A mine water reinjection well type structure determination method based on distributed optical fiber monitoring

Abstract

The application provides a mine water reinjection well type structure determination method based on distributed optical fiber monitoring, comprising the following steps: step one, distributed optical fiber layout and installation; step two, probe well water injection test and distributed optical fiber monitoring; step three, seepage layer section judgment and main seepage layer section identification; and step four, determination of the well type structure of the reinjection well. The application installs distributed optical fibers in the whole well section of an existing probe well and performs a water injection test, and on this basis, calculates the temperature difference proportion by using the distributed optical fiber formation temperature, and then quantitatively identifies the main seepage layer section of the deep formation. The main seepage layer section is further divided into types, and different well type structures are determined according to different types by using the Jiaobui formula. The application constructs a well type structure determination method, which can significantly improve the mine water reinjection amount, and realizes long-term stable and efficient reinjection of mine water at low cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of drilling in soil or rock, and relates to a reinjection well type structure, in particular to a mine water reinjection well type structure determination method based on distributed optical fiber monitoring. BACKGROUND

[0002] The ecological environment in arid and semi-arid areas is extremely fragile, and the water quality of mine water in the region is typically characterized by high salt. Deep well reinjection technology is an effective means for disposing of high salinity mine water, which is to inject high salinity mine water into deep sandstone aquifers with developed fractures and good permeability through a drill well with a casing, so as to reduce the impact of high salinity mine water discharge on the ecological environment. However, the current regional reinjection horizon in arid and semi-arid areas is mostly deep Liujiagou and Shiqianfeng formations, which are low-permeability sandstone layers, resulting in limited mine water reinjection capacity, which cannot meet the disposal needs of a large amount of high salinity mine water in the region.

[0003] The existing process for improving the reinjection capacity of low-permeability rock layers mainly includes fracturing process and changing the well type structure (such as L-shaped well or multi-branch well), but the fracturing process is high in cost and not suitable for this working condition. The selection of well type structure is mostly based on field experience and lacks theoretical basis, resulting in problems such as insignificant improvement of water injection capacity and low water injection efficiency. Therefore, how to scientifically and reasonably determine the well type structure of the reinjection well is the key to the water injection effect. SUMMARY

[0004] In view of the deficiencies in the prior art, the purpose of the present application is to provide a mine water reinjection well type structure determination method based on distributed optical fiber monitoring, which solves the technical problem that the mine water reinjection capacity needs to be further improved in the prior art.

[0005] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0006] A mine water reinjection well type structure determination method based on distributed optical fiber monitoring, which comprises the following steps:

[0007] Step 1: Distributed optical fiber layout and installation

[0008] The installation process of the distributed optical fiber is to directly lower the distributed optical fiber into the probe well to cover the entire test water injection section in the probe well, and a DTS modem is installed at the wellhead.

[0009] Step 2: Probe well water injection test and distributed optical fiber monitoring

[0010] The water injection test is carried out in the probe well, and the DTS modem is used to monitor the formation temperature during the water injection test.

[0011] Step three, percolation layer section judgment and main percolation layer section identification:

[0012] Step 301, respectively extract the depth-temperature curve of the pre-injection stage, injection stage and post-injection stage, and judge the percolation layer section.

[0013] Step 302, according to the judgment result of the percolation layer section obtained in step 301, the percolation layer section is divided into segmented formations, and the formation temperature difference of different segmented formations before and after water injection in the probe well is used to calculate the formation temperature difference proportion of the segmented formation. If ≥20%, the segmented formation is the main percolation layer section; if 10%≤ <20%, the segmented formation is the secondary percolation layer section; if <10%, the segmented formation is the general percolation layer section.

[0014] Step four, determination of the well type structure of the injection well:

[0015] Step 401, according to the main percolation layer section identified in step three, the percolation layer section is divided into the following three formation structures.

[0016] The first formation structure is that the entire percolation layer section is a general percolation layer section.

[0017] The second formation structure is that the main percolation layer section is concentrated in a local section.

[0018] The third formation structure is that the main percolation layer section is two or more sections.

[0019] Step 402, determine the well type structure according to the Jibui formula:

[0020] If the percolation layer section is the first formation structure, the permeability coefficient of the injection section formation in the Jibui formula , the thickness of the injection section , the water level increase in the injection well and the influence radius are unchanged, according to the Jibui formula, if the injection volume is to be increased, the entire injection well radius needs to be increased, and the well type structure of the injection well is selected as a vertical injection well.

[0021] If the percolation layer section is the second formation structure, the permeability coefficient of the injection section formation in the Jibui formula , the thickness of the injection section , the water level increase in the injection well and the influence radius Under the condition that the injection well radius of the main seepage layer section is increased , the injection well radius of each main seepage layer section needs to be increased , and the well type structure of the injection well is selected as a multi-horizontal branch injection well, and the target zones of different horizontal branch sections of the multi-horizontal branch injection well are arranged respectively corresponding to different main seepage layer sections.

[0022] If the seepage layer section is the third type of stratum structure, under the condition that the permeability coefficient of the injection section stratum , the injection section thickness , the water level increase in the injection well and the influence radius are unchanged, according to the Dupuit formula, if the injection water volume needs to be increased , the injection well radius of each main seepage layer section needs to be increased , and the well type structure of the injection well is selected as a multi-horizontal branch injection well, and the target zones of different horizontal branch sections of the multi-horizontal branch injection well are arranged respectively corresponding to different main seepage layer sections.

[0023] Compared with the prior art, the present application has the following technical effects:

[0024] The present application installs a full-well-section distributed optical fiber in an existing exploration well and performs a water injection test, and on this basis, calculates the sectional temperature difference proportion by using the distributed optical fiber stratum temperature, and then quantitatively identifies the main seepage layer section of the deep stratum. Further, the main seepage layer section type is divided, and different well type structures are determined according to different types by using the Dupuit formula. The present application constructs a well type structure determination method, which can significantly improve the mine water injection volume and realize long-term stable and efficient mine water injection at low cost. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic diagram of distributed optical fiber layout and installation.

[0026] Figure 2 is a depth-temperature curve diagram of the pre-injection stage, the injection stage and the post-injection stage.

[0027] Figure 3 is a quantitative identification result schematic diagram of the main seepage layer section.

[0028] Figure 4 is a layout schematic diagram of a straight well injection well.

[0029] Figure 5 is a layout schematic diagram of an L-shaped well injection well.

[0030] Figure 6 is a layout schematic diagram of a multi-horizontal branch injection well.

[0031] The meanings of the various reference numbers in the figures are as follows: 1 - probe well, 2 - wellhead gate valve, 3 - distributed optical fiber, 4 - DTS modem, 5 - optical cable weight rod, 6 - straight well injection well, 7 - L-shaped well injection well, 8 - multi-level branch injection well.

[0032] 101 - first real pipe section, 102 - first screen pipe section, 103 - first actual injection section.

[0033] 601 - first real pipe section, 602 - first screen pipe section, 603 - first actual injection section.

[0034] 701 - second real pipe section, 702 - second screen pipe section, 703 - second actual injection section, 704 - horizontal section.

[0035] 801 - third real pipe section, 802 - third screen pipe section, 803 - third actual injection section, 804 - first horizontal branch section, 805 - second horizontal branch section.

[0036] The specific content of the present application is further explained in detail in connection with the following examples. DETAILED DESCRIPTION

[0037] It should be noted that all the devices and components in the present application, if not specifically stated, all use the devices and components known in the prior art.

[0038] The following gives specific embodiments of the present application, it should be noted that the present application is not limited to the following specific embodiments, any equivalent transformation made on the basis of the technical solutions of the present application falls within the protection scope of the present application.

[0039] Embodiment:

[0040] The present embodiment gives a mine water injection well well type structure determination method based on distributed optical fiber monitoring, which comprises the following steps:

[0041] Step one, distributed optical fiber layout and installation:

[0042] The installation process of the distributed optical fiber 3 is to directly lower the distributed optical fiber 3 into the probe well 1, covering the entire test injection section 103 in the probe well 1, and installing a DTS (Digital Transmission System) modem 4 at the wellhead.

[0043] In step one, the distributed optical fiber 3 uses the probe well to install the full well section distributed optical fiber. In the present embodiment, the probe well installs the full well section distributed optical fiber using the probe well to install the full well section distributed optical fiber known in the art.

[0044] In the present embodiment, the DTS modem 4 uses the DTS modem known in the art.

[0045] In this specific embodiment, such as... Figure 1 As shown, the previously constructed exploratory well 1, with a depth of approximately 2300m, was utilized. The exploratory well screen section 102, ranging from 1500m to 2300m, was used as the test water injection section 103, covering the entire Liujiagou Formation. A distributed optical fiber 3, equipped with a counterweight rod at the front end, was lowered into the casing of exploratory well 1 using a logging vehicle. The fiber optic cable reached the bottom of the well, covering the entire 800m test water injection section 103. A DTS modem 4 was installed at the wellhead to monitor the mine water injection process.

[0046] Step two: Exploration well water injection test and distributed optical fiber monitoring:

[0047] A water injection test was conducted in exploration well 1, and the formation temperature during the water injection test was monitored using a DTS modem 4.

[0048] In step two, the formation temperature during the water injection test includes different depths. Formation temperature before water injection Formation temperature during the water injection stage and formation temperature after water injection The monitoring time for formation temperature at each stage shall not be less than 1 hour.

[0049] In this specific embodiment, the first stage is monitoring the formation temperature before water injection. The monitoring period lasts approximately 2 hours; the second stage involves monitoring the formation temperature during the water injection phase. The maximum water injection volume is approximately 100m³. 3 / h, water injection time is about 3 hours; the third stage is to monitor the formation temperature after water injection. The monitoring time is approximately 10 hours.

[0050] Step 3, Identification of seepage zones and main seepage zones:

[0051] Step 301: Extract the depths of the pre-injection, injection, and post-injection stages, respectively. )-temperature( The curve is used to determine the seepage layer.

[0052] In this embodiment, the depth-temperature curves for the pre-injection stage, the injection stage, and the post-injection stage are as follows: Figure 2 As shown.

[0053] Step 301, the process of determining the seepage zone includes:

[0054] Step 30101: Compare the depth-temperature curves before and during water injection:

[0055] Before water injection, the depth-temperature curve equals the geothermal gradient; during the water injection stage, the seepage layer exhibits thermal convection due to the injection of ambient temperature fluid, resulting in a significant temperature difference in the depth-temperature curve; during the water injection stage, the non-seepage layer lacks thermal convection due to the absence of fluid injection, exhibiting only heat exchange, and thus the depth-temperature curve equals the geothermal gradient. Based on this, the seepage layer can be preliminarily identified.

[0056] In this embodiment, during the water injection stage, the low temperature state of the flow temperature monitored by the optical fiber extends to around 1950m, indicating that the injected water has not reached the bottom of the exploration well 1, but only to around 1950m, which is the bottom boundary of the water injection.

[0057] Step 30102: Compare the depth-temperature curves before and after water injection.

[0058] Before water injection, the depth-temperature curve equals the geothermal gradient. In the seepage zone after water injection, due to fluid heat convection, the temperature recovery is slow in the depth-temperature curve of the well shut-in temperature recovery. In the non-seepage zone after water injection, due to the lack of fluid heat convection, the temperature recovery is fast in the depth-temperature curve of the well shut-in temperature recovery. Based on this, the seepage zone can be further determined.

[0059] In this embodiment, the depth-temperature curve of the well shut-in after water injection shows a slow recovery at a depth of 1530m to 1950m. This section is determined to be the layer with the most water absorption in the entire well, which is the seepage layer.

[0060] Step 302: Based on the judgment result of the seepage zone obtained in step 301, the seepage zone is divided into... The formation is divided into several sections, and the formation temperature difference between the different sections before and after water injection in the exploration well is utilized. Find the first The percentage of formation temperature differences in each segment of the formation ;like If ≥20%, then this stratum is the main flow zone; if 10% ≤ If <20%, then this segment of the strata is a minor flow zone; if If the percentage is less than 10%, then the stratum in this segment is a typical seepage layer.

[0061] In this embodiment, the seepage zone is divided into twelve sub-strata, with a depth difference of 35m between each sub-strata.

[0062] In step 302, the formation temperature difference for:

[0063] ;

[0064] In the formula:

[0065] Indicates the first the formation temperature difference of the i-th segment formation in the post-injection stage, unit: ℃;

[0066] denotes the serial number of the segment formation in the seepage layer section;

[0067] denotes the formation temperature of the i-th segment formation in the post-injection stage, unit: ℃;

[0068] denotes the formation temperature of the i-th segment formation in the pre-injection stage, unit: ℃.

[0069] the calculation formula of the formation temperature difference proportion of the i-th segment formation in step 302 is:

[0070] ;

[0071] In the formula:

[0072] denotes the serial number of the segment formation in the seepage layer section;

[0073] denotes the total amount of the segment formation in the seepage layer section;

[0074] denotes the formation temperature difference of the i-th segment formation, unit: ℃. In this embodiment, as shown in Table 1, the calculation results are that the formation temperature difference proportions of two consecutive segment formations in the well depth of 1880-1950 m are 25% and 30% respectively, which are the main seepage layer sections; the formation temperature difference proportions of other segment formations are all <10%, which are the general seepage layer sections.

[0075] Figure 3 Step four, determination of the well type structure of the injection well:

[0076] Step 401, according to the main seepage layer sections identified in step three, the seepage layer section is divided into the following three formation structures.

[0077] The first formation structure is that the entire seepage layer section is a general seepage layer section.

[0078] The second formation structure is that the main seepage layer sections are concentrated in a local section.

[0079] The third formation structure is that the main seepage layer sections are two or more sections.

[0080] In this embodiment, as shown in Table 1, the calculation results are that the formation temperature difference proportions of two consecutive segment formations in the well depth of 1880-1950 m are 25% and 30% respectively, which are the main seepage layer sections; the formation temperature difference proportions of other segment formations are all <10%, which are the general seepage layer sections.

[0081] In this embodiment, as shown in Table 1, the calculation results are that the formation temperature difference proportions of two consecutive segment formations in the well depth of 1880-1950 m are 25% and 30% respectively, which are the main seepage layer sections; the formation temperature difference proportions of other segment formations are all <10%, which are the general seepage layer sections. Figure 3 ​​​​​As shown, the main seepage layer section is concentrated in the strata of 1880-1950 m, which is the second strata structure.

[0082] In step 402, each well type structure is determined according to the Dupuit formula:

[0083] In step 403, the Dupuit formula is:

[0084] In the formula:

[0085] Q represents the injection volume, and the unit is m 3 / h;

[0086] K represents the permeability coefficient of the injection section strata, and the unit is m / h;

[0087] H represents the injection section thickness, and the unit is m;

[0088] Δh represents the water level increase in the injection well, and the unit is m;

[0089] R represents the influence radius, and the unit is m;

[0090] r represents the injection well radius, and the unit is m.

[0091] If the seepage layer section is the first strata structure, the permeability coefficient K of the injection section strata, the injection section thickness H, the water level increase Δh in the injection well, and the influence radius R in the Dupuit formula are unchanged, according to the Dupuit formula, if the injection volume Q is to be increased, the entire injection well radius r needs to be increased, and the well type structure of the injection well is selected as a straight well injection well 6 as shown in FIG. 6. Figure 4

[0092] If the seepage layer section is the second strata structure, the permeability coefficient K of the injection section strata, the injection section thickness H, the water level increase Δh in the injection well, and the influence radius R in the Dupuit formula are unchanged, according to the Dupuit formula, if the injection volume Q is to be increased, only the injection well radius r of the main seepage layer section needs to be increased, and the well type structure of the injection well is selected as an L-shaped well injection well 7 as shown in FIG. 7, and the target area of the horizontal section 704 of the L-shaped well injection well 7 is arranged in the main seepage layer section. Figure 5 ​​​​​​​​​​​​​​​

[0093] If the seepage zone is of the third type of formation structure, the permeability coefficient of the injected zone in the Jubuy formula is... Thickness of water injection section Increase in water level in injection wells and radius of influence Under the condition that remains unchanged, according to the Jubuy formula, if the water injection volume is to be increased... This would require increasing the radius of the injection wells in each major seepage zone. The well type structure of the water injection well should be selected as follows: Figure 6 The multi-horizontal branch injection well 8 shown has different target areas arranged for different main seepage layers in different horizontal branch segments.

[0094] In this embodiment, based on the above results, the well structure type is determined to be as follows: Figure 5 The L-shaped injection well 7 shown has its target area (horizontal section 704) located in the main flow zone of the formation at depths of 1880–1950 m. After the reinjection well was constructed, further water injection tests were conducted, with a maximum injection volume reaching 180 m³ / s. 3 / h, the maximum water injection volume is increased by about 80%, which is a significant effect.

Claims

1. A method for determining the well type and structure of mine water reinjection wells based on distributed optical fiber monitoring, characterized in that, The method includes the following steps: Step 1, Distributed Fiber Deployment and Installation: The installation process of distributed optical fiber involves directly laying distributed optical fiber into the exploration well to cover the entire test water injection section within the well, and installing a DTS modulator / demodulator at the wellhead. Step two: Exploration well water injection test and distributed optical fiber monitoring: Water injection tests were conducted in the exploration wells, and the formation temperature during the water injection test was monitored using a DTS modem. Step 3, Identification of seepage zones and main seepage zones: Step 301: Extract the depth-temperature curves for the pre-injection stage, the injection stage, and the post-injection stage, and determine the seepage layer. Step 302: Based on the judgment result of the seepage zone obtained in step 301, the seepage zone is divided into... The formation is divided into several sections, and the formation temperature difference between the different sections before and after water injection in the exploration well is utilized. Find the first The percentage of formation temperature differences in each segment of the formation ;like If ≥20%, then this stratum is the main flow zone; if 10% ≤ If <20%, then this segment of the strata is a minor flow zone; if If the percentage is less than 10%, then the stratum in this segment is a typical flow zone. Step 4: Determine the well type and structure of the reinjection well: Step 401: Based on the main seepage zones identified in Step 3, the seepage zones are divided into the following three types of stratigraphic structures; The first type of geological structure is where the entire seepage zone is a typical seepage zone. The second type of stratigraphic structure is where the main seepage zone is concentrated in a localized section; The third type of stratigraphic structure is characterized by two or more main seepage zones; Step 402: Determine the structure of each well type according to the Djubouyi formula: If the seepage zone is of the first type of formation structure, the permeability coefficient of the injection zone in the Dubuis formula is... Thickness of water injection section Increase in water level in injection wells and radius of influence Under the condition that remains unchanged, according to the Jubuy formula, if the water injection volume is to be increased... Then the radius of the entire injection well needs to be increased. If so, the well type of the water injection well should be a vertical well injection well; If the seepage zone is of the second type of formation structure, the permeability coefficient of the injection zone in the Jubuy formula... Thickness of water injection section Increase in water level in injection wells and radius of influence Under the condition that remains unchanged, according to the Jubuy formula, if the water injection volume is to be increased... Then it is only necessary to increase the radius of the injection wells in the main seepage zone. If so, the well type structure of the injection well is selected as an L-shaped injection well, and the target area of ​​the horizontal section of the L-shaped injection well is arranged in the main seepage layer section. If the seepage zone is of the third type of formation structure, the permeability coefficient of the injected zone in the Jubuy formula is... Thickness of water injection section Increase in water level in injection wells and radius of influence Under the condition that remains unchanged, according to the Jubuy formula, if the water injection volume is to be increased... This would require increasing the radius of the injection wells in each major seepage zone. If the well type structure of the injection well is selected as a multi-horizontal branch injection well, the target areas of different horizontal branch sections of the multi-horizontal branch injection well are arranged to correspond to different main seepage layers.

2. The method for determining the well type and structure of mine water reinjection wells based on distributed optical fiber monitoring as described in claim 1, characterized in that, In step one, the distributed optical fiber is installed along the entire well section in the exploratory well.

3. The method for determining the well type and structure of mine water reinjection wells based on distributed optical fiber monitoring as described in claim 1, characterized in that, In step two, the formation temperature during the water injection test includes the formation temperature before water injection, the formation temperature during water injection, and the formation temperature after water injection. The monitoring time for the formation temperature in each stage is no less than 1 hour.

4. The method for determining the well type and structure of mine water reinjection wells based on distributed optical fiber monitoring as described in claim 1, characterized in that, In step 301, the process of determining the seepage zone includes: Step 30101: Compare the depth-temperature curves before and during water injection: Before water injection, the depth-temperature curve equals the geothermal gradient; during the water injection stage, the seepage layer has thermal convection due to the injection of normal temperature fluid, and the temperature difference of the depth-temperature curve is obvious; during the water injection stage, the non-seepage layer has no thermal convection due to the absence of fluid injection, and only heat exchange, so the depth-temperature curve equals the geothermal gradient. Based on this, the seepage layer can be preliminarily identified. Step 30102: Compare the depth-temperature curves before and after water injection. Before water injection, the depth-temperature curve equals the geothermal gradient. In the seepage zone after water injection, due to fluid heat convection, the temperature recovery is slow in the depth-temperature curve of the well shut-in temperature recovery. In the non-seepage zone after water injection, due to the lack of fluid heat convection, the temperature recovery is fast in the depth-temperature curve of the well shut-in temperature recovery. Based on this, the seepage zone can be further determined.

5. The method for determining the well type and structure of mine water reinjection wells based on distributed optical fiber monitoring as described in claim 1, characterized in that, In step 302, the formation temperature difference for: ； In the formula: Indicates the first The formation temperature difference of each segment of the formation is expressed in °C. Indicates the sequence number of the segmented strata within the seepage zone; Indicates the stage after water injection Formation temperature of each segment of the strata, in °C; Indicates the first stage before water injection Formation temperature of each segment of the strata, in °C; In step 302, the first The percentage of formation temperature differences in each segment of the formation The calculation formula is: ； In the formula: Indicates the sequence number of the segmented strata within the seepage zone; This indicates the total amount of segmented strata within the seepage zone; Indicates the first The formation temperature difference of each segment of the formation is expressed in °C.

6. The method for determining the well type and structure of mine water reinjection wells based on distributed optical fiber monitoring as described in claim 1, characterized in that, In step 403, the Qiubuyi formula is as follows: ; In the formula: This indicates the water injection volume, in meters (m³). 3 / h; This represents the permeability coefficient of the injected formation, expressed in m / h. This indicates the thickness of the water injection section, in meters (m). This indicates the increase in water level in the injection well, expressed in meters (m). Indicates the radius of influence, in meters (m). This indicates the radius of the injection well, in meters (m).

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