modulation and demodulation instrument 3 at the top end of the armored optical cable 2 (figure 2);
(c) respectively arranging at least two separators 6 at the upper part and the lower part of a depth position needing ground stress measurement, and filling water or inflating gas into the separators 6 until the fluid exchange with a well section outside the two separators 6 is completely cut off;
(d) injecting high-pressure water into the ground stress measuring well section which is respectively provided with the two separators 6 through a water injection pipe column 7;
(e) continuously increasing water injection pressure until the rock outside the casing pipe begins to crack, demodulating the phase change of backward Rayleigh scattering light caused by pressure change on a high-temperature-resistant pressure-sensitive optical cable 4 in the ground stress measurement well-segment armored optical cable 2 by a DPS/DTS composite modulation and demodulation instrument 3 to obtain the initial cracking pressure P of the rocki；
(f) Continuously increasing the water injection pressure to expand the rock fracture, closing the high-pressure water system when the fracture is expanded to the depth three times of the diameter of the well hole, keeping the water pressure constant, and measuring the closing pressure P by a DPS modulation and demodulation instrument on the groundsThen releasing the pressure to close the crack, wherein the closing pressure is Ps0；
(g) Simultaneously recording the pressure-time curve (figure 4) and the flow-time curve during the whole pressurizing process, and determining PiAnd PsA value;
(h) the high-pressure water is added into the sealed well section again to reopen the rock crack, and the DPS/DTS composite modulation and demodulation instrument 3 simultaneously measures the pressure P when the crack reopensrAnd a subsequent constant closing pressure Ps；
(i) Repeating the pressure relief-repressurization process for 2-3 times, and improving the accuracy of pressure measurement data;
(j) determining P by recording both the pressure-time graph (FIG. 4) and the flow-time graph throughout the repeated pressure relief-repressurization processrAnd PsA value;
(j) the temperature change in the whole well section sleeve is monitored and measured in real time by using the high-temperature resistant multimode optical fiber 5 and the DPS/DTS composite modulation and demodulation instrument 3 which are arranged in the armored optical cable 2 in the sleeve, and the temperature correction is carried out on the pressure (strain) data measured by the DPS/DTS composite modulation and demodulation instrument 3 according to the monitored and measured temperature change data in the stress measurement well section in the metal sleeve 1.
In strain/temperature measurements using distributed fiber optic sensors, back rayleigh scattering is measured using wavelength-scanning interferometry as a function of position on the fiber. The rayleigh scattering in an optical fiber occurs due to refractive index fluctuations in the length direction of the fiber. Although the scattering is random, for a given fiber, if the state of the fiber does not change, the same wavelength of reflected light is always generated, and this characteristic is called the inherent texture information of the fiber. If a certain position of the optical fiber is deformed due to the influence of load or temperature, only the wavelength of the reflected light at the position is deviated, and by comparing the reflected light before and after the deformation, it is possible to confirm at which position of the optical fiber the deformation occurs. Under normal conditions, the spectrum of the scattered light in the fiber shifts primarily due to strain or temperature changes. The spectral drift obtained from the strain epsilon or the temperature t response is similar to the drift of resonance wave delta lambda or the spectral drift of Bragg grating delta upsilon, namely: using the formula:
Δλ/λ＝-Δυ/υ＝KTΔt+Kεε
in the formula: λ and υ are average light wavelength and frequency, respectively; kTAnd KεTemperature and strain standard constants, respectively, for most germanosilicate core fibers, KT＝6.45μ℃-1，Kε＝0.78。
Correcting data measured by the DPS by using the temperature value of a specific measurement position to perform drift of a scattered light spectrum in the optical fiber caused by temperature change, and obtaining a real pressure value in the stress measurement well section in the metal casing 1 with temperature influence eliminated;
(k) the fracture water pressure at the ground stress measurement depth separation section is P0The tensile strength of the rock is T according to the formula
Pi＝3σ2-σ1+T-P0,Pr＝3σ2-σ1-P0And Ps＝σ2Calculating two-dimensional stress field (sigma) of ground stress measurement position2,σ1). The two-dimensional ground stress sigma is obtained by the above two latter formulas2And σ1The tensile strength of the rock need not be known and therefore measuring the raw rock stress by the hydrofracturing method will not involve the physico-mechanical properties of the rock but will be determined entirely by the measured and recorded pressure values.
The underground ground stress measuring system based on distributed optical fiber sensing and the measuring method thereof are a method and a technology for measuring underground whole well section rock stratum ground stress distribution change and monitoring dynamic change with low cost, high precision and high reliability. The utility model provides an use the metal casing that the installation finishes in the drilling, the armor optical cable that the metal casing inner wall was laid, install the divider in the pit for fill the water injection tubular column of water under high pressure in the pit, and place in the underground stress measuring device based on distributed optical fiber sensing that distributed optical fiber pressure sensing/distributed optical fiber temperature sensing (DPS/DTS) composite modulation demodulation instrument constitutes jointly near the well head, utilize the hydraulic fracturing methodMeasuring two-dimensional ground stress fields (sigma) of different depths point by point along a wellbore2,σ1) The method can lay pressure and temperature sensing armored optical cables from the well bottom to the well mouth at one time, quickly, accurately and reliably measure the two-dimensional ground stress field of rocks around the whole well section from a shallow well to an ultra-deep well, provide powerful support for the whole well section ground stress field data for the implementation scheme of underground engineering, effectively ensure the long-term stable, safe and reliable work of an oil and gas production well, a water injection well and a monitoring or observation well, and provide indispensable means, systems and methods for scientific management and improvement of recovery ratio of oil and gas reservoirs.
Claims (8)
1. The underground stress measuring device based on distributed optical fiber sensing is characterized by comprising a metal sleeve (1) arranged in a drill hole, wherein an armored optical cable (2) is distributed on the inner wall of the metal sleeve (1); the armored optical cable (2) comprises more than one high-temperature-resistant pressure-sensitive optical cable (4) and more than two high-temperature-resistant multimode optical fibers (5);
the underground stress measuring well further comprises at least two separators (6) arranged underground, and a sealed ground stress measuring well section is arranged between the two separators (6); the underground stress measuring well also comprises a water injection pipe column (7) for injecting high-pressure water into the underground stress measuring well section, and a high-pressure pump truck (9) for providing a high-pressure water source for the underground stress measuring well section; the water injection pipe column (7) is connected with a high-pressure pump truck (9);
the high-temperature-resistant and pressure-sensitive optical cable is characterized by further comprising a DPS/DTS composite modulation and demodulation instrument (3) arranged near a wellhead, wherein the DPS/DTS composite modulation and demodulation instrument (3) is respectively connected with a high-temperature-resistant pressure-sensitive optical cable (4) and a high-temperature-resistant multimode optical fiber (5) in the armored optical cable (2).
2. The distributed optical fiber sensing-based underground stress measuring device according to claim 1, wherein the DPS/DTS composite modem instrument (3) is a distributed optical fiber pressure sensing and distributed optical fiber temperature sensing composite modem instrument, and comprises a data acquisition module and a modem module.
3. The underground stress measuring device based on the distributed optical fiber sensing according to claim 1, wherein the high temperature resistant pressure sensitive optical cable (4) is internally provided with a high temperature resistant single-mode or high temperature resistant special pressure sensitive optical fiber, and the high temperature resistant pressure sensitive optical cable (4) and the high temperature resistant multi-mode optical fiber (5) are respectively encapsulated in a first metal tubule (41) and a second metal tubule (51) which are continuous.
4. A distributed optical fiber sensing-based underground stress measuring device according to claim 3, wherein the high temperature resistant pressure sensitive optical cable (4) is a single mode pressure sensitive optical fiber, or a high density continuous grating optical fiber with a spacing less than 1 meter, or a high density array type normal poise cavity pressure sensor optical fiber with a spacing of 1 meter to 5 meters.
5. A distributed optical fiber sensing-based underground stress measuring device according to claim 3, wherein the first metal thin tube (41) and the second metal thin tube (51) are wrapped with single-layer or multi-layer protective armored steel wires.
6. The underground stress measuring device based on the distributed optical fiber sensing of claim 3, wherein the first metal thin tube (41) is internally provided with a high temperature resistant pressure sensitive optical cable (4) which is tightly wrapped by a high temperature resistant high strength composite material or is manufactured by wrapping an optical fiber by one-step molding of an injection molding machine, the high temperature resistant pressure sensitive optical cable is tightly attached to the wall and sealed in the first metal thin tube (41), and the tail end of the high temperature resistant pressure sensitive optical cable (4) is provided with a deluster (8).
7. The distributed optical fiber sensing-based subsurface stress measuring device according to claim 3, wherein the second metal tubule (51) is further provided with high temperature resistant optical fiber paste.
8. A distributed optical fibre sensing based subsurface stress measuring device according to claim 1, wherein said downhole separator (6) is of a pressure-expandable type, the pressure medium being a liquid or a gas.
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