Segmented well killing process for reserve heavy grout with large longitudinal and transverse difference in ultrahigh-pressure stratum

Abstract

The invention discloses a reserve heavy slurry segmented well killing process for ultrahigh-pressure strata with large longitudinal and transverse differences, which comprises the following steps of: immediately closing a well when overflow is found, and recording related data; performing segmented well killing, namely performing circumferential well killing at the first section, and replacing drilling fluid in use with well site reserve heavy slurry for well killing circulation; during heavy slurry well killing circulation, new well killing fluid is calculated and prepared according to the related data in the first step; carrying out segmented well killing-second-section circulating circumferential well killing, and carrying out well killing circulation according to new well killing fluid obtained through calculation instead of well site reserve heavy grout; when the wellhead pressure does not fluctuate any more, whether the vertical pressure and the casing pressure are zero or not is observed at the same time, and after the pressure in the shaft is balanced, the reserve heavy slurry segmented well killing method is started to complete well killing. According to the method, the problems that the original slurry column pressure in the first cycle of a driller method is low and the wellhead pressure is high can be solved, and the high-pressure risk caused by shaft gas slippage in the period when an engineer method waits for well killing fluid can be eliminated.

Description

Technical Field

[0001] The invention relates to a staged well-killing process for a reserve heavy slurry in an ultra-high pressure formation with large vertical and horizontal differences, belonging to the technical field of safe well control engineering for oil and gas wells. Background Art

[0002] At present, the commonly used conventional well-killing methods, the driller method and the engineer method, both emphasize preparing enough well-killing fluid at one time to ensure the continuity of the well-killing process. As the geology of deep wells is particularly complex and the formations have large vertical and horizontal differences, ultra-high pressure formations with a density far higher than the actual drilling fluid used are often encountered. Well-killing practice shows that during the well-killing process of the driller method, the first cycle uses positive circulation of drilling fluid, the wellhead vertical pressure and casing pressure are high, and the well control risk is high; at the same time, the high-density well-killing fluid preparation cycle is long, and the engineer method (the second cycle) requires waiting for several hours or even more than ten hours. Gas slippage may cause the wellhead pressure and wellbore pressure to be too high, resulting in high casing pressure events. The wellhead, casing shoe and open hole section are at extremely high risk, and even endanger the internal pressure resistance of the upper casing, which brings great risks to well control. Summary of the invention

[0003] In order to overcome the defects in the prior art, the present invention aims to provide a staged well-killing process of reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences.

[0004] The technical solution provided by the present invention to solve the above technical problems is: a staged well killing process of reserve heavy slurry in ultra-high pressure formations with large vertical and horizontal differences, comprising the following steps:

[0005] Step 1: Shut down the well immediately upon discovery of overflow and record relevant data;

[0006] Step 2: Staged well killing - the first stage is cyclic well killing, where the drilling fluid in use is replaced with the reserved heavy slurry at the well site for well killing circulation;

[0007] Step 3: While the heavy slurry is circulating, new well killing fluid is calculated and prepared according to the relevant data in step 1;

[0008] Step 4: Staged well killing - second stage cyclic well killing, the new well killing fluid is calculated to replace the reserve heavy slurry in the well site for well killing circulation;

[0009] Step 5: When the wellhead pressure no longer fluctuates, observe whether the vertical pressure and casing pressure are zero. When the pressure in the wellbore reaches equilibrium, activate the reserve heavy slurry staged well killing method to complete the well killing.

[0010] A further technical solution is that the relevant data in step one includes vertical pressure, casing pressure, and mud pool increment.

[0011] A further technical solution is that the reserve heavy slurry in the well site has a specific gravity higher than that of the drilling fluid in use by at least 0.3.

[0012] A further technical solution is that the well killing displacement of the first cycle well killing in step 2 is constant.

[0013] A further technical solution is that in step 2, the well pressure circulation process of the reserve heavy slurry at the well site includes the stage where the reserve heavy slurry enters the drill pipe, the stage where the reserve heavy slurry enters the annulus, and the stage where the reserve heavy slurry fills the annulus. First, the maximum casing pressure value of each stage is calculated, and then the casing pressure is monitored in real time during the well pressure process. If the real-time casing pressure is greater than the maximum casing pressure value, the displacement or the density of the reserve heavy slurry at the well site is adjusted until the real-time monitored casing pressure is less than or equal to the maximum casing pressure value.

[0014] A further technical solution is that the maximum casing pressure in the stage where the reserve heavy slurry enters the drill pipe is calculated as follows:

[0015] P a1 =P hole -P yi1 -0.0098ρ mud1 (y H -y g1 -f i y i ')-0.0098(ρ mud2 -ρ mud1 )f i y i '

[0016] Where: P a1 The maximum casing pressure when the reserve heavy slurry enters the drill pipe, MPa; P yi1 The distance from the wellhead to the gas invasion section during the drilling pipe stage is y i Gas invasion pressure, MPa; P hole is the open hole formation pressure, MPa; y g1 The length of the gas invasion section when the reserve heavy slurry enters the drill pipe, m; f i is the miscible phase coefficient of heavy slurry and drilling fluid, which is related to the length of heavy slurry entering the drill pipe; y i ' is the length of the heavy slurry entering the drill pipe, m; y H is the depth of the wellbore, m; ρ mud1 is the density of the drilling fluid currently used, g / cm 3 ρ mud2 is the reserve weight pulp density, g / cm 3 .

[0017] A further technical solution is that the calculation formula for the maximum casing pressure when the reserve heavy slurry enters the annulus is:

[0018] P a2 =P hole -P yi2 -0.0098ρmud1 (y H -y g2 -2f i y mud2 '-y mud2 ')-0.0098ρ mud2 (1+f i )

[0019] Where: P a2 The maximum casing pressure when the reserve heavy slurry enters the annulus, MPa; y mud2 ' is the length of the heavy slurry entering the annulus, m; y g2 P is the length of the gas invasion section when the reserve heavy slurry enters the annulus, m; yi2 The distance from the wellhead to the gas invasion section during the stage of the reserve heavy slurry entering the annulus is y i Gas invasion section pressure, MPa.

[0020] A further technical solution is that the calculation formula for the maximum casing pressure in the stage where the reserve heavy slurry fills the annulus is:

[0021] P a3 =P hole -P yi3 -0.0098ρ mud2 (y H -y g3 )

[0022] Where: P a3 The maximum casing pressure during the stage of the annulus being filled with reserve heavy slurry, MPa; P yi3 The distance from the wellhead to the gas invasion section during the stage of the reserve heavy slurry entering the annulus is y i Gas invasion section pressure, MPa; y g3 The length of the gas invasion section during the annulus filling stage with reserve heavy slurry, m.

[0023] A further technical solution is that the density calculation formula of the well killing fluid in step 3 is:

[0024]

[0025] Where: mud3 is the new killing fluid density, g / cm 3 ; Δρ is the well-killing safety margin, g / cm 3 ;P sp It is the stable standing pressure after well shut-in, MPa.

[0026] The present invention has the following beneficial effects:

[0027] 1. Reserve heavy slurry is used in the first cycle of staged well killing. While eliminating the invasion of annular gas into the original drilling fluid, a higher liquid column pressure is quickly established in the annulus, reducing the wellhead pressure and reducing the risk of well control. It can not only solve the problem of low original slurry liquid column pressure and high wellhead pressure in the first cycle of the driller method, but also eliminate the high pressure risk caused by wellbore gas slippage during the waiting period for killing fluid in the engineer method;

[0028] 2. When drilling into high-pressure medium-permeability or high-pressure high-permeability gas layers, the gas invasion speed is fast and the mud pool increment is large. It is obviously advantageous to use the reserve heavy slurry for staged well killing in time. The invading gas is discharged earlier and the casing pressure is first reduced to 0 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the first cycle of the reserve heavy slurry staged well killing process. DETAILED DESCRIPTION

[0030] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The present invention provides a staged well-killing process for ultra-high pressure formations with large vertical and horizontal differences in reserve weight slurry, comprising the following steps:

[0032] Step 1: Shut down the well immediately if overflow is found, and record relevant data (vertical pressure, casing pressure, and mud pool increment);

[0033] Step 2: Staged well killing - the first stage is cyclic well killing, where the drilling fluid in use is replaced with the reserved heavy slurry at the well site for well killing circulation;

[0034] After the well is shut in, the drilling fluid in use is directly replaced with the reserve heavy slurry at the well site (usually 0.3 higher than the specific gravity of the drilling fluid in use) to kill the well;

[0035] The well site reserve heavy slurry for well killing circulation process includes the stage of reserve heavy slurry entering the drill pipe, the stage of reserve heavy slurry entering the annulus, and the stage of reserve heavy slurry filling the annulus. First, the highest casing pressure value of each stage is calculated, and then the casing pressure is monitored in real time during the well killing process. If the real-time casing pressure is greater than the highest casing pressure value, the displacement or the density of the well site reserve heavy slurry is adjusted until the real-time monitored casing pressure is less than or equal to the highest casing pressure value;

[0036] like Figure 1 As shown, Figure 1 (a) Schematic diagram showing the drilling bit opening the high-pressure reservoir and gas invasion; Figure 1(b) indicates the first cycle of starting the reserve heavy slurry for staged well killing, and the reserve heavy slurry has circulated to the drill bit and entered the annulus; Figure 1 (c) indicates that the reserve heavy slurry has completely replaced the original drilling fluid at the reservoir mouth, and the reserve heavy slurry has filled the wellbore; the reserve heavy slurry circulation at the well site includes three stages;

[0037] (1) Reserve heavy slurry enters the drill pipe stage (t0-t1)

[0038] t0=0, heavy slurry begins to enter the drill pipe, min;

[0039] The time required for the heavy slurry to reach the drill bit, min;

[0040] When the distance between the gas invasion section and the wellhead is y i At this time, the fluid in the wellbore annulus is the gas and drilling fluid that invade the wellbore, and the annulus pressure system can be obtained:

[0041] Pressure of gas invasion section when reserve heavy slurry enters drill pipe:

[0042] P yi1 =P hole -0.0098ρ mud1 y i -0.0098(ρ mud2 -ρ mud1 )f i y i '

[0043]

[0044] Where: P yi1 The distance from the wellhead to the gas invasion section during the drilling pipe stage is y i Gas invasion pressure, MPa; P hole is the open hole formation pressure, MPa; ρ mud1 is the density of the drilling fluid currently used, g / cm 3 ρ mud2 is the reserve weight pulp density, g / cm 3 ;y i is the distance from the top of the gas invasion section to the wellhead (vertical depth TVD), m; f i is the miscible phase coefficient of heavy slurry and drilling fluid, which is related to the length of heavy slurry entering the drill pipe; y i ' is the length of heavy slurry entering the drill pipe, m.

[0045] The pressure at the top of the gas column can be obtained from the real gas state equation:

[0046]

[0047] Where: Zhole , Z yi The intrusion gas is at the bottom of the well and at a distance y from the wellhead. i The compression factor at T hole 、T yi is the bottom of the well, and the distance from the wellhead is y i Annular space temperature at, K; V hole 、V yi The intrusion gas is at the bottom of the well and at a distance y from the wellhead. i The volume at the 3 .

[0048] Length of air intrusion section:

[0049]

[0050] Where: y g1 The length of the gas invasion section when the reserve heavy slurry enters the drill pipe, m; x in1 is the distance between the inner wall of the wellbore and the origin, m; x out2 is the distance from the outer wall of the drill pipe to the origin, m.

[0051] Then the sleeve pressure at this time is:

[0052] P a1 =P hole -P yi1 -0.0098ρ mud1 (y H -y g1 -f i y i ')-0.0098(ρ mud2 -ρ mud1 )f i y i '

[0053] Where: P a1 The distance between the gas invasion section and the wellhead y i Wellhead casing pressure, MPa; H is the depth of the wellbore (vertical depth TVD), m.

[0054] (2) Reserve heavy slurry enters the annulus stage (t1-t2)

[0055] The time required for the heavy slurry to reach the drill bit, min;

[0056] The time required for the heavy slurry to reach the wellhead, min;

[0057] Due to the entry of reserve heavy slurry, the pressure of the liquid column below the gas column increases greatly, and the casing pressure at the wellhead decreases. However, due to the decrease in the pressure acting on the top of the gas column, the gas column expands, pushing out the upper drilling fluid, and the casing pressure at the wellhead increases. Therefore, the casing pressure change trend at this time is mainly due to the influence of reserve heavy slurry and gas expansion on the wellhead casing pressure. From the annular pressure system, we get:

[0058] Pressure of gas invasion section when reserve heavy slurry enters the annulus:

[0059] P yi2 =P hole -0.0098ρ mud1 y i -0.0098(ρ mud2 -ρ mud1 )f i y mud2 '-0.0098ρ mud2 y mud2 '

[0060] Where: y mud2 ' is the length of the heavy slurry entering the annulus, m.

[0061] The length of the gas invasion section when the reserve heavy slurry enters the annulus can be obtained from the real gas state equation:

[0062]

[0063] Then the sleeve pressure at this time is:

[0064] P a2 =P hole -P yi2 -0.0098ρ mud1 (y H -y g2 -2f i y mud2 '-y mud2 ')-0.0098ρ mud2 (1+f i )

[0065] (3) The stage where the reserve heavy slurry fills the annulus (>t2)

[0066] The time required for the heavy slurry to reach the wellhead, min;

[0067] The pressure of gas invasion section when the annulus is filled with reserve heavy slurry:

[0068] P yi3 =P hole -0.0098ρ mud2 y i

[0069] The length of the gas invasion section when the annulus is filled with reserve heavy slurry can be obtained from the real gas state equation:

[0070]

[0071] Then the sleeve pressure at this time is:

[0072] P a3 =P hole -P yi3 -0.0098ρ mud2 (y H -y g3 )

[0073] Step 3: While the heavy slurry is circulating, new well killing fluid is calculated and prepared according to the relevant data in step 1;

[0074]

[0075] Where: mud3 is the new killing fluid density, g / cm 3 ; Δρ is the well-killing safety margin, g / cm 3 ;P sp is the stable standing pressure after shutting in, MPa;

[0076] Step 4: Staged well killing - second stage cyclic well killing, the new well killing fluid is calculated to replace the reserve heavy slurry in the well site for well killing circulation;

[0077] Step 5: When the wellhead pressure no longer fluctuates, observe whether the vertical pressure and casing pressure are zero. When the pressure in the wellbore reaches equilibrium, activate the reserve heavy slurry staged well killing method to complete the well killing.

[0078] Example 1

[0079] (1) Overview of overflow occurrence and well killing

[0080] The well was drilled to a depth of 4616.65m and the liquid level rose by 1.8m. 3 , shut-in vertical pressure 0MPa, casing pressure 6.7MPa, density 2.10g / cm 3 The killing fluid is positively circulated to kill the well.

[0081] Table 1 xxx-xx1 well killing parameters

[0082]

[0083]

[0084] Table 2 Comparison of different well killing results in Example 1

[0085]

[0086]

[0087] As shown in Table 2, in the first cycle of the staged well killing with reserve heavy slurry, the pump pressure of the staged well killing method is 9.4 MPa lower than that of the driller method, and the free gas arrives at the wellhead earlier, so the casing pressure drops earlier. The casing pressure of the engineer method continues to rise while waiting for the well killing. In the second cycle, compared with the driller method, the staged well killing method completes the well killing first, with a well killing time of 902.3 minutes, and the highest casing pressure is 6.3 MPa, followed by the driller method and the engineer method.

[0088] Implementation Case 2

[0089] Table 3 Well Killing Parameters of Example 2

[0090]

[0091]

[0092] Table 4 Comparison of different well killing results in Example 2

[0093]

[0094] As shown in Table 4, in the first cycle of the staged well killing with reserve heavy slurry, the pump pressure of the staged well killing method is lower than that of the driller method. The casing pressure of the engineer method continued to rise while waiting for the well killing, with the highest casing pressure reaching 57.3MPa. In the second cycle, compared with the driller method, the staged well killing method completed the well killing first, with a well killing time of 1180min and a highest casing pressure of 17.2MPa.

[0095] The above description is not intended to limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A staged well-killing process of reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences, characterized in that: The following steps are involved: Step 1: Shut down the well immediately upon discovery of overflow and record relevant data; Step 2: Staged well killing - the first stage is cyclic well killing, where the drilling fluid in use is replaced with the reserved heavy slurry at the well site for well killing circulation; Step 3: While the heavy slurry is circulating, new well killing fluid is calculated and prepared according to the relevant data in step 1; Step 4: Staged well killing - second stage cyclic well killing, the new well killing fluid is calculated to replace the reserve heavy slurry in the well site for well killing circulation; Step 5: When the wellhead pressure no longer fluctuates, observe whether the vertical pressure and casing pressure are zero. When the pressure in the wellbore reaches equilibrium, activate the reserve heavy slurry staged well killing method to complete the well killing.

2. The staged well killing process of reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences according to claim 1 is characterized in that: The relevant data in step 1 include vertical pressure, casing pressure, and mud pool increment.

3. The staged well-killing process of reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences according to claim 1 is characterized in that: The reserve heavy slurry at the well site has a specific gravity higher than that of the drilling fluid in use by more than 0.

3.

4. The process for staged well killing with reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences according to claim 1 is characterized in that: The well-killing displacement of the first cycle well-killing in step 2 is constant.

5. The staged well killing process of reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences according to claim 1 is characterized in that: The step 2 is to perform a well-killing circulation process with the reserve heavy slurry at the well site, including the stage where the reserve heavy slurry enters the drill pipe, the stage where the reserve heavy slurry enters the annulus, and the stage where the reserve heavy slurry fills the annulus. First, the maximum casing pressure value of each stage is calculated, and then the casing pressure is monitored in real time during the well-killing process. If the real-time casing pressure is greater than the maximum casing pressure value, the displacement or the density of the reserve heavy slurry at the well site is adjusted until the real-time monitored casing pressure is less than or equal to the maximum casing pressure value.

6. The staged well-killing process of reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences according to claim 5 is characterized in that: The calculation formula for the maximum casing pressure when the reserve heavy slurry enters the drill pipe is: P a1 =P hole -P yi1 -0.0098ρ mud1 (y H -y g1 -f i y i ')-0.0098(ρ mud2 -ρ mud1 )f i y i ' Where: P a1 The maximum casing pressure when the reserve heavy slurry enters the drill pipe, MPa; P yi1 The distance from the wellhead to the gas invasion section during the drilling pipe stage is y i Gas invasion pressure, MPa; P hole is the open hole formation pressure, MPa; y g1 The length of the gas invasion section when the reserve heavy slurry enters the drill pipe, m; f i is the miscible phase coefficient of heavy slurry and drilling fluid, which is related to the length of heavy slurry entering the drill pipe; y i ' is the length of the heavy slurry entering the drill pipe, m; y H is the depth of the wellbore, m; ρ mud1 is the density of the drilling fluid currently used, g / cm 3 ; ρ mud2 is the reserve weight pulp density, g / cm 3 .

7. The staged well-killing process of reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences according to claim 6 is characterized in that: The calculation formula for the maximum casing pressure when the reserve heavy slurry enters the annulus is: P a2 =P hole -P yi2 -0.0098ρ mud1 (y H -y g2 -2f i y mud2 '-y mud2 ')-0.0098ρ mud2 (1+f i ) Where: P a2 The maximum casing pressure when the reserve heavy slurry enters the annulus, MPa; y mud2 ' is the length of the heavy slurry entering the annulus, m; y g2 P is the length of the gas invasion section when the reserve heavy slurry enters the annulus, m; yi2 The distance from the wellhead to the gas invasion section during the stage of the reserve heavy slurry entering the annulus is y i Gas invasion section pressure, MPa.

8. The staged well-killing process of reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences according to claim 7 is characterized in that: The calculation formula for the maximum casing pressure during the stage when the reserve heavy slurry fills the annulus is: P a3 =P hole -P yi3 -0.0098ρ mud2 (y H -y g3 ) Where: P a3 The maximum casing pressure during the stage of the annulus being filled with reserve heavy slurry, MPa; P yi3 The distance from the wellhead to the gas invasion section during the stage of the reserve heavy slurry entering the annulus is y i Gas invasion section pressure, MPa; y g3 The length of the gas invasion section during the annulus filling stage with reserve heavy slurry, m.

9. The staged well killing process of reserve weight slurry in ultra-high pressure formations with large vertical and horizontal differences according to claim 1 is characterized in that: The density calculation formula of the well killing fluid in step 3 is: Where: mud3 is the new killing fluid density, g / cm 3 ; Δρ is the well-killing safety margin, g / cm 3 ;P sp It is the stable standing pressure after well shut-in, MPa.

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