Patent Grant
12000237
The present application is a national stage entry of International (PCT) Patent Application Number PCT/GB2019/051755, filed Jun. 21, 2019, which in turn claims priority to Patent Application No. GB 1810418.2, filed Jun. 25, 2018, the subject matter of which are expressly incorporated herein by reference.
The present invention relates to a well sealing material, a plug made from the material and a method of producing a plug. More particularly, the present invention relates to bismuth-based alloys and the use of plugs made from such alloys to seal wells as well as the plugs themselves.
In the oil and gas extraction industries, abandoned wells have to be plugged to keep the contents of deep high pressure environments which communicate with those wells from invading levels at or adjacent the surface. Plugs can be inserted at any point in a well, for example adjacent the surface or at a substantial depth. Typically, plugs are formed by injecting cement or resin into the well so as to fill for example a fifty metre length of the well. Experience has proven, however, that such plugs are not particularly reliable and often leak.
The known plugs tend to leak for a variety of reason. Firstly, as the well wall is typically not particularly clean and is covered with a hydrocarbon film, it is difficult to produce a contiguous seal. Often a contiguous seal of only a metre or so in length is formed with a plug fifty times that length. Furthermore, as cement and resin based plugs solidify, they contract which tends to open up a gap between the plug and a well wall. Although when a plug is initially inserted there may be little dynamic pressure in the well, after the plug is in situ substantial pressures can build up and as a result a plug which appears initially to be working satisfactorily may subsequently be found to leak. If hydrocarbons leak past the plug, contamination of the surface environment or, for example, a sub-surface aquifer can result. It is well known in the industry that a significant proportion of abandoned wells leak. As a result, leaking abandoned wells often have to be re-plugged which is an expensive and time consuming operation. It is therefore an object of the present invention to provide an alloy suitable for using as a plug in a well which can withstand the substantial pressures of a well.
It is also known to form a plug in a well by delivering a metal alloy, for example a low-melting point bismuth-containing alloy such as Rose's metal, Kraft's alloy, or Homberg's alloy. These alloys expand upon solidification and thus once deposited in a well they lose heat into the surrounding environment, solidify, and in solidifying expand to form a secure plug within the well. These alloys are comprised of varying amounts of bismuth, tin, and lead. WO02/27137, the contents of which are hereby incorporated by reference, discloses a well sealing method and apparatus in which a length of the well which is being plugged is filled with a molten material which has a melting point higher than the well temperature and which expands as it solidifies. The molten material is delivered to the well in a molten state where it cools, solidifies, and expands.
It is known that in certain circumstances, metals can be weakened by contact with liquid metals. This is known as liquid metal embrittlement (LME), which is also referred to as liquid metal induced embrittlement. In LME, certain ductile metals experience drastic loss in tensile ductility or undergo brittle fracture when in the presence of certain liquid metals. LME is a form of cracking which results when certain molten metals come into contact with specific alloys. It is important to avoid the embrittlement of the well casing during deployment of the liquid alloy. It is an object of the present invention to provide a well sealing material, such as an alloy, which has improved LME characteristics compared with prior art alloys used to plug abandoned wells.
Due to the environmental problems associated with leaking wells, solutions for permanently sealing wells for a minimum life of 3000 years are sought. Current metallic plug seals are designed to function effectively at operating temperatures of around 70 to 160° C. and at pressures in excess of 34 MPa. As a result of the extreme operating conditions and the length of time the plugs are in place, the issue of metal creep needs to be considered. Creep is the tendency of solid materials to move or deform permanently under the influence of mechanical stresses. Creep can occur as a result of long-term levels of stress, even where the stress levels are below the yield strength of the material. Creep is increased near the melting point of materials so the temperature of the environment in which the alloy is used will affect the choice of alloy.
It is therefore another object of the present invention to provide a well sealing material, such as an alloy, which obviates or mitigates the problem of creep outlined above. It is also an object of the present invention to provide a well sealing material, such as an alloy, which can provide a seal under the conditions within a well and which can last for a minimum lifetime of 3000 years.
The temperatures of abandoned oil wells can vary depending on a range of factors and it is therefore desirable to provide a well sealing material for use to form a plug which maintains its desirable properties at the temperature of the well.
Known alloys which are used to seal abandoned oil wells comprise alloys of bismuth and tin, or alloys of bismuth and zinc. The alloys of bismuth and tin are used in low temperature wells, which are wells which require plugs which can operate at temperatures up to around 80° C., and the alloys of bismuth and zinc are used in high temperature wells, which are wells which require plugs which can operate at temperatures up to around 150° C. If the temperature of a well is higher than around 40° C., the alloys of the prior art would be susceptible to creep and this would make them unsuitable for sealing the well. At even higher temperatures, the coefficients of expansion of the casing of the wells and the alloy used to form a plug need to be considered more closely. In addition, the melting point of the alloy needs to be high enough for the alloy to be able to form a stable plug at temperatures up to around 150° C., but it needs to be low enough so that it can be melted using the limited energy available for melting. Since the plugs are formed at locations remote from sources of power and in relatively confined spaces, the alloys are generally melted in situ using the heat generated by exothermic reactions or resistive heating. The amount of chemicals used in the exothermic reactions is limited by the space in which the plug is to be formed and this consequently limits the amount of energy available for melting the alloy. Equally the amount of energy available for melting the alloy via resistive heating is limited by the electric current that can be supplied downhole from conventional power generators.
Known bismuth-tin alloys are eutectic and have one definite melting temperature. When the plug is formed, if there are any gaps, the molten alloy will move away from the desired location before it can cool and solidify. The molten alloy could then solidify in an undesirable location and block further access to the plug. It is thus a further object of the present invention to provide a well sealing material, such as an alloy, which has an increased solidification rate when compared to conventional alloys.
Further disadvantages of the bismuth-tin alloys of the prior art is that the tin can leach out of the alloy and this can weaken the plug and allow gas to percolate through the plug. In addition, on cooling, the alloys of the prior art can crack which will weaken the plug and increase the likelihood of the plug failing at some point during its 3000 year life.
Whilst the alloys are presently used to form plugs to seal abandoned oil wells, it has been found that these alloys are susceptible to creep and it would not be possible to guarantee that they would have an effective working life of at least 3000 years. It is therefore an object of the present invention to provide a well sealing material, such as an alloy, which is capable of performing satisfactorily at temperatures around those typically found in wells and/or which demonstrate improved creep characteristics.
It has surprisingly been found that an alloy comprising bismuth, tin, and antimony has the necessary physical characteristics for use in sealing abandoned wells.
According to a first aspect of the present invention, there is provided an alloy of bismuth, tin, and antimony comprising at least about 50% by weight bismuth, about 30 to about 35% by weight tin, and about 1.8 to about 2.8% by weight antimony.
The alloy may comprise at least about 60% by weight bismuth.
The alloy may comprise about 65% by weight bismuth.
The alloy may comprise about 31 to about 33% by weight tin.
The alloy may comprise about 32% by weight tin.
The alloy may comprise about 2.0 to about 2.6% by weight antimony.
The alloy may comprise about 2.1 to about 2.4% by weight antimony.
The alloy may comprise about 2.28% by weight antimony.
Preferably, the amount of bismuth is varied such that the total amount of bismuth, tin, and antimony totals around 100% by weight of the alloy.
According to a second aspect of the present invention, there is provided a plug comprising an alloy of bismuth, tin, and antimony in accordance with the first aspect of the present invention. The plug may be used to seal a well. As such, there is provided the use of a bismuth alloy to seal a well, wherein the alloy comprises bismuth, tin, and antimony. The alloy may comprise an alloy according to the first aspect of the present invention.
According to a third aspect of the present invention, there is provided a method for producing a plug comprising an alloy of bismuth, tin, and antimony, wherein a length of a well is filled with the molten alloy and the molten alloy is allowed to solidify. In particular, the method may comprise introducing an alloy of bismuth, tin, and antimony into a well, wherein the alloy comprises an alloy according to the first aspect of the present invention. The alloy may comprise at least about 50% by weight bismuth, about 30 to about 35% by weight tin, and about 1.8 to about 2.8% by weight antimony.
The alloy according to the first aspect of the present invention exhibits improved creep and LME characteristics when compared with the known materials used for sealing abandoned oil wells. Due to its improved physical characteristics over conventional materials used to form plugs, it is possible to use the alloy of the present invention and the plugs made therefrom at a greater depth where the pressures are higher. If used at the same depth as a plug made from known alloys, the plug made from the alloy of the present invention will last longer and perform better. It is advantageous to plug wells at greater depths, so a plug which can operate at higher pressures is desirable.
It has also surprisingly been found that an alloy comprising bismuth and silver has the necessary physical characteristics for use in sealing abandoned wells.
According to a fourth aspect of the present invention, there is provided an alloy of bismuth and silver comprising about 91 to about 97% by weight bismuth and about 3 to about 9% by weight silver.
The alloy of silver and bismuth may comprise about 5.7 to about 7.5% by weight silver.
The alloy of silver and bismuth may comprise about 5.9 to about 6.5% by weight silver.
The alloy of silver and bismuth may comprise about 6.2% by weight silver.
Preferably, the amount of bismuth is varied such that the total amount of bismuth and silver totals around 100% by weight of the alloy.
According to a fifth aspect of the present invention, there is provided a plug comprising an alloy of bismuth and silver. The plug may be used to seal a well. As such, there is provided the use of a bismuth alloy to seal a well, wherein the alloy comprises bismuth and silver. The alloy may comprise an alloy according to the fourth aspect of the present invention.
According to a sixth aspect of the present invention, there is provided a method of forming a plug in a well comprising an alloy of bismuth and silver, wherein a length of the well is filled with the molten alloy and then allowed to solidify.
The alloy according to the fourth aspect of the present invention exhibits improved creep and LME characteristics when compared with the known materials used for sealing abandoned oil wells. The bismuth-silver alloy of the fourth aspect of the present invention is able to perform satisfactorily at increased temperatures where the alloys of the prior art would melt and would therefore be unsuitable.
In all of the aforementioned aspects and embodiments, the impurity content is preferably as close to zero as practically achievable, but it will be appreciated that there may be one or more additional metals as incidental impurities in the alloy at low, functionally insignificant concentrations. The impurities may be one or more of lead, gold, chromium, copper, vanadium, silver, aluminium, arsenic, cadmium, iron, tellurium, selenium, and zinc. It will also be appreciated that other impurities may be present and that these may be metallic, semi-metallic, or non-metallic in nature.
Although the description refers to the sealing of abandoned oil or petrochemical wells, it will be appreciated that the materials and methods according to the present inventions described herein are not limited to abandoned oil or petrochemical wells and may be used to create seals in other structures which may require sealing, including but not limited to, vents, aquifers, pipes, and the like.
Bismuth-Tin-Antimony Alloy (Alloy-80)
The alloy composition according to the first aspect of present invention has been optimised to provide enhanced creep resistance, a better blend of mechanical properties, including ultimate tensile stress and yield stress necessary for effective plug sealing performance, corrosion characteristics as well as enhanced liquid metal embrittlement properties compared with known alloys used for sealing wells. Moreover, it will be appreciated by the skilled person that the alloy composition of the first aspect of the present invention is eminently suitable for use as a plug for sealing wells. In particular, the alloy according to the first aspect of the present invention possesses a stable and balanced composition which provides a high degree of creep resistance, corrosion and mechanical characteristics which make it suitable for sealing wells for extended periods of time, and improved liquid metal embrittlement properties.
As mentioned above, presently an alloy of bismuth and tin is used to form plugs in abandoned oil wells. Upon cooling and solidifying, bismuth expands, which is unlike most other materials which shrink on solidification.
The skilled person will appreciate that bismuth is incorporated into the alloy of the first aspect of the present invention is due to its property of expanding upon solidification. This property is utilised when sealing wells as the alloy expands upon solidification and exerts a radial force on the sides of the well. Since most other metals contract upon solidification, it is important to have a high percentage of bismuth in the alloy so that it has the property of expanding upon solidification. Since the other metals in the alloy contract upon solidification, the bismuth needs to be present in an amount which is sufficient to overcome the shrinkage of the other metals present in the alloy so that overall the alloy expands upon solidification.
Tin is included in the alloy of the first aspect of the present invention to increase the ductility of the alloy. The addition of tin to the alloy increases the ductility and the strength of the alloy and also reduces its melting temperature. Thus, the alloy of the first aspect of the present invention is better able to cope with the pressure it is exposed to when used as a plug. The skilled person will appreciate that lower amounts of tin will have a reduced effect on the changes to the ductility, strength, and melting point of the alloy. On the other hand, if too great an amount of tin is incorporated into the alloy, this may alter the ductility, strength, and melting point of the alloy, such that it no longer has the desired properties for use in the production of a plug for an oil well.
Furthermore, adding more tin at the expense of bismuth reduces the propensity for the alloy to expand upon solidification, which is undesirable for the reasons discussed above. It is preferred that the alloy comprises about 30 to about 35% by weight tin, preferably about 31 to about 33% by weight tin. Most preferably, the tin content of the alloy of the first aspect of the present invention is about 32% by weight. The aforementioned ranges for the tin content of the alloy are important in ensuring the correct balance of the characteristics described above, in particular the ductility, strength, and melting point of the alloy.
Antimony is added to the alloy of the first aspect of the present invention in order to improve the creep resistance. It will be appreciated that since the alloy is intended to be used to form plugs which are required to last for extended periods of time and since during that time the plug will be under pressure from the walls of the well or any pressure differences which exist between the top and bottom of the plug, it is important that the alloy is resistant to creep. In addition, it has been found that the addition of antimony increases the solidification rate of the alloy and therefore, if there is any space between the mandrel in which the alloy is held whilst the plug is being formed and the well casing, the increased solidification rate will mean that less of the alloy is lost. It is preferred that the alloy comprises about 1.8 to about 2.8% by weight antimony, preferably about 2.0 to about 2.6% by weight antimony, more preferably about 2.1 to about 2.4% by weight antimony. Most preferably, the antimony content of the alloy of the first aspect of the present invention is about 2.28% by weight antimony. The aforementioned amounts for the antimony content of the alloy are important in ensuring the creep resistance of the alloy. It has also surprisingly been found that the aforementioned amounts for the antimony content of the alloy are also important in improving the liquid metal embrittlement properties of the alloy, which will be described in more detail below. Furthermore, the addition of antimony in the amounts of the first aspect of the present invention prevents the selective leaching of tin from the alloy. Leaching of tin from the alloy would increase the concentration of bismuth, which would make the alloy more brittle. With increasing bismuth content, the alloy becomes more enriched in bismuth phase making its overall mechanical properties tend towards that of pure bismuth. With decreasing tin content, the increased ductility conferred on the alloy diminishes with similar consequences. In addition, the antimony content of the alloy at these levels increases the corrosion resistance of the alloy.
It is preferred that the alloy of the first aspect of the present invention expands upon solidification. Preferably, the alloy expands by about 0.5% to about 1.0%, more preferably about 0.6% to about 0.9%, and most preferably by about 0.7% upon solidification, all measured by volume.
With regards to the hardness of the alloy of the first aspect of the present invention, it is preferred that the Vickers hardness, measured at room temperature in accordance with the ASTM-E384-11 standard using a 5 kg load cell and a test dwell time of 10 seconds, is from about 21 to about 27 Hv.
With regards to the tensile strength of the alloy of the first aspect of the present invention, it is preferred that the ultimate tensile strength, measured at room temperature in accordance with the ASTM E8/E8M standard at a constant strain rate of 104 s−1, is from about 40 to about 70 MPa. Under the same conditions, the yield strength is preferably from about 30 to about 45 MPa.
With regards to the operating temperature of the alloy of the first aspect of the present invention, it is preferred that the alloy is stable and does not creep at temperatures of from about 60 to about 100° C., more preferably at temperatures of from about 70 to about 90° C., and most preferably at temperatures of around 80° C. In this context, the alloy is considered to be stable and not to creep if it is able to seal a well for a minimum of 3000 years.
Bismuth-Silver Alloy (Alloy 150)
The alloy composition according to the fourth aspect of present invention has been optimised to provide enhanced creep resistance, a better blend of mechanical properties, including ultimate tensile stress and yield stress necessary for effective plug sealing performance, corrosion characteristics as well as enhanced liquid metal embrittlement properties compared with known alloys used for sealing wells. Moreover, it will be appreciated by the skilled person that the alloy composition of the fourth aspect of the present invention is eminently suitable for use as a plug for sealing wells. In particular, the alloy according to the fourth aspect of the present invention possesses a stable and balanced composition which provides a high degree of creep resistance, corrosion and mechanical characteristics which make it suitable for sealing wells for extended periods of time, and improved liquid metal embrittlement properties.
As mentioned above, presently an alloy of bismuth and tin is used to form plugs in abandoned oil wells. Upon cooling and solidifying, bismuth expands, which is unlike most other materials which shrink on solidification.
The skilled person will appreciate that bismuth is incorporated into the alloy of the fourth aspect of the present invention is due to its property of expanding upon solidification. This property is utilised when sealing wells as the alloy expands upon solidification and exerts a radial force on the sides of the well. Since most other metals contract upon solidification, it is important to have a high percentage of bismuth in the alloy so that it has the property of expanding upon solidification. Since the other metal in the alloy contract upon solidification, the bismuth needs to be present in an amount which is sufficient to overcome the shrinkage of the other metal present in the alloy so that overall the alloy expands upon solidification.
The addition of silver to the alloy increases the ductility and the strength of the alloy and also reduces its solidus temperature below that of pure bismuth. Increasing the silver content of the alloy widens the range when the alloy is partly solid and partly liquid/molten, and also raises the liquidus temperature of the alloy. Thus, the alloy of the fourth aspect of the present invention is better able to cope with the pressure it is exposed to when used as a plug. The skilled person will appreciate that lower amounts of silver will have a reduced effect on the changes to the ductility, strength, and melting point of the alloy as the chemistry of the resultant alloy approaches that of pure bismuth. On the other hand, if too great an amount of silver is incorporated into the alloy, this may alter the ductility, strength, and melting point of the alloy, such that it no longer has the desired properties for use in the production of a plug for an oil well. Furthermore, adding more silver at the expense of bismuth reduces the propensity for the alloy to expand upon solidification, which is undesirable for the reasons discussed above. It is preferred that the alloy comprises about 3 to about 9% by weight silver, preferably about 5.7 to about 7.5% by weight silver. More preferably, the silver content of the alloy of the fourth aspect of the present invention is about 5.9 to about 6.5% by weight, and most preferably the alloy of the fourth aspect of the present invention comprises about 6.2% silver by weight. The aforementioned ranges for the silver content of the alloy are important in ensuring the correct balance of the characteristics described above, in particular the ductility, strength, and melting point of the alloy.
It is preferred that the alloy of the fourth aspect of the present invention expands upon solidification. Preferably, the alloy expands by about 1.0% to about 3.2%, more preferably about 2.0% to about 3.0%, and most preferably by about 2.82% upon solidification, all measured by volume.
With regards to the hardness of the alloy of the fourth aspect of the present invention, it is preferred that the Vickers hardness, measured at room temperature in accordance with the ASTM-E384-11 standard using a 5 kg load cell and a test dwell time of 10 seconds, is from about 10 to about 20 Hv.
With regards to the tensile strength of the alloy of the fourth aspect of the present invention, it is preferred that the ultimate tensile strength, measured at room temperature in accordance with the ASTM E8/E8M standard at a constant strain rate of 104 s−1, is from about 35 to about 40 MPa. Under the same conditions, the yield strength is preferably from about 25 to about 30 MPa.
With regards to the operating temperature of the alloy of the fourth aspect of the present invention, it is preferred that the alloy is stable and does not creep at temperatures of from about 100° C. to about 200° C., more preferably at temperatures of from about 125° C. to about 175° C., and most preferably at temperatures of around 150° C. In this context, the alloy is considered to be stable and not to creep if it is able to seal a well for a minimum of 3000 years.
The invention of the first and fourth aspects of the present invention will now be further described with reference to the following non-limiting examples and figures in which:
Test samples were prepared according to the elemental specification shown below in Table 1.
A number of tests to determine the physical characteristics of the alloys according to the first aspect of the present invention were undertaken and the results of these tests are shown in the figures and explained below.
As can be seen from this figure, the ultimate tensile stress of the alloy of the first aspect of the present invention comprising bismuth, tin, and antimony is higher than the ultimate tensile stress of the conventional bismuth-tin alloy. This is advantageous for when the alloy of the first aspect of the present invention is used to form a plug to seal a well due to the forces acting upon the plug.
Mechanical testing of the alloy of the first aspect of the present invention and the conventional bismuth-tin alloy, of which both
From this figure, it can be seen that there is significant improvement in creep resistance above the conventional bismuth-tin alloy for the alloy of the first aspect of the present invention as well as the alloy comprising bismuth and silver of the fourth aspect of the present invention.
In order to accurately assess the physical characteristics of the alloy of the first aspect of the present invention, as-cast tensile specimens of the alloys of the first aspect of the present invention were tested at a constant temperature of 80° C. and pressure of 8.3 MPa. In view of the fact that the alloy of the first aspect of the present invention would be deployed to operate at and withstand down-hole differential pressure of 5000 psi (about 34.5 MPa), test specimens of the alloy of the first aspect of the present invention were machined from samples of the alloy which were pressure cast in a stainless steel autoclave filled with simulated fluid and gaseous environments, namely:
The pure argon gas environment was used to determine the effect of casting under pressure on the properties of the alloy of the first aspect of the present invention.
The starting mass and dimensions of the alloy sample to be tested and of the cylindrical Pyrex glass are measured, and a starting density is calculated. The total piston length and the overall unit length when assembled are also measured. The overall unit is then subjected to a heating/cooling cycle in a mechanical dilatometer under a small axial force. During testing, a heating/cooling rate of 0.5° C./min was used with data being logged every minute. As the unit is heated, the alloy sample expands lengthwise. When the alloy begins to melt, the cylindrical cavity beneath the ceramic piston becomes completely filled leading to a decrease in the length of the unit. With further heating, the alloy expands volumetrically and pushes the piston out again. On cooling, the reverse process occurs.
As such, by measuring the relative displacement of the ceramic piston, and hence the volume of the cavity created but subsequently filled with the alloy, as the unit was heated or cooled relative to the starting volume, the volumetric expansion of the alloy may be determined. The ‘zero’ volume is the starting unit volume and the ‘relative’ volume refers to the displace volume after subtracting the starting unit volume.
This figure demonstrates that the alloy of the first aspect of the present invention expands by as much as 0.7% in volume upon freezing. Since the alloy of the first aspect of the present invention is non-eutectic in composition, the expansion does not occur instantaneously at a particular temperature on freezing, but rather over a temperature range as shown in
As shown in
a, 22b, 23, 24a, 24b, 25, 26a, and 26b each relate to the mechanical properties of the alloy of the first aspect of the present invention.
Nevertheless, it can be seen from
Based on extensive Finite Element Analysis (FEA) modelling, it is apparent that the plug in an abandoned well will not be exposed to the uniaxial tensile forces as determined for the alloy of the first aspect of the present invention above. Rather the plug will be confined by the casing of the well and will be under lateral compressive stress transferred through the casing from the surrounding reservoir fluids. It will initially experience a uniaxial compressive force imposed by the gravity head of abandonment brine that will be greater than the reservoir fluid pressure. Over time, the uniaxial compressive force will decay as the pressure difference between the head of the abandonment brine and reservoir fluids decays such that the plug will begin to experience tri-axial compressive forces approximating hydrostatic conditions.
The unconfined compressive strength of the alloy of the first aspect of the present invention in different environments was conducted using the ASTM standards E9 (room temperature) and E29 (elevated temperature). However, the compression test was only conducted up to 120° C. for the air cast version of the alloy of the first aspect of the present invention. In contrast to the tensile test results shown in
Table 3 below details the shear strengths as a function of temperature for Alloy-80 cast in the four different environments detailed above (in air, under pressure of 5000 psi (about 34.5 MPa), under pressure of 5000 psi (about 34.5 MPa) and sour deaerated seawater, and under pressure of 5000 psi (about 34.5 MPa) and deaerated seawater).
The limitations of the ASTM B769-11 standard in determining the shear modulus of the alloy of the first aspect of the present invention meant that an alternative test method was used. In particular, the ASTM B769-11 standard is, in principle, limited to only the determination of the ultimate shear strength of the test material. In order to address this issue, alternative test methods, namely ASTM E1876-09 and EN 843-2/EN 821-2 standards, had to be used for the determination of the shear modulus of the alloy of the first aspect of the present invention. Therefore, further measurements were conducted in accordance with the ASTM E1876-09 and EN 843-2/EN 821-2 standards, using the so-called “impact excitation” or “natural frequency” methods.
Finally, as mentioned previously, beside creep, it is also necessary to consider corrosion control. It is believed that the ternary alloy of the first aspect of the present invention has improved corrosion behaviour over the alloys of the prior art.
The tests conducted on the alloy of the fourth aspect of the present invention were conducted on as-cast specimens which had not been given any further heat treatment. However, since the alloy of the fourth aspect of the present invention is intended to be used to form a plug to seal a well, tests were also conducted on samples which were cast under pressure and under similar conditions to those found in wells, in particular oil wells. Such test samples were machined from samples of the alloy according to the fourth aspect of the present invention under pressure in a stainless steel autoclave filled with simulated fluid and gaseous environments.
The simulated environments were deaerated sweater adjusted to pH 10-11 to represent a low-corrosivity environment; deaerated seawater made biologically sour to a “NACE Solution” composition which was around 600 mg/l dissolved in H2S at a pH range of 4.5-6.5 reference: NACE MR0175/section B.3.5.4 (Type 3a and 3b environments); and pure argon gas. The pure argon gas environment was used to determine the effect of casting the alloy of the fourth aspect of the present invention under pressure.
The starting mass and dimensions of the alloy sample to be tested and of the cylindrical Pyrex glass are measured, and a starting density is calculated. The total piston length and the overall unit length when assembled are also measured. The overall unit is then subjected to a heating/cooling cycle in a mechanical dilatometer under a small axial force. During testing, a heating/cooling rate of 0.5° C./min was used with date being logged every minute. As the unit is heated, the alloy sample expands lengthwise. When the alloy begins to melt, the cylindrical cavity beneath the ceramic piston becomes completely filled leading to a decrease in the length of the unit. With further heating, the alloy expands volumetrically and pushes the piston out again. On cooling, the reverse process occurs.
As such, by measuring the relative displacement of the ceramic piston, and hence the volume of the cavity created but subsequently filled with the alloy, as the unit was heated or cooled relative to the starting volume, the volumetric expansion of the alloy may be determined. The ‘zero’ volume is the starting unit volume and the ‘relative’ volume refers to the displace volume after subtracting the starting unit volume.
The alloys of the first and fourth aspects of the present invention are suitable for use as well sealing materials and are able to operate under the conditions found within wells. They are able to operate under these conditions for the minimum lifespan of 3000 years and offer improved performance characteristics over known alloys.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1810418 | Jun 2018 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2019/051755 | 6/21/2019 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2020/002887 | 1/2/2020 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20210262313 A1 | Aug 2021 | US |
