A pump water injection energy supplementing process suitable for under injection wells of low permeability sandstone reservoirs

Abstract

The application provides a pump water injection energy supplement process suitable for under-injection wells in low-permeability sandstone reservoirs, and mainly solves the problem of the increase of the proportion of low-yield wells and the influence on water drive development level caused by the unsatisfactory effect of the existing low-permeability block plugging removal and injection increase measures. The process comprises the following steps: S1: screening under-injection wells according to the selection conditions of the pry-mounted pump water injection energy supplement process; S2: determining the single-well and single-layer water injection amount and construction parameters for the selected under-injection wells; S3: completing the preparation work before water injection construction; and S4: based on the determined single-well and single-layer water injection amount, cooperating with the separate-layer water injection process string to perform pry-mounted pump water injection precise construction. The pump water injection energy supplement process is suitable for precise energy supplement of under-injection wells in low-permeability sandstone reservoirs, and has the advantages of on-demand energy supplement, precise energy supplement, concentrated energy storage and improvement of the layer production degree by adopting the mode of cooperating with the separate-layer water injection process string to perform fixed-layer precise concentrated energy supplement.

Description

Technical Field

[0001] The invention relates to the technical field of oil production engineering, in particular to a pump water injection energy replenishment process suitable for under-injection wells in low-permeability sandstone reservoirs. Background Art

[0002] In low-permeability oilfield blocks, the reservoirs are characterized by small pore throats, low permeability, high capillary resistance, and high sensitivity. As development progresses, the injection capacity of water injection wells within the blocks gradually declines. To address this issue, various augmentation measures, such as acidizing and fracturing, are currently being implemented on-site. However, due to geological conditions, acidizing is ineffective, fracturing is costly, and unblocking and augmentation measures are less than ideal. Commonly used augmentation measures, such as acidizing and fracturing, are ineffective in low-permeability areas, with a return on investment (ROI) often below 1:1.5. Generalized water replenishment, on the other hand, suffers from uneven distribution among strata and fails to provide on-demand water injection. Furthermore, due to the annual decline in water absorption by injection wells, formation pressure in the blocks is declining, leading to a severe under-injection situation. This has directly led to an increase in the proportion of low-yielding wells and a severe situation where both oil and water wells are unable to inject water and produce oil, compromising the effectiveness of water flooding development. Summary of the Invention

[0003] The technical problem to be solved by this invention is to overcome the problem of existing low-permeability block deblocking and injection measures being ineffective, leading to an increased proportion of low-yielding wells and impacting water flooding development. This invention provides a pump-injection recharge process suitable for under-injected wells in low-permeability sandstone reservoirs. This process is suitable for precisely recharging under-injected wells in low-permeability sandstone reservoirs, offering on-demand and precise energy replenishment, centralized energy storage, and improved in-layer production.

[0004] The present invention solves the problem by the following technical solution: the pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs comprises the following steps:

[0005] S1: Screen under-injected wells based on the well selection conditions of the skid-mounted pump water injection and energy replenishment process;

[0006] S2: For the selected under-injection wells, determine the single-well and single-layer water replenishment volume Qi and construction parameters;

[0007] S3: Complete the preparation work before water injection construction;

[0008] S4: Based on the determined single-well and single-layer water replenishment volume Qi, precise skid-mounted pump water injection construction is carried out in conjunction with the stratified water injection process string.

[0009] Furthermore, in step S1, the wells selected for the skid-mounted pump water injection and energy replenishment process are: medium to high under-injection wells and wells with serious interlayer conflicts among under-injection wells.

[0010] Furthermore, an under-injection well is defined as one where the difference between the reservoir fracture pressure of the injection layer and the wellhead injection pressure is less than 0.5 MPa, one of the following conditions is met, and the continuous water injection time is more than 15 days:

[0011] 1) Daily injection volume ≤ 10m 3 , daily actual water injection volume < 70% of the daily allocated water injection volume;

[0012] 2) 10m 3 <Daily injection volume≤50m 3 , daily actual water injection volume < 80% of daily allocated water injection volume; daily allocated water injection volume > 50m 3 , daily actual water injection volume is less than 85% of the daily allocated water injection volume.

[0013] Furthermore, the well selection conditions for the skid-mounted pump water injection and energy replenishment process in step S1 are:

[0014] The actual daily water injection volume is less than 65% of the daily allocated water injection volume;

[0015] The ratio of the actual water injection volume of a certain layer to the actual water injection volume of other layers is greater than 3.5.

[0016] Furthermore, the method for determining the water replenishment amount of a single layer in step S2 is:

[0017] Calculate the water replenishment volume for each single layer with the goal of increasing formation pressure, taking into account the degree of reservoir pressure deficit, current water injection level, well control volume, and driving difficulty;

[0018] The calculation formula for the water replenishment of each single layer is:

[0019] Single layer water replenishment formula Qi=f (x) ×V×γ+Q 目前注水程度

[0020] Where: f (x) =1-(P 目前连通油井地层压力 / P 原始地层压力 ) 2 / 3 ;

[0021] V=L×L×H 折算厚度 ×Φ×π / 9;

[0022] H 折算厚度 =H 有效 +(H 射开 -H 有效 ) / 3;

[0023] γ=(N 连通方向数 / 6) 1 / 2 ;

[0024] Q 目前注水程度 =(V 单层累计注水量 -V+V连通井层累计采出量 )×(1-γ);

[0025] Where: Q i is the water replenishment of a single layer; f (x) is the degree of deficit; V is the control volume; γ is the driving coefficient; Q 目前注水程度 The current level of water injection into the well;

[0026] L is the distance between connected oil and water wells, m;

[0027] φ is the porosity, a decimal (0 to 1);

[0028] V 单层累计注水量 is the cumulative water injection volume of a single layer, m 3 ;

[0029] V 连通井层累计采出量 is the cumulative production of connected well layers, m 3 ;

[0030] N is the number of connected directions;

[0031] H 折算厚度 is the converted oil layer thickness, m;

[0032] H 有效 is the effective oil layer thickness, m;

[0033] H 射开 is the thickness of the perforated oil layer, m.

[0034] Furthermore, the water replenishment amount of the single well in step S2 is the sum of the water replenishment amounts of each single layer;

[0035] The formula for determining the water replenishment volume of a single well is: Q = ∑Qi;

[0036] Where: Q is the water replenishment volume of a single well.

[0037] Furthermore, the preparatory work before construction in step S3 includes:

[0038] Put in the water nozzle of the test well to be replenished in the layer, and put in the dead nozzle in other layers;

[0039] Transfer the construction equipment to the well site for arrangement;

[0040] Connect the power supply and water source and test their safety and integrity;

[0041] Assemble skid-mounted pump injection system;

[0042] The pressure test of wellhead, manifold, valve group, etc. is 24.5MPa, and the pressure drop within 10 minutes is less than 0.7MPa, which is qualified.

[0043] Furthermore, the method of assembling the skid-mounted pump water injection system is:

[0044] The liquid inlet end of the pry-mounted hydraulic piston injection pump device is connected with the water storage pool;

[0045] The liquid outlet end of the pry-mounted hydraulic piston injection pump device is connected with the wellhead of the under-injection well through a high-pressure pipeline.

[0046] Further, step S4 determines the single-well and single-layer water injection amount, and then performs pry-mounted pump injection construction process, which includes:

[0047] Connect the ground equipment to test the pressure, and perform pry-mounted pump injection single-layer quantitative Q i Construction, the maximum injection pressure is less than the wellhead pressure;

[0048] After the single-layer construction is completed, the next step of layer fishing is performed, the layer is fished into a dead mouth, the next construction layer position pulls out the dead mouth, and the preset quantitative Q i Construction, the maximum injection pressure is less than the wellhead pressure;

[0049] After the single-layer construction is completed, the next step of layer fishing is performed, the layer is fished into a dead mouth, the next construction layer position pulls out the dead mouth, and the preset quantitative Q

[0050] The actual maximum injection rate is injected on site, and the injection rate is adjusted in time according to the pressure change in the construction process;

[0051] After the injection amount required by the design is completed, the original injection amount is injected normally the next day.

[0052] Further, the actual maximum injection rate is injected on site, and the injection rate is adjusted in time according to the pressure change in the construction process;

[0053] The control pressure rising speed is less than 1.0 MPa / d, and the maximum wellhead pressure is about 20.0 MPa;

[0054] When the pressure rising speed is too fast, the instantaneous injection rate is reduced, when the rising speed is too slow, the instantaneous injection rate is increased, the stable trend of injection pressure is maintained, and the fluctuation of injection pressure is reduced;

[0055] The reference value of the actual maximum injection rate injected on site is 50-300 m 3 / d.

[0056] Compared with the above background art, the present application can have the following beneficial effects:

[0057] The present invention discloses a pump water injection energy replenishment process suitable for under-injection wells in low-permeability sandstone reservoirs. The process is suitable for precise energy replenishment of under-injection wells in low-permeability sandstone reservoirs. By adopting a skid-mounted hydraulic piston injection pump device and a stratified water injection process string for construction, energy replenishment on demand in a fixed layer and precise centralized energy replenishment are performed, thereby increasing the maximum working pressure and construction displacement, and continuously operating for 24 hours. Under the conditions of high pressure difference and large displacement, preset metered clean water is respectively added to different layers of the under-injection well. The process has the advantages of on-demand energy replenishment, precise energy replenishment, centralized energy storage, and improved utilization within the layer.

[0058] The present invention has the characteristics of personalized construction, fast and safe construction, and strong single-well targeting. It has the technical advantages of on-demand energy replenishment, precise energy replenishment, centralized energy storage, and improved intra-layer utilization.

[0059] By optimizing the under-injection well numbers, designing the single-well and single-layer water replenishment volume and construction parameters, the skid-mounted pump water injection construction is guided.

[0060] The application of this pump water injection and energy replenishment technology is suitable for the precise energy replenishment of under-injection wells in low-permeability sandstone reservoirs. It can greatly increase the underground water storage rate in the layer, effectively replenish the formation energy, enhance the driving power within the well group layer, improve the utilization capacity within the well group layer, increase the swept volume, and improve the ability to tap the remaining oil in the potential layer.

[0061] Commonly used blockage-removal and injection-enhancing measures, such as acidification and fracturing, are less effective in treating low-permeability areas, often with an input-output ratio below 1:1.5. Generalized water replenishment suffers from uneven distribution among layers and fails to achieve on-demand energy replenishment. The skid-mounted pump water injection and energy replenishment process of the present invention, however, allows for a one-time investment of the skid-mounted pump equipment, which can be reused subsequently. Only labor and electricity costs are required, allowing for personalized energy replenishment based on the underfill volume of the injection well. This method offers stable results, achieving the goal of "replenishing the required amount" with an input-output ratio exceeding 1:2. This effectively replenishes formation energy, improves water injection effectiveness in low-permeability areas, achieves injection-production balance, increases recovery within the area, and enables efficient oilfield development. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Attachment Figure 1 The present invention discloses a process block diagram of pump water injection and energy replenishment applicable to under-injection wells in low-permeability sandstone reservoirs;

[0063] Attachment Figure 2 This is a schematic diagram of the well site construction layout of the skid-mounted pump water injection equipment of the present invention. DETAILED DESCRIPTION

[0064] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0065] As attached Figure 1 As shown, the present invention discloses a pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs, comprising the following steps:

[0066] S1: Screen under-injected wells based on the well selection conditions of the pump water injection and energy replenishment process;

[0067] The well selection conditions for the pump water injection and energy replenishment process include the following steps:

[0068] The wells selected for the pump water injection energy replenishment process are medium to high under-injection wells and wells with serious interlayer conflicts.

[0069] The well selection conditions for the pump water injection and energy replenishment process are one of the following:

[0070] 1) The actual daily water injection volume is less than 65% of the daily allocated water injection volume;

[0071] 2) The ratio of the actual water injection volume of a certain layer to the actual water injection volume of other layers is greater than 3.5;

[0072] The definition of under-injection wells: Except for injection wells that are planned to be shut down or controlled, an injection well is defined as an under-injection well if the difference between the reservoir fracture pressure of the injection layer section and the wellhead injection pressure is less than 0.5 MPa and one of the following conditions exists and lasts for more than 15 days.

[0073] 1) Daily injection volume ≤ 10m 3 , daily actual water injection volume < 70% of the daily allocated water injection volume;

[0074] 2) 10m 3 <Daily injection volume≤50m 3 , daily actual water injection volume < 80% of the daily allocated water injection volume;

[0075] 3) Daily injection volume > 50m 3 , daily actual water injection volume is less than 85% of the daily allocated water injection volume.

[0076] S2: For the selected under-injection wells, determine the single-well and single-layer water replenishment volume Qi and construction parameters;

[0077] Taking into account the degree of reservoir pressure deficit, current water injection level, water well control volume, driving difficulty (connection direction, well spacing, permeability, porosity), and intra-layer differences (reservoir effective thickness and effective porosity), the water replenishment volume of each single layer is calculated with the purpose of increasing formation pressure. The formula for single-layer water replenishment volume is as follows:

[0078] Qi=f (x) ×V×γ+Q 目前注水程度

[0079] Where: Q i is the water replenishment of a single layer; f (x) is the degree of deficit; V is the control volume; γ is the driving coefficient; Q 目前注水程度 The current level of water injection into the well;

[0080] The amount of water replenishment required for a single well, that is, the total amount of water replenishment for each single layer, is the amount of water replenishment required for a single well.

[0081] S3: Complete the preparatory work before water injection construction, such as Figure 2 As shown, specifically including:

[0082] Assemble the skid-mounted pump water injection equipment; connect the skid-mounted hydraulic piston injection pump to the water storage tank, and the test team casts out the water nozzle in the layer to be replenished with water; connect it to the wellhead of the under-injection well through a high-pressure pipeline, and test the wellhead, manifold, valve group, etc. with a pressure of 24.5MPa. The pressure drop within 10 minutes is less than 0.7MPa, which is qualified.

[0083] S4: Based on the determined single-well and single-layer water replenishment volume Qi, the skid-mounted pump water injection precision construction process is carried out in conjunction with the stratified water injection process string:

[0084] The maximum injection pressure is less than the wellhead pressure. Injection is carried out at the actual maximum displacement on site, with a reference value of 50-300m 3 / d, timely adjust the displacement according to the pressure changes during the construction process, and after completing the design injection volume, inject normally according to the original injection volume the next day.

[0085] Example 1

[0086] Screening the under-injection well N-1 in the low-permeability M block outside Daqing Oilfield. The well is located in the L fault block. The whole well perforates 8 sedimentary units. The daily injection rate is 30m in the initial production period. 3 , actual daily injection is 14m 3 , in line with the "10m 3 <Daily injection volume≤50m 3 The well selection condition of the pump water injection construction well meets the requirement of "daily actual water injection volume < 80% of daily allocated water injection volume"; the well selection condition of the pump water injection construction well meets the requirement of "daily actual water injection volume < 65% of daily allocated water injection volume"; the well has a cumulative water injection of 2.4×10 4 m 3 , the water injection was affected by the problem of insufficient injection by 1.24×10 4 m 3 , resulting in a serious lack of formation energy. There are four oil wells connected to the surrounding area, with a cumulative liquid production of 0.2652×10 4 t, meeting the well selection conditions for skid-mounted pump water injection and energy replenishment technology;

[0087] b. Design the water replenishment volume Qi for each well and layer. Considering the reservoir pressure deficit, current water injection level, well control volume, driving difficulty (connection direction, well spacing, permeability, porosity), and intra-layer differences (effective reservoir thickness and effective porosity), calculate the water replenishment volume for each layer with the goal of increasing formation pressure. The formula is as follows:

[0088] Single layer water replenishment formula Qi=f (x) ×V×γ+Q 目前注水程度

[0089] Where: f (x) =1-(P 目前连通油井地层压力 / P 原始地层压力 ) 2 / 3 ;

[0090] V=L×L×H 折算厚度 ×Φ×π / 9;

[0091] H 折算厚度 =H 有效 +(H 射开 -H 有效 ) / 3;

[0092] γ=(N 连通方向数 / 6) 1 / 2 ;

[0093] Q 目前注水程度 =(V 单层累计注水量 -V+V 连通井层累计采出量 )×(1-γ);

[0094] Where: Q i is the water replenishment of a single layer; f (x) is the degree of deficit; V is the control volume; γ is the driving coefficient; Q 目前注水程度 The current level of water injection into the well;

[0095] L is the distance between connected oil and water wells, m;

[0096] φ is the porosity, a decimal (0 to 1);

[0097] V 单层累计注水量 is the cumulative water injection volume of a single layer, m 3 ;

[0098] V 连通井层累计采出量 is the cumulative production of connected well layers, m 3 ;

[0099] N is the number of connected directions;

[0100] H 折算厚度 is the converted oil layer thickness, m;

[0101] H 有效 is the effective oil layer thickness, m;

[0102] H 射开 is the thickness of the perforated oil layer, m.

[0103] The total amount of water replenishment for each single layer is the amount of water replenishment required for a single well:

[0104] The formula for determining the water replenishment volume of a single well is: Q = ∑Qi;

[0105] Where: Q is the water replenishment volume of a single well.

[0106] The basic data of each layer of a single well in the above formula are shown in Table 1; the calculation and input data of each layer of a single well are shown in Table 2.

[0107] Table 1

[0108]

[0109] Table 2

[0110]

[0111] c. Prepare the skid-mounted hydraulic piston injection pump and supporting equipment, connect the skid-mounted hydraulic piston injection pump to the water storage tank, and the test team will cast in the water nozzle of the layer to be replenished, connect it to the wellhead of the under-injection well through a high-pressure pipeline, and test the wellhead, manifold, valve group, etc. to a pressure of 24.5MPa. The pressure drop within 10 minutes is less than 0.7MPa, which is qualified.

[0112] d. Connect the skid-mounted pump water injection equipment and the ground pipeline to test the water nozzle. First, construct the first layer PI1, and then cast the dead nozzle in the other two layers. The construction pressure is 20.2MPa and the instantaneous injection volume is 9.2m 3 / h, the construction period is 8 days, and the cumulative injection volume is 1688m 3 , completed the first floor construction;

[0113] e. Carry out the test of casting and fishing water nozzles, construct the second layer PI2, and cast dead nozzles in the other two layers. The construction pressure is 20.1MPa and the instantaneous injection volume is 9.6m 3 / h, the construction period is 11 days, and the cumulative injection volume is 2391m 3 , completed the second floor construction;

[0114] f. Test the water nozzle and construct the third layer PI4. The other two layers are dead nozzles. The construction pressure is 19.5MPa and the instantaneous injection volume is 10.9m 3 / h, the construction period is 8 days, and the cumulative injection volume is 1829m 3 , completed the construction of the third floor;

[0115] g. After the injection is completed, preparations are made to resume conventional water injection. The basic data of the well, the injection pressure and speed during the construction process, and other data are imported into the CMG numerical simulation software. The time for resuming water injection of the well is predicted through calculation. The wellhead pressure is continuously observed on site and the time for resuming water injection is determined by actual measurement.

[0116] h. After the test, the well group effect was tracked and observed. The initial daily fluid increase of the connected well group was 2.7m 3 , with a daily oil increase of 2.1t, an effective period of 423 days, a cumulative oil increase of 1,035t, and a significant oil increase effect.

[0117] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation of the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Therefore, the content of the present invention is not limited to the examples listed, and any equivalent transformations of the technical solutions of the present invention made by ordinary technicians in this field after reading the specification of the present invention are all covered by the claims of the present invention.

Claims

1. A pump water injection and energy replenishment process suitable for under-injection wells in low-permeability sandstone reservoirs, characterized by: The following steps are involved: S1: Screen under-injected wells based on the well selection conditions of the skid-mounted pump water injection and energy replenishment process; S2: For the selected under-injected wells, optimize the design to determine the single-well, single-layer water replenishment volume Qi and construction parameters; the single-layer water replenishment volume determination method is: Calculate the water replenishment volume for each single layer with the goal of increasing formation pressure, taking into account the degree of reservoir pressure deficit, current water injection level, well control volume, and driving difficulty; The calculation formula for the water replenishment of each single layer is: Qi=f （x） ×V×γ+Q 目前注水程度 Where: f （x） =1-(P 目前连通油井地层压力 / P 原始地层压力 ) 2 / 3 ; V = L×L×H 折算厚度 ×φ×π / 9; H 折算厚度 =H 有效 +(H 射开 -H 有效 ) / 3; γ=(N 连通方向数 / 6) 1 / 2 ; Q 目前注水程度 =(V 单层累计注水量 -V +V 连通井层累计采出量 )×(1-γ); Where: Q i is the water replenishment of a single layer; f （x） is the degree of deficit; V is the control volume; γ is the driving coefficient; Q 目前注水程度 The current level of water injection for the well; L is the distance between connected oil and water wells, m; φ is the porosity, a decimal (0 to 1); V 单层累计注水量 is the cumulative water injection volume of a single layer, m 3 ; V 连通井层累计采出量 is the cumulative production of connected well layers, m 3 ; N is the number of connected directions; H 折算厚度 is the converted oil layer thickness, m; H 有效 is the effective oil layer thickness, m; H 射开 is the thickness of the perforated oil layer, m; S3: Complete the preparation work before water injection construction; S4: Based on the determined single-well and single-layer water replenishment volume Qi, precise skid-mounted pump water injection construction is carried out in conjunction with the stratified water injection process string.

2. The pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs according to claim 1 is characterized in that: The wells selected for the skid-mounted pump water injection and energy replenishment process in step S1 are: medium to high under-injection wells and wells with serious interlayer conflicts.

3. The pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs according to claim 2 is characterized in that: An under-injection well is defined as one in which the difference between the reservoir fracture pressure of the injection layer and the wellhead injection pressure is less than 0.5 MPa, and one of the following conditions is met, and the continuous water injection time is more than 15 days: 1) Daily water injection volume ≤ 10m 3 , daily actual water injection volume < 70% of the daily allocated water injection volume; 2) 10m 3 <Daily water injection volume≤50m 3 , daily actual water injection volume < 80% of daily allocated water injection volume; daily allocated water injection volume > 50m 3 , daily actual water injection volume is less than 85% of the daily allocated water injection volume.

4. The pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs according to claim 3 is characterized in that: The well selection conditions for the skid-mounted pump water injection and energy replenishment process in step S1 are: The daily actual water injection volume is less than 65% of the daily allocated water injection volume; The ratio of the actual water injection volume of a certain layer to the actual water injection volume of other layers is greater than 3.

5.

5. The pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs according to claim 1 is characterized in that: The water replenishment amount of a single well in step S2 is the sum of the water replenishment amounts of each single layer; The formula for determining the water replenishment volume for a single well is: ; Where: Q is the water replenishment volume of a single well.

6. The pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs according to claim 1 is characterized in that: The preparatory work before construction in step S3 includes: Put in the water nozzle of the test well to be replenished in the layer, and put in the dead nozzle in other layers; Transfer the construction equipment to the well site for arrangement; Connect the power supply and water source and test their safety and integrity; Assemble skid-mounted pump injection system; The wellhead, manifold and valve group are tested for pressure of 24.5MPa, and the pressure drop within 10 minutes is less than 0.7MPa, which is qualified.

7. The pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs according to claim 6 is characterized in that: To assemble the skid mounted pump injection system: Connect the liquid inlet end of the skid-mounted hydraulic piston injection pump equipment to the water reservoir; Connect the liquid outlet of the skid-mounted hydraulic piston injection pump equipment to the wellhead of the under-injection well through a high-pressure pipeline.

8. The pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs according to claim 5 is characterized in that: Step S4: Based on the determined single-well and single-layer water replenishment volume, the skid-mounted pump water injection construction process includes: Connect the ground equipment for pressure test and perform single-layer quantitative water injection with skid-mounted pump. i During construction, the maximum injection pressure is less than the wellhead pressure; After the single layer construction is completed, the next step of layer casting and fishing is carried out, and the single layer is cast into a dead mouth. The next construction layer pulls out the dead mouth and performs the preset quantitative Q i During construction, the maximum injection pressure is less than the wellhead pressure; After the single layer construction is completed, repeat the previous step until the entire designed construction section is completed; Inject on site according to the actual maximum displacement and adjust the displacement in time according to the pressure changes during the construction process; After completing the injection volume required by the design, normal injection will be carried out according to the original injection volume the next day.

9. The pump water injection energy replenishment process applicable to under-injection wells in low permeability sandstone reservoirs according to claim 8, characterized in that: The method of injecting according to the actual maximum displacement on site and adjusting the displacement in time according to the pressure changes during the construction process is as follows: Control the pressure rise rate to less than 1.0 MPa / d, and the maximum wellhead pressure is around 20.0 MPa; When the pressure rises too quickly, reduce the instantaneous injection displacement; when the pressure rises too slowly, increase the instantaneous injection displacement to maintain a stable trend of the injection pressure and reduce injection pressure fluctuations; The reference value of injection according to the actual maximum displacement on site is 50~300m 3 / d.

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