A model for calculating frictional loss pressure during gas lift circulation drilling.

Abstract

This invention discloses a friction loss pressure calculation model for gas lift circulation drilling during the drilling process, comprising the following steps: S1. Calculating the hydrostatic pressure at the bottom of the inner tube of the double-walled drill pipe; S2. Calculating the friction loss pressure of compressed air in the outer annulus of the double-walled drill pipe; S3. Calculating the friction loss pressure of compressed air flowing through the surface gas transmission channel; S4. Calculating the local pressure loss of compressed air from the outer tube of the double-walled drill pipe through the orifice on the gas-liquid mixer; S5. Calculating the friction pressure loss of liquid phase flow in the inner tube of the double-walled drill pipe; S6. Calculating the friction pressure loss of liquid phase flow in the slag discharge pipeline; S7. Calculating the three-phase flow pressure drop in the inner tube of the double-walled drill pipe; S8. Calculating the start-up pressure and the circulation gas supply pressure. This invention's friction loss pressure calculation model for gas lift circulation drilling during the drilling process accurately calculates the pressure of each part of the gas lift reverse circulation drilling process, thereby enabling accurate and convenient calculation of the start-up pressure and circulation gas supply pressure of gas lift reverse circulation drilling, providing a theoretical basis for ensuring the stable and efficient operation of the circulation system.

Description

Technical Field

[0001] This invention belongs to the field of soil or rock drilling technology, specifically relating to a friction loss pressure calculation model for air lift circulation drilling during the drilling process. Background Technology

[0002] In geothermal drilling, to allow sufficient space for submersible pumps and reduce construction risks, wellbore structures are often large-diameter and multi-stage, with the lower casing not returning to the wellhead, resulting in a large annular cross-sectional area in the upper section. When using forward circulation drilling, a large volume of drilling fluid is often required to meet the rock-carrying requirements of the large-diameter upper section. To alleviate these problems, gas lift reverse circulation drilling is now commonly used. Gas lift reverse circulation technology is used to extract oil, gas, water, and other substances from the well.

[0003] Successful establishment of circulation in gas lift reverse circulation is crucial for stable drilling, and changes in injection pressure during the startup phase have always been an important research topic in gas lift pump applications. Insufficient injection pressure during startup can lead to repeated rebounds in the circulating volumetric flow rate during drilling, potentially causing drilling accidents such as cuttings falling back and blockage. Furthermore, the tightness of high-pressure pipelines can deteriorate over time, and the rotational friction of the drill string during gas lift reverse circulation drilling can also cause equipment problems such as pipeline leaks, all of which contribute to changes in startup pressure.

[0004] The drilling fluid circulation pressure during gas lift reverse circulation drilling reflects the frictional pressure loss within the well and is an important indicator of gas lift reverse circulation drilling accidents. To ensure stable and efficient operation of the circulation system, the circulation pressure must be calculated appropriately.

[0005] Currently, the method for determining the start-up pressure of gas lift reverse circulation drilling technology is not clear enough, and there is no accurate and convenient method for determining the circulating gas supply pressure of gas lift reverse circulation technology. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a calculation model for frictional loss pressure during the drilling process in gas lift circulation drilling. The method proposed in this invention is also applicable to lift technology, which can be used to extract substances such as oil, gas, and water from wells.

[0007] The friction loss pressure calculation model for gas lift circulation drilling during the drilling process of this invention includes the following steps:

[0008] S1. Calculate the hydrostatic pressure at the bottom of the inner tube of the double-walled drill pipe;

[0009] S2. Calculate the frictional loss pressure of compressed air in the outer annulus of the double-walled drill pipe;

[0010] S3. Calculate the pressure loss due to friction of compressed air flowing through the surface gas transport channel;

[0011] S4. Calculate the local pressure loss of compressed air from the outer tube of the double-walled drill pipe through the orifice on the gas-liquid mixer;

[0012] S5. Calculate the frictional pressure loss of the liquid phase flow in the inner tube of the double-walled drill pipe;

[0013] S6. Calculate the frictional pressure loss of the liquid phase flow in the slag discharge pipeline;

[0014] S7. Calculate the pressure drop of the three-phase flow inside the double-walled drill pipe;

[0015] S8. Calculate the start-up pressure and the circulating gas supply pressure.

[0016] The formula for calculating the frictional loss pressure of the compressed air in the outer annulus of the double-walled drill pipe is as follows:

[0017]

[0018] In the formula, ΔP gf0 —Frictional loss pressure of compressed air in the outer annulus of the double-walled drill pipe, Pa; p g0 —Pressure of compressed air in the outer annulus of the double-walled drill pipe, Pa; S g —The relative density of air is generally taken as 1.0; T g0 —The average thermodynamic temperature, K; R, inside the annulus pipe outside the double-walled drill pipe. e —Engineering gas constant, typically taken as 29.31 N·m / (N·K); f g0 —Fanning friction coefficient of the outer annulus of the double-walled drill pipe, dimensionless; L dp —Length of the outer annulus pipe of the double-walled drill pipe, in meters; D dpoid —Inner diameter of the outer tube of the double-walled drill pipe, in meters; D dpiod —Outer diameter of the inner tube of the double-walled drill pipe, in meters; P atm —Standard atmospheric pressure, taken as 101325 Pa; T atm —Ambient temperature, °C; Q0—Rated air injection capacity of air compressor, m³ 3 / min.

[0019] The formula for calculating the frictional loss pressure of compressed air flowing through the surface gas transmission channel is as follows:

[0020]

[0021] In the formula, P g1 —Pressure of compressed air at ground level in the gas delivery channel, Pa; S g —The relative density of air, typically taken as 1.0; R e —Engineering gas constant, typically taken as 29.31 N·m / (N·K); T atm —Atmospheric temperature, °C; fg1 —Surface pipeline friction factor, dimensionless; L1—Pipeline length, m; D1—Pipeline diameter, m; P atm —Standard atmospheric pressure, taken as 101325Pa; Q0—Rated air injection capacity of the air compressor, m³ / s 3 / min.

[0022] The formula for calculating the local pressure loss of compressed air passing through the orifice on the gas-liquid mixer from the outer tube of the double-walled drill pipe is as follows:

[0023]

[0024] In the formula, V g0 —Air velocity at the contraction section of the air-water mixer at the bottom of the double-walled drill pipe, m / s; ξ—Local frictional resistance coefficient; A0 / A c —Porosity of the gas-water mixer.

[0025] The formula for calculating the frictional pressure loss of the liquid phase flow in the inner tube of the double-walled drill pipe is as follows:

[0026]

[0027] In the formula, ρ L —Density of the flushing fluid; when the flushing fluid is clean water, take 1000 kg / m³. 3 Q g0 —The volumetric flow rate of compressed air in the outer annulus of the double-walled drill pipe. Since compressed air replaces the flushing fluid, the flow rates of compressed air and flushing fluid are the same. Here, it is used to represent the flow rate of flushing fluid in the inner tube of the double-walled drill pipe, in meters (m). 3 / s;D dpiid —Inner diameter of the double-walled drill pipe, in meters; h dp —Length of the inner tube of the double-walled drill pipe, in meters.

[0028] The formula for calculating the flow velocity of the flushing fluid in the inner tube of the double-walled drill pipe is as follows:

[0029]

[0030] In the formula, Q g0 —Volume flow rate of compressed air in the outer annulus of the double-walled drill pipe, m³ 3 / s;Q L It is the volumetric flow rate of the flushing fluid in the inner tube of the double-walled drill pipe, in m. 3 / s.

[0031] The formula for calculating the frictional pressure loss of the liquid phase flow in the slag discharge pipeline is as follows:

[0032]

[0033] In the formula, R e,l2—Reynolds number of liquid phase flow inside the slag discharge pipeline; ε p —Pipe roughness, m; Q g0 —Volume flow rate of compressed air in the outer annulus of the double-walled drill pipe, m³ 3 / s; h0—height of slag discharge pipeline, m; D0—inner diameter of slag discharge pipeline, m.

[0034] The pressure drop of the three-phase flow in the inner tube of the double-walled drill pipe refers to the following: when compressed air enters the inner cavity of the double-walled drill pipe from the annulus between the inner and outer tubes via the gas-water mixer, it rises together with the rock cuttings and flushing fluid in the inner cavity, forming a gas-liquid-solid three-phase mixed flow. The formula for calculating the change trend of the pressure gradient of the three-phase mixed flow with increasing depth is as follows:

[0035]

[0036] In the formula, P t —Three-phase mixed flow pressure, Pa; w t —Three-phase flow rate, N / s; Q L1 —Wellhead flushing fluid volume flow rate, m³ 3 / s;f t —Fanning friction coefficient for three-phase mixed flow, dimensionless; P atm —Standard atmospheric pressure, taken as 101325 Pa; T atm —Atmospheric temperature, °C; d dpiid — is the inner diameter of the double-walled drill pipe, in meters; T g0 —Average thermodynamic temperature within the outer annulus of the double-walled drill pipe, K; Q0—Rated air injection capacity of the air compressor, m³ / s 3 / min; g—acceleration due to gravity, m / s² 2 .

[0037] The formula for calculating the starting pressure is as follows:

[0038] P s =ΔP gf +ΔP m +ΔP Lf1 +ΔP Lf2 +P L +P atm (43)

[0039] P L =ρ Lg (h dp +h0) (44)

[0040] In the formula, P s —Starting pressure; ΔP gf —Frictional loss pressure during gas flow, Pa; ΔP m —Pressure loss of gas passing through the gas-liquid mixer, Pa; ΔPLf1 —Pressure loss due to frictional flow of liquid phase in the inner tube of the double-walled drill pipe, Pa; ΔP Lf2 —Pressure loss due to frictional flow in the slag discharge pipeline, Pa; P L —Hydrostatic pressure at the bottom of the inner tube of the double-walled drill pipe, Pa; P atm —Standard atmospheric pressure, taken as 101325 Pa; h dp —Length of the inner tube of the double-walled drill pipe, m; h0—Height of the slag discharge pipeline, m; ρ L — Fluid density, kg / m³ 3 .

[0041] The circulating gas supply pressure

[0042] P c =ΔP gf +ΔP m +ΔP t +P atm (45)

[0043] In the formula, P c —Recirculating gas supply pressure; ΔP gf —Frictional loss pressure during gas flow, Pa; ΔP m —Pressure loss of gas passing through the gas-liquid mixer, Pa; ΔP t —Pressure drop of the three-phase flow (gas, liquid, solid) inside the double-walled drill pipe, Pa; P atm —Standard atmospheric pressure, taken as 101325 Pa.

[0044] The beneficial effects of this invention are that the friction loss pressure calculation model for gas lift reverse circulation drilling during the drilling process accurately calculates the pressure of each part of the gas lift reverse circulation drilling process, thereby enabling accurate and convenient calculation of the start-up pressure and circulation gas supply pressure of gas lift reverse circulation drilling, providing a theoretical basis for ensuring the stable and efficient operation of the circulation system. This invention also assists in the pre-drilling construction design of gas lift reverse circulation drilling technology and the analysis of pressure anomalies during drilling. Attached Figure Description

[0045] Figure 1 This is a detailed diagram of the layout of an air-lift reverse circulation drilling system.

[0046] Figure 2 This is a flowchart for calculating the start-up pressure of gas lift reverse circulation drilling.

[0047] Figure 3 This is a flowchart for calculating the circulating gas supply pressure in gas lift reverse circulation drilling.

[0048] Figure 4 This is a schematic diagram showing the change in air compressor supply pressure during the air lift reverse circulation process. Detailed Implementation

[0049] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0050] The friction loss pressure calculation model for gas lift circulation drilling during the drilling process of this invention includes the following steps:

[0051] First, determine the parameters that can be measured, including: the rated air supply pressure of the air compressor, the inner diameter of the air pipeline, the specifications of the double-walled drill pipe (including the inner diameter of the outer tube, the outer diameter of the inner tube, and the inner wall diameter), the length of the double-walled drill pipe, the height of the slag discharge pipeline, the dynamic water level in the wellbore, atmospheric pressure, atmospheric temperature, and flushing fluid temperature. These parameters can be obtained through specific measurements and are not difficult to perform.

[0052] S1. Calculate the hydrostatic pressure at the bottom of the inner tube of the double-walled drill pipe;

[0053] S101. Determine the sinking ratio. The formula for calculating the sinking ratio is:

[0054] R = h 沉没 / (h 双壁 +h 排渣 (1)

[0055] In the formula, h 沉没 —Length of the double-walled drill pipe below the annular water level, in meters (h) 双壁 —Length of double-walled drill pipe, m; h 排渣 — Height of the slag discharge pipeline, in meters.

[0056] S102. The height of the hydrostatic column when the air lift reverse circulation reaches the starting pressure is calculated as follows:

[0057] For φ168 / 108, φ140 / 89, φ127 / 76 and φ114 / 73 double-wall drill pipes, the height is:

[0058] h max =h 双壁 +h 排渣 (2)

[0059] For φ89 / 57 double-walled drill pipe, if the submersion ratio (R) is less than 0.59, the height is:

[0060] h max =(h 双壁 +h 排渣 (3) For φ89 / 57 double-walled drill pipe, if the submersion ratio (R) is greater than or equal to 0.59, the height is:

[0061] h max =h 双壁 +h排渣 (4)

[0062] S103. Static pressure is

[0063] P L =ρ L gh max (5)

[0064] In the formula, P L —Hydrostatic pressure at the bottom of the inner tube of the double-walled drill pipe, Pa; ρ L —Liquid density, kg / m³ 3 g—acceleration due to gravity, taken as 9.81 m / s² 2 .

[0065] S2. Calculate the frictional loss pressure of compressed air in the outer annulus of the double-walled drill pipe;

[0066] S201. The frictional loss pressure of compressed air in the outer annulus of a double-walled drill pipe is calculated by the following equation:

[0067]

[0068] In the formula, Δp gf0 —Frictional loss pressure of compressed air in the outer annulus of the double-walled drill pipe, Pa;

[0069] γ g0 —Specific weight of compressed air in the outer annulus of the double-walled drill pipe, N / m³ 3 ;

[0070] L dp —Length of the outer annular pipe of the double-walled drill pipe, in meters;

[0071] V g0 —The velocity of compressed air in the annular pipe outside the double-walled drill pipe, m / s.

[0072] f g0 —The friction factor is a dimensionless coefficient that depends on the Reynolds number (Re) and the relative roughness of the pipe;

[0073] D dpoid —Inner diameter of the outer tube of the double-walled drill pipe, in meters;

[0074] D dpiod —Outer diameter of the inner tube of the double-walled drill pipe, in meters.

[0075] S202. The flow of compressed air in a pipe can be considered as turbulent flow, then according to the Haaland relation:

[0076]

[0077] In the formula, f g0—Fanning friction coefficient of the outer annulus of the double-walled drill pipe, dimensionless;

[0078] ε p —The absolute roughness of the pipe is taken as 0.0002m;

[0079] R e,g0 —The Reynolds number of the gas inside the outer annulus of the double-walled drill pipe;

[0080] ρ g0 —The density of the gas inside the outer annulus of the double-walled drill pipe is related to pressure and temperature, in kg / m³. 3 ;

[0081] μ g0 —The dynamic viscosity of the gas inside the outer annulus of the double-walled drill pipe can be obtained by consulting relevant materials, and the dynamic viscosity data of air at different temperatures can be obtained in Pa·s.

[0082] S203. The specific gravity of compressed air in the outer annulus of the double-walled drill pipe is:

[0083]

[0084] In the formula, P g0 —Pressure of compressed air in the annular pipe outside the double-walled drill pipe, Pa;

[0085] T g0 —The average thermodynamic temperature, K, inside the annular pipe outside the double-walled drill pipe;

[0086] S g —The relative density of air is generally taken as 1.0;

[0087] R e —The engineering gas constant is generally taken as 29.31 N·m / (N·K).

[0088] S204. The density of compressed air in the annular pipe outside the double-walled drill pipe is:

[0089]

[0090] The air inside the pipe is affected by the back pressure of the fluid inside the double-walled drill pipe, resulting in:

[0091] P g0 =P L (11) In the formula, P g0 —Pressure of compressed air in the annular pipe outside the double-walled drill pipe, Pa;

[0092] P L —Hydrostatic pressure at the bottom of the inner tube of the double-walled drill pipe, Pa.

[0093] S205. The weight flow rate of compressed air has the following relationship:

[0094] γ g0 Q g0 =w g0 =w0=γ0Q0 (12)

[0095] In the formula, W g0 —The weight flow rate of compressed air in the annular pipe outside the double-walled drill pipe, N / s;

[0096] γ g0 —Specific weight of compressed air in the outer annulus of the double-walled drill pipe, N / m³ 3 ;

[0097] Q g0 —Volume flow rate of compressed air in the outer annulus of the double-walled drill pipe, m³ 3 / s;

[0098] Q0—Rated air supply capacity of the air compressor, in meters. 3 / s;

[0099] w0 is the mass flow rate of air at the Earth's surface, in N / s;

[0100] γ0 — Specific weight of air at surface temperature, N / m 3 .

[0101]

[0102] In the formula, P atm —Atmospheric pressure at Earth's surface temperature, in Pa;

[0103] T atm —Surface temperature, K.

[0104] After sorting, we get:

[0105]

[0106] In the formula, Q g0 —Volume flow rate of compressed air in the outer annulus of the double-walled drill pipe, m³ 3 / s;

[0107] Therefore, from equations (12), (13), and (14), the flow velocity of compressed air in the annular pipe between the inner and outer tubes of the double-walled drill pipe can be obtained as follows:

[0108]

[0109] In summary, the frictional pressure of the compressed air in the outer annulus of the double-walled drill pipe is...

[0110]

[0111] S3. Calculate the pressure loss due to friction of compressed air flowing through the surface gas transport channel;

[0112] The frictional loss pressure of compressed air flowing through the surface gas transport channel is calculated by the following equation:

[0113]

[0114] In the formula, Δp gf1 —Frictional loss pressure of compressed air at ground level in the gas transmission channel, Pa;

[0115] γ g1 —Specific weight of compressed air at ground level in the gas transmission channel, N / m³ 3 ;

[0116] L1—Length of the pipe, in meters;

[0117] D1—Diameter of the pipe, in meters;

[0118] V g1 —The velocity of compressed air at the ground surface in the gas delivery channel, m / s;

[0119] f g1 —The friction factor of the surface pipeline is a dimensionless coefficient that depends on the Reynolds number (Re) and the relative roughness of the pipeline.

[0120] Friction factor f g1 Calculated by the following formula:

[0121]

[0122] In the formula, f g1 —Fanning friction coefficient for surface pipelines, dimensionless;

[0123] ε p —The absolute roughness of the pipe is taken as 0.0002m;

[0124] R e,g1 —The Reynolds number of the gas inside the surface pipeline;

[0125] ρ g1 —The density of gas inside surface pipelines is related to pressure and temperature, in kg / m³. 3 ;

[0126] μ g1 — The dynamic viscosity of gas inside a surface pipeline, Pa·s.

[0127] The specific gravity of compressed air at ground level in the gas delivery channel is:

[0128]

[0129] In the formula, —Specific weight of compressed air at ground level in the gas transmission channel, N / m³ 3 ;

[0130] P g1 —Pressure of compressed air on the ground in the air delivery channel, Pa.

[0131] The pressure of compressed air in the surface gas transmission channel can be expressed as the sum of the annular air pressure inside and outside the double-walled drill pipe and the frictional loss pressure of the annular air inside and outside the double-walled drill pipe, which can be calculated by the following formula:

[0132] P g1 =P g0 +ΔP gf0 (twenty one)

[0133] The weight flow rate of compressed air in surface gas transport channels has the following relationship:

[0134] γ g1 Q g1 =wg1=w0=γ0Q0 (22)

[0135] In the formula, W g1 —The weight flow rate of compressed air at ground level in the gas delivery channel, N / s;

[0136] Q g1 —Volume flow rate of compressed air at the surface in the gas delivery channel, m 3 / s.

[0137] After sorting, we get:

[0138]

[0139] Therefore, the flow velocity of compressed air inside the surface gas pipeline can be obtained as follows:

[0140]

[0141] After processing, the frictional loss pressure of compressed air in the surface gas pipeline is obtained as follows:

[0142]

[0143] S4. Calculate the local pressure loss of compressed air from the outer tube of the double-walled drill pipe through the orifice on the gas-liquid mixer;

[0144] Compressed gas enters the central channel of the double-walled drill pipe from the outer tube through an orifice on the gas-liquid mixer, mixing with drilling fluid and cuttings. When the compressed air passes through the orifice, the flow cross-sectional area suddenly decreases, forming a contraction section with the smallest possible flow area, denoted as Ac. The local pressure loss is calculated using the following formula:

[0145]

[0146] When the cross-section contracts, we have:

[0147]

[0148] In the formula, V g0 —The air velocity in the contraction section at the bottom air-water mixer of the double-walled drill pipe is the same as the compressed air velocity in the annular pipe of the inner and outer pipes of the double-walled drill pipe, m / s;

[0149] ξ—is the local friction resistance coefficient;

[0150] A0 / A c —Porosity of the gas-water mixer.

[0151] S5. Calculate the frictional pressure loss of the liquid phase flow in the inner tube of the double-walled drill pipe;

[0152] The pressure loss ΔP due to fluid phase flow friction in the inner tube of the double-walled drill pipe Lf1 The expression is as follows:

[0153]

[0154] In the formula, ρ L —Rinsing fluid density, when the rinsing fluid is clean water, take 1000 kg / m³. 3 ;

[0155] f L1 —Fanning friction coefficient for liquid flow in the inner tube of double-walled drill pipe;

[0156] V L1 —Flow velocity of flushing fluid in the inner tube of the double-walled drill pipe, m / s;

[0157] D dpiid —Inner diameter of the double-walled drill pipe, in meters;

[0158] h dp —Length of the inner tube of the double-walled drill pipe, in meters.

[0159] Fanning coefficient of friction f for liquid phase flow in the inner tube of double-walled drill pipe L1 Calculated by the following formula:

[0160]

[0161] In the formula, R e,l1 —Reynolds number of the flushing fluid in the inner tube of the double-walled drill pipe;

[0162] μ l —The dynamic viscosity of the rinsing fluid is 0.001 Pa·s for water.

[0163] When the air in the outer annulus of the double-walled drill pipe displaces the fluid in the outer annulus, the following occurs:

[0164] Q g0 =Q L (31)

[0165] Therefore, the flow velocity of the flushing fluid in the inner tube of the double-walled drill pipe is:

[0166]

[0167] In summary, the frictional pressure loss P of the liquid phase flow in the inner tube of the double-walled drill pipe Lf1 The expression is as follows:

[0168]

[0169] S6. Calculate the frictional pressure loss of the liquid phase flow in the slag discharge pipeline;

[0170] Liquid phase flow friction pressure loss ΔP in slag discharge pipeline Lf2 The expression is as follows:

[0171]

[0172] In the formula, D0 is the inner diameter of the slag discharge pipeline (m).

[0173] f L2 —Fanning friction coefficient for liquid phase flow in slag discharge pipeline;

[0174] V L2 —Flow rate of flushing fluid in the slag discharge pipeline, m / s;

[0175] h0—Height of the slag discharge pipeline, in meters.

[0176] The van der nigra coefficient f of liquid flow in the slag discharge pipeline L2 Calculated by the following formula:

[0177]

[0178] In the formula, R e,l2 —Reynolds number of liquid phase flow inside the slag discharge pipeline.

[0179] The flow rate of the flushing fluid in the slag discharge pipeline is:

[0180]

[0181] In summary, the frictional pressure loss ΔP during liquid phase flow in the slag discharge pipeline is... Lf2 The expression is as follows:

[0182]

[0183] S7. Calculate the pressure drop of the three-phase flow inside the double-walled drill pipe;

[0184] Parameters that can be directly measured include: rated air supply of the air compressor, air lift reverse circulation flow rate, drilling flushing fluid density, double-wall drill string parameters, and environmental parameters.

[0185] When compressed air enters the inner cavity of the double-walled drill pipe through the annulus between the inner and outer pipes via the gas-water mixer, it rises along with the rock cuttings and flushing fluid within the inner cavity, forming a gas-liquid-solid three-phase mixed flow. The pressure gradient's variation with increasing depth can be approximated as:

[0186]

[0187] In the formula: P t —Three-phase mixed flow pressure, Pa

[0188] γ mix —Specific gravity of three-phase flow, N / m 3 ;

[0189] f t —Fanning friction coefficient for three-phase mixed flow;

[0190] V t —Three-phase flow velocity, m / s;

[0191] g—acceleration due to gravity, m / s² 2 .

[0192] γ mix dh represents the hydrostatic pressure in the inner cavity of the double-walled drill pipe. This represents the pressure loss due to flow friction generated by the fluid flow within the inner cavity of the double-walled drill pipe.

[0193] For a gas-liquid-rock cuttings three-phase mixed flow system, the volume proportion of rock cuttings is small, so it is ignored as a minor factor in the analysis. Therefore, the specific gravity and velocity of the three-phase flow are as follows:

[0194]

[0195] In the formula, w t —Three-phase flow rate, N / s;

[0196] Q L1 —Wellhead flushing fluid volume flow rate, m³ 3 / s;

[0197] f t —Fanning friction coefficient for three-phase mixed flow, dimensionless;

[0198] P atm —Standard atmospheric pressure, taken as 101325 Pa;

[0199] T atm —Atmospheric temperature, °C;

[0200] d dpiid — is the inner diameter of the double-walled drill pipe;

[0201] T g0 —The average thermodynamic temperature, K, inside the annular pipe outside the double-walled drill pipe;

[0202] Q0—Rated air injection capacity of the air compressor, in m³ 3 / min; g—acceleration due to gravity, m / s² 2 .

[0203] The following formula shows the trend of the pressure gradient of the three-phase flow with increasing depth. After integration, the pressure at the bottom of the double-walled drill pipe can be calculated.

[0204]

[0205] S8. Calculate the start-up pressure and the circulating gas supply pressure.

[0206] S801. Calculate starting pressure

[0207] The startup pressure Ps must meet the following requirements:

[0208] P s =ΔP gf +ΔP m +ΔP Lf1 +ΔP Lf2 +P L +P atm (43)

[0209] P L =ρ L g(h dp +h0) (44)

[0210] In the formula, P s —Startup pressure;

[0211] ΔP gf —Frictional loss pressure during compressed air flow, Pa;

[0212] ΔP m —Pressure loss of compressed air passing through the gas-liquid mixer, Pa;

[0213] ΔP Lf1 —Pressure loss due to frictional flow of liquid phase in the inner tube of the double-walled drill pipe, Pa;

[0214] ΔP Lf2 —Pressure loss due to frictional flow in the slag discharge pipeline, Pa;

[0215] P L —Hydrostatic pressure at the bottom of the inner tube of the double-walled drill pipe, Pa;

[0216] P atm —Standard atmospheric pressure, taken as 101325 Pa;

[0217] h dp —Length of the inner tube of the double-walled drill pipe, m; h0—Height of the slag discharge pipeline, m;

[0218] ρ L — Fluid density, kg / m³ 3 .

[0219] S802. Calculate the circulating gas supply pressure

[0220] The circulating gas supply pressure Pc must satisfy the following formula (the calculation methods for gas friction loss pressure in surface pipelines, gas friction loss pressure in the annulus between the inner and outer pipes of the double-wall drill pipe, and pressure loss at the mixer are the same as before):

[0221] P c =ΔP gf +ΔP m +ΔP t +P atm (45)

[0222] In the formula, P c —Circulating gas supply pressure;

[0223] ΔP gf —The frictional loss pressure during compressed air flow (including the frictional loss pressure during compressed air flow in surface pipelines and the frictional loss pressure during compressed air flow in the annulus inside and outside the double-wall drill pipe, i.e., ΔP) gf =ΔP gf1 +ΔP gf0 ), Pa;

[0224] ΔP m —Pressure loss of gas passing through the gas-liquid mixer, Pa;

[0225] ΔP t —Pressure drop of gas-liquid-solid three-phase flow inside the double-walled drill pipe, Pa;

[0226] P atm —Standard atmospheric pressure, taken as 101325 Pa.

[0227] Example

[0228] The equipment used in the calculation mainly includes drilling rigs, air compressors, triangular weir boxes, etc. The parameters of these devices are shown in Tables 1-3.

[0229] Table 1 Equipment Parameter Data Table

[0230]

[0231] Table 2 Gas Flow Pipeline Parameters

[0232]

[0233] Table 3 Drill string assembly parameters

[0234]

[0235] The highest point of the slag discharge pipeline in the gas-lift reverse circulation geothermal well is 20m. Table 4 shows the calculation of different double-wall drill pipe insertion depths and starting pressures for different double-wall drill pipe specifications using the formula in this application. Based on the field test conditions, the surface temperature is approximately 25℃, and the temperature inside the double-wall drill pipe is approximately 20℃; other parameters are consistent with the above conditions.

[0236] Table 4. Startup Pressure Analysis of Kuancheng Air Lift Reverse Cycle

[0237]

[0238] The calculation was performed using a three-phase flow model, taking the air compressor injection pressure and the water return volume at the slag discharge port during the test. It was observed that the water return volume at the slag discharge port also changed when the air compressor injection pressure changed during drilling of each drill rod. Therefore, the submersion depth of different double-wall drill rods was calculated, and the results are shown in Table 5.

[0239] Table 5. Calculation of Gas Pressure at the Bottom of Double-Wall Drill Pipe

[0240]

[0241]

[0242] Figure 4 This diagram illustrates the changes in air compressor supply pressure during the air-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 supply pressure during the circulation process.

[0243] Calculations show that the analysis results for the starting pressure and circulating gas supply pressure are similar to the measured results, and can be used as the calculation method.

[0244] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0245] 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 to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A calculation model for frictional loss pressure during the drilling process in gas lift circulation drilling, characterized in that, The frictional loss pressure includes the frictional loss pressure of compressed air flowing through the outer annulus of the double-walled drill pipe, the frictional loss pressure of compressed air in the surface gas transmission pipeline, the frictional loss pressure of liquid phase flow in the inner tube of the double-walled drill pipe, and the frictional loss pressure of liquid phase flow in the slag discharge pipeline. The calculation model for the frictional loss pressure is as follows: Frictional loss pressure = In the formula, —Frictional loss pressure of compressed air in the outer annulus of the double-walled drill pipe, Pa; —Pressure loss due to friction of compressed air in surface gas pipelines, Pa; P Lf1 —Pressure loss due to frictional flow of liquid phase in the inner tube of the double-walled drill pipe, Pa; P Lf2 —Pressure loss due to frictional flow in the slag discharge pipeline, Pa; The formula for calculating the frictional loss pressure of compressed air in the outer annulus of the double-walled drill pipe is as follows: In the formula, —Pressure of compressed air in the annular pipe outside the double-walled drill pipe, Pa; —The relative density of air, taken as 1.0; —The average thermodynamic temperature, K; R, inside the annulus pipe outside the double-walled drill pipe. e —Engineering gas constant, taken as 29.31 N·m / (N·K); f g0 —Fanning friction coefficient of the outer annulus of the double-walled drill pipe, dimensionless; L dp —Length of the outer annular pipe of the double-walled drill pipe, in meters; —Inner diameter of the outer tube of the double-walled drill pipe, in meters; —Outer diameter of the inner tube of the double-walled drill pipe, in meters; —Standard atmospheric pressure, taken as 101325 Pa; —Atmospheric temperature, °C; Q0—Rated air injection capacity of air compressor, m³ / min; The formula for calculating the frictional pressure loss due to liquid phase flow in the inner tube of the double-walled drill pipe is as follows: In the formula, —Pressure loss due to frictional flow of liquid phase in the inner tube of the double-walled drill pipe, Pa; ρ L —Rinsing fluid density, when the rinsing fluid is clean water, take 1000 kg / m³. 3 ; —Flow rate of flushing fluid in the inner tube of the double-walled drill pipe, m³ / s; D dpiid —Inner diameter of the double-walled drill pipe, in meters; h dp —Length of the inner tube of the double-walled drill pipe, in meters. —Reynolds number of the flushing fluid in the inner tube of the double-walled drill pipe; The formula for calculating the frictional pressure loss during liquid phase flow in the slag discharge pipeline is as follows: In the formula, —Pressure loss due to frictional flow in the slag discharge pipeline; —Reynolds number of liquid phase flow inside the slag discharge pipeline; —Pipe roughness, m; V L2 —Flow velocity of flushing fluid in slag discharge pipeline, m / s; h0—Height of slag discharge pipeline, m; D0—Inner diameter of slag discharge pipeline, m.

2. The friction loss pressure calculation model for gas lift circulation drilling during the drilling process according to claim 1, characterized in that, The frictional loss pressure of the compressed air during its flow in the surface gas pipeline is: In the formula, P gf1 —Frictional loss pressure of compressed air during its flow in surface gas pipelines, Pa; P g1 —Pressure of compressed air at ground level in the gas delivery channel, Pa; —Relative density of air, taken as 1.0; R e —Engineering gas constant, taken as 29.31 N·m / (N·K); —Atmospheric temperature, °C; f g1 —Surface pipeline friction factor, dimensionless; L1—Pipe length, m; D1—Diameter of the pipe, in meters; —Standard atmospheric pressure, taken as 101325Pa; Q0—Rated air injection capacity of air compressor, m³ / min.

3. The friction loss pressure calculation model for gas lift circulation drilling during the drilling process according to claim 2, characterized in that, The flow velocity of the compressed air in the surface gas pipeline is... In the formula, V g1 —The velocity of compressed air inside surface gas pipelines, m / s; Q g1 —Volume flow rate of compressed air at the surface in the gas delivery channel, m 3 / s; Q0—Rated air supply capacity of the air compressor, m 3 / s.

4. The friction loss pressure calculation model for gas lift circulation drilling during the drilling process according to claim 1, characterized in that, The flow rate of the flushing fluid in the inner tube of the double-walled drill pipe is: In the formula, V L1 —Flow rate of flushing fluid in the inner tube of the double-walled drill pipe, m / s.

5. The friction loss pressure calculation model for gas lift circulation drilling during the drilling process according to claim 1, characterized in that, The flow rate of the flushing fluid in the slag discharge pipeline is: In the formula, V L2 —Flow rate of flushing fluid in the slag discharge pipeline, m / s; —Flow rate of flushing fluid in the inner tube of the double-walled drill pipe, m³ / s.

6. The friction loss pressure calculation model for gas lift circulation drilling during the drilling process according to claim 1, characterized in that, The flow velocity of compressed air inside the annular pipe of the double-walled drill pipe is: In the formula, —The velocity of compressed air in the annular pipe between the inner and outer tubes of the double-walled drill pipe, m / s; P g0 —Pressure of compressed air in the outer annulus of the double-walled drill pipe, Pa; Q0—Rated air supply capacity of the air compressor, m³ / s 3 / s.

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