CN118110508B

CN118110508B - Method for determining deformation track of sleeve by using distributed optical fibers

Info

Publication number: CN118110508B
Application number: CN202410256066.0A
Authority: CN
Inventors: 顾洪代; 李国臣; 于强; 杨淑峰; 陈晖�
Original assignee: Vision Tianjin Energy Technology Co ltd
Current assignee: Vision Tianjin Energy Technology Co ltd
Priority date: 2024-03-06
Filing date: 2024-03-06
Publication date: 2025-07-15
Anticipated expiration: 2044-03-06
Also published as: CN118110508A

Abstract

A method for determining deformation track of sleeve by using distributed optical fibers includes setting shaft direction as Z axis and plane vertical to Z axis as XY plane, determining deformation track in XZ plane including determination of deformation start and stop point, determination of bending inflection point and software drawing, determining deformation track in XY plane including reading depth and curvature value of deformation start point A of one optical fiber in XZ plane, and reading depth and curvature value of start point of adjacent optical fiber to obtain distance between two points along sleeve surface and forming net track graph.

Description

Method for determining deformation track of sleeve by using distributed optical fibers

Technical Field

The invention belongs to the field of oil gas development, and particularly relates to a method for determining a deformation track of a sleeve by using distributed optical fibers.

Background

The petroleum casing is a steel pipe for supporting the well wall of the oil and gas well so as to ensure the smooth completion of the drilling operation and the normal operation of the oil and gas well in the production process after the completion of the well. However, the casing often deforms as a result of the combined effects of multiple factors such as cementing operations, perforating operations, fracturing operations, and ground stress changes during the completion process. As shown in fig. 1. The original intact sleeve as shown in fig. 1 (a) may be changed to the shape shown in fig. 1 (b) or 1 (c) for the aforementioned reasons, or even more complicated. At this time, the depth, track and other data of the deformation of the casing are required to be determined, and reference information is provided for casing repair and subsequent underground other operations.

At present, a commonly used method for measuring the deformation of the casing is multi-arm borehole logging, namely, an instrument is lowered into the well in a logging cable or pumping mode, borehole legs are opened after the instrument reaches a target layer, and the measurement of the radius of the casing in all directions is completed in the lifting process of the instrument, so that a track curve of the deformation of the casing is obtained. The biggest challenges faced by this approach are resistance and jamming, and once the instrument string is stuck in the well, it is subject to great construction difficulties and economic losses.

If distributed optical fiber sensors are arranged on the outer surface of the sleeve in a permanent manner, the deformation of the sleeve can be measured. When the sleeve is deformed under the action of external force, the optical fiber is bent along with the deformation of the sleeve, so that the propagation of light in the optical fiber sensor is obviously lost at the bending position, and the depth range and the track of the deformation of the sleeve can be obtained through monitoring the loss of the optical signal. The method can fundamentally avoid the problem that the instrument string encounters a card.

Disclosure of Invention

The invention aims to provide a method for determining a deformation track of a sleeve by using distributed optical fibers, which replaces the traditional measuring method and process of a tool string in the sleeve, and avoids risks and losses caused by engineering accidents such as blocking, blocking and the like of the tool string caused by deformation of the sleeve.

The technical scheme adopted by the invention is as follows:

A method for determining deformation track of sleeve by using distributed optical fiber includes setting shaft direction as Z axis and plane vertical to Z axis as XY plane, determining deformation track in XZ plane and determining deformation track in XY plane again, connecting all deformation tracks in XZ plane and XY plane to form a net-shaped deformation track map of sleeve;

The method for determining the deformation track in the XZ plane comprises the following steps of:

(1) Determination of deformation start and stop points

Measuring the optical loss when the optical fiber is not bent through an Optical Time Domain Reflectometer (OTDR), and calculating a bending value of each measuring point, namely a background value, wherein the value is recorded as 0+/-n DEG (n is a real number which is larger than 0 and is close to 0);

when the sleeve is not deformed, the optical fiber is not bent, the measurement result under the condition is used as a bending background value, the used optical fibers are different, and the properties and the wavelength of the optical fibers are different, but the optical fibers are required to be consistent and stable in the whole length range of the optical fibers.

Measuring the light loss of the optical fiber in the whole length range by an optical time domain reflectometer, calculating the curvature (the depth interval is 0.5-1 m) of each depth sampling point, and judging the point A as a starting point of sleeve deformation when the difference between the curvature of a certain point A and the curvature background value is larger than n and the difference between the curvature of 3-10 sampling points and the curvature background value is larger than n from the point A, and judging the point B as an ending point of sleeve deformation when the difference between the curvature of a certain point B and the curvature background value is smaller than n and the difference between the curvature of 3-10 sampling points and the curvature background value is gradually close to 0 from the point B;

the judgment is based on the fact that when the sleeve is deformed, the track graph of the sleeve shows the characteristics that the deformation area is generally symmetrical up and down, and the deformation has continuity and gradual change.

(2) Determination of inflection point of bending

Sequentially calculating the difference value of the bending degree of two adjacent sampling points from the point A to the point B, taking the difference value as an ordinate, and simultaneously, drawing by taking the depth of the sampling points as an abscissa, wherein the peak point in the drawing is an inflection point;

(3) Software drawing

And starting from the starting point of deformation, changing the depth by 0.5-1 m, changing the corresponding value of the curvature change of the curve, and finally reaching the deformation ending point after a plurality of inflection points, thereby completing the description of the deformation track of the XZ plane inner sleeve.

Wherein, the method for determining the deformation track in the XY plane comprises the following steps:

The XY plane, namely the expansion of the cylindrical surface of the sleeve, is characterized in that the accuracy of the deformation track of the sleeve depends on the number of optical fibers deployed outside the sleeve, all the optical fibers are parallel to the Z axis and are arranged at equal intervals along the circumferential direction (the more the deployment number is, the more accurate the description of the corresponding track);

(1) Reading the depth and curvature value of a deformation starting point A of one optical fiber K1 in an XZ plane;

(2) Reading the depth and curvature value of a deformation starting point A' of the adjacent optical fiber K2 in the XZ plane;

(3) The distance from the point a to the point a 'along the surface of the sleeve is calculated, and the difference of the curvature of the point a and the point a' is divided into m parts (m=2, 3.) within the distance range, so that the curvature value of each part is obtained, and the larger the m value is, the finer the track description is.

(4) Drawing a change track from the point A to the point A' according to the obtained distance and the curvature value of each part;

(5) Making a change track between two deformation termination points B and B' of the two optical fibers K1 and K2 in the XZ plane in the same way;

(6) Dividing the distance between a and B along the parallel to the Z axis into d parts (d=10, 20,..50, 100, etc., as the case may be), thereby obtaining depth point a ₁,A₂,…,A_d-1;B₁,B₂,…,B_d-1;

(7) Making a track between A ₁～B₁,A₂～B₂,…,A_d～B_d according to the above-mentioned method;

(8) And then reading the depth and curvature value of the deformation starting point A' of the optical fiber K3 adjacent to the optical fiber K2 in the XZ plane, obtaining the track of all points between the optical fiber K2 and the optical fiber K3 according to the method, and then reading the corresponding value of the optical fiber K4 adjacent to the optical fiber K3 until all the optical fibers are read.

Further, the method for calculating the curvature comprises the following steps:

(1) The optical fiber with the determined optical fiber parameters (wavelength, refractive index and the like) is folded into different curvatures, and the optical loss values of the optical fibers with the different curvatures are measured by utilizing an optical time domain reflectometer;

(2) Substituting the light loss values corresponding to different curvatures in the step (1) into the following formula to establish a function relation between the two to obtain a plurality of groups of a and b coefficient values:

wherein a and b are constants related to wavelength; Is the curvature (curvature), α is the optical loss;

(3) The standard deviation of the coefficients a and b is respectively obtained by a plurality of groups of data in the step (2), then a normal distribution curve of the coefficients a and b is made, whether the values of the data a and b accord with the 3 sigma principle of normal distribution is checked through the normal distribution curve, if the values of the data a and b accord with the 3 sigma principle, the plurality of groups of data are effective, the arithmetic average value of the a and the arithmetic average value of the b are selected as final coefficients to be substituted into the relational expression so as to obtain a functional relation between the light loss and the curvature, if the values do not accord with the 3 sigma principle, the step (1) and the step (2) are repeated, if the values do not accord with the 3 sigma principle of normal distribution after repeated measurement and calculation, the functional relation model is considered to be incapable of achieving qualified matching with experimental data in the whole measurement range (the curvature is from 3 to 120), and the functional relation which is uniformly applicable in the whole measurement range is not established by using the arithmetic average value of the a and the arithmetic average value of the b, and the values of the a and the b in each group of data are directly substituted into the functional relation in the step (2) so as to obtain each functional relation;

(4) And (3) according to the functional relation established in the step (3), the bending degree of the optical fiber can be calculated after the optical loss of the optical fiber with a certain unit length is measured through OTDR.

The light intensity is one of the main parameters of the optical signal, and after the optical fiber enters the well, the difference value of the light intensity at two depth positions along the well bore is the optical loss of the optical signal between the two points. The optical fiber attached to the surface of the ferrule is bent by the deformation of the ferrule, and the more serious the bending is, the larger the optical loss is. The change of the tangential inclination angle of the surface of the inner sleeve in unit length (0.5 m) is defined as the curvature of the sleeve(Curvature) in degrees/meter.

The known optical loss is defined as α= (10/L) log (P _in/P_out) in db/m, where L is the length of the fiber and P _in and P _out are the input and output optical powers, respectively.

Further, the method for determining the n value is as follows:

① Measuring the optical loss value of each depth sampling point of the unbent optical fiber by using OTDR;

② Substituting the light loss value into a curvature-light loss function relation, and obtaining the curvature value of each sampling point, wherein the value is n.

The invention has the beneficial effects that:

The invention adopts the distributed optical fiber externally arranged on the surface of the sleeve as the sensor, replaces the traditional measuring method and process of the instrument string put in the sleeve on the premise of keeping the precision of the traditional sleeve deformation measuring method, and avoids the risks and losses caused by engineering accidents such as blocking, blocking and the like of the instrument string caused by the sleeve deformation.

Drawings

FIG. 1 is a sleeve deformation;

FIG. 2 is a normal distribution curve of coefficients a and b;

FIG. 3 is a schematic view of wellbore coordinate directions;

FIG. 4 is a graph of the difference in curvature between two adjacent sample points versus the depth of the sample points;

FIG. 5 is a depiction of the deformation trajectory of the sleeve in the XZ plane;

Fig. 6 is a complete trace diagram.

Detailed Description

Firstly, determining a functional relation between the curvature and the light loss value through experiments indoors, further obtaining a curvature calculating method, and then selecting an indoor experimental simulation well for actual calculation and evaluation.

1. A method of calculating tortuosity comprising the steps of:

An optical fiber (model: OF-PEC, wavelength: 1550nm, refractive index: 1.467) having a length OF 1.0 m was folded into different curvatures in Table 1, and the optical loss was measured to obtain the following data:

TABLE 1 Experimental results of the relationship between tortuosity and light loss

(2) Substituting the light loss values corresponding to different curvatures in the step (1) into the following formula to establish a functional relation between the two to obtain 40 groups of coefficient values of a and b, wherein the coefficient values are shown in Table 2:

table 2 calculated a, b coefficient values

(3) And (2) respectively solving standard deviations of the coefficients a and b from the 39 groups of data in the step (2), and then making a normal distribution curve of the coefficients a and b, as shown in figure 2, and checking whether the values of the data a and b accord with the 3 sigma principle of normal distribution or not through the normal distribution curve.

Through inspection, the values of a and b are found to accord with the 3 sigma principle of normal distribution, so that the obtained curvature and light loss function relation is as follows:

2. A method for determining deformation track of sleeve by using distributed optical fiber includes setting shaft direction as Z axis and plane vertical to Z axis as XY plane, determining deformation track in XZ plane and determining deformation track in XY plane again, connecting all deformation tracks in XZ plane and XY plane to form a net-shaped deformation track map of sleeve;

Wherein, the method for determining the deformation track in the XZ plane (shown in fig. 3) comprises the following steps:

(1) Determination of deformation start and stop points

Measuring the optical loss when the optical fiber is not bent through an Optical Time Domain Reflectometer (OTDR), and calculating a bending value of each measuring point, namely a background value, wherein the value is recorded as 0+/-n DEG (n is a real number which is larger than 0 and is close to 0), and the method for determining the value of n is as follows:

① Measuring the optical loss value of each depth sampling point of the unbent optical fiber by using an OTDR, wherein the value is 0.083,0.060,0.089,0.100,0.073;

② Substituting the light loss value into a curvature-light loss functional relation (a), solving a curvature value n= 0.35,0.20,0.39,0.46,0.28 of each sampling point, and taking an average value 33.6 as a background n value;

Measuring the light loss of the optical fiber in the whole length range by an optical time domain reflectometer, calculating the curvature (the depth interval is 1 meter) of each depth sampling point, and judging the point A as a starting point of sleeve deformation when the difference between the curvature of a certain point A and the curvature background value is larger than n and the difference between the curvature of 3-10 sampling points and the curvature background value is larger than n from the point A, and judging the point B as an ending point of sleeve deformation when the difference between the curvature of a certain point B and the curvature background value is smaller than n and the difference between the curvature of 3-10 sampling points and the curvature background value is closer to 0 from the point B;

the judgment is based on the fact that when the sleeve is deformed, the track graph of the sleeve shows the characteristics that the deformation area is generally symmetrical up and down, and the deformation has continuity and gradual change, as shown in figure 1.

In this example, when the depth point 3551 m, the difference between the measured curvature value and the background value is larger than n, then the curvature values of the 5 consecutive points are 5.6,9.3,14.4,20.1,23.9 m, so that the depth of the deformation starting point a is 3551 m, then the measured curvature value is 1.015,0.943,1.101,0.869,0.991, the difference between the measured curvature value and the curvature background value is close to n, when the depth point 3489 m, the difference between the measured curvature value and the background value is smaller than n, then the curvature values of the 5 consecutive points are 0.37,0.43,0.51,0.29,0.40, and the depth of the termination point B is 3489 m, so that the deformation range is obtained.

(2) Determination of inflection point of bending

Sequentially calculating the difference value of the bending degree of two adjacent sampling points from the point A to the point B, taking the difference value as an ordinate, and simultaneously, drawing by taking the depth of the sampling points as an abscissa, wherein the peak point in the drawing is an inflection point, as shown in fig. 4;

(3) Software drawing

And starting from the starting point of deformation, after each time the depth changes by 1 meter and the curvature of the curve changes by a corresponding value, a deformation ending point is finally reached after a plurality of inflection points are passed, so that the description of the deformation track of the inner sleeve in the XZ plane is completed, and the description is shown in fig. 5.

The XY plane, i.e. the expansion of the cylindrical surface of the sleeve, in which the accuracy of the deformation trajectory of the characterization sleeve depends on the number of optical fibers deployed outside the sleeve, all of which are parallel to the Z axis and are equally spaced along the circumferential direction (the more the number of deployments, the more accurate the description of the corresponding trajectory);

(1) Reading the depth and curvature values of a deformation starting point A of one optical fiber K1 in an XZ plane, wherein the depth and curvature values are 3551m and 0.882 degrees/m respectively;

(2) Reading the depth and curvature values of a deformation starting point A' of the adjacent optical fiber K2 in the XZ plane, wherein the depth and curvature values are 3551m and 0.797 degrees/m respectively;

(3) And (3) obtaining the distance from the point A to the point A 'along the surface of the sleeve to be 35.73cm, dividing the bending difference between the point A and the point A' into 5 parts within the distance range, and obtaining the bending value of 0.6 DEG/m of each part, wherein the larger the number of parts is, the finer the track description is.

(6) Dividing the distance between A and B along the direction parallel to the Z axis into 62 parts, thereby obtaining depth points 3551,3552,3553,3554,3555m, 3493, 3491,3490, 3499 m;

(8) And then reading the depth and curvature value of the deformation starting point A' of the optical fiber K3 adjacent to the optical fiber K2 in the XZ plane, obtaining the track of all points between the optical fiber K2 and the optical fiber K3 according to the method, and then reading the corresponding value of the optical fiber K4 adjacent to the optical fiber K3 until all the optical fibers are read. Finally, a complete trace diagram is obtained, see fig. 6, in which all the graphical contents of steps (4) -step (8) are contained.

Working process

(1) Optical fiber run-in

The casing deformation monitoring optical fiber is deployed on the outer surface of the casing, so that the casing deformation monitoring optical fiber is sealed between the casing and the cement sheath after well cementation in the well completion casing process, namely, along with the casing deployment into the well.

(2) Optical fiber detection

In order to grasp the underground state of the optical fiber, the optical loss condition of the optical fiber is required to be measured periodically through an optical time domain reflectometer (half month and one month), and in the process, the background value of the bending degree of the optical fiber is obtained.

(3) Measurement of optical loss

When the sleeve deformation event occurs and the sleeve deformation track description is needed, the change of the optical loss in the target depth range is measured through the optical time domain reflectometer, and further the data of the change of the optical fiber curvature along with the depth is obtained.

(4) Description of deformation trajectory of casing

By using the method and the steps, the deformation track curve of the sleeve is drawn through software.

Claims

1. A method for determining casing deformation trajectory using distributed optical fiber, characterized in that, first, the wellbore direction is set as the Z axis, and the plane perpendicular to the Z axis is the XY plane; secondly, the deformation trajectory in the XZ plane is determined, and the deformation trajectory in the XY plane is determined again; finally, all deformation trajectories in the XZ plane and the XY plane are connected to form a mesh casing deformation trajectory map;

The method for determining the deformation trajectory in the XZ plane includes the following steps:

(1) Determination of deformation start and end points

The optical loss of the optical fiber when it is not bent is measured by an optical time domain reflectometer, and the bending value of each measuring point, i.e., the background value, is calculated and recorded as 0°±n°;

Then, the optical loss of the optical fiber in the entire length range is measured by an optical time domain reflectometer, and the curvature at each depth sampling point is calculated. When it is found that the difference between the curvature of a certain point A and the curvature background value is greater than n, and starting from point A, the difference between the curvature and the curvature background value of the subsequent 3-10 sampling points is greater than n, then point A is determined to be the starting point of casing deformation; when it is found that the difference between the curvature of a certain point B and the curvature background value is less than n, and starting from point B, the difference between the curvature and the curvature background value of the subsequent 3-10 sampling points is getting closer and closer to 0, then point B is determined to be the end point of casing deformation;

(2) Determination of bending inflection point

From point A to point B, calculate the difference in curvature between two adjacent sampling points in sequence, and use the difference as the ordinate. At the same time, draw a graph with the depth of the sampling point as the abscissa. The peak point in the graph is the inflection point.

(3) Software drawing

Starting from the starting point of deformation, the curvature of the curve changes by a corresponding value for every 0.5-1 meter change in depth. After passing through several inflection points, it finally reaches the deformation end point, thus completing the description of the deformation trajectory of the casing in the XZ plane.

The method for determining the deformation trajectory in the XY plane comprises the following steps:

The XY plane is the expansion of the cylindrical surface of the sleeve. In this plane, the accuracy of characterizing the deformation trajectory of the sleeve depends on the number of optical fibers deployed outside the sleeve. All optical fibers are parallel to the Z axis and are arranged at equal intervals along the circumferential direction.

1) Read the depth and curvature value of the deformation starting point A of one of the optical fibers K1 in the XZ plane;

2) Read the depth and curvature value of the deformation starting point A' of the adjacent optical fiber K2 in the XZ plane;

3) Calculate the distance from point A to point A’ along the casing surface. Within this distance range, divide the difference between the curvatures of point A and point A’ into m parts, and obtain the curvature value of each part;

4) From point A to point A’, draw the change trajectory from point A to point A’ based on the obtained distance and the curvature value of each portion;

5) Similarly, draw the change trajectory between the deformation end points B and B' of the two optical fibers K1 and K2 in the XZ plane;

6) Divide the distance between A and B parallel to the Z axis and the distance between A' and B' into d parts, thereby obtaining depth points A ₁ , A ₂ , ..., A _d-1 ; B ₁ , B ₂ , ..., B _d-1 ;

7) Draw the trajectories between A ₁ ～B ₁ , A ₂ ～B ₂ , …, A _d ～B _d ;

8) Then read the depth and curvature value of the deformation starting point A" of the optical fiber K3 adjacent to the optical fiber K2 in the XZ plane, and obtain the trajectory of all points between the optical fiber K2 and the optical fiber K3 according to the above method; then read the corresponding value of the optical fiber K4 adjacent to the optical fiber K3 until all optical fibers are read.

2. A method for determining a sleeve deformation trajectory using a distributed optical fiber according to claim 1, characterized in that the method for calculating the curvature comprises the following steps:

S1: The optical fiber with determined optical fiber parameters is folded into different curvatures, and the optical loss values of the optical fibers with different curvatures are measured using an optical time domain reflectometer;

S2: Substitute the light loss values corresponding to different curvatures in step S1 into the following formula to establish a functional relationship between the two and obtain multiple sets of a and b coefficient values:

Where a and b are constants related to wavelength; is the curvature, α is the light loss;

S3: Calculate the standard deviation of coefficients a and b from the multiple sets of data in step S2, and then make normal distribution curves of coefficients a and b; through the normal distribution curve, check whether the values of data a and b meet the 3σ principle of normal distribution. If they meet the 3σ principle, it means that the multiple sets of data are valid, and the arithmetic mean of a and the arithmetic mean of b are selected as the final coefficients and substituted into the relationship formula in step S2, so as to obtain the functional relationship between light loss and curvature; if they do not meet the 3σ principle, repeat steps S1 and S2; if they still do not meet the 3σ principle of normal distribution after repeated measurement and calculation, it is considered that the functional relationship model in step S2 cannot achieve qualified matching with the experimental data in the entire measurement range, and the arithmetic mean of a and the arithmetic mean of b are no longer used to establish a uniformly applicable functional relationship in the entire measurement range, but the a and b values in each set of data are directly substituted into the functional relationship formula in step S2 to obtain the functional relationship of each curvature;

S4: Based on the functional relationship established in step S3, after the optical loss of a certain unit length of optical fiber is measured by OTDR, the curvature of the optical fiber section can be calculated.

3. A method for determining a sleeve deformation trajectory using a distributed optical fiber according to claim 2, characterized in that the method for determining the n value is:

① Use OTDR to measure the optical loss value of each depth sampling point of the unbent optical fiber;

②Substitute the light loss value into the curvature-light loss function relationship to obtain the curvature value of each sampling point, which is n.