Underbalanced drilling, system and prediction method for geothermal well

Abstract

The invention relates to the technical field of geothermal wells, in particular to a geothermal well underbalanced drilling well and system and a prediction and installation method. The drill rod and the casing pipe are coaxially arranged, the outer diameter of the drill rod is smaller than the inner diameter of the casing pipe, and an annulus exists between the drill rod and the casing pipe; and the gas injection pipe is arranged on the outer side of the casing pipe and communicates with the annulus, and the gas injection pipe is used for injecting variable-flow gas to be mixed with the drilling fluid in the annulus to form gas-liquid two-phase flow. The gas injection pipe is communicated with the annulus of the casing pipe, and the mixing density of liquid in the annulus is changed by injecting gas into the casing pipe, so that the well bottom pressure is smaller than the formation pressure, the unbalanced drilling effect is achieved, the drilling speed can be increased, and a large amount of drilling fluid can be prevented from leaking into formation cracks.

Description

Technical Field

[0001] The present invention relates to the field of geothermal well technology, and in particular to an underbalanced drilling, system, prediction and method for a geothermal well. Background Art

[0002] During the drilling of a geothermal well, as the drill bit penetrates deeper into the ground, the hydrostatic pressure generated by the column of drilling fluid circulating within the wellbore increases. When this hydrostatic pressure exceeds the natural pore pressure of the formation being drilled, the wellbore enters a state of "overbalance." This high differential pressure creates numerous challenges for drilling operations.

[0003] First, excessive bottomhole pressure exerts a significant reaction force on the rock below the drill bit, making it difficult for the drill bit to effectively break and cut the rock. This phenomenon is known as "holding force." This directly reduces the drill bit's cutting efficiency, significantly slowing the rate of penetration (ROP). This reduction in ROP not only prolongs the drilling cycle but also increases overall operating costs.

[0004] Secondly, the over-equilibrium state may also cause a series of complex problems downhole. High-pressure drilling fluid and the solid particles it carries may be forced into the formation, blocking the reservoir pores, causing irreversible damage to the natural permeability of the geothermal reservoir, and thus affecting the production capacity of geothermal resources. In addition, if the pressure at the bottom of the hole exceeds the fracture pressure of the formation, a large amount of drilling fluid will be lost into the formation cracks, resulting in serious circulation losses, which not only wastes precious drilling fluid, but may also cause well control risks. In some cases, the filter cake formed by the drilling fluid on the well wall may also cause the drill pipe to be stuck by the pressure difference, further increasing the drilling risk and non-productive time. Therefore, effectively managing the pressure at the bottom of the hole and avoiding the negative impact of over-equilibrium are the key to ensuring efficient and safe geothermal drilling. The purpose of the present invention is to derive a calculation method for predicting and adjusting the injection flow rate based on the data relationship between the pressure at the bottom of the hole and the pressure at the formation pressure. Summary of the Invention

[0005] Some simplifications or omissions may be made in this section and the abstract and title of the present application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions shall not be used to limit the scope of the invention.

[0006] In order to address the deficiencies of the prior art, one object of the present invention is to provide an underbalanced drilling of a geothermal well, comprising a casing; a drill pipe, which is coaxially arranged with the casing, the outer diameter of the drill pipe is smaller than the inner diameter of the casing, and there is an annulus between the drill pipe and the casing; a gas injection pipe, which is arranged on the outside of the casing and connected to the annulus, and the gas injection pipe is used to inject a variable flow of gas to mix with the drilling fluid in the annulus to form a gas-liquid two-phase flow.

[0007] As a preferred solution for the underbalanced drilling of geothermal wells described in the present invention, it further comprises: a base, which includes an inlet and an outlet; a through hole is provided on the casing, the through hole is connected to the annulus in the casing, the outlet is connected to the through hole, and the inlet is used to connect the gas injection pipe.

[0008] As a preferred solution for the underbalanced drilling of geothermal wells described in the present invention, it further includes: a fixing member, which is arranged on the casing, and a limiting cavity is provided on the fixing member, the inner wall of the limiting cavity is in conflict with the outer peripheral wall of the gas injection pipe, and the direction of the force applied by the limiting cavity to the gas injection pipe is toward the central axis of the gas injection pipe.

[0009] Another object of the present invention is to provide a geothermal well underbalanced drilling system, including: an acquisition module, which is used to collect the bottom layer depth and water head depth of the borehole in real time and generate a depth signal; a calculation module, which is used to calculate the formation pressure and bottom hole pressure in real time according to the depth signal and generate a pressure signal; a control module, which is used to determine the quantitative relationship between the bottom hole pressure and the formation pressure according to the pressure signal, and if the bottom hole pressure is greater than the formation pressure, an overbalanced state signal is generated and fed back to the calculation module; the calculation module continues to calculate the target mixing density according to the liquid column pressure in the equilibrium state, and the control module again generates an airflow control signal according to the target mixing density; and an injection module, which adjusts the injection flow in real time according to the airflow control signal.

[0010] As a preferred solution of the geothermal well underbalanced drilling system described in the present invention, it includes: m opening depth, m is an integer ≥ 2; there are n casings, and the n casings are arranged in a one-to-one correspondence with the m opening depth; the n casings are coaxial in the horizontal direction and are arranged in sequence from the outside to the inside, and the n casings are arranged in sequence from top to bottom along the vertical direction, and there is an overlapping section between two adjacent casings in the vertical direction; there is an annulus between the drill pipe and the n casings, and the n annuli are connected; the gas injection pipe is connected to the annulus in the casing at an opening depth.

[0011] Another object of the present invention is to provide a method for predicting and installing underbalance in a geothermal well, comprising: completing drilling of a first opening depth and installing a suitable casing in the first opening depth; continuing drilling of a second opening depth, collecting the bottom depth of the borehole and the water head depth in real time, and calculating the formation pressure and bottom hole pressure in real time; judging the quantitative relationship between the bottom hole pressure and the formation pressure, and if the bottom hole pressure is greater than the formation pressure, injecting gas into the casing in the first opening depth; adjusting the gas injection flow in real time; completing drilling of the second opening depth and installing the suitable casing in the second opening depth; repeating the above steps and completing drilling of an opening depth of m, where m is an integer ≥2.

[0012] As a preferred solution of the geothermal well underbalance prediction and installation method of the present invention, the target mixing density is calculated respectively. , gas density , liquid volume fraction Annulus area , drilling fluid flow in the annulus , Hydrostatic pressure at the gas injection point and downhole gas flow .

[0013] As a preferred solution of the geothermal well underbalance prediction and installation method of the present invention, the downhole gas flow rate is Converted to standard gas flow , expressed as: ; in, is the standard gas flow rate, is the downhole gas flow rate, is the average pressure, is the pressure at the wellhead under standard atmospheric pressure, is the temperature at the wellhead under standard atmospheric pressure, is the average temperature.

[0014] As a preferred embodiment of the method for predicting and installing underbalanced geothermal wells according to the present invention, the method further includes correcting the equivalent average pressure, which is expressed as: ; in, is the average pressure, The hydrostatic pressure at the gas injection point is high. It is the pressure under standard atmospheric pressure at the wellhead.

[0015] As a preferred solution of the geothermal well underbalance prediction and installation method of the present invention, the following calculation steps are also included: ; ; ; ; ; ; in, is the downhole gas flow rate, is the flow rate of drilling fluid in the annulus, is the liquid volume fraction, is the annulus area, is the annular reverse velocity, is the inner diameter of the casing at an opening depth, is the outer diameter of the drill pipe, is the target mixture density, is the drilling fluid density, is the gas density, is the depth of the gas injection port, is the bottom layer depth, is the formation pressure, is the specific gravity of water, is the water head depth.

[0016] The beneficial effects of the present invention are as follows: the gas injection pipe is connected to the annulus of the casing, and gas is injected into the casing to change the mixed density of the liquid in the annulus, so that the bottom hole pressure is lower than the formation pressure, thereby achieving an underbalanced drilling effect, which can increase the drilling speed and prevent a large amount of drilling fluid from being lost into the formation cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 It is a structural schematic diagram of the underbalanced drilling of the geothermal well according to the present invention.

[0019] Figure 2 This is a structural diagram of the underbalanced drilling of a geothermal well according to the present invention.

[0020] Figure 3 This is a diagram of the parts coordination for underbalanced drilling of a geothermal well according to the present invention.

[0021] Figure 4 It is a cross-sectional view of the components of the underbalanced drilling of a geothermal well according to the present invention.

[0022] Figure 5 This is a connection diagram of the geothermal well underbalanced drilling system of the present invention.

[0023] Figure 6 It is a structural schematic diagram of the geothermal well underbalanced drilling system of the present invention.

[0024] In the figure: 100, casing; 101, overlapping section; 102, annulus; 103, through hole; 200, drill pipe; 300, gas injection pipe; 400, base; 401, inlet; 402, outlet; 500, fixing part; 501, limit cavity; 600, acquisition module; 700, calculation module; 800, control module; 900, gas injection module. DETAILED DESCRIPTION

[0025] In order to make the objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0026] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0027] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0028] Example 1, reference Figure 1 This embodiment is the first embodiment of the invention, which includes a casing 100, a drill pipe 200 and a gas injection pipe 300.

[0029] Specifically, the drill rod 200 drills a hole in the vertical direction, first drilling a one-kilometer hole, and then setting a casing 100 in the hole. It is worth noting that a casing 100 here refers to a combination of multiple segmented casings 100, not a whole one-kilometer-long pipe. The existing technology can achieve segmented installation, which will not be elaborated here.

[0030] When drilling at a subsequent depth, the drill rod 200 is coaxially arranged with the casing 100. The outer diameter of the drill rod 200 is smaller than the inner diameter of the casing 100. There is an annulus 102 between the drill rod 200 and the casing 100. Since the interior of the drill rod 200 is hollow, it is used to inject drilling fluid into the borehole. After the drilling fluid flows out from the bottom of the drill rod 200, it then flows from bottom to top along the vertical annulus 102.

[0031] The gas injection pipe 300 is arranged on the outside of the casing 100, and the axis of the gas injection pipe 300 is parallel to the axis of the casing 100. The annulus 102 between the drill pipe 200 and the casing 100 is connected to the gas injection pipe 300. When drilling at a subsequent depth, a variable flow rate of gas is injected into the casing 100 through the gas injection pipe 300. The gas is mixed with the drilling fluid in the annulus 102 to form a gas-liquid two-phase flow. Through such mixing, the mixed density is reduced, and ultimately the bottom hole pressure is made lower than the formation pressure, achieving an underbalanced drilling effect, thereby increasing the drilling speed and reducing the risk of drilling fluid loss.

[0032] Example 2, reference Figures 1 to 4This embodiment is the second embodiment of the invention, and this embodiment is based on embodiment 1.

[0033] Specifically, it also includes a base 400, which is arranged on the casing 100, and the base 400 includes an inlet 401 and an outlet 402; the inlet 401 is vertically arranged, and a coupling is provided on the side wall of the casing 100, and the coupling is provided with a through hole, and a through hole 103 is provided on the side wall of the casing 100, and the through hole 103 is connected to the annulus 102 in the casing 100, and the outlet 402 is connected to the through hole 103, and the inlet 401 is used to connect the gas injection pipe 300; the through hole 103 is 500 meters away from the ground surface; a single gas injection pipe 300 (length 1m, outer diameter 42mm) is connected to the male connector through the female connector, wherein the male connector is screwed into the base 400 and fixed to form the starting point of the gas injection channel, and the hexagonal outer wall of the female connector of the gas injection pipe 300 is convenient for tightening with a wrench to ensure sealing.

[0034] Furthermore, it also includes a fixing part 500, which is set on the casing 100. The fixing part 500 is provided with a limiting cavity 501. The inner wall of the limiting cavity 501 conflicts with the outer wall of the gas injection pipe 300. The direction of the force applied by the limiting cavity 501 to the gas injection pipe 300 is toward the central axis of the gas injection pipe 300. Each time a gas injection pipe 300 is installed, the fixing part 500 of the gas injection pipe 300 is immediately welded 25 cm away from the female connector. The fixing part 500 of this embodiment is a U-shaped steel bar, which rigidly fixes the gas injection pipe 300 to the outer wall of the casing 100 to prevent it from falling off due to vibration. Repeat this step, extending the gas injection pipes 300 one by one to 1 m above the ground surface. An air compressor interface is reserved at the top of the gas injection pipe 300.

[0035] It is worth noting that the inner diameter of the casing 100 is Φ339.7mm; the coupling of the casing 100 has a 30mm through hole; the base 400 of the gas injection pipe 300 is welded to the coupling, and the outlet 402 is 30mm; the male connector of the gas injection pipe 300 has an outer diameter of 36mm and an inner diameter of 30mm, and is threadedly connected to the base; the gas injection pipe 300 has an outer diameter of 42mm and an inner diameter of 30mm; the fixing part 500 of the gas injection pipe 300 (U-shaped steel bar, welded to the outer wall of the casing 100); the female connector of the gas injection pipe 300 has an outer diameter of 54mm and an inner diameter of 36mm, and is threadedly connected to the gas injection pipe 300; the ground air compressor interface is connected to the top of the gas injection pipe 300 through a hose.

[0036] Example 3, reference Figure 5 This embodiment is the third embodiment of the invention, and is based on embodiment 1 or embodiment 2. This embodiment provides a geothermal well underbalanced drilling system, including an acquisition module 600, a calculation module 700, a control module 800, and a gas injection module 900.

[0037] Specifically, the acquisition module 600 is used to collect the bottom depth and water head depth of the borehole in real time and generate a depth signal; the calculation module 700 is used to calculate the formation pressure and bottom hole pressure in real time according to the depth signal and generate a pressure signal; the control module 800 is used to determine the quantitative relationship between the bottom hole pressure and the formation pressure according to the pressure signal. If the bottom hole pressure is greater than the formation pressure, an over-balanced state signal is generated and fed back to the calculation module 700; the calculation module 700 continues to calculate the target mixing density according to the liquid column pressure in the equilibrium state, and the control module 800 again generates an airflow control signal according to the target mixing density; the gas injection module 900 adjusts the gas injection flow in real time according to the airflow control signal.

[0038] Specifically, the drill rod 200 can gradually drill a borehole with a depth of m, where m is an integer ≥ 2; and in this embodiment, m=2, the drill rod 200 of this embodiment can drill a borehole with a depth of two, and there are n casings 100, and the n casings 100 are arranged in a one-to-one correspondence with the depth of m; this embodiment has two casings 100, after the drilling of the first depth is completed, a casing 100 is provided in the borehole of the first depth, and after the drilling of the second depth is completed, a casing 100 is also provided in the borehole of the second depth.

[0039] Preferably, n casings 100 are coaxial in the horizontal direction and arranged in sequence from the outside to the inside, and n casings 100 are arranged in sequence from top to bottom along the vertical direction, and there is an overlapping section 101 between two adjacent casings 100 in the vertical direction; however, in this embodiment, since there are two casings 100, the two casings 100 are respectively arranged in a borehole with one opening depth and a borehole with two opening depths, the casing 100 in the first opening depth and the casing 100 in the second opening depth are coaxially arranged, and the inner diameter of the casing 100 in the first opening depth is greater than the inner diameter of the casing 100 in the second opening depth, and there is an overlapping section 101 between the upper and lower casings 100 in the vertical direction, and the length of the overlapping section 101 is 30 meters.

[0040] Preferably, there is an annulus 102 between the drill pipe 200 and the n casings 100, and the n annuli 102 are connected; in this embodiment, there is an annulus 102 between the drill pipe 200 and the two casings 100, and the upper and lower annuli 102 are connected, so that the drilling fluid released from the bottom of the drill pipe 200 flows from bottom to top in the two annuli 102; by utilizing the characteristic of the overlapping section 101, the upper and lower annuli 102 can be connected, and the continuous penetration of the gas injection pipe 300 in the drilling of m depth can be achieved, simplifying the gas injection process and improving reliability, and there is no need to connect each casing 100 in the borehole of m depth to the gas injection pipe 300 separately; multiple openings and penetrations are a feature of the adaptability of geothermal wells. When the casing 100 is lowered in subsequent openings, there is no need to add new pipelines, and gas injection can be directly drilled in.

[0041] Preferably, the gas injection pipe 300 is connected to the annulus 102 within the casing 100 at the first drilling depth. During the drilling process, if the bottomhole pressure is greater than the formation pressure, gas can be injected into the annulus 102 within the casing 100 at the first drilling depth through the gas injection pipe 300 to reduce the mixed density of the drilling fluid and gas in the annulus 102 within the casing 100 at the first drilling depth, ultimately making the bottomhole pressure lower than the formation pressure, thereby achieving an underbalanced drilling effect.

[0042] When the drill pipe 200 is circulating and drilling, compressed air (pressure 0.5-2 MPa) is injected into the gas injection pipe 300 through the gas injection module 900, and the gas enters the annulus 102 of the casing 100 at a certain depth through the base 400.

[0043] After the gas is mixed with the drilling fluid, the density of the liquid column in the annulus 102 in the casing 100 at the first drilling depth drops from 1.2g / cm³ to 0.75-1.0g / cm³, while the bottom hole pressure drops by 1.5-3MPa, forming an underbalanced state and increasing the drilling speed by 20%-35%.

[0044] Example 4: This example provides a method for predicting and installing underbalanced geothermal wells.

[0045] S100: Complete drilling of a hole to a certain depth and install an adapted casing 100 in the hole to a certain depth.

[0046] S200: Continue drilling at the second opening depth, collect the bottom depth and water head depth of the bottom layer of the borehole in real time, and calculate the formation pressure and bottom hole pressure in real time. At this time, the bottom hole pressure is first set to be equal to the liquid column pressure; ; ; is the formation pressure, is the specific gravity of water, is the water head depth, is the liquid column pressure, is the target mixed density (when first collected = ), is the depth of the gas injection port (if gas is not injected during the first collection, Calculated as 0), The bottom depth.

[0047] S300: Determine the quantitative relationship between the bottom hole pressure and the formation pressure. If the bottom hole pressure is greater than the formation pressure, inject gas into the casing 100 at the first opening depth.

[0048] S400: Adjust the gas injection flow in real time.

[0049] S401: Calculate target mixed density separately , gas density , liquid volume fraction Annulus area , drilling fluid flow in the annulus , Hydrostatic pressure at the gas injection point and downhole gas flow ; ; ; ; ; is the downhole gas flow rate, is the flow rate of drilling fluid in the annulus, is the liquid volume fraction, is the annulus area, is the annular reverse velocity, is the inner diameter of the casing 100 at an opening depth, is the outer diameter of the drill pipe, is the target mixture density, is the drilling fluid density, is the gas density.

[0050] S402: The gas injection flow model includes a correction to the equivalent average pressure, which is expressed as: ; in, is the average pressure, The hydrostatic pressure at the gas injection point is high. It is the pressure under standard atmospheric pressure at the wellhead.

[0051] S403: Finally, the downhole gas flow Converted to standard gas flow , expressed as: ; in, is the standard gas flow rate, is the downhole gas flow rate, is the average pressure, is the pressure at the wellhead under standard atmospheric pressure, is the temperature at the wellhead under standard atmospheric pressure, is the average temperature.

[0052] S500: Complete the drilling of the second opening depth and install the matching casing 100 in the second opening depth.

[0053] S600: Repeat the above steps and complete drilling to a depth of m, where m is an integer ≥ 2.

[0054] Embodiment 5: This embodiment is the fifth embodiment of the invention and is based on embodiment 4. This embodiment is an embodiment of the calculation process of embodiment 4 using specific parameters.

[0055] S100: Complete drilling to a depth of 1000 meters and install an appropriate casing 100 in the drilling depth.

[0056] S200: Continue drilling at the second drilling depth. At this time, the second drilling depth is drilled to 1100 meters, and the water head is 100 meters below the surface. The formation pressure calculation formula is: ; in, is the specific gravity of water, take 9.81kN / m³, It represents the vertical distance from the groundwater level to the target point, i.e. 1100m - 100m = 1000m; therefore: .

[0057] Calculation of bottomhole pressure: The diameter of the first casing of the geothermal well is 339.7mm, the depth of the first casing is 1000m, the first casing has been drilled to a depth of 100m, and the second casing has been drilled to a depth of 1100m. The diameter of the second casing bit is 311.2mm, the density of the drilling fluid is 1.2g / cm³, and the density of the drilling fluid at all locations in the wellbore is assumed to be the same. At this time, let the bottomhole pressure be equal to the liquid column pressure. The calculation formula for the bottomhole pressure is: ; in, is the target mixed density (when first collected = ), is the drilling fluid density, take 1.2g / cm³, is the depth of the gas injection port (if gas is not injected during the first collection, Calculated as 0), The bottom depth is taken as 1100m; therefore: .

[0058] S300: Determine the quantitative relationship between the bottom hole pressure and the formation pressure. If the pressure is greater than the formation pressure u, the well is in an overbalanced state. Adjust the gas injection and change the bottom hole pressure. To achieve an underbalanced drilling state, the bottom hole pressure needs to be Less than the formation pressure u.

[0059] At this time, assuming that the pressure of the liquid column when it reaches equilibrium is ,but, ; Calculation yields: ; At this point, critical equilibrium is reached, and further reducing the density can achieve underbalance.

[0060] But when Although underbalance is not achieved, the bottom hole pressure is still significantly reduced, which helps to increase the drilling speed.

[0061] S400: Real-time adjustment of gas injection flow rate and calculation of specific parameters.

[0062] (1) Annulus geometric parameters, annulus area: ; (2) Drilling fluid velocity and flow rate, assuming annular return velocity =1m / s, then the flow rate of drilling fluid in the annulus for: ; (3) Pressure at the gas injection point, hydrostatic pressure at 500 meters, ; (4) Due to the target mixture density: ; (5) Gas density calculation (pressure 58.86 bar, temperature 299.4 K): ; Where: P (pressure) is the absolute pressure of the gas at the injection point (unit: Pa or bar); M (molar mass) is the molar mass of air (unit: kg / mol); R (universal gas constant) is 8.314 J / (mol·K); T (temperature) is the absolute temperature at the injection point (unit: K); Values: P is the pressure at the gas injection point (500 meters deep), which is 5.886 MPa; R is the international standard value; T is the assumed geothermal gradient of 3°C / 100m and the surface temperature of 25°C; The temperature at the gas injection point is: ; Assume that the liquid volume fraction , solve , substitute into the formula to solve: ; The solution is =43.59%, gas volume fraction =56.41%; (6) Downhole gas flow calculation , ; (7) Equivalent mean pressure correction: Assuming that the gas expansion is approximately a linear pressure decrease (from 5.886 MPa to 0.1 MPa), then for: ; (8) Converted into standard gas flow, downhole gas flow , Convert to standard condition, ; (Surface standard temperature: 20°C), (Average temperature) = (313.15K (gas injection point temperature) + 293.15) / 2, (standard atmospheric pressure at the surface).

[0063] When the gas injection rate is ≥83.2m³ / min, the bottomhole pressure is lower than the formation pressure (9.81MPa), achieving underbalance. In the underbalanced state, the mechanical drilling speed can be increased by 30% to 50%, and the leakage loss is reduced by more than 70%.

[0064] The purpose of this calculation was to estimate the gas injection rate required to achieve an underbalanced downhole condition. The calculated theoretical gas injection rate was approximately 83.2 m³ / min (under standard operating conditions). This value falls within the mid-range of the operating range of conventional air compressors (0-200 m³ / min), confirming that existing gas injection equipment can meet the process requirements. The calculation results validate the technical feasibility of achieving underbalanced drilling through wellhead gas injection.

[0065] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for predicting and installing underbalanced geothermal wells, characterized by: Complete drilling of a first depth and install a suitable casing (100) in the first depth; Continue drilling at the second opening depth, collect the bottom depth and water head depth of the borehole in real time, and calculate the formation pressure and bottom hole pressure in real time; Determine the quantitative relationship between the bottom hole pressure and the formation pressure, and if the bottom hole pressure is greater than the formation pressure, inject gas into the casing (100) at an opening depth; Adjust the gas injection flow in real time; Complete the drilling of the second opening depth and install the matching casing (100) in the second opening depth; Repeat the above steps and complete the drilling of a hole with a depth of m, where m is an integer ≥ 2; It also includes a correction for the equivalent mean pressure, expressed as: ； in, is the average pressure, The hydrostatic pressure at the gas injection point is high. It is the pressure under standard atmospheric pressure at the wellhead.

2. The geothermal well underbalance prediction and installation method according to claim 1, characterized in that: Calculate the target mixture density separately , gas density , liquid volume fraction Annulus area , drilling fluid flow in the annulus , Hydrostatic pressure at the gas injection point and downhole gas flow .

3. The geothermal well underbalance prediction and installation method according to claim 1, characterized in that: The downhole gas flow Converted to standard gas flow , expressed as: ； in, is the standard gas flow rate, is the downhole gas flow rate, is the average pressure, is the pressure at the wellhead under standard atmospheric pressure, is the temperature at the wellhead under standard atmospheric pressure, is the average temperature.

4. The method for predicting and installing a geothermal well underbalance according to any one of claims 1 to 3, wherein: The following calculation steps are also included: ； ； ； ； ； ； in, is the downhole gas flow rate, is the flow rate of drilling fluid in the annulus (102), is the liquid volume fraction, is the area of ​​the annulus (102), is the annulus (102) reverse velocity, is the inner diameter of the casing (100) at the opening depth, is the outer diameter of the drill rod (200), The pressure of the liquid column when it reaches equilibrium is the target mixture density, is the drilling fluid density, is the gas density, is the depth of the gas injection port, is the bottom layer depth, is the formation pressure, is the specific gravity of water, is the water head depth.

5. A geothermal well underbalanced drilling method, characterized by: include, Casing (100); a drill rod (200) coaxially arranged with the casing (100), the outer diameter of the drill rod (200) being smaller than the inner diameter of the casing (100), and an annulus (102) existing between the drill rod (200) and the casing (100); The gas injection pipe (300) is arranged outside the casing (100) and is connected to the annulus (102). The gas injection pipe (300) is used to inject variable flow gas to mix with the drilling fluid in the annulus (102) to form a gas-liquid two-phase flow.

6. The underbalanced drilling of a geothermal well according to claim 5, characterized in that: Also includes, a base (400) comprising an inlet (401) and an outlet (402); The casing (100) is provided with a through hole (103), the through hole (103) is connected to the annulus (102) in the casing (100), the outlet (402) is connected to the through hole (103), and the inlet (401) is used to connect to the gas injection pipe (300).

7. The underbalanced drilling of a geothermal well according to claim 5 or 6, characterized in that: Also includes, A fixing member (500) is arranged on the sleeve (100), and a limiting cavity (501) is provided on the fixing member (500), the inner wall of the limiting cavity (501) is in conflict with the outer peripheral wall of the gas injection tube (300), and the direction of the force applied by the limiting cavity (501) to the gas injection tube (300) is toward the central axis of the gas injection tube (300).

8. A geothermal well underbalanced drilling system, characterized by: include, A collection module (600) for collecting the bottom depth and water head depth of the borehole in real time and generating a depth signal; A calculation module (700) is used to calculate the formation pressure and bottom hole pressure in real time based on the depth signal and generate a pressure signal; The control module (800) is used to determine the quantitative relationship between the bottom hole pressure and the formation pressure based on the pressure signal, and if the bottom hole pressure is greater than the formation pressure, an over-equilibrium state signal is generated and fed back to the calculation module (700); the calculation module (700) continues to calculate the target mixed density based on the liquid column pressure in the equilibrium state, and the control module (800) again generates an airflow control signal based on the target mixed density; A gas injection module (900) which adjusts the gas injection flow rate in real time according to the gas flow control signal; m opening depth, m is an integer ≥ 2; There are n sleeves (100), and the n sleeves (100) are arranged in a one-to-one correspondence with the m opening depths; The n sleeves (100) are coaxial in the horizontal direction and arranged sequentially from the outside to the inside, and the n sleeves (100) are arranged sequentially from top to bottom along the vertical direction, and two adjacent sleeves (100) have an overlapping section (101) in the vertical direction; There are annular spaces (102) between the drill pipe (200) and the n casings (100), and the n annular spaces (102) are connected; The gas injection pipe (300) is connected to the annulus (102) in the casing (100) at an opening depth.

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