Drilling fluid flow calculation method for gas lift reverse circulation drilling

Abstract

The invention discloses a drilling fluid flow calculation method for gas lift reverse circulation drilling. The drilling fluid flow calculation method comprises the following steps: S1, defining a gas lift reverse circulation lifting force and friction loss pressure model; s2, assuming that the drilling fluid flow in the circulation process is Qm; s3, calculating the total friction pressure of gas lift reverse circulation; s4, calculating the gas lift reverse circulation lifting force; and S5, according to the gas-lift reverse circulation lifting force and the gas-lift reverse circulation total friction force, the upward backflow amount of the drilling fluid is calculated. According to the invention, by inputting the gas lift reverse circulation well depth structure and the drilling related parameters, the influence of the gas lift reverse circulation well depth structure and the drilling related parameters on the backflow amount of the drilling fluid is researched, so that the optimal operation parameters of the optimal gas lift reverse circulation are obtained. According to the method, parameters of the air compressor air supply amount, the double-wall drill rod tripping-in depth, the double-wall drill rod specification and the single-wall drill rod specification selected for drilling of the gas lift reverse circulation geothermal well drilling can be optimized, and a reasonable theoretical basis is provided for more reasonably achieving gas lift reverse circulation drilling.

Description

Technical Field

[0001] This invention belongs to the field of geothermal drilling technology, specifically relating to a method for calculating drilling fluid flow rate in gas lift reverse circulation drilling. Background Technology

[0002] With increasing human demand for geothermal energy, gas lift reverse circulation drilling technology, which can protect geothermal reservoirs and reduce costs, has gradually become a key technology for geothermal energy development and utilization. Gas lift reverse circulation drilling uses water as the drilling fluid and injects compressed air through a double-walled drill string. The compressed air expands within the drill string, carrying water and cuttings from inside the drill string to the wellhead in a reverse circulation manner. Using gas lift reverse circulation technology to extract oil, water, and other substances from the well, the drilling fluid flow rate can reflect whether there is leakage or formation water intrusion, thus assessing the formation conditions downhole. Simultaneously, the drilling fluid flow rate can be used to calculate the cuttings return rate, which is also important for determining whether the cuttings at the bottom of the well have been properly cleared and for controlling the circulation and cleaning time.

[0003] Currently, the calculation of drilling fluid return flow rate in gas lift reverse circulation is mainly based on a two-phase flow model within the annulus and drill pipe. This calculation, under specific injection parameters (gas volume, fluid volume, injection pressure, well depth, etc.), determines the flow rate of the mixture within the drill pipe and the average return velocity. However, existing calculation processes do not consider the influence of well depth, wellbore structure, and drill string assembly. Therefore, the actual drilling fluid return flow rate in practical gas lift reverse circulation drilling operations is only a reference value. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a method for calculating drilling fluid flow rate in gas lift reverse circulation drilling. This invention considers the influence of well depth, wellbore structure, drill string assembly, and drill string specifications on the drilling fluid return flow rate, and couples the lift force and total frictional pressure loss of gas lift reverse circulation, resulting in a smaller error in the calculated drilling fluid return flow rate.

[0005] The drilling fluid flow rate calculation method for gas lift reverse circulation drilling of the present invention includes the following steps: S1. Define the air lift reverse circulation lifting force and friction loss pressure model; S2. Assume the drilling fluid flow rate during the circulation process is... Q m ; S3. Calculate the total frictional pressure of the air-lift reverse circulation; S4. Calculate the air lift reverse circulation lifting force; S5. Calculate the drilling fluid return flow rate based on the gas lift reverse circulation lifting force and the total friction force of the gas lift reverse circulation.

[0006] The air lift reverse circulation lifting force model is as follows: (5) In the formula,P lift The air lift reverse circulation lifting force is measured in MPa. P ams The hydrostatic pressure, in MPa, is the section from the annular mixer between the double-walled drill pipe and the well wall to the wellhead. P ims The hydrostatic pressure at the mixer inside the double-walled drill pipe is measured in MPa.

[0007] The airlift reverse circulation friction loss pressure model is as follows: (6) In the formula, P f The pressure of the total frictional loss of the circulating fluid in the wellbore during gas lift reverse circulation drilling is expressed in MPa. P af The total frictional loss pressure in the annulus is expressed in MPa. ΔP bit The pressure is the frictional loss pressure of the drill bit, in MPa; P irf The pressure is the frictional loss pressure inside the tail rod section, in MPa; P imf The frictional loss pressure in the upper section of the mixer inside the double-walled drill pipe is measured in MPa.

[0008] The formula for calculating the total frictional loss pressure in the annulus is as follows: (7) In the formula, H i The length of the annular segment with the same annular diameter, in meters (m). D hi — is the wellbore diameter for the same annulus diameter, in meters; D pi For drill pipes with the same annular diameter, the diameter is in meters (m). f Li For the same annular diameter, the Fanning friction coefficient is dimensionless; V Li The velocity of drilling fluid with the same annular diameter is expressed in m / s.

[0009] The formula for calculating the frictional loss pressure of the drill bit is as follows: (11) In the formula, ΔP bit The pressure loss generated by drilling fluid passing through the drill bit water holes is Pa; k is the number of drill bit water holes of the same diameter, dimensionless. D i Let be the diameter of the water inlet of the i-th drill bit, in meters.

[0010] The formula for calculating the frictional loss pressure of the inner tube of the tail rod section is as follows: (12) In the formula, h i The length of the tailpipe section with the same inner diameter is in meters (m). D pi Let be the inner diameter of the tailpipe, in meters (m). f li is the Fanning friction coefficient of the fluid inside the tailpipe, which is dimensionless; V li The velocity of the drilling fluid in the tailpipe is m / s.

[0011] The formula for calculating the frictional loss pressure of the upper section of the mixer in the inner tube of the double-walled drill pipe is as follows: (20) In the formula, The mass flow rate is for three-phase flow, in N / s; Q g Air supply volume for the air compressor, m 3 / s; Q m The volumetric flow rate of drilling fluid returned from the wellhead, in m 3 / s; h 0 represents the center line from the dynamic water level to the highest point of the bend in the gas faucet pipe; P Let be the pressure at any point inside the inner cavity of the double-walled drill pipe, in Pa; T g The atmospheric thermodynamic temperature at the wellhead, in K; T av The average atmospheric thermodynamic temperature of the three-phase flow is K; P g The local atmospheric pressure is expressed in Pa.

[0012] The formula for calculating the hydrostatic pressure at the mixer inside the double-walled drill pipe is as follows: (twenty two) (twenty four) In the formula, γ mix The specific gravity of the three-phase mixed flow is N / m³. 3 ; h 0 represents the center line from the dynamic water level to the center line of the highest point of the air faucet bend; h 1 represents the submersion depth of the air-water mixer below the dynamic water level, in meters (m). The mass flow rate is for three-phase flow, in N / s; Q The air volume flow rate at any point inside the inner cavity of the double-walled drill pipe is given in m. 3 / s.

[0013] The formula for calculating the airlift reverse circulation lifting force is as follows: (34) In the formula, γ l The specific gravity of the annular drilling fluid, N / m 3 ; h 0 represents the center line from the dynamic water level to the highest point of the bend in the gas faucet pipe; h 1 represents the submersion depth of the air-water mixer below the dynamic water level, in meters (m). The mass flow rate is for three-phase flow, in N / s; Q g Air supply volume for the air compressor, m 3 / s; Q m The volumetric flow rate of drilling fluid returned from the wellhead, in m 3 / s; P Let be the pressure at any point inside the inner cavity of the double-walled drill pipe, in Pa; T g The atmospheric thermodynamic temperature at the wellhead, in K; T av The average atmospheric thermodynamic temperature of the three-phase flow is K; P g The local atmospheric pressure is expressed in Pa.

[0014] S5 refers to the fact that, according to the gas lift reverse circulation principle, since the lifting force generated by gas injection mainly overcomes the frictional pressure loss caused by the upward flow of drilling fluid, the difference is zero during normal drilling, i.e.: (4) By substituting the relevant drilling parameters into the formula, the drilling fluid return flow rate under the corresponding conditions can be obtained, i.e., the volumetric flow rate of the drilling fluid returning from the wellhead. Q m .

[0015] The beneficial effects of this invention are: 1. This invention studies the influence of inputting gas lift reverse circulation well depth structure and drilling-related parameters on drilling fluid return flow rate in order to obtain the optimal operating parameters for gas lift reverse circulation.

[0016] 2. This invention can optimize the parameters of air compressor supply, double-wall drill pipe insertion depth, double-wall drill pipe specifications, and single-wall drill pipe specifications for gas lift reverse circulation geothermal drilling, providing a reasonable theoretical basis for more rationally realizing gas lift reverse circulation drilling.

[0017] 3. This invention can analyze the upward flow rate of drilling fluid during gas lift reverse circulation drilling, and can estimate the formation water output, providing a reference value for subsequent pumping applications of geothermal wells.

[0018] 4. This invention considers the influence of well depth, well structure, drill string assembly, and drill string specifications on the drilling fluid return flow rate, and couples the lifting force of gas lift reverse circulation with the total friction pressure loss, resulting in a smaller error in the calculated drilling fluid return flow rate. Attached Figure Description

[0019] Figure 1 This is a diagram illustrating the working principle and supporting facilities of the air-lift reverse circulation system of this invention.

[0020] Figure 2 This is a schematic diagram of the air-lift reverse circulation theoretical mechanism of the present invention.

[0021] Figure 3 This invention relates to the calculation process for the upward flow rate of air-lift reverse circulation drilling fluid.

[0022] Figure 4 This is a comparison chart of test data and simulation calculations of drilling fluid return flow rate when using different single-wall drill pipes in Xiong'an D19 well according to an embodiment of the present invention. Detailed Implementation

[0023] 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.

[0024] like Figure 3 As shown, the drilling fluid flow rate calculation method for gas lift reverse circulation drilling of the present invention includes the following steps: S1. Define the air lift reverse circulation lifting force and friction loss pressure model; like Figure 2 As shown, according to the principle of fluid continuity, the pressure of the drilling fluid in the wellbore of a gas-lift reverse circulation drilling well is continuous, that is, the annular bottomhole pressure is equal to the bottomhole pressure inside the drill string, which can be described by the following formula: (1) In the formula, P b The bottom hole pressure is in MPa. P ab The pressure at the bottom of the annulus well is MPa. P ib The bottom hole pressure is the pressure inside the drill string, in MPa.

[0025] Specifically, the pressure at the bottom of the annulus well. P ab for: (2) In the formula, P ams The hydrostatic pressure, in MPa, is the section from the annular mixer between the double-walled drill pipe and the well wall to the wellhead. Pamf The frictional loss pressure in the upper section of the annular mixer between the double-walled drill pipe and the well wall, in MPa; P ars The hydrostatic pressure in the annulus section from the drill bit to the gas-water mixer, in MPa; P arf The frictional loss pressure in the annulus section from the drill bit to the gas-water mixer, in MPa; P g Atmospheric pressure, MPa; P af The total frictional loss pressure in the annulus is P amf and P arf The sum of these values ​​is MPa.

[0026] Drill string bottom hole pressure P ib It can be described by the following formula: (3) In the formula, P ims The hydrostatic pressure at the mixer inside the double-walled drill pipe, in MPa; P imf The frictional loss pressure of the upper section of the mixer in the inner tube of the double-walled drill pipe is expressed in MPa. P irs The hydrostatic pressure of the tail rod section is MPa; P irf The pressure is the frictional loss pressure inside the tail rod section, in MPa; ΔP bit The pressure is the frictional loss pressure of the drill bit, in MPa.

[0027] Simplifying the above formulas, since P irs = P ars We can obtain the following formula: (4) The left side of the equal sign represents the difference between the hydrostatic pressure of the annulus fluid between the drill string and the wellbore at the gas-water mixer of the double-walled drill pipe and the hydrostatic pressure of the three-phase fluid (gas, liquid, and solid) inside the double-walled drill pipe. This difference is defined as the lifting force of the gas lift reverse circulation. P lift : (5) In the formula, P lift The air lift reverse circulation lifting force is measured in MPa. P ams The hydrostatic pressure, in MPa, is the section from the annular mixer between the double-walled drill pipe and the well wall to the wellhead. P imsThe hydrostatic pressure at the mixer inside the double-walled drill pipe is measured in MPa.

[0028] The right side of the equals sign represents the total frictional loss pressure of the circulating fluid within the wellbore during gas lift reverse circulation drilling. P f : (6) In the formula, P f The pressure of the total frictional loss of the circulating fluid in the wellbore during gas lift reverse circulation drilling is expressed in MPa. P af The total frictional loss pressure in the annulus is expressed in MPa. ΔP bit The pressure is the frictional loss pressure of the drill bit, in MPa; P irf The pressure is the frictional loss pressure inside the tail rod section, in MPa; P imf The frictional loss pressure in the upper section of the mixer inside the double-walled drill pipe is measured in MPa.

[0029] S2. Assume the drilling fluid flow rate during the circulation process is... Q m ; S3. Calculate the total frictional pressure of the air-lift reverse circulation; S301. Since the annulus contains only drilling fluid in deep geothermal well gas lift reverse circulation drilling, the formula for calculating the total annulus friction loss pressure is: (7) In the formula, H i The length of the annular segment with the same annular diameter, in meters (m). D hi — is the wellbore diameter for the same annulus diameter, in meters; D pi For drill pipes with the same annular diameter, the diameter is in meters (m). f Li For the same annular diameter, the Fanning friction coefficient is dimensionless; V Li The velocity of drilling fluid with the same annular diameter is expressed in m / s.

[0030] The Fanning friction coefficient of each annular segment is determined by the Reynolds number of that segment: (8) In the formula, N Ri The dimensionless Reynolds number for the two-phase flow in each segment of the annulus; u is the kinematic viscosity of the drilling fluid, m 2 / s.

[0031] likeN Ri If it is less than 2000, then: (9) like N Ri If it is greater than 2000, then: (10) In the formula, e p This refers to the roughness of the drill pipe's outer wall. D h Let the diameter of the annulus be m; D p Where is the drill pipe diameter, in meters (m). For annular flow, it is generally taken as 0.0002 m.

[0032] S302. When drilling fluid enters the drill string cavity through the annulus via the drill bit's water holes, pressure loss occurs due to friction, causing the pressure at the bottom of the tail rod to be lower than the bottom hole pressure. Assuming a water hole efficiency of 0.95, the formula for calculating the frictional pressure loss of drilling fluid through the drill bit is as follows: (11) In the formula, ΔP bit The pressure loss generated by drilling fluid passing through the drill bit water holes is Pa; k is the number of drill bit water holes of the same diameter, dimensionless. D i Let the diameter of the water inlet of the i-th drill bit be m; The specific gravity of drilling fluid is N / m³. 3 .

[0033] S303. The formula for calculating the frictional loss pressure of the inner tube of the tail rod section is as follows: (12) In the formula, h i The length of the tailpipe section with the same inner diameter is in meters (m). d pi Let be the inner diameter of the tailpipe, in meters (m). f li is the Fanning friction coefficient of the fluid inside the tailpipe, which is dimensionless; V li The velocity of the drilling fluid in the tailpipe is m / s.

[0034] The Fanning friction coefficient of the fluid inside the tailpipe is determined by the Reynolds number: (13) In the formula, N ri The dimensionless two-phase Reynolds number is denoted by ν, where ν is the kinematic viscosity of the drilling fluid (m). 2 / s.

[0035] like N ri If it is less than 2000, then: (14) like N ri If it is greater than 2000, then: (15) In the formula, e p This refers to the roughness of the inner wall of the drill pipe. It is generally taken as 0.0002 μm.

[0036] S304. Pressure loss due to friction in the inner tube of the mixer in double-walled drill pipe. P imf for: (16) In the formula, f is the Fanning friction coefficient at the mixer inside the double-walled drill pipe, which is dimensionless; V The three-phase flow velocity at this pressure is expressed in m / s. d Let be the inner diameter of the double-walled drill pipe, in meters (m). The specific gravity of the three-phase mixed flow is N / m³. 3 .

[0037] Since the density of the gas-liquid-solid three-phase flow within the double-walled drill pipe changes with pressure, the frictional pressure gradient of the three-phase flow can be approximated by the three-phase flow frictional loss pressure formula as the depth increases, as follows: (17) The velocity of the three-phase flow can be obtained using the following formula: (18) The Fanning friction coefficient of three-phase flow is determined by the Reynolds number: (19) In the formula, N R The Reynolds number for a three-phase flow is dimensionless. u Let m be the kinematic viscosity of the three-phase flow. 2 / s.

[0038] The formula for calculating the frictional loss pressure in the upper section of the mixer within the double-walled drill pipe is as follows: (20) In the formula, The mass flow rate is for three-phase flow, in N / s; Q g Air supply volume for the air compressor, m3 / s; Q m The volumetric flow rate of drilling fluid returned from the wellhead, in m 3 / s; h 0 represents the center line from the dynamic water level to the highest point of the bend in the gas faucet pipe; P Let be the pressure at any point inside the inner cavity of the double-walled drill pipe, in Pa; T g The atmospheric thermodynamic temperature at the wellhead, in K; T av The average atmospheric thermodynamic temperature of the three-phase flow is K; P g The local atmospheric pressure is expressed in Pa.

[0039] S4. Calculate the air lift reverse circulation lifting force; S401. Hydrostatic pressure at the outer annulus mixer of the double-walled drill pipe. P ams The pressure is generated by the weight of the drilling fluid in the annulus and is calculated by the following formula: (twenty one) In the formula, γ l The specific gravity of the annular drilling fluid, N / m 3 ; h 1 represents the submersion depth of the air-water mixer below the dynamic water level, in meters (m).

[0040] The formula for calculating the hydrostatic pressure at the mixer in the inner tube of the S402 double-walled drill pipe is as follows: (twenty two) In the formula, γ mix The specific gravity of the three-phase mixed flow is N / m³. 3 ; h 0 represents the centerline of the water level from the highest point of the bend in the gas faucet pipe. 。

[0041] Since the density of the gas-liquid-cuttings three-phase flow within the double-wall drill pipe varies with pressure, the hydrostatic pressure gradient of the three-phase flow can be approximated by the hydrostatic column pressure formula for three-phase flow as depth increases: (twenty three) For a three-phase mixed flow system of gas, liquid, and rock cuttings, the volume proportion occupied by rock cuttings is extremely small, and therefore can be ignored in the analysis. The specific gravity of the three-phase flow can then be expressed as: (twenty four) In the formula, The mass flow rate is for three-phase flow, in N / s; QThe air volume flow rate at any point inside the inner cavity of the double-walled drill pipe is given in m. 3 / s; Q g Air supply volume for the air compressor, m 3 / s; Q m The volumetric flow rate of drilling fluid returned from the wellhead, in m 3 / s; P Let be the pressure at any point inside the inner cavity of the double-walled drill pipe, in Pa; T g The atmospheric thermodynamic temperature at the wellhead, in K; T av The average atmospheric thermodynamic temperature of the three-phase flow is K; P g The local atmospheric pressure is expressed in Pa.

[0042] Among them, the three-phase flow weight flow rate in the inner cavity of the double-walled drill pipe It can be represented as (25) In the formula, The air mass flow rate entering the compressor, in N / s; The value is the drilling fluid weight flow rate, in N / s; denoted as the weight flow rate of rock cuttings, in N / s.

[0043] Specifically, the weight flow rate of the air entering the compressor for: (26) In the formula, Q g The volumetric flow rate of air entering the compressor, m 3 / s; γ g The specific gravity of the air entering the air compressor, in N / m³. 3 ; Specifically, the density of the air entering the air compressor equipment γ g for: (27) In the formula, P g The local atmospheric pressure is in Pa. S g Let S be the relative density of the gas, and for air under standard conditions, S = 1.0; R e This is the engineering gas constant, typically taken as 29.31 N·m / (N·K); T g The atmospheric thermodynamic temperature at the wellhead is K.

[0044] Specifically, the atmospheric thermodynamic temperature at the wellhead T g for: (28) In the formula, t g —Atmospheric temperature at the wellhead, °C.

[0045] Weight flow rate of drilling fluid in the inner cavity of double-walled drill pipe for: (29) In the formula, The value is the drilling fluid weight flow rate, in N / s; γ m The specific gravity of drilling fluid is N / m³. 3 .

[0046] Cuttings weight flow rate in the inner cavity of double-wall drill pipe for : (30) In the formula, D b The diameter of the wellbore is in meters (m). γ w The unit weight of rock cuttings, N / m 3 ; ROP The value is the mechanical drilling speed, in m / s.

[0047] The average relative density of sedimentary rocks is approximately 2.7. If the strata encountered during drilling are igneous or metamorphic rocks, their average relative densities are 2.8 and 3.0, respectively.

[0048] Based on the equivalent relationship between the specific gravity, volumetric flow rate, and weight flow rate of gas at any point inside the inner cavity of the double-walled drill pipe. (31) In the formula, γ The specific weight of air at any point inside the inner cavity of the double-walled drill pipe, in N / m³. 3 ; The air volume flow rate Q at any point in the inner tube of the double-walled drill pipe can be obtained as: (32) In the formula, T av The average atmospheric thermodynamic temperature of the three-phase flow is K; Specifically, the average atmospheric thermodynamic temperature of the three-phase flow T av for: (33) In the formula, t av The average temperature of the three-phase flow is ℃.

[0049] Finally, the formula for calculating the air lift reverse circulation lift force can be obtained as follows: (34) In the formula, γ l The specific gravity of the annular drilling fluid, N / m 3 ; h 0 represents the center line from the dynamic water level to the highest point of the bend in the gas faucet pipe; h 1 represents the submersion depth of the air-water mixer below the dynamic water level, in meters (m). The mass flow rate is for three-phase flow, in N / s; Q g Air supply volume for the air compressor, m 3 / s; Q m The volumetric flow rate of drilling fluid returned from the wellhead, in m 3 / s; P Let be the pressure at any point inside the inner cavity of the double-walled drill pipe, in Pa; T g The atmospheric thermodynamic temperature at the wellhead, in K; T av The average atmospheric thermodynamic temperature of the three-phase flow is K; P g The local atmospheric pressure is expressed in Pa.

[0050] S5. Calculate the drilling fluid return flow rate based on the gas lift reverse circulation lifting force and the total friction force of the gas lift reverse circulation.

[0051] According to the principle of gas lift reverse circulation, since the lifting force generated by gas injection mainly overcomes the frictional pressure loss caused by the upward flow of drilling fluid, the difference is zero during normal drilling, that is: (4) By substituting the relevant drilling parameters into the formula, the drilling fluid return flow rate under the corresponding conditions can be obtained, i.e., the volumetric flow rate of the drilling fluid returning from the wellhead. Q m .

[0052] Example Using the calculation model of lifting force and frictional resistance of this invention, the upward flow rate of drilling fluid is calculated and predicted, and the actual construction parameters of drilling at Xiong'an D19 site are simulated and calculated. The calculation results are shown in Tables 1 and 2 below.

[0053] D19 is an exploration borehole in the Xiong'an New Area Geothermal Clean Energy Survey and Evaluation Project. The completed well depth is 4021.78 m. The well structure and gas lift reverse circulation working principle are described in [link to documentation]. Figure 1 In simple terms, the working principle of air-lift reverse circulation drilling is to reduce the equivalent circulation density of the fluid inside the drill string by injecting gas, thereby creating a pressure difference between the inside and outside of the drill string and causing the fluid to flow. Specifically, compressible gas (mostly air) is driven by air compression equipment (air compressor, booster compressor) and flows through the annulus between the inner and outer pipes of the double-wall drill pipe after passing through the air-water tap or air box, reaching the air-water mixer. It is then injected into the inner pipe of the double-wall drill pipe and forms a three-phase mixture of gas, liquid, and cuttings with the drilling fluid and cuttings. As high-pressure gas enters the inner tube, it forms countless small bubbles. These bubbles rise rapidly along the inner tube while continuously expanding, mixing with the drilling fluid (mostly water) in the inner tube of the double-walled drill pipe. This creates a gas-water mixture with a lower specific gravity in the inner tube, while the drilling fluid in the annulus has a higher specific gravity, resulting in an unstable "U"-shaped tube effect in the wellbore. The drilling fluid in the drill string cavity flows upward, continuously carrying the broken rock cuttings to the surface wellhead. The rock cuttings are separated by a solids control device (mostly a vibrating screen) and discharged into a sedimentation tank or collected.

[0054] To address severe leakage during drilling of the thermal reservoir and to protect the reservoir, an air-lift reverse circulation drilling technique was selected. In well D19, double-wall drill pipe was lowered to depths of 347.76 m (subsidence ratio 0.5), 492.66 m (subsidence ratio 0.65), and 695.52 m (subsidence ratio 0.75), with an air volume of 8 Nm³. 3 / min, 10Nm 3 / min, 12 Nm 3 The return water volume was tested at a rate of / min. Two sets of drill string combinations were used for the test. The drill string combinations were Ø215.9 mm drill bit + Ø165 mm drill collar + Ø89 mm conventional drill pipe + Ø127 mm double-wall drill pipe and Ø215.9 mm drill bit + Ø165 mm drill collar + Ø114 mm conventional drill pipe + Ø127 mm double-wall drill pipe. The return flow rate was measured on-site, and the dynamic water level was maintained at 173m. See Tables 1 and 2. Figure 4 .

[0055] Table 1. Measured and simulated values ​​of drilling fluid return flow rate when using Ø89 mm drill pipe.

[0056] Table 2. Test data and simulation calculations of drilling fluid return flow rate in Xiong'an D19 well using Ø114 mm drill pipe.

[0057] Figure 4This figure compares the experimental data and simulated calculations of drilling fluid return flow rate when using different single-wall drill pipes in the Xiong'an D19 well. Figure (a) shows the measured and simulated values ​​of drilling fluid return flow rate when using an Ø89 mm drill pipe; (b) shows the measured and simulated values ​​of drilling fluid return flow rate when using an Ø114 mm drill pipe. Combined with… Figure 2 As can be seen from Tables 1 and 2, the error between the simulated and measured values ​​of drilling fluid return flow rate is 0.57-8.89%, and the model of this application is relatively reliable in predicting the drilling fluid return flow rate in gas lift reverse circulation drilling.

[0058] 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 method for calculating drilling fluid flow rate in gas lift reverse circulation drilling, characterized in that, Includes the following steps: S1. Define the air lift reverse circulation lifting force and friction loss pressure model; S2. Assume the drilling fluid flow rate during the circulation process is... Q m ; S3. Calculate the total frictional pressure of the air-lift reverse circulation; S4. Calculate the air lift reverse circulation lift force; S5. Calculate the drilling fluid return flow rate based on the gas lift reverse circulation lifting force and the total friction force of the gas lift reverse circulation.

2. The drilling fluid flow rate calculation method for gas lift reverse circulation drilling according to claim 1, characterized in that, The air lift reverse circulation lifting force model is as follows: （5） Where, P lift The air lift reverse circulation lifting force is measured in MPa. P ams The hydrostatic pressure, in MPa, is the section from the annular mixer between the double-walled drill pipe and the well wall to the wellhead. P ims The hydrostatic pressure at the mixer inside the double-walled drill pipe is measured in MPa.

3. The drilling fluid flow rate calculation method for gas lift reverse circulation drilling according to claim 1, characterized in that, The airlift reverse circulation friction loss pressure model is as follows: （6） In the formula, P f The pressure of the total frictional loss of the circulating fluid in the wellbore during gas lift reverse circulation drilling is expressed in MPa. P af The total frictional loss pressure in the annulus is expressed in MPa. ΔP bit The pressure is the frictional loss pressure of the drill bit, in MPa; P irf The pressure is the frictional loss pressure inside the tail rod section, in MPa; P imf The frictional loss pressure in the upper section of the mixer inside the double-walled drill pipe is measured in MPa.

4. The drilling fluid flow rate calculation method for gas lift reverse circulation drilling according to claim 3, characterized in that, The formula for calculating the total frictional loss pressure in the annulus is as follows: （7） In the formula, i is the number of annular rings with the same annular diameter; H i The length of the annular segment with the same annular diameter, in meters (m). D hi — is the wellbore diameter for the same annulus diameter, in meters; D pi The drill pipe diameter is the same as the annulus diameter, in meters (m). f Li For the same annular diameter, the Fanning friction coefficient is dimensionless; V Li The velocity of drilling fluid with the same annular diameter is given in m / s; g is the acceleration due to gravity, 9.81 m / s². 2 .

5. The drilling fluid flow rate calculation method for gas lift reverse circulation drilling according to claim 3, characterized in that, The formula for calculating the frictional loss pressure of the drill bit is as follows: （11） In the formula, ΔP bit The pressure loss generated by drilling fluid passing through the drill bit water holes is Pa; k is the number of drill bit water holes of the same diameter, dimensionless. D i Let the diameter of the water inlet of the i-th drill bit be m; γ m The specific gravity of the annular drilling fluid, N / m 3 ; Q m The volumetric flow rate of drilling fluid returned from the wellhead, in m 3 / s; g is the acceleration due to gravity, 9.81 m / s². 2 .

6. The drilling fluid flow rate calculation method for gas lift reverse circulation drilling according to claim 3, characterized in that, The formula for calculating the frictional loss pressure of the inner tube of the tail rod section is as follows: （12） Where, h i The length of the tailpipe section with the same inner diameter is in meters (m). d pi Let be the inner diameter of the tailpipe, in meters (m). f li is the Fanning friction coefficient of the fluid inside the tailpipe, which is dimensionless; V li The velocity of the drilling fluid in the tailpipe is m / s.

7. The method for calculating drilling fluid flow rate in gas lift reverse circulation drilling according to claim 3, characterized in that, The formula for calculating the frictional loss pressure of the upper section of the mixer in the inner tube of the double-walled drill pipe is as follows: （20） Where, The mass flow rate is for three-phase flow, in N / s; Q g Air supply volume for the air compressor, m 3 / s; Q m The volumetric flow rate of drilling fluid returned from the wellhead, in m 3 / s; h 0 represents the center line from the dynamic water level to the highest point of the bend in the gas faucet pipe; P Let be the pressure at any point inside the inner cavity of the double-walled drill pipe, in Pa; T g The atmospheric thermodynamic temperature at the wellhead, in K; T av The average atmospheric thermodynamic temperature of the three-phase flow is K; P g The local atmospheric pressure is expressed in Pa.

8. The method for calculating drilling fluid flow rate in gas lift reverse circulation drilling according to claim 2, characterized in that, The formula for calculating the hydrostatic pressure at the mixer inside the double-walled drill pipe is as follows: （22） （24） Where, γ mix The specific gravity of the three-phase mixed flow is N / m³. 3 ; h 0 represents the center line from the dynamic water level to the center line of the highest point of the air faucet bend; h 1 represents the submersion depth of the air-water mixer below the dynamic water level, in meters (m). The mass flow rate is for three-phase flow, in N / s; Q The air volume flow rate at any point inside the inner cavity of the double-walled drill pipe is given in m. 3 / s.

9. The method for calculating drilling fluid flow rate in gas lift reverse circulation drilling according to claim 1, characterized in that, The formula for calculating the airlift reverse circulation lifting force is as follows: （34） Where, γ l The specific gravity of the annular drilling fluid, N / m 3 ; h 0 represents the center line from the dynamic water level to the highest point of the bend in the gas faucet pipe; h 1 represents the submersion depth of the air-water mixer below the dynamic water level, in meters (m). The mass flow rate is for three-phase flow, in N / s; Q g Air supply volume for the air compressor, m 3 / s; Q m The volumetric flow rate of drilling fluid returned from the wellhead, in m 3 / s; P Let be the pressure at any point inside the inner cavity of the double-walled drill pipe, in Pa; T g The atmospheric thermodynamic temperature at the wellhead, in K; T av The average atmospheric thermodynamic temperature of the three-phase flow is K; P g The local atmospheric pressure is expressed in Pa.

10. The method for calculating drilling fluid flow rate in gas lift reverse circulation drilling according to claim 1, characterized in that, S5 refers to the fact that, according to the gas lift reverse circulation principle, since the lifting force generated by gas injection mainly overcomes the frictional pressure loss caused by the upward flow of drilling fluid, the difference is zero during normal drilling, i.e.: （4） By substituting the relevant drilling parameters into the formula, the drilling fluid return flow rate under the corresponding conditions can be obtained, i.e., the volumetric flow rate of the drilling fluid returning from the wellhead. Q m .

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