A method for quantitatively evaluating the gas sealing performance of annular blowout preventer

Abstract

The invention relates to the technical field of oil and gas well safety, and in particular to a method for quantitatively evaluating the gas sealing performance of an annular blowout preventer. The equivalent average contact pressure of a tubing-rubber core sealing surface is obtained based on the principle of equivalent sealing contact energy. The elastic-plastic normal flattening contact between a rigid smooth plate and a rough plate with uniformly distributed spherical micro-convex bodies is used to simulate the microscopic contact state of the tubing-rubber core, and the actual contact area of ​​a single spherical micro-convex body under the equivalent average contact pressure of the tubing-rubber core sealing surface is obtained. Then, the circumferential width and average height of a microscopic leakage channel of the tubing-rubber core contact interface are calculated. The gas leakage volume rate of gas passing through the tubing-rubber core interface is obtained by using a parallel plate model in fluid mechanics and compared with the allowable gas leakage volume rate. The sealing safety of an annular blowout preventer is quickly and economically quantitatively evaluated, and the reliability is high.

Description

Technical Field

[0001] This invention relates to the field of oil and gas well safety technology, and in particular to a method for quantitatively evaluating the gas sealing performance of annular blowout preventers. Background Technology

[0002] Gas well live-line operations involve running tubing or drill pipe under pressure at the wellhead to perform drilling, completion, fracturing, acidizing, and workover operations. They are highly effective in protecting unconventional reservoirs and increasing production. The annular blowout preventer (BOP) is a crucial piece of equipment for the safety and success of gas well live-line operations. It achieves a loose seal by having a piston pressurize the rubber core against the tubing to form a tubing-rubber core contact pair. Failure of the annular BOP seal can easily lead to wellhead natural gas leakage, posing a significant threat to the safety and environmental risks of gas well live-line operations. Therefore, quantitatively and reliably evaluating the gas seal safety of the annular BOP is essential for the safe management of gas well live-line operations.

[0003] Existing methods for evaluating the gas-tight performance of annular blowout preventers (BOPs) mainly include theoretical methods, finite element methods, and experimental methods. Theoretical and finite element methods primarily obtain the macroscopic contact pressure distribution on the sealing surface by establishing a macroscopic contact mechanics model of the tubing-rubber core contact pair. Then, they simply judge whether the BOP meets the sealing requirements by whether the contact pressure exceeds the wellhead annular pressure. Alternatively, based on sealing contact energy theory, they compare the sealing index (the product of contact pressure and contact length) with the critical sealing index to determine whether the BOP meets the gas-tight requirements. In reality, due to the influence of the surface roughness of the tubing-rubber core contact pair, annular BOP leakage is essentially a gas flow problem through the microscopic gaps in the tubing-rubber core contact pair. However, existing methods for evaluating the gas-tight performance of annular BOPs based on the macroscopic contact pressure of the sealing surface cannot consider the influence of the microscopic contact state of the tubing-rubber core contact pair on the gas leakage path. Therefore, they cannot directly and quantitatively reliably evaluate the gas leakage rate and sealing safety of the tubing-rubber core contact pair of annular BOPs under pressurized gas well operations. While experimental methods can simulate the dynamic leakage rate of the tubing-insulator contact pair by establishing physical models of the blowout preventer's sealing structure (full-size or small-size), this method is costly, time-consuming, and carries certain safety risks, and is generally only used for a small number of verification experiments. Therefore, experimental methods are difficult to use for rapid and economical evaluation of the gas-tight performance of annular blowout preventers. Summary of the Invention

[0004] The purpose of this invention is to provide a method for quantitatively evaluating the gas-tight performance of annular blowout preventers, which solves the problem that existing methods are difficult to quickly and economically quantitatively evaluate the sealing safety of annular blowout preventers, and has high reliability.

[0005] To achieve the above objectives, the present invention provides a method for quantitatively evaluating the gas-tight performance of an annular blowout preventer, comprising the following steps:

[0006] S1. Obtain the equivalent average contact pressure p of the oil pipe-rubber core sealing surface. cm ;

[0007] S2. Obtain the contact area A of a single spherical micro-protrusion on the tubing-core sealing surface under the equivalent average contact pressure. c ;

[0008] S3. Obtain the circumferential width B of the microscopic leakage channel at the oil pipe-rubber core contact interface;

[0009] S4. Obtain the average height H of the microscopic leakage channel at the oil pipe-rubber core contact interface;

[0010] S5. Obtain the leakage volume rate Q at the interface between the annular blowout preventer tubing and rubber core during pressurized gas well operations. v ;

[0011] S6, Q v With the allowable leakage volume rate Q a In comparison, if Q is satisfied v ≥Q a If the seal fails, the annular blowout preventer will fail; otherwise, it will be safe.

[0012] In step S1, the formula for calculating the equivalent average contact pressure of the oil pipe-rubber core sealing surface is as follows:

[0013]

[0014] In the calculation formula: p cm The equivalent average contact pressure of the oil pipe-rubber core sealing surface, in MPa; L c p is the axial contact length of the oil pipe-rubber core sealing surface, in mm; c (l) represents the contact pressure distribution of the oil pipe-rubber core sealing surface, in MPa; a represents the sealing contact energy index, which is dimensionless.

[0015] Step S2 further includes: treating the oil pipe-rubber core contact pair as an elasto-plastic normal flattening contact between a rigid smooth plate and a uniformly distributed spherical micro-protrusion rough plate, and using finite element software to simulate and obtain the equivalent average contact pressure p. cm The contact area A of the next single spherical micro-protrusion c .

[0016] In step S3, the formula for calculating the circumferential width of the micro-leakage channel at the oil pipe-rubber core contact interface is as follows:

[0017]

[0018] In the calculation formula: B is the circumferential width of the microscopic leakage channel at the oil pipe-rubber core contact interface, in μm; D oR is the outer diameter of the oil pipe, in mm. a A represents the circumferential surface roughness of the rubber core, in μm. c The contact area of ​​a single spherical micro-protrusion is expressed in μm. 2 .

[0019] In step S4, the formula for calculating the average height of the micro-leakage channel at the tubing-rubber core contact interface is as follows:

[0020]

[0021] In the calculation formula: H is the average height of the microscopic leakage channel at the oil pipe-rubber core contact interface, in μm.

[0022] In step S5, the formula for calculating the leakage volume rate at the tubing-rubber core contact interface is as follows:

[0023]

[0024] In the calculation formula: Q v The gas leakage volume rate at the tubing-rubber core contact interface is expressed in cm³. 3 / s;p whg p represents the maximum permissible live pressure in the annulus of the wellhead casing, in MPa. atm η is atmospheric pressure, in MPa; η is the dynamic viscosity of the pressurized gas at the wellhead, in MPa·s.

[0025] This invention provides a method for quantitatively evaluating the gas-tight performance of annular blowout preventers. Based on the principle of equivalent sealing contact energy, the method obtains the equivalent average contact pressure of the tubing-rubber core sealing surface. It simulates the microscopic contact state of the tubing-rubber core using an elasto-plastic normal flattening contact between a rigid smooth plate and a uniformly distributed spherical micro-protrusion rough plate. The method obtains the actual contact area of ​​a single spherical micro-protrusion under the equivalent average contact pressure of the tubing-rubber core sealing surface, and then calculates the circumferential width and average height of the microscopic leakage channel at the tubing-rubber core contact interface. Finally, it uses a parallel plate model from fluid mechanics to obtain the gas leakage volume rate through the tubing-rubber core interface and compares it with the allowable gas leakage volume rate. This method provides a rapid, economical, and quantitative evaluation of the sealing safety of the annular blowout preventer with high reliability. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0027] Figure 1 This is a schematic diagram of the sealing surface of the annular blowout preventer oil pipe-rubber core of the present invention.

[0028] Figure 2This is a simulation diagram of the elasto-plastic normal flattening contact of the oil pipe-rubber core contact pair of the present invention.

[0029] Figure 3 This is a flowchart of the present invention for quantitatively evaluating the gas-tight performance of an annular blowout preventer. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0031] Please see Figures 1 to 3 ,in, Figure 1 This is a schematic diagram of the sealing surface of the oil pipe and rubber core of the annular blowout preventer. Figure 2 This is a simulation diagram of the elasto-plastic normal flattening contact of the tubing-rubber core contact pair. Figure 3 This is a flowchart for quantitatively evaluating the gas-tight performance of an annular blowout preventer. This invention provides a method for quantitatively evaluating the gas-tight performance of an annular blowout preventer, comprising the following steps:

[0032] S1. Obtain the equivalent average contact pressure p of the oil pipe-rubber core sealing surface. cm ;

[0033] Specifically, obtain p c (l), L c a, and based on the principle of equivalent sealing contact energy, the following formula is used:

[0034]

[0035] Calculate and obtain the equivalent average contact pressure p of the tubing-rubber core sealing surface cm ;

[0036] Where: p cm The equivalent average contact pressure of the oil pipe-rubber core sealing surface, in MPa; L c p is the axial contact length of the oil pipe-rubber core sealing surface, in mm; c (l) represents the contact pressure distribution of the oil pipe-rubber core sealing surface, in MPa; a represents the sealing contact energy index, which is dimensionless.

[0037] S2. Obtain the contact area A of a single spherical micro-protrusion on the tubing-core sealing surface under the equivalent average contact pressure. c ;

[0038] Specifically, such as Figure 2 As shown, the tubing-rubber core contact pair is considered as an elasto-plastic normal flattening contact between a rigid smooth plate and a rough plate with uniformly distributed spherical micro-protrusions. The average contact pressure p is obtained by finite element software simulation. cm The contact area A of the next single spherical micro-protrusionc .

[0039] S3. Obtain the circumferential width B of the micro-leakage channel at the oil pipe-rubber core contact interface;

[0040] Specifically, obtain D o R a And use the formula:

[0041]

[0042] Calculate the circumferential width B of the micro-leakage channel at the tubing-rubber core contact interface.

[0043] Where: B is the circumferential width of the micro-leakage channel at the oil pipe-rubber core contact interface, in μm; D o R is the outer diameter of the oil pipe, in mm. a A represents the circumferential surface roughness of the rubber core, in μm. c The contact area of ​​a single spherical micro-protrusion is expressed in μm. 2 .

[0044] S4. Obtain the average height H of the microscopic leakage channel at the oil pipe-rubber core contact interface;

[0045] Specifically, the formula is as follows:

[0046]

[0047] Calculate and obtain the average height H of the micro-leakage channel at the tubing-rubber core contact interface;

[0048] Where: H is the average height of the microscopic leakage channel at the oil pipe-rubber core contact interface, in μm.

[0049] S5. Obtain the leakage volume rate Q at the interface between the annular blowout preventer tubing and rubber core during pressurized gas well operations. v ;

[0050] Specifically, obtain p whg p atm , η, and use the formula:

[0051]

[0052] Calculate the leakage volume rate Q at the contact interface between the tubing and rubber core of the annular blowout preventer during pressurized gas well operations. v ;

[0053] Among them: Q v The gas leakage volume rate at the tubing-rubber core interface is expressed in cm³. 3 / s;p whg p represents the maximum permissible live pressure in the annulus of the wellhead casing, in MPa.atm η is atmospheric pressure, in MPa; η is the dynamic viscosity of the pressurized gas at the wellhead, in MPa·s.

[0054] S6, Get Q a The gas leakage volume rate Q calculated in step S5 is used as the reference. v With the allowable leakage volume rate Q a In comparison, if Q is satisfied v ≥Q a If the seal fails, the annular blowout preventer will fail; otherwise, it will be safe.

[0055] In the above steps, p c (l) and L c This can be obtained through numerical simulation or online ultrasonic testing; D o This can be obtained by checking the tubing parameters; R a This information can be obtained by consulting the product parameters of the adhesive core or through experiments; p whg p atm This can be obtained by consulting engineering data on live-line operations; 'a' can be obtained through sealing tests; 'η' can be obtained through experiments or on-site operating parameters; Q a It shall be determined by relevant standards or actual requirements for safety management of live-line operations.

[0056] Example 1:

[0057] like Figure 1 As shown, the contact pressure distribution p at the oil pipe-rubber core sealing surface was obtained through numerical simulation. c (l) Axial contact length L of oil pipe-rubber core sealing surface c The outer diameter is 109.51 mm; the outer diameter D of the tubing was obtained by consulting the tubing parameters. o The surface roughness R along the circumferential direction of the rubber core is 88.9 mm; this was obtained by referring to the product parameters of the rubber core or through experimental testing. a The value is 1.2 μm; the maximum allowable pressure value p in the wellhead annulus was obtained by consulting engineering data on live-line operations. whg 35 MPa, atmospheric pressure p atm The pressure was 0.101325 MPa; the sealing contact energy index α was 1.4 obtained through sealing experiments; and the dynamic viscosity η of the pressurized gas at the wellhead was 3.2 × 10⁻⁶ MPa obtained through field operating parameters. -11 MPa·s; refer to relevant industry standards to obtain the allowable leakage volume rate Q. a 0.9cm 3 / 15min.

[0058] Step 1: Based on the principle of equivalent sealing contact energy, the formula is used. Calculate and obtain the equivalent average contact pressure p of the tubing-rubber core sealing surface cm It is 45.84 MPa.

[0059] Step 2: Treat the tubing-rubber core contact pair as an elasto-plastic normal flattening contact between a rigid smooth plate and a rough plate with uniformly distributed spherical micro-protrusions, and use finite element software to simulate and obtain the average contact pressure p. cm The contact area A of the next single spherical micro-protrusion c 3.167μm 2 .

[0060] Step 3: Use the formula The circumferential width B of the micro-leakage channel at the tubing-rubber core contact interface was calculated to be 45.619 mm.

[0061] Step 4: Use the formula The average height H of the micro-leakage channel at the tubing-rubber core contact interface was calculated to be 0.211 μm.

[0062] Step 5: Use the formula Calculate the leakage volume rate Q at the contact interface between the tubing and rubber core of the annular blowout preventer during pressurized gas well operations. v It is 0.0092 cm³ / 15 min.

[0063] Step 6: Calculate the gas leakage volume rate Q v With the allowable leakage volume rate Q a In comparison, satisfying Q v <Q a The seal of the annular blowout preventer was determined to be safe.

[0064] In this embodiment, the equivalent average contact pressure of the tubing-rubber core sealing surface is obtained based on the principle of equivalent sealing contact energy. An elastoplastic normal flattening contact between a rigid smooth plate and a rough plate with uniformly distributed spherical micro-protrusions is used to simulate the microscopic contact state of the tubing-rubber core. The actual contact area of ​​a single spherical micro-protrusion under the equivalent average contact pressure of the tubing-rubber core sealing surface is obtained. Then, the circumferential width and average height of the microscopic leakage channel at the tubing-rubber core contact interface are calculated. A parallel plate model from fluid mechanics is used to obtain the gas leakage volume rate through the tubing-rubber core interface and compare it with the allowable gas leakage volume rate. Compared with existing methods that evaluate the gas sealing performance of annular blowout preventers based on macroscopic contact pressure of the sealing surface and experimental methods, this method can consider the influence of the microscopic contact state of the tubing-rubber core contact pair on the gas leakage channel. It can quickly, economically, and quantitatively evaluate the gas leakage rate and sealing safety of the tubing-rubber core contact pair of annular blowout preventers under pressurized gas well operations, with high reliability.

[0065] The above-disclosed embodiments are merely one or more preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art can understand that all or part of the processes for implementing the above embodiments and equivalent changes made in accordance with the claims of this application still fall within the scope of this application.

Claims

1. A method for quantitatively evaluating the gas sealing performance of an annular blowout preventer, characterized in that: The following steps are involved: S1. Obtain the equivalent average contact pressure p of the oil pipe-rubber core sealing surface cm ; S2. Obtain the contact area A of a single spherical microconvex body on the oil pipe-rubber core sealing surface under the equivalent average contact pressure c ; S3, obtaining the circumferential width B of the micro leakage channel at the oil pipe-rubber core contact interface; S4, obtaining the average height H of the microscopic leakage channel at the contact interface between the tubing and the rubber core; S5. Obtain the leakage volume rate Q of the annular BOP tubing-rubber core contact interface during gas well pressure operation v ; S6, Q v and allowable leakage volume rate Q a In contrast, if Q is satisfied v ≥Q a , then the annular blowout preventer seal fails, otherwise it is safe; In step S1, the calculation formula for obtaining the equivalent average contact pressure of the oil pipe-rubber core sealing surface is: In the calculation formula: p cm is the equivalent average contact pressure between the oil pipe and the rubber core sealing surface, in MPa; L c is the axial contact length between the oil pipe and the rubber core sealing surface, in mm; p c (l) is the contact pressure distribution of the oil pipe-rubber core sealing surface, in MPa; a is the sealing contact energy index, dimensionless; In step S3, the calculation formula for obtaining the circumferential width of the microscopic leakage channel at the oil pipe-rubber core contact interface is: In the calculation formula: B is the circumferential width of the microscopic leakage channel at the oil pipe-rubber core contact interface, in μm; D o is the outer diameter of the oil pipe, in mm; R a A is the circumferential roughness of the rubber core surface, in μm; c is the contact area of ​​a single spherical microconvex body, in μm 2 ; In step S4, the calculation formula for obtaining the average height of the microscopic leakage channel at the oil pipe-rubber core contact interface is: In the calculation formula: H is the average height of the microscopic leakage channel at the oil pipe-rubber core contact interface, in μm; In step S5, the calculation formula for obtaining the leakage volume rate of the oil pipe-rubber core contact interface is: In the calculation formula: Q v is the gas leakage volume rate at the oil pipe-rubber core contact interface, in cm 3 / s;p whg is the maximum allowable pressure value of the wellhead casing annulus, in MPa; p atm is the atmospheric pressure, in MPa; η is the dynamic viscosity of the pressurized gas at the wellhead, in MPa·s.

2. A method for quantitatively evaluating the gas sealing performance of an annular blowout preventer according to claim 1, characterized in that: Step S2 also includes: considering the tubing-rubber core contact pair as an elastic-plastic normal flattening contact between a rigid smooth plate and a rough plate with uniformly distributed spherical micro-convex bodies, and using finite element software to simulate and obtain the equivalent average contact pressure p cm The contact area A of a single spherical microconvex body c .

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