A method for heat exchange testing in deep geothermal development wellbores

Abstract

A method for testing the heat exchange of deep geothermal development wells. This method primarily addresses the problem of existing geothermal development wells being unable to obtain relevant data on outlet water temperature, outlet flow rate, and water temperature at different stages within the wellbore. Its key features include: S1, fixing a temperature-sensing optical fiber to an optical fiber carrier string, which is then lowered into the bottom of the geothermal development well; S2, setting temperature measurement points on the temperature-sensing optical fiber; S3, collecting temperature data during the initial stage, the heat extraction stage, and the temperature field recovery stage; S4, calculating the heat exchange power of the geothermal development well based on the collected temperature data and determining the temperature field recovery status. When the temperature at the corresponding measurement point during the temperature field recovery stage is equal to the initial stage temperature, the temperature field is considered fully recovered. This method for testing the heat exchange of deep geothermal development wells can record the temperature, outlet temperature, and outlet flow rate of different well sections during the heat extraction stage and the cessation of heat extraction, providing a basis for large-scale development and well location deployment.

Description

Technical Field

[0001] This invention relates to the field of geothermal energy development, specifically a method for testing heat exchange in deep geothermal wells. Background Technology

[0002] Deep geothermal development wells refer to geothermal development wells with a vertical depth exceeding 2500m. Wellbore heat exchange technology is the main development method for deep geothermal energy, including U-shaped wells and vertical wells, with water as the primary heat exchange medium. Specifically, U-shaped or vertical wells are drilled to the target deep heat extraction layer, and then circulating water is injected into the wellbore for heating and extraction of geothermal energy. Wellbore heat exchange generally includes three stages: the initial stage, the heat extraction stage, and the temperature recovery period (heat extraction cessation stage). During these three stages, heat testing is conducted to obtain relevant data on outlet water temperature, outlet flow rate, and water temperature within the wellbore at different times, providing a basis for large-scale development and well location deployment. However, current geothermal development wells do not utilize this heat testing method. Summary of the Invention

[0003] To overcome the problem that existing geothermal development wells cannot obtain relevant data on outlet water temperature, outlet flow rate, and water temperature at different times within the wellbore, this invention provides a deep geothermal development wellbore heat exchange testing method. This method can record the temperature, outlet temperature, and outlet flow rate of different well sections during the initial stage, the heat extraction stage, and the temperature field recovery stage, providing a basis for large-scale development and geothermal development well location deployment.

[0004] The technical solution of this invention is: a method for testing heat exchange in a deep geothermal development wellbore, comprising:

[0005] S1. Fix the temperature-measuring optical fiber onto the optical fiber carrier string and lower it into the bottom of the geothermal development well along with the optical fiber carrier string.

[0006] S2. Set the temperature measurement point of the temperature measuring fiber;

[0007] S3. Collect data, including temperature data for the initial stage, heat collection stage, and temperature field recovery stage.

[0008] S4. Calculate the heat exchange power of the geothermal development well based on the collected temperature data, and determine the temperature field recovery status. When the temperature of the temperature field recovery stage at the corresponding temperature measurement point is equal to the initial stage temperature, the temperature field is fully recovered.

[0009] The geothermal development well is a U-shaped well, which includes a vertical section and a horizontal section. In the vertical section, the temperature-sensing optical fiber is fixed on the sucker rod and lowered to the bottom of the well along with the sucker rod. In the horizontal section, the temperature-sensing optical fiber is prefabricated inside the coiled tubing and lowered to the bottom of the well along with the coiled tubing. The spacing between temperature-sensing points in the vertical section is no more than 20m, and the spacing between temperature-sensing points in the horizontal section is no more than 10m.

[0010] Furthermore, when the local geothermal development well is a U-shaped well, step S3 includes:

[0011] S3.1. Collect the temperature of each temperature measuring point in the initial stage. The temperatures of the temperature measuring points inside the horizontal wellbore that make up the U-shaped well are recorded as Th1, Th2...Th1 from the wellhead to the bottom of the well. n The temperatures at the temperature measuring points inside the vertical wellbore, from the wellhead to the bottom, are sequentially denoted as Ts1, Ts2, ..., Ts n ;

[0012] S3.2. Collect the inlet flow rate Q and the temperature at each temperature measuring point during the heat extraction stage. The temperatures of the temperature measuring points inside the horizontal wellbore that make up the U-shaped well are denoted as Th1', Th2', ... Th1' from the wellhead to the bottom of the well. n The temperatures at the temperature measuring points inside the vertical wellbore, from the wellhead to the bottom, are sequentially recorded as Ts1', Ts2', ..., Ts n ';

[0013] S3.3. During the temperature field recovery phase, the temperatures at each measuring point are collected. The temperatures at the measuring points within the horizontal wellbore that make up the U-shaped well are sequentially denoted as Th1", Th2", ... Th1" from the wellhead to the bottom. n The temperatures at the temperature measuring points inside the vertical wellbore, from the wellhead to the bottom, are sequentially denoted as Ts1", Ts2", ..., Ts n ".

[0014] Furthermore, in step S4, the heat exchange power W = Q × Δt / 0.86, where W: heat exchange power (kW); Q: flow rate (m³ / kg). 3 / h); Δt: Ts1'-Th1'.

[0015] Furthermore, in step S4, during the temperature field recovery phase, when Th n -Th n "When the temperature is ≤2℃, the temperature field is considered to have been completely restored."

[0016] The geothermal development well is a vertical well, and the temperature measuring fiber is tied to the heat exchange tube string and lowered to the bottom of the well along with the heat exchange tube string, wherein the spacing between temperature measuring points is no more than 20m.

[0017] Furthermore, when the local geothermal development well is a vertical well, step S3 includes:

[0018] S3.1. Collect the temperatures at each measurement point during the initial stage, and record them sequentially from the wellhead to the bottom of the well as T1, T2...T n Where T1 is the wellbore inlet temperature, T n The temperature at the lowest measuring point;

[0019] S3.2. Collect the inlet flow rate Q and the temperature at each temperature measuring point during the heat extraction stage. Measure the cold water inlet temperature through the temperature measuring point on the temperature measuring fiber, and record it as T1'. The hot water outlet temperature is measured by the thermometer at the outlet of the heat exchange tube column and recorded as T. c ;

[0020] S3.3. During the temperature field recovery phase, the temperatures at each measuring point are collected. The temperatures inside the wellbore from the wellhead to the bottom are recorded as T1", T2", ... T. n ".

[0021] Furthermore, in step S4, the heat exchange power W = Q × Δt / 0.86, where W: heat exchange power (kW); Q: flow rate (m³ / kg). 3 / h); Δt: T c -T1'.

[0022] Furthermore, in step S4, during the temperature field recovery phase, when T... n -T n "When the temperature is ≤2℃, the temperature field is considered to have been completely restored."

[0023] Furthermore, the temperature measurement frequency of the temperature measurement point is 1 time / 4 hours to 1 time / day.

[0024] The present invention has the following beneficial effects: By adopting the above scheme and using this heat exchange testing method, the temperature changes of each section of the wellbore in each stage of heat exchange can be collected, the heat exchange power at different time periods of the heat extraction stage can be determined, and the temperature field recovery law of each section of the wellbore can be intuitively studied during the stage when the heat extraction stops; it can provide a basis for numerical simulation study of the influence radius of the heat exchange temperature field of U-shaped wells and vertical wells, and for the design of large-scale geothermal energy well networks. Attached Figure Description

[0025] Figure 1 This is a flowchart of the present invention;

[0026] Figure 2 This is a schematic diagram of a U-shaped well heat exchanger;

[0027] Figure 3 This is a schematic diagram of heat exchange in a vertical well. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings:

[0029] Depend on Figure 1 As shown, a heat exchange testing method for deep geothermal development wells is described. Since geothermal development wells include U-shaped wells and vertical wells, for ease of description, U-shaped wells and vertical wells are described separately here.

[0030] When the geothermal development well is a U-shaped well, the heat exchange testing method for the deep geothermal development wellbore includes the following steps:

[0031] S1. Select a suitable temperature-sensing fiber optic cable. Fix one fiber optic cable to the sucker rod and lower it into the bottom of the vertical well of the U-shaped well. For example, if the completion casing of the horizontal well is φ177.8mm, a CT80 steel grade φ50.08mm×4mm coiled tubing and a DOSC-150℃-180Mpa-316L-8.0mm-2MM-2L temperature-sensing fiber optic cable can be selected. Pre-fabricate another temperature-sensing fiber optic cable inside the coiled tubing and lower it into the bottom of the horizontal well of the U-shaped well. For example, if the completion casing of the vertical well is φ177.8mm, a φ19mm sucker rod and a DOSC-150℃-180Mpa-316L-8.0mm-2MM-2L temperature-sensing fiber optic cable can be selected. Figure 2 .

[0032] S2. Set the temperature measurement points of the temperature measuring fiber. In the vertical section of the U-shaped well, the temperature measurement point spacing shall not exceed 20m. In the horizontal section of the U-shaped well, the temperature measurement point spacing shall not exceed 10m.

[0033] S3. Data Acquisition: Collect temperature data during the initial stage, heat extraction stage, and temperature field recovery stage, respectively. The temperature acquisition frequency is 1 time / 4 hours to 1 time / day. Specifically:

[0034] S3.1. Collect the temperature at each measuring point during the initial stage before heat exchange begins. In the horizontal wellbore that makes up the U-shaped well, the temperatures at the measuring points from the wellhead to the bottom are sequentially recorded as Th1, Th2…Th… n Where Th1 is the inlet temperature of the horizontal well section, Th n The temperature of the last temperature measuring point in the horizontal well section is denoted as Ts1, Ts2, ..., Ts in the vertical wellbore. n Ts n Ts1 is the temperature of the measuring point at the lowest point of the vertical well section, and Ts2 is the outlet temperature of the vertical well section.

[0035] S3.2. Collect the inlet flow rate Q and the temperature at each measuring point during the heat exchange stage. The temperatures at the measuring points inside the horizontal wellbore that make up the U-shaped well are denoted as Th1', Th2', ... Th1' from the wellhead to the bottom of the well. n The temperatures at the temperature measuring points inside the vertical wellbore, from the wellhead to the bottom, are sequentially recorded as Ts1', Ts2', ..., Ts n '.

[0036] S3.3. Collect the temperatures at each measuring point during the temperature field recovery phase after one round of heat exchange. The temperatures at the measuring points inside the horizontal wellbore that make up the U-shaped well are sequentially denoted as Th1", Th2", ... Th1" from the wellhead to the bottom. n The temperatures at the temperature measuring points inside the vertical wellbore, from the wellhead to the bottom, are sequentially denoted as Ts1", Ts2", ..., Ts n ".

[0037] S4. During the heat extraction stage, calculate the heat exchange power of the geothermal development well based on the temperature data collected in step S3, where the heat exchange power W = Q × Δt / 0.86, and W: heat exchange power (kW); Q: flow rate (m³ / kg). 3 / h); Δt: Ts1'-Th1'.

[0038] During the temperature field recovery phase, the recovery status of the temperature field is continuously assessed. At a certain point during the temperature field recovery phase, the initial stage temperature data (Th) of the horizontal well section is compared. n Temperature data Th during the temperature field recovery phase n ", when Th n -Th n "When the temperature is ≤2℃, the temperature field is considered to have been completely restored."

[0039] When the geothermal development well is a straight well, the heat exchange testing method for the deep geothermal development wellbore includes the following steps:

[0040] S1. Select a suitable temperature-sensing fiber optic cable and bundle it onto the heat exchange tubing string, then lower it into the bottom of the vertical well. For example, if the completion casing is φ139.7mm, an N80 grade φ89mm×62mm insulated pipe can be selected as the heat exchange tubing string, along with a DOSC-150℃-180Mpa-316L-8.0mm-2MM-2L type temperature-sensing fiber optic cable. Figure 3 .

[0041] S2. Set the temperature measurement points of the temperature measuring fiber. For vertical well heat exchange wells, the spacing between temperature measurement points should not exceed 20m.

[0042] S3. Data Acquisition: Collect temperature data during the initial stage, heat extraction stage, and temperature field recovery stage, respectively. The temperature acquisition frequency is 1 time / 4 hours to 1 time / day. Specifically:

[0043] S3.1. Collect the temperatures at each measurement point during the initial stage, and record them sequentially from the wellhead to the bottom of the well as T1, T2...T n Where T1 is the wellbore inlet temperature, T n The temperature at the lowest measuring point;

[0044] S3.2. Collect the inlet flow rate Q and the temperature at each temperature measuring point during the heat extraction stage. Measure the cold water inlet temperature through the temperature measuring point on the temperature measuring fiber, and record it as T1'. The hot water outlet temperature is measured by the thermometer at the outlet of the heat exchange tube column and recorded as T. c ;

[0045] S3.3. During the temperature field recovery phase, the temperatures at each measuring point are collected. The temperatures inside the wellbore from the wellhead to the bottom are recorded as T1", T2", ... T. n ".

[0046] S4. In the extraction stage, the heat exchange power of the geothermal development well is calculated based on the temperature data collected in step S3. The heat exchange power W = Q × Δt / 0.86, where W is the heat exchange power (kW) and Q is the flow rate (m³ / kg). 3 / h); Δt: T c -T1'.

[0047] During the temperature field recovery phase, the recovery status of the temperature field is assessed. At a certain point during the temperature field recovery phase, the initial temperature data T is compared with the data from the previous phase. n Temperature data T during the temperature field recovery phase n ", when T n -T n "When the temperature is ≤2℃, the temperature field is considered to have been completely restored."

[0048] Example 1: Heat test of CRR3-U1 well group

[0049] Well CRR3-U1 is a U-shaped well. The well group was tested under the following conditions: six months of operation followed by six months of temperature field recovery.

[0050] (1) Initial stage: Record the temperature inside the wellbore every 4 hours, and record the temperature Th at the last temperature measurement point in the horizontal section before the heat extraction operation. n It is 123℃;

[0051] (2) Heat extraction stage: Record the inlet flow rate, running time and temperature, record the outlet temperature and calculate the heat exchange power. Record once every 4 hours, see Table 1 for details.

[0052] Table 1. Heat exchange test parameters for U-shaped wellbore.

[0053]

[0054] Example of heat exchange power calculation: The heat exchange power calculated based on the last recorded data on the 180th day of operation of this well group is as follows:

[0055] Inlet flow rate Q = 40m 3 / h, inlet temperature Th1'=30℃, outlet temperature Ts1'=62℃, Δt=Ts1'-Th1'=32℃, then the power

[0056] W = Q × Δt / 0.86, at this time the operating power W = 1488KW.

[0057] (3) Temperature field recovery stage: Record the temperature Ts1"~Ts at each temperature measuring point in the vertical well. n ", the temperature Th1"~Th at each temperature measurement point within the horizontal well was recorded. n Admissions are accepted every 4 hours.

[0058] Temperature field recovery assessment: The temperature field recovery period for this well group was six months during the six-month heating production period, recovering to the Th value recorded in the first four hours on the 170th day. n "At 122℃, Th..." n -Th n If 1℃ ≤ 2℃, then the temperature field is considered to have fully recovered.

[0059] Example 2: LS4 Well Heat Test

[0060] Well LS4 is a vertical heat exchange well. The heat testing conditions are six months of heat extraction operation and six months of temperature field recovery.

[0061] (1) Initial stage: Record the temperature inside the wellbore every 4 hours, and record the temperature Tn at the lowest temperature measuring point before the heat extraction operation as 120℃.

[0062] (2) Heat extraction stage: including inlet flow rate, running time, temperature setting, outlet recording and power calculation, recording once every 4 hours, see Table 2 for details.

[0063] Table 2. Heat exchange parameter settings for vertical wells.

[0064]

[0065] Example of heat exchange power calculation: The heat exchange power calculated based on the last recorded data on the 180th day of operation of this well group is as follows:

[0066] Inlet flow rate Q = 15m 3 / h, inlet temperature T1'=30℃, outlet temperature T c =50℃,

[0067] Δt=T c -T1'=20℃

[0068] Calculation formula: W = Q × Δt / 0.86

[0069] At this time, the operating power W = 349KW

[0070] (3) Temperature field recovery stage: Collect the temperature of each temperature measuring point during the temperature field recovery stage. The temperature inside the well is recorded as T1", T2", ... Tn" from the wellhead to the bottom of the well, and is recorded once every 4 hours.

[0071] Temperature field recovery assessment: The well's heat exchange period was six months, and the temperature field recovery period was also six months. The temperature recovered to 118℃ at the first 4-hour record on day 160. n -Th n If 120℃ - 118℃ = 2℃, then the temperature field is completely restored.

Claims

1. A method for testing heat exchange in deep geothermal wellbores, characterized in that... include: S1. Fix the temperature-measuring optical fiber onto the optical fiber carrier string and lower it into the bottom of the geothermal development well along with the optical fiber carrier string. S2. Set the temperature measurement point of the temperature measuring fiber; S3. Collect data, including temperature data for the initial stage, heat collection stage, and temperature field recovery stage. When the local geothermal development well is a U-shaped well, step S3 includes: S3.

1. Collect the temperature of each temperature measuring point in the initial stage. The temperatures of the temperature measuring points inside the horizontal wellbore that make up the U-shaped well are recorded as Th1, Th2...Th1 from the wellhead to the bottom of the well. n The temperatures at the temperature measuring points inside the vertical wellbore, from the wellhead to the bottom, are sequentially denoted as Ts1, Ts2, ..., Ts n ; S3.

2. Collect the inlet flow rate Q and the temperature at each temperature measuring point during the heat extraction stage. The temperatures of the temperature measuring points inside the horizontal wellbore that make up the U-shaped well are denoted as Th1', Th2', ... Th1' from the wellhead to the bottom of the well. n The temperatures at the temperature measuring points inside the vertical wellbore, from the wellhead to the bottom, are sequentially denoted as Ts1', Ts2', ..., Ts n '; S3.

3. During the temperature field recovery phase, the temperatures at each measuring point are collected. The temperatures at the measuring points within the horizontal wellbore that make up the U-shaped well are sequentially denoted as Th1", Th2", ... Th1" from the wellhead to the bottom. n The temperatures at the temperature measuring points inside the vertical wellbore, from the wellhead to the bottom, are sequentially denoted as Ts1", Ts2", ..., Ts n "; S4. Calculate the heat exchange power of the geothermal development well based on the collected temperature data, and determine the temperature field recovery status. When the temperature of the temperature field recovery stage at the corresponding temperature measurement point is equal to the initial stage temperature, the temperature field is fully recovered. When the local geothermal development well is a U-shaped well, the heat exchange power W = Q × Δt / 0.86, where W: heat exchange power (kW); Q: flow rate (m³ / kg). 3 / h); Δt: Ts1'-Th1'; During the temperature field recovery phase, when Th n - Th n "When the temperature is ≤2℃, the temperature field is considered to have been completely restored." 2. The deep geothermal development wellbore heat exchange testing method according to claim 1, characterized in that: The geothermal development well is a U-shaped well, which includes a vertical section and a horizontal section. In the vertical section, the temperature-sensing optical fiber is fixed on the sucker rod and lowered to the bottom of the well along with the sucker rod. In the horizontal section, the temperature-sensing optical fiber is prefabricated inside the coiled tubing and lowered to the bottom of the well along with the coiled tubing. The spacing between temperature-sensing points in the vertical section is no more than 20m, and the spacing between temperature-sensing points in the horizontal section is no more than 10m.

3. The deep geothermal development wellbore heat exchange testing method according to claim 1, characterized in that: The geothermal development well is a vertical well, and the temperature measuring fiber is tied to the heat exchange tube string and lowered to the bottom of the well along with the heat exchange tube string, wherein the spacing between temperature measuring points is no more than 20m.

4. The deep geothermal development wellbore heat exchange testing method according to claim 3, characterized in that: When the local geothermal development well is a vertical well, step S3 includes: S3.

1. Collect the temperatures at each measurement point during the initial stage, and record them sequentially from the wellhead to the bottom of the well as T1, T2...T n Where T1 is the wellbore inlet temperature, T n The temperature at the lowest measuring point; S3.

2. Collect the inlet flow rate Q and the temperature at each temperature measuring point during the heat extraction stage. Measure the cold water inlet temperature through the temperature measuring point on the temperature measuring fiber, and record it as T1'. The hot water outlet temperature is measured by the thermometer at the outlet of the heat exchange tube column and recorded as T. c ; S3.

3. During the temperature field recovery phase, the temperatures at each measuring point are collected. The temperatures inside the wellbore from the wellhead to the bottom are recorded as T1", T2", ... T. n ".

5. The deep geothermal development wellbore heat exchange testing method according to claim 4, characterized in that: In step S4, the heat exchange power W = Q × Δt / 0.86, where W: heat exchange power (kW); Q: flow rate (m³ / kg). 3 / h); Δt:T c -T1'.

6. The deep geothermal development wellbore heat exchange testing method according to claim 5, characterized in that: In step S4, during the temperature field recovery phase, when T... n - T n "When the temperature is ≤2℃, the temperature field is considered to have been completely restored." 7. The deep geothermal development wellbore heat exchange testing method according to any one of claims 1-6, characterized in that: The temperature measurement frequency of the temperature measurement point is 1 time / 4 hours to 1 time / day.

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