A method for calculating the flow rate of a drilling fluid for air-lift reverse circulation drilling

Abstract

The application discloses a kind of gas lift reverse circulation drilling's drilling fluid flow calculation method, comprising the following steps: S1.gas lift reverse circulation lifting force and friction loss pressure model are defined;S2.during circulation, drilling fluid flow is assumed Q m ;S3.gas lift reverse circulation total friction pressure is calculated;S4.gas lift reverse circulation lifting force is calculated;S5.according to gas lift reverse circulation lifting force and gas lift reverse circulation total friction, the flow of drilling fluid is calculated.This application inputs gas lift reverse circulation well depth structure and drilling relevant parameters, studies its influence on the flow of drilling fluid, to obtain the best operating parameters of gas lift reverse circulation.The application can optimize the air supply amount of air compressor selected for gas lift reverse circulation geothermal drilling, the depth of double-wall drill pipe, double-wall drill pipe specification, single-wall specification drill pipe specification, and provide a reasonable theoretical basis for more reasonable realization of gas lift reverse circulation drilling.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of geothermal drilling, and particularly relates to a drilling fluid flow calculation method for air-lift reverse circulation drilling. BACKGROUND

[0002] With the increasing demand for geothermal energy, the air-lift reverse circulation drilling process capable of protecting the heat reservoir and reducing the cost gradually becomes a key technology for the development and utilization of geothermal energy. The air-lift reverse circulation drilling process uses clean water as the drilling fluid, and injects compressed air through the double-wall drill rod. The compressed air expands in the drill string to drive the clean water to carry the rock to the wellhead at the ground surface in a reverse circulation manner. The air-lift reverse circulation technology is used to mine oil, water and other substances from the well, wherein the drilling fluid flow can reflect whether there is leakage or formation water influx, and further judge the formation condition at the downhole; meanwhile, the drilling fluid flow can be used to calculate the cuttings upflow rate, which is of great significance to the judgment of whether the cuttings at the well bottom are cleaned up and the control of the circulating cleanout time.

[0003] At present, the calculation of the upflow flow of the drilling fluid for the air-lift reverse circulation is mainly based on the annulus-drill rod two-phase flow model, and the upflow flow and the average upflow speed of the mixture in the drill rod are calculated under specific injection parameters (air volume, liquid volume, injection pressure, well depth, etc.). However, the existing calculation process does not consider the influence of the well depth, the well structure and the drilling assembly, and the actual drilling fluid upflow flow of the air-lift reverse circulation drilling operation is a reference value. SUMMARY

[0004] In order to solve the above problems, the application provides a drilling fluid flow calculation method for air-lift reverse circulation drilling. The application considers the influence of the well depth, the well structure, the drilling assembly and the drilling assembly procedure on the drilling fluid upflow flow, couples the lifting force of the air-lift reverse circulation and the total friction pressure loss, and the error of the calculated drilling fluid upflow flow is small.

[0005] The drilling fluid flow calculation method for air-lift reverse circulation drilling of the application comprises the following steps:

[0006] S1. defining the air-lift reverse circulation lifting force and the friction loss pressure model;

[0007] S2. assuming that the drilling fluid flow in the circulation process is Q m ;

[0008] S3. calculating the total friction pressure of the air-lift reverse circulation;

[0009] S4. calculating the air-lift reverse circulation lifting force;

[0010] S5. calculating the drilling fluid upflow flow according to the air-lift reverse circulation lifting force and the total friction force of the air-lift reverse circulation.

[0011] The gas lift reverse circulation lifting force model is

[0012] (5)

[0013] wherein, P lift is the gas lift reverse circulation lifting force, MPa; P ams is the annulus mixer to wellhead section hydrostatic pressure between the double-wall drill pipe and the well wall, MPa; P ims is the inner tube mixer hydrostatic pressure of the double-wall drill pipe, MPa.

[0014] The gas lift reverse circulation friction loss pressure model is

[0015] (6)

[0016] wherein, P f is the total friction loss pressure of the circulating fluid in the wellbore during the gas lift reverse circulation drilling process, MPa; P af is the annulus total friction loss pressure, MPa; ΔP bit is the drill bit friction loss pressure, MPa; P irf is the inner tube friction loss pressure of the tail rod section, MPa; P imf is the double-wall drill pipe inner tube mixer upper section friction loss pressure, MPa.

[0017] The calculation formula of the annulus total friction loss pressure is

[0018] (7)

[0019] wherein, H i is the annulus section length of the same annulus diameter, m; D hi is the borehole diameter of the same annulus diameter, m; D pi is the drill pipe diameter of the same annulus diameter, m; f Li is the Fann friction factor of the same annulus diameter, dimensionless; V Li is the flow rate of the drilling fluid of the same annulus diameter, m / s.

[0020] The calculation formula of the drill bit friction loss pressure is

[0021] (11)

[0022] wherein ΔP bit is the pressure loss of the drilling fluid passing through the bit water hole, Pa; k is the number of the bit water holes with the same diameter, dimensionless; D i is the diameter of the i-th bit water hole, m.

[0023] The calculation formula of the friction loss pressure of the inner tube of the tail rod section is

[0024] (12)

[0025] wherein, h i is the length of the tail pipe section with the same inner diameter, m; D pi is the inner diameter of the tail pipe, m; f li is the Fann friction factor of the fluid in the tail pipe, dimensionless; V li is the flow rate of the drilling fluid in the tail pipe, m / s.

[0026] The calculation formula of the friction loss pressure of the upper section of the double-wall drill pipe inner tube mixer is

[0027] (20)

[0028] wherein, is the weight flow rate of the three-phase flow, N / s; Q g is the air supply of the air compressor, m 3 / s; Q m is the volume flow rate of the drilling fluid returned at the wellhead, m 3 / s; h 0 is the center line from the dynamic water level to the highest point of the gas-water tap elbow; P is the pressure at any point in the inner cavity of the double-wall drill pipe inner tube, Pa; T g is the atmospheric thermodynamic temperature at the wellhead, K; T av is the average atmospheric thermodynamic temperature of the three-phase flow, K; P g is the local atmospheric pressure, Pa.

[0029] The calculation formula of the hydrostatic pressure at the double-wall drill pipe inner tube mixer is

[0030] (22)

[0031] (24)

[0032] wherein,γ mix N / m 3 ; h 0 is the center line from the dynamic water level to the center line of the highest part of the gas-water tap elbow pipe; h 1 is the submerged depth of the gas-water mixer below the dynamic water level, m; N / s Q m 3 / s.

[0033] The calculation formula of the gas lift reverse circulation lifting force is

[0034] (34)

[0035] In the formula, γ l N / m 3 ; h 0 is the center line from the dynamic water level to the center line of the highest part of the gas-water tap elbow pipe; h 1 is the submerged depth of the gas-water mixer below the dynamic water level, m; N / s Q g m 3 / s; Q m m 3 / s; P Pa; T g K; T av K; P g Pa.

[0036] S5 refers to, according to the principle of gas lift reverse circulation, the lifting force generated by gas injection mainly overcomes the friction loss pressure generated by the upward flow of drilling fluid, and when normal drilling, the difference is zero, that is:

[0037] (4)

[0038] By substituting the related parameters of drilling into the formula, the drilling fluid upward flow under the corresponding conditions, that is, the wellhead return drilling fluid volume flow can be obtained Q m .

[0039] The beneficial effects of the present application are,

[0040] 1. The present application inputs the air-lift reverse circulation well depth structure and drilling related parameters, studies the influence on the drilling fluid upflow, so as to obtain the optimal operation parameters of the air-lift reverse circulation.

[0041] 2. The present application can optimize the air supply amount of the selected air compressor, the double-wall drill pipe depth, the double-wall drill pipe specification and the single-wall specification drill pipe specification parameters for the drilling of the air-lift reverse circulation geothermal well, and provide a reasonable theoretical basis for more reasonable air-lift reverse circulation drilling.

[0042] 3. The present application can analyze the drilling fluid upflow in the process of air-lift reverse circulation drilling, and can estimate the formation water yield, thereby providing a reference value for subsequent geothermal well pump water pumping applications.

[0043] 4. The present application considers the influence of well depth, well structure, drilling tool assembly and drilling tool specification on the drilling fluid upflow, couples the lifting force of the air-lift reverse circulation and the total friction pressure loss, and has a smaller error in the calculation of the drilling fluid upflow. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is the air-lift reverse circulation working principle and supporting facility diagram of the present application.

[0045] Figure 2 is the air-lift reverse circulation theoretical mechanism schematic diagram of the present application.

[0046] Figure 3 is the drilling fluid upflow calculation flow of the air-lift reverse circulation of the present application.

[0047] Figure 4 is the drilling fluid upflow test data and simulation calculation comparison diagram of the present application embodiment when different single-wall drill pipes are used in Xiongan D19 well. DETAILED DESCRIPTION

[0048] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the drawings. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0049] As shown in Figure 3 , the drilling fluid flow calculation method of the air-lift reverse circulation drilling of the present application comprises the following steps:

[0050] S1. Define the air-lift reverse circulation lifting force and friction loss pressure model;

[0051] As shown in Figure 2 , according to the fluid continuity principle: the pressure of the drilling fluid in the wellbore of the air-lift reverse circulation drilling has continuity, that is, the annulus bottom hole pressure is equal to the drill string inner tube bottom hole pressure, which can be described by the following formula:

[0052] (1)

[0053] wherein, P b Pb is the bottom hole pressure, MPa; P ab Pab is the annulus bottom hole pressure, MPa; P ib Pbi is the bottom hole pressure inside the drill string, MPa.

[0054] In particular, the annulus bottom hole pressure P ab is:

[0055] (2)

[0056] wherein, P ams Pm is the static hydraulic pressure of the annulus mixer to the wellhead section between the double wall drill pipe and the well wall, MPa; P amf Pm1 is the friction loss pressure of the upper section of the annulus mixer between the double wall drill pipe and the well wall, MPa; P ars Pd is the static hydraulic pressure of the drill bit to the annulus section of the gas-water mixer, MPa; P arf Pd1 is the friction loss pressure of the drill bit to the annulus section of the gas-water mixer, MPa; P g Pa is the atmospheric pressure, MPa; P af Pf is the total annulus friction loss pressure, which is P amf and P arf , MPa.

[0057] The bottom hole pressure inside the drill string P ib can be described by the following formula:

[0058] (3)

[0059] wherein, P ims Pm2 is the static hydraulic pressure of the inner tube mixer of the double wall drill pipe, MPa; P imf Pm3 is the friction loss pressure of the upper section of the inner tube mixer of the double wall drill pipe, MPa; P irs Pd2 is the static hydraulic pressure of the tail rod section, MPa; P irf Pd3 is the inner tube friction loss pressure of the tail rod section, MPa; ΔP bitPf, MPa.

[0060] The above formula is arranged, and since P irs = P ars The following formula can be obtained:

[0061] (4)

[0062] Where the left side of the equation is the difference between the annular fluid static pressure of the drill string and the gas, liquid, and solid three-phase fluid static pressure in the inner tube of the double-wall drill pipe at the gas-water mixer of the double-wall drill pipe, defined as the lifting force of the gas-lift reverse circulation, P lift :

[0063] (5)

[0064] In the formula, P lift Pf is the lifting force of the gas-lift reverse circulation, MPa; P ams Pf is the static liquid pressure of the annulus mixer between the double-wall drill pipe and the well wall to the wellhead section, MPa; P ims Pf is the static liquid pressure at the mixer in the inner tube of the double-wall drill pipe, MPa.

[0065] The right side of the equation is the total friction loss pressure of the circulating fluid in the wellbore during gas-lift reverse circulation drilling, P f :

[0066] (6)

[0067] In the formula, P f Pf is the total friction loss pressure of the circulating fluid in the wellbore during gas-lift reverse circulation drilling, MPa; P af Pf is the total friction loss pressure in the annulus, MPa; ΔP bit Pf is the friction loss pressure of the drill bit, MPa; P irf Pf is the friction loss pressure in the inner tube of the tail rod section, MPa; P imf Pf is the friction loss pressure in the upper section of the inner tube of the double-wall drill pipe mixer, MPa.

[0068] S2. Assuming that the flow rate of the drilling fluid during circulation is Q m ;

[0069] S3. Calculate the total friction pressure of gas-lift reverse circulation;

[0070] S301. Since there is only one phase of drilling fluid in the annulus in the geothermal deep well gas lift reverse circulation drilling, the calculation formula of the total friction loss pressure of the annulus is

[0071] (7)

[0072] wherein, H i is the length of the annulus section with the same annulus diameter, m; D hi is the borehole diameter with the same annulus diameter, m; D pi is the drill pipe diameter with the same annulus diameter, m; f Li is the Fann friction factor with the same annulus diameter, dimensionless; V Li is the flow rate of the drilling fluid with the same annulus diameter, m / s.

[0073] wherein, the Fann friction factor of each annulus section is determined by the Reynolds number of the section:

[0074] (8)

[0075] wherein, N Ri is the two-phase flow Reynolds number in each annulus section, dimensionless; u is the kinematic viscosity of the drilling fluid, m 2 / s.

[0076] If N Ri is less than 2000, then:

[0077] (9)

[0078] If N Ri is greater than 2000, then:

[0079] (10)

[0080] wherein, e p is the roughness of the outer wall of the drill pipe, D h is the annulus diameter, m; D p is the drill pipe diameter, m. For annular pipe flow, generally 0.0002 m is taken.

[0081] S302. When the drilling fluid enters the inner cavity of the drill string from the annulus through the water eye of the drill bit, pressure loss will be caused by the friction, so that the pressure at the bottom of the tail rod is less than the bottom hole pressure. Assuming that the water eye efficiency is 0.95, the calculation formula of the friction loss pressure of the drilling fluid through the drill bit is

[0082] (11)

[0083] where, ΔP bit is the pressure loss of the drilling fluid through the water eye of the drill bit, Pa; k is the number of water eyes of the drill bit with the same water eye diameter, dimensionless; D i is the diameter of the i-th water eye of the drill bit, m; is the specific gravity of the drilling fluid, N / m 3 .

[0084] S303. The calculation formula of the friction loss pressure of the tail rod section inner tube is

[0085] (12)

[0086] where, h i is the length of the tail pipe section with the same inner diameter, m; d pi is the inner diameter of the tail pipe, m; f li is the Fanning friction factor of the fluid in the tail pipe, dimensionless; V li is the flow rate of the drilling fluid in the tail pipe, m / s.

[0087] Wherein, the Fanning friction factor of the fluid in the tail pipe is determined by the Reynolds number:

[0088] (13)

[0089] where, N ri is the two-phase flow Reynolds number of each section of the tail rod inner tube, dimensionless; u is the kinematic viscosity of the drilling fluid, m 2 / s.

[0090] If N ri is less than 2000, then:

[0091] (14)

[0092] If N ri is greater than 2000, then:

[0093] (15)

[0094] wherein, e p is the roughness of the inner wall of the drill pipe. Generally taken as 0.0002 m.

[0095] S304. The inner pipe friction loss pressure at the double-wall drill pipe inner mixer P imf is:

[0096] (16)

[0097] wherein, f is the Fanning friction factor of the three-phase flow at the double-wall drill pipe inner mixer, dimensionless; V is the three-phase flow velocity at the pressure, m / s; d is the inner pipe inner diameter of the double-wall drill pipe, m; is the specific gravity of the three-phase mixed flow, N / m 3 .

[0098] Since the density of the gas-liquid-solid three-phase flow in the double-wall drill pipe varies with the change of pressure, the change of the friction pressure gradient of the three-phase flow with the increase of the depth can be approximately expressed as:

[0099] (17)

[0100] wherein the flow velocity of the three-phase flow can be obtained by the following formula:

[0101] (18)

[0102] wherein the Fanning friction factor of the three-phase flow is determined by the Reynolds number:

[0103] (19)

[0104] wherein, N R is the Reynolds number of the three-phase flow, dimensionless; u is the kinematic viscosity of the three-phase flow, m 2 / s.

[0105] The calculation formula of the friction loss pressure of the upper section of the inner pipe mixer of the double-wall drill pipe is

[0106] (20)

[0107] wherein, is the weight flow of the three-phase flow, N / s; Q g is the air supply of the air compressor, m 3 / s; Q mV is the volume flow rate of the drilling fluid returned to the wellhead, m3 / s 3 / s; h 0 is the centerline from the dynamic water level to the highest centerline of the gas-water swivel elbow P P is the pressure at any point in the inner cavity of the double-wall drill pipe, Pa T g T is the atmospheric thermodynamic temperature at the wellhead, K T av T is the average atmospheric thermodynamic temperature of the three-phase flow, K P g P is the local atmospheric pressure, Pa.

[0108] S4. Calculate the gas-lift reverse circulation lifting force

[0109] S401. The hydrostatic pressure at the double-wall drill pipe outer annular mixer P ams is the pressure generated by the weight of the drilling fluid in the annulus, calculated by the following formula:

[0110] (21)

[0111] where, γ l is the specific weight of the annular drilling fluid, N / m 3 ; h 1 is the submergence depth of the gas-water mixer below the dynamic water level, m.

[0112] S402. The formula for calculating the hydrostatic pressure at the double-wall drill pipe inner tube mixer is

[0113] (22)

[0114] where, γ mix is the specific weight of the three-phase mixed flow, N / m 3 ; h 0 is the centerline from the dynamic water level to the highest centerline of the gas-water swivel elbow 。

[0115] Since the density of the gas-liquid-cuttings three-phase flow in the double-wall drill pipe changes with the change of pressure, the calculation is carried out using the three-phase flow hydrostatic pressure formula, and the change of the three-phase flow hydrostatic pressure gradient with the increase of depth can be approximately expressed as:

[0116] (23)

[0117] For the gas-liquid-cuttings three-phase mixed flow system, the volume proportion occupied by the cuttings is extremely small, and therefore can be ignored in the analysis process, so the specific weight of the three-phase flow can be expressed as:

[0118] (24)

[0119] wherein, is the weight flow rate of the three-phase flow, N / s; Q is the air volume flow rate at any point in the inner cavity of the inner tube of the double-wall drill pipe, m 3 / s; Q g is the air supply of the air compressor, m 3 / s; Q m is the volume flow rate of the drilling fluid returned at the wellhead, m 3 / s; P is the pressure at any point in the inner cavity of the inner tube of the double-wall drill pipe, Pa; T g is the atmospheric thermodynamic temperature at the wellhead, K; T av is the average atmospheric thermodynamic temperature of the three-phase flow, K; P g is the local atmospheric pressure, Pa.

[0120] wherein, the weight flow rate of the three-phase flow in the inner cavity of the inner tube of the double-wall drill pipe may be expressed as

[0121] (25)

[0122] wherein, is the weight flow rate of the air entering the compressor, N / s; is the weight flow rate of the drilling fluid, N / s; is the weight flow rate of the cuttings, N / s.

[0123] Specifically, the weight flow rate of the air entering the compressor is:

[0124] (26)

[0125] wherein, Q g is the volume flow rate of the air entering the compressor, m 3 / s; γ g is the air specific gravity entering the air compression device, N / m 3 ;

[0126] Specifically, the air specific gravity entering the air compression device γ g is:

[0127] (27)

[0128] wherein, Pg P is the local atmospheric pressure, Pa; S g S is the gas relative density, S = 1.0 for air at standard conditions; R e R is the engineering gas constant, generally taken as 29.31 N·m / (N·K); T g T is the atmospheric thermodynamic temperature at the wellhead, K.

[0129] Specifically, the atmospheric thermodynamic temperature at the wellhead T g is:

[0130] (28)

[0131] wherein, t g P is the atmospheric temperature at the wellhead, ℃.

[0132] The weight flow rate of the drilling fluid in the inner cavity of the inner tube of the double-wall drill pipe is:

[0133] (29)

[0134] wherein, is the weight flow rate of the drilling fluid, N / s; γ m is the specific weight of the drilling fluid, N / m 3 .

[0135] The weight flow rate of the cuttings in the inner cavity of the inner tube of the double-wall drill pipe is :

[0136] (30)

[0137] wherein, D b is the borehole diameter, m; γ w is the specific weight of the cuttings, N / m 3 ; ROP is the mechanical drilling speed, m / s.

[0138] The average relative density of sedimentary rocks is about 2.7. If the lithology of the drilled formation is magmatic rock or metamorphic rock, the average relative density of the rock is 2.8 and 3.0, respectively.

[0139] According to the equivalent relationship between the specific weight, volume flow rate and weight flow rate of the gas at any point in the inner cavity of the inner tube of the double-wall drill pipe,

[0140] (31)

[0141] wherein, γ is the air density at any point in the inner cavity of the inner tube of the double-wall drill pipe, N / m 3 ;

[0142] The air volume flow rate Q at any point in the inner tube of the double-wall drill pipe can be obtained as:

[0143] (32)

[0144] wherein, T av is the average atmospheric thermodynamic temperature of the three-phase flow, K;

[0145] Specifically, the average atmospheric thermodynamic temperature of the three-phase flow T av is:

[0146] (33)

[0147] wherein, t av is the average temperature of the three-phase flow, ℃.

[0148] The final arrangement can obtain the calculation formula of the air-lifting reverse circulation lifting force as:

[0149] (34)

[0150] wherein, γ l is the density of the annular drilling fluid, N / m 3 ; h 0 is the center line from the dynamic water level to the highest point of the gas-water tap elbow; h 1 is the submerged depth of the gas-water mixer below the dynamic water level, m; is the weight flow rate of the three-phase flow, N / s; Q g is the air supply of the air compressor, m 3 / s; Q m is the volume flow rate of the drilling fluid returned from the wellhead, m 3 / s; P is the pressure at any point in the inner cavity of the inner tube of the double-wall drill pipe, Pa; T g is the atmospheric thermodynamic temperature at the wellhead, K; T av is the average atmospheric thermodynamic temperature of the three-phase flow, K; P g is the local atmospheric pressure, Pa.

[0151] S5. According to the air-lifting reverse circulation lifting force and the total friction of the air-lifting reverse circulation, the drilling fluid return flow rate is calculated.

[0152] According to the principle of gas lift reverse circulation, the lifting force generated by gas injection mainly overcomes the friction loss pressure generated by the upward flow of drilling fluid. When drilling normally, the difference is zero, that is:

[0153] (4)

[0154] Substitute the relevant parameters of the drilling into the formula, the drilling fluid return flow under the corresponding conditions can be obtained, that is, the volume flow rate of the drilling fluid returned from the wellhead Q m .

[0155] Embodiment

[0156] Through the calculation of the lifting force and friction resistance model of the present application, the drilling fluid return flow is calculated and predicted, and the actual construction parameters of the D19 site drilling in Xiongan are simulated and calculated. The calculation results are shown in Tables 1 and 2.

[0157] D19 is an exploration hole of the Xiongan New Area Geothermal Clean Energy Investigation and Evaluation Project, and the drilled well depth is 4021.78 m. The well structure and the working principle of the gas lift reverse circulation are shown in Figure 1 The working principle of the gas lift reverse circulation drilling is simply to reduce the equivalent circulating density of the fluid in the inner cavity of the drill string by injecting gas, so that a pressure difference is generated between the inside and outside of the drill string to make the fluid flow. Specifically, the compressible gas (mostly air) flows through the annulus between the inner and outer pipes of the double-wall drill pipe to the gas-water mixer after the gas-water swivel or gas box under the drive of the air compression equipment (air compressor, booster), and is injected into the inner pipe of the double-wall drill pipe to form a gas-liquid-cutting three-phase mixed flow with the drilling fluid and cutting. After the high-pressure gas enters the inner pipe, countless small bubbles are formed, the bubbles rise rapidly along the inner pipe and continuously expand, mix with the drilling fluid (mostly clean water) in the inner pipe of the double-wall drill pipe, and form a gas-water mixture with lower specific gravity in the inner pipe of the double-wall drill pipe, while the drilling fluid in the annulus has a higher specific gravity, so that an unstable "U" shaped pipe effect is generated in the wellbore. The drilling fluid in the inner cavity of the drill string flows upward, continuously carrying the cutting generated by the crushing to the surface wellhead. The cutting is separated by the solid control device (mostly vibrating screen) and discharged into the sedimentation tank or collected.

[0158] In order to cope with the serious loss of drilling in the hot reservoir and protect the hot reservoir, the gas lift reverse circulation drilling process is selected. The double-wall drill pipe is used to drill deep 347.76 m (submergence ratio 0.5), 492.66 m (submergence ratio 0.65), and 695.52 m (submergence ratio 0.75) in D19 well site, with air volume of 8 Nm 3 / min, 10 Nm 3 / min, and 12 Nm 3The test of the amount of the drilling fluid returning at 1000 m3 / h was carried out. Two groups of drilling assemblies were used to test the amount of the drilling fluid returning. The drilling assemblies 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, and the measurement of the amount of the drilling fluid returning was measured on site, and the hydrodynamic level was kept at 173 m. See Tables 1 and 2, Figure 4 .

[0159] Table 1. The measured and simulated values of the amount of the drilling fluid returning when using the Ø89 mm drill pipe

[0160]

[0161] Table 2. The test data and simulation calculation of the amount of the drilling fluid returning when using the Ø114 mm drill pipe in Xiongan D19 well

[0162]

[0163] Figure 4 The comparison chart of the test data and simulation calculation of the amount of the drilling fluid returning when using different single-wall drill pipes in Xiongan D19 well, in which (a) is the measured and simulated values of the amount of the drilling fluid returning when using the Ø89 mm drill pipe; (b) is the measured and simulated values of the amount of the drilling fluid returning when using the Ø114 mm drill pipe. It can be seen from Tables 1 and 2 that the error between the simulated and measured values of the amount of the drilling fluid returning is 0.57-8.89%, and the value of the amount of the drilling fluid returning in the gas lift reverse circulation drilling predicted by the model of the present application is relatively reliable. Figure 2

[0164] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and the changes, modifications, replacements and variations of the above embodiments made by those of ordinary skill in the art are within the protection scope of the present application.​

Claims

1. A method for calculating the flow rate of a drilling fluid for air-lift reverse circulation drilling, characterized in that, The method comprises the following steps: S1. Defining a gas lift reverse circulation lifting force and friction loss pressure model; The gas lift reverse circulation lifting force model is （5） In the formula, P lift is the gas lift reverse circulation lifting force, MPa; P ams is the annular mixer to wellhead section static pressure between the double-wall drill pipe and the well wall, MPa; P ims is the static pressure at the inner tube mixer of the double-wall drill pipe, MPa; The gas lift reverse circulation friction loss pressure model is （6） wherein P f is the total frictional loss pressure of circulating fluid in the wellbore during the gas lift reverse circulation drilling process, MPa; P af is the annular total frictional loss pressure, MPa; ΔP bit is the drill bit frictional loss pressure, MPa; P irf is the tail rod section inner tube frictional loss pressure, MPa; P imf is the double-wall drill pipe inner tube mixer upper section frictional loss pressure, MPa; S2. Assume that the drilling fluid flow rate during the circulation is Q m ; S3. Calculating a total gas lift reverse circulation friction pressure; The calculation formula of the double-wall drill pipe inner tube mixer upper section friction loss pressure is （20） wherein, Q is the weight flow rate of three-phase flow, N / s; Q g Q is the air supply of the air compressor, m 3 Q is the weight flow rate of three-phase flow, N / s; Q m Q is the volume flow rate of the returned drilling fluid at the wellhead, m 3 Q is the weight flow rate of three-phase flow, N / s; Q g Q is the atmospheric thermodynamic temperature at the wellhead, K; T av Q is the average atmospheric thermodynamic temperature of three-phase flow, K; P g Q is the local atmospheric pressure, Pa; The calculation formula of the double-wall drill pipe inner tube mixer static liquid pressure is （22） （24） where γ mix is the specific weight of the three-phase mixture, N / m 3 ; h1 is the submergence depth of the air-water mixer below the dynamic water level, m; Q is the air volume flow rate at any point in the inner cavity of the inner tube of the double-wall drill pipe, m 3 / s; S4. Calculating a gas lift reverse circulation lifting force; The calculation formula of the gas lift reverse circulation lifting force is （34） wherein γ l is the density of the annular drilling fluid, N / m 3 ; S5. Calculating a drilling fluid upflow according to the gas lift reverse circulation lifting force and the gas lift reverse circulation total friction; According to the gas lift reverse circulation principle, the lifting force generated by gas injection mainly overcomes the friction loss pressure generated by the drilling fluid upflow, and the difference is zero when normal drilling, that is, there is: （4） Substitute the relevant parameters of the drilling well into the formula to obtain the drilling fluid return flow under the corresponding conditions, that is, the wellhead return drilling fluid volume flow Q m .

2. The method of claim 1, wherein, The calculation formula of the annular total friction loss pressure is （7） where i is the number of annuli with the same annulus diameter; H i is the length of the annulus segment with the same annulus diameter, m; D hi is the borehole diameter with the same annulus diameter, m; D pi is the drill pipe diameter with the same annulus diameter, m; f Li is the Fann friction factor with the same annulus diameter, dimensionless; V Li is the flow rate of the drilling fluid with the same annulus diameter, m / s; g is the acceleration of gravity, 9.81 m / s 2 .

3. The method of claim 1, wherein, The calculation formula of the drill bit friction loss pressure is （11） In the formula, ΔP bit D represents the pressure loss generated by drilling fluid passing through the drill bit's water holes, measured in Pa; k is the number of drill bit water holes of the same diameter, dimensionless; D i Let γ be the diameter of the water inlet of the i-th drill bit, in meters; 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 .

4. The method of claim 1, wherein, The calculation formula of the tail rod section inner tube friction loss pressure is （12） wherein h i is the length of the tailpipe section having the same inner diameter, m; d pi is the inner diameter of the tailpipe, m; f li f is the Fanning friction factor for the fluid in the tailpipe, dimensionless; V li V is the flow rate of the drilling fluid in the tailpipe, m / s.

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