US 20080027693 A1
A method of manufacturing, certifying, and optimizing a seal for a blowout preventer. The method includes generating a finite element analysis seal model, smoothing the finite element analysis seal model, and analyzing a strain plot of the smoothed finite element analysis seal model based upon a displacement condition.
1. A method of manufacturing a seal of a blowout preventer, the method comprising:
selecting a seal design;
generating a first finite element analysis seal model from the selected seal design;
smoothing the first finite element analysis seal model;
analyzing a strain plot of the smoothed first finite element analysis seal model based on a displacement condition; and
manufacturing a seal.
3. The method of
5. The method of
6. The method of
7. The method of
8. The method of
9. The method of
10. The method of
generating a second finite element analysis seal model based on the analyzed strain plot of the smoothed first finite element analysis seal model; and
analyzing a strain plot of the second finite element analysis seal model based on the displacement condition.
12. The method of
13. The method of
14. The method of
15. The method of
16. The method of
21. The method of
23. The method of
24. The method of
25. A method to certify a seal of a blowout preventer, the method comprising:
generating a first finite element analysis seal model;
smoothing the first finite element analysis seal model;
analyzing a strain plot of the smoothed first finite element analysis seal model based upon a displacement condition; and
comparing the strain plot of the smoothed first finite element analysis seal model against at least one specified criteria.
26. The method of
generating a second finite element analysis seal model based on the analyzed strain plot;
analyzing a strain plot of the second finite element analysis seal model based on the displacement condition; and
comparing the strain plot of the second finite element analysis seal model against the at least one specified criteria.
27. The method of
28. The method of
30. The method of
31. A method of optimizing a seal of a blowout preventer, the method comprising:
smoothing a first finite element analysis seal model;
analyzing a strain plot of the smoothed first finite element analysis seal model based upon a displacement condition;
generating a second finite element analysis seal model based on the analyzed strain plot of the smoothed first finite element analysis seal model;
smoothing the second finite element analysis seal model;
analyzing a strain plot of the second smoothed finite element analysis seal model based upon a displacement condition; and
repeating the analyzing and generating of smoothed finite element analysis seal models until an optimized seal model is reached.
32. The method of
33. The method of
34. The method of
This application claims the benefit of the following provisional applications under 35 U.S.C. 119(e): U.S. Provisional Patent Application Ser. No. 60/820,723 filed on Jul. 28, 2006; U.S. Provisional Patent Application Ser. No. 60/847,760 filed on Sep. 28, 2006; U.S. Provisional Patent Application Ser. No. 60/862,392 filed on Oct. 20, 2006; and U.S. Provisional Patent Application Ser. No. 60/912,809 filed on Apr. 19, 2007, all of which are incorporated by reference in their entirety herein.
1. Field of the Invention
Embodiments disclosed herein generally relate to blowout preventers used in the oil and gas industry. Specifically, embodiments selected relate to methods of designing and manufacturing seals for use in blowout preventers, in which the seals may include elastomer and a rigid material.
2. Background Art
Well control is an important aspect of oil and gas exploration. When drilling a well, for example, safety devices must be put in place to prevent injury to personnel and damage to equipment resulting from unexpected events associated with the drilling activities.
Drilling wells involves penetrating a variety of subsurface geologic structures, or “layers.” Occasionally, a wellbore will penetrate a layer having a formation pressure substantially higher than the pressure maintained in the wellbore. When this occurs, the well is said to have “taken a kick.” The pressure increase associated with a kick is generally produced by an influx of formation fluids (which may be a liquid, a gas, or a combination thereof) into the wellbore. The relatively high-pressure kick tends to propagate from a point of entry in the wellbore uphole (from a high-pressure region to a low-pressure region). If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. Such “blowouts” may result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and substantial injury or death of rig personnel.
Because of the risk of blowouts, devices known as blowout preventers are installed above the wellhead at the surface or on the sea floor in deep water drilling arrangements to effectively seal a wellbore until active measures can be taken to control the kick. Blowout preventers may be activated so that kicks are adequately controlled and “circulated out” of the system. There are several types of blowout preventers, the most common of which are annular blowout preventers (including spherical blowout preventers) and ram blowout preventers. Each of these types of blowout preventers will be discussed in more detail.
Annular blowout preventers typically use large annular, rubber or elastomeric seals having metal inserts, which are referred to as “packing units.” The packing units may be activated within a blowout preventer to encapsulate drillpipe and well tools to completely seal an “annulus” between the pipe or tool and a wellbore. In situations where no drillpipe or well tools are present within the bore of the packing unit, the packing unit may be compressed such that its bore is entirely closed. As such, a completely closed packing unit of an annular blowout preventer acts like a shutoff valve. Typically, packing units seal about a drillpipe, in which the packing unit may be quickly compressed, either manually or by machine, to affect a seal thereabout to prevent well pressure from causing a blowout.
An example of an annular blowout preventer having a packing unit is disclosed in U.S. Pat. No. 2,609,836, issued to Knox, assigned to the assignee of the present invention, and incorporated herein by reference in its entirety. The packing unit of Knox includes a plurality of metal inserts embedded in an elastomeric body, in which the metal inserts are completely bonded with the elastomeric body. The metal inserts are spaced apart in radial planes in a generally circular fashion extending from a central axis of the packing unit and the wellbore. The inserts provide structural support for the elastomeric body when the packing unit is radially compressed to seal against the well pressure. Upon compression of the packing unit about a drillpipe or upon itself, the elastomeric body is squeezed radially inward, causing the metal inserts to move radially inward as well.
Referring now to
Annular blowout preventer 101 is actuated by fluid pumped into opening 113 of a piston chamber 112. The fluid applies pressure to a piston 117, which moves piston 117 upward. As piston 117 moves upward, piston 117 translates force to packing unit 105 through a wedge face 118. The force translated to packing unit 105 from wedge face 118 is directed upward toward a removable head 119 of annular blowout preventer 101, and inward toward a central axis of wellbore 103 of annular blowout preventer 101. Because packing unit 105 is retained against removable head 119 of annular blowout preventer 101, packing unit 105 does not displace upward from the force translated to packing unit 105 from piston 117. However, packing unit 105 does displace inward from the translated force, which compresses packing unit 105 toward central axis of wellbore 103 of the annular blowout preventer 101. In the event drillpipe is located within bore 120, with sufficient radial compression, packing unit 105 will seal about the drillpipe into a “closed position.” The closed position is shown in
Annular blowout preventer 101 goes through an analogous reverse movement when fluid is pumped into opening 115 of piston chamber 112, instead of opening 113. The fluid translates downward force to piston 117, such that wedge face 118 of piston 117 allows the packing unit 105 to radially expand to an “open position.” The open position is shown in
Referring now to
Referring now to
Similarly, spherical blowout preventers use large, semi-spherical, elastomeric seals having metal inserts as packing units. Referring to
Additionally, ram blowout preventers may also include elastomeric seals having metal inserts. The large seals are typically disposed on top of ram blocks or on a leading edge of ram blocks to provide a seal therebetween. Referring now to
Referring now to
Referring now to
Referring now to
For any seal mechanism comprising elastomers and metal in blowout preventers (e.g., packing units in the annular and spherical blowout preventers and top seals and ram packers in the ram blowout preventer), loads may be applied to contain pressures between various elements of the blowout preventers. For example, with respect to the annular blowout preventer shown in
As stress is incurred by blowout preventer seals, the material of the seals will strain to accommodate the stress and provide sealing engagement. The amount of strain occurring in the material of the seal is dependent on a modulus of elasticity of the material. The modulus of elasticity is a measure of the ratio between stress and strain and may be described as a material's tendency to deform when force or pressure is applied thereto. For example, a material with a high modulus of elasticity will undergo less strain than a material with a low modulus of elasticity for any given stress. Of the materials used in blowout preventer seals, the metal inserts have substantially larger moduli of elasticity than the elastomeric portions. For example, the modulus of elasticity for steel (typically about 30,000,000 psi; 200 GPa) is approximately 20,000-30,000 times larger than the moduli of elasticity for most elastomers (typically about 1,500 psi; 0.01 GPa).
Historically, when examining, designing, and manufacturing seals for blowout preventers, such as packing units for blowout preventers, the locations and amounts of stress and/or strain (i.e., stress concentrations, strain concentrations) occurring within the seal have been the largest concern and received the most attention and analysis. As the seal is subject to loads (e.g., repetitive and cyclic closures of a packing unit of an annular blowout preventer about a drillpipe or about itself), the magnitude and directions of the stresses and strains occurring across the seal are evaluated to determine the performance of the seal. A common technique used for this evaluation is finite element analysis (“FEA”). Specifically, the FEA may be used to simulate and evaluate the stress and/or strain concentrations which occur across the seal under given displacement conditions.
Traditionally with FEA, seals for blowout preventers are modeled with finite elements to determine the performance of the seal under various displacement conditions. For example, using FEA modeling, the packing unit of an annular blowout preventer may be simulated with a displacement condition to move into the closed position around a drillpipe, in which the packing unit would be compressed between the piston and the removable head from the annular blowout preventer and the drillpipe. The FEA model may be used to produce a strain plot of the seal (packing unit in this example) to display the strain concentrations within the seal under that specific displacement condition.
However, this evaluation of the strain concentrations may not result in the most accurate prediction and representation of the performance of the seals used in blowout preventers. Typically, the seals used in blowout preventers experience extremely high amounts of strain from the stresses that may be incurred. For example, when a packing unit is compressed into the closed position to seal about a section of drillpipe, an elastomeric body of the packing unit may experience strains in excess of 300% in the areas of the strain concentrations. Further, in a case where no drillpipe is present, the packing unit may begin experiencing strains of about 400-450% in seating about itself These elevated strains, especially when repetitively and cyclically performed upon the packing seal, usually lead to the ultimate failure of the seal.
Furthermore, as described above, the metal and elastomers used for seals in blowout preventers typically have large differences in their moduli of elasticity. Because of this difference between the moduli of elasticity, when bonded together, the metal will tend to control the “flow” and deformation of the elastomers in the seals when compressed in the blowout preventers. With the large amounts of strain, especially the strain resulting from repetitive and cyclic displacements, coupled with the significant difference between the moduli of elasticity of the seal's materials, FEA evaluating strain concentrations may not accurately represent the capabilities of the seals.
In FEA applications, the seal comprising a rigid material and elastomer may be represented by a geometrically similar representation consisting of many finite elements (i.e. discrete regions), commonly referred to as a mesh. The finite elements interact with one another to model the seal and provide simulated data and results for various displacement conditions. However, the finite elements within areas of high stress and/or strain (i.e., stress and/or concentrations) with substantial differences between materials' moduli of elasticity may improperly deform. Common improper deformations of the finite elements that may occur include the elements collapsing upon themselves, distorting without bound, or sustaining losses in stress, strain, and/or energy. These, in addition to other improper deformations of the finite elements may produce inaccurate results for the stress and strain occurring across the model.
Historically, when the FEA is producing erroneous results, the number of finite elements of the mesh is increased for better resolution in at least some selected locations (e.g., areas of high stress or strain concentration). Thus, it is common for areas with stress and/or strain concentrations to receive more localized “attention” when modeling in FEA than other areas. However, this process may allow the analysis to become inherently localized on the areas of the seal models with the stress and/or strain concentrations, leading to solutions that may be narrowly constructed and/or inaccurate. For example, it is common PEA practice to increase the number of elements of (and thus further complicate) the seal model in the areas of these concentrations to increase the accuracy of the simulated stress and strain within the concentration regions. The same may also be done for a seal model in the areas of strain concentrations. However, it should be understood that by increasing the number of elements, or decreasing the mesh size, the solution time and the amount of computing power required may be increased. This may lead to solution stalling (due to computational error) and/or the generation of inaccurate results.
Referring now to
In this approach, the resolution of the finite elements in the mesh (seal model) is increased with each iteration. Specifically, as mentioned above, it is ordinary practice to increase the resolution of the finite elements of the mesh in regions that experience large amounts of stress and/or strain. However, because of the characteristics of metal reinforced elastomer seals, such localized analysis may result in an FEA stress and/or strain output that fails to correlate to an experimentally observed solution. Furthermore, because of the complexity, the FEA stress and/or strain output may not even be capable of converging to a solution at all.
As shown, theoretical strain of the finite element occurring in the direction of the simulated principal strain from the y-axis in
Therefore, as shown, when designing and manufacturing high strain elastomeric seals containing rigid inserts, there may be a significant discrepancy between the theoretical stress and strain predicted by FEA and actual stress and strain. Thus, current modeling and analysis techniques for blowout preventer seals may not provide adequate information to improve their design and manufacture.
In one aspect, embodiments disclosed herein relate to a method of manufacturing a seal of a blowout preventer. The method comprises selecting a seal design, generating a first finite element analysis seal model from the selected seal design, smoothing the first finite element analysis seal model, analyzing a strain plot of the smoothed first finite element analysis seal model based on a displacement condition, and manufacturing a seal.
In another aspect, embodiments disclosed herein relate to a method to certify a seal of a blowout preventer. The method comprises generating a first finite element analysis seal model, smoothing the first finite element analysis seal model, analyzing a strain plot of the smoothed first finite element analysis seal model based upon a displacement condition, and comparing the strain plot of the smoothed first finite element analysis seal model against at least one specified criteria.
Further, in another aspect, embodiments disclosed herein relate to a method of optimizing a seal of a blowout preventer. The method comprises smoothing a first finite element analysis seal model, analyzing a strain plot of the smoothed first finite element analysis seal model based upon a displacement condition, generating a second finite element analysis seal model based on the analyzed strain plot of the smoothed first finite element analysis seal model, smoothing the second finite element analysis seal model, analyzing a strain plot of the second smoothed finite element analysis seal model based upon a displacement condition, and repeating the analyzing and generating of smoothed finite element analysis seal models until an optimized seal model is reached.
Other aspects and advantages of the embodiments disclosed herein will be apparent from the following description and the appended claims.
In one aspect, embodiments disclosed herein relate to a method of manufacturing a seal for a blowout preventer. In another aspect, embodiments disclosed herein relate to a method of optimizing a seal for a blowout preventer that incorporates using a strain plot in the method. In another aspect, embodiments disclosed herein relate to a method of certifying a seal model for a blowout preventer using FEA to produce a strain plot after the model has been smoothed and bulk analyzed in response to a displacement condition.
As used herein, a “rigid material” refers to any material that may provide structure to a seal of a blowout preventer, both metal and non-metal. Examples for a rigid material may include, but are not limited to, steel, bronze, and high strength composites (e.g., carbon composites, epoxy composites, thermoplastics). Further, as used herein, a “seal” refers to a device that is capable of separating zones of high pressure from zones of low pressure. Examples of blowout preventer seals include, but are not limited to, annular packing units, top seals, and variable bore rams.
As mentioned above, techniques and models historically used to design and manufacture seals having elastomer and rigid materials for blowout preventers may not provide accurate information to improve the performance of the seal's design. Therefore, in designing, manufacturing, and certifying a seal for a blowout preventer in accordance with embodiments disclosed herein, a method including FEA of bulk strain and generating a strain plot may be used to yield more accurate convergent results under a given displacement condition. This FEA method, in addition to certain techniques for generating and modifying the seal models, may more accurately calculate the strain in the seal because it is tailored to accommodate the large amounts of stress and strain experienced by blowout preventer seals. Suitable software to perform such FEA includes, but is not limited to, ABAQUS (available from ABAQUS, Inc.), MARC (available from MSC Software Corporation), and ANSYS (available from ANSYS, Inc.).
Specifically, embodiments and methods disclosed herein may advantageously provide techniques for generating and analyzing seal models within FEA to determine the seal's response under displacement conditions characterized by large amounts of strain. Methods disclosed herein may use a simplified seal design and/or model of a seal to assist in the analysis of the seal. For example, methods disclosed herein may avoid analyzing stress and strain concentrations of a complex seal design by “smoothing” that design.
As used herein, the term “smoothing” refers to various techniques to simplify a complex geometry of a seal design for use with FEA. These techniques may allow the analysis of a smoothed model (i.e., a FEA model constructed from a smoothed design) to correlate with experimentally observed conditions and to converge to a definitive result when analysis of a non-smoothed model may not. As such, a model constructed from a smoothed design may be analyzed within FEA to determine an overall, or “bulk”, strain condition. By analyzing this bulk (i.e., non-localized) strain, the performance, and/or possibly failure, of a seal under various displacement conditions may be predicted with more accuracy. Following the analysis of the smoothed model for the bulk strain condition, knowledge obtained therefrom may be incorporated into a (non-smoothed) seal design that is to be manufactured.
Referring now to
Next, displacement conditions are simulated in FEA using the smoothed seal model 1230. Preferably, these simulated displacement conditions reflect the forces, load states, or strains that the seal may expect to experience in operation. Further, after simulating displacement conditions, a strain plot showing the strain and deformation occurring in the seal model is generated and analyzed 1240. Ideally, the strain plot shows the location and amount of strain occurring in the seal model in response to the simulated displacement conditions. The strain plot may be analyzed and reviewed 1240 to determine the performance characteristics of the seal model. If the seal model requires improvement, the method may loop back to 1210 to determine material properties of another material for the seal, or alternatively may loop back to 1220 for generation and analysis of another seal model. This loop allows the seal model to be further simulated in FEA to determine its performance after further modifications or models. Otherwise, if the seal model is considered acceptable and meets a specified criteria, the seal model may be used to manufacture a seal for a blowout preventer 1250.
In initial step 1210, the properties of the seal's materials are determined. Of the materials, the elastomeric materials will have lower moduli of elasticity than the rigid materials. Thus, when the seal is subjected to large amounts of stress, the elastomeric portion of the seal will strain more than the rigid material portions. For example, when the packing unit in an annular blowout preventer is stressed in the closed position, the elastomeric body of the packing unit will strain significantly more than the metal inserts. Because elastomers strain significantly more than the rigid materials for any given stress input, it may be especially important to determine the material properties of an elastomer used in the seal, specifically the relationship between stress and strain across the elastomer.
In viscoelastic materials under constant stress, the strain may increase with time (i.e., creep). Conversely, under a constant level of strain, the stress within viscoelastic materials decreases over time (i.e., relaxation). Furthermore, higher levels of strain and lower temperatures may lead to an increase in the moduli of elasticity for viscoelastic materials. Elongation of a material refers to the percentage change in length of a material. The maximum amount of tensile strain to which a material may be subjected, or elongated to, before failure is referred to as the elongation at break. A material may have a high or low modulus of elasticity, but may exhibit a low elongation at break such that the material will fail without experiencing much strain. Further, the tensile strength of a material is the maximum amount of stress (in tension) a material may be subjected to before failure. As stress is exerted upon the material, the material strains to accommodate the stress. Once the stress is too much for the material, it will no longer be able to strain, and the material fails. The failure point of the material is known as the ultimate tensile strength.
Furthermore, if cyclic displacements are applied to an elastomeric material, hysteresis (phase lag) may occur, leading to a dissipation of mechanical energy within the elastomeric material. Hysteresis may occur when there is softening induced by stress. This may be described as an instantaneous and irreversible softening for a material that occurs when an applied displacement increases beyond any prior maximum value, resulting in a shift of the stress-strain curve of the material. This induced softening, which may also be referred to as the Mullin's effect, is thought to be at least partially attributed to the microscopic breakage of links in a elastomeric material. This weakens the elastomeric material during an initial deformation so that the material is, in turn, weaker in subsequent deformations of the material.
Thus, in one embodiment of the present disclosure, to determine at least one of the material properties of the elastomer for the seal of the blowout preventer, as described above, empirical testing of the elastomer may be used. Specifically, tests may be performed to determine the properties of the elastomeric material. Examples of tests that may be performed include, but are not limited to, a uniaxial tension test, a uniaxial compression test, a lap shear test, and a biaxial tension test. A uniaxial tension test applies tensile load in one direction to a material and measures the corresponding strain induced in the material. A uniaxial compression test applies compressive load in one direction to a material and measures the corresponding strain induced in the material. A lap shear test applies shear loads to a material and measures the corresponding shear strain of the material. Further, a biaxial tension test applies tensile loads in two directions to a material and measures the corresponding strain of the material. The use of these tests, in addition to other tests commonly known in the art, may assist in analyzing and determining the material properties of the elastomer. Furthermore, it should be understood by one of ordinary skill in the art, that as material properties of most materials vary by temperature, the performance of multiple tests at differing temperatures may be prudent to establish certain material properties.
In step 1220, a model (i.e., a mesh) for the seal is generated. When generating the model of the seal, design features of the seal are chosen and applied to the model. For example, for a packing unit for an annular blowout preventer, the number of inserts used, the width of the rigid material inserts, and the specific material used for the rigid material inserts may be chosen when generating the seal model. The seal models may be created in a computer aided design (“CAD”) software package (e.g., AutoCAD available from Autodesk, Inc., and Pro/Engineer available from Parametric Technology Corporation) and imported into the FEA software package or, in the alternative, may be generated within the FEA packages (e.g., ABAQUS and PATRAN) themselves.
Referring now to
From here, as shown in
Further, as shown, seal design 1501 and model or mesh 1601 (discussed below) may only represent a radial portion of packing unit 105. However, the remainder of packing unit 105 may be easily generated by taking advantage of the symmetrical geometry of packing unit 105. Those having ordinary skill in the art will appreciate that in the case of radially symmetric models, symmetric portions and profiles may be used and replicated to simplify the generation of the model.
Referring now to
Similarly, finite elements 1603 of metal inserts 109 of packing unit 105 will simulate and respond to stress and forces corresponding to the material properties of the metal inserts. Thus, finite elements 1603 deform and strain to simulate the response of the different materials (e.g., elastomers and rigid materials) of the seal in accordance with their material properties. While finite elements 1603 are shown as eight-noded elements (i.e., brick elements), finite elements of any shape known in the art may be used.
Further, while generating a seal model 1220, a number of smoothing techniques may be used on the seal design 1222. In many circumstances, as mentioned above, analyzing the actual manufactured geometry of the seal using FEA may lead to complications when large amounts of stress and strain are simulated. Particularly, as manufactured, the geometry of metal seal components include radiused corners and other stress-concentration reducing features to more evenly distribute stress across the component as it is loaded. However, it has been discovered that these techniques may adversely affect FEA models in FEA in that they increase the complexity of the model and may prevent the FEA from producing accurate results. Therefore, a seal model generated from a smoothed design may include removing as-manufactured stress concentration features in an effort to improve the results of FEA.
In one embodiment, the seal design's rigid material may be modified (i.e., smoothed) to reduce their complexity. Referring now to
Furthermore, in another embodiment, instead of smoothing the design by modifying internal and external corners of the rigid material insert, the smoothing may include modifying the shape of the rigid material insert and its position within the elastomeric body. Referring now to
However, referring to
Further still, the elastomeric body of the seal design may be smoothed as well. Referring again to
Those having ordinary skill in the art will appreciate that, in addition to these described smoothing techniques and modifications, other techniques may be used as well in addition. For example, in another embodiment, the web of the rigid material insert may be modified, such as hollowing the web of the insert, as long as the rigid material insert provides sufficient structural support for the seal to sustain the forces applied thereto when under any and all displacement conditions.
Preferably, when generating the seal models in step 1220, especially when smoothing the seal design 1222 of the seal model, the volume of the elastomeric body and the rigid material inserts of the seal model remains substantially constant. If the volume does not remain constant, the results and simulated strain from the strain plots created by the FEA may not be accurate or consistent. For example, when applying a force to an element, the force upon the element will stress the element, causing the element to strain to accommodate the stress. The stress applied to the element, though, is directly proportional to the force applied to the element and inversely proportional to the area or volume of the element. Thus, if the force applied to the element increases and/or the volume of the element decreases, the stress will correspondingly increase in the element.
Using this concept, the respective volumes of the elastomeric body and the rigid material inserts preferably remain substantially constant to provide accurate results. For example, if the volume of the overall seal model has substantially changed from the actual seal, the strain plots of the seal model may show an increase in strain in the elastomeric body with corresponding displacement conditions. Further, if the volume of the seal model changes from the smoothing techniques applied to the seal design of the seal model, such as increasing the volume of the elastomeric body of the seal model during the smoothing process, the strain plots of the smoothed model may show a decrease in simulated strain with corresponding displacement conditions. Thus, if the volume of the elastomeric body and the rigid material insert of the model of the seal increases or decreases, the simulated strain in the model would inherently change, independent if the seal model was modified for any improvements. Furthermore, if the overall volume of the seal remains consistent between non-smoothed and smoothed models but the relative volumes of the elastomeric body and the rigid inserts change, the strain plots may be similarly compromised.
Continuing now with step 1230, displacement conditions are simulated upon a seal for a blowout preventer in FEA using the generated seal model. Preferably, the simulated displacement conditions are loads and strains the seal may expect to experience in service. For example, a model of a packing unit of an annular blowout preventer may require a simulated displacement condition correlating to compressing into a closed position to seal about a section of drillpipe. Further, if no drillpipe is present, the model may experience a simulated displacement condition correlating to compressing to close about itself to seal the bore.
In step 1240, a strain plot, showing strain and deformation occurring in the seal model in response to displacement conditions may be analyzed and reviewed to determine the performance of the modeled seal. Referring now to
Referring now to
Similarly, referring to
Similarly still, referring to
As shown in
Referring now to
As such, in contrast to what one of ordinary skill in the art would intuitively believe, a simplified, smoothed model may produce a more convergent and accurate FEA solution than more complex, detailed models. As shown in this embodiment, the simulated strain produced using FEA correlates with experimentally observed solutions and converges to a definitive and correct result about the theoretical strain and within the tolerance band limitations. As the number of iterations increases (and as the model is further smoothed), the simulated strain solution produced by the FEA corresponds to the strain found in the seal through empirical testing. With these results, bulk strain FEA may provide useful results for simulation of seals for blowout preventers to further improve their designs.
For example, referring now to
Further, when analyzing the strain plot in step 1240, the strain plots may be used to certify the seal model for use in a blowout preventer. Specifically, the strain plots may be compared against one or more specified criteria to determine if the performance of the seal model meets necessary requirements. Specified criteria, for example, may include performance requirements, customer's requirements, or even industry requirements for seals. Furthermore, such criteria may be compared against the strain plots of an analyzed seal model to determine if a seal manufactured in accordance with the model would be in compliance with such requirements. For example, a customer may require packing units of annular blowout preventers to be capable of experiencing strains in excess of 300%. A strain plot of the seal model packing unit in a closed position displacement conditions may then be compared against the specified criteria to determine if the seal model is capable of satisfying such requirements.
In another example, industry requirements, such as API 16A/ISO 13533:2001, may be used as specified criteria to compare and certify a seal model. In particular, API 16A, Section 5.7.2 references a “closure test” for ram-type blowout preventers, while API 16A, Section 5.7.3 references a closure test for annular-type blowout preventers. Under API 16A/ISO 13533:2001, a packing unit may be required to undergo six closures about the drill pipe and, on a seventh closure, be capable of effectively sealing against pressure of about 200-300 psi (1.4-2.1 MPa). Thus, displacement conditions from industry requirements may be used in conjunction with a simulation to determine if a seal is capable of satisfying such requirements. Using methods and embodiments disclosed herein, the seal model may then be certified by comparing the strain plots of the seal model against these specified criteria.
If the seal model generated in step 1220 and analyzed in step 1240 may be improved further (e.g., if the model does not meet the specified criteria), the method may loop back to step 1210 to determine material properties for another material of the seal, or the method may loop back to step 1220 to have the seal model regenerated or modified as necessary. This loop of generating the seal model 1220 and analyzing the seal model 1240 may be repeated several times until an “optimized” seal model is reached.
In one embodiment, selected portions of an elastomeric body of a packing unit may be de-bonded from the rigid material inserts when looping back and re-generating the seal model 1220 to reduce to reduce the amount and location of strain. Typically, the elastomeric body is completely bonded to metallic inserts for the packing unit to maintain maximum rigidity, as discussed above with respect to the prior art. However, if selected portions of the elastomeric body are not bonded to the rigid material inserts, this may reduce strain in the elastomer of the packing unit when the packing unit is modeled in FEA to show the strain plots.
Referring now to
Referring now to
Similarly, referring to
Similarly still, referring to
Each of the strain plots of the packing unit model with a selectively de-bonded elastomeric body (i.e.,
Similar to above with respect to generating a seal model in step 1220, when simulating displacement conditions across the seal models 1230, it is preferable for the volumes of the seal model and its components to remain substantially constant. If the volumes do not remain constant, the results of the strain plots and simulated strain in FEA may not correlate with experimentally observed results or with one another, thereby providing inaccurate results. For example, if the volume of the seal models of the packing units shown in the strain plots of
In step 1250, after being generated, analyzed, and possibly re-generated (if necessary), the seal model may be used to manufacture a seal for a blowout preventer 1250. Specifically, using techniques known in the art, a seal based upon the three-dimensional seal model may be manufactured for use in a blowout preventer, such as a packing unit for an annular blowout preventer or a top seal or variable bore ram packer a ram blowout preventer. For example, the seal model of the packing unit for the annular blowout preventer having selective de-bonding, as discussed above and shown in
Aspects of embodiments disclosed herein, such as generating and analyzing a seal model of a seal for a blowout preventer using FEA, may be implemented on any type of computer regardless of the platform being used. For example, as shown in
Advantageously, methods and embodiments disclosed herein may provide improved and more accurate results when using FEA. Methods and embodiments disclosed herein use strain within FEA to determine the performance characteristics of seals for blowout preventers under simulated displacement conditions. This allows the finite elements within the seal model to displace when accommodating large amounts of strain.
Further, methods and embodiments disclosed herein may provide techniques for analyzing, smoothing, simplifying, and modifying seal models for use in FEA. Using these techniques, the accuracy of the results of the strain plots created using FEA may be improved. Additionally, using these techniques, the seal model may be modified to reduce the amount and location of strain (e.g., strain concentrations) occurring in the seal model from the simulated strain plots.
Furthermore, methods and embodiments disclosed herein may provide for a seal for a blowout preventer with an increased working lifespan. For example, the packing unit may be modeled with simulated displacement conditions of repeated closures (i.e., repeatably closing the seal about a drillpipe or itself) to determine design features that may extend the working lifespan (i.e., number of closures) of the packing unit.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.