Accordingly, the casing strings are utilized to assist in maintaining the weight of the drilling mud within the PPG and FG to continue drilling operations to greater depths. With subsurface formations being located at greater depths, the cost and time associated with the forming the wellbore increases. For instance, with the nested configuration, the initial casing strings have to be sufficiently large to provide a wellbore diameter of a specific size for the tools and other devices near the subsurface formations.
As a result the diameter of the initial casing strings is relatively large to provide a final useable wellbore diameter. The large diameter increases the costs of the drilling operations because of the cost associated with the increased size of the casing string, increased volume of cuttings that have to be managed, and increased volume of cement and drilling mud utilized to form the wellbore. As such, the cost of typically drilling operations results in some subsurface formations being economically unfeasible.
To reduce the diameter of casing strings, various processes are utilized. For example, drilling operations may utilize variable density drilling mud to maintain the drilling mud within the PPG and FG. As noted in Intl. Patent Application Publication No. These compressible objects may be recirculated as part of the variable density drilling mud to provide volume changes that reduce the number of intermediate casing string intervals in the wellbore. However, the use of compressible objects in the variable density drilling mud can be challenging.
For instance, the compressible objects have to be fabricated to provide a certain amount of compression and to be resilient. Further, the compressible objects have to be designed to compress at certain pressures to provide the volume changes in specific intervals within the wellbore. In addition, the drilling fluid, which is combined with the compressible objects, may be selected and include certain additives to interact with the compressible objects to enhance the variable density drilling mud.
As such, there is a need for a method for selecting and fabricating compressible objects for use with drilling fluids to form the variable density drilling mud. Other related material may be found in at least U. In one embodiment, a compressible object is described. The shell experiences less strain when the external pressure is about equal to the internal pressure than when the external pressure is above or below a predetermined compression interval of the compressible object.
Further, the shell experiences less strain when the external pressure is above or below the internal pressure than when the external pressure is about equal to the internal pressure. In a first alternative embodiment, a drilling mud is described. The drilling mud includes compressible objects, each of at least a portion of the compressible objects has a shell that encloses an interior region, wherein the shell experiences less strain when the external pressure is about equal to the internal pressure than when the external pressure is above or below a predetermined compression interval of the compressible object.
The drilling mud further includes a drilling fluid, wherein the density of the drilling mud changes due to the volume change of compressible objects in response to pressure changes as the drilling fluid and compressible objects circulate toward the surface of a wellbore. In a second alternative embodiment, a method associated with drilling a well is described. The method includes selecting compressible objects having a shell that encloses an interior region, wherein the shell is configured to experience less strain when the external pressure is about equal to the internal pressure than when the external pressure is above or below a predetermined compression interval of the compressible object; selecting a drilling fluid; introducing the compressible objects to the drilling fluid to form a variable density drilling mud, wherein the variable density drilling mud provides a density between a pore pressure gradient and a fracture pressure gradient for at least one interval as the variable density drilling mud circulates toward the surface of a well; and drilling a wellbore with the variable density drilling mud at the location of the well.
Further, once the wellbore is formed, hydrocarbons may be produced from the wellbore. In a third alternative embodiment, a method for forming a variable density drilling mud is described. The method includes selecting compressible objects having a shell that encloses an interior region, wherein the shell experiences less strain when the external pressure is about equal to the internal pressure than when the external pressure is above or below a predetermined compression interval of the compressible object; selecting a drilling fluid to be combined with the compressible objects; blending the compressible objects with the drilling fluid to form a variable density drilling mud, wherein the variable density drilling mud maintains a density between a pore pressure gradient and a fracture pressure gradient for an interval of a well as the variable density drilling mud circulates toward the surface of a well.
In a fourth alternative embodiment, a system associated with drilling a wellbore is described. The system includes a wellbore and a variable density drilling mud disposed in the wellbore. The variable density drilling mud comprises compressible objects and each of at least a portion of the compressible objects has a shell that encloses an interior region, wherein the shell experiences less strain when the external pressure is about equal to the internal pressure than when the external pressure is above or below a predetermined compression interval of the compressible object.
Further, the system includes a drilling string disposed within the wellbore; and a bottom hole assembly coupled to the drilling string and disposed within the wellbore. The foregoing and other advantages of the present technique may become apparent upon reading the following detailed description and upon reference to the drawings in which:.
In the following detailed description and example, the invention will be described in connection with its preferred embodiments. However, to the extent that the following description is specific to a particular embodiment or a particular use of the invention, this is intended to be illustrative only. Accordingly, the invention is not limited to the specific embodiments described below, but rather, the invention includes all alternatives, modifications, and equivalents falling within the true scope of the appended claims.
The present technique is directed to a method, composition and system for selecting, fabricating, and utilizing compressible objects in a variable density drilling mud. In particular, the compressible objects may be utilized with a drilling fluid to form the variable density drilling mud for drilling operations in a well.
The compressible objects and the drilling fluid are selected to maintain the drilling mud weight between the pore pressure gradient PPG and the fracture pressure gradient FG within a wellbore. Specifically, under the present techniques, the compressible objects have a shell configured to experience less strain when the external pressure is about equal to the internal pressure than when the external pressure is greater than the internal pressure or less than the internal pressure.
Accordingly, various methods and systems are described to select and fabricate the compressible objects. Further, it should be noted that the following methods and procedures are not limited to drilling operations, but may also be utilized in completion operations, or any operations benefiting from variable density fluids. Turning now to the drawings, and referring initially to FIG. In the exemplary drilling system , a drilling rig is utilized to drill a well The well may penetrate the surface of the Earth to reach the subsurface formation As may be appreciated, the subsurface formation may include various layers of rock that may or may not include hydrocarbons, such as oil and gas, and may be referred to as zones or intervals.
As such, the well may provide fluid flow paths between the subsurface formation and production facilities not shown located at the surface The production facilities may process the hydrocarbons and transport the hydrocarbons to consumers. However, it should be noted that the drilling system is illustrated for exemplary purposes and the present techniques may be useful in circulating fluids in a wellbore for any purpose, such as performing drilling operations or producing fluids from a subsurface location.
To access the subsurface formation , the drilling rig may include drilling components, such as a bottom hole assembly BHA , drilling strings , casing strings and , drilling fluid processing unit for processing the variable density drilling mud and other systems to manage wellbore drilling and production operations. Each of these drilling components is utilized to form the wellbore of the well The BHA may include a drill bit and be used to excavate formation, cement or other materials from the wellbore.
The casing strings and may provide support and stability for the access to the subsurface formation , which may include a surface casing string and an intermediate or production casing string The production casing string may extend down to a depth near or through the subsurface formation The drilling fluid processing unit may include equipment that may be utilized to manage the variable density drilling fluid.
For example, the drilling fluid processing unit may include shakers, separators, hydrocyclones and other suitable devices e. During drilling operations, the use of a variable density drilling mud as a drilling mud allows the operator to drill deeper below the surface , maintain sufficient hydrostatic pressure, prevent an influx of formation fluid gas or liquid , and remain below an FG that the subsurface formation can support.
As noted in Patent Application Publication No. That is, the compressible objects should have substantially recoverable load bearing walls and low permeability for the gas within the compressible objects. Substantially recoverable is defined to mean that the accumulation of plastic strain in the shell wall as a consequence of repeated cycling of the compressible objects between the surface and the bottom of the wellbore does not cause substantial failure of the load bearing wall or significant loss of the internal gas pressure during repeated cycles i.
Also, low permeability is defined to mean that the internal pressure of the compressible objects, while in use, remains within acceptable limits for a predetermined time period required to drill the wellbore to the target depth. While adding compressible objects to drilling mud to control the density of the drilling mud based on depth has been described in Patent Application Publication No. In particular, the repeated compression cycles typically experienced by a recirculating variable density drilling mud within the constraints imposed by the mechanical properties of existing materials may be a limitation for the compressible objects.
As such, the process of fabricating the compressible objects may have to include various factors that influence the durability and performance of the compressible objects, as discussed further below. To begin, it should be noted that large compression ratios are required to achieve the desired change in the drilling fluid density with depth within the limits set by the maximum volume fraction of the compressible objects allowed by the effect of the compressible objects on the fluid rheology, as described in Patent Application No.
Accordingly, the compressible objects should have certain properties configured to provide large compression ratios and to begin compression within certain pressure ranges or levels. The compression ratio of a hollow object, which is one embodiment of the compressible objects, may be limited by the ratio of the initial uncompressed volume i.
Large compression ratios are provided by the wall of the compressible objects being thin and flexible. Accordingly, the compressible objects may preferably be designed such that the compression and re-expansion of the compressible objects may be accomplished without significant permanent deformation of the walls i. In addition, the predetermined external pressure or depth of compression and the predetermined compression interval of the compressible objects may be tailored to provide a change in the density of the drilling mud at or near specific depths within the wellbore.
Typically, object compression that begins at the surface has limited value. In these applications, the compressible objects compress from the surface for a predetermined compression interval or range, which extends down to a specific depth. As a result, these compressible objects may be utilized for some specific land drilling applications, but may not be useful in deepwater environments or deeper drilling intervals.
To provide a change in the density over a specific predetermined pressure interval for specific depths or external pressure, the starting depth and depth interval for the predetermined pressure interval over which the compression occurs may preferably be adjusted by the compressible objects. For example, the initial internal pressure of the compressible object may be selected based on the depth at which a transition in the compressibility is desired.
At depths in the mud column i. At depths for which the pressure in the mud column is above the initial internal pressure, the volume change of the compressible objects gradually becomes dominated by the compressibility of the gas. That is, the predetermined compression interval is a pressure range from an external pressure that is about equal to the internal pressure of the compressible object to an external pressure that substantially compresses the compressible object i.
To compress at a specific depth, the walls of the compressible objects may be designed to maintain a predetermined internal pressure. The initial internal pressure of the compressible objects for a given drilling mud density is determined by the depth at which a transition to gas compression is dominated by volume change of the compressible objects.
Typically, an internal pressure greater than about psi pounds per square inch at atmospheric pressure, greater than psi at atmospheric pressure, greater than psi at atmospheric pressure or more preferably greater than psi at atmospheric pressure, may be utilized.
For a given initial internal pressure, the achievable object compression ratio is dependent on the ratio of the wall thickness to the effective diameter of the compressible object. While the wall thickness is preferably as thin as possible, the lower limit of the wall thickness is defined by the minimum thickness capable of containing the desired internal gas pressure at an external pressure of about 1 atmosphere, which is typically encountered at the surface Accordingly, a material with a tensile strength greater than 10, psi may typically be utilized, as discussed below, to maintain the internal pressure for the compressible object.
Further, for a given internal pressure and diameter of a compressible object, the minimum wall thickness that may be used is therefore defined by the elastic limit of the tensile strength of the wall material. Within these strength limitations, it is desirable to minimize the wall thickness because the ratio of the volume of the wall material to the total volume of the compressible object sets an upper limit on the magnitude of the achievable compression ratio, as noted above.
Accordingly, while the compressible object may include a variety of shapes, such as cubes, pyramids, oblate or prolate spheroids, cylinders, pillows, for example, spherical and elliptical objects with spherical or near spherical inflated geometries are useful for reasons related to the optimization of the compressible mud rheology. The design of the compressible object may be further complicated by structural instabilities. For instance, a spherical object for a given internal pressure and diameter may be restricted by structural instabilities characteristic of the spherical object's architecture.
The structural instabilities may include local strains, such as equatorial buckling instability during the inflation phase and the cap buckling instability during the compression phase. As such, the design of the compressible object may also be adjusted to compensate for, or reduce, the localized strains and instabilities during expansion and compression of the compressible objects. In the chart , a compressible object is a nearly spherical object, which has an aspect ratio of about 1.
The aspect ratio of an object is defined as the ratio of the major axis over the minor axis, which is discussed further below. In FIG. The maximum strain is the largest strain at any point on the compressible object in that state. Along the response curve , the maximum elastic deformation does not occur uniformly over the object surface during compression, but is localized due to buckling instabilities during compression.
Specific examples of the localized strain on the object are shown in FIG. The elastic deformation of the object as it is compressing is dominated by strain localization associated with a cap buckling instability, which is indicated by the depressed region The cap buckling instability is a collapse of the depressed region due to the inability of the structure to resist the external pressure loaded on that region.
In particular, the regions are the locations or areas of the largest localized strain, which are plotted in the response curve of FIG. The severity of this instability has been shown to increase with increasing wall thickness. Based on the discussion above, the compressible object should have a tensile strength sufficient to handle the internal pressure and a recoverable linear elongation or elastic strain large enough to handle the required deformation.
To provide the required recoverable linear elongation, the compressible object may be designed to divide the deformation of the compressible object into different states. For instance, the compressible objects may have three different states, such as an initial state, an expanded state, and a compressed state. In one embodiment the initial state may be, for example, an oblate spheroid with an aspect ratio less than 1. As noted above, the aspect ratio of the object in the initial state is defined as the ratio of the major axis over the minor axis With these states, the required deformation of the compressible object is divided into two phases.
The overall required deformation may be divided between an expanded state and a compressed state. In particular, in FIG. The maximum in the elastic deformation of the object as it is expanding is dominated by strain localization associated with equatorial wall buckling, which is indicated by the depressed regions and The equatorial wall buckling instability is a collapse of the regions and due to the contraction of the equatorial belt associated with the inflation of the oblate spherical object In general it has been shown that the susceptibility of the compressible object to equatorial buckling increases as the initial aspect ratio of the compressible object increases, the internal pressure increases and the wall thickness decreases.
In this example, the expanded state may be an equilibrium state with the outside pressure of one atmosphere and where the compressible object has a spherical or near spherical shape i. The second phase may involve the compression of the object from the expanded state back to about the initial state during which the deformation due to the initial expansion is nearly fully recovered and a subsequent further compression to the fully compressed state, which may again be limited by the elastic strain of the wall material of the fully compressed object.
The compressed state may be, for example, an equilibrium compressed shape based on the hydrostatic compression exerted on the compressible object at a certain downhole depth. Accordingly, the compressible objects may be designed using these states to provide a suitable compression ratio that is beneficial for use within a wellbore. In the embodiments of FIGS.
Each of these FIGS. As shown in FIG. Compressible objects having different initial aspect ratios is discussed further in FIG. FEA modeling is utilized to generate the chart of the maximum strain versus compression ratio for different compressible objects having a wall thickness of 15 microns. The chart includes a first response curve for a spherical object, a second response curve of an elliptical object having a aspect ratio, a third response curve of an elliptical object having a aspect ratio, a fourth response curve of an elliptical object having a aspect ratio, which may be the elliptical object in FIGS.
As indicated by the response curves - , the maximum strain increases and decreases between the various states. For objects with an initial aspect ratio less than , the maximum linear elastic strain behavior for compression ratios less than is dominated by cap buckling instabilities described above. For compressible objects with an initial aspect ratio greater than , the maximum strain decreases from the expanded state to a minimum value at or close to the initial state, which is a global minimum for the strain on the compressible object.
Then, the maximum strain increases from the initial state until the fully compressed state is reached. As such, the maximum strain at the initial state of the compressible objects is near zero as indicated by the response curves - This aspect is clearly demonstrated by the fourth response curve Along the response curve , the expanded state is located at the point , the initial state is located at the point and the compressed state is located at the point Clearly, the initial state of the compressible object has the lowest strain in comparison to the expanded and compressed states.
In addition, this compressible object has a maximum strain of about 0. That is, the response curve indicates that the elliptical object having a initial aspect ratio is a suitable structure and wall thickness to provide the specified compression ratio of greater than with an internal pressure useful for the practice of the invention disclosed in International Patent Application Publication No.
Each of the other response curves - and exceed the maximum recoverable strain of 0. From this chart , the inflation and subsequent compression of the compressible object is bounded by an equatorial buckling instability during the inflation phase and the cap buckling instability described earlier during the compression phase.
By modeling the inflation and subsequent compression, the initial architecture of the compressible object may be designed to minimize the recoverable elongation for the specific compression ratio. As noted above, to be useful for the practice of Patent Application No. Based on the modeling methods discussed above, compressible objects may be designed of a certain material and having a specific architecture to provide specific compression ratios that are within the deformation limitations of existing materials.
With these compression ratios, the compressible objects may be useful for certain applications, such as drilling and production operations, which are described above. As an example, the compressible objects may be useful if they provide a recoverable compression ratio greater than or equal to five times the expanded state at a specific depth interval of interest. In particular for a deep-water application, the number of casing intervals may be reduced substantially below that achievable with dual gradient or multi-gradient systems without major modification of existing hardware or equipment.
Accordingly, the selection of the compressible objects and fabrication of the compressible objects is discussed further below in FIG. This flow chart, which is referred to by reference numeral , may be best understood by concurrently viewing FIGS.
In this flow chart , compressible objects and drilling fluid may be selected to formulate a variable density drilling mud for a well. Then, the variable density drilling mud may be utilized to enhance the drilling operations of the well. This process may enhance the drilling operations by providing a variable density drilling mud that extends the drilling operations to further limit or reduce the installation of additional casing strings.
Accordingly, drilling operations performed in the described manner may reduce inefficiencies from utilizing additional casing strings from drilling operations. The flow chart begins at block Then, compressible objects may be selected to provide specific volumetric changes, as shown in block The selection of compressible objects may include operational considerations, such as removal of the compressible objects from the drilling mud for re-circulation at the surface, limiting potentially detrimental effects of the high volume fraction of compressible objects on the rheology of the drilling mud and facilitating the flow of the compressible objects through the pumps and orifices in the flow path.
As such, the compressible objects may be sized to have an equivalent diameter between 0. The equivalent diameter is defined as the diameter of a sphere of equal volume as the fully expanded compressible object at atmospheric pressure. The selection of the compressible objects is further described in FIG.
At block , the drilling fluid may be selected. The drilling fluid, which may include various weighting agents, may be selected to provide a specific density that may interact with the compressible objects to maintain the drilling mud density between the FG and PPG, which is discussed further below. The compressible objects and the drilling fluid may be combined in block The combination of the compressible objects and the drilling fluid may involve mixing or blending the compressible objects with the drilling fluid, as described in International Patent Application No.
Further, the compressible objects and the drilling fluid may be combined prior to shipping to the drilling location or shipped individually with the compressible objects and the drilling fluid being combined at the drilling location. It should be noted that the compressible objects may be shipped in refrigerated vehicles, such as trucks and ships, to reduce risks associated with the release of internal pressure within the compressible objects.
At the drilling location, the compressible objects and the drilling fluid, which may be the variable density drilling mud FIG. Once the well is drilled, the hydrocarbons may be produced in block Then, the process ends at block In this flow chart , a process for selecting compressible objects to maintain the density of a drilling mud within the well between the PPG and FG is described. Beneficially, the use of compressible objects in the variable density drilling mud may enhance drilling operations by reducing the size of the wellbore and casing strings, and may provide access to greater depths.
Then, a structure for each of the compressible objects is selected, as shown in block The selection of the structure for the compressible objects may include using finite element analysis FEA methods to match structures and geometries of compressible objects to properties of the available materials, as described above.
At block , wall materials for the compressible objects are selected. The metal layer may be formed on the inside or outside surface of the compressible objects or incorporated within a polymer wall or polymer laminate of the same or different polymers. Surface treatments may be selected for the fabrication of the compressible objects in block Once selected, the compressible objects are fabricated in block The fabrication of the compressible objects may include various polymerizations, depositions, surface treatments and other fabrication processes used to form the wall structures of the compressible object.
The vacuum deposition methods may or may not include reducing the internal pressure inside the compressible object prior to deposition. This may be accomplished for example, by first reducing the internal pressure of the compressible hollow object by cooling the pressurized compressible hollow object preferably to a temperature below which the gas inside the compressible hollow object may condense.
At block , the compressible objects may be verified or tested. The verification and testing may include cyclic compression tests to verify the internal pressure and to quantify the fatigue life of the compressible objects with or without micro-structural analysis of the structural wall and the joints if any.
Then, the compressible objects may be stored, as shown in block The storage of the compressible objects may include placing the compressible objects in a storage vessel. The compressible objects may be stored at ambient pressure or at a pressure equal to or higher than the internal pressure of the compressible objects to facilitate packing of the compressible objects in the storage vessel.
Alternatively, the compressible objects may be stored in a cold environment to reduce the internal pressure inside the compressible objects. The cold compressible objects may then be stored in a vessel at ambient pressure or at elevated pressure to facilitate packing of the compressible objects in the storage vessel and shipping the compressible objects to another location, such as the drilling location, for storage or other similar activities.
The process ends at block Accordingly, based on the discussion above, the selection and use of these compressible objects may involve different aspects that affect the design of the compressible objects. For instance, the nature of the transition to gas compression controlled deformation is dependent on the mechanical properties of the shell or wall material and the evolution of those properties in repeated compression cycles.
As such, the compression of hollow objects results in a different gradient of mud density above and below the depth defined by the initial internal pressure of the hollow objects. Because the use of compressible objects having different initial internal pressures may be beneficial to enhance or extend drilling operations, changing the volume fraction and distribution of initial pressures of compressible objects may achieve the desired result of maintaining the effective mud weight between the PPG and FG.
Further, the use of different gases may also influence the design of the compressible objects. For instance, the hollow object may be filled with a mixture of condensable and non-condensable gases. The addition of a condensable gas allows additional flexibility in tailoring the variation of drilling mud density with depth. The decrease in internal volume of the hollow object results in a step increase in effective mud density at the depth and temperature corresponding to the phase transition.
An additional benefit of using a gas mixture containing a condensable gas is the finite internal volume occupied by the condensed gas at depths once it has condensed because the compressibility of the condensed liquid is generally lower than that of the non-condensable gas. As a result, the condensed liquid volume may be used to set an upper limit on the deformation experienced by the wall of the hollow object.
This may be utilized to control the fatigue life of the flexible objects as they cycle between the bottom of the wellbore and the surface. Moreover, the operational use may influence the design of the compressible objects. To create a usable variable density drilling mud, the initial properties of the fluid phase for a given compressible solid volume fraction is selected to suspend both the rock cuttings and the compressible objects in the wellbore annulus during non-circulating operations.
In addition, the viscosity of the composite mud has to be configured to be pumped within the wellbore by mud and rig pumps within acceptable limits. Also, the use of different sized compressible objects may further enhance the operational use. These aspects and others are discussed further below. To determine the architecture of the compressible objects, as noted in block of FIG. The finite element numerical model may be used to simulate the entire three dimensional object or a segment of the object related to the three dimensional object by symmetry.
Further, the architecture of the compressible objects may be influenced by various criteria, such as the materials and use of the compressible objects, which are discussed in this and other portions of the application. With regard to the use of the compressible objects, it should be noted that the architecture of the compressible objects may facilitate periodic removal of the compressible objects from the re-circulating drilling mud.
As such, the compressible objects may include structures having an equivalent diameter in the range of about 0. The equivalent diameter is again defined as the diameter of a sphere of equal volume as the fully expanded compressible object at an external pressure of one atmosphere. In addition, the shape of the compressible objects may be adjusted to increase the packing density and reduce effects on fluid flow. For instance, a spherical or elliptical object may provide the highest packing density and lowest effects on the fluid flow within the wellbore in comparison to pillow or rod shaped objects.
Another criterion for the architecture is the wall thickness. As noted above, the wall thickness should be as thin as possible within the constraints imposed by structural instabilities and the properties of existing materials to maximize the compression limit of the compressible object. However, the lower limit of the wall thickness is defined by the minimum thickness able to contain the desired internal gas pressure at an external pressure of about 1 atmosphere typically encountered at the surface of the Earth.
To determine the optimal geometry of the compressible objects, methods of finite element numerical modeling may be utilized. Finite element numerical modeling is well known to those skilled in the art. These methods may include modeling the walls as shell elements of the compressible objects or as a mesh object with variable mesh size and shape.
Further, the model may be used to simulate the entire three dimensional 3D compressible object, a segment of the compressible object, or a portion of the compressible object that may be related to the 3D compressible object structure by symmetry. In this model, an explicit method may be used to monitor for contact between the internal surfaces of the compressible objects during compression. To minimize oscillations during external pressure modifications, the external pressure may initially be set equal to the internal pressure.
Then, the external pressure may be slowly decreased down to ambient, which may be done over a period e. Depending on the flow behavior of the wall material and any occurrence of buckling, the amplitude and rate of external pressurization and depressurization may be adjusted to minimize oscillations. Once the finite element numerical model has been constructed, other analysis may be performed.
For instance, the compressible object may undergo a pressurization cycle test. In addition, if the numerical model is constructed using shell elements, sudden changes in mesh geometry should be avoided to reduce the potential for anomalies in local stress calculations. As a specific example, the finite element numerical model of the compressible object of FIGS.
In these embodiments, the compressible object has the shape of an oblate ellipsoid. The initial aspect ratio may be in the range of 1 to 10, with a more preferred aspect ratio being in the range of 2 to 5. The use of an internally pressurized oblate ellipsoid hollow compressible object with an initial aspect ratio greater than 1 has the advantage that at ambient external surface pressure, the ellipsoid object inflates and approaches an aspect ratio of about 1 depending on the internal pressure and material properties, as shown in FIG.
If the ellipsoid object has an initial aspect ratio of , a uniform NiTi alloy wall thickness of 10 microns and an internal pressure of psig, the aspect ratio in the expanded state is about 1. As the external pressure increases, the ellipsoid object tends to return to an initial state In the initial state , the aspect ratio of the ellipsoid object is that of the original design with little elastic strain, as shown in FIGS.
Then, as the pressure continues to increase, the ellipsoid object is compressed further into a compressed state , as shown in FIG. In addition to the architecture, various materials may be utilized for the wall of the compressible objects based on the criteria discussed above, as noted in block of FIG.
In particular, the shell or wall materials may be divided into two classes of commercially available materials, which are metal materials and polymer materials. The metal materials may include metals, metal alloys, and alloys with pseudo-elastic behavior e. Further, the super-plastic behavior of ultra thin i.
Specifically, the metal materials may include, but are not limited to, binary or near binary NiTi, ternary alloys of NiTi with iron and chromium alloying additions, MagnesiumCopper MgCu alloys, Beta-Titanium The polymeric materials may include polymers and polymer blends with or without reinforcement e. Examples of polymers with suitable properties include but are not limited to commercially available polyimide, such as Ubilex-R and Ubilex-S.
Because each of these materials has specific properties, such as tensile strength and recoverable elongation, the material utilized in the walls of the compressible objects is a factor in determining the thickness of the wall. The determination may be based upon finite element numerical modeling, as noted above, to evaluate different thicknesses of the shell or wall with different materials.
For instance, if the load bearing wall material is a metal or metal alloy, only metals and metal alloys with sufficiently high elastic or pseudo-elastic behavior should be selected because deformations associated with a reversible stress induced structural phase transformation have to be recoverable for reuse of the compressible objects.
As noted above, even these selected materials have to be combined with careful design of the geometry of the exterior shell of the compressible object to avoid strain localization during compression and re-expansion. Accordingly, these various factors are considered in selecting a material for the compressible objects.
As an example of the variation of wall thickness, the wall material may be utilized to influence the compression ratios of the compressible object, such as the elliptical object discussed above in FIGS. The FEA calculations may provide compressible objects having an aspect ratio between 2 to 5, with an equivalent-diameter-to-wall-thickness ratio between 20 and , or more preferably between 50 and For sphere-shaped compressible objects, curve has a compression ratio of 3.
For the ellipse shaped compressible objects, curve has a compression ratio between 3. It is clear from the chart that compressible objects having an aspect ratio greater than unity with a thinner wall i. Also, it may be preferable to maintain the maximum strain below a specific value, of about 0.
Typically, a minimum fatigue life of at least to cycles is desirable. Based on this limitation, an ellipsoid object with an aspect ratio at 2 or more and equivalent-diameter-to-wall-thickness ratio greater than 65 provides a compressible object that is below the specific value, as shown on curve In addition to being a single material, the walls of the compressible objects may include two or more layers.
For instance, the layered composite shell may include a load bearing structural layer or wall and a gas permeation barrier wall or layer. The load bearing wall may be a relatively thick wall having a thickness in the range of 1 micron to 50 microns and a gas barrier wall may be a thin wall having a thickness in the range of less than or equal to 5 microns. For example, the load bearing polymer wall, which may have a hollow interior or be deposited on a polymer foam template, may be utilized to provide the structure of the compressible object.
The gas barrier wall, which may be internal or external to the load bearing wall may be a metal or metal alloy permeation barrier layer that contains the internal pressure and has a thickness below Angstrom. Alternatively, the compressible objects may have a thin i. Selection of Surface Treatments for Compressible Objects. As discussed in block of FIG. Accordingly, the surface treatments may be utilized to enhance specific properties, such as compatibility with the base fluid and the permeability of the shell layers to maintain the internal pressure, which is discussed further below.
Accordingly, in addition to the incorporation of exfoliated inorganic fillers in the polymer wall, the deposition of a continuous, thin i. In particular, the deposition coating may be less than A in thickness and include Al, NiTi, or any other suitable material.
One of the factors that may influence the selection of deposition method is the internal pressure of the compressible object. For instance, if little or no initial internal gas pressure is contained within the compressible objects, then a low permeability metal, metal alloy or inorganic coating may be utilized through various low pressure physical and chemical deposition methods to uniformly coat the non-planar geometry of the compressible objects.
If the compressible object's internal pressure and the wall permeability is such that the low pressure environment i. In this example, the compressible objects may be maintained in a high pressure gas or liquid environment to prevent loss of internal pressure through the wall of the compressible object during storage and coating.
For a high pressure liquid environment, the coating of the wall surface may be accomplished, for example, by electro or electro-less plating using methods familiar to those skilled in the art. For the high pressure gas environment, the coating of the wall surface may be accomplished by, for example, chemical vapor deposition CVD or ultraviolet chemical vapor deposition UV-CVD deposition.
Alternatively, the internal gas pressure inside the compressible objects may be reduced to a level that allows application of a range of commercial low pressure physical and chemical deposition methods available for an un-pressurized object or polymer sheet. In this example, a gas, which may be condensed by lowering the temperature of the compressible object, may be utilized for the internal pressurization of the compressible object. The metal or metal alloy load bearing wall in this example may have a thickness from about 5 microns to 50 microns.
These fabrication techniques may include various processes, such as patterning, deposition, thermo-mechanical processing and other similar fabrication processes. The patterning processes, which are processes that shape material into another form, such as compressible objects, may include chemical etching, mechanical etching and the like. The etching processes are processes that remove material from a base material. The thermo-mechanical processes, which are processes that form or change a materials shape and microstructure, may include cold rolling, hot rolling, swaging, drawing, cutting, tempering, solution annealing and the like.
The fabrication of compressible objects may use various techniques that are combined to provide desirable properties of the compressible objects, as described above. The fabrication route of the compressible objects may be determined based on certain desirable properties of the compressible objects.
Accordingly, the fabrication processes may be configured to create compressible objects that are gas filled polymer objects including internal structures being either hollow or at least partially filled with foam. For instance, FIGS. Similarly, FIGS. Fabrication of Compressible Objects as Hollow Objects. The fabrication processes described below relate to the fabrication of compressible objects that are formed as hollow objects, which may or may not be gas filled.
While a variety of fabrication processes are described, FIGS. In this embodiment , compressible objects, such as hollow polymer shells or polymer foam structures, may be fabricated in a pressurized environment formed by a pressurized chamber For exemplary purposes, the compressible objects are shown as hollow polymer shells with a gas interior , but may include polymer foam structures and other compressible objects discussed above.
In this fabrication process example, a coaxial bubble blowing orifice at the end of the center tube is enclosed in a coaxial tube in a pressurized chamber Sufficient differential pressure is independently applied within the annulus formed between the center tube and the coaxial tube and within the center tube of the orifice to shape the polymer material into hollow polymer shells that are filled with gas from the center tube In this manner, a gas filled polymer bubble is formed and subsequently detaches from the coaxial bubble blowing orifice The pressurized chamber may be filled with gas or liquid or a combination thereof and the separation in the case of bubble formation may be caused by surface tension, gravity, buoyancy, fluid flow or any combination thereof.
Once the polymer bubble detaches, the polymer bubble may be dropped into a crosslinking bath within a bath vessel that promotes crosslinking of the polymer wall. The chemical nature of the crosslinking bath may be determined by the specific polymer chosen for the wall material and well known to those skilled in the art of polymer synthesis. Following the hardening bath, the hollow polymer shells with a gas interior is formed and may then be removed by transfer to a pressure interlock chamber not shown where the crosslinking fluid is separated from the pressurized compressible objects and the compressible objects are transferred to a container for storage.
This expanded state may be predetermined by wall thickness, material mechanical properties, object architecture and internal pressure before, during or after cooling of the walls. If the polymer wall is the load bearing member, expansion of the diameter following synthesis may be used to alter the mechanical properties of the polymer wall. Specific adjustments may be incorporated for the fabrication process based on the materials utilized.
For instance, if the polymer material is a polymer melt with or without reinforcement, the orifice may be heated to reduce the melt viscosity to achieve the desired flow properties of the polymer melt. Also, if the polymer material is a polymer monomer or a mixture of monomers with or without reinforcement and with or without an initiator, the polymerization of the walls of the polymer bubble after separation from the orifice may be accomplished by a variety of processes, such as ultra violet polymerization, free radical polymerization, thermo-chemical polymerization, etc.
In this embodiment , compressible objects, such as hollow polymer shells or polymer foam structures, may be fabricated in a pressurized environment formed in a pressurized chamber The pressurized chamber is divided into a lower chamber having a gas inlet and an upper chamber having a fluid inlet and a fluid outlet In this fabrication process example, a thin film of a suitable polymer melt or polymer precursor may be formed on a plate perforated by a large number of orifices or holes The size and spacing of the holes may be arranged to cause the continuous formation of gas filled bubbles , which have a hollow polymer shell with a gas interior , that separate and float off the plate and into a pressurized fluid filling the upper chamber when the plate is pressurized from below at a desired differential pressure between the upper and lower chambers and The gas filled bubbles may exit the upper chamber through the fluid outlet and may be separated from the fluid by density difference and subsequently transferred to a container for storage.
In this fabrication process, compressible objects are formed from a tube material by cutting the tube material into desired lengths and closing the ends of the tube material using mechanical, chemical or thermal methods. The internal pressure of the resulting compressible objects, which may be formed in the shape of a pillow, sphere, oblate spheroid, ellipsoid of revolution or any other desirable shape may be controlled by closing the cut ends of the tube and forming the desired shape in a controlled pressure environment.
The pressurized environment may be a pressurized chamber, which is similar to the pressurized chambers discussed above. As another alternative example method for creating compressible objects, preformed sheets may be utilized to form the compressible objects. In this method, mechanical, thermal or chemical joining of preformed sheets may be utilized to fabricate compressible objects. The preformed sheets may include a layered composite structure, which may include two embodiments.
In particular, the structural load bearing polymer wall may have a wall thickness between about 5 micron and 50 microns, while the continuous metal or metal alloy permeation barrier layer may have a wall thickness that is less than about Angstrom.
The second embodiment being a thin polymer sheet as a template for the deposition of a relatively thick metal or metal alloy layer that serves as both a structural wall and a barrier to gas permeation. For instance, the thin polymer sheet may be less than about 5 micron, while the metal or metal alloy layer may have a wall thickness between about 5 micron and 50 microns.
Any combination of layered or multiply layered embodiments with polymer thickness and metal or metal alloy thickness within these limits may be utilized for other embodiments. Examples include metalized polymer sheet for food packaging, metalized Mylar sheet for party balloons, decorative metal coatings on polymers films and metalized polyimide film for aerospace thermal barriers.
If the pre-formed object components are to be joined to form the compressible objects, the joining of the preformed object components may be accomplished by a variety of methods familiar to those practiced in the art of polymer film joining. Examples include but are not limited to, thermal bonding, adhesive bonding, mechanical joining and the like. The coated polymer wall may then be thermo-mechanically molded into the pre-form to have the metal or metal alloy layer on the interior surface, the exterior surface or both.
As an additional fabrication technique, the method of composite sheet fabrication outlined above may also be used to fabricate free standing relatively thick metal and metal alloy sheet suitable for mechanical forming into the components of compressible or collapsible objects or particles.
This approach to the fabrication of free standing metal or metal alloy sheet is particularly useful when thin metallic sheet is difficult to fabricate by conventional thermo-mechanical methods used in the fabrication of metal sheet. Bias mediated DNA denaturation. Big Data Analytics. Bilayer Graphene FET. Bilayer QD Stacks. Bio integrated electronics. Biobased Chemicals; chemical and energy; biotechnology; biofuel. Biochemical Systems. Bioelectrical Impedance Analysis. Bioinorganic Chemistry.
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Physical vapor deposition process is also used in laboratories. This metal alloy is denoted by the symbols of its constituent metals. The formula for this alloy is NiTi. This material derived its name from its constituents and its place of discovery. In , William J. Buehler and Frederick Wang first discovered the unique properties of this metal at the Naval Ordnance Laboratory.
Commercialization of this alloy was not possible until a decade later. This delay was mainly caused by the difficulty of melting, machining and processing the material. The shape memory and superelasticity properties are the most unique properties of this alloy. It happens due to the different crystal structures of nickel and titanium.
This pseudo-elastic metal also shows incredible elasticity which is approximately 10 to 30 times more than that of any ordinary metal. Resistivity: It has a resistivity of 82 ohm-cm in higher temperatures and 76 ohm-cm in lower temperatures. Magnetic Susceptibility: Its magnetic susceptibility is 3. Ultimate Tensile Strength: The ultimate tensile strength of this material ranges between and MPa.
Hot working of this material is relatively easy than cold working. The enormous elasticity of this material makes cold working difficult by increasing roll contact. This results in extreme tool wear and frictional resistance. These reasons also make machining of this alloy extremely difficult. The fact that this material has poor thermal conductivity does not help in this purpose.
Heat treatment of this material is very critical and delicate. The heat treatment-cold working combination is important for controlling the useful properties of this metal. Nitinol is used for making shape-memory actuator wire used for numerous industrial purposes. This wire is used for guidewires, stylets and orthodontic files. This wire is ideal for applications requiring high loading and unloading plateau-stresses as well as for eyeglass frames and cell phone antennas.
However, the main uses of this wire are in stents and stone retrieval baskets. This alloy is used for manufacturing endovascular stents which are highly useful in treating various heart diseases. It is used to improve blood flow by inserting a collapsed Nickel titanium stent into a vein and heating it. These stents are also used as a substitute for sutures.
Nickel titanium wire baskets are well-suited for many medical applications as it is springier and less collapsible than many other metals. This basket instrument is highly useful for the gallbladder. Nickel titanium is available in various forms including wires, tubes, sheets and springs. NDC is one of the leading manufacturer and supplier of this metal alloy. However, there are many other suppliers of Nitinol wires, tubes, springs etc.
Different forms of this metal are also available online at reasonable prices. Nitinol is counted among the most useful metal alloys with numerous industrial and medical applications. It is often the best choice for many applications that require enormous motion and flexibility.
Nitinol is half nickel, and thus there has been a great deal of concern in the medical industry regarding the release of nickel, a known allergen and possible carcinogen. It has been repeatedly shown that nitinol releases nickel at a slower pace than stainless steel, for example. With that said, very early medical devices were made without electropolishing, and corrosion was observed.
There are constant and long-running discussions [ by whom? As in all other metals and alloys, inclusions can be found in Nitinol. The size, distribution and type of inclusions can be controlled to some extent. Theoretically, smaller, rounder and few inclusions should lead to increased fatigue durability. In literature, some early works report to have failed to show measurable differences,   while novel studies demonstrate a dependence of fatigue resistance on the typical inclusion size in an alloy.
Nitinol is difficult to weld, both to itself and other materials. Laser welding nitinol to itself is a relatively routine process. More recently, strong joints between NiTi wires and stainless steel wires have been made using nickel filler. More research is ongoing into other processes and other metals to which nitinol can be welded.
Actuation frequency of nitinol is dependent on heat management, especially during the cooling phase. Numerous methods are used to increase the cooling performance, such as forced air,  flowing liquids,  thermoelectric modules i. Peltier or semiconductor heat pumps ,  heat sinks,  conductive materials  and higher surface-to-volume ratio  improvements up to 3.
The fastest nitinol actuation recorded was carried by a high voltage capacitor discharge which heated an SMA wire in a manner of microseconds, and resulted in a complete phase transformation and high velocities in a few milliseconds. Recent advances have shown that processing of nitinol can expand thermomechanical capabilities, allowing for multiple shape memories to be embedded within a monolithic structure.
A process of making parts and forms of Type 60 Nitinol having a shape memory effect, comprising: selecting a Type 60 Nitinol. Washington State. From Wikipedia, the free encyclopedia. High-durability alloy. A nitinol paperclip bent and recovered after being placed in hot water.
Main article: Nitinol biocompatibility. Journal of Applied Physics. Bibcode : JAP The Chemical Educator. S2CID Chemistry World. Royal Society of Chemistry. Retrieved 29 January Journal of the American Chemical Society. Progress in Materials Science.
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At high temperatures, nitinol assumes an interpenetrating simple cubic structure referred to as austenite (also known as the parent phase). At. Nitinol Medical Devices Market to Grow at a CAGR of % to reach US$ Million from to According to The Insight Partners latest study on. "Nickel titanium, also known as nitinol, is a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages.