The disclosure generally relates to downhole equipment in wells. Specifically, the disclosure relates to equipment for centralizing tubing inserted into wellbores, including oil and gas wells, geothermal wells, and other wells.
To properly position the casing within the middle of the wellbore, centralizers are placed at intervals along the length of the casing. Among the various types of centralizers, one type is referred to as a “bow-spring centralizer.” The bow-spring centralizer generally has a pair of collars that surround the casing diameter and a plurality of bows or ribs that bow outwardly in a resting state. The casing with the centralizer can be inserted into the well bore or a larger casing to form the annulus therebetween. The centralizer is inserted into the annulus with a starting force that compresses the bows around the casing radially inward and biases the casing toward a central portion of the well bore or larger casing. As the casing continues downward in the compressed state with a running force, the bows are biased to expand radially within the constraints of the annulus. Importantly, the bows need to be able to expand radially outward with sufficient restoring force into a larger space after passing through the annulus to maintain the centralized alignment of the casing in the larger space.
Historically, such a performance has been difficult due to a combination of factors, such as strength, available thickness of the annulus, and compressibility of the bow while balancing with sufficient restoring force, sometimes high heat temperatures, and other factors.
The need for a thinner bow-spring centralizer has arisen from the operators seeking improved efficiencies in production for deeper wells and specifying casing sizes that have tighter fits, by closing the annular spacing currently down to one-quarter inch (¼″) (6.4 mm) radially, that is, down to one-half inch (½″) (12.7 mm) on the diameter. Casing roundness and size tolerances are available to allow this. This trend has resulted in a need for a slim designed bow spring centralizer for use in casing centralization particularly in deep water applications throughout the world, including the Gulf of Mexico (GOM). The tighter annulus is likely to press the current bow-spring centralizers beyond their capabilities. Current bow-spring centralizers are typically made from ASTM 4130 steel, with the bows of the centralizer being nominally 0.167″ thick. These existing centralizers are too tight for the above current standards and may get stuck. Even if the centralizers do not stick, the tighter annulus does not provide current centralizers with sufficient radial distance to compress and then expand with sufficient restoring force. The material can be made thinner to allow more radial compression and expansion, but current centralizer materials lack the desired restoring force to help maintain the centrality of the casing within the well bore or other casing to meet industry standards. Current centralizers present a risk that many operators are not willing to take.
A current option being used to comply with the requirements of a tighter annulus is a fully machined integral blade stabilizer/centralizer, or hybrid tool. The integral blade stabilizer resembles a short tube with solid lugs extending radially outward longitudinally down the tube. The hybrid tool can be described as a close tolerance machined bow-spring centralizer with a short tube that has been machined to a reduced diameter in the center and a bow-spring fabricated into the reduced diameter machined space. The reduced diameter effectively increases the thickness of the annulus between the casing and the reduced diameter, so the bow-spring can flex in a customary manner. The typical current cost of these machined parts ranges from $8,000-20,000 each. Several units are needed per casing run.
Further, many of these wells encounter high pressure and/or high temperature (“HPHT”) conditions of up to 450 F, and the ASTM 4130 steel weakens rapidly with temperature.
The tighter annulus and the HTHP conditions, especially in deeper wells, has created a need for an improved centralizer that can accommodate these conditions. The need includes the ability to overcome the required thickness reduction to fit within the tighter annulus, to be able to operate at increased temperatures of deeper well that is generally greater than 200 F and averages 400 F, to provide a sufficiently strong and resilient bow at the reduced thickness that can spring back radially after passing through the tighter annulus and sufficiently centralize the casing in the wellbore.
The present disclosure provides a bow-spring centralizer by using thinner bows of advanced alloys and thermal conditioning that can reduce the thickness of the bows compared to traditional bows, and yet provide sufficient restoring force after compression in a tight annulus with little radial thickness. The present disclosure also provides a specially shaped centralizer bow with cross sections that can reduce running force, increase stiffness and strength, and/or still maintain a sufficient restoring force.
The present disclosure provides a bow-spring centralizer comprising a first and second collar and a plurality of bows disposed between the collars, the bows being formed of precipitation hardening metal. The precipitation hardening metal may comprise at least one of a precipitation hardening stainless steel and a precipitation hardening nickel alloy. The plurality of bows may be sized between 0.030 inches (0.8 mm) to 0.130 inches (3.3 mm) thick. The ultimate tensile strength at room temperature of at least one of the plurality of bows may exceed 100 KSI (690 MPa). The plurality of bows may be shaped longitudinally asymmetrical or symmetrical.
At least one of the plurality of bows may be formed with a longitudinal flat portion. The flat portion may be disposed along the bow length symmetrically or asymmetrically relative to the collars. A transverse cross section of the bow may be curved along all or just part of the bow, including along a flat portion of the bow. At least a portion of at least one of the plurality of bows may be formed with longitudinal peaks and valleys, and may include both faces of the bow or just one face of the bow. The centralizer may also comprise dimples formed in at least one of the plurality of bows. The centralizer may also include a protrusion extending longitudinally from at least one end of the centralizer.
The present disclosure also provides a method of manufacturing a bow-spring centralizer, comprising forming at least a portion of the centralizer from precipitation hardening steel and heat treating at least the portion of the centralizer by precipitation hardening. The method may further comprise forming a protrusion extending longitudinally on at least one end of the centralizer. The method may further comprise forming a plurality of bows from the precipitation hardening steel. The method may comprise performing the heat treating step after the centralizer is formed.
The method of manufacturing may further comprise cutting one or more centralizer elements in a sheet of precipitation hardening steel, forming a plurality of bows in a longitudinally curved shape from the one or more centralizer elements, and forming the centralizer with the one or more plurality of bows. The one or more centralizer elements may comprise a plurality of collars and a plurality of bows. The method may further comprise forming the one or more plurality of bows into a transversely curved structure.
The Figures described above and the written description of specific structures and functions below are not presented to limit the scope of what Applicants have invented or the scope of the appended claims. Rather, the Figures and written description are provided to teach any person skilled in the art to make and use the inventions for which patent protection is sought. Those skilled in the art will appreciate that not all features of a commercial embodiment of the inventions are described or shown for the sake of clarity and understanding. Persons of skill in this art will also appreciate that the development of an actual commercial embodiment incorporating aspects of the present disclosure will require numerous implementation-specific decisions to achieve the developer's ultimate goal for the commercial embodiment. Such implementation-specific decisions may include, and likely are not limited to, compliance with system-related, business-related, government-related, and other constraints, which may vary by specific implementation, location, and from time to time. While a developer's efforts might be complex and time-consuming in an absolute sense, such efforts would be, nevertheless, a routine undertaking for those of ordinary skill in this art having benefit of this disclosure. It must be understood that the inventions disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. The use of a singular term, such as, but not limited to, “a,” is not intended as limiting of the number of items. Also, the use of relational terms, such as, but not limited to, “top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,” “side,” and the like are used in the written description for clarity in specific reference to the Figures and are not intended to limit the scope of the invention or the appended claims. Where appropriate, one or more numbered elements may have been labeled with an letter, such as “A” or “B,” (or if lettered elements, then with numbers, such as “1” or “2”) to designate various members of a given class of an element. When referring generally to such elements, the number without the letter can be used. Further, such designations do not limit the number of members that can be used for that function. The various methods and embodiments of the system can be included in combination with each other to produce variations of the disclosed methods and embodiments. Discussion of singular elements can include plural elements and vice-versa. References to at least one item may include one or more items. Also, various aspects of the embodiments could be used in conjunction with each other to accomplish the understood goals of the disclosure. Unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising,” should be understood to imply the inclusion of at least the stated element or step or group of elements or steps or equivalents thereof, and not the exclusion of a greater numerical quantity or any other element or step or group of elements or steps or equivalents thereof. The device or system may be used in a number of directions and orientations. The term “coupled,” “coupling,” “coupler,” and like terms are used broadly herein and may include any method or device for securing, binding, bonding, fastening, attaching, joining, inserting therein, forming thereon or therein, communicating, or otherwise associating, for example, mechanically, magnetically, electrically, chemically, operably, directly or indirectly with intermediate elements, one or more pieces of members together and may further include without limitation integrally forming one functional member with another in a unity fashion. The coupling may occur in any direction, including rotationally.
The present disclosure provides a bow-spring centralizer by using thinner bows of advanced alloys and thermal conditioning that can reduce the thickness of the bows compared to traditional bows, and yet provide sufficient restoring force after compression in a tight annulus with little radial thickness. The present disclosure also provides a specially shaped centralizer bow with cross sections that can reduce running force, increase stiffness and strength, and/or still maintain a sufficient restoring force.
The bows 24A can be formed longitudinally symmetrical, so that the bow curves symmetrically from a longitudinal midpoint 40 on the bow toward each of the collars 20, 22 as measured from a centerline 38 of the centralizer. An example of a symmetrical bow is illustrated as the bow on the centralizer in
In these exemplary bows and others that are contemplated or feasible, the shape of the bow can be optimized for starting and running forces, and these and other shapes are contemplated or possible.
As referenced above, a typical thickness of a prior art bow is 0.167″ of ASTM 4130 that is needed for sufficient restoring force with prior designs in the field. Yet, this thickness has almost no ability to significantly compress and then expand to a significant amount when inserted in a tighter annulus, for example, of 0.25″ annulus thickness. By contrast, in at least one non-limiting example, the thickness B of the present disclosure can be ⅓ to about ⅔ of the above typical thickness, that is, for example, about 0.03 inches (0.8 mm) to about 0.13 inches (3.3 mm). The thinner cross section of the material disclosed herein allows for a variety of shapes that normally would not be suitable due to the required greater thickness of traditional material in a given annulus.
Further variations can include forming the peaks and valleys along a longitudinal portion of the bow. For example, the longitudinal portion having the peaks and valleys could be the portion that initially enters the annulus, which can assist with reducing a starting force and/or running force for the bow to be compressed as it enters into and/or travels through the annulus.
In the present disclosure, the centralizer collars 10, 18 can be substantially thinner than a typical centralizer as described herein and meet the requirements of a centralizer within the limited annular clearances between the wellbore and the casing. Further, the stop collars are required to be correspondingly thinner than a typical stop collar as well due to the same limited annular clearances. To assist the thinner centralizer abutting a corresponding thinner stop collar from becoming dislodged from the intended position by radially expanding over the stop collar, an end 56 of the centralizer collar (see
While various methods exists for manufacturing the bow-spring centralizers, an exemplary non-limiting method could include cutting the material through waterjetor laser cutting, forming the centralizer shape, welding portions together such as the cylindrical ends, inert atmosphere heat treating including a vacuum atmosphere, and low temperature thermal treatments as a type of further heat treating. In other embodiments, the collars can be formed separately from the bows and the components welded together, and heat treated. The shapes and variations described herein and others that are in keeping with the underlying principles disclosed herein can be optimized using modeling and simulations using computational fluid dynamics, finite element analysis, thermal analysis and applying computer aided engineering integration of different meshers, solvers, and other codes as appropriate for design capability, performance, and reliability. Exemplary factors could include optimizing contact pressure between two curved surfaces that depends on that type and radius of curvature, magnitude of contact force, elastic modulus, and Poisson's ratio of contact surfaces, among others.
From the hundreds of possible metals, the inventors have realized that the material for the centralizer can advantageously be a precipitation-hardening, corrosion-resistant steel. This type of material differs from customary materials used in the oil field service industry that typically rely on ASTM 4130 (or other similar materials, such as ASTM 4140, 4340). Expectations in the oil field industry would teach away from precipitation-hardening steels due to the perception that many such steels are subject to stress corrosion cracking under oil field conditions. Contrary to such expectations, the inventors utilize a thermal conditioning procedure that allows such steels to harden into a high strength steel to allow a relatively thin centralizer bow yet reduce the stress corrosion cracking tendency. These steels have ultimate tensile strengths at room temperature that exceed 100 KSI (690 MPa), many exceed 140 KSI (965 MPa), and various levels therebetween, and some are higher. Further, these steels have higher temperature resistance to loss of strength compared to the customary ASTM 4130 steel and similar steels.
The selected materials can withstand the higher stress and the higher temperatures that current designs are not in general able to meet performance criteria. Precipitation hardening stainless steels and their desired upper operating temperatures include, but are not limited to, 15-5PH (600 F), 17-4PH (600 F), 17-7PH (500 F), 15-7MoPH (900 F). Precipitation hardening nickel alloys and their desired operating temperatures include, but are not limited to, alloy 718 (1300 F+) and alloy750 (1300 F+), and other precipation hardening nickel alloys.
Further, the embodiments of
One example of a suitable precipitation-hardening metal is 17-7PH stainless steel. Exemplary specifications for this precipitation hardening steel shows a composition of the following with all numerical values given in weight percent with the balance being iron with trace percentages of other elements:
Chromium 16.00-18.00
Nickel 6.50-7.75
Aluminum 0.75-1.50
Carbon 0.09 max.
Manganese 1.00 max.
Phosphorus 0.040 max.
Sulfur 0.030 max.
Silicon 1.00 max.
Another example of a suitable precipitation-hardening steel is alloy 718. Exemplary specifications for this precipitation hardening steel shows composition of the following with all numerical values given in weight percent with the balance being iron with trace percentages of other elements:
Chromium 17.00-21.00
Nickel (plus Cobalt) 50.00-55.00
Niobium (plus Tantalum) 4.75-5.50
Molybdenum 2.80-3.30
Titanium 0.65-1.15
Aluminum 0.20-0.80
Cobalt 1.00 max.
Carbon 0.08 max.
Manganese 0.35 max.
Phosphorus 0.015 max.
Sulfur 0.015 max.
Silicon 0.35 max.
Boron 0.006 max.
Copper 0.30 max.
A further example of a suitable precipitation hardening material is 15-7MoPH stainless steel with molybdenum. Specifications for the material list a composition of the following with all numerical values given in weight percent with the balance being iron with trace percentages of other elements:
Chromium 14.00-16.00
Nickel 6.50-7.75
Molybdenum 2.00-3.00
Aluminum 0.75-1.50
Carbon 0.09 max.
Manganese 1.00 max.
Phosphorus 0.040 max.
Sulfur 0.040 max.
Silicon 1.00 max.
Some precipitation hardening metals, but not all, are subject to hydrogen embrittlement with extended exposure to environmental conditions, including salt water. The general operational requirement of a centralizer is to be sufficiently strong for one pass downhole before the annulus is cemented for permanency. Thus, in such instances where the particular precipitation hardening metal might be susceptible to embrittlement, a simple coating can be applied, including paint, or tape that can be easily removed if desired, and other protective coatings for a temporary period before use.
The above materials can be heat treated for precipitation hardening, which can vary depending on the particular participation hardening steel used and the performance results desired. Below are representative heat treatment processes that are believed to be suitable for the desired use described herein and other heat treatments can be found in the relevant art.
For the 17-7PH stainless steel, the metal is generally purchased in an annealed state (or can be annealed subsequent to the purchase). An exemplary annealing process includes heating the metal to a temperature of 1950 F+/−25 F (1066 C+/−14 C). Optionally, fabrication can be performed in this condition. The subsequent heat treatment to develop the strength and hardness includes three overall steps: austenite conditioning, cooling to transform the austenite to martensite, and precipitation hardening. For austenite conditioning, the steps can include heating to 1750 F+/−15 F (954 C+/−8 C), holding for 10 minutes, and air cooling to room temperature. For cooling to transform the austenite to martensite, the steps can include within an hour of the air cooling to room temperature starting to cool to −100 F+/−10 F (−73 C+/−5.5 C), holding for eight hours, and then air warming to room temperature. For precipitation hardening, the steps include heating to 950 F+/−10 F (510 C+/−5.5 C), holding for one hour, then air cooling to room temperature. This process develops a high strength participation-hardened metal of about 230 KSI ultimate tensile strength (UTS), 201 KSI yield strength (YS), with elongation of approximately 7% at room temperature. Each of the above steps can be varied to produce different results with the metal.
For alloy718, the metal is generally heat treated by solution annealing and precipitation hardening (age hardening). An exemplary heat treatment process includes solution annealing at a temperature between 1700-1950 F followed by rapid cooling, usually in water, plus precipitation hardening between 1325-1450 F for six to ten hours, and sometimes followed by a lower aging temperature of 1200 F for several more hours. Within these general parameters, three exemplary variations are as follows. One variation is solution annealing at 1700-1850 F, followed by rapid cooling, usually in water, plus precipitation hardening at 1325 F for eight hours, furnace cooling to 1150 F, holding at 1150 F for a total aging time of 18 hours, followed by air cooling. The UTS is about 180 KSI, the YS is about 150 KSI, and elongation is about 12% at room temperature. A second variation is solution annealing at 1900-1950 F, followed by rapid cooling, plus precipitation hardening at 1400 F for ten hours, furnace cooling to 1200 F, holding at 1200 F for total aging time of 20 hours, followed by air cooling. The UTS is about 180 KSI, the YS is about 150 KSI, and elongation is about 15% at room temperature. A third variation is solution annealing at 1850-1900 F, rapid cooling, and aging at 1450 F for six to eight hours, and then air cooling. The UTS is about 150 KSI, the YS is about 140 KSI, and elongation is about 20% at room temperature. Each of the above steps can be varied to produce different results with the material.
For the 15-7PH stainless steel with molybdenum, the metal is generally purchased in an annealed state or can be annealed subsequent to the purchase. An exemplary annealing process includes heating the metal to a temperature of 1950 F+/−25 F (1066 C+/−14 C). Optionally, fabrication can be performed in this condition. The subsequent heat treatment to develop the strength and hardness includes three overall steps: austenite conditioning, cooling to transform the austenite to martensite, and precipitation hardening. For austenite conditioning, the steps can include heating to 1750 F+/−15 F (954 C+/−8 C), holding for 10 minutes, and air cooling to room temperature. For cooling to transform the austenite to martensite, the steps can include within an hour of the air cooling to room temperature starting to cool to −100 F+/−10 F (−73 C+/−5.5 C), holding for eight hours, and then air warming to room temperature. For precipitation hardening, the steps include heating to 950 F+/−10 F (510 C+/−5.5 C), holding for one hour, then air cooling to room temperature. This process develops a high strength participation-hardened metal of about 240 KSI ultimate tensile strength (UTS), 225 KSI yield strength (YS), with an elongation of approximately 6% at room temperature. Each of the above steps can be varied to produce different results with the material.
Specimens of the typical ASTM 4130 material used for centralizers were cut from a commercially manufactured bow spring centralizer. The exemplary centralizer bows are about 21 inches long when flat (that is, not bowed in an arc), about 1.5 inches wide, and about 0.167 inches thick. Two other sets of bow springs were prepared of 17-7PH stainless steel and alloy 718 of about the same dimensions but only about 0.092 inches thick so that these bow springs could fit within a tighter annulus with less radial thickness that is desired for current drilling needs.
For the 17-7PH stainless steel, the heat treat of an annealed bar after being formed in an equivalent shaped bow-spring as the ASTM 4130 bow was austenite conditioning at 1735-1765 F for 10 minutes in a vacuum atmosphere, then cooling to −100 F+/−10 F for eight hours an air atmosphere, then precipitation hardening at 950 F+/−10 F for one hour in a vacuum atmosphere.
For the alloy 718, the heat treat of an annealed bar after being formed in an equivalent shaped bow-spring as the ASTM 4130 bow was solution annealing at a temperature between 1725-1825 F in a vacuum atmosphere, followed by rapid cooling plus precipitation hardening at 1325 F+/−15 F for 495 minutes+/−15 minutes in a vacuum atmosphere, and then holding at 1150 F+/−15 F for another 480 minutes for a total of about 16 to 16.5 hours.
The bows were each measured to determine the maximum height of the arc in the bow in an uncompressed state when its ends were resting on a horizontal surface. Each bow was then subjected to a sufficient load on the arc to push the bow substantially flat on the horizontal surface, held momentarily, and then the load was released to simulate the bow passing through a tight annulus between a casing and pipe and then springing back to reform an arc after passing through the annulus. The resulting height after the flattening was then measured to determine the resulting permanent deformation by the difference in heights and percentage of change as a spring back percentage.
The results are shown in the below table:
The results show that even with thinner material in the precipitation hardening steels of the two exemplary materials, the spring back percentage was advantageously far greater than the typical ASTM 4130 material. The thickness can be reduced by at least 30% and more, thereby allowing the fabrication of the thinner bow springs that can meet the application requirements. The spring back percentages were advantageously even more noticeable at the higher tested temperatures.
The order of steps can occur in a variety of sequences unless otherwise specifically limited. The various steps described herein can be combined with other steps, interlineated with the stated steps, and/or split into multiple steps. Similarly, elements have been described functionally and can be embodied as separate components or can be combined into components having multiple functions.
The invention has been described in the context of preferred and other embodiments and not every embodiment of the invention has been described. For example, other sizes could be similarly designed with the resulting differences in flow volumes described above. Obvious modifications and alterations to the described embodiments are available to those with ordinary skill in the art given the teachings disclosed herein. In conformity with the patent laws, the claims determine the scope or range of equivalents, rather than the disclosed exemplary embodiments, with the understanding that other embodiments within the scope of such claims exist.
This application claims priority to U.S. provisional patent application No. 62/319,386, filed on Apr. 7, 2016, the entire content of which is incorporated herein by reference.
Number | Date | Country | |
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62319386 | Apr 2016 | US |