Unconventional coordinated well killing device and method for high-pressure gas wells

Abstract

The present invention relates to an unconventional coordinated well-killing device and method for high-pressure gas wells, and belongs to the field of drilling well control technology. A pressure sensor and a flow meter installed on a pipeline connecting the wellhead and the blowout preventer collect pressure and flow data; different data collection points are connected to a computer and transmitted to the computer in real time; the computer processes and analyzes the collected data in real time, thereby controlling the opening of each valve on the pipeline and the power of the well-killing fluid injection pump group; the two ends of the well-killing fluid injection pump group are respectively connected to the well-killing fluid storage tank and the injection pipeline, and the well-killing fluid is injected into the drill pipe or the annulus, respectively, to achieve safe and efficient well-killing of the high-pressure gas well. The present invention ensures the safety and timeliness of the well-killing of the high-pressure gas well by combining the two unconventional well-killing methods of displacement method and pressure-back method, and invents a corresponding coordinated well-killing device to provide a guarantee for the safe and efficient drilling of high-pressure gas wells.

Description

Technical Field

[0001] The invention relates to an unconventional coordinated well killing device and method for a high-pressure gas well, belonging to the technical field of drilling well control. Background Art

[0002] Existing well control methods With the development of the national economy, my country's demand for oil and gas resources is growing. Oil and gas resource exploration is gradually moving into deep and ultra-deep areas. The oil and gas fields in the Tarim Basin, Junggar Basin, Sichuan Basin and other regions in my country are characterized by high yield, high pressure and even ultra-high pressure. Once gas invasion occurs during the drilling process, it is very easy to cause the risk of blowout and face severe well control problems.

[0003] Safe well killing of high-pressure gas wells is a key technical problem that needs to be solved urgently in the exploration and development of most oil and gas fields in Northwest and Southwest my country at this stage. It can be mainly divided into conventional well killing methods and unconventional well killing methods. Conventional well killing methods include engineer method, driller method, etc., and unconventional well killing methods include displacement method, pressure back method, etc. For oil and gas wells with low formation pressure, conventional well killing methods such as engineer method and driller method can meet the well killing requirements and resume normal drilling. For high-pressure gas wells, the volume and pressure of the intrusion wellbore annulus are both high. Conventional well killing methods may cause the pressure at the wellhead or casing shoe to exceed the pressure range, causing more serious well kick or well leakage problems, so it is difficult to apply. In the case of more gas invading the wellbore, the difference between the wellhead pressure and the formation pressure is small. The pressure back method in the unconventional well killing method also faces the above problems, while the displacement method has problems such as low efficiency, long time, and cumbersome operation. In the process of drilling high-pressure gas wells, if the well is not successfully killed in time, it will cause immeasurable economic losses and even cause casualties, which urgently needs to be studied in depth.

[0004] In summary, the existing well killing methods have certain shortcomings for high-pressure gas well killing. At present, there is still a lack of a safe and efficient well killing method suitable for high-pressure gas wells, which is also the key difficulty restricting the safe and efficient drilling of high-pressure gas wells. For this reason, the present invention is proposed. Summary of the invention

[0005] In view of the shortcomings of the existing technology, especially the problems that the existing well-killing methods are not applicable and have low efficiency in high-pressure gas wells, the present invention proposes an unconventional collaborative well-killing device and method for high-pressure gas wells, which ensures the safety and timeliness of the well-killing of high-pressure gas wells by combining two unconventional well-killing methods, namely the displacement method and the pressure-back method, and invents a corresponding collaborative well-killing device to provide a guarantee for the safe and efficient drilling of high-pressure gas wells.

[0006] The difficult problems of low output, short duration and poor economy in the process of natural gas hydrate exploitation are proposed in the present invention. A method for efficiently increasing the production of natural gas hydrate is proposed, which improves the reservoir seepage capacity and stability by means of horizontal well fracturing and injection of foam cement slurry, and improves the production of natural gas hydrate by means of horizontal well pressure reduction + heat injection exploitation, thus providing guarantee for the commercial exploitation of offshore natural gas hydrate deposits in the future.

[0007] The present invention adopts the following technical solution:

[0008] An unconventional coordinated well-killing device for a high-pressure gas well, comprising a data acquisition device and a well-killing control device, wherein the data acquisition device comprises a wellhead, a blowout preventer, a pressure sensor A, a pressure sensor B, a flow meter A, a flow meter B and a computer;

[0009] The well-killing control device comprises a well-killing fluid injection pump group, a three-way control valve and a well-killing fluid storage tank. One end of the well-killing fluid injection pump group is connected to the three-way control valve, and the other end is connected to the well-killing fluid storage tank to provide power for well-killing fluid injection. One end of the three-way control valve is connected to the wellhead through a pipeline, and the other end is connected to the blowout preventer through a main line. The three-way control valve is installed at the intersection of the pipeline connected to the wellhead and the main line connected to the blowout preventer. The pressure sensor A and the flow meter A are installed on the pipeline connected to the wellhead, and are used to collect the wellhead pressure and the fluid flow flowing through the wellhead; the pressure sensor B and the flow meter B are installed on the main line connected to the blowout preventer, and are used to collect the annulus casing pressure and the fluid flow flowing through the annulus;

[0010] A valve A is also provided on the pipeline connected to the wellhead for controlling the flow rate in the pipeline; a valve B is provided on the main line connected to the blowout preventer, a branch pipeline is connected to the main line, the other end of the branch pipeline is connected to the atmosphere, and valves C and valves D are provided on the branch pipeline. The well-killing fluid injection pump group, pressure sensor A, pressure sensor B, flow meter A, flow meter B, valve A, valve B, valve C, and valve D are all connected to a computer, and the computer receives and processes the pressure and flow data collected by the pressure sensor A, pressure sensor B, flow meter A, and flow meter B, and controls the opening of valves A, valve B, valve C, and valve D and the start and stop of the well-killing fluid injection pump group.

[0011] The working method of the above device is:

[0012] The pressure sensor and flow meter installed on the pipeline connecting the wellhead and the blowout preventer collect pressure and flow data; different data collection points are connected to the computer and transmitted to the computer in real time; the computer processes and analyzes the collected data in real time, and then controls the opening of each valve on the pipeline and the power of the well-killing fluid injection pump group; the two ends of the well-killing fluid injection pump group are respectively connected to the well-killing fluid storage tank and the injection pipeline, and the well-killing fluid is injected into the drill pipe or the annulus, thereby achieving safe and efficient well killing of high-pressure gas wells.

[0013] The branch line of the present invention is provided with two valves, namely valve C and valve D, which can more accurately control the change of wellhead back pressure. When opening: first open valve D, then open valve C, and adjust the opening size of the two valves in real time according to the on-site well killing fluid injection situation and the change of wellhead pressure, so as to reduce the fluctuation of wellhead pressure and achieve accurate control of wellhead back pressure. When closing: first close valve C, then close valve D.

[0014] On the other hand, the throttling and cooling effect caused by wellhead exhaust can be reduced because: in the case of one valve, the gas changes directly from a very high pressure to normal pressure (i.e., high pressure before the valve and normal pressure after the valve), and the throttling and cooling effect is very obvious, which often causes ice to form; designing two valves, the first valve makes the high-pressure gas transition to a lower pressure, and the second valve makes the lower pressure transition to normal pressure. Although the throttling and cooling effect will still occur at the two valves, their respective cooling effects are much smaller than the case of one valve, and there is also a certain distance between the two valves (valves C and D can be designed to be 5-10 meters apart). The temperature recovery effect caused by the high external environment temperature after throttling and cooling also helps to alleviate the throttling and cooling effect at these two places. In addition, even if heating and temperature-raising measures are taken on site, it is easier for the case of two valves, which helps to alleviate the throttling and cooling effect at the valves more quickly.

[0015] An unconventional coordinated well killing method for a high-pressure gas well is implemented by the above-mentioned device and comprises the following steps:

[0016] (1) Calculation of injection volume of well killing fluid

[0017] The injection parameters such as the density of the well killing fluid and the injection flow rate required for the displacement well killing are calculated according to the displacement well killing calculation formula, and the pollution-free well killing fluid with little damage to the reservoir is quickly configured to prepare for the displacement well killing as soon as possible; if there is no time to prepare the well killing fluid on site, the drilling fluid used for drilling can be injected first, so as to carry out the initial displacement well killing operation as soon as possible.

[0018] (2) Injecting well-killing fluid from the drill pipe to displace the annular gas

[0019] According to the well-killing fluid injection flow rate obtained in step (1), valve A is opened, the well-killing fluid of the well-killing fluid injection pump group is injected into the drill pipe, the well-killing fluid is injected into the annulus from the drill pipe, and valves C and valve D are opened in sequence to discharge the gas in the annulus (the discharged gas is generally burned at the outlet of the branch pipeline on site), thereby replacing the gas in the annulus; to improve the replacement efficiency, the well-killing fluid injection and gas discharge are carried out simultaneously; the rate and pressure of the well-killing fluid injection from the drill pipe and the flow rate and pressure data of the gas discharged from the annulus are monitored, and the openings of valves A, valves C and valve D4 and the power of the well-killing fluid injection pump group are adjusted in real time according to the monitored data;

[0020] (3) Inject well-killing hydraulic pressure from the annulus to return the remaining gas

[0021] According to the real-time monitored pressure and flow data, when the pressure-back well killing conditions are met, valve A is closed to stop injecting the well killing fluid from the drill pipe, and valve B is opened, valves C and D are closed, and the remaining gas in the annulus is pressed back into the formation by injecting well killing fluid into the annulus. At the same time, the flow and pressure data of the well killing fluid are monitored in real time during the pressure-back process, and the power of the well killing fluid injection pump group is adjusted in real time;

[0022] (4) Inject plugging material into the formation from the drill pipe

[0023] When the well is successfully killed, valve B is closed, valve A is opened, and drilling fluid containing plugging material is injected into the target layer through the drill pipe. The bridging effect between the plugging material particles is used to plug the leakage cracks, thereby improving the pressure bearing capacity of the target layer and providing guarantee for later safe production.

[0024] Through the above technical scheme, in view of the difficulty of well killing in high-pressure gas wells, combined with the advantages of the displacement method and the pressure-back method in unconventional well killing methods, the displacement method is used to inject well killing fluid into the drill pipe in the early stage of well killing to replace part of the high-pressure gas in the annulus, and the pressure-back method is used to inject well killing fluid into the annulus in the later stage to press the remaining gas back into the formation, thereby improving the efficiency and success rate of well killing in high-pressure gas wells. The present invention can effectively improve the efficiency and safety of well killing in high-pressure gas wells, and provide theoretical support and technical guarantee for safe drilling of high-pressure gas wells.

[0025] Preferably, in step (1), during the well killing process by displacement method, in order to maintain the balance of bottom hole pressure, the gravity difference generated by the well killing fluid injected from the drill pipe to the bottom hole and the gas discharged from the annulus is equal to the reduction value of the annulus pressure, as shown in the following formula:

[0026] ρ z gh z -g(ρ g0 h g0- ρ g h g )=p a0 -p a (1)

[0027] In the formula, ρ z is the density of the well-killing fluid injected from the drill pipe to the bottom of the well, kg / m 3 ; g is the acceleration due to gravity, g / cm 3 ;h z is the height of the wellbore pressure fluid, m; ρ g0 is the gas density at the initial moment, kg / m 3 ρ g is the gas density at time t, kg / m 3 ;h g0 is the height of the gas column in the wellbore at the initial moment, m; h g is the height of the gas column in the wellbore at time t, m; p a0 is the casing pressure at the initial moment, MPa; p a is the casing pressure at time t, MPa, and the casing pressure refers to the casing annulus pressure at the wellhead (i.e., the pressure at the uppermost end of the annulus);

[0028] According to the law of conservation of matter, the volume of the injected well-killing fluid is equal to the sum of the volume of the exhausted gas and the volume of the gas reduced due to the pressure change, as shown in the following formula:

[0029]

[0030] In the formula, Q z Q is the injection flow rate of the well-killing fluid by displacement method, L / s; g is the gas displacement, L / s; C g is the gas compressibility coefficient, MPa -1 ; V g is the gas volume in the wellbore annulus.

[0031] Preferably, in step (1), the density of the injected well-killing fluid is affected by the pore pressure of the formation. To meet the well-killing requirements, the density of the injected well-killing fluid is z Calculated by the following formula:

[0032] p k / (gh)<ρ z <(p p -p f ) / (gh) (3)

[0033] In the formula, p k is the formation pore pressure, MPa; p p is the formation fracture pressure, MPa; p f is the friction resistance of the annular wellbore fluid during flow, MPa; h is the vertical depth of the well, m.

[0034] Preferably, in step (3), when the power of the surface well-killing injection pump equipment is capable of carrying out the well-killing operation by the pressure-back method, it is considered that the well-killing conditions by the pressure-back method are met.

[0035] Preferably, in step (3), in the process of pressing the gas in the annulus into the formation, the downward velocity of the well-killing fluid must be greater than the upward velocity of the gas in order to achieve a smooth pressure-back operation. This places requirements on the displacement of the well-killing fluid. According to the gas-liquid two-phase flow theory, the upward velocity of the gas is calculated using the formula for the upward velocity of the gas in the slug flow:

[0036]

[0037] In the formula, v s is the slippage and rising velocity of the gas in the annular space in the well-killing fluid, m / s; g is the gravitational acceleration, m / s 2 ρ L is the density of the well killing fluid, kg / m 3 ; D is the hydraulic diameter, m; C is a dimensionless constant, which can be calculated by the Barnea model:

[0038] C=0.1725[(π+1)+K(π-1)] 0.5 (5)

[0039]

[0040] Where D to D is the outer diameter of the drill pipe, m; ci is the inner diameter of the casing, m;

[0041] According to the above calculation, v s The displacement of the well-killing fluid in the pressure-back method can be determined. The displacement of the well-killing fluid is related to the slippage and rising speed v of the gas in the well-killing fluid. s Proportional to, calculated by the following formula:

[0042] Q a >v s A (7)

[0043] Where A is the cross-sectional area of ​​the annulus, m 2 ;Q a is the well-killing fluid displacement, m 3 / s.

[0044] Preferably, in step (4), after the well is successfully pressured, the drill pipe is lifted to a predetermined plugging layer, and then drilling fluid containing plugging material is injected into the formation to increase the pressure bearing capacity of the formation, thereby re-establishing the safe drilling pressure window. During the process of lifting the drill pipe, the annular liquid level drops and the suction pressure caused by the drill pipe lifting will cause the bottom hole pressure to decrease. Therefore, it is necessary to continue to inject pressure-killing fluid into the annulus to maintain the stability of the bottom hole pressure to prevent the recurrence of bottom hole gas invasion. During this process, the changes in the annular casing pressure are monitored in real time, and the power and injection displacement of the pressure-killing fluid injection pump group are adjusted accordingly.

[0045] Preferably, the safe drilling pressure window established by plugging and pressurizing can be expressed by the following formula:

[0046] ΔP s =P b -Max{P c ,P k} (8)

[0047] Where: ΔP s The safe drilling pressure window established by plugging and pressurizing, MPa; P b is the formation fracture pressure after plugging and pressure bearing, MPa; P c is the formation collapse pressure, MPa; P k is the formation pore pressure, MPa.

[0048] For any details not provided in the present invention, please refer to the prior art.

[0049] The beneficial effects of the present invention are:

[0050] In view of the difficulty in well killing of high-pressure gas wells, the present invention combines the advantages of the displacement method and the pressure-back method in unconventional well killing methods. In the early stage of well killing, the displacement method is used to inject well killing fluid into the drill pipe to replace part of the high-pressure gas in the annulus. In the later stage, the pressure-back method is used to inject well killing fluid into the annulus to press the remaining gas back into the formation, thereby improving the well killing efficiency and success rate of the high-pressure gas well. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic diagram of the unconventional coordinated well killing device for high-pressure gas wells of the present invention;

[0052] Figure 2 Schematic diagram of the unconventional coordinated well-killing process of a high-pressure gas well of the present invention, (a) is a schematic diagram of step (2) injecting well-killing fluid from the drill pipe to replace the gas in the annulus; (b) is a schematic diagram of step (3) injecting well-killing fluid from the annulus to drive back the remaining gas; (c) is a schematic diagram of step (4) injecting plugging material from the drill pipe into the formation;

[0053] Among them, 1. Reservoir; 2. Formation; 3. Drill bit; 4. Cement ring; 5. Annulus; 6. Drill pipe; 7. Casing; 8. BOP; 9. Wellhead; 10. Pressure sensor A; 11. Pressure sensor B; 12. Flow meter A; 13. Flow meter B; 14. Valve A; 15. Valve B; 16. Valve C; 17. Valve D; 18. Three-way control valve; 19. Well-killing fluid injection pump group; 20. Well-killing fluid storage tank; 21. Computer; 22. Well-killing fluid; 23. High-pressure gas in the annulus; 24. Drilling fluid containing plugging materials. DETAILED DESCRIPTION

[0054] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described below, but are not limited to this. Anything not fully described in the present invention shall be based on conventional techniques in the art.

[0055] Example 1

[0056] An unconventional coordinated well killing device for high-pressure gas wells, such as Figure 1 As shown, it includes a data acquisition device and a well-killing control device, the data acquisition device includes a wellhead 9, a blowout preventer 8, a pressure sensor A10, a pressure sensor B11, a flow meter A12, a flow meter B13 and a computer 21, wherein 1 is a reservoir, 2 is a formation, 3 is a drill bit, 4 is a cement ring, 5 is an annulus, 6 is a drill pipe, and 7 is a casing;

[0057] The well-killing control device includes a well-killing fluid injection pump group 19, a three-way control valve 18 and a well-killing fluid storage tank 20. One end of the well-killing fluid injection pump group 19 is connected to the three-way control valve 18, and the other end is connected to the well-killing fluid storage tank 20 to provide power for well-killing fluid injection. One end of the three-way control valve 18 is connected to the wellhead 9 through a pipeline, and the other end is connected to the blowout preventer 8 through a main line. The three-way control valve is installed at the intersection of the pipeline connected to the wellhead and the main line connected to the blowout preventer. The pressure sensor A10 and the flow meter A12 are installed on the pipeline connected to the wellhead to collect the wellhead pressure and the fluid flow flowing through the wellhead; the pressure sensor B11 and the flow meter B13 are installed on the main line connected to the blowout preventer to collect the annulus casing pressure and the fluid flow flowing through the annulus;

[0058] A valve A14 is also provided on the pipeline connected to the wellhead to control the flow rate in the pipeline; a valve B15 is provided on the main line connected to the blowout preventer, a branch pipeline is connected to the main line, the other end of the branch pipeline is connected to the atmosphere, valves C16 and valves D17 are provided on the branch pipeline, and the well-killing fluid injection pump group 19, pressure sensor A10, pressure sensor B11, flow meter A12, flow meter B13, valve A14, valve B15, valve C16, valve D17 are all connected to the computer 21, and the computer 21 receives and processes the pressure and flow data collected by the pressure sensor A10, pressure sensor B11, flow meter A12, flow meter B13, and controls the opening of valves A14, valve B15, valve C16, valve D17 and the start and stop of the well-killing fluid injection pump group.

[0059] The working method of the above device is:

[0060] The pressure sensor and flow meter installed on the pipeline connecting the wellhead and the blowout preventer collect pressure and flow data; different data collection points are connected to the computer and transmitted to the computer in real time; the computer processes and analyzes the collected data in real time, and then controls the opening of each valve on the pipeline and the power of the well-killing fluid injection pump group; the two ends of the well-killing fluid injection pump group are respectively connected to the well-killing fluid storage tank and the injection pipeline, and the well-killing fluid is injected into the drill pipe or the annulus, thereby achieving safe and efficient well killing of high-pressure gas wells.

[0061] The branch line of the present invention is provided with two valves, namely valve C16 and valve D17, which can more accurately control the change of wellhead back pressure. When opening: first open valve D17, then open valve C16, and adjust the opening of the two valves in real time according to the on-site well killing fluid injection situation and the change of wellhead pressure, so as to reduce the fluctuation of wellhead pressure and achieve accurate control of wellhead back pressure. When closing: first close valve C16, then close valve D17.

[0062] On the other hand, the throttling and cooling effect caused by wellhead exhaust can be reduced because: in the case of one valve, the gas changes directly from a very high pressure to normal pressure (i.e., high pressure before the valve and normal pressure after the valve), and the throttling and cooling effect is very obvious, which often causes ice to form; designing two valves, the first valve makes the high-pressure gas transition to a lower pressure, and the second valve makes the lower pressure transition to normal pressure. Although the throttling and cooling effect will still occur at the two valves, their respective cooling effects are much smaller than the case of one valve, and there is also a certain distance between the two valves (valves C and D can be designed to be 5-10 meters apart). The temperature recovery effect caused by the high external environment temperature after throttling and cooling also helps to alleviate the throttling and cooling effect at these two places. In addition, even if heating and temperature-raising measures are taken on site, it is easier for the case of two valves, which helps to alleviate the throttling and cooling effect at the valves more quickly.

[0063] Example 2

[0064] An unconventional coordinated well killing method for a high-pressure gas well is implemented by the above-mentioned device and comprises the following steps:

[0065] (1) Calculation of injection volume of well killing fluid

[0066] The injection parameters such as the density of the well killing fluid and the injection flow rate required for the displacement well killing are calculated according to the displacement well killing calculation formula, and the pollution-free well killing fluid with little damage to the reservoir is quickly configured to prepare for the displacement well killing as soon as possible; if there is no time to prepare the well killing fluid on site, the drilling fluid used for drilling can be injected first, so as to carry out the initial displacement well killing operation as soon as possible.

[0067] In the process of displacement well killing, in order to maintain the balance of bottom hole pressure, the gravity difference between the well killing fluid injected from the drill pipe to the bottom of the hole and the gas discharged from the annulus is equal to the reduction value of the annular pressure, as shown in the following formula:

[0068] ρ z gh z -g(ρ g0 h g0- ρ g h g )=p a0 -p a (1)

[0069] In the formula, ρ z is the density of the well-killing fluid injected from the drill pipe to the bottom of the well, kg / m 3 ; g is the acceleration due to gravity, g / cm 3 ;h z is the height of the wellbore pressure fluid, m; ρ g0 is the gas density at the initial moment, kg / m 3 ρ g is the gas density at time t, kg / m 3 ;h g0 is the height of the gas column in the wellbore at the initial moment, m; h g is the height of the gas column in the wellbore at time t, m; p a0 is the casing pressure at the initial moment, MPa; p a is the casing pressure at time t, MPa, and the casing pressure refers to the casing annulus pressure at the wellhead (i.e., the pressure at the uppermost end of the annulus);

[0070] According to the law of conservation of matter, the volume of the injected well-killing fluid is equal to the sum of the volume of the exhausted gas and the volume of the gas reduced due to the pressure change, as shown in the following formula:

[0071]

[0072] In the formula, Q z Q is the injection flow rate of the well-killing fluid by displacement method, L / s; g is the gas displacement, L / s; C g is the gas compressibility coefficient, MPa -1 ; V g is the gas volume in the wellbore annulus.

[0073] The density of the injected killing fluid is affected by the pore pressure of the formation. To meet the well killing requirements, the density of the injected killing fluid ρ z Calculated by the following formula:

[0074] p k / (gh)<ρ z <(p p -p f) / (gh) (3)

[0075] In the formula, p k is the formation pore pressure, MPa; p p is the formation fracture pressure, MPa; p f is the friction resistance of the annular wellbore fluid during flow, MPa; h is the vertical depth of the well, m.

[0076] (2) Injecting well-killing fluid from the drill pipe to displace the annular gas

[0077] According to the injection flow rate of the well-killing fluid obtained in step (1), valve A14 is opened, the well-killing fluid of the well-killing fluid injection pump group is injected into the drill pipe 6, and the well-killing fluid 22 is injected into the annulus 5 from the drill pipe 6, and valves C16 and D17 are opened in sequence to discharge the high-pressure gas 23 in the annulus (the discharged gas is generally burned at the outlet of the branch pipeline on site), so that the high-pressure gas in the annulus is replaced by the injected well-killing fluid;

[0078] The well-killing fluid injected into the annulus maintains the stability of the bottom hole pressure due to the gravity, the gravity of the annular air and the wellhead back pressure, preventing the formation fluid from continuing to invade the wellbore. Two valves C16 and valve D17 are designed on the exhaust pipeline at the wellhead to achieve multi-stage throttling. On the one hand, it can more accurately control the change of the wellhead back pressure, and on the other hand, it can reduce the throttling and cooling effect caused by the wellhead exhaust, reducing the risk of ice or hydrate blocking the pipeline. In addition, in order to avoid the problem of wellhead throttling blockage, a heating device can also be installed near valves C16 and D17.

[0079] In order to improve the displacement efficiency of high-pressure gas in the annulus, a dynamic displacement method is adopted, that is, the injection of well-killing fluid at the bottom of the hole and the discharge of gas from the wellhead are carried out simultaneously. In this process, the rate and pressure of well-killing fluid injection from the drill pipe and the flow rate and pressure data of gas discharged from the annulus are monitored in real time. The dynamic changes of the injection displacement of well-killing fluid are calculated in real time based on the monitored data. Based on this, the opening of valves A, C, and D and the power of the well-killing fluid injection pump group are adjusted in real time to improve the displacement efficiency of high-pressure gas in the annulus and gain precious time for the on-site well-killing operation where every second counts.

[0080] According to the flow rate and pressure data of the gas discharged from the annulus, the injection rate of the well-killing fluid is calculated in real time and compared with the monitored injection rate of the well-killing fluid, so as to increase, decrease or maintain the injection rate of the well-killing fluid. The injection rate is affected by the opening of valve A and the power of the well-killing fluid injection pump group, and they are positively correlated. Then, the opening of valve A and the power of the well-killing fluid injection pump group are adjusted according to the needs of the well-killing fluid injection rate. In addition, if the flow rate of the gas discharged from the annulus is too small, it is necessary to increase the opening of valves C and D appropriately, which depends on the on-site conditions.

[0081] (3) Inject well-killing hydraulic pressure from the annulus to return the remaining gas

[0082] According to the pressure and flow data monitored in real time by the pressure sensor A10, the pressure sensor B11 and the flowmeter A12 and the flowmeter B13, when the pressure-back well killing condition is met (i.e., the power of the surface well killing injection pump equipment can carry out the pressure-back well killing operation), the valve A14 is closed to stop the injection of the well killing fluid 22 from the drill pipe 6, and the valve B15 is opened, and the valve C16 and the valve D17 are closed, and the well killing fluid is injected into the annulus to press the remaining gas in the annulus back into the formation. At the same time, the flow and pressure data of the well killing fluid are monitored in real time during the pressure-back process, and the power of the well killing fluid injection pump group is adjusted in real time;

[0083] In the process of pressing the gas in the annulus into the formation, the downward velocity of the killing fluid must be greater than the rising velocity of the gas in order to achieve smooth pressure-back operation. This puts forward requirements for the displacement of the killing fluid. According to the gas-liquid two-phase flow theory, the gas rising velocity is calculated using the gas rising velocity in slug flow:

[0084]

[0085] In the formula, v s is the slippage and rising velocity of the gas in the annular space in the well-killing fluid, m / s; g is the gravitational acceleration, m / s 2 ρ L is the density of the well killing fluid, kg / m 3 ; D is the hydraulic diameter, m; C is a dimensionless constant, which can be calculated by the Barnea model:

[0086] C=0.1725[(π+1)+K(π-1)] 0.5 (5)

[0087]

[0088] Where D to D is the outer diameter of the drill pipe, m; ci is the inner diameter of the casing, m;

[0089] According to the above calculation, v s The displacement of the well-killing fluid in the pressure-back method can be determined. The displacement of the well-killing fluid is related to the slippage and rising speed v of the gas in the well-killing fluid. s Proportional to, calculated by the following formula:

[0090] Q a >v s A (7)

[0091] Where A is the cross-sectional area of ​​the annulus, m 2 ;Q a is the well-killing fluid displacement, m 3 / s.

[0092] At the same time, during the pressure back process, the flow rate of the well-killing fluid and the change data of the wellhead casing pressure are monitored in real time, and the power of the well-killing fluid injection pump group and the injection rate of the well-killing fluid are adjusted in real time: according to the real-time monitoring of the flow rate of the well-killing fluid and the change data of the wellhead casing pressure, when the wellhead casing pressure is found to increase significantly, it means that the injection rate of the well-killing fluid is too high. At this time, it is necessary to reduce the injection rate of the well-killing fluid by reducing the power of the well-killing fluid injection pump group; if the wellhead casing pressure is stable, the current power of the well-killing fluid injection pump group is maintained unchanged. As the well-killing fluid is gradually injected into the annulus, the gas is gradually pressed back into the formation. Due to the increase in the pressure of the well-killing fluid column, the annulus casing pressure will gradually decrease. When the remaining gas in the annulus is completely pressed back into the formation, the annulus casing pressure will remain unchanged, indicating that the well is successfully killed.

[0093] (4) Inject plugging material into the formation from the drill pipe

[0094] During the well-killing process of the pressure-back method, the formation may be fractured and cracks may appear, and there may also be cracks in the formation itself, which may lead to the loss of drilling fluid. When the well is killed successfully, the drill pipe is lifted to the predetermined plugging layer, and then the drilling fluid containing plugging materials is injected into the formation to increase the pressure bearing capacity of the formation, and then the safe drilling pressure window is re-established. During the process of lifting the drill pipe, the annular liquid level drops and the suction pressure caused by the drill pipe lifting will cause the bottom hole pressure to decrease, so it is necessary to continue to inject the well-killing fluid into the annulus to keep the bottom hole pressure stable to prevent the recurrence of bottom hole gas invasion. In this process, the change of the annular casing pressure is monitored in real time, and the power and injection displacement of the well-killing fluid injection pump group are adjusted accordingly. Specifically: if the annular casing pressure increases, it means that the pressure of the liquid column in the annulus decreases (that is, the liquid level drops), and it is necessary to increase the well-killing fluid injection displacement by increasing the power of the well-killing fluid injection pump group, so as to replenish the well-killing fluid into the annulus and avoid the recurrence of gas invasion at the bottom of the well.

[0095] When the drill pipe 6 is lifted to the predetermined plugging layer, the valve B15 is closed, the valve A14 is opened, and the drilling fluid 24 containing the plugging material prepared in advance is injected into the target layer through the well killing fluid injection pump group through the drill pipe, and the plugging material enters the leakage layer with the drilling fluid. The leakage cracks are plugged by the bridging effect between the plugging material particles, thereby improving the pressure bearing capacity of the target layer.

[0096] The safe drilling pressure window established by plugging and pressurizing can be expressed by the following formula:

[0097] ΔP s =P b -Max{P c ,P k} (8)

[0098] Where: ΔP sThe safe drilling pressure window established by plugging and pressurizing, MPa; P b is the formation fracture pressure after plugging and pressure bearing, MPa; P c is the formation collapse pressure, MPa; P k is the formation pore pressure, MPa.

[0099] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An unconventional coordinated well killing method for a high-pressure gas well, characterized in that: It is achieved by an unconventional coordinated well-killing device for high-pressure gas wells, which includes a data acquisition device and a well-killing control device, wherein the data acquisition device includes a wellhead, a blowout preventer, a pressure sensor A, a pressure sensor B, a flow meter A, a flow meter B and a computer; The well-killing control device comprises a well-killing fluid injection pump group, a three-way control valve and a well-killing fluid storage tank. One end of the well-killing fluid injection pump group is connected to the three-way control valve, and the other end is connected to the well-killing fluid storage tank to provide power for well-killing fluid injection. One end of the three-way control valve is connected to the wellhead through a pipeline, and the other end is connected to the blowout preventer through a main line. The pressure sensor A and the flow meter A are installed on the pipeline connected to the wellhead, and are used to collect the wellhead pressure and the fluid flow flowing through the wellhead; the pressure sensor B and the flow meter B are installed on the main line connected to the blowout preventer, and are used to collect the annulus casing pressure and the fluid flow flowing through the annulus; The pipeline connected to the wellhead is also provided with a valve A for controlling the flow rate in the pipeline; a valve B is provided on the main line connected to the blowout preventer, a branch pipeline is connected to the main line, the other end of the branch pipeline is connected to the atmosphere, and valves C and valves D are provided on the branch pipeline. The well-killing fluid injection pump group, pressure sensor A, pressure sensor B, flow meter A, flow meter B, valve A, valve B, valve C, and valve D are all connected to a computer, and the computer receives and processes the pressure and flow data collected by the pressure sensor A, pressure sensor B, flow meter A, and flow meter B, and controls the opening of valves A, valve B, valve C, and valve D and the start and stop of the well-killing fluid injection pump group; The unconventional coordinated well killing method for high-pressure gas wells includes the following steps: (1) Calculation of injection volume of well killing fluid Calculate the density and injection flow rate of the well-killing fluid required for displacement well-killing according to the displacement well-killing calculation formula, and configure the storage well-killing fluid; (2) Injecting well-killing fluid from the drill pipe to displace the annular gas According to the well-killing fluid injection flow rate obtained in step (1), valve A is opened, the well-killing fluid of the well-killing fluid injection pump group is injected into the drill pipe, the well-killing fluid is injected into the annulus from the drill pipe, and valves C and valve D are opened in sequence to discharge the gas in the annulus, thereby replacing the gas in the annulus; in order to improve the replacement efficiency, the well-killing fluid injection and gas discharge are carried out simultaneously; the rate and pressure of the well-killing fluid injection from the drill pipe and the flow rate and pressure data of the gas discharged from the annulus are monitored, and the openings of valves A, valves C and valve D and the power of the well-killing fluid injection pump group are adjusted in real time according to the monitored data; (3) Inject well-killing hydraulic pressure from the annulus to return the remaining gas According to the real-time monitored pressure and flow data, when the pressure-back well killing conditions are met, valve A is closed to stop injecting the well killing fluid from the drill pipe, and valve B is opened, valves C and D are closed, and the remaining gas in the annulus is pressed back into the formation by injecting well killing fluid into the annulus. At the same time, the flow and pressure data of the well killing fluid are monitored in real time during the pressure-back process, and the power of the well killing fluid injection pump group is adjusted in real time; (4) Inject plugging material into the formation from the drill pipe When the well is successfully killed, valve B is closed, valve A is opened, and drilling fluid containing plugging material is injected into the target layer through the drill pipe to plug the leakage cracks by utilizing the bridging effect between the plugging material particles.

2. The unconventional coordinated well killing method for high-pressure gas wells according to claim 1, characterized in that: In step (1), during the displacement well killing process, in order to maintain the balance of the bottom hole pressure, the gravity difference between the well killing fluid injected from the drill pipe to the bottom hole and the gas discharged from the annulus is equal to the reduction value of the annular pressure, as shown in the following formula: ρ z gh z -g(ρ g0 h g0- ρ g h g )=p a0 -p a (1) In the formula, ρ z is the density of the well-killing fluid injected from the drill pipe to the bottom of the well, kg / m 3 ; g is the acceleration due to gravity, g / cm 3 ;h z is the height of the wellbore pressure fluid, m; ρ g0 is the gas density at the initial moment, kg / m 3 ; ρ g is the gas density at time t, kg / m 3 ;h g0 is the height of the gas column in the wellbore at the initial moment, m; h g is the height of the gas column in the wellbore at time t, m; p a0 is the casing pressure at the initial moment, MPa; p a is the casing pressure at time t, MPa, and the casing pressure refers to the casing annulus pressure at the wellhead; According to the law of conservation of matter, the volume of the injected well-killing fluid is equal to the sum of the volume of the exhausted gas and the volume of the gas reduced due to the pressure change, as shown in the following formula: In the formula, Q z Q is the injection flow rate of the well-killing fluid by displacement method, L / s; g is the gas displacement, L / s; C g is the gas compressibility coefficient, MPa -1 ; V g is the gas volume in the wellbore annulus.

3. The unconventional coordinated well killing method for high-pressure gas wells according to claim 2, characterized in that: In step (1), the density of the injected well-killing fluid is affected by the pore pressure of the formation. To meet the well-killing requirements, the density of the injected well-killing fluid is z Calculated by the following formula: p k / (gh)<ρ z <(p p -p f ) / (gh) (3) In the formula, p k is the formation pore pressure, MPa; p p is the formation fracture pressure, MPa; p f is the friction resistance of the annular wellbore fluid during flow, MPa; h is the vertical depth of the well, m.

4. The unconventional coordinated well killing method for high-pressure gas wells according to claim 3 is characterized in that: In step (3), when the power of the surface well-killing injection pump equipment is capable of carrying out the well-killing operation by the pressure-back method, it is considered that the well-killing conditions by the pressure-back method are met.

5. The unconventional coordinated well killing method for high-pressure gas wells according to claim 4 is characterized in that: In step (3), in the process of pressing the gas in the annulus into the formation, the downflow velocity of the well-killing fluid must be greater than the gas rise velocity. According to the gas-liquid two-phase flow theory, the gas rise velocity is calculated using the gas rise velocity in slug flow formula: In the formula, v s is the slippage and rising velocity of the gas in the annular space in the well-killing fluid, m / s; g is the gravitational acceleration, m / s 2 ; ρ L is the density of the well-killing fluid, kg / m 3 ; D is the hydraulic diameter, m; C is a dimensionless constant, calculated by the Barnea model: C=0.1725[(π+1)+K(π-1)] 0.5 (5) Where D to D is the outer diameter of the drill pipe, m; ci is the inner diameter of the casing, m; According to the above calculation, v s Determine the displacement of the well-killing fluid in the pressure-back method. The displacement of the well-killing fluid is related to the slippage and rising speed v of the gas in the well-killing fluid. s Proportional, calculated by the following formula: Q a >v s A (7) Where A is the cross-sectional area of ​​the annulus, m 2 ;Q a is the well-killing fluid displacement, m 3 / s.

6. The unconventional coordinated well killing method for high-pressure gas wells according to claim 5, characterized in that: In step (4), when the well is successfully killed, the drill pipe is lifted to the predetermined plugging layer, and then drilling fluid containing plugging material is injected into the formation to increase the pressure bearing capacity of the formation, thereby re-establishing the safe drilling pressure window. During the process of lifting the drill pipe, the annular liquid level drops and the suction pressure caused by the drill pipe lifting will cause the bottom hole pressure to decrease. Therefore, it is necessary to continue to inject killing fluid into the annulus to maintain the stability of the bottom hole pressure to prevent the recurrence of bottom hole gas invasion. During this process, the changes in the annular casing pressure are monitored in real time, and the power and injection displacement of the killing fluid injection pump group are adjusted accordingly.

7. The unconventional coordinated well killing method for high-pressure gas wells according to claim 6, characterized in that: The safe drilling pressure window established by plugging and pressurizing is expressed by the following formula: αP s =P b -Max{P c ,P k } (8) Where: αP s The safe drilling pressure window established by plugging and pressurizing, MPa; P b is the formation fracture pressure after plugging and pressure bearing, MPa; P c is the formation collapse pressure, MPa; P k is the formation pore pressure, MPa.

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