Gas lift reverse circulation drilling starting pressure and circulation gas supply pressure calculation method

Abstract

The invention discloses a gas lift reverse circulation drilling starting pressure and circulation gas supply pressure calculation method. The method comprises the following steps that S1, hydrostatic pressure of the bottom of an inner pipe of a double-wall drill rod is calculated; s2, calculating the friction loss pressure of compressed air of an outer annulus of the double-wall drill rod; s3, calculating the friction loss pressure of the compressed air flowing through the earth surface gas transmission channel; s4, calculating the local pressure loss of the compressed air passing through the orifice in the gas-liquid mixer from the outer pipe of the double-wall drill rod; s5, calculating the liquid phase flow friction pressure loss of the inner pipe of the double-wall drill pipe; s6, calculating the liquid-phase flow friction pressure loss of the deslagging pipeline; s7, calculating the three-phase flow pressure drop of the inner pipe of the double-wall drill pipe; and S8, the starting pressure and the circulating air supply pressure are calculated. According to the method for calculating the starting pressure and the circulating gas supply pressure of the gas lift reverse circulation drilling, the starting pressure and the circulating gas supply pressure of the gas lift reverse circulation drilling can be accurately and conveniently calculated by accurately calculating the pressure of each part of the gas lift reverse circulation drilling process, and a theoretical basis is provided for stable and efficient operation of a circulating system.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil layer or rock drilling, and particularly relates to a method for calculating the starting pressure and circulating air supply pressure of air-lift reverse circulation drilling. Background Art

[0002] In the field of geothermal drilling, in order to reserve enough space for submersible pumps and reduce construction risks, the wellbore mostly adopts a large-diameter multi-opening structure, and the lower casing does not return to the wellhead, so the annulus cross-sectional area of the upper well section is relatively large. When using positive circulation drilling, in order to meet the rock-carrying requirements of the upper large-diameter well section, it is often necessary to inject a large volume of drilling fluid. To alleviate the above problems, air-lift reverse circulation drilling is now mostly used for rock drilling, and the air-lift reverse circulation technology is used to extract substances such as oil, gas, and water from wells.

[0003] Whether the air-lift reverse circulation can successfully establish a circulation is the key to ensuring stable drilling, and the change of the injection air pressure during the starting stage has always been an important research content in the application of air-lift pumps. Insufficient injection air pressure during the starting stage will lead to repeated rebounds of the circulating volume flow rate during drilling, which may cause drilling accidents such as rock cuttings falling back and blocking the drill. In addition, the airtightness of the high-pressure pipeline will have problems with the increase of service time, and the rotational friction of the drill string during air-lift reverse circulation drilling will also cause equipment problems such as pipeline air leakage, which will cause changes in the starting pressure.

[0004] The circulating air supply pressure of the drilling fluid during air-lift reverse circulation drilling can reflect the frictional pressure loss in the well, and is an important index for characterizing air-lift reverse circulation drilling accidents. In order to make the circulation system operate stably and efficiently, it is necessary to reasonably calculate the circulating air supply pressure.

[0005] At present, the method for determining the starting pressure of the air-lift reverse circulation drilling process is not clear enough, and there is no relatively accurate and convenient method for determining the circulating air supply pressure of the air-lift reverse circulation process. Summary of the Invention

[0006] In order to solve the above problems, the present invention proposes a method for calculating the starting pressure and circulating air supply pressure of air-lift reverse circulation drilling. The method proposed by the present invention is also applicable to the lifting technology, and this lifting technology can be applied to extract substances such as oil, gas, and water from wells.

[0007] The method for calculating the starting pressure and circulating air supply pressure of the air-lift reverse circulation drilling of the present invention includes the following steps: S1. Calculate the static liquid pressure at the bottom of the inner pipe of the double-wall drill pipe; S2. Calculate the frictional loss pressure of the compressed air in the annulus of the double-wall drill pipe; S3. Calculate the frictional loss pressure of the compressed air flowing through the surface gas transmission channel; [[ID= S5. Calculate the liquid-phase flow friction pressure loss in the inner pipe of the double-walled drill pipe; S6. Calculate the liquid-phase flow friction pressure loss in the slag discharge pipeline; S7. Calculate the three-phase flow pressure drop in the inner pipe of the double-walled drill pipe; S8. Calculate the starting pressure and the circulating air supply pressure. The calculation formula for the friction loss pressure of the compressed air in the annulus of the double-walled drill pipe is (16) In the formula, — The friction loss pressure of the compressed air in the annulus of the double-walled drill pipe, Pa; — The pressure of the compressed air in the annulus of the double-walled drill pipe, Pa; — The relative density of air, generally taken as 1.0; — The average thermodynamic temperature in the annulus of the double-walled drill pipe, K; R e — Engineering gas constant, generally taken as 29.31 N·m / (N·K); f g0 — The Fanning friction coefficient of the annulus of the double-walled drill pipe, dimensionless; L dp — The length of the annulus of the double-walled drill pipe, m; — The inner diameter of the outer pipe of the double-walled drill pipe, m; — The outer diameter of the inner pipe of the double-walled drill pipe, m; — Standard atmospheric pressure, taken as 101325 Pa; — Atmospheric temperature, °C; Q 0 — The rated air injection volume of the air compressor, m³ / min.

[0008] The calculation formula for the friction loss pressure of the compressed air flowing through the surface gas transmission channel is (25) In the formula, P g1 — The pressure of the surface compressed air in the gas transmission channel, Pa; — The relative density of air, generally taken as 1.0; R e — Engineering gas constant, generally taken as 29.31 N·m / (N·K); — Atmospheric temperature, °C; f g1 — The surface pipe friction factor, dimensionless; L 1— The length of the pipe, m; D 1— The diameter of the pipe, m; — Standard atmospheric pressure, taken as 101325 Pa; Q0 — Rated air injection volume of air compressor, m³ / min.

[0009] The calculation formula for the local pressure loss of the compressed air passing through the orifice of the gas-liquid mixer from the outer pipe of the double-wall drill pipe is (26) In the formula, — Air flow velocity at the contraction section of the air-water mixer at the bottom of the double-wall drill pipe, m / s; — Local friction resistance coefficient; , A0 / A c — Porosity of the air-water mixer.

[0010] The calculation formula for the frictional pressure loss of the liquid phase flow in the inner pipe of the double-wall drill pipe is

[0011] In the formula, ρ L — Density of the flushing fluid. When the flushing fluid is clear water, take 1000 kg / m 3 ; — Volume flow rate of the compressed air in the annulus pipeline of the double-wall drill pipe. Since the compressed air displaces the flushing fluid, the flow rates of the compressed air and the flushing fluid are the same. Here, it is used to represent the flow rate of the flushing fluid in the inner pipe of the double-wall drill pipe, m³ / s; D dpiid — Inner diameter of the inner pipe of the double-wall drill pipe, m; h dp — Length of the inner pipe of the double-wall drill pipe, m.

[0012] The calculation formula for the flow velocity of the flushing fluid in the inner pipe of the double-wall drill pipe is

[0013] : In the formula, Q g0 — Volume flow rate of the compressed air in the annulus pipeline of the double-wall drill pipe, m 3 / s; Q L is the volume flow rate of the flushing fluid in the inner pipe of the double-wall drill pipe, m 3 / s.

[0014] The calculation formula for the frictional pressure loss of the liquid phase flow in the slag discharge pipeline is

[0015] In the formula, R e,l2 — Reynolds number of the liquid phase flow in the inner pipe of the slag discharge pipeline; — Pipe roughness, m; Q g0—Volume flow rate of compressed air in the annular space of the double-wall drill pipe, m 3 / s; h 0 — Height of the slag discharge pipeline, m; D 0 — Inner diameter of the slag discharge pipeline, m.

[0016] The pressure drop of the three-phase flow in the inner pipe of the double-wall drill pipe means that when the compressed air enters the inner cavity of the inner pipe of the double-wall drill pipe through the annular space between the inner and outer pipes of the double-wall drill pipe and passes through the gas-liquid mixer, it will return upward together with the cuttings and flushing fluid in the inner cavity of the double-wall drill pipe, forming a gas-liquid-solid three-phase mixed flow. The calculation formula for the changing trend of the pressure gradient of the three-phase mixed flow with the increase of depth is

[0017] In the formula, P t —Pressure of the three-phase mixed flow, Pa; —Weight flow rate of the three-phase flow, N / s; Q L1 —Volume flow rate of the flushing fluid returned to the wellhead, m 3 / s; f t —Fanning friction coefficient of the three-phase mixed flow, dimensionless; —Standard atmospheric pressure, taken as 101325 Pa; —Atmospheric temperature, °C; d dpiid —Inner diameter of the inner pipe of the double-wall drill pipe, m; —Average thermodynamic temperature in the annular space of the double-wall drill pipe, K; Q 0 —Rated gas injection volume of the air compressor, m³ / min; g —Acceleration of gravity, m / s 2 .

[0018] The calculation formula for the starting pressure is

[0019] In the formula, P s —Starting pressure; —Friction loss pressure during gas flow, Pa; —Pressure loss of the gas passing through the gas-liquid mixer, Pa; —Friction loss pressure of the liquid phase flow in the inner pipe of the double-wall drill pipe, Pa; —Friction loss pressure of the liquid phase flow in the slag discharge pipeline, Pa; P L —Static liquid pressure at the bottom of the inner pipe of the double-wall drill pipe, Pa; — Standard atmospheric pressure, taking 101325 Pa; h dp — Inner pipe length of the double-wall drill pipe, m; h 0 — Height of the slag discharge pipeline, m; ρ L — Density of the flushing fluid, kg / m³.

[0020] The circulating air supply pressure (45) In the formula, P c — Circulating air supply pressure; — Frictional loss pressure during gas flow, Pa; — Pressure loss of gas passing through the gas-liquid mixer, Pa; — Pressure drop of gas-liquid-solid three-phase flow in the double-wall drill pipe, Pa; — Standard atmospheric pressure, taking 101325 Pa.

[0021] The beneficial effect of the present invention is that the calculation method of the startup pressure and the circulating air supply pressure of the air-lift reverse circulation drilling of the present invention can accurately and conveniently calculate the startup pressure and the circulating air supply pressure of the air-lift reverse circulation drilling by accurately calculating the pressures of each part of the air-lift reverse circulation drilling process, providing a theoretical basis for the stable and efficient operation of the circulation system.The present invention helps in the pre-drilling construction design of the air-lift reverse circulation drilling process and the analysis of abnormal pressures during drilling. Description of the Drawings

[0022] Figure 1 is the layout detail drawing of the air-lift reverse circulation drilling.

[0023] Figure 2 is the calculation flow chart of the startup pressure of the air-lift reverse circulation drilling.

[0024] Figure 3 is the calculation flow chart of the circulating air supply pressure of the air-lift reverse circulation drilling.

[0025] Figure 4 is the schematic diagram of the change of the air supply pressure of the air compressor during the process of establishing the air-lift reverse circulation. Specific Embodiments

[0026] The following describes in detail the embodiments of the present invention, and the examples of the embodiments are shown in the drawings.The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0027] The calculation method of the startup pressure and the circulating air supply pressure of the air-lift reverse circulation drilling of the present invention includes the following steps: First, determine the parameters that can be obtained through measurement, including: the rated air supply pressure of the air compressor, the inner diameter of the gas transmission pipeline, the specifications of the double-wall drill pipe (including the inner diameter of the outer pipe of the double-wall drill pipe, the outer diameter of the inner pipe of the double-wall drill pipe, and the inner wall of the inner pipe of the double-wall drill pipe), the length of the double-wall drill pipe, the height of the slag discharge pipeline, the height of the dynamic water level in the wellbore, the atmospheric pressure, the atmospheric temperature, and the temperature of the flushing fluid. These parameters can be obtained through specific measurement and have no operational difficulty.

[0028] S1. Calculate the static liquid pressure at the bottom of the inner pipe of the double-wall drill pipe; S101. Determine the submergence ratio. The calculation formula for the submergence ratio is In formula (1), h 沉没 —The length of the double-wall drill pipe below the annulus water level, m; h 双壁 —The length of the double-wall drill pipe, m; h 排渣 —The height of the slag discharge pipeline, m.

[0029] S102. The static liquid column height when the air-lift reverse circulation reaches the starting pressure is calculated as follows: For φ168 / 108, φ140 / 89, φ127 / 76, and φ114 / 73 double-wall drill pipes, the height is: (2) For φ89 / 57 double-wall drill pipes, if the submergence ratio (R) is less than 0.59, the height is: (3) For φ89 / 57 double-wall drill pipes, if the submergence ratio (R) is greater than or equal to 0.59, the height is: (4) S103. The static liquid pressure is [[ID=3,6]] (5) In the formula, P L —The static liquid pressure at the bottom of the inner pipe of the double-wall drill pipe, Pa; ρ L —The liquid density, kg / m³; g—the acceleration of gravity, take 9.81m / s 2 .

[0030] S2. Calculate the frictional loss pressure of the compressed air in the annulus of the double-wall drill pipe; S201. The frictional loss pressure of the compressed air in the annulus of the double-wall drill pipe is calculated by the following equation: (6) In the formula, —The frictional loss pressure of the compressed air in the annulus pipeline of the double-wall drill pipe, Pa; — Specific weight of compressed air in the annulus of the double-walled drill pipe, N / m 3 ; L dp — Length of the annulus of the double-walled drill pipe, m; V g0 — Flow velocity of compressed air in the annulus of the double-walled drill pipe, m / s.

[0031] f g0 — Friction factor, which is a dimensionless coefficient and depends on the Reynolds number (Re) and the relative roughness of the pipe; — Inner diameter of the outer pipe of the double-walled drill pipe, m; — Outer diameter of the inner pipe of the double-walled drill pipe, m.

[0032] S202. The flow of compressed air in the pipe can be regarded as turbulent flow. Then, according to the Haaland relation: (7) (8) In the formula, f g0 — Fanning friction coefficient of the annulus of the double-walled drill pipe, dimensionless; — Absolute roughness of the pipe, taking 0.0002 m; R e,g0 — Reynolds number of the gas in the annulus of the double-walled drill pipe; ρ g0 — Density of the gas in the annulus of the double-walled drill pipe, related to pressure and temperature, kg / m³; μ g0 — Dynamic viscosity of the gas in the annulus of the double-walled drill pipe. By referring to relevant materials, the dynamic viscosity data of air at different temperatures can be obtained, Pa·s.

[0033] S203. The specific weight of compressed air in the annulus of the double-walled drill pipe is: (9) In the formula, P g0 — Pressure of compressed air in the annulus of the double-walled drill pipe, Pa; T g0 — Average thermodynamic temperature in the annulus of the double-walled drill pipe, K; S g — Relative density of air, generally taken as 1.0; R e — Engineering gas constant, generally taken as 29.31 N·m / (N·K).

[0034] S204. The density of compressed air in the annulus pipeline of the double-wall drill pipe is: (10) Affected by the back pressure of the fluid in the inner pipe of the double-wall drill pipe, for the air in the pipeline, there is: (11) In the formula, P g0 — Pressure of compressed air in the annulus pipeline of the double-wall drill pipe, Pa; P L — Static liquid pressure at the bottom of the inner pipe of the double-wall drill pipe, Pa.

[0035] S205. The weight flow rate of compressed air has the following relationship: (12) In the formula, W g0 — Weight flow rate of compressed air in the annulus pipeline of the double-wall drill pipe, N / s; — Specific weight of compressed air in the annulus pipeline of the double-wall drill pipe, N / m 3 ; Q g0 — Volume flow rate of compressed air in the annulus pipeline of the double-wall drill pipe, m 3 / s; Q 0 — Rated air supply of the air compressor, m 3 / s; w 0 is the weight flow rate of air on the ground surface, N / s; — Specific weight of air at ground surface temperature, N / m 3 .

[0036] In formula (13), — Atmospheric pressure at ground surface temperature, Pa; — Ground surface temperature, K.

[0037] After arrangement, we get: (14) In the formula,Q g0 — The volume flow rate of compressed air in the annulus pipeline of the double-wall drill pipe, m 3 / s; Thus, from equations (12), (13), and (14), the flow velocity of compressed air in the annulus pipelines of the inner and outer pipes of the double-wall drill pipe can be obtained as (15) In summary, the frictional loss pressure of compressed air in the annulus of the double-wall drill pipe is (16) S3. Calculate the frictional loss pressure of compressed air flowing through the surface gas transmission channel; The frictional loss pressure of compressed air flowing through the surface gas transmission channel is calculated by the following equation: (17) Wherein, — The frictional loss pressure of surface compressed air in the gas transmission channel, Pa; — The specific weight of surface compressed air in the gas transmission channel, N / m 3； L 1 — The length of the pipeline, m; D 1 — The diameter of the pipeline, m; V g1 — The flow velocity of surface compressed air in the gas transmission channel, m / s; f g1 — The surface pipeline friction factor, which is a dimensionless coefficient and depends on the Reynolds number (Re) and the relative roughness of the pipeline.

[0038] The friction factor f g1 Is calculated by the following formula: (18) In formula (19), f g1 — The Fanning friction coefficient of the surface pipeline, dimensionless; — The absolute roughness of the pipeline, take 0.0002 m; R e,g1 — The Reynolds number of the gas in the surface pipeline; ρ g1 — The density of the gas in the surface pipeline, related to pressure and temperature, kg / m³; μ g1 — Dynamic viscosity of the gas in the surface pipeline, Pa·s.

[0039] The specific weight of the surface compressed air in the gas transmission channel is: (20) In the formula, — Specific weight of the surface compressed air in the gas transmission channel, N / m 3 ; P g1 — Pressure of the surface compressed air in the gas transmission channel, Pa.

[0040] The pressure of the compressed air in the surface gas transmission channel can be expressed as the sum of the air pressure in the annulus between the inner and outer pipes of the double-wall drill pipe and the frictional loss pressure of the air in the annulus between the inner and outer pipes of the double-wall drill pipe, and can be calculated by the following formula, that is: (21) The weight flow rate of the compressed air in the surface gas transmission channel has the following relationship: (22) In the formula, W g1 — Weight flow rate of the surface compressed air in the gas transmission channel, N / s; Q g1 — Volume flow rate of the surface compressed air in the gas transmission channel, m 3 / s.

[0041] After arrangement, we get: (23) From this, the flow velocity of the compressed air in the surface gas transmission pipeline can be obtained as (24) After arrangement, the frictional loss pressure of the compressed air in the surface gas transmission pipeline is: (25) S4. Calculate the local pressure loss of the compressed air passing through the orifice on the gas-liquid mixer from the outer pipe of the double-wall drill pipe; The compressed gas passes through the orifice on the gas-liquid mixer from the outer pipe of the double-wall drill pipe and enters the central channel of the double-wall drill pipe, where it mixes with the drilling fluid and cuttings. When the compressed air passes through the orifice, due to the sudden reduction of the cross-sectional area of the flow-through section, a contraction section with the smallest cross-sectional area of the flow-through section will be formed, and its area is Ac. The formula for calculating the local pressure loss is (26) When the cross-section contracts, there is: (27) Wherein, — the air flow velocity at the contraction section of the air-water mixer at the bottom of the double-wall drill pipe, which is the same as the flow velocity of the compressed air in the annulus between the inner and outer pipes of the double-wall drill pipe in front, m / s; — is the local friction resistance coefficient; A0 / A c — the porosity of the air-water mixer.

[0042] S5. Calculate the frictional pressure loss of the liquid phase flow in the inner pipe of the double-wall drill pipe; Frictional pressure loss of the liquid phase flow in the inner pipe of the double-wall drill pipe The expression is as follows: (28) Wherein, ρ L — the density of the flushing fluid. When the flushing fluid is clear water, take 1000 kg / m 3 ; f L1 — the Fanning friction coefficient of the liquid phase flow in the inner pipe of the double-wall drill pipe; V L1 — the flow velocity of the flushing fluid in the inner pipe of the double-wall drill pipe, m / s; D dpiid — the inner diameter of the inner pipe of the double-wall drill pipe, m; h dp — the length of the inner pipe of the double-wall drill pipe, m.

[0043] Fanning friction coefficient of the liquid phase flow in the inner pipe of the double-wall drill pipe f L1 Is calculated by the following formula: (29) (30) Wherein, R e,l1 — the Reynolds number of the flushing fluid in the inner pipe of the double-wall drill pipe; μ l — the dynamic viscosity of the flushing fluid. Take 0.001 Pa·s for clear water.

[0044] Since the air in the outer annulus of the double-wall drill pipe displaces the liquid in the outer annulus of the double-wall drill pipe, there is: (31) Therefore, the flow velocity of the flushing fluid in the inner pipe of the double-wall drill pipe is: (32) In summary, the liquid-phase flow frictional pressure loss in the inner pipe of the double-wall drill pipe P L f1 The expression is as follows: (33) S6. Calculate the liquid-phase flow frictional pressure loss in the slag discharge pipeline; The liquid-phase flow frictional pressure loss in the slag discharge pipeline The expression is as follows: (34) In the formula, D 0—the inner diameter of the slag discharge pipeline, m; f L2 —The Fanning friction coefficient of the liquid-phase flow in the slag discharge pipeline; V L2 —The flow velocity of the flushing fluid in the slag discharge pipeline, m / s; h 0—the height of the slag discharge pipeline, m.

[0045] The Fanning friction coefficient of the liquid-phase flow in the inner pipe of the slag discharge pipeline f L2 It is calculated by the following formula: (35) (36) In the formula, R e,l2 —The Reynolds number of the liquid-phase flow in the inner pipe of the slag discharge pipeline.

[0046] The flow velocity of the flushing fluid in the slag discharge pipeline is: (37) In summary, the liquid-phase flow frictional pressure loss in the inner pipe of the slag discharge pipeline The expression is as follows: (38) S7. Calculate the pressure drop of the gas-liquid-solid three-phase flow in the inner pipe of the double-wall drill pipe; Parameters that can be directly measured: the rated air supply volume of the air compressor, the upward return flow of the air-lift reverse circulation, the density of the drilling flushing fluid, the parameters of the double-wall drill tool, and the environmental parameters.

[0047] When the compressed air enters the inner cavity of the double-wall drill pipe through the annulus between the inner and outer pipes of the double-wall drill pipe and passes through the gas-liquid mixer, it will flow upward together with the cuttings and flushing fluid in the inner cavity of the double-wall drill pipe, forming a gas-liquid-solid three-phase mixed flow. The changing trend of its pressure gradient with the increase in depth can be approximately expressed as: (39) In the formula:P t — Three-phase mixed flow pressure, Pa; — Specific weight of three-phase flow, N / m 3 ; f t — Fanning friction coefficient of three-phase mixed flow; V t — Flow velocity of three-phase flow, m / s; g — Acceleration due to gravity, m / s 2 .

[0048] It represents the hydrostatic pressure in the inner cavity of the inner pipe of the double-wall drill pipe, and it represents the flow friction loss pressure generated by the fluid flow in the inner cavity of the inner pipe of the double-wall drill pipe.

[0049] For the gas-liquid-cuttings three-phase mixed flow system, the volume proportion of cuttings is tiny, so it is regarded as a minor factor and ignored in the analysis process. Then, the specific weight and flow velocity of the three-phase flow are respectively: (40) (41) In the formula — Weight flow rate of three-phase flow, N / s; Q L1 — Volume flow rate of the flushing fluid returned to the wellhead, m 3 / s; f t — Fanning friction coefficient of three-phase mixed flow, dimensionless; — Standard atmospheric pressure, taken as 101325 Pa; — Atmospheric temperature, °C; d dpiid — Inner diameter of the inner pipe of the double-wall drill pipe; — Average thermodynamic temperature in the annulus of the double-wall drill pipe, K; Q 0 — Rated air injection volume of the air compressor, m³ / min; g — Acceleration due to gravity, m / s 2 .

[0050] After sorting out, the variation trend of the pressure gradient of the three-phase flow with the increase of depth is as follows. After integration, the bottom pressure of the double-wall drill pipe can be calculated (42) S8. Calculate the starting pressure and the circulating air supply pressure.

[0051] S801. Calculate the starting pressure The starting pressure Ps shall satisfy:

[0052] In the formula, P s — Starting pressure; — Frictional loss pressure during the flow of compressed air, Pa; — Pressure loss of compressed air passing through the gas-liquid mixer, Pa; — Frictional loss pressure of the liquid phase flow in the inner pipe of the double-wall drill pipe, Pa; — Frictional loss pressure of the liquid phase flow in the slag discharge pipeline, Pa; P L — Hydrostatic pressure at the bottom of the inner pipe of the double-wall drill pipe, Pa; — Standard atmospheric pressure, taking 101325 Pa; h dp — Length of the inner pipe of the double-wall drill pipe, m h 0 — Height of the slag discharge pipeline, m; ρ L — Density of the flushing liquid, kg / m³.

[0053] S802. Calculate the circulating air supply pressure The circulating air supply pressure Pc shall satisfy the following formula (the calculation methods of the gas frictional loss pressure in the surface pipeline, the gas frictional loss pressure in the annulus between the inner and outer pipes of the double-wall drill pipe, and the pressure loss at the mixer are the same as before): (45) In the formula, P c — Circulating air supply pressure; — Frictional loss pressure during the flow of compressed air (including the frictional loss pressure of compressed air during the flow in the surface pipeline and the frictional loss pressure of compressed air during the flow in the annulus between the inner and outer pipes of the double-wall drill pipe, that is )), Pa; — Pressure loss of gas passing through the gas-liquid mixer, Pa; — Pressure drop of the gas-liquid-solid three-phase flow in the inner pipe of the double-wall drill pipe, Pa; —Standard atmospheric pressure, take 101325Pa.

[0054] Example

[0055] The equipment used in the calculation mainly includes drilling rigs, air compressors, triangular weir boxes, etc. The parameters of these equipment are shown in Tables 1 to 3.

[0056] Table 1 Equipment parameter data table

[0057] Table 2 Gas flow pipeline parameters

[0058] Table 3 Drilling tool assembly parameters

[0059] The highest point of the slag discharge pipeline in a gas-lift reverse circulation geothermal well is 20 m. The formula used in this application calculates the starting pressure for different double-wall drill pipe installation depths and specifications, as shown in Table 4. Based on field test conditions, the ground surface temperature was approximately 25°C, the temperature inside the double-wall drill pipe was approximately 20°C, and the remaining parameters were consistent with the aforementioned conditions.

[0060] Table 4 Kuancheng gas lift reverse circulation startup pressure analysis table

[0061] The three-phase flow model was used for calculation. The air compressor injection pressure and the return water volume at the slag outlet during the test were taken for calculation. It was observed that when the air compressor injection pressure changed during the drilling of each drill pipe, the return water volume at the slag outlet would also change. Therefore, the sinking depths of different double-wall drill pipes were calculated. The results are shown in Table 5.

[0062] Table 5 Calculation table of gas pressure at the bottom of double-wall drill pipe

[0063] Figure 4 This is a schematic diagram of the changes in the air compressor supply pressure during the gas lift reverse circulation process. The pressure value at point C is the starting pressure during the circulation process, and the pressure value at point F is the circulating air supply pressure during the circulation process.

[0064] After calculation, the analysis of the starting pressure and circulating air supply pressure is slightly different from the measured results, and can be used as the calculation method.

[0065] In the present invention, terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0066] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.

Claims

1. A calculation method for the startup pressure and circulating gas supply pressure of air-lift reverse circulation drilling, characterized in that, It includes the following steps: S1. Calculate the static liquid pressure at the bottom of the inner pipe of the double-wall drill pipe; S2. Calculate the frictional loss pressure of the compressed air in the outer annulus of the double-wall drill pipe; S3. Calculate the frictional loss pressure of the compressed air flowing through the surface gas transmission channel; S4. Calculate the local pressure loss of the compressed air passing through the orifice on the gas-liquid mixer from the outer pipe of the double-wall drill pipe; S5. Calculate the frictional pressure loss of the liquid phase flow in the inner pipe of the double-wall drill pipe; S6. Calculate the frictional pressure loss of the liquid phase flow in the slag discharge pipeline; S7. Calculate the three-phase flow pressure drop in the inner pipe of the double-wall drill pipe; S8. Calculate the starting pressure and the circulating air supply pressure.

2. The calculation method of the startup pressure and circulating gas supply pressure for air-lift reverse circulation drilling according to claim 1, wherein The calculation formula for the frictional loss pressure of compressed air in the outer annulus of the double-wall drill pipe is as follows In formula (16), —The frictional loss pressure of compressed air during the flow in the outer annulus pipe of the double-wall drill pipe, Pa; —The pressure of compressed air in the outer annulus pipe of the double-wall drill pipe, Pa; —The relative density of air, generally taken as 1.0; —The average thermodynamic temperature in the outer annulus pipe of the double-wall drill pipe, K; R e — Engineering gas constant, generally taken as 29.31 N·m / (N·K); f g0 —The Fanning friction coefficient of the outer annulus pipe of the double-wall drill pipe, dimensionless; L dp — Length of the annulus pipe of the double-wall drill pipe, m; — Inner diameter of the outer pipe of the double-wall drill pipe, m; — Outer diameter of the inner pipe of the double-wall drill pipe, m; — Standard atmospheric pressure, taken as 101325 Pa; — Atmospheric temperature, °C; Q 0 — Rated air injection volume of air compressor, m³ / min.

3. The calculation method of the starting pressure and circulating air supply pressure for air-lift reverse circulation drilling according to claim 1, characterized in that The calculation formula for the frictional loss pressure of the compressed air flowing through the surface gas transmission channel is （25） In the formula, — Frictional loss pressure during the flow of compressed air in surface pipelines, Pa; P g1 — Pressure of surface compressed air in the gas transmission channel, Pa; — Relative density of air, generally taken as 1.0; R e — Engineering gas constant, generally taken as 29.31 N·m / (N·K); — Atmospheric temperature, °C; f g1 — Friction factor of surface pipelines, dimensionless; L 1—Length of the pipeline, m; D 1—Diameter of the pipeline, m; —Standard atmospheric pressure, taken as 101325 Pa; Q 0 —Rated air injection volume of the air compressor, m³ / min.

4. The method for calculating the startup pressure and circulating gas supply pressure of air-lift reverse circulation drilling according to claim 1, wherein The calculation formula for the local pressure loss of the compressed air passing through the orifice on the gas-liquid mixer from the outer pipe of the double-wall drill pipe is （26） In the formula, — Pressure loss of compressed air passing through the gas-liquid mixer, Pa; — Air flow velocity at the contraction section of the gas-water mixer at the bottom of the double-wall drill pipe, m / s; — is the local friction coefficient; , A0 / A c — Porosity of the gas-water mixer.

5. The calculation method of the startup pressure and the circulating gas supply pressure for air-lift reverse circulation drilling according to claim 1, wherein The calculation formula for the frictional pressure loss of the liquid phase flow in the inner pipe of the double-wall drill pipe is （33） In the formula, — The pressure loss due to liquid-phase flow friction in the inner pipe of the double-wall drill pipe, Pa; ρ L — The density of the flushing fluid. When the flushing fluid is clear water, take 1000 kg / m 3 ; — The flow rate of the flushing fluid in the inner pipe of the double-wall drill pipe, m³ / s; D dpiid — The inner diameter of the inner pipe of the double-wall drill pipe, m; h dp — The length of the inner pipe of the double-wall drill pipe, m.

6. The calculation method of the startup pressure and the circulating gas supply pressure for air-lift reverse circulation drilling according to claim 5, wherein The calculation formula for the flow velocity of the flushing fluid in the inner pipe of the double-wall drill pipe is （32） Wherein, V L1 — Flow velocity of the flushing fluid in the inner pipe of the double-wall drill pipe, m / s; Q g0 — Volume flow rate of the flushing fluid in the annulus pipeline of the double-wall drill pipe, m 3 / s; Q L is the volume flow rate of the flushing fluid in the inner pipe of the double-wall drill pipe, m 3 / s; D dpiid — Inner diameter of the inner pipe of the double-wall drill pipe, m.

7. The calculation method of the startup pressure and the circulating gas supply pressure for air-lift reverse circulation drilling according to claim 1, wherein The calculation formula for the frictional pressure loss of the liquid phase flow in the slag discharge pipeline is （38） In the formula, — Liquid-phase flow frictional pressure loss of the slag discharge pipeline; R e,l2 — Liquid-phase flow Reynolds number in the inner pipe of the slag discharge pipeline; — Pipe roughness, m; V L2 — Flow velocity of the flushing liquid in the slag discharge pipeline, m / s, ; h 0 — Height of the slag discharge pipeline ，m ; D 0 — Inner diameter of the slag discharge pipeline, m .

8. The method for calculating the starting pressure and circulating gas supply pressure of air-lift reverse circulation drilling according to claim 1, wherein The three-phase flow pressure drop in the inner pipe of the double-wall drill pipe means that when the compressed air enters the inner cavity of the inner pipe of the double-wall drill pipe through the gas-water mixer from the annulus between the inner and outer pipes of the double-wall drill pipe, it will rise together with the cuttings and the flushing fluid in the inner cavity of the double-wall drill pipe to form a gas-liquid-solid three-phase mixed flow. The calculation formula for the change trend of the pressure gradient of the three-phase mixed flow with the increase of depth is （42） wherein, P t — three-phase mixed flow pressure, Pa; — three-phase flow mass flow rate, N / s; Q L1 — wellhead returned flushing fluid volume flow rate, m 3 / s; f t — Fanning friction coefficient of three-phase mixed flow, dimensionless; — standard atmospheric pressure, taking 101325 Pa; — atmospheric temperature, °C; d dpiid — inner pipe inner diameter of double-wall drill pipe, m; — average thermodynamic temperature in the annulus pipeline of double-wall drill pipe, K; Q 0 — Rated air injection volume of air compressor, m³ / min; g — Acceleration of gravity, m / s 2 .

9. The method for calculating the startup pressure and circulating air supply pressure of air-lift reverse circulation drilling according to claim 1, wherein The calculation formula for the starting pressure is （43） （44） Wherein, P s — Starting pressure; — Frictional loss pressure of compressed air in the outer annulus pipeline of the double-walled drill pipe, Pa; — Frictional loss pressure of compressed air in the surface gas transmission pipeline, Pa; — Pressure loss of gas passing through the gas-liquid mixer, Pa; — Frictional loss pressure of liquid phase flow in the inner pipe of the double-walled drill pipe, Pa; — Frictional loss pressure of liquid phase flow in the slag discharge pipeline, Pa; P L — Static liquid pressure at the bottom of the inner pipe of the double-walled drill pipe, Pa; — Standard atmospheric pressure, taking 101325 Pa; h dp — Length of the inner pipe of the double-walled drill pipe, m; h 0 — Height of slag discharge pipeline, m; ρ L — Density of flushing fluid, kg / m³.

10. The calculation method of the startup pressure and circulating gas supply pressure for air-lift reverse circulation drilling according to claim 1, characterized in that, The circulating air supply pressure （45） Wherein, P c —Circulating air supply pressure; —Frictional loss pressure of compressed air in the annular space pipeline of the double-wall drill pipe, Pa; —Frictional loss pressure of compressed air in the surface gas transmission pipeline, Pa; P m —Pressure loss of gas passing through the gas-liquid mixer, Pa; P t —Pressure drop of gas-liquid-solid three-phase flow in the double-wall drill pipe, Pa; —Standard atmospheric pressure, taking 101325 Pa.

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