A fiber optic DTS well logging temperature drift correction method

Abstract

The application discloses a fiber DTS logging temperature drift correction method and belongs to the field of oil logging. The fiber logging time, the storage type instrument recording time, the winch recording time and the speed measuring data are matched to realize time-depth conversion. Before the DTS instrument is lowered into a well, the influence of temperature drift on the detectors at different positions of the optical cable is determined. Then, during the lowering and lifting of the DTS instrument, the temperature drift correction method and the chart of the optical cable at the same position under different temperature and pressure environment conditions are established. Then, the temperature drift correction chart of the different positions of the monitoring well under the different downhole DTS measurement temperature environments is established. Then, the temperature data monitored by the DTS in a short time after the instrument is lowered into the well bottom is used to correct the established chart. Finally, the temperature drift correction of the measured DTS curve is carried out by using the correction method, and the data after the temperature drift correction is secondarily corrected by using the temperature monitored by the well bottom storage type instrument, so that the final correction data is formed.

Description

Technical Field

[0001] This invention relates to the field of oil well logging and pertains to a fiber optic DTS well logging temperature drift correction method. Background Technology

[0002] Distributed fiber optic DTS logging offers advantages such as real-time, continuous, and distributed monitoring. The optical cable itself acts as a detector, enabling temperature measurements throughout the wellbore at regular intervals, facilitating long-term downhole monitoring. However, factors such as excitation source fluctuations, improper refractive index settings, cable conditions during drum operation and extension, and complex temperature and pressure environments in wells can cause temperature drift in DTS logging, significantly impacting data quality. Therefore, temperature drift correction using electronic instruments is necessary to improve the accuracy of DTS monitoring data.

[0003] Typically, during distributed fiber optic DTS logging, a high-resolution storage thermobarometer is attached to the bottom to accurately record the changes in downhole temperature and pressure over time. Before DTS data interpretation, the data is shifted based on the difference between the temperature at the bottom of the DTS and the temperature measured by the storage thermobarometer, without considering the segmented and multi-patterned changes in temperature drift. Furthermore, during the lowering and raising of the DTS logging instrument, both the storage thermobarometer and the fiber optic cable record temperature data in real time at various points in time. Each segment of the DTS fiber optic cable is essentially an array of temperature logging instruments, but due to the lack of depth-related information, this data is often discarded as invalid, resulting in wasted data acquisition. These technical problems with DTS logging urgently need to be addressed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a fiber optic DTS logging temperature drift correction method.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A fiber optic DTS logging temperature drift correction method includes the following steps:

[0007] (1) Match the fiber optic logging time, the storage thermobarometer recording time with the winch recording time and velocity measurement data to achieve time-depth conversion;

[0008] (2) Obtain the ground temperature measurement data of DTS, determine the temperature drift of DTS optical cable at different locations in the ground environment based on the ground temperature measurement data and surface temperature of DTS, establish the functional relationship between the temperature drift y1 of DTS optical cable at different locations in the ground environment and the distance x1 of DTS optical cable detector from optical cable head, y1=f(x1), and establish the temperature drift correction pattern of DTS optical cable at different locations in the ground environment based on y1=f(x1).

[0009] (3) During the lowering and raising of the DTS instrument, the temperature change with depth at the same position of the DTS optical cable under different temperature and pressure conditions is obtained, and the temperature change with depth is obtained by the corresponding storage thermometer. The temperature difference between the two at the same depth is calculated as the temperature change with the DTS optical cable measurement temperature. A functional relationship is established between the temperature drift y2 and the DTS measurement temperature x2 at the same position of the DTS optical cable under different temperature and pressure conditions, y2=g(x2). Based on y2=g(x2), a temperature drift correction pattern for the same position of the DTS optical cable under different temperature and pressure conditions is established.

[0010] (4) Based on the above y1=f(x1) and y2=g(x2), establish the functional relationship between the total temperature drift correction z and the actual logging depth and DTS logging temperature value under different downhole DTS measurement temperature conditions at different locations of the monitoring well, z=f(x1`)+g(x2), x1` is the actual logging depth, x1`=x1+logging zero point depth distance to fiber optic head;

[0011] (5) After the instrument is lowered to the bottom of the well, the instantaneous temperature of the DTS at each position at the depth is obtained and the temperature measured by the storage thermometer during the instrument lowering process is obtained. The instantaneous temperature of the DTS at each position at the depth is corrected by z = f(x1`) + g(x2). The corrected data is compared with the temperature measured by the storage thermometer during the instrument lowering process. The total temperature drift correction function is corrected again based on the temperature measured by the storage thermometer, so that the corrected data is consistent with the temperature measured by the storage thermometer during the instrument lowering process.

[0012] (6) Use the modified total temperature drift correction function to correct the temperature drift of the measured DTS curve to complete the correction.

[0013] Furthermore, step (6) also includes using a bottom-of-well storage thermobarometer to monitor the temperature for secondary correction, forming the final correction data.

[0014] Furthermore, the time-depth conversion in step (1) specifically involves:

[0015] During the instrument lowering and logging and the instrument retraction process, fiber optic DTS logging continuously collects temperature data and records the time corresponding to the start of instrument lowering, the instrument reaching the bottom, the instrument starting to be pulled up after logging, and the instrument being pulled out of the wellhead. Combined with the monitoring time and temperature data of the storage thermobarometer during the DTS instrument lowering and retraction process, it is matched with the winch measurement time and speed data to realize the time-depth conversion of the storage thermobarometer measurement data.

[0016] Furthermore, the time-depth conversion in step (1) also includes:

[0017] The DTS optical cable is matched with the temperature data of each detection point during the winch measurement process to realize the time-depth conversion of the DTS measurement data of each sampling point.

[0018] Furthermore, the sampling interval is <5s / time.

[0019] Furthermore, the winch measurement time begins to correspond to the moment the instrument is lowered into the wellhead.

[0020] Furthermore, the distance from the zero point calibration of the storage thermobarometer to the core is equal to the core height minus (the height of the wellhead + the distance from the sampling point of the storage thermobarometer to the bottom of the instrument).

[0021] The distance d from the first point of the DTS from bottom to top to the center is equal to the center height minus (weighting length + electronic instrument length + tree height).

[0022] Furthermore, if the DTS sampling interval is k meters, then the distance from the nth sampling point from the bottom to the center is the distance from the first DTS point from the bottom to the center as d-(n-1)×k.

[0023] The depth of the first sampling point from the bottom of the DTS at the time of deployment is L, and the depth of the nth sampling point is L-(n-1)×k. Compared with the prior art, the present invention has the following advantages:

[0024] This invention provides a method for correcting temperature drift in fiber optic DTS logging. The method matches the fiber optic logging time, the storage instrument recording time, the winch recording time, and velocity data to achieve time-depth conversion. Secondly, before lowering the DTS instrument into the well, a method and chart for correcting temperature drift at different locations on the surface are determined, and the extent to which the detectors at different locations are affected by temperature drift is assessed. Then, during the lowering and raising of the DTS instrument, a method and chart for correcting temperature drift at the same location of the fiber optic cable under different temperature and pressure conditions are established. Next, based on the above method and chart, a temperature drift correction chart is established for different locations of the monitoring well under different downhole DTS measurement temperatures. Then, the established chart is corrected using temperature data monitored by the DTS for a short period after the instrument is lowered into the well. Finally, the corrected DTS curve is corrected for temperature drift using the correction method, and the temperature monitored by the bottom-hole storage instrument is used to perform a secondary correction on the temperature-corrected data, forming the final corrected data. This invention utilizes stored temperature data to correct temperature drift in DTS monitoring data at various stages, including the surface, during deployment, and at the bottom of the well. The corrected data is then interpreted to fully leverage the value of fiber optic DTS logging data, solving the problem of temperature drift correction in existing fiber optic DTS logging data. Its application in oilfield fiber optic logging has yielded good results. Attached Figure Description

[0025] Figure 1 For DTS data temperature drift correction process;

[0026] Figure 2 This is a schematic diagram of the serial connection of fiber optic logging instruments;

[0027] Figure 3 A graph showing the relationship between temperature drift and DTS sampling point length under DTS ground monitoring conditions;

[0028] Figure 4 Temperature profiles of the DTS bottom measurement points and storage thermobarometers obtained during the DTS deployment process;

[0029] Figure 5 A chart for temperature drift correction at the same measurement point under different temperatures in DTS.

[0030] Figure 6 To compare the temperature profile measured shortly after DTS reaches the bottom with the temperature profile measured in the well using a storage thermobarometer.

[0031] Figure 7 This is a graph showing the temperature drift correction effect of temperature data measured shortly after DTS reaches its destination. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0033] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0034] Temperature drift correction is a key technology that restricts the promotion of fiber optic logging technology. The existing fiber optic temperature drift correction method moves the DTS temperature curve as a whole, without taking into account the different temperature drift effects that the optical cable will produce in different locations and under different temperature and pressure environments. There is still a large error between the corrected temperature and the actual temperature data of the wellbore, which greatly affects the accuracy of fiber optic logging data interpretation.

[0035] This invention proposes a method for correcting temperature drift in fiber optic DTS logging. By comparing the DTS temperature with the surface temperature before running the cable downhole, a method and chart for temperature drift correction at different locations under the same temperature and pressure environment (surface environment) are established. Furthermore, by comparing the DTS temperature with the temperature of a storage-type thermobarometer during the running-in process, a method and chart for temperature drift correction at the same location on the fiber optic cable (10 sampling points at the bottom) under different temperature and pressure conditions are established. Finally, a comprehensive temperature drift correction chart is created for different locations under different temperature and pressure environments. Using this chart for DTS temperature drift correction can improve the accuracy of DTS monitoring data.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings:

[0037] See Figure 1 , Figure 1 The flowchart of this invention illustrates a fiber optic DTS logging temperature drift correction method, comprising the following steps:

[0038] Step 1: Match the fiber optic logging time, the storage thermobarometer recording time, the winch recording time, and the velocity measurement data to achieve time-depth conversion. Specifically:

[0039] During the lowering and raising of the fiber optic DTS logging instrument, the data acquisition volume is increased to ensure a sampling interval of <5s / time. The times corresponding to the start of lowering, reaching the bottom, raising the instrument after logging, and raising the instrument out of the wellhead are recorded. Combined with the monitoring time and temperature data of the storage thermobarometer during the lowering and raising of the DTS, the data is matched with the winch measurement time and speed data to achieve time-depth conversion of the storage thermobarometer measurement data. At the same time, the temperature data of each detection point of the DTS optical cable during the winch measurement time is matched with the time-depth conversion of the DTS measurement data at each sampling point.

[0040] As shown in Table 1, the winch measurement time begins when the instrument is at the wellhead and just starts to be lowered; before calculating the depth, the distances from the core-filling position to each sampling point on the storage thermobarometer and DTS are calculated first, such as... Figure 1As shown, the distance from the zero point of the storage thermobarometer to the core is equal to the core height minus (the height of the production tree plus the distance from the sampling point of the storage thermobarometer to the bottom of the instrument). In the logging operation of well XX9-15 in the example, the core height is 5m, the production tree height is 1.8m, and the distances from the sampling point of the storage thermobarometer to the bottom of the instrument are 0.3m and 0.5m respectively. Therefore, the distance from the storage thermometer to the core is 5 - (1.8 + 0.3) = 2.9m, and the distance from the storage pressure gauge to the core is 5 - (1.8 + 0.5) = 2.7m. The first sampling point of the DTS from bottom to top... The distance from the sampling point to the core is equal to the height of the core, which is then reduced by (weight length + electronic instrument length + tree height) to 5, which is equal to (1.8 + 1.5 + 4.45) to -2.75m. Assuming the DTS sampling interval is k meters, the distance from the nth sampling point from the bottom to the core is -2.75 - (n-1) × km, as shown in Table 1. The depth of the storage thermobarometer at the time of descent is 2.7m, the depth of the first sampling point from the bottom of the DTS is -2.75m, and the depth of the nth sampling point is -2.75 - (n-1) × km. The data are shown in Table 2.

[0041] Table 1. Time-matching data for monitoring the lowering process of the winch, storage instrument, and DTS.

[0042] Winch measurement time Matching storage instrument time Measurement time DTS time Storage instrument temperature DTS-1 point temperature winch speed 2022 / 3 / 27 14:07:43 2022 / 3 / 27 14:07:40 2022 / 3 / 27 14:07:41 25.87 24.87 0.71 2022 / 3 / 27 14:07:47 2022 / 3 / 27 14:07:40 2022 / 3 / 27 14:07:46 25.69 24.69 0.71 2022 / 3 / 27 14:07:51 2022 / 3 / 27 14:07:50 2022 / 3 / 27 14:07:51 25.53 24.53 0.71 2022 / 3 / 27 14:07:55 2022 / 3 / 27 14:07:50 2022 / 3 / 27 14:07:56 25.39 24.39 0.71 2022 / 3 / 27 14:07:59 2022 / 3 / 27 14:07:50 2022 / 3 / 27 14:08:01 25.27 24.27 0.69 2022 / 3 / 27 14:08:03 2022 / 3 / 27 14:08:00 2022 / 3 / 27 14:08:06 25.12 24.12 0.69 2022 / 3 / 27 14:08:07 2022 / 3 / 27 14:08:00 2022 / 3 / 27 14:08:11 24.96 23.96 0.69 2022 / 3 / 27 14:08:11 2022 / 3 / 27 14:08:10 2022 / 3 / 27 14:08:11 24.66 23.66 0.69 2022 / 3 / 27 14:08:15 2022 / 3 / 27 14:08:10 2022 / 3 / 27 14:08:16 24.25 23.25 0.69 2022 / 3 / 27 14:08:19 2022 / 3 / 27 14:08:10 2022 / 3 / 27 14:08:21 23.69 22.69 0.69 2022 / 3 / 27 14:08:23 2022 / 3 / 27 14:08:20 2022 / 3 / 27 14:08:21 23.1 22.1 0.69 2022 / 3 / 27 14:08:27 2022 / 3 / 27 14:08:20 2022 / 3 / 27 14:08:26 22.49 21.49 0.69 2022 / 3 / 27 14:08:31 2022 / 3 / 27 14:08:30 2022 / 3 / 27 14:08:31 21.91 20.91 0.69 2022 / 3 / 27 14:08:35 2022 / 3 / 27 14:08:30 2022 / 3 / 27 14:08:36 21.38 20.38 0.69 2022 / 3 / 27 14:08:39 2022 / 3 / 27 14:08:30 2022 / 3 / 27 14:08:41 20.88 19.88 0.68 2022 / 3 / 27 14:08:43 2022 / 3 / 27 14:08:40 2022 / 3 / 27 14:08:40 20.45 19.45 0.68 2022 / 3 / 27 14:08:47 2022 / 3 / 27 14:08:40 2022 / 3 / 27 14:08:46 20.05 19.05 0.68 2022 / 3 / 27 14:08:51 2022 / 3 / 27 14:08:50 2022 / 3 / 27 14:08:51 19.72 18.72 0.68 2022 / 3 / 27 14:08:55 2022 / 3 / 27 14:08:50 2022 / 3 / 27 14:08:56 19.42 18.42 0.68 2022 / 3 / 27 14:08:59 2022 / 3 / 27 14:08:50 2022 / 3 / 27 14:09:01 19.16 18.16 0.68 2022 / 3 / 27 14:09:03 2022 / 3 / 27 14:09:00 2022 / 3 / 27 14:09:01 18.94 17.94 0.68

[0043] Table 2. Depth-domain storage instrument and DTS deployment process monitoring time-depth conversion data

[0044]

[0045]

[0046] Step 2: Before running the DTS (Digital Transmission System) into the well, determine the temperature drift correction method and chart for different locations of the DTS optical cable under the same temperature and pressure environment (surface environment), and determine the extent to which the detectors at different locations of the optical cable are affected by temperature drift; for example... Figure 3 The image shows the surface temperature data measured before the DTS (Digital Tunneling System) was run into well XX. Figure 3 From the top, nearly 10,000 meters of optical cable has a temperature drift of -3.7℃ from top to bottom. The relationship between temperature drift and length is given by the formula y = -0.0004x - 0.0643, where y represents temperature drift and x represents the distance between the DTS optical cable detector and the optical cable head.

[0047] Step 3: Based on the calculation results of Step 1, during the DTS lowering and raising process, establish a temperature drift correction method and diagram for the same location of the optical cable (10 sampling points at the bottom, which are less affected by positional temperature drift and can be approximated as the same location) under different temperature and pressure conditions; such as Figure 4As shown, the DTS measured temperature is the average depth-domain temperature profile of the 10 sampling points at the bottom during the DTS deployment process; the thick line represents the temperature of the storage thermometer. It can be seen from the figure that there is a significant difference between the two. Figure 5 for Figure 4 The relationship between DTS temperature drift and corresponding DTS measured temperature is calculated by subtracting the two curves. As can be seen from the figure, the temperature drift and DTS measured temperature change linearly, with the relationship being y = -0.024x + 0.1115, where y represents the temperature drift and x represents the DTS measured temperature data corresponding to the DTS sampling point.

[0048] Step 4: Based on the methods and charts formed in Steps 2 and 3, establish temperature drift correction charts for different locations of the monitoring well under different downhole DTS measurement temperatures;

[0049] In this embodiment, the distance between the logging zero point depth and the fiber optic head is 6261m, and the total temperature drift formula is:

[0050] z = -0.0004(x+6261)-0.0643-0.024y+0.1115 = -0.0004x-0.024y-2.4572, where z is the total temperature drift correction, x is the actual measured depth, and y is the corresponding DTS logging temperature value;

[0051] Based on the total temperature drift formula, a temperature drift correction chart was established for different locations of the monitoring well and different downhole DTS measurement temperatures.

[0052] Step 5: Correct the chart established in Step 4 using temperature data monitored by the DTS for a short period after the instrument is lowered to the bottom of the well. After the instrument is lowered to the bottom, the temperature at various locations at different depths should be basically consistent with the temperature measured by the storage thermometer during the instrument's descent. Based on this, use the formula established in Step 4 to perform temperature difference correction on the DTS data monitored for a short period after the instrument is lowered to the bottom of the well. Compare the corrected value with the storage temperature, such as... Figure 6 As shown, the total temperature drift correction formula is modified based on the results. The modified formula is z = -0.0004x - 0.024y - 2.2572.

[0053] Step 6: Use the correction method formed in Step 5 to correct the temperature drift of the measured DTS curve. At the same time, use a bottom-hole storage thermobarometer to monitor the temperature and perform a second correction on the temperature drift corrected data to form the final corrected data.

[0054] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for correcting temperature drift in fiber optic DTS logging, characterized in that, Includes the following steps: (1) Match the fiber optic logging time, the storage thermobarometer recording time with the winch recording time and velocity measurement data to achieve time-depth conversion; (2) Obtain the ground temperature measurement data of DTS, determine the temperature drift of DTS optical cable at different locations in the ground environment based on the ground temperature measurement data of DTS and the ground surface temperature, establish the functional relationship between the temperature drift y1 of DTS optical cable at different locations in the ground environment and the distance x1 of DTS optical cable detector from the optical cable head, y1=f(x1), and establish the temperature drift correction pattern of DTS optical cable at different locations in the ground environment based on y1=f(x1). (3) During the lowering and raising of the DTS instrument, the temperature change with depth at the same position of the DTS optical cable under different temperature and pressure conditions is obtained, and the temperature change with depth is obtained by the corresponding storage thermometer. The temperature difference between the two at the same depth is calculated as the temperature change with the DTS optical cable measurement temperature. The functional relationship between the temperature drift y2 and the DTS measurement temperature x2 at the same position of the DTS optical cable under different temperature and pressure conditions is established, y2 = g(x2). Based on y2 = g(x2), the temperature drift correction pattern of the same position of the DTS optical cable under different temperature and pressure conditions is established. (4) Based on y1=f(x1) and y2=g(x2), establish a functional relationship between the total temperature drift correction z and the actual logging depth and DTS logging temperature value under different downhole DTS measurement temperatures at different locations of the monitoring well, z=f(x1) 、 ) + g(x2), x1 、 x1 represents the actual logging depth. 、 =x1 + distance from the zero-point depth of the well logging fiber optic head; (5) After the instrument is lowered to the bottom of the well, the real-time temperature measured at each position of the DTS at the depth and the temperature measured by the storage thermometer during the instrument's descent are obtained. Using z = f(x1) 、 The real-time temperature measurement of the DTS at each position in the depth is corrected by g(x2). The corrected data is compared with the temperature measured by the storage thermometer during the instrument descent. The total temperature drift correction function is corrected again based on the temperature measured by the storage thermometer, so that the corrected data is consistent with the temperature measured by the storage thermometer during the instrument descent. (6) Use the modified total temperature drift correction function to correct the temperature drift of the measured DTS curve to complete the correction.

2. The fiber optic DTS logging temperature drift correction method according to claim 1, characterized in that, Step (6) also includes using a bottom-of-well storage thermobarometer to monitor the temperature for secondary correction, forming the final correction data.

3. The fiber optic DTS logging temperature drift correction method according to claim 1, characterized in that, The time-depth conversion in step (1) is specifically as follows: During the instrument lowering and logging and the instrument retraction process, fiber optic DTS logging continuously collects temperature data and records the time corresponding to the start of instrument lowering, the instrument reaching the bottom, the instrument starting to be pulled up after logging, and the instrument being pulled out of the wellhead. Combined with the monitoring time and temperature data of the storage thermobarometer during the DTS instrument lowering and retraction process, it is matched with the winch measurement time and speed data to realize the time-depth conversion of the storage thermobarometer measurement data.

4. The fiber optic DTS logging temperature drift correction method according to claim 3, characterized in that, The time-depth conversion in step (1) also includes: The DTS optical cable is matched with the temperature data of each detection point during the winch measurement process to realize the time-depth conversion of the DTS measurement data of each sampling point.

5. The fiber optic DTS logging temperature drift correction method according to claim 3, characterized in that, Sampling interval < 5s / time.

6. The fiber optic DTS logging temperature drift correction method according to claim 3, characterized in that, The start time of the winch measurement corresponds to the moment when the instrument is lowered at the wellhead.

7. The fiber optic DTS logging temperature drift correction method according to claim 6, characterized in that, Zero-point calibration distance of storage thermobarometer = Repair core height - (Norm height + Distance from sampling point of storage thermobarometer to bottom of instrument); The distance d from the first point of the DTS from bottom to top to the center is equal to the center height minus (weighting length + electronic instrument length + tree height).

8. The fiber optic DTS logging temperature drift correction method according to claim 7, characterized in that, If the DTS sampling interval is k meters, then the distance from the nth sampling point from the bottom to the center is the distance from the first DTS point from the bottom to the center as d - (n-1) × k. The depth of the first sampling point from the bottom of the DTS at the time of the drop-down is L, and the depth of the nth sampling point is L - (n-1)×k.

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