A method for calculating the starting pressure and circulating gas supply pressure in gas lift reverse circulation drilling

Abstract

The present invention discloses a method for calculating the starting pressure and circulating gas supply pressure of gas lift reverse circulation drilling, comprising the following steps: S1. calculating the hydrostatic pressure at the bottom of the inner tube of a double-wall drill pipe; S2. calculating the friction loss pressure of the compressed air in the outer annulus of the double-wall drill pipe; S3. calculating the friction loss pressure of the compressed air flowing through the surface gas transmission channel; S4. calculating the local pressure loss of the compressed air from the outer tube of the double-wall drill pipe through the orifice on the gas-liquid mixer; S5. calculating the friction pressure loss of the liquid phase flow in the inner tube of the double-wall drill pipe; S6. calculating the friction pressure loss of the liquid phase flow in the slag discharge pipeline; S7. calculating the three-phase flow pressure drop in the inner tube of the double-wall drill pipe; S8. calculating the starting pressure and circulating gas supply pressure. The method for calculating the starting pressure and circulating gas supply pressure of gas lift reverse circulation drilling of the present invention can accurately and conveniently calculate the starting pressure and circulating gas supply pressure of gas lift reverse circulation drilling by accurately calculating the pressure of each part of the gas lift reverse circulation drilling process, providing a theoretical basis for the stable and efficient operation of the circulation system.

Description

Technical Field

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

[0002] In geothermal drilling, to reserve sufficient space for submersible pumps and reduce construction risks, wellbores often utilize large-diameter, multi-opening structures. The lower casing is not returned to the wellhead, resulting in a larger annular cross-sectional area in the upper wellbore section. When using positive circulation drilling, large pump volumes of drilling fluid are often required to meet the rock-carrying requirements of the upper, large-diameter wellbore section. To alleviate these issues, gas lift reverse circulation is now widely used for rock drilling. Gas lift reverse circulation technology is used to extract oil, gas, water, and other substances from wells.

[0003] Successfully establishing a gas lift reverse circulation system is crucial for ensuring stable drilling performance. Fluctuations in injection pressure during the startup phase have long been a key area of ​​research for gas lift pump applications. Insufficient injection pressure during the startup phase can lead to repeated rebound in the circulating volume flow rate during drilling, potentially causing drilling accidents such as drill bit blockages and falling cuttings. 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 pipeline leaks and other equipment issues, all of which can contribute to fluctuations in startup pressure.

[0004] The circulating gas supply pressure of the drilling fluid during gas lift reverse circulation drilling reflects the friction pressure loss within the well and is a key indicator of gas lift reverse circulation drilling accidents. Reasonable calculation of the circulating gas supply pressure is essential for stable and efficient operation of the circulation system.

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

[0006] To address the above issues, the present invention proposes a method for calculating the start-up pressure and circulating gas supply pressure in gas lift reverse circulation drilling. The method proposed in the present invention is also applicable to lift technology, which can be used to extract oil, gas, water and other substances from wells.

[0007] The method for calculating the start-up pressure and circulating gas supply pressure of gas lift reverse circulation drilling of the present invention comprises the following steps:

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

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

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

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

[0012] S5. Calculate the frictional pressure loss of the liquid phase flow in the double-wall drill pipe inner tube; S6. Calculate the frictional pressure loss of the liquid phase flow in the slag discharge pipeline;

[0013] S7. Calculate the pressure drop of three-phase flow in the inner tube of double-wall drill pipe;

[0014] S8. Calculate the starting pressure and circulating air supply pressure. The calculation formula for the friction loss pressure of compressed air in the outer annulus of the double-wall drill pipe is: (16)

[0015] Where, —Friction loss pressure of compressed air in the annular pipe outside the double-wall drill pipe, Pa; —Pressure of compressed air in the annular pipe outside the double-wall drill pipe, Pa; —Relative density of air, generally taken as 1.0; —Average thermodynamic temperature in the annulus outside the double-wall drill pipe, K; R e — The engineering gas constant is generally taken as 29.31N·m / (N·K); f g0 —Fanning friction coefficient of the outer annulus of double-wall drill pipe, dimensionless; L dp —The length of the annular pipe outside the double-wall drill pipe, m; —Inner diameter of double-wall drill pipe outer tube, m; —Outer diameter of the inner tube of double-wall drill pipe, m; —Standard atmospheric pressure, 101325Pa; —atmospheric temperature, °C; Q 0 —Rated air injection volume of the air compressor, m³ / min.

[0016] The calculation formula for the friction loss pressure of the compressed air flowing through the surface gas transmission channel is:

[0017] (25)

[0018] Where, P g1 —Pressure of surface compressed air in the gas transmission channel, Pa; —Relative density of air, generally taken as 1.0; R e — The engineering gas constant is generally taken as 29.31 N·m / (N·K); —atmospheric temperature, °C;f g1 —Surface pipeline friction factor, dimensionless; L 1—length of the pipeline, m; D 1—diameter of the pipe, m; —Standard atmospheric pressure, 101325Pa; Q 0 —Rated air injection volume of the air compressor, m³ / min.

[0019] The calculation formula for the local pressure loss of the compressed air from the outer tube of the double-wall drill pipe through the orifice on the gas-liquid mixer is:

[0020] (26)

[0021] Where, —Air velocity at the contraction section of the air-water mixer at the bottom of the double-wall drill pipe, m / s; — is the local friction resistance coefficient; , A0 / A c —Porosity of the air-water mixer.

[0022] The calculation formula for the friction pressure loss of the liquid phase flow in the inner tube of the double-wall drill pipe is:

[0023]

[0024] Where, r L —Density of flushing fluid: when the flushing fluid is water, take 1000kg / m 3 ; —The volume flow rate of compressed air in the outer annulus of 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 tube of the double-wall drill pipe, m³ / s; D dpiid —Inner diameter of double-wall drill pipe, m; h dp —Inner tube length of double-wall drill pipe, m.

[0025] The calculation formula for the flow rate of the flushing fluid in the double-wall drill pipe inner tube is:

[0026]

[0027] Where, Q g0 —Volume flow rate of compressed air in the annular pipe outside the double-wall drill pipe, m 3 / s; Q L is the volume flow rate of the flushing fluid in the inner tube of the double-wall drill pipe, m 3 / s.

[0028] The calculation formula for the friction pressure loss of the liquid phase flow in the slag discharge pipeline is:

[0029]

[0030] Where, R e,l2 —Reynolds number of liquid flow in the slag discharge pipeline; —Pipeline roughness, m; Q g0 —Volume flow rate of compressed air in the annular pipe outside the double-wall drill pipe, m 3 / s; h 0 — Height of slag discharge pipeline, m; D 0 — Inner diameter of slag discharge pipeline, m.

[0031] The three-phase flow pressure drop of the double-wall drill pipe inner tube refers to the following: when compressed air enters the inner cavity of the double-wall drill pipe from the annulus between the inner and outer tubes of the double-wall drill pipe through the gas-water mixer, it will return upward together with the cuttings and 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 increasing depth is:

[0032]

[0033] Where, P t —Three-phase mixed flow pressure, Pa; —Three-phase flow weight flow rate, N / s; Q L1 —Volume flow rate of flushing fluid returned from the wellhead, m 3 / s; f t —Fanning friction coefficient of three-phase mixed flow, dimensionless; —Standard atmospheric pressure, 101325Pa; —atmospheric temperature, °C; d dpiid — is the inner diameter of the double-wall drill pipe, m; —Average thermodynamic temperature in the annulus outside the double-wall drill pipe, K; Q 0 —Rated air injection volume of air compressor, m³ / min; g —Acceleration due to gravity, m / s 2 .

[0034] The calculation formula of the starting pressure is:

[0035]

[0036] Where, P s —Starting pressure; —Friction loss pressure during gas flow, Pa; —Pressure loss of gas passing through the gas-liquid mixer, Pa; —Friction loss pressure of liquid phase flow in the inner tube of double-wall drill pipe, Pa; —Friction loss pressure of liquid phase flow in slag discharge pipeline, Pa; P L —Hydrostatic pressure at the bottom of the inner tube of double-wall drill pipe, Pa; —Standard atmospheric pressure, 101325Pa; h dp —Inner tube length of double-wall drill pipe, m; h 0 —Height of slag discharge pipeline, m; r L —Density of flushing fluid, kg / m³.

[0037] The circulating gas supply pressure

[0038] (45)

[0039] Where, P c —Circulating gas supply pressure; —Friction loss pressure during gas flow, Pa; —Pressure loss of gas passing through the gas-liquid mixer, Pa; —Gas-liquid-solid three-phase flow pressure drop in double-wall drill pipe, Pa; —Standard atmospheric pressure, take 101325Pa.

[0040] The present invention has the beneficial effect of accurately and conveniently calculating the startup pressure and circulating gas supply pressure for gas lift reverse circulation drilling by precisely calculating the pressures of various components of the gas lift reverse circulation drilling process. This provides a theoretical basis for ensuring stable and efficient operation of the circulation system. The invention also assists in pre-drilling design of gas lift reverse circulation drilling processes and in analyzing pressure anomalies during drilling. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a detailed diagram of the layout of gas lift reverse circulation drilling.

[0042] Figure 2 This is a flow chart for calculating the start-up pressure for gas lift reverse circulation drilling.

[0043] Figure 3 This is a flow chart for calculating circulating gas supply pressure in gas lift reverse circulation drilling.

[0044] Figure 4 This is a schematic diagram of the changes in air compressor supply pressure during the gas lift reverse circulation establishment process. DETAILED DESCRIPTION

[0045] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0046] The method for calculating the start-up pressure and circulating gas supply pressure of gas lift reverse circulation drilling of the present invention comprises the following steps:

[0047] First, determine the parameters that can be measured, including: the rated air supply pressure of the air compressor, the inner diameter of the gas pipeline, the specifications of the double-wall drill pipe (including the inner diameter of the double-wall drill pipe outer tube, the outer diameter of the double-wall drill pipe inner tube, and the inner surface of the double-wall drill pipe inner tube), the length of the double-wall drill pipe, the height of the slag discharge pipeline, the dynamic water level in the wellbore, the atmospheric pressure, the atmospheric temperature, and the flushing fluid temperature. These parameters can be obtained through specific measurement and are not difficult to operate.

[0048] S1. Calculate the hydrostatic pressure at the bottom of the inner tube of the double-wall drill pipe; S101. Determine the sinking ratio. The calculation formula for the sinking ratio is: (1) In the formula, h 沉没 —The length of the double-wall drill pipe below the annular water level, m; h 双壁 —Double-wall drill pipe length, m; h 排渣 —Height of slag discharge pipeline, m.

[0049] S102. The height of the static liquid column when the gas lift reverse circulation reaches the starting pressure is calculated as follows:

[0050] For φ168 / 108, φ140 / 89, φ127 / 76 and φ114 / 73 double-wall drill pipes, the height is:

[0051] (2)

[0052] For φ89 / 57 double-wall drill pipe, if the sinking ratio (R) is less than 0.59, the height is:

[0053] (3)

[0054] For φ89 / 57 double-wall drill pipe, if the sinking ratio (R) is greater than or equal to 0.59, the height is:

[0055] (4)

[0056] S103. Hydrostatic pressure is

[0057] (5)

[0058] Where, P L —Hydrostatic pressure at the bottom of the inner tube of double-wall drill pipe, Pa; r L —Liquid density, kg / m³; g—acceleration due to gravity, taken as 9.81 m / s 2 .

[0059] S2. Calculate the friction loss pressure of compressed air in the outer annulus of double-wall drill pipe;

[0060] S201. The pressure loss of compressed air friction in the outer annulus of double-wall drill pipe is calculated using the following equation:

[0061] (6)

[0062] Where, —Friction loss pressure of compressed air in the annular pipe outside the double-wall drill pipe, Pa;

[0063] —The density of compressed air in the annular pipe outside the double-wall drill pipe, N / m 3 ;

[0064] L dp —The length of the annular pipe outside the double-wall drill pipe, m;

[0065] V g0 —Flow rate of compressed air in the annular pipe outside the double-wall drill pipe, m / s.

[0066] f g0 — friction factor, which is a dimensionless coefficient that depends on the Reynolds number (Re) and the relative roughness of the pipe;

[0067] —Inner diameter of double-wall drill pipe outer tube, m;

[0068] —Outer diameter of inner tube of double-wall drill pipe, m.

[0069] S202. The flow of compressed air in the pipeline can be considered turbulent. According to the Haaland relationship:

[0070] (7)

[0071] (8)

[0072] Where, fg0 —Fanning friction coefficient of the outer annulus of double-wall drill pipe, dimensionless;

[0073] —The absolute roughness of the pipeline is 0.0002m;

[0074] R e,g0 —Reynolds number of the gas in the annular pipe outside the double-wall drill pipe;

[0075] r g0 —The density of the gas in the annular pipe outside the double-wall drill pipe is related to pressure and temperature, kg / m³;

[0076] m g0 —The dynamic viscosity of the gas in the annulus outside the double-wall drill pipe. By consulting relevant data, the dynamic viscosity data of air at different temperatures can be obtained, in Pa·s.

[0077] S203. The density of compressed air in the annulus outside the double-wall drill pipe is:

[0078] (9)

[0079] Where, P g0 —Pressure of compressed air in the annular pipe outside the double-wall drill pipe, Pa;

[0080] T g0 —Average thermodynamic temperature in the annulus outside the double-wall drill pipe, K;

[0081] S g —Relative density of air, generally taken as 1.0;

[0082] R e —Engineering gas constant, generally taken as 29.31 N·m / (N·K).

[0083] S204. The density of compressed air in the annulus outside the double-wall drill pipe is:

[0084] (10)

[0085] The air in the pipeline is affected by the back pressure of the fluid in the double-wall drill pipe, which is:

[0086] (11)

[0087] Where, P g0—Pressure of compressed air in the annular pipe outside the double-wall drill pipe, Pa;

[0088] P L —Hydrostatic pressure at the bottom of the inner tube of double-wall drill pipe, Pa.

[0089] S205. The weight flow rate of compressed air has the following relationship:

[0090] (12)

[0091] Where, W g0 —The weight flow rate of compressed air in the annular pipe outside the double-wall drill pipe, N / s;

[0092] —The density of compressed air in the annular pipe outside the double-wall drill pipe, N / m 3 ;

[0093] Q g0 —Volume flow rate of compressed air in the annular pipe outside the double-wall drill pipe, m 3 / s;

[0094] Q 0—Rated air supply volume of the air compressor, m 3 / s;

[0095] w 0 is the weight flow rate of air at the surface, N / s;

[0096] —Air density at surface temperature, N / m 3 .

[0097] (13) In formula, —Atmospheric pressure at surface temperature, Pa;

[0098] —Surface temperature, K.

[0099] After sorting, we get:

[0100] (14)

[0101] Where, Q g0 —Volume flow rate of compressed air in the annular pipe outside the double-wall drill pipe, m 3 / s;

[0102] Therefore, from equations (12), (13), and (14), the flow rate of compressed air in the annulus of the inner and outer tubes of the double-wall drill pipe can be obtained as follows:

[0103] (15)

[0104] In summary, the friction loss pressure of compressed air in the outer annulus of double-wall drill pipe is

[0105] (16)

[0106] S3. Calculate the friction loss pressure of compressed air flowing through the surface gas transmission channel;

[0107] The friction loss pressure of compressed air flowing through the surface gas transmission channel is calculated by the following equation:

[0108] (17)

[0109] Where, —Friction loss pressure of surface compressed air in the gas transmission channel, Pa;

[0110] — The density of surface compressed air in the gas transmission channel, N / m 3；

[0111] L 1—length of the pipeline, m;

[0112] D 1—diameter of the pipe, m;

[0113] V g1 —Flow rate of surface compressed air in the gas transmission channel, m / s;

[0114] f g1 —Surface pipeline friction factor, which is a dimensionless coefficient that depends on the Reynolds number (Re) and the relative roughness of the pipeline.

[0115] Friction factor f g1 Calculated by the following formula:

[0116] (18)

[0117] (19) Where, f g1 —Fanning friction coefficient of surface pipeline, dimensionless;

[0118] —The absolute roughness of the pipeline is 0.0002m;

[0119] R e,g1—Reynolds number of the gas in the surface pipeline;

[0120] r g1 —The density of gas in the surface pipeline, which is related to pressure and temperature, kg / m³;

[0121] m g1 —Dynamic viscosity of gas in surface pipeline, Pa·s.

[0122] The density of surface compressed air in the gas transmission channel is:

[0123] (20)

[0124] Where, —The density of the surface compressed air in the gas transmission channel, N / m 3 ;

[0125] P g1 —Pressure of surface compressed air in the gas transmission channel, Pa.

[0126] The pressure of 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 tubes of the double-wall drill pipe and the air friction loss pressure in the annulus between the inner and outer tubes of the double-wall drill pipe, which can be calculated by the following formula:

[0127] (twenty one)

[0128] The weight flow rate of compressed air in the surface gas transmission channel has the following relationship:

[0129] (twenty two)

[0130] Where, W g1 —The weight flow rate of surface compressed air in the gas transmission channel, N / s;

[0131] Q g1 —Volume flow rate of surface compressed air in the gas transmission channel, m 3 / s.

[0132] After sorting, we get:

[0133] (twenty three)

[0134] Therefore, the flow rate of compressed air in the surface gas pipeline can be obtained as

[0135] (twenty four)

[0136] After sorting, the friction loss pressure of compressed air in the surface gas pipeline is obtained as follows:

[0137] (25)

[0138] S4. Calculate the local pressure loss of compressed air from the outer tube of the double-wall drill pipe through the orifice on the gas-liquid mixer;

[0139] The compressed gas enters the central channel of the double-wall drill pipe from the outer tube through the orifice on the gas-liquid mixer and mixes with the drilling fluid and cuttings. When the compressed air passes through the orifice, the cross-sectional area of ​​the flow suddenly decreases, forming a contraction section with the smallest flow cross-section. Its area is Ac. The local pressure loss calculation formula is:

[0140] (26)

[0141] When the cross section shrinks, there are:

[0142] (27)

[0143] Where, —The air velocity at the contraction section of the air-water mixer at the bottom of the double-wall drill pipe is the same as the compressed air velocity in the annulus of the inner and outer pipes of the double-wall drill pipe, m / s;

[0144] — is the local friction resistance coefficient;

[0145] A0 / A c —Porosity of the gas-water mixer.

[0146] S5. Calculate the frictional pressure loss of the liquid phase flowing in the inner tube of the double-wall drill pipe;

[0147] Friction pressure loss of liquid flow in the inner tube of double-wall drill pipe The expression is as follows:

[0148] (28)

[0149] Where, r L —Density of flushing fluid: when the flushing fluid is clear water, take 1000kg / m 3 ;

[0150] f L1 —Fanning friction coefficient of liquid flow in the inner tube of double-wall drill pipe;

[0151] V L1 —Flow rate of flushing fluid in the inner tube of double-wall drill pipe, m / s;

[0152] D dpiid —Inner diameter of double-wall drill pipe, m;

[0153] h dp —Inner tube length of double-wall drill pipe, m.

[0154] Fanning friction coefficient of liquid flow in the inner tube of double-wall drill pipe f L1 Calculated by the following formula:

[0155] (29)

[0156] (30)

[0157] Where, R e,l1 —Reynolds number of the flushing fluid in the inner tube of the double-wall drill pipe;

[0158] m l —Dynamic viscosity of flushing fluid: 0.001 Pa·s for clean water.

[0159] When 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 are:

[0160] (31)

[0161] Therefore, the flow rate of the flushing fluid in the inner tube of the double-wall drill pipe is:

[0162] (32)

[0163] In summary, the friction pressure loss of the liquid phase flow in the inner tube of the double-wall drill pipe P L f1 The expression is as follows:

[0164] (33)

[0165] S6. Calculate the friction pressure loss of the liquid phase flow in the slag discharge pipeline;

[0166] Friction pressure loss of liquid phase flow in slag discharge pipeline The expression is as follows:

[0167] (34)

[0168] Where, D 0—inner diameter of slag discharge pipeline, m;

[0169] f L2 —Fanning friction coefficient of liquid flow in slag discharge pipeline;

[0170] V L2 —Flow rate of flushing liquid in the slag discharge pipeline, m / s;

[0171] h 0—Slag discharge pipeline height, m.

[0172] Fanning friction coefficient of liquid flow in slag discharge pipeline f L2 Calculated by the following formula:

[0173] (35) (36)

[0174] Where, R e,l2 —Reynolds number of liquid flow in the slag discharge pipeline.

[0175] The flow rate of the flushing liquid in the slag discharge pipeline is:

[0176] (37)

[0177] In summary, the friction pressure loss of the liquid phase flow in the slag discharge pipeline The expression is as follows:

[0178] (38)

[0179] S7. Calculate the pressure drop of three-phase flow in the inner tube of double-wall drill pipe;

[0180] Parameters that can be directly measured include: rated air supply volume of the air compressor, gas lift reverse circulation return flow, drilling flushing fluid density, double-wall drilling tool parameters and environmental parameters.

[0181] When compressed air enters the inner tube cavity of the double-wall drill pipe through the air-water mixer from the annulus between the inner and outer tubes of the double-wall drill pipe, it will return upward along 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 change trend of its pressure gradient with increasing depth can be approximately expressed as:

[0182] (39)

[0183] Where: P t —Three-phase mixed flow pressure, Pa;

[0184] —Three-phase flow density, N / m 3 ;

[0185] f t —Fanning friction coefficient of three-phase mixed flow;

[0186] V t —Three-phase flow velocity, m / s;

[0187] g—acceleration due to gravity, m / s 2 .

[0188] It represents the hydrostatic pressure in the inner cavity of the double-wall drill pipe. It represents the flow friction loss pressure caused by the fluid flow in the inner cavity of the double-wall drill pipe inner tube.

[0189] For the gas-liquid-cuttings three-phase mixed flow system, the volume proportion of cuttings is very small, so it is regarded as a secondary factor and ignored in the analysis process. The density and flow rate of the three-phase flow are:

[0190] (40)

[0191] (41)

[0192] In the formula —Three-phase flow weight flow rate, N / s;

[0193] Q L1 —Volume flow rate of flushing fluid returned from the wellhead, m 3 / s;

[0194] f t —Fanning friction coefficient of three-phase mixed flow, dimensionless;

[0195] —Standard atmospheric pressure, 101325Pa;

[0196] —atmospheric temperature, °C;

[0197] d dpiid — is the inner diameter of the double-wall drill pipe inner tube;

[0198] —Average thermodynamic temperature in the annulus outside the double-wall drill pipe, K;

[0199] Q 0 —Rated air injection volume of air compressor, m³ / min;

[0200] g —Acceleration due to gravity, m / s 2 .

[0201] The pressure gradient of the three-phase flow changes with increasing depth as shown in the following formula. After integration, the bottom pressure of the double-wall drill pipe can be calculated:

[0202] (42)

[0203] S8. Calculate the starting pressure and circulating air supply pressure.

[0204] S801. Calculate starting pressure

[0205] The starting pressure Ps must meet the following requirements:

[0206]

[0207] Where, P s —Starting pressure;

[0208] —Friction loss pressure during compressed air flow, Pa; —Pressure loss of compressed air passing through the gas-liquid mixer, Pa;

[0209] —Friction loss pressure of liquid phase flow in the inner tube of double-wall drill pipe, Pa;

[0210] —Friction loss pressure of liquid phase flow in slag discharge pipeline, Pa;

[0211] P L —Hydrostatic pressure at the bottom of the inner tube of double-wall drill pipe, Pa;

[0212] —Standard atmospheric pressure, 101325Pa;

[0213] h dp —Inner tube length of double-wall drill pipe, m h 0 —Height of slag discharge pipeline, m;

[0214] r L —Density of flushing fluid, kg / m³.

[0215] S802. Calculate circulating air supply pressure

[0216] The circulating gas supply pressure Pc must satisfy the following formula (the calculation method for the gas friction loss pressure in the surface pipeline, the gas friction loss pressure in the annulus of the inner and outer pipes of the double-wall drill pipe, and the pressure loss at the mixer is the same as before):

[0217] (45)

[0218] Where, P c —Circulating gas supply pressure; —Friction loss pressure during compressed air flow (including friction loss pressure during compressed air flow in surface pipelines and friction loss pressure during compressed air flow in the annulus of double-wall drill pipe inner and outer pipes, i.e. ), Pa;

[0219] —Pressure loss of gas passing through the gas-liquid mixer, Pa;

[0220] —Gas-liquid-solid three-phase flow pressure drop in double-wall drill pipe, Pa;

[0221] —Standard atmospheric pressure, take 101325Pa.

[0222] Example

[0223] 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.

[0224] Table 1 Equipment parameter data table

[0225]

[0226] Table 2 Gas flow pipeline parameters

[0227]

[0228] Table 3 Drilling tool assembly parameters

[0229]

[0230] 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.

[0231] Table 4 Kuancheng gas lift reverse circulation startup pressure analysis table

[0232]

[0233] 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.

[0234] Table 5 Calculation table of gas pressure at the bottom of double-wall drill pipe

[0235]

[0236] 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.

[0237] 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.

[0238] In the present invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations 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 appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless they are mutually inconsistent.

[0239] Although the above embodiments have been shown and described, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those skilled in the art are all within the scope of protection of the present invention.

Claims

1. A method for calculating the start-up pressure and circulating gas supply pressure of gas lift reverse circulation drilling, characterized in that: The following steps are involved: S1. Calculate the hydrostatic pressure at the bottom of the inner tube of the double-wall drill pipe; S2. Calculate the friction loss pressure of compressed air in the outer annulus of double-wall drill pipe; S3. Calculate the friction loss pressure of compressed air flowing through the surface gas transmission channel; S4. Calculate the local pressure loss of compressed air from the outer tube of the double-wall drill pipe through the orifice on the gas-liquid mixer; The calculation formula for the local pressure loss of the compressed air from the outer tube of the double-wall drill pipe through the orifice on the gas-liquid mixer is: Where ΔP m —Pressure loss of compressed air passing through the gas-liquid mixer, Pa; V g0 —Air velocity at the contraction section of the air-water mixer at the bottom of the double-wall drill pipe, m / s; ξ—is the local friction resistance coefficient; A0 / A c —Porosity of the gas-water mixer; S5. Calculate the frictional pressure loss of the liquid phase flowing in the inner tube of the double-wall drill pipe; S6. Calculate the friction pressure loss of the liquid phase flow in the slag discharge pipeline; S7. Calculate the pressure drop of three-phase flow in the inner tube of double-wall drill pipe; The three-phase flow pressure drop of the double-wall drill pipe inner tube refers to the following: when compressed air enters the inner cavity of the double-wall drill pipe from the annulus between the inner and outer tubes of the double-wall drill pipe through the gas-water mixer, it will return upward together with the cuttings and 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 increasing depth is: Where, P t —Three-phase mixed flow pressure, Pa; w t —Three-phase flow weight flow rate, N / s; Q L1 —Volume flow rate of flushing fluid returned from the wellhead, m 3 / s;f t —Fanning friction coefficient of three-phase mixed flow, dimensionless; P atm —Standard atmospheric pressure, take 101325Pa; T atm —Atmospheric temperature, °C; d dpiid — is the inner diameter of the double-wall drill pipe, m; T g0 —Average thermodynamic temperature in the annulus outside the double-wall drill pipe, K; Q0—Rated gas injection volume of the air compressor, m 3 / min; g—acceleration due to gravity, m / s 2 ; S8. Calculate the starting pressure and circulating gas supply pressure; The calculation formula of the starting pressure is: P s =ΔP gf0 +ΔP gf1 +ΔP m +ΔP Lf1 +ΔP Lf2 +PL+Patm Where, P s —Starting pressure; ΔP gf0 —Friction loss pressure of compressed air in the annulus outside the double-wall drill pipe, Pa; ΔP gf1 —Friction loss pressure of compressed air in surface gas pipeline, Pa; ΔP m —Gas pressure loss through the gas-liquid mixer, Pa; ΔP Lf1 —Friction loss pressure of liquid phase flow in double-wall drill pipe inner tube, Pa; ΔP Lf2 —Friction loss pressure of liquid phase flow in slag discharge pipeline, Pa; P L —Hydrostatic pressure at the bottom of the inner tube of double-wall drill pipe, Pa; P atm —Standard atmospheric pressure, 101325Pa; The circulating gas supply pressure P c =ΔP gf0 +ΔP gf1 +ΔP m +ΔP t +P atm Where, P c —Circulating air supply pressure; ΔP t —Pressure drop of gas-liquid-solid three-phase flow in double-wall drill pipe, Pa.

2. The method for calculating the starting pressure and circulating gas supply pressure of gas lift reverse circulation drilling according to claim 1, characterized in that: The calculation formula for the friction loss pressure of compressed air in the outer annulus of the double-wall drill pipe is: Where ΔP gf0 —Friction loss pressure of compressed air flowing in the annular pipe outside the double-wall drill pipe, Pa; p g0 —Pressure of compressed air in the annulus outside the double-wall drill pipe, Pa; S g —Relative density of air, take 1.0; T g0 —Average thermodynamic temperature in the annulus outside the double-wall drill pipe, K; R e —Engineering gas constant, take 29.31N·m / (N·K); f g0 —Fanning friction coefficient of the outer annulus of double-wall drill pipe, dimensionless; L dp —The length of the annular pipe outside the double-wall drill pipe, m; D dpoid —Inner diameter of double-wall drill pipe outer tube, m; D dpiod —Outer diameter of inner tube of double-wall drill pipe, m; P atm —Standard atmospheric pressure, take 101325Pa; T atm —Atmospheric temperature, °C; Q0—Rated air injection volume of air compressor, m 3 / min.

3. The method for calculating the starting pressure and circulating gas supply pressure of gas lift reverse circulation drilling according to claim 1, characterized in that: The calculation formula for the friction loss pressure of the compressed air flowing through the surface gas transmission channel is: Where ΔP gf1 —Friction loss pressure of compressed air flowing in surface pipelines, Pa; P g1 —Pressure of surface compressed air in the gas transmission channel, Pa; S g —Relative density of air, take 1.0; R e —Engineering gas constant, take 29.31N·m / (N·K); T atm —Atmospheric temperature, °C; f g1 —Surface pipeline friction factor, dimensionless; L1—length of pipeline, m; D1—diameter of the pipe, m; P atm —Standard atmospheric pressure, take 101325Pa; Q0—rated air injection volume of air compressor, m 3 / min.

4. The method for calculating the starting pressure and circulating gas supply pressure of gas lift reverse circulation drilling according to claim 1, characterized in that: The calculation formula for the friction pressure loss of the liquid phase flow in the inner tube of the double-wall drill pipe is: Where ΔP Lf1 —Friction loss pressure of liquid phase flow in double-wall drill pipe inner tube, Pa; ρ L —Density of flushing fluid: when the flushing fluid is clear water, take 1000kg / m 3 ;Q g0 —Flow rate of flushing fluid in the inner tube of double-wall drill pipe, m 3 / s;D dpiid —Inner diameter of double-wall drill pipe, m; h dp —Double-wall drill pipe inner tube length, m, R e,l1 —Reynolds number of the flushing fluid in the inner tube of the double-wall drill pipe.

5. The method for calculating the starting pressure and circulating gas supply pressure of gas lift reverse circulation drilling according to claim 4, characterized in that: The calculation formula for the flow rate of the flushing fluid in the double-wall drill pipe inner tube is: Where V L1 —Flow rate of flushing fluid in the inner tube of double-wall drill pipe, m / s; Q g0 —Volume flow rate of flushing fluid in the annular pipe outside the double-wall drill pipe, m 3 / s;Q L is the volume flow rate of the flushing fluid in the inner tube of the double-wall drill pipe, m 3 / s;D dpiid —Inner diameter of double-wall drill pipe inner tube, m.

6. The method for calculating the start-up pressure and circulating gas supply pressure of gas lift reverse circulation drilling according to claim 1, characterized in that: The calculation formula for the friction pressure loss of the liquid phase flow in the slag discharge pipeline is: Where ΔP Lf2 —Frictional pressure loss of liquid phase flow in slag discharge pipeline; R e,l2 —Reynolds number of liquid phase flow in the slag discharge pipeline; ε p —Pipeline roughness, m; V L2 —Flow rate of flushing liquid in the slag discharge pipeline, m / s, h0—height of slag discharge pipeline, m; D0—inner diameter of slag discharge pipeline, m.

7. The method for calculating the start-up pressure and circulating gas supply pressure of gas lift reverse circulation drilling according to claim 1, characterized in that: The calculation formula of the starting pressure also includes P L =ρ Lg (h) dp +h0) Where, P L —Hydrostatic pressure at the bottom of the inner tube of double-wall drill pipe, Pa; h dp —Inner tube length of double-wall drill pipe, m; h0—Height of slag discharge pipeline, m; ρ L —Density of flushing fluid, kg / m 3 .

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