Depth calibration method for distributed optical fiber testing in horizontal wells

Abstract

The present invention relates to a method for calibrating the depth of distributed optical fiber testing in horizontal wells. The method comprises the following steps: construction preparation, equipment installation and commissioning, testing the length difference between the optical fiber and the coiled tubing, placing a heating device, calculating the length difference between a coiled tubing of a fixed length L and the optical fiber within the tubing, continuing to lower the coiled tubing by a length L, calculating the length difference between the optical fiber and the tubing, placing a heating block every time the coiled tubing is lowered by a length L to calculate the length difference, calculating the length of the optical fiber within the wellbore based on temperature characteristic points, calibrating the coiled tubing length within the wellbore using magnetic positioning data, and calibrating the segmented depth to obtain a precise test depth. The present invention effectively calibrates the test depth during distributed optical fiber testing of coiled tubing, improving data acquisition quality when using different optical fibers, different monitoring equipment, and different monitoring wells.

Description

Technical Field

[0001] The present invention relates to the field of distributed optical fiber testing of continuous oil pipes in oil and gas fields, and more particularly to a depth calibration method for distributed optical fiber testing of horizontal wells. Background Art

[0002] In recent years, with the rapid development of fiber optic sensing technology, the application of fiber optic testing technology in the oil industry has garnered increasing attention. An optical fiber is inserted into a coiled tubing (CT) and transported to a testing location in the horizontal section of a horizontal well. Using the fiber itself as a sensor and a measurement technique based on the fiber's one-dimensional characteristics, it is possible to continuously measure environmental parameters distributed along the entire length of the fiber. By analyzing these environmental parameters along the horizontal section, the recovery rate of each layer cluster can be determined. Measuring the depth of the horizontal section directly affects the accuracy of the measured data and ultimately the analysis and interpretation results. There are two existing depth measurement methods. One uses a CT depth encoder counter to read the data. The CT is raised and lowered, driving a depth measuring wheel. The depth is calculated based on the pulse count of a photoelectric encoder. The other method uses an optical fiber to measure the temperature of characteristic points at the wellhead and bottom of the wellbore after it is lowered into the wellbore. This allows the length of the CT in the wellbore to be estimated. In actual operation, due to the large annular difference between the outer diameter of the optical fiber and the inner diameter of the coiled tubing, the optical fiber bends inside the coiled tubing during penetration, resulting in a significant difference in length between the optical fiber and the coiled tubing. Neither of the above two methods can accurately determine the optical fiber test depth. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a horizontal well distributed optical fiber test depth calibration method, which can calibrate and determine the depth of the test formation during the continuous tubing distributed optical fiber test, making the test data recording more accurate.

[0004] The technical solution adopted by the present invention to solve the technical problem is to construct a horizontal well distributed optical fiber test depth calibration method, including the following steps:

[0005] S1. After moving the fiber-optic coiled tubing and other construction equipment to the well, ensure sufficient working space around the wellhead; install the coiled tubing guide and injection head, insert the coiled tubing, and test the blowout preventer function; install the wellhead conversion flange, connect the injection head, blowout preventer box, blowout preventer, and lubricant preventer to complete the wellhead installation; connect the downhole tools, including the fiber-optic sealing nipple and the storage magnetic positioning logging tool;

[0006] S2. Conduct fiber testing on the ground. Use a fiber fusion splicer to fusion-splice the quick connector between the ground fiber and the coiled tubing test fiber. Connect the fiber to the distributed temperature measurement system (DTS) and adjust the system parameters until a complete temperature curve is measured along the entire cable.

[0007] S3. Record the overall length of the coiled tubing at the factory, L t Calculate the internal fiber length L of the coiled tubing by using the fiber's factory refractive index and the quick connector attenuation position measured by the distributed fiber temperature measurement system (DTS). o , calculate the difference between the optical fiber length and the coiled tubing length L d =L o -L t .

[0008] S4. Select the location of the fiber optic sealing sub on the coiled tubing as the depth zero point. Set a fixed length L based on the horizontal section length and DTS performance. Lower the coiled tubing to the depth L and mark the location L. Mark the location for easy placement of the heating device. Connect the optical fiber to the distributed fiber optic temperature measurement system (DTS) via a quick connector. Install the device at the marked location on the coiled tubing, connect the power supply, turn on the heating device, set the temperature to above 50°C, and heat for at least 10 minutes.

[0009] S5. After the distributed fiber optic temperature measurement system (DTS) measures the complete temperature curve, the location of the heating point is observed. The length D1 from the heating point to the distal end of the coiled tubing is calculated based on the temperature characteristic positions of the tubing top and the heating point. The length difference between the tubing and the internal optical fiber is calculated as L1 = D1 - L.

[0010] S6, continue to lower the coiled tubing of length L, repeat step S4, calculate the length D2 from the heating point to the far end of the coiled tubing through the distributed optical fiber temperature measurement system (DTS), and the difference between the length of the coiled tubing and the internal optical fiber of the first 2L length is L s , obtain the length difference between the coiled tubing and the internal optical fiber L2=L s -L1;

[0011] S7, continue to lower the coiled tubing, repeat S4 and S5 for each lowered length L, and obtain the length difference L between each length L of coiled tubing and the internal optical fiber. n , until the coiled tubing reaches the test position.

[0012] S8. After the fiber optic coiled tubing is lowered to the test location, the ground optical fiber is re-fused and connected to the distributed optical fiber temperature measurement system. The total length of the optical fiber in the wellbore is calculated based on the temperature characteristic points at the wellhead and bottom of the fiber optic tubing. The optical fiber sensing test is then performed.

[0013] S9. After the test is completed, the oil pipe is pulled out and the running depth of the coiled tubing is calibrated using the casing coupling data measured by magnetic positioning.

[0014] S10. After calibrating the bottom depth of the coiled tubing, depth adjustment is performed on the fiber optic sensing test curve in sections by obtaining the length difference between the coiled tubing and the internal optical fiber for each L of the horizontal section, ultimately obtaining a more accurate test depth.

[0015] According to the above solution, the optical fiber is a single-mode optical fiber or a multi-mode optical fiber.

[0016] According to the above solution, the length of the heating device is not less than 1 meter.

[0017] According to the above scheme, in step S4, the fixed length L is set according to the test well depth structure, horizontal section length, DTS equipment performance tubing, and the smaller the L value, the lower the depth calibration error.

[0018] According to the above solution, in step S5, the distributed optical fiber temperature measurement system must detect the location of the heating point. If no heating point is detected, the DTS parameters need to be adjusted to adjust the temperature sampling interval to within 1m.

[0019] According to the above solution, in step S7, after the fiber optic coiled tubing is lowered into a depth exceeding the horizontal section length, the heating test can be stopped and the fiber optic coiled tubing can be directly lowered to the bottom of the well for testing.

[0020] The implementation of the horizontal well distributed optical fiber test depth calibration method of the present invention has the following beneficial effects:

[0021] 1. The specific implementation scheme of the present invention calculates the length of the optical fiber in the wellbore based on the temperature characteristic points of the wellbore. First, after descending to the test position, the test optical fiber is connected to the distributed optical fiber temperature measurement system (DTS) to obtain the temperature curve of the entire well section. Based on the temperature characteristic points at the wellhead and bottom of the well, the length of the optical fiber inside the wellbore is calculated, thereby obtaining the optical fiber test depth.

[0022] 2. The present invention uses a heating module to perform segmented calibration of the length of the coiled tubing and the internal optical fiber, allowing real-time understanding of the distribution of the optical fiber inside the coiled tubing. By analyzing the distribution of the optical fiber and formulating protective measures for the optical cable, the service life of the optical cable inside the coiled tubing can be greatly extended.

[0023] 3. The present invention obtains the accurate depth of the distributed optical fiber testing formation by segmentally calibrating the length of the optical fiber lowered into the horizontal well, which can greatly improve the accuracy of the test data acquisition. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0025] Figure 1 It is a schematic diagram of the testing process of the present invention;

[0026] Figure 2It is a test process flow chart of the present invention;

[0027] Figure 3 Schematic diagram of characteristic points of the DTS temperature curve of the present invention;

[0028] Figure 4 Schematic diagram of the heating device of the present invention. DETAILED DESCRIPTION

[0029] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0030] like Figure 1-4 As shown, the horizontal well distributed optical fiber depth calibration method of the present invention includes the following steps:

[0031] (1) Construction preparation

[0032] After moving the fiber-optic coiled tubing and other construction equipment to the well, ensure sufficient working space around the wellhead. Install the coiled tubing guide and injector head, insert the coiled tubing, and test the blowout preventer. Install the wellhead adapter flange, connect the injector head, blowout preventer cartridge, blowout preventer, and lubricant preventer, and complete the wellhead installation. Connect downhole tools, including the fiber-optic sealing nipple and stored magnetic positioning logging tool.

[0033] (2) Equipment installation and commissioning

[0034] Conduct fiber testing on the ground, using a fiber fusion splicer to splice the ground fiber to the coiled tubing test fiber quick-connect plug. Connect the fiber to a distributed temperature measurement system (DTS), adjusting system parameters until a complete temperature profile is measured along the entire cable.

[0035] (3) Test the difference in length between optical fiber and coiled tubing

[0036] The fiber length inside the coiled tubing is calculated using the factory refractive index of the fiber and the attenuation position of the quick connector measured by the distributed temperature measurement system (DTS). The difference between the total fiber length and the coiled tubing length is then obtained.

[0037] (4) Place the heating device

[0038] Select the position of the fiber optic sealing pup joint of the coiled tubing as the depth zero point, set a fixed length L, lower the coiled tubing to the depth L, and mark the position L; mark the position for easy placement of the heating device; turn on the heating device, install the device at the marked position on the coiled tubing, connect the power supply, turn on the heating device, set the temperature to above 50℃, and heat for no less than 10 minutes.

[0039] (5) Calculate the difference between the length L of the coiled tubing and the internal optical fiber length

[0040] The heating point position is observed by the DTS temperature measurement curve. The length D1 from the heating point to the distal end of the coiled tubing is calculated based on the temperature characteristic positions of the tubing top and the heating point. The difference between the coiled tubing and the internal optical fiber is calculated as L1 = D1-L.

[0041] (6) Continue to lower the coiled tubing of length L and calculate the difference in length between the optical fiber and the tubing.

[0042] Continue to lower the coiled tubing length L, place the heating block, and calculate the length D2 from the heating point to the far end of the coiled tubing through DTS. The difference between the length of the first 2L coiled tubing and the internal optical fiber is L. s , the length difference between the coiled tubing of length L and the internal optical fiber is obtained, L2=L s -L1;

[0043] (7) Calculate the length difference by placing the heating block for each lowering length L

[0044] Continue to lower the coiled tubing and obtain the length difference L between the coiled tubing and the internal optical fiber for each length L. n , until the coiled tubing reaches the test position.

[0045] (8) Calculate the length of the optical fiber in the wellbore based on the temperature characteristic point

[0046] After the fiber optic coiled tubing is lowered to the test location, the ground optical fiber is re-splice and connected to the distributed optical fiber temperature measurement system (DTS). The temperature test is started and the total length of the optical fiber in the wellbore is calculated based on the temperature characteristic points at the wellhead and bottom of the optical fiber tubing. Figure 3 ).

[0047] (9) Calibrate the length of the coiled tubing in the wellbore using magnetic positioning data

[0048] After the test is completed, the oil pipe is pulled out and the casing coupling data measured by magnetic positioning is used to calibrate the running depth of the coiled tubing.

[0049] (10) Obtaining accurate test depth

[0050] After calibrating the bottom depth of the coiled tubing, the fiber optic sensing test curve is segmented and depth adjustment is performed by obtaining the length difference between the coiled tubing and the internal optical fiber at each horizontal section length L, ultimately obtaining a more accurate test depth.

[0051] Preferably, the method is applicable to distributed temperature sensing operations, and the optical fiber is a single-mode or multi-mode optical fiber.

[0052] Preferably, the requirement in step (1) is that after the coiled tubing operation preparation is completed, the coiled tubing is passed through the injection head or into the well.

[0053] Preferably, the test equipment involved in step (2) is a distributed fiber temperature measurement system (DTS). Fiber fusion splicing must be performed after the coiled tubing stops lowering, and the DTS needs to measure the temperature curve along the entire length of the fiber.

[0054] Preferably, the coiled tubing heating device involved in step (4) is not less than 1 meter in length and contains a mechanical fixing device, a heating system, and a temperature sensing and display system. When the coiled tubing is selected to place the heating device, the heating device is installed between the coiled tubing injection head and the drum. The construction diagram is shown in FIG. Figure 1 .

[0055] Preferably, in step (5), the DTS temperature measurement system must detect the location of the heating point. If no heating point is detected, the DTS parameters need to be adjusted to adjust the temperature sampling interval to within 1 m.

[0056] Preferably, in step (8), according to ( Figure 3 ) as shown in FIG5 , determine the temperature characteristic points of the wellhead and bottom hole, and calculate the temperature distance difference of the characteristic points.

[0057] Preferably, when the DTS uses a heating device to calculate the length difference between the coiled tubing and the internal optical fiber of length L, the temperature sampling interval of the adjustment system must be less than the length of the heating device, and the length difference is calculated once every interval L, and finally the length differences L1, L2, ..., Ln of the optical fiber and the tubing of each length L in the horizontal section are obtained.

[0058] Preferably, when calibrating the optical fiber test depth, first go down to the test position, connect the test optical fiber to the distributed optical fiber temperature measurement system (DTS), and obtain the temperature curve of the entire well section. Figure 3 As shown in the figure, based on the temperature characteristic points at the wellhead and bottom of the well, the fiber length inside the wellbore is calculated, and the bottom depth data of the coiled tubing is calibrated using the magnetic positioning test coupling data. The fiber depth is calibrated in sections based on the length difference L1, L2…Ln between the fiber and the tubing at each length L in the horizontal section, thereby obtaining an accurate fiber test depth.

[0059] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A horizontal well distributed optical fiber test depth calibration method, characterized in that: The following steps are involved: S1. After moving the fiber-optic coiled tubing and other construction equipment to the well, ensure sufficient working space around the wellhead; install the coiled tubing guide and injection head, insert the coiled tubing, and test the blowout preventer function; install the wellhead conversion flange, connect the injection head, blowout preventer box, blowout preventer, and lubricant preventer to complete the wellhead installation; connect the downhole well tools, including the fiber-optic sealing nipple and the storage magnetic positioning logging tool; S2. Conduct fiber optic testing on the ground. Use a fiber optic fusion splicer to fusion-splice the quick connector between the ground fiber and the coiled tubing test fiber. Connect the fiber to the distributed fiber optic temperature measurement system and adjust the system parameters until a complete temperature curve is measured along the entire optical cable. S3. Record the total length of the coiled tubing at the factory (L) t Calculate the internal fiber length L of the coiled tubing using the factory refractive index of the fiber and the attenuation position of the quick connector measured by the distributed fiber temperature measurement system. o , calculate the difference between the optical fiber length and the coiled tubing length L d =L o -L t ; S4. Select the position of the fiber optic sealing sub on the coiled tubing as the depth zero point. Set a fixed length L according to the depth structure of the test well. Lower the coiled tubing of length L and mark it. Install the device at the marked position on the coiled tubing. Connect the power supply and start the heating device. Set the temperature to above 50°C and heat for at least 10 minutes. S5. Calculate the length D1 from the heating point to the distal end of the coiled tubing optical fiber based on the temperature characteristic positions of the tubing top and the heating point. Calculate the length difference between the coiled tubing and the internal optical fiber before the L-length length L1 = D1-L. S6, continue to lower the coiled tubing of length L, calculate the length D2 from the heating point to the far end of the coiled tubing through the distributed optical fiber temperature measurement system, and the difference between the length of the first 2L coiled tubing and the internal optical fiber is L s , the difference between the length of the coiled tubing and the internal optical fiber L2=L s -L1; S7, lower the oil pipe, and obtain the length difference L between the coiled oil pipe and the internal optical fiber for each L length lowered. n , until the coiled tubing reaches the test position; S8. After the fiber optic coiled tubing is lowered to the test position, the total length of the optical fiber in the wellbore is calculated based on the temperature characteristic points at the wellhead and bottom of the well in the fiber optic tubing; S9. Calibrate the running depth of the coiled tubing using casing collar data measured by magnetic positioning; S10. After calibrating the bottom depth of the coiled tubing, depth adjustment is performed on the fiber optic sensing test curve segment by segment by obtaining the length difference between the coiled tubing and the internal optical fiber in each L length section of the horizontal section, and ultimately a more accurate test depth is obtained.

2. The horizontal well distributed optical fiber test depth calibration method according to claim 1, characterized in that: The optical fiber is a single-mode optical fiber or a multi-mode optical fiber.

3. The horizontal well distributed optical fiber test depth calibration method according to claim 1, characterized in that: The length of the heating device is not less than 1 meter.

4. The horizontal well distributed optical fiber test depth calibration method according to claim 1, characterized in that: In step S4, the set fixed length L is related to the depth of the test well, the length of the horizontal section, and the performance of the distributed optical fiber temperature measurement system. The smaller the L value, the lower the depth calibration error.

5. The horizontal well distributed optical fiber testing depth calibration method according to claim 1, characterized in that: In step S5, the distributed optical fiber temperature measurement system must detect the location of the heating point. If no heating point is detected, the distributed optical fiber temperature measurement system parameters need to be adjusted to adjust the temperature sampling interval to within 1 m.

6. The horizontal well distributed optical fiber test depth calibration method according to claim 1, characterized in that: In step S7, after the fiber optic coiled tubing is lowered to a depth exceeding the horizontal section length, the heating test is stopped and the fiber optic coiled tubing is directly lowered to the bottom of the well for testing.

Images