Patent Application
20150308227
1. Field of the Invention
Embodiments of the present invention relate generally to apparatuses and methods for reducing a pressure of a fluid in a wellbore. More specifically, embodiments relate generally to an apparatus and method for reducing a pressure differential across a valve.
2. Description of the Related Art
A wellbore is formed by using a drill bit on a drill string to drill through a geological formation. After drilling through the formation to a predetermined length or depth, the drill string and drill bit are removed, and the wellbore is lined with a string of casing. The space between the outer diameter of the casing and the wellbore is referred to as an annulus. In order to prevent the casing from moving within the wellbore, the annulus is filled with cement using a cementing operation. In addition to preventing the casing from moving within the wellbore, the cemented annulus also provides for a stronger wellbore for hydrocarbon production.
When the casing is sent downhole, the casing is typically filled with a fluid, such as drilling mud, and the fluid is maintained at a predetermined pressure. The fluid within the casing ensures that the casing does not collapse within the wellbore. A bottom end of the casing usually includes a float assembly, such as a float collar or a float shoe. The float assembly includes one or more unidirectional valves that allow fluid from inside the casing to flow out to the annulus, but prevents fluid from the annulus to enter the casing. An upper end of the float assembly may also include a receptacle for receiving a device, such as a cement plug.
During a cementing operation, it is preferred that the cement is isolated or separated from other fluids within the casing. When fluids such as drilling mud mix with cement, it can cause the cement to sour and fail when it sets. Accordingly, a first plug is usually sent down in front of the cement during a cementing operation. The first plug includes one or more fins around its circumference which acts to separate the drilling fluid below the first plug from the cement above the first plug. The fins also clean the inner walls of the casing as the first plug descends in the casing. Because the first plug provides both a separation and cleaning function, the outer diameter of the first plug is equal to or larger than the inner diameter of the casing. The first plug includes a bore through a center longitudinal portion of its body. The first plug also includes a rupture membrane, such as rupture disc, positioned across the bore, which prevents the drilling fluid below the first plug from comingling with the cement above the first plug. As the first plug descends in the casing, the drilling fluid is forced through the float assembly and out into the annulus. The unidirectional valve within the float assembly prevents the drilling fluid from moving back into the casing.
After the first plug reaches the float assembly, hydrostatic pressure builds on the upper side of the rupture membrane. Once the first plug reaches a rupture pressure, the rupture membrane ruptures, and the cement flows through the bore of the first plug, through the float assembly, and into the annulus.
A second plug is usually sent down the casing behind the cement, and the second plug is usually pushed downward with drilling fluid. The second plug includes one or more fins that separate the cement below the second plug from the drilling fluid above the second plug. The fins also clean the sidewalls of the casing as the second plug descends down the casing. As the second plug is pushed through the casing, the cement is squeezed out of the float assembly into the annulus until the second plug reaches the first plug. In the prior art, at least one of the first or second plugs form a seal within the casing, which prevents fluid from moving past the first or second plugs. Thereafter, the cement is given time to cure and set up as a constant pressure is maintained within the casing.
The pressure of the drilling fluid above the first and second plugs is bled off, or reduced, while the pressure of the cement at the base of the casing is maintained due to the unidirectional valve. The change in pressure results in a significant pressure differential across the unidirectional valve of the float assembly within the casing. To prevent the float assembly from failing or yielding, the float assembly is designed with materials that can withstand high pressure differentials. Accordingly, the materials required for high pressure float assemblies are often expensive.
As the foregoing illustrates, what is needed are cost effective apparatuses and methods for handling high pressure differentials across a valve. There is also a need for apparatus and methods of reducing the pressure difference across float assemblies during cementing operations.
Embodiments of the present invention generally relate to a method of regulating a pressure of a fluid in a wellbore. First, a tubular is positioned within the wellbore. The tubular is equipped with a first float assembly and a second float assembly. Each float assembly includes a unidirectional valve with an inlet and an outlet. Next, a pressure differential between the outlet and the inlet of the first unidirectional valve is reached. Then, the pressure differential across the first unidirectional valve is reduced when a pressure at the outlet is higher than a pressure at the inlet by a predetermined amount.
In another embodiment, a method of regulating a pressure of a fluid in a wellbore includes positioning a tubular equipped with a first float assembly and a second float assembly, wherein each float assembly includes a unidirectional valve with an inlet and an outlet; reaching a pressure differential between an upstream pressure and a downstream pressure of the unidirectional valve of the first float assembly; and reducing the pressure differential across the unidirectional valve of the first float assembly when the downstream pressure is higher than the upstream pressure by a predetermined amount.
In one embodiment, reducing the pressure differential across the first unidirectional valve includes opening a relief valve to allow fluid to move across the first float assembly. In yet another embodiment, the fluid flowing through the first float assembly pressurizes an area between the first and second float assemblies.
In another embodiment, a method of regulating a pressure of a fluid in a wellbore includes positioning a tubular equipped with a first float assembly having a first unidirectional valve and a second float assembly having a second unidirectional valve, wherein each of the first and second unidirectional valves include an inlet and an outlet; and reducing a pressure differential across the first unidirectional valve when a pressure at the outlet is higher than a pressure at the inlet by a predetermined amount.
The present invention also relates to a system of regulating a pressure of a fluid in a wellbore. The system contains a tubular with a first float assembly and a second float assembly disposed therein. The first float assembly includes a first unidirectional valve for allowing fluid to flow in a first direction. The first float assembly is also equipped with a pressure regulating device configured to actuate when a predetermined pressure differential is reached. The second float assembly includes a second unidirectional valve for allowing fluid to flow in the first direction.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
The present invention relates to apparatuses and methods of reducing pressure differentials during wellbore operations such as a cementing operation. In one embodiment, a plurality of float assemblies, each equipped with a relief valve and unidirectional valve, may be used to obtain a desired pressure differential across the plurality of unidirectional valves.
A method of regulating a pressure of a fluid in a wellbore includes urging a fluid through a plurality of unidirectional valves disposed in a plurality of float assemblies in a casing. For example, the fluid may be urged in the casing by at least one plug. Next, a fluid pressure differential across at least one of the plurality of unidirectional valves is reached. The fluid pressure differential is prevented from increasing above a predetermined fluid pressure differential. Preventing the first fluid pressure differential from exceeding the predetermined fluid differential may include providing a relief valve to permit the fluid to re-enter a portion of the casing. The re-entered fluid may pressurize the portion of the casing above the at least one of the plurality of float assemblies. Preventing the first fluid pressure differential from exceeding the predetermined fluid differential may also include moving the at least one of the plurality of float assemblies. Moving the at least one of the plurality of float assemblies pressurizes the portion of the casing above the at least one of the plurality of float assemblies.
As shown, the second float assembly 114 includes a bore 116 and a unidirectional valve 118. The second float assembly 114 also includes an optional relief valve 120 and optional spacer 124. The unidirectional valve 118 controls fluid flow through the bore 116 and is configured to allow fluid to flow through the bore 116 and out of the casing 102, but prevent fluid from re-entering the casing 102 through the bore 116. Exemplary unidirectional valves include a check valve, a plunger valve, and a flapper valve.
The relief valve 120 controls fluid flow through a second bore 122 of the second float assembly 114. The relief valve 120 may be added to any type of valve or any type of downhole tool. For example, the relief valve 120 may be added to a plunger valve or ball valve and resides on a packer. The relief valve 120 is configured to allow fluid to move across the second float assembly 114 at a predetermined pressure differential. Exemplary relief valves 120 include a check valve, a ball valve, a plunger valve, and other suitable valves known to a person of ordinary skill in the art. In this embodiment, the relief valve 120 allows the fluid to move across the second float assembly 114 through the second bore 122 in a direction opposite the direction of the unidirectional valve 118. The second bore 122 may extend longitudinally and/or radially to couple an upper portion and a lower portion of the second float assembly 114. The relief valve 120 may also be configured to restrict fluid flow through the second bore 122 upon reaching a predetermined reduced pressure differential across the second float assembly 114. For example, fluid may flow downwards in the casing 102 through bore 116 and unidirectional valve 118 and, when a predetermined pressure differential is reached, the fluid may re-enter an upper portion of the casing 102 through second bore 122 and the relief valve 120. The relief valve 120 may again restrict re-entry of fluid into an upper portion of the casing 102 upon reaching the reduced fluid pressure differential across the second float assembly 114. In another example, the relief valve 120 may open at a predetermined pressure differential and then closes at or below the predetermined pressure differential. In yet another example, the relief valve 120 may open at a first pressure differential and stay open below the first pressure differential until a lower, second pressure differential is reached, at which time, the relief valve 120 will close.
The optional spacer 124 is generally located on an upper portion of the second float assembly 114 and couples the second float assembly 114 to adjacent apparatuses in the casing 102. For example, the spacer 124 may include a landing collar on which the first plug 106 lands during the primary cementing operation. In one embodiment, the spacer 124 may be integral with the second float assembly 114. The spacer 124 includes a channel 126 configured to fluidly couple the second bore 122 to the bore of the casing 102. For example, fluid ascending in the second bore 122 travels through channel 126 before occupying the inner diameter of the casing 102 above the second float assembly 114. As shown, the channel 126 may extend longitudinally and/or radially within the spacer 124.
Although only a first float assembly and a second float assembly have been described herein, it is contemplated that any suitable number of float assemblies may be inserted into the casing. Furthermore, although only references to the second float assembly have been described herein, any components described with respect to the second float assembly may be incorporated into any float assembly, including the first float assembly, inserted in the casing. In one example, a multiple float assembly system may be used in which all float assemblies are equipped with the relief valve. In another example, a first float assembly and a second float assembly equipped with relief valves may be disposed in the casing.
As shown, the first plug 106 and the second plug 108 are used to separate fluids in the casing 102. For example, the first plug 106 and the second plug 108 are used to separate cement 104 from fluid in front of the cement 104 and fluid behind the cement 104. The fluid in front of the cement 104 may be a drilling fluid and the fluid behind the cement 104 may be a push fluid, such as a drilling fluid. In some applications, a spacer fluid may be disposed between the cement 104 and the fluid in front of the cement 104, disposed between the cement 104 and the push fluid behind the cement 104, or both. In one embodiment, the first plug 106 may be a cement plug having a bore 128 through the first plug 106, and a rupture disc 130 positioned within the bore 128 to prevent flow therethrough. The rupture disc 130 is configured to break at a predetermined pressure. The first plug 106 and the second plug 108 may include one or more fins 132 circumferentially positioned on its exterior surface for sealingly contacting the wall of the casing 102. The fins 132 act as a barrier to prevent comingling of fluids from above and below the respective plugs 106, 108. The fins 132 may also clean the wall of the casing 102 as the first plug 106 descends in the casing 102. It is contemplated that the first plug 106 may be any suitable cement plug known to a person of ordinary skill in the art.
Although only a single first plug has been described herein, it is contemplated any suitable number of plugs may be inserted into the casing prior to the insertion of the second plug. In one example, a multiple plug system may be used to separate several types of fluids that may be required for certain operations.
During a cementing operation, the first and second float assemblies 112,114 are positioned downhole with the casing 102. As shown in
In one example, while the injection fluid pushes the second plug 108 down the casing 102, the pressure differential across the unidirectional valve 118 of the first float assembly 112 is below a first predetermined pressure differential. However, after the second plug 108 reaches the first plug 106, the fluid pressure above the second plug 108 may be reduced by bleeding off the injection fluid. Bleeding off the injection fluid results in an increase in the fluid pressure differential between the fluid above the second plug 108 and the fluid below the first float assembly 112. Accordingly, the fluid pressure differential between the top and bottom of the unidirectional valve 118 of the first float assembly 112 may exceed the first predetermined pressure differential.
When this occurs, the relief valve 120 in the first float assembly 112 opens to reduce the fluid pressure differential across the unidirectional valve 118 of the first float assembly 112. In this respect, the relief valve 120 permits the cement 104 below the first float assembly 112 to re-enter the casing 102. For example, the cement 104 re-enters the casing 102 by ascending in the second bore 122. The cement 104 leaving the second bore 122 is retained in the space between the first float assembly 112 and the second float assembly 114. The unidirectional valve 118 and the relief valve 120 of the second float assembly 114 prevent the cement 104 from flowing through the second float assembly 114. Re-entry of the cement 104 into the casing 102 decreases the pressure of the cement 104 acting on the lower side of the first float assembly 112 while increasing the pressure of the cement 104 between the first and second float assemblies 112, 114. Thus, the fluid pressure differential across the unidirectional valve 118 of the first float assembly 112 is reduced. In one embodiment, the relief valve 120 closes when the pressure differential is at or below the first pressure differential. In another embodiment, the relief valve 120 remains open until a closing pressure differential below the first pressure differential is reached. For example, the relief valve may remain open until the pressure differential is less than 95 %, less than 90 %, or less than 80 % of the first pressure differential. In other examples, the relief valve may remain open until the pressure differential is from 75 % to 95 %, from 75 % to 90 %, or from 65 % to 80 % of the first pressure differential.
The pressure differential across the unidirectional valve 118 of the second float assembly 114 increases as the pressure between the first and second float assemblies 112, 114 increases. When the pressure differential across the unidirectional valve 118 of the second float assembly 114 reaches a second predetermined pressure differential, the relief valve 120 in the second float assembly 114 opens to permit cement 104 to re-enter the casing 102 above the second float assembly 114. As a result, the pressure difference across the unidirectional valve 118 of the second float assembly 114 is reduced. In one embodiment, the relief valve 120 in the second float assembly 114 closes when the pressure differential is at or below the first pressure differential. In another embodiment, the relief valve 120 remains open until a closing pressure differential below the first pressure differential is reached. For example, the relief valve may remain open until the pressure differential is less than 95 %, less than 90 %, or less than 80% of the second pressure differential. In other examples, the relief valve may remain open until the pressure differential is from 75 % to 95 %, from 75 % to 90 %, or from 65 % to 80 % of the second pressure differential. In this manner, a plurality of float assemblies 112, 114 equipped with a plurality of relief valves 120 may be used to obtain a desired total pressure drop across the first float assembly 112 and the second plug 108.
In the embodiment shown in
In one example, the pressure differential across the unidirectional valve 118 of the first float assembly 172 may be below the first predetermined pressure differential while the injection fluid pushes the second plug 108 down the casing 102. However, after the second plug 108 reaches the first plug 106, the fluid pressure above the second plug 108 may be reduced by bleeding off the injection fluid. Bleeding off the injection fluid results in an increase in the fluid pressure differential between the fluid above the second plug 108 and the fluid below the first float assembly 172. Accordingly, the fluid pressure differential between the top and bottom of the unidirectional valve of the first float assembly 172 may exceed the first predetermined fluid pressure differential.
In order to reduce the fluid pressure differential across the unidirectional valve 118 of the first float assembly 172, the first float assembly 172 may ascend or descend within the casing 102. In order to ascend or descend, the first float assembly 172 is equipped with a dynamic seal, which seals the first float assembly 172 to the casing 102. In one embodiment, the dynamic seal includes an O-ring disposed around the circumference of the first float assembly 172. Accordingly, the first float assembly 172 is not cemented in place in the casing 102. A biasing member, such as a spring, may be disposed between the first float assembly 172 and the second float assembly 114 to control the ascent of the first float assembly 172 in the casing 102. For example, the spring may bottom out to end the ascent of the first float assembly 102 when the pressure differential across the unidirectional valve 118 of the second float assembly 114 reaches a second predetermined pressure. Other instruments known to persons having ordinary skill in the art may be used to end the ascent of the first float assembly 102. For example, a stop may be used. Thus, the first float assembly 172 may ascend from its original position at the foot of the casing 102 and move toward the second float assembly 114 when the first predetermined fluid pressure differential is reached across the unidirectional valve 118. As a result, the pressure exerted on the lower side of the first float assembly 172 decreases, thereby reducing the pressure differential across the unidirectional valve 118 of the first float assembly 172.
Movement of the first float assembly 172 also causes the pressure between the first and second float assemblies 172, 114 to increase, which increases the pressure differential across the unidirectional valve 118 of the second float assembly 114. When the pressure differential across the unidirectional valve 118 of the second float assembly 114 reaches the second predetermined pressure differential, the relief valve 120 in the second float assembly 114 may open to reduce the pressure differential across the unidirectional valve 118 of the second float assembly 114. In this manner, the overall pressure differential across the unidirectional valves 118 of the first and second float assemblies 172, 114 may be reduced. In
In yet another embodiment, the second float assembly 114 may be configured to ascend in response to the second predetermined pressure differential. In this respect, after the second predetermined pressure differential is reached due to movement of the first float assembly 172, the second float assembly 114 may begin to move in order to reduce the pressure differential across the unidirectional valve 118 of the second float assembly 114.
In yet another embodiment, each or both of the first and second float assemblies may be equipped with at least one relief valve, movable configuration, or both. For example, a relief valve 120 in the first float assembly 112 may allow cement 104 to enter the casing 102 between the first and second float assemblies 112,114. In response, the second float assembly 114 may either ascend in the casing 102 or the relief valve 120 may open, or both, to reduce the pressure across the unidirectional valve 118 of the second float assembly 114.
In one embodiment, rather than using a single piece of equipment to counteract the fluid pressure in the casing, multiple pieces of equipment with pressure regulating devices may be added to the system to limit the maximum fluid pressure counteracted by each piece of equipment. By dividing the overall fluid pressure differential among the float assemblies in the casing, the system may counteract a higher fluid pressure differential as compared to using only one float assembly. Furthermore, because float assemblies with high fluid pressure capacities are more costly than float assemblies with low fluid pressure capacities, the system may be less expensive to implement even with multiple low fluid pressure float assemblies. It must be noted that although embodiments are described herein using a plurality of float assemblies, it is contemplated that these embodiments are equally applicable to any suitable valve equipped with a relief valve, configured to move, or both. For example, two unidirectional valves equipped with relief valves may be used to counteract a predetermined pressure differential.
In one embodiment, a method of regulating a pressure of a fluid in a wellbore includes positioning a tubular equipped with a first float assembly and a second float assembly, wherein each float assembly includes a unidirectional valve with an inlet and an outlet; reaching a pressure differential between an upstream pressure and a downstream pressure of the unidirectional valve of the first float assembly; and reducing the pressure differential across the unidirectional valve of the first float assembly when the downstream pressure is higher than the upstream pressure by a predetermined amount.
In another embodiment, a method of regulating a pressure of a fluid in a wellbore includes positioning a tubular equipped with a first float assembly having a first unidirectional valve and a second float assembly having a second unidirectional valve in a wellbore, wherein each of the first and second unidirectional valves include an inlet and an outlet; and reducing a pressure differential across the first unidirectional valve when a pressure at the outlet of the first unidirectional valve is higher than a pressure at the inlet of the second unidirectional valve by a predetermined amount.
In another embodiment, reducing the pressure differential across the first unidirectional valve includes opening a relief valve to allow fluid to move across the first float assembly.
In one more of the embodiments described herein, the fluid flowing through the first float assembly pressurizes an area between the first and second float assemblies.
In one more of the embodiments described herein, the method includes reducing a pressure differential across the second unidirectional valve when the pressure differential across the second unidirectional valve reaches a second predetermined pressure differential.
In one more of the embodiments described herein, the relief valve closes when the pressure differential is at or below the predetermined amount.
In one more of the embodiments described herein, the relief valve closes when the pressure differential is below the predetermined amount of pressure differential.
In one more of the embodiments described herein, the relief valve remains open until the pressure differential is less than 80% of the predetermined amount of pressure differential.
In one more of the embodiments described herein, reducing the pressure differential across the first unidirectional valve pressurizes an area between the first and second float assemblies.
In one more of the embodiments described herein, reducing the pressure differential across the first unidirectional valve includes moving the first float assembly toward the second float assembly.
In one more of the embodiments described herein, moving the first float assembly pressurizes an area between the first and second float assemblies.
In another embodiment, a system for regulating a pressure of a fluid in a wellbore includes a tubular; a first float assembly disposed in the tubular, wherein the first float assembly includes a first unidirectional valve for allowing fluid to flow in a first direction; and a second float assembly disposed in the tubular, wherein the second float assembly includes a second unidirectional valve for allowing fluid to flow in the first direction; wherein the first float assembly is equipped with a pressure regulating device configured to actuate when a predetermined pressure differential is reached.
In one more of the embodiments described herein, the pressure regulating device includes a relief valve for allowing fluid to flow in a second direction.
In one more of the embodiments described herein, the pressure regulating device includes a movable first float assembly.
In one more of the embodiments described herein, the system includes a first plug and a second plug, wherein the first plug includes a removable seal.
In one more of the embodiments described herein, the removable seal includes a rupture disc.
In one more of the embodiments described herein, reducing the pressure differential across the first unidirectional valve includes opening a relief valve to allow fluid to move across the first float assembly.
In one more of the embodiments described herein, reducing a pressure differential across the second unidirectional valve when a pressure at the outlet is higher than a pressure at the inlet by a predetermined second amount.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
| Number | Date | Country | |
|---|---|---|---|
| 61985159 | Apr 2014 | US |
