CN101397904B - Method for monitoring downhole casing strain by using optical fibre sensor - Google Patents
Method for monitoring downhole casing strain by using optical fibre sensor Download PDFInfo
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Abstract
The invention relates to a method for monitoring the stress of a casing in a well by applying optical-fiber sensors, which mainly solves the problem that the existing research field of the casing erosion of an oil field and oil-water well does not have a direct method for monitoring the stress loading process of the casing in the well and the morphological characters of the casing erosion. The method is characterized in that: optical-fiber grating sensors are circumferentially arranged along the outer surface of the casing; a ground optical-fiber grating demodulation instrument connected with the optical-fiber grating sensors is utilized to monitor the circumferential strain Epsilon Theta of the casing and obtain the circumferential strain data of the casing; meanwhile, Brilliouin optical-fiber sensors are axially arranged along the outer surface of the casing; a ground Brilliouin optical-fiber demodulation instrument connected with the Brilliouin optical-fiber sensors is utilized to monitor the axial strain Epsilon Z of the casing and obtain the axial stain data of the casing; and the obtained circumferential strain Epsilon Theta and the axial strain Epsilon Z of the casing are utilized to obtain the stress of the outer layer of the casing in the well according to a ground stress explanation model. The method is characterized by being capable of permanently monitoring the deformation of the casing and obtaining corresponding stratum pressure under the condition without knowing the casing erosion and the stratum pressure.
Description
Technical field:
The present invention relates to the method for a kind of monitoring downhole casing strain in the sleeve in oil field damage research field, relate to the method for a kind of using optical fibre grating sensor and optical fiber Brillouin sensing device monitoring downhole casing strain specifically.
Background technology:
At present, the oilfield oil well cover decreases research and has just analyzed the influence of cover being decreased owing to aspects such as clay mineral, injection water quality and geostatic stress from mechanism, but lacks the method for directly monitoring for downhole casing strain process and cover disfigurement attitude characteristic.
Summary of the invention:
Decrease in the research field problem that downhole casing strain process and cover disfigurement attitude characteristic is lacked direct monitoring method in order to solve existing oilfield oil well cover; The present invention provides the method for a kind of using optical fibre grating sensor and optical fiber Brillouin sensing device monitoring downhole casing strain; Use this method; Can measure sleeve circumferential strain and axial strain; And theoretical according to the geostatic stress interpretation model, can unknown cover in advance decrease with the strata pressure situation under permanent monitoring sleeve deformation with obtain correspondingly stressor layer, for oil field development cover damage is monitored and specific aim takes system pressure adjustment measure that foundation is provided.
Technical scheme of the present invention is: the method for this kind monitoring downhole casing strain by using optical fibre sensor; May be summarized to be: along the circumferential laying optical fiber grating sensor of bushing outer surface, the ground fiber Bragg grating (FBG) demodulator monitoring sleeve circumferential strain ε that utilizes fiber-optic grating sensor therewith to be connected
θAnd obtain the sleeve circumferential strain data, and simultaneously along the axial laying optical fiber Brillouin sensing of said bushing outer surface device, the ground optical fiber Brillouin (FBG) demodulator monitoring sleeve axial strain ε that utilizes optical fiber Brillouin sensing device therewith to be connected
zAnd obtain quill to strain data, with the sleeve circumferential strain ε that is obtained
θWith axial strain ε
zThe constitutive equation group (1) of the cylindrical coordinate setting of casing stress and strain below the substitution and equation group (2) can be obtained horizontal major principal stress and horizontal minimum principal stress, i.e. σ under the main stress bar coordinate system
hAnd σ
H, because the suffered strata pressure P=of down-hole casing σ
Original-σ
Calculate, wherein, σ
OriginalBe original geostatic stress, can get σ by geostress survey
CalculateBe horizontal major principal stress or the horizontal minimum principal stress that calculates, therefore can obtain the suffered strata pressure P of corresponding down-hole casing at last;
Said constitutive equation group (1) is:
σ
r＝(λ+2G)ε
r+λε
θ+λε
z
σ
θ＝(λ+2G)ε
θ+λε
r+λε
z
σ
z＝(λ+2G)ε
z+λε
r+λε
θ…………(1)
σ wherein
θ, σ
r, σ
zBe respectively circumferential stress, radial stresses and axial stress under the cylindrical coordinate when being the z axle with the sleeve pipe center line, θ is a polar angle, and λ is a Lame constants, and G is the cannula scissors shear modulu, σ
vCan obtain by the density log integration;
Said equation group (2) is a geostatic stress distribution relation on the straight well sleeve pipe, that is:
σ
r＝p
w
σ
θ＝σ
H+σ
h-2(σ
H-σ
h)cos2θ-p
w
σ
z＝σ
v-2v(σ
H-σ
h)cos2θ…………(2)
P wherein
wFor pressing in the pit shaft, v is a poisson's ratio, σ
v, σ
H, σ
hBe respectively vertical main stress bar under the main stress bar coordinate system, horizontal major principal stress and horizontal minimum principal stress.
The present invention has following beneficial effect: the present invention adopts along the circumferential laying optical fiber grating sensor of sleeve pipe off-balancesheet; While is along the method for the axial laying optical fiber Brillouin sensing of sleeve pipe off-balancesheet device; Measure sleeve circumferential strain and axial strain; Theoretical according to the geostatic stress interpretation model again, can unknown cover in advance decrease with the strata pressure situation under permanent monitoring sleeve deformation and stressor layer correspondingly, for oil field development cover damage is monitored and specific aim takes system pressure adjustment measure that foundation is provided.And this method can realize full well section monitoring, measures accurately, and precision is high.
Description of drawings:
Fig. 1 is the course of work sketch map of related method among the present invention.
Fig. 2 is the structural representation of employed transmission cable among the present invention.
Fig. 3 is along the fiber-optic grating sensor of sleeve circumferential layout and the sectional drawing of optical fiber Brillouin sensing device among the present invention.
1-sleeve pipe among the figure, 2-casing coupling, 3-fiber optic temperature compensation sensor, 4-landing nipple, 5-stratum; 6-target zone casing coupling, 7-fiber-optic grating sensor, 8-epoxide-resin glue and glass fabric, 9-cable protection cover, 10-transmission cable; The 11-fiber Bragg grating (FBG) demodulator, 12-optical fiber Brillouin (FBG) demodulator, PU sheath in the 13-optical fiber Brillouin sensing device, 14-, the mesh grid of 15-inner layer metal; The 16-Kafra fiber, 17-metal hose, 18-optical fiber, the outer PU sheath of 19-, the mesh grid of 20-outer layer metal.
The specific embodiment:
Below in conjunction with accompanying drawing the present invention is described further:
Major programme of the present invention is: along the circumferential laying optical fiber grating sensor of bushing outer surface, and the ground fiber Bragg grating (FBG) demodulator monitoring sleeve circumferential strain ε that utilizes fiber-optic grating sensor therewith to be connected
θAnd obtain the sleeve circumferential strain data, and simultaneously along the axial laying optical fiber Brillouin sensing of said bushing outer surface device, the ground optical fiber Brillouin (FBG) demodulator monitoring sleeve axial strain ε that utilizes optical fiber Brillouin sensing device therewith to be connected
zAnd obtain quill to strain data, with the sleeve circumferential strain ε that is obtained
θWith axial strain ε
zThe constitutive equation group (1) of the cylindrical coordinate setting of casing stress and strain below the substitution and equation group (2) can be obtained horizontal major principal stress and horizontal minimum principal stress, i.e. σ under the main stress bar coordinate system
hAnd σ
H, because the suffered strata pressure P=of down-hole casing σ
Original-σ
Calculate, wherein, σ
OriginalBe original geostatic stress, can get σ by geostress survey
CalculateBe horizontal major principal stress or the horizontal minimum principal stress that calculates, therefore can obtain the suffered strata pressure P of corresponding down-hole casing at last;
Said constitutive equation group (1) is:
σ
r＝(λ+2G)ε
r+λε
θ+λε
z
σ
θ＝(λ+2G)ε
θ+λε
r+λε
z
σ
z＝(λ+2G)ε
z+λε
r+λε
θ…………(1)
σ wherein
θ, σ
r, σ
zBe respectively circumferential stress, radial stresses and axial stress under the cylindrical coordinate when being the z axle with the sleeve pipe center line, θ is a polar angle, and λ is a Lame constants, and G is the cannula scissors shear modulu, σ
vCan obtain by the density log integration;
Said equation group (2) is a geostatic stress distribution relation on the straight well sleeve pipe, that is:
σ
r＝p
w
σ
θ＝σ
H+σ
h-2(σ
H-σ
h)cos2θ-p
w
σ
z＝σ
v-2v(σ
H-σ
h)cos2θ…………(2)
Wherein Pw presses in the pit shaft, and v is a poisson's ratio, σ
v, σ
H, σ
hBe respectively vertical main stress bar under the main stress bar coordinate system, horizontal major principal stress and horizontal minimum principal stress.
Specifically, at first, for accomplish described in the such scheme along the circumferential laying optical fiber grating sensor of bushing outer surface, the ground fiber Bragg grating (FBG) demodulator monitoring sleeve circumferential strain ε that utilizes fiber-optic grating sensor therewith to be connected
θAnd the step of obtaining the sleeve circumferential strain data is: after one group of fiber-optic grating sensor 7 of arranging along sleeve circumferential and fiber optic temperature compensation sensor 3 polyphones are connected; Through glass fabric and epoxide-resin glue parcel; The holding wire of being drawn is connected with transmission cable 10; The other end of said transmission cable 10 is connected to the fiber Bragg grating (FBG) demodulator 11 that rest on the ground, will be by the grating centre wavelength information of said fiber Bragg grating (FBG) demodulator 11 acquisitions, after temperature-compensating and initial value compensation; Be converted into the sleeve circumferential deformation information according to following secondary demodulation method, wherein said secondary demodulation method is:
In the actual monitoring process, use said fiber Bragg grating (FBG) demodulator 11 test sample the centre wavelength information of each fiber-optic grating sensor 7, i.e. λ constantly;
The centre wavelength of the sampling instant fiber-optic grating sensor 7 in the said fiber Bragg grating (FBG) demodulator 11 is derived through movable memory equipment;
Use the centre wavelength information of said fiber Bragg grating (FBG) demodulator 11 measuring fiber temperature compensation sensors 3, i.e. λ
T
The centre wavelength information of the sampling instant fiber optic temperature compensation sensor 3 in the said fiber Bragg grating (FBG) demodulator is derived through movable memory equipment;
Because fiber optic temperature compensation sensor 3 does not receive external force, so its centre wavelength is λ
T=C
TΔ T combines it, promptly with temperature, strain coupling model
Δλ＝C
εΔε+C
TΔT (3)
Obtain: λ
ε=Δ λ-Δ λ
T=C
εΔ ε (5)
Wherein, Δ λ, Δ λ
T, C
ε, C
TAnd Δ ε is followed successively by the sensitivity coefficient of center wavelength variation amount, optical grating axial strain and the center wavelength variation relation of fiber-optic grating sensor center wavelength variation amount, fiber optic temperature compensation sensor, the sensitivity coefficient and the deflection of fiber grating temperature sensor respectively, and Δ T is a variations in temperature;
By above-mentioned formula (3)～formula (5) data of being stored are calculated; Can obtain the relation between the centre wavelength of deflection and fiber-optic grating sensor (7); Because fiber-optic grating sensor (7) is to lay along sleeve circumferential, with the sleeve circumferential cooperative transformation, the deflection λ that is therefore asked for
εIt is exactly the circumferential distortion of sleeve pipe.
Secondly, for accomplish described in the such scheme along the axial laying optical fiber Brillouin sensing of bushing outer surface device, the ground optical fiber Brillouin (FBG) demodulator monitoring sleeve axial strain ε that utilizes optical fiber Brillouin sensing device therewith to be connected
zAnd obtain quill and be to the step of strain data:
1. the optical fiber Brillouin sensing device 13 of fiber-reinforced resin encapsulation is gone into the well with single sleeve pipe; And axially lay along bunch tube; Closer adopts the monitoring optical cable to connect said optical fiber Brillouin sensing device far from ground in the down-hole; The other end of this monitoring optical cable is connected to ground optical fiber Brillouin (FBG) demodulator 12, and said optical fiber Brillouin (FBG) demodulator has lasing light emitter to produce optical signal;
2. use the initial value frequency displacement information that the fibre strain analyzer records said optical fiber Brillouin sensing device, i.e. V
B0, this initial value frequency displacement information is derived and preserves;
3. use the fibre strain analyzer and test the frequency displacement information of said optical fiber Brillouin sensing device in sampling instant, i.e. V
B, the frequency displacement information of the sampling instant that is obtained is derived and preserves;
4. utilize the basic principle formula (6) of optical fiber Brillouin sensing device, promptly
V
B＝C
εΔε+C
TΔT+V
B0…………(6)
Will be 2. and the V that is 3. obtained through step
B0With V
BAfter the numerical value substitution, formula (6) is converted into formula (7), Δ v
B=C
εΔ ε+C
TΔ T ... (7), promptly there be not temperature, the strain coupling model of initial value affecting,
Wherein, C
εBe Brillouin's ga(u)ge factor, C
TBe Brillouin's temperature control coefficient, Δ ε is the deflection of the sharp deep sensor of said optical fiber cloth, and Δ T is a variations in temperature;
5. use the Brillouin shift information of fibre strain analyzer test, i.e. V with the said optical fiber Brillouin sensing device of sleeve pipe G.I.H
B, and data are derived the back store;
6. the Brillouin shift data with sampling instant monitoring optical cable in the fibre strain analyzer derive, because the optical fiber in the monitoring optical cable does not receive external force, so its Brillouin shift is formula (8),
V
BT＝C
TΔT…………(8)
C
TBe Brillouin's temperature control coefficient, Δ T is a variations in temperature;
7. with step 6. in resulting Brillouin shift combine with temperature, the strain coupling model of no initial value affecting, be about to formula (8) and combine with formula (7), obtain formula (9),
Δv
Bε＝ΔV
B-ΔV
BT＝C
εΔε…………(9)
Wherein, Δ ε is the deflection of said optical fiber Brillouin sensing device, C
εBe Brillouin's ga(u)ge factor, Δ v
B εThe Brillouin shift that collects in real time for the fibre strain analyzer;
8. owing to said optical fiber Brillouin sensing device is axially laid along oil, well bunch tube; With said oil, well bunch tube cooperative transformation, therefore by step 7. in the deflection Δ ε of resulting said optical fiber Brillouin sensing device be exactly the axial deflection of said oil, well bunch tube.
The concrete technology of above-mentioned steps when construction is following:
1. confirm to lay under the predetermined sleeve pipe of sensor dark, and on the predetermined sleeve pipe in ground installing and locating joint 4;
2. 4 fiber-optic grating sensors and 1 fiber optic temperature compensation sensor are welded together;
3. measure sleeve pipe, confirm the sensor installation position, the polishing and use the alcohol wash sleeve surface, guarantee its surperficial free from admixture;
4. the position of sleeve surface perpendicular alignmnet landing nipple 4 is confirmed as the position of first bare optical fibers and bare optical gratings sensor L-1, be fixed in sleeve surface with chemical glue;
5. according to the method described above sleeve circumferential at interval certain angle lay all the other bare optical fibers and bare optical gratings sensors, by numbering L-2 clockwise, L-3, L-4;
6. organize 0.3 meter of fiber-optic grating sensor laying optical fiber temperature compensation sensor apart from this, and lifting one's head and transmission cable 10 weldings a plurality of sensors;
7. Optical Fiber Transmission optical cable part being arranged on sensor place, the sleeve pipe and carrying out three layers of coating with epoxide-resin glue and glass fabric in 3 meters scopes vertically;
8. at the transmission cable one end welding wire jumper head in exit, connect fiber Bragg grating (FBG) demodulator 11, prepare setting of casing;
9. in the setting of casing process, when being lowered to the target zone sleeve pipe, the end of optical fiber Brillouin sensing device 13 is fixed on the pre-position of this sleeve pipe;
10. before each root sleeve pipe is gone into the well; The transmission cable 10 and optical fiber Brillouin sensing device 13 about 15m need be reserved in ground; So that its smooth G.I.H; With single sleeve pipe G.I.H, every casing coupling place adopts 1 protective cover that transmission cable and optical fiber Brillouin sensing device are protected, after fiber-optic grating sensor transmission cable and optical fiber Brillouin sensing device transmission cable pick out well head by rig floor well head place for transmission cable 10 and optical fiber Brillouin sensing device 13 in the setting of casing process; Difference is welding wire jumper head again, and protects in the thereto.
In the present invention in sleeve in oil field damage research field; Theory of the fiber optical and optical fiber Brillouin sensing principle have at first been used; Fiber-optic grating sensor is laid along sleeve circumferential, and to laying, wherein a plurality of bare optical fibers and bare optical gratings sensors are distributed on around the sleeve pipe optical fiber Brillouin sensing device that will be called intelligent muscle along quill; Adjacent spacing cross section is angled, is organizing sensor respective place laying optical fiber temperature compensation sensor apart from this.Using optical fibre grating sensor monitoring little deformation of sleeve pipe and the force-bearing situation thereof in the sensor certain limit, the application of temperature compensation sensor is monitored with downhole temperature as the temperature-compensating of strain transducer simultaneously.Sensor is sent to ground through transmission cable with underground signal, can be converted into the pressure and temperature that needs through the (FBG) demodulator subsequent treatment.
For improving tensile strength and lateral pressure resistant intensity; The transmission cable 10 that is adopted is made up of optical fiber 18, metal hose 17, Kafra fiber 16, inner layer metal mesh grid 15, interior PU sheath 14, outer layer metal mesh grid 20 and outer PU sheath 19 successively from inside to outside; As shown in Figure 2; After improving like this, tensile strength and lateral pressure resistant intensity have increased by 4 times and 5 times respectively, are fit to very much the bad working environments of down-hole.In addition, can fiber optic temperature compensation sensor 3 be placed in the draw point needle tubing, so both can protect sensor, and because metal has good thermal conductivity, the numerical value that can guarantee sensor again reaction temperature accurately changes the strain value that causes.
In the specific implementation, fiber-optic grating sensor is the Harbin City Taida that GFRP-OFBG sensor that Science and Technology Ltd. produced, and its 60 ℃ of base strength loss lates of 2 months (PH＞13) are lower than 24.8%, and acid strength loss late (PH＜1) is lower than 12.5%; Salt loss of strength rate (NaCl) is lower than 6.8%, and its precision can reach ± 5 μ ε, and specific targets are as shown in table 1.
Table 1
The SM125 fiber Bragg grating (FBG) demodulator that used fiber Bragg grating (FBG) demodulator selects for use Micron Optics Inc. to produce.Used optical fiber Brillouin (FBG) demodulator is the AQ8603 fibre strain analyzer that Shanghai Yokogawa International Trading Company Ltd produces, and the parameter of fibre strain analyzer is chosen as: monitoring maximum length 2km, spatial resolution 0.5m, equalization number of times 2x10
13Inferior, under this parameter, monitor.In addition; Optical fiber Brillouin sensing device to common has carried out the fiber-reinforced resin encapsulation; And inner encapsulation two core fibres, make this optical fiber Brillouin sensing device that has improved can adapt to the abominable operating condition in down-hole thus, guaranteed stability to the casing damage monitoring.
Said method is implemented in apricot 10-4-third 3132 well test, wherein, 803 meters of the apricot 10-4-third 3132 tender II segment standard of the well layer depth, under the landing nipple dark 809.52 meters, sensor is laid in apart from 1.5 meters, landing nipple top, following dark 808.02 meters.
In accomplishing the above-mentioned course of work; Because having lot of data calculates; Therefore can development computer software will pass through and obtain information after a fiber Bragg grating (FBG) demodulator and the demodulation of optical fiber Brillouin (FBG) demodulator and change into needed sleeve circumferential strain information; Promptly realize the computerization of secondary demodulation method, to save a large amount of manual calculation.
Claims (4)
1. the method for a monitoring downhole casing strain by using optical fibre sensor is characterized in that: along the circumferential laying optical fiber grating sensor of bushing outer surface, and the ground fiber Bragg grating (FBG) demodulator monitoring sleeve circumferential strain ε that utilizes fiber-optic grating sensor therewith to be connected
θAnd obtain the sleeve circumferential strain data, and simultaneously along the axial laying optical fiber Brillouin sensing of said bushing outer surface device, the ground optical fiber Brillouin (FBG) demodulator monitoring sleeve axial strain ε that utilizes optical fiber Brillouin sensing device therewith to be connected
zAnd obtain quill to strain data, with the sleeve circumferential strain ε that is obtained
θWith axial strain ε
zThe constitutive equation group of the cylindrical coordinate setting of casing stress and strain below the substitution
(1) and equation group (2) can obtain horizontal major principal stress and horizontal minimum principal stress, i.e. σ under the main stress bar coordinate system
hAnd σ
H, because the suffered strata pressure P=of down-hole casing σ
Original-σ
Calculate, wherein, σ
OriginalBe original geostatic stress, can get σ by geostress survey
CalculateBe horizontal major principal stress or the horizontal minimum principal stress that calculates, therefore can obtain the suffered strata pressure P of corresponding down-hole casing at last;
Said constitutive equation group (1) is:
σ
r＝(λ+2G)ε
r+λε
θ+λε
z
σ
θ＝(λ+2G)ε
θ+λε
r+λε
z
σ
z＝(λ+2G)ε
z+λε
r+λε
θ…………(1)
σ wherein
θ, σ
r, σ
zBe respectively circumferential stress, radial stresses and axial stress under the cylindrical coordinate when being the z axle with the sleeve pipe center line, θ is a polar angle, and λ is a Lame constants, and G is the cannula scissors shear modulu, σ
vCan obtain by the density log integration;
Said equation group (2) is a geostatic stress distribution relation on the straight well sleeve pipe, that is:
σ
r＝p
w
σ
θ＝σ
H+σ
h-2(σ
H-σ
h)cos2θ-p
w
σ
z＝σ
v-2v(σ
H-σ
h)cos2θ…………(2)
P wherein
wFor pressing in the pit shaft, v is a poisson's ratio, σ
v, σ
H, σ
hBe respectively vertical main stress bar under the main stress bar coordinate system, horizontal major principal stress and horizontal minimum principal stress.
2. the method for a kind of monitoring downhole casing strain by using optical fibre sensor according to claim 1; It is characterized in that accomplishing described in the claim 1 along the circumferential laying optical fiber grating sensor of bushing outer surface the ground fiber Bragg grating (FBG) demodulator monitoring sleeve circumferential strain ε that utilizes fiber-optic grating sensor therewith to be connected
θAnd the step of obtaining the sleeve circumferential strain data is: after one group of fiber-optic grating sensor (7) of arranging along sleeve circumferential and a fiber optic temperature compensation sensor (3) polyphone are connected; Through glass fabric and epoxide-resin glue parcel; The holding wire of being drawn is connected with transmission cable (10); The other end of said transmission cable (10) is connected to the fiber Bragg grating (FBG) demodulator (11) that rest on the ground, will be by the grating centre wavelength information of said fiber Bragg grating (FBG) demodulator (11) acquisition, after temperature-compensating and initial value compensation; Be converted into the sleeve circumferential deformation information according to following secondary demodulation method, wherein said secondary demodulation method is:
In the actual monitoring process, use said fiber Bragg grating (FBG) demodulator (11) test sample the centre wavelength information of each fiber-optic grating sensor (7), i.e. λ constantly;
The centre wavelength of the sampling instant fiber-optic grating sensor (7) in the said fiber Bragg grating (FBG) demodulator (11) is derived through movable memory equipment;
Use the centre wavelength information of said fiber Bragg grating (FBG) demodulator (11) measuring fiber temperature compensation sensor (3), i.e. λ
T
The centre wavelength information of the sampling instant fiber optic temperature compensation sensor (3) in the said fiber Bragg grating (FBG) demodulator is derived through movable memory equipment;
Because fiber optic temperature compensation sensor (3) does not receive external force, so its centre wavelength is λ
T=C
TΔ T combines it, promptly with temperature, strain coupling model
Δλ＝C
εΔε+C
TΔT (3)
Obtain: λ
ε=Δ λ-Δ λ
T=C
εΔ ε (5)
Wherein, Δ λ, Δ λ
T, C
ε, C
TAnd Δ ε is followed successively by the sensitivity coefficient of center wavelength variation amount, optical grating axial strain and the center wavelength variation relation of fiber-optic grating sensor center wavelength variation amount, fiber optic temperature compensation sensor, the sensitivity coefficient and the deflection of fiber grating temperature sensor respectively, and Δ T is a variations in temperature;
By above-mentioned formula (3)～formula (5) data of being stored are calculated; Can obtain the relation between the centre wavelength of deflection and fiber-optic grating sensor (7); Because fiber-optic grating sensor (7) is to lay along sleeve circumferential, with the sleeve circumferential cooperative transformation, the deflection λ that is therefore asked for
εIt is exactly the circumferential distortion of sleeve pipe.
3. the method for a kind of monitoring downhole casing strain by using optical fibre sensor according to claim 2; It is characterized in that accomplishing described in the claim 1 along the axial laying optical fiber Brillouin sensing of bushing outer surface device the ground optical fiber Brillouin (FBG) demodulator monitoring sleeve axial strain ε that utilizes optical fiber Brillouin sensing device therewith to be connected
zAnd obtain quill and be to the step of strain data:
1. the optical fiber Brillouin sensing device (13) of fiber-reinforced resin encapsulation is gone into the well with single sleeve pipe; And axially lay along bunch tube; Closer adopts the monitoring optical cable to connect said optical fiber Brillouin sensing device far from ground in the down-hole; The other end of this monitoring optical cable is connected to ground optical fiber Brillouin (FBG) demodulator (12), and said optical fiber Brillouin (FBG) demodulator has lasing light emitter to produce optical signal;
2. use the initial value frequency displacement information that the fibre strain analyzer records said optical fiber Brillouin sensing device, i.e. V
B0, this initial value frequency displacement information is derived and preserves;
3. use the fibre strain analyzer and test the frequency displacement information of said optical fiber Brillouin sensing device in sampling instant, i.e. V
B, the frequency displacement information of the sampling instant that is obtained is derived and preserves;
4. utilize the basic principle formula (6) of optical fiber Brillouin sensing device, promptly
V
B＝C
εΔε+C
TΔT+V
B0…………(6)
Will be 2. and the V that is 3. obtained through step
B0With V
BAfter the numerical value substitution, formula (6) is converted into formula (7), Δ v
B=C
εΔ ε+C
TΔ T ... (7), promptly there be not temperature, the strain coupling model of initial value affecting,
Wherein, C
εBe Brillouin's ga(u)ge factor, C
TBe the sensitivity coefficient of fiber grating temperature sensor, Δ ε is the deflection of fiber-optical grating temperature sensor, and Δ T is a variations in temperature;
5. use the Brillouin shift information of said fibre strain analyzer test, i.e. V with the said optical fiber Brillouin sensing device of sleeve pipe G.I.H
B, and data are derived the back store;
6. the Brillouin shift data with sampling instant monitoring optical cable in the said fibre strain analyzer derive, because the optical fiber in the monitoring optical cable does not receive external force, so its Brillouin shift is formula (8),
V
BT＝C
TΔT…………(8)
C
TBe the sensitivity coefficient of fiber grating temperature sensor, Δ T is a variations in temperature;
7. with step 6. in resulting Brillouin shift combine with temperature, the strain coupling model of no initial value affecting, be about to formula (8) and combine with formula (7), obtain formula (9),
ΔV
Bε＝ΔV
B-ΔV
BT＝C
εΔε…………(9)
Wherein, Δ ε is the deflection of said optical fiber Brillouin sensing device, C
εBe Brillouin's ga(u)ge factor, Δ v
B εThe Brillouin shift that collects in real time for said fibre strain analyzer;
8. owing to said optical fiber Brillouin sensing device is axially laid along oil, well bunch tube; With said oil, well bunch tube cooperative transformation, therefore by step 7. in the deflection Δ ε of resulting said optical fiber Brillouin sensing device be exactly the axial deflection of said oil, well bunch tube.
4. the method for a kind of monitoring downhole casing strain by using optical fibre sensor according to claim 3; It is characterized in that accomplishing described in the claim 2 along a sleeve circumferential arranged light fiber grating sensor (7) and a fiber optic temperature compensation sensor (3), and draw step described in process that holding wire is connected with transmission cable (10) and the claim 3 and 1. carry out according to following method:
1. confirm to lay under the predetermined sleeve pipe of sensor dark, and on the predetermined sleeve pipe in ground installing and locating joint (4);
2. 4 fiber-optic grating sensors and 1 fiber optic temperature compensation sensor are welded together;
3. measure sleeve pipe, confirm the sensor installation position, the polishing and use the alcohol wash sleeve surface, guarantee its surperficial free from admixture;
4. the position of sleeve surface perpendicular alignmnet landing nipple (4) is confirmed as the position of first bare optical fibers and bare optical gratings sensor L-1, be fixed in sleeve surface with chemical glue;
5. according to the method described above sleeve circumferential at interval certain angle lay all the other bare optical fibers and bare optical gratings sensors, by numbering L-2 clockwise, L-3, L-4;
6. organize 0.3 meter of fiber-optic grating sensor laying optical fiber temperature compensation sensor apart from this, and lifting one's head and transmission cable (10) welding a plurality of sensors;
7. the part that Optical Fiber Transmission optical cable (10) is arranged on sensor place, the sleeve pipe and carry out three layers of coating with epoxide-resin glue and glass fabric in 3 meters scopes vertically;
8. at the transmission cable one end welding wire jumper head in exit, connect fiber Bragg grating (FBG) demodulator (11), prepare setting of casing;
9. in the setting of casing process, when being lowered to the target zone sleeve pipe, the end of optical fiber Brillouin sensing device (13) is fixed on the pre-position of this sleeve pipe;
10. before each root sleeve pipe is gone into the well; Transmission cable (10) and the optical fiber Brillouin sensing device (13) about 15m need be reserved in ground; So that its smooth G.I.H; With single sleeve pipe G.I.H, every casing coupling place adopts 1 protective cover that transmission cable and optical fiber Brillouin sensing device are protected, after fiber-optic grating sensor transmission cable and optical fiber Brillouin sensing device transmission cable pick out well head by rig floor well head place for transmission cable in the setting of casing process (10) and optical fiber Brillouin sensing device (13); Difference is welding wire jumper head again, and protects in the thereto.
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