Gas lift reverse circulation drilling method

Abstract

The invention relates to the field of geothermal well drilling, and discloses a gas lift reverse circulation well drilling method, which comprises the following steps of: determining formation pore pressure based on the height of a static water level in a well; setting the annulus bottom hole pressure to be equal to the formation pore pressure, and determining the reference dynamic water level height of the drilling fluid according to the annulus bottom hole pressure, the relevant parameters of the gas lift reverse circulation drilling equipment and the relevant parameters of the drilling fluid; based on the reference dynamic water level height, a first target dynamic water level height is determined, in the drilling process, the dynamic water level height of the drilling fluid is controlled to be the first target dynamic water level height, and the first target dynamic water level height is lower than the reference dynamic water level height. By controlling the dynamic water level height of the drilling fluid in the drilling process to be lower than the corresponding reference dynamic water level height when the annulus bottom hole pressure is equal to the formation pore pressure, the annulus bottom hole pressure can be controlled to be lower than the formation pore pressure, the drilling process is kept in an unbalanced state, the drilling fluid can be prevented from leaking into the formation, and the drilling efficiency is improved. The heat storage is damaged.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal drilling, and particularly to a gas-lift reverse circulation drilling method. Background Art

[0002] In the field of geothermal drilling, in order to reserve sufficient space for submersible pumps and reduce construction risks, the wellbore often adopts a large-diameter and multi-opening structure, and the lower casing does not return to the wellhead. Therefore, the annulus cross-sectional area of the upper well section is relatively large. When using positive circulation drilling, in order to meet the rock-carrying requirements of the upper large-diameter well section, it is often necessary to inject a large pump volume of drilling fluid. The injection of a large pump volume of drilling fluid, on the one hand, requires higher configuration requirements for equipment such as mud pumps, and on the other hand, it will cause the upward return speed of the drilling fluid to be too high in the lower small-diameter well section, which will lead to the erosion and instability of the wellbore wall.

[0003] To alleviate the above problems, gas-lift reverse circulation drilling is often used. When using gas-lift reverse circulation drilling, considering the protection of the heat reservoir, generally, the drilling process is further controlled in an underbalanced state where the bottom hole pressure in the annulus is less than the formation pore pressure. However, in the case of low formation pore pressure, the prior art is difficult to accurately control the bottom hole pressure in the annulus, and thus it is difficult to keep the drilling process in an underbalanced state, which is likely to cause the drilling fluid to leak into the formation and damage the heat reservoir. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems in the prior art that it is difficult to accurately control the bottom hole pressure in the annulus, and thus it is difficult to keep the drilling process in an underbalanced state, which is likely to cause the drilling fluid to leak into the formation and damage the heat reservoir, and to provide a gas-lift reverse circulation drilling method.

[0005] To achieve the above purpose, the present invention provides a gas-lift reverse circulation drilling method, which includes:

[0006] Determine the formation pore pressure based on the static water level height in the well;

[0007] Set the bottom hole pressure in the annulus equal to the formation pore pressure, and determine the reference dynamic water level height of the drilling fluid according to the bottom hole pressure in the annulus, the relevant parameters of the gas-lift reverse circulation drilling equipment, and the relevant parameters of the drilling fluid;

[0008] Based on the reference dynamic water level height, determine the first target dynamic water level height, and during the drilling process, control the dynamic water level height of the drilling fluid to be the first target dynamic water level height, and the first target dynamic water level height is lower than the reference dynamic water level height.

[0009] In the embodiment of the present application, the determination of the formation pore pressure based on the static water level height in the well is carried out according to the following formula:

[0010] Pp = P 0 + ρ w gh j ;

[0011] Wherein, P p is the formation pore pressure, with the unit of MPa; P 0 is the standard atmospheric pressure; ρ w is the water density, with the unit of kg / m 3 ; g is the acceleration of gravity; h j is the static water level height in the well, with the unit of m.

[0012] In the embodiments of the present application, the reference dynamic water level height of the drilling fluid is determined according to the annulus bottom hole pressure, the relevant parameters of the air-lift reverse circulation drilling equipment, and the relevant parameters of the drilling fluid, based on the following formulas:

[0013] P b = P 0 + P h - ∑P fi ;

[0014] P h = ρ 1 gh d ;

[0015]

[0016] Wherein, P b is the annulus bottom hole pressure, with the unit of MPa; P 0 is the standard atmospheric pressure; P h is the static liquid pressure of the drilling fluid in the annulus, with the unit of MPa; P fi is the frictional resistance corresponding to the i-th opening of the annulus, with the unit of MPa; ρ 1 is the density of the drilling fluid, with the unit of kg / m 3 ; g is the acceleration of gravity; h d is the reference dynamic water level height of the drilling fluid, with the unit of m; f i is the Fanning friction coefficient corresponding to the i-th opening of the annulus; v ai is the flow velocity of the drilling fluid in the annulus corresponding to the i-th opening, with the unit of m / s; h i is the liquid column height of the drilling fluid corresponding to the i-th opening of the annulus, with the unit of m; d wbi is the wellbore diameter corresponding to the i-th opening, with the unit of m; d toi is the outer diameter of the drill pipe corresponding to the i-th opening, with the unit of m.

[0017] In the embodiments of the present application,

[0018]

[0019]

[0020] Among them, Q m is the flow rate of the drilling fluid in the adjacent well, with the unit of m 3 / s; e p is the absolute roughness of the annulus surface, with the unit of m; N R is the Reynolds number of the drilling fluid in the annulus.

[0021] In the embodiment of the present application, after controlling the dynamic water level height of the drilling fluid to be the first target dynamic water level height, the method further includes:

[0022] Obtain the actual flow velocity of the drilling fluid during the drilling process;

[0023] Based on the actual flow velocity and the first target dynamic water level height, determine the actual annulus bottom hole pressure during the drilling process;

[0024] Judge whether the actual annulus bottom hole pressure is less than the formation pore pressure;

[0025] In response to the actual annulus bottom hole pressure not being less than the formation pore pressure, control the dynamic water level height of the drilling fluid to be the second target dynamic water level height during the subsequent drilling process, and the second target dynamic water level height is lower than the first target dynamic water level height.

[0026] In the embodiment of the present application, after controlling the dynamic water level height of the drilling fluid to be the first target dynamic water level height, the method further includes:

[0027] Determine the minimum flow velocity required for the drilling fluid to carry rock cuttings with a target particle size;

[0028] Control the flow velocities of the drilling fluid corresponding to different parts of the drill pipe inner cavity to be greater than the minimum flow velocity.

[0029] In the embodiment of the present application, the determination of the minimum flow velocity required for the drilling fluid to carry rock cuttings with a target particle size is based on the following formulas:

[0030] v f = v c + v t ;

[0031]

[0032] Among them, ν f is the minimum flow velocity required for the drilling fluid to carry rock cuttings with a target particle size, with the unit of m / s; ν c is the critical velocity of the drilling fluid for carrying rock cuttings, with the unit of m / s; v t$v$ is the settling velocity of cuttings with the target particle size, in m / s; $\kappa$ is the instantaneous mechanical penetration rate, in m / h; $C$ is the cuttings concentration coefficient.

[0033] In the embodiments of the present application,

[0034]

[0035] wherein, $D$ c is the particle size of cuttings with the target particle size, in m; $\gamma$ s is the specific weight of cuttings with the target particle size, in N / m 3 ; $\gamma$ f is the specific weight of the drilling fluid, in N / m 3 ; $f$ p is the friction coefficient of cuttings with the target particle size.

[0036] In the embodiments of the present application, controlling the flow velocity of the drilling fluid corresponding to different parts of the drill pipe inner cavity to be greater than the minimum flow velocity includes:

[0037] Increasing the proportion of double-wall drill pipes in the drill pipe.

[0038] In the embodiments of the present application, controlling the flow velocity of the drilling fluid corresponding to different parts of the drill pipe inner cavity to be greater than the minimum flow velocity includes: reducing the inner diameter of single-wall drill pipes in the drill pipe.

[0039] Through the above technical solution, the technical solution includes: determining the formation pore pressure based on the static water level height in the well; setting the annulus bottom hole pressure equal to the formation pore pressure, and determining the reference dynamic water level height of the drilling fluid according to the annulus bottom hole pressure, relevant parameters of the air-lift reverse circulation drilling equipment, and relevant parameters of the drilling fluid; determining the first target dynamic water level height based on the reference dynamic water level height, and during drilling, controlling the dynamic water level height of the drilling fluid to be the first target dynamic water level height, where the first target dynamic water level height is lower than the reference dynamic water level height. Based on the solution provided by the embodiments of the present application, by controlling the dynamic water level height of the drilling fluid during drilling to be lower than the reference dynamic water level height corresponding to the equal annulus bottom hole pressure and formation pore pressure, the annulus bottom hole pressure can be controlled to be less than the formation pore pressure, so that the drilling process remains in an underbalanced state. Thus, it is possible to avoid the leakage of the drilling fluid into the formation and cause damage to the heat reservoir.

[0040] Other features and advantages of the embodiments of the present application will be described in detail in the subsequent specific implementation part. Brief Description of the Drawings

[0041] The accompanying drawings are used to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the embodiments of the present application, but do not limit the embodiments of the present application. In the accompanying drawings:

[0042] Figure 1 Schematically shows a structural schematic diagram of an air-lift reverse circulation drilling device and a wellbore structure schematic diagram according to an embodiment of the present application;

[0043] Figure 2 Schematically shows a flow schematic diagram of an air-lift reverse circulation drilling method according to an embodiment of the present application;

[0044] Figure 3 Schematically shows a flow schematic diagram of another air-lift reverse circulation drilling method according to an embodiment of the present application.

[0045] Description of the reference numerals

[0046] 101 - Air compressor; 102 - Air box; 1031 - Inner pipe of the double-wall drill pipe; 1032 - Outer pipe of the double-wall drill pipe; 104 - Air-liquid mixer; 1041 - Air mixing hole; 105 - Single-wall drill pipe; 106 - Drill bit; 1061 - Drill teeth; 1062 - Drill bit slag suction port; 107 - Sand discharge pipeline; 108 - Mud pit; 109 - Mud pump; 110 - Drilling fluid input pipeline; 111 - Flowmeter; 112 - Throttle valve; 113 - Annular check valve; 114 - Annular fluid level monitoring echo sounder; 115 - Swivel; 201 - Formation; 202 - Wellbore wall; 203 - Cementing; 204 - Casing. Specific embodiments

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. It should be understood that the specific embodiments described herein are only used to illustrate and explain the embodiments of the present application, and do not limit the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0048] It should be noted that if there are directional indications (such as up, down, left, right, front, back...) involved in the embodiments of the present application, the directional indications are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0049] In addition, if descriptions such as "first" and "second" are involved in the embodiments of this application, the descriptions of "first", "second", etc. are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between various embodiments may be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0050] As described in the background art, in the field of geothermal drilling, the wellbore mostly adopts a large-diameter and multi-opening structure, and the lower casing does not return to the wellhead, resulting in a relatively large annular cross-sectional area in the upper well section. When using normal circulation drilling, this wellbore structure leads to a relatively low cuttings-carrying capacity of the drilling fluid in the upper large-diameter well section. To meet the cuttings-carrying requirements in the upper large-diameter well section, it is often necessary to inject a large pump volume of drilling fluid. The injection of a large pump volume of drilling fluid, on the one hand, requires higher configuration requirements for equipment such as mud pumps, and on the other hand, causes an excessive upward return velocity of the drilling fluid in the lower small-diameter well section, which in turn leads to erosion and instability of the wellbore wall. It can be seen that normal circulation drilling either has a poor cuttings-carrying capacity in the large-diameter well section or is prone to erosion of the wellbore wall in the small-diameter well section.

[0051] To alleviate the above problems existing in normal circulation drilling, air-lift reverse circulation drilling is mostly used now. The drilling equipment used in air-lift reverse circulation drilling can be as Figure 1 shown. The equipment includes an air compressor 101, an air box 102, a double-wall drill pipe, an air-liquid mixer 104, a single-wall drill pipe 105, a drill bit 106, a sand discharge pipeline 107, a mud pit 108, a mud pump 109 (the mud pump 109 can specifically be a variable-frequency mud pump capable of adjusting the injection volume of the drilling fluid), a drilling fluid input pipeline 110, a flowmeter 111, a throttle valve 112, an annular check valve 113, an annular fluid level monitoring echo sounder 114, and a swivel 115. Among them, the double-wall drill pipe includes a double-wall drill pipe inner pipe 1031 and a double-wall drill pipe outer pipe 1032; the air-liquid mixer 104 has air mixing holes 1041; the drill bit 106 includes drill teeth 1061 and a drill bit slag suction port 1062. The wellbore structure can be as Figure 1 shown, including a formation 201, a wellbore wall 202, a cement casing 203, and a casing 204.

[0052] Air-lift reverse circulation drilling is to transport compressed air A through the annular space between the inner and outer pipes of a double-wall drill pipe to a certain depth; then, the compressed air A is mixed with the drilling fluid in the inner cavity of the drill pipe through an air-liquid mixer 104, causing a density difference between the fluids inside and outside the drill pipe, and thus forming a reverse circulation: the drilling fluid B is injected into the well through the annulus, and after carrying the cuttings C, the drilling fluid B flows into the bit nozzle (the direction in which the drilling fluid B carries the cuttings C towards the drill pipe can be as shown by the arrow pointing to the drill pipe in Figure 1 ), and then returns to the surface through the inner cavity of the drill pipe. Since the cross-sectional area of the inner cavity of the drill pipe is small and the upward flow velocity of the drilling fluid is fast, the cuttings-carrying capacity is better than that of normal circulation drilling. At the same time, during reverse circulation drilling, the bottom hole pressure in the annulus is relatively low, so the wellbore wall can be avoided from being eroded as much as possible.

[0053] Generally, the geothermal reservoir has well-developed fractures and relatively low formation pressure. If the drilling process is controlled in an overbalanced state where the bottom hole pressure in the annulus is greater than the formation pore pressure, under the action of the pressure difference, cuttings and other substances will enter the geothermal reservoir channels along with the drilling fluid and damage the geothermal reservoir, thus affecting the single-well water production during subsequent heat extraction. Therefore, when using air-lift reverse circulation drilling, the drilling process is generally further controlled in an underbalanced state where the bottom hole pressure in the annulus is less than the formation pore pressure. However, in the case of relatively low formation pore pressure, it is difficult for the existing technology to accurately control the bottom hole pressure in the annulus, and thus it is difficult to keep the drilling process in an underbalanced state, which is likely to cause the drilling fluid to leak into the formation and damage the geothermal reservoir.

[0054] In view of this, in one embodiment of the present application, an air-lift reverse circulation drilling method is provided. As shown in Figure 2 , the air-lift reverse circulation drilling method may include the following steps:

[0055] Step 301: Determine the formation pore pressure based on the static water level height in the well.

[0056] Wherein, the static water level height may be the liquid level height of the liquid in the well in a static state when air-lift reverse circulation drilling is not carried out. The liquid in the well is usually water. The static water level height can be obtained by an annulus liquid level monitoring echo sounder.

[0057] In the embodiment of the present application, the static water level in the well may be lower than the wellhead surface, indicating relatively low formation pore pressure. That is, the air-lift reverse circulation drilling method provided in the embodiment of the present application can be applied to the case of relatively low formation pore pressure.

[0058] During drilling, the static water level usually does not change or changes very little. Therefore, as the depth increases, the formation pore pressure increases linearly. Thus, in specific implementation, step 301 of determining the formation pore pressure based on the static water level height in the well can be carried out based on the following formula (1):

[0059] P p =P0 +ρ w gh j (1);

[0060] Wherein, P p is the formation pore pressure, with the unit of MPa; P 0 is the standard atmospheric pressure; ρ w is the water density, with the unit of kg / m 3 ; g is the acceleration of gravity; h j is the static water level height in the well, with the unit of m. In practical applications, P 0 can be taken as 0.1 MPa; ρ w can be selected according to the temperature. For example, when the temperature is 4°C, it is taken as 10 3 kg / m 3 ; g can be taken as 9.8 m / s 2 .

[0061] Step 302, set the bottom hole pressure in the annulus equal to the formation pore pressure, and determine the reference dynamic water level height of the drilling fluid according to the bottom hole pressure in the annulus, the relevant parameters of the air-lift reverse circulation drilling equipment, and the relevant parameters of the drilling fluid.

[0062] Wherein, the bottom hole pressure in the annulus being equal to the formation pore pressure can be as shown in the following formula (2):

[0063] P b =P p (2);

[0064] Wherein, P b is the bottom hole pressure in the annulus, with the unit of MPa.

[0065] The relevant parameters of the air-lift reverse circulation drilling equipment can include the dimensions of each part of the equipment, frictional resistance, friction coefficient, roughness, etc. The relevant parameters of the drilling fluid can include the density, flow velocity, flow rate, viscosity, etc. of the drilling fluid.

[0066] In the embodiments of the present application, the reference dynamic water level height can be the liquid level height of the drilling fluid flowing in the well assuming that the air-lift reverse circulation drilling process is in a state where the bottom hole pressure in the annulus is equal to the formation pore pressure. This reference dynamic water level height is a calculated reference value rather than a measured value.

[0067] In specific implementation, step 302 determines the reference dynamic water level height of the drilling fluid according to the bottom hole pressure in the annulus, the relevant parameters of the air-lift reverse circulation drilling equipment, and the relevant parameters of the drilling fluid, which can be based on the following formula (3), formula (4), and formula (5):

[0068] P b =P 0 +P h-∑P fi (3);

[0069] In the above formula (3),

[0070] P h = ρ 1 gh d (4);

[0071]

[0072] wherein, P h is the hydrostatic pressure of the drilling fluid in the annulus, with the unit of MPa; P fi is the frictional resistance corresponding to the i-th open annulus, with the unit of MPa; ρ 1 is the density of the drilling fluid, with the unit of kg / m 3 ; h d is the reference dynamic water level height of the drilling fluid, with the unit of m; f i is the Fanning friction coefficient corresponding to the i-th open annulus; v ai is the flow velocity of the drilling fluid in the annulus corresponding to the i-th open annulus (i = 1, 2, 3...), with the unit of m / s; h i is the liquid column height of the drilling fluid corresponding to the i-th open annulus, with the unit of m; d wbi is the wellbore diameter corresponding to the i-th open, with the unit of m; d toi is the outer diameter of the drill pipe corresponding to the i-th open, with the unit of m.

[0073] In the above formula (5), the flow velocity v of the drilling fluid in the annulus corresponding to the i-th open annulus ai can be calculated based on the following formula (6)

[0074]

[0075] wherein, Q m is the flow rate of the drilling fluid of the adjacent well, with the unit of m 3 / s. Q m can also be understood as the initial value of the assumed volume flow rate of the drilling fluid injected into the wellhead.

[0076] Generally speaking, for a certain drilling area, multiple wells are usually drilled. That is to say, near the well where gas lift reverse circulation drilling is about to be carried out in the embodiments of the present application, there are usually other wells that have completed drilling or are in the process of drilling. When calculating v ai , the volume flow rate of the drilling fluid returned from the wellhead of such nearby wells can be used as Q m . The volume flow rate of the drilling fluid returned from the wellhead of the nearby wells is generally an empirical value, so the calculated v ai has a relatively high accuracy and a small error.

[0077] In practical applications, when the flow type of the drilling fluid in the annulus corresponding to the opening of annulus i is laminar flow, i.e., the Reynolds number N R is 0 - 2000, the Fanning friction coefficient f corresponding to the opening of annulus i in the above formula (5) i can be calculated by the following formula (7):

[0078]

[0079] where, N R is the Reynolds number of the drilling fluid in the annulus.

[0080] When the flow type of the drilling fluid in the annulus corresponding to the opening of annulus i is transitional flow or turbulent flow, i.e., the Reynolds number N R is greater than 2000, the Fanning friction coefficient f corresponding to the opening of annulus i in the above formula (5) i can be calculated based on the following formula (8), formula (9), formula (10) and formula (11):

[0081]

[0082] In the above formula (8),

[0083]

[0084]

[0085]

[0086] where, e p is the absolute roughness of the annulus surface, in m; e wb is the absolute roughness of the open hole surface, in m; e t is the absolute roughness of the drill pipe and casing surfaces, in m; v is the kinematic viscosity of the drilling fluid, in m 2 / s; μ is the dynamic viscosity of the drilling fluid, in m 2 / s. In practical applications, e wb can be taken as 0.003 m, e t can be taken as 0.0002 m. Since water is mostly used for drilling, μ can be taken as 0.001 Pa·s.

[0087] In practical applications, the flow type of the drilling fluid in the annulus is mostly transitional flow or turbulent flow. Therefore, the Fanning friction coefficient f corresponding to the opening of annulus i can be calculated based on the above formula (8), formula (9), formula (10) and formula (11) i .

[0088] Step 303: Based on the reference flowing water level height, determine the first target flowing water level height. During the drilling process, control the flowing water level height of the drilling fluid to be the first target flowing water level height, where the first target flowing water level height is lower than the reference flowing water level height.

[0089] It can be understood that the reference flowing water level height corresponds to the state where the annulus bottom hole pressure is equal to the formation pore pressure; and generally, the higher the flowing water level height, the greater the annulus bottom hole pressure usually is, and the lower the flowing water level height, the smaller the annulus bottom hole pressure usually is. Therefore, during the drilling process, controlling the water level height of the drilling fluid to be the first target flowing water level height lower than the reference flowing water level height can make the annulus bottom hole pressure less than the formation pore pressure in the actual drilling process, and further control the drilling process to be in an underbalanced state.

[0090] In practical applications, in order to improve the upward return velocity of the drilling fluid as much as possible, thereby improving the rock-carrying capacity of the drilling fluid, it is possible to control the water level height of the drilling fluid to be slightly lower than the reference flowing water level height and as close to the reference flowing water level height as possible on the premise of controlling the water level height of the drilling fluid to be lower than the reference flowing water level height during the drilling process.

[0091] During specific construction, at the beginning, a large pump volume method can be used to inject the drilling fluid into the well to quickly establish a reverse circulation, and the flowing water level is monitored in real time through an annulus liquid level monitoring echo sounder. When the flowing water level height reaches the first target flowing water level height, control the circulation volume of the drilling fluid delivered by the mud pump to a smaller pumping volume to make the reverse circulation relatively stable.

[0092] It can be understood that the air-lift reverse circulation drilling method provided by the embodiments of the present application includes: determining the formation pore pressure based on the static water level height in the well; setting the annulus bottom hole pressure equal to the formation pore pressure, and determining the reference flowing water level height of the drilling fluid according to the annulus bottom hole pressure, relevant parameters of the air-lift reverse circulation drilling equipment, and relevant parameters of the drilling fluid; based on the reference flowing water level height, determining the first target flowing water level height, and during the drilling process, controlling the water level height of the drilling fluid to be the first target flowing water level height, where the first target flowing water level height is lower than the reference flowing water level height. Based on the solution provided by the embodiments of the present application, by controlling the flowing water level height of the drilling fluid during the drilling process to be lower than the reference flowing water level height corresponding to the equal state of the annulus bottom hole pressure and the formation pore pressure, the annulus bottom hole pressure can be controlled to be less than the formation pore pressure, and the drilling process can be maintained in an underbalanced state. Thus, it is possible to avoid the drilling fluid leaking into the formation and causing damage to the heat reservoir.

[0093] Considering Q in formula (6) mis obtained from other wells, so that during the drilling process, after controlling the water level height of the drilling fluid to the first target dynamic water level height, it is possible that the annulus bottom hole pressure is not less than the formation pore pressure and the drilling process is not in an underbalanced state. Therefore, in order to further ensure that the drilling process is in an underbalanced state, in one embodiment, after step 303 of controlling the water level height of the drilling fluid to the first target dynamic water level height, the air-lift reverse circulation drilling method provided by the embodiments of the present application further includes step one, step two, step three, and step four, which can be specifically as follows:

[0094] Step one, obtain the actual flow rate of the drilling fluid during the drilling process.

[0095] Step two, based on the actual flow rate and the first target dynamic water level height, determine the actual annulus bottom hole pressure during the drilling process.

[0096] In specific implementation, the actual flow rate of the drilling fluid can be taken as v ai and the first target dynamic water level height can be taken as h d Then, based on the above formula (3), calculate the current actual annulus bottom hole pressure P b .

[0097] Step three, determine whether the actual annulus bottom hole pressure is less than the formation pore pressure.

[0098] It can be understood that if the actual annulus bottom hole pressure is less than the formation pore pressure, it means that the current drilling process is in an underbalanced state; if the actual annulus bottom hole pressure is not less than the formation pore pressure, it means that the current drilling process is not in an underbalanced state.

[0099] Step four, in response to the actual annulus bottom hole pressure not being less than the formation pore pressure, control the water level height of the drilling fluid to the second target dynamic water level height during the subsequent drilling process, and the second target dynamic water level height is lower than the first target dynamic water level height.

[0100] In response to the actual annulus bottom hole pressure being less than the formation pore pressure, during the subsequent drilling process, the water level height of the drilling fluid can be controlled to be maintained at the first target dynamic water level height.

[0101] In practical applications, after controlling the water level height of the drilling fluid to the second target dynamic water level height, the actual annulus bottom hole pressure corresponding to the second target dynamic water level height can be continuously calculated to determine whether it is less than the formation pore pressure. If it is not less than, the water level height of the drilling fluid can be continuously reduced until the actual annulus bottom hole pressure is less than the formation pore pressure.

[0102] In order to further improve the rock-carrying capacity of the drilling fluid, in one embodiment, after step 303 controls the dynamic water level height of the drilling fluid to be the first target dynamic water level height, the air-lift reverse circulation drilling method provided by the embodiments of the present application further includes:

[0103] Step 401, determining the flow velocity of the drilling fluid corresponding to different parts of the inner cavity of the drill pipe and determining the minimum flow velocity required for the drilling fluid to carry rock cuttings with a target particle size.

[0104] If the actual annulus bottom hole pressure is not less than the formation pore pressure after controlling the water level height of the drilling fluid to be the first target dynamic water level height, and the water level height of the drilling fluid is further adjusted. Then, step 401 can be executed after controlling the actual annulus bottom hole pressure to be less than the formation pore pressure.

[0105] In the embodiments of the present application, the drill pipe may include a double-wall drill pipe part and a single-wall drill pipe part. Furthermore, the inner cavity of the drill pipe may include a double-wall drill pipe inner cavity and a single-wall drill pipe inner cavity.

[0106] In specific implementation, step 401 determines the flow velocity of the drilling fluid corresponding to different parts of the inner cavity of the drill pipe, which can be based on the following formula (12):

[0107]

[0108] where Q L is the volume flow rate of the drilling fluid returned to the wellhead, with the unit of m 3 / s; d ti is the inner diameter of the drill pipe, with the unit of m; ν pi is the flow velocity of the drilling fluid in the inner cavity of the drill pipe, with the unit of m / s.

[0109] Step 401 determines the minimum flow velocity required for the drilling fluid to carry rock cuttings with a target particle size, which can be based on the following formula (13) and formula (14):

[0110] ν f = ν c + ν t (13);

[0111]

[0112] where v f is the minimum flow velocity required for the drilling fluid to carry rock cuttings with a target particle size, with the unit of m / s; v c is the critical velocity of the drilling fluid for carrying rock, with the unit of m / s; v t is the settling velocity of the rock cuttings with a target particle size, with the unit of m / s; κ is the instantaneous mechanical drilling rate, with the unit of m / h; C is the rock cutting concentration coefficient.

[0113] In practical applications, the particle size of the target-sized cuttings can be the particle size of the cuttings returned at the wellhead of an adjacent well. For example, if most of the particle sizes of the cuttings returned at the wellhead of an adjacent well are M, then the particle size of the target-sized cuttings can be set to M. The cuttings concentration coefficient C can be taken as 0.04.

[0114] When the fluid flow type in the drill pipe inner cavity is laminar flow, ν in the above formula (13) t can be calculated by the following formula (15):

[0115]

[0116] where D c is the particle size of the target-sized cuttings, with the unit of m; η is the absolute viscosity of the drilling fluid, with the unit of N·s / m 2 ; γ s is the specific weight of the target-sized cuttings, with the unit of N / m 3 ; γ f is the specific weight of the drilling fluid, with the unit of N / m 3 .

[0117] When the fluid flow type in the drill pipe inner cavity is transitional flow or turbulent flow, v in the above formula (13) t can be calculated by the following formula (16):

[0118]

[0119] where f p is the friction coefficient of the target-sized cuttings.

[0120] Step 402, control the flow rates of the drilling fluids corresponding to different parts in the drill pipe inner cavity to be greater than the minimum flow rate.

[0121] In practical applications, after adjustment, if the flow rate of the drilling fluid at a certain part of the drill pipe still cannot reach the flow rate required for cuttings carrying, then step 402 can further include: increasing the proportion of double-wall drill pipes in the drill pipe. That is, increasing the extended depth of the double-wall drill pipes and increasing the sink ratio (the ratio of the double-wall drill pipes to the whole drill pipe). Thereby, the pressure difference between the inside and outside of the drill pipe can be increased, so that the upward return flow rate of the drilling fluid can be increased and the cuttings carrying capacity can be improved.

[0122] In specific implementation, the minimum length of the double-wall drill pipes that can meet the cuttings carrying requirements can be determined first, and then on the basis of this minimum length, the length of the double-wall drill pipes can be further increased.

[0123] Since the top of the central passage of the single-wall drill pipe is connected to the double-wall drill pipe and the bottom of the single-wall drill pipe is connected to the drill bit, the length of the single-wall drill pipe is equal to the difference between the well depth and the depth of the double-wall drill pipe run in. Moreover, in the central passage of the single-wall drill pipe, the pressure difference between its bottom and top is equal to the difference between the pressure upstream of the drill bit and the pressure of the mixed flow at the bottom of the double-wall drill pipe. The minimum depth or the minimum length of the double-wall drill pipe run in can be determined by the bottom hole pressure in the annulus, the pressure loss at the nozzles of the drill bit, and the pressure of the mixed flow at the bottom of the inner pipe of the double-arm drill pipe. Specifically, it can be calculated based on the following formulas (17), (18), (19), and (20):

[0124] P b -ΔP b -P h1 =γ Ls (H - h 1 ) (17);

[0125] In the above formula (17),

[0126]

[0127]

[0128]

[0129] where, ΔP b is the pressure loss at the nozzles of the drill bit, with the unit of MPa; P h1 is the pressure of the mixed flow at the bottom of the inner pipe of the double-wall drill pipe, with the unit of MPa; γ Ls is the specific weight of the mixed flow in the central passage of the single-wall drill pipe, with the unit of N / m 3 ; H is the well depth, with the unit of m; h 1 is the minimum length of the double-wall drill pipe, with the unit of m; is the number of nozzles of the drill bit; D ki is the diameter of the i-th nozzle of the drill bit, with the unit of m; is the weight flow rate of the mixed flow in the inner pipe of the double-wall drill pipe, with the unit of N / s; P gh1 is the pressure of the compressed air at the gas-liquid mixer, with the unit of Pa; Q gh1 is the volume flow rate of the compressed air at the gas-liquid mixer, with the unit of m 3 / s; d is the inner diameter of the double-wall drill pipe, with the unit of m.

[0130] When the total length of the double-wall drill pipe equipped on site is limited and it is impossible to meet the rock-carrying requirement by adjusting the length of the double-wall drill pipe, step 402 may include, when safety conditions permit: reducing the inner diameter of the single-wall drill pipe in the drill pipe. That is, the current single-wall drill pipe can be replaced with a single-wall drill pipe with a finer available specification, and the upward flow velocity of the drilling fluid can be increased by reducing the cross-sectional area of the inner cavity of the drill pipe, thereby improving the rock-carrying capacity.

[0131] It can be understood that based on the air-lift reverse circulation drilling method provided in the embodiments of the present application, the drilling process can be in an underbalanced state and high-efficiency rock carrying can also be achieved.

[0132] It should also be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, commodity or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, commodity or device including the element.

[0133] The above are only the embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the scope of the claims of the present application.

Claims

1. A gas lift reverse circulation drilling method, characterized in that: The method comprises: Determine the formation pore pressure based on the static water level in the well; Setting the annulus bottom hole pressure equal to the formation pore pressure, and determining the reference dynamic water level height of the drilling fluid according to the annulus bottom hole pressure, relevant parameters of the gas lift reverse circulation drilling equipment and relevant parameters of the drilling fluid; Based on the reference dynamic water level, a first target dynamic water level is determined. During drilling, the dynamic water level of the drilling fluid is controlled to be the first target dynamic water level, which is lower than the reference dynamic water level.

2. The gas lift reverse circulation drilling method according to claim 1, characterized in that: The formation pore pressure is determined based on the static water level in the well, based on the following formula: P p =P0+ρ w gh j ; Among them, P p is the formation pore pressure, in MPa; P0 is the standard atmospheric pressure; ρ w is the water density in kg / m 3 ; g is the acceleration due to gravity; h j is the static water level in the well, in m.

3. The gas lift reverse circulation drilling method according to claim 1, characterized in that: The reference dynamic water level height of the drilling fluid is determined according to the annular bottom hole pressure, relevant parameters of the gas lift reverse circulation drilling equipment and relevant parameters of the drilling fluid, based on the following formulas: P b =P0+P h -∑P fi ; P h =ρ1gh d ; Among them, P p is the annulus bottom pressure, in MPa; P0 is the standard atmospheric pressure; P h is the hydrostatic pressure of the drilling fluid in the annulus, in MPa; P fi is the friction resistance corresponding to the annulus i opening, in MPa; ρ1 is the density of the drilling fluid, in kg / m 3 ; g is the acceleration due to gravity; h d is the reference dynamic water level height of drilling fluid, in m; f i is the Fanning friction coefficient corresponding to the annulus i; v ai is the flow rate of drilling fluid in the annulus corresponding to the annulus i opening, in m / s; h i is the height of the drilling fluid column corresponding to the annulus i opening, in m; d wbi is the well diameter corresponding to i, in m; d toi The outer diameter of the drill pipe corresponding to the i-th opening, in m.

4. The gas lift reverse circulation drilling method according to claim 3, characterized in that: Among them, Q m is the flow rate of drilling fluid in the adjacent well, in m 3 / s;e p is the absolute roughness of the annulus surface, in m; N R is the Reynolds number of the drilling fluid in the annulus.

5. The gas lift reverse circulation drilling method according to claim 1, characterized in that: After the dynamic water level of the drilling fluid is controlled to be the first target dynamic water level, the method further includes: Obtaining the actual flow rate of the drilling fluid during drilling; Determining actual annular bottom hole pressure during drilling based on the actual flow rate and the first target dynamic water level height; Determining whether the actual annulus bottom hole pressure is less than the formation pore pressure; In response to the actual annulus bottom hole pressure being not less than the formation pore pressure, the dynamic water level of the drilling fluid is controlled to be a second target dynamic water level during subsequent drilling, and the second target dynamic water level is lower than the first target dynamic water level.

6. The gas lift reverse circulation drilling method according to claim 1, characterized in that: After controlling the dynamic water level of the drilling fluid to be the first target dynamic water level, the method further includes: Determining a minimum flow rate of the drilling fluid required to carry cuttings of a target particle size; The flow rates of the drilling fluid corresponding to different parts of the inner cavity of the drill pipe are controlled to be greater than the minimum flow rate.

7. The gas lift reverse circulation drilling method according to claim 6, characterized in that: The determination of the minimum flow rate required for the drilling fluid to carry the target particle size cuttings is based on the following formulas: n f =n c +n t ; Among them, ν f The minimum flow rate required for the drilling fluid to carry the target particle size cuttings, in m / s; ν c is the critical velocity of drilling fluid carrying rock, in m / s; ν t is the settling velocity of the target particle size cuttings, in m / s; κ is the instantaneous mechanical drilling speed, in m / h; C is the cuttings concentration coefficient.

8. The gas lift reverse circulation drilling method according to claim 7, characterized in that: Among them, D c is the particle size of the target particle size cuttings, in m; γ s is the density of the target particle size cuttings, in N / m 3 ; γ f is the density of drilling fluid, in N / m 3 ;f p is the friction coefficient of the target particle size cuttings.

9. The gas lift reverse circulation drilling method according to claim 6, characterized in that: The control method of controlling the flow rates of the drilling fluid corresponding to different parts of the inner cavity of the drill pipe to be greater than the minimum flow rate comprises: Increase the proportion of double-wall drill pipe in drill pipe.

10. The gas lift reverse circulation drilling method according to claim 6, characterized in that: The controlling the flow rates of the drilling fluid corresponding to different parts of the inner cavity of the drill pipe to be greater than the minimum flow rate includes: reducing the inner diameter of the single-wall drill pipe in the drill pipe.

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