Geothermal well casing size design method based on energy conservation

Abstract

The invention belongs to the field of geothermal well lifting processes and matching technologies, and discloses a geothermal well casing size design method based on energy conservation. Comprising the steps that the sizes are arranged from small to large, a sleeve with the minimum size is selected, and the rated lift of the centrifugal pump is calculated; calculating the lift h required by water sampling; and judging whether the sleeve with the size meets the water sampling requirement or not, and ending or increasing the first-level size to continue calculation. According to the method, the blank of geothermal well casing size design is filled, the problem that unreasonable casing size design affects geothermal development benefits and effects is solved, a casing size design method considering geothermal well drilling cost and water sampling capacity is established, and geothermal well economic benefits are improved.

Description

Technical Field

[0001] This invention belongs to the field of geothermal well lifting technology and supporting technology, specifically relating to a geothermal well casing size design method based on energy conservation. Background Technology

[0002] Geothermal wells typically use centrifugal pumps for water extraction. The pump body and motor are installed inside the downhole casing. The motor power is limited by the casing size, which determines the centrifugal pump's water extraction capacity. A casing that is too large increases drilling difficulty and costs; a casing that is too small increases fluid friction, requiring a higher head to ensure normal water extraction. Simultaneously, the rated head that the centrifugal pump can provide within a small casing is reduced, resulting in decreased water extraction capacity. Currently, geothermal well casing sizes are mainly determined based on experience, and relevant design methods are lacking. Inappropriate casing size design negatively impacts the efficiency and effectiveness of geothermal development. Therefore, it is necessary to establish a casing size design method that balances geothermal well drilling costs and water extraction capacity. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a geothermal well casing size design method based on energy conservation. The method calculates the rated head of the centrifugal pump and the required head for water production under different casing sizes step by step. The reasonable casing size for the geothermal well is determined when the rated head of the centrifugal pump is greater than the required head for water production. This casing size can meet the water production needs of the geothermal well while ensuring the lowest drilling cost.

[0004] The above-mentioned objective of this invention is achieved through the following technical solution: a method for designing the casing size of a geothermal well based on energy conservation, comprising the following steps:

[0005] 1. Arrange the dimensions from smallest to largest, select the smallest size sleeve, and calculate the rated head of the centrifugal pump;

[0006] 2. Calculate the required head h for water intake;

[0007] 3. Determine whether the casing size meets the water intake requirements, and then end the calculation or increase the size by one level to continue.

[0008] Furthermore, step 1 specifically involves: under the premise of meeting the lifting capacity requirements, and in accordance with the principle of minimizing the size of the selected tubing to save investment, initially selecting the smallest casing and calculating the rated head of the centrifugal pump.

[0009] Furthermore, the formula for calculating the rated head of the centrifugal pump in step 1 is as follows:

[0010]

[0011] In the formula: P is the motor power, kW; η is the motor efficiency, dimensionless; Q is the centrifugal pump displacement, m³ / s. 3 / d; g is the acceleration due to gravity, m / s²2 .

[0012] Furthermore, step 2 specifically includes the following steps:

[0013] 2-1. Calculate the frictional resistance h along the route. ft and h fc ;

[0014] 2-2. Calculate the head h required for water intake.

[0015] Furthermore, step 2-1 is detailed as follows:

[0016] 2-1-1. Calculate the Reynolds number R for the tubing and casing sections respectively. et and R ec ;

[0017] 2-1-2. Calculate the friction coefficient λ of the tubing and casing sections respectively. t and λ c ;

[0018] 2-1-3. Calculate the hydraulic friction h along the tubing and casing sections respectively. ft and h fc .

[0019] Furthermore, in step 2-1-1, the Reynolds numbers Re for the tubing and casing sections are calculated respectively. t and Re c The formula used is:

[0020]

[0021] In the formula: Q is the daily output of the water well, m 3 / d; r is the pipe radius, in meters; v is the kinematic viscosity of the fluid, in meters. 2 / s, the fluid in this case is water, and the kinematic viscosity is taken as 1.006×10⁻⁶. -6 m 2 / s.

[0022] Furthermore, in step 2-1-2, the friction coefficient λ along the tubing and casing sections is calculated respectively. t and λ c The formula used is:

[0023]

[0024] Furthermore, in steps 2-1-3, the hydraulic friction h along the tubing and casing sections is calculated respectively. ft and h fc The formula used is:

[0025]

[0026] In the formula: v is the fluid velocity in the tubing, m / s; h1 is the well depth, m; h3 is the pump hanger depth, m; D is the inner diameter of the tubing string, m.

[0027] Furthermore, the formula for calculating the required head h for water intake in step 2-2 is as follows:

[0028]

[0029] In the formula: P wf P is the bottom hole flowing pressure, MPa; wh ρ is the wellhead oil pressure, MPa; ρ is the liquid density, kg / m³ 3 h1 is the well depth, in meters; h2 is the liquid level, in meters; P c The pressure is measured in MPa.

[0030] Furthermore, step 3 specifically involves: based on the established model, when the pump's rated head H > the required head h, the oil jacket assembly can meet the lifting requirements and should be selected; otherwise, the size of the oil jacket assembly needs to be increased to the next level, and the above steps are repeated until the lifting requirements are met.

[0031] The beneficial effects of this invention compared with the prior art are: this invention fills the gap in geothermal well casing size design, solves the problem that unreasonable casing size design affects the benefits and effects of geothermal development, establishes a casing size design method that takes into account both geothermal well drilling costs and water production capacity, and improves the economic benefits of geothermal wells. Attached Figure Description

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0033] Figure 1 This is a schematic diagram of the geothermal well casing size design model in this invention;

[0034] Figure 2 This is a flowchart of the sleeve size optimization design in this invention. Detailed Implementation

[0035] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially.

[0036] Example 1

[0037] Geothermal Well Casing Size Design Method Based on Energy Conservation

[0038] The well depth is h1 = 1931m, and the wellhead oil pressure is P. wh =0.3MPa, liquid level h2=20m, pump hanger h3=120m, casing pressure P c=0MPa, daily output Q = 2000m³ 3 / d. Since the smaller the pipe diameter, the lower the investment cost, under the premise of simultaneously meeting the lifting requirements, the preliminary design is 5” 1 / 2 casing and 3” 1 / 2 tubing. The commonly used submersible pump models and parameters for different casing sizes refer to the standard GB / T 2816-2014 "Submersible Pumps for Wells".

[0039] Table 1. Maximum power of motors that can be installed with different sleeve sizes.

[0040] Sleeve specifications 5" 1 / 2" casing 7" casing 9" 5 / 8 sleeve 13" 3 / 8 sleeve Inner diameter of casing / mm 121.4 157.1 222.4 315.3 Motor power kW 22 45 125 355 Motor efficiency % 63 66 76 77

[0041] (1) Initial selection of casing, calculation of rated head of centrifugal pump under 5” 1 / 2” casing:

[0042]

[0043] (2) Calculate the various forces acting on the geothermal water flow during the water extraction process.

[0044] (2-1) Calculate the frictional resistance h along the way ft and h fc

[0045] ① Calculate the Reynolds number Re for the tubing and casing sections respectively. t and Re c :

[0046]

[0047] ② Calculate the friction coefficient λ of the tubing and casing sections respectively. t and λ c :

[0048]

[0049] ③ Calculate the hydraulic friction h along the tubing and casing sections respectively. ft and h fc :

[0050]

[0051] In the formula: v is the fluid velocity in the tubing, m / s; h3 is the pump mounting depth, m; D is the inner diameter of the tubing string, m.

[0052] (2-3) Calculate the head h required for water intake:

[0053]

[0054] (3) Determine whether the casing size meets the water intake requirements, and end or increase the size by one level to continue the calculation.

[0055] According to the established model, the pump's rated head H is less than the required head h. The current oil-casing combination cannot meet the lifting requirements. It should be enlarged to an oil-casing combination of 7” casing and 4” 1 / 2 oil pipe, and the above calculation steps should be repeated.

[0056] (4) Calculate the rated head H' of the centrifugal pump under the 7” casing: 131m

[0057] (5) Calculate the frictional resistance h' of the 4” 1 / 2” tubing and the 7” casing section respectively. ft and h' fc

[0058] 1) Calculate the Reynolds number Re' for each tubing segment. t =303438; Reynolds number Re' of casing section c =187734:

[0059] 2) Calculate the friction coefficient λ' along the oil pipe section respectively. t =0.013; λ' is the coefficient of hydraulic friction along the casing section. c =0.015

[0060] 3) Calculate the hydraulic friction h' along the oil pipe section respectively. ft = 8.28m; hydraulic frictional resistance along the casing section h' fc =11.96m

[0061] (6) Calculate the required lifting head h' = 70m

[0062] (7) Determine whether the oil jacket combination meets the requirements.

[0063] Since the pump's rated head H' is greater than the required head h' for water intake, the combination of a 7” casing and a 4” 1 / 2” oil pipe can meet the lifting requirements and should be selected.

[0064] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for designing the casing size of a geothermal well based on energy conservation, characterized by the following steps: include: S1. Arrange the dimensions from smallest to largest, select the smallest size sleeve, and calculate the rated head of the centrifugal pump; S2. Calculate the required head h for water intake; S3. Determine whether the casing size meets the water intake requirements, and end the calculation or increase the size by one level to continue.

2. The geothermal well casing size design method based on energy conservation according to claim 1, characterized in that, Step S1 specifically involves: under the premise of meeting the lifting capacity requirements, initially selecting the sleeve with the smallest size, and calculating the rated head of the centrifugal pump.

3. The geothermal well casing size design method based on energy conservation according to claim 2, characterized in that, The formula for calculating the rated head of the centrifugal pump in step S1 is as follows: In the formula: P is the motor power, kW; η is the motor efficiency, dimensionless; Q is the centrifugal pump displacement, m³ / s. 3 / d; g is the acceleration due to gravity, m / s² 2 .

4. The geothermal well casing size design method based on energy conservation according to claim 1, characterized in that, Step S2 specifically includes the following steps: S2-1. Calculate the frictional resistance h along the route. ft and h fc ; S2-2. Calculate the required head h for water intake.

5. The geothermal well casing size design method based on energy conservation according to claim 4, characterized in that, Step S2-1 is as follows: 2-1-1. Calculate the Reynolds number R for each section of the pipeline. et Reynolds number R of casing section ec ; 2-1-2. Calculate the friction coefficient λ along the oil pipeline section respectively. t The friction coefficient λ of the casing section c ; 2-1-3. Calculate the hydraulic friction h along the oil pipe section respectively. ft Hydraulic friction along the casing section h fc .

6. The geothermal well casing size design method based on energy conservation according to claim 5, characterized in that, In step S2-1-1, the Reynolds number R of the tubing and casing sections is calculated respectively. et and R ec The formula used is: In the formula: Q is the daily output of the water well, m 3 / d; r is the pipe radius, in meters; v is the kinematic viscosity of the fluid, in meters. 2 / s, the fluid in this case is water, and the kinematic viscosity is taken as 1.006×10⁻⁶. -6 m 2 / s.

7. The geothermal well casing size design method based on energy conservation according to claim 5, characterized in that, In step S2-1-2, the friction coefficient λ of the tubing and casing sections along the pipe is calculated respectively. t and λ c The formula used is:

8. The geothermal well casing size design method based on energy conservation according to claim 5, characterized in that, In step S2-1-3, the hydraulic friction h along the tubing and casing sections is calculated respectively. ft and h fc The formula used is: In the formula: v is the fluid velocity in the tubing, m / s; h1 is the well depth, m; h3 is the pump hanger depth, m; D is the inner diameter of the tubing string, m.

9. The geothermal well casing size design method based on energy conservation according to claim 4, characterized in that, The formula for calculating the required head h for water intake in step S2-2 is as follows: In the formula: P wf P is the bottom hole flowing pressure, MPa; wh Wellhead oil pressure, MPa; ρ is the density of the liquid, kg / m³ 3 h1 is the well depth, in meters; h2 is the liquid level, in meters; P c The pressure is measured in MPa.

10. The geothermal well casing size design method based on energy conservation according to claim 1, characterized in that, Specifically, step S3 is as follows: According to the established model, when the pump's rated head H > the required head h, the oil jacket combination can meet the lifting requirements and should be selected; otherwise, the size of the oil jacket combination needs to be increased to the next level, and the above steps are repeated until the lifting requirements are met.

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