Patent Application
20180142528
The present invention relates generally to wiper plugs that are used in the oil and gas industry to wipe a well casing, and more particularly to an improved apparatus for sealing a well casing.
In the oil and gas producing industry, the process of cementing casing into the wellbore of an oil or gas well generally comprises several steps. For example, a conductor pipe is positioned in the hole or wellbore and may be supported by the formation and/or cemented. Next, a section of a wellbore is drilled with a drill bit which is slightly larger than the outside diameter of the casing which will be run into the well.
Thereafter, a string of casing is run into the wellbore to the required depth where the casing lands in and is supported by a well head in the conductor. Next, cement slurry is pumped into the casing to fill the annulus between the casing and the wellbore. The cement serves to secure the casing in position and prevent migration of fluids between formations through which the casing has passed.
The primary cementing can form a protective sheath around the casing, segregating producing formations to prevent migration of undesirable fluids. Secondary cementing takes place after the primary cementing and can be used to squeeze cement into the perforations in the casing or to seal off, isolate or repair parts of the well. Plug back cementing is used to place cement at desired points in the well or to shut off the bottom water or reduce the depth of the well.
Two of the apparatuses or pipe attachments routinely used in the cementing operations are the collar and the shoe. These are typically cement restrictions or shoulders which are attached to a pipe string as a part of the pipe string. The collar, for example, a float collar, is inserted between the top and bottom of a casing string usually one or two joints above a float shoe which is attached to the bottom of a pipe string. Shoes and collars, among a number of things, help prevent the back flow of cement during the cementing operation. The collars and the shoes are usually equipped with a check valve (often a ball valve means) to aid in the prevention of back flow of cement. The shoes and collars are typically an outer cylindrical housing or pipe and an inner cement tube communicating with and fixed to the inner surface of the cylindrical housing, with a fluid passage running the length of the cement tube. When there is a check valve, it is usually part of an inner housing in concentric spaced relationship with the outer housing so that the cement tube fills the space between the two housings and the inner housing forms part of the fluid passage.
In addition to the collars and shoes, typical cementing operations employ one or more pump down plugs. Pump down wipe plugs can serve three purposes: (1) to separate or serve as the interface between the wet cement from the fluid it is displacing or the fluid which is being used to pump the wet cement to the desired level; (2) to wipe off the inner surface of the pipe string as it passes; and (3) to help prevent back flow while the cement is setting up.
The wiper plug designs used in today's horizontal wellbores were initially developed for use in vertical wellbores. The horizontal wellbores present a more challenging trajectory for the equipment due to the extended casing length and concentrated friction on only one side of the wiper plug. As a consequence, the elastomeric fins can become worn on one side and rendered incapable of sealing properly in the dimensions of the conventional shoe joint. This causes a phenomena called “wet shoe.”
As generally seen in the flow chart of
The prior art as detailed above suffers from a number of deficiencies. First, prior art systems do not provide for effectively avoiding wet shoe in a horizontal wellbore casing. Once the wiper plug is damaged, cement will flow past it. Also, prior art systems do not provide for efficient wiper plug seal integrity in a horizontal wellbore casing. A need exists for a system of ensuring that even a damaged wiper plug creates an effective seal. Prior art systems do not provide for efficiently locking wiper plug fins that are undersized to the actual casing. Finally, prior art systems and methods do not provide for inexpensive solutions to prevent wet shoe conditions.
The present invention in various embodiments addresses one or more of the above objectives in the following manner. The present invention provides a system which includes a wellbore casing installed into a wellbore along with restriction elements, a secondary engagement sub, a float collar and a shoe. A wiper plug is deployed into the wellbore casing after cement slurry is pumped into the wellbore casing. The secondary engagement sub provides a tapered entry guide directly above the float collar. The entry guide has a reduced inside diameter that serves to enhance the sealing integrity of the wiper plug and also aligns the wiper plug to properly latch into a locked position. In another system, a 3 stepped diameter wiper plug with a reduced nose is disclosed. The reduced nose provides for an improved seal integrity that fits and latches into a smaller internal diameter secondary engagement sub.
The present invention system may be utilized in the context of an overall wiper plug seal integrity method, wherein the wiper plug seal integrity apparatus as described previously is controlled by a method having the following steps:
Integration of this and other preferred exemplary embodiment methods in conjunction with a variety of preferred exemplary embodiment systems are described herein in anticipation by the overall scope of the present invention.
For a fuller understanding of the advantages provided by the invention, reference should be made to the following detailed description together with the accompanying drawings wherein:
While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detailed preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiment illustrated.
The numerous innovative teachings of the present application will be described with particular reference to the presently preferred embodiment, wherein these innovative teachings are advantageously applied to the particular problems of a wiper plug seal integrity system and method. However, it should be understood that this embodiment is only one example of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others.
Accordingly, the present invention will address the deficiencies in the prior art and achieve a number of objectives. For example, the present system will prevent wet shoe in a horizontal wellbore casing. Specifically, it will provide for efficient plug seal integrity in a horizontal wellbore casing. The present invention provides a reduced internal seal bore into which the fins of the wiper plug can fully and properly seat. It also provides for efficiently locking wiper plug fins that are undersized to the actual casing. Finally, it is an inexpensive solution to prevent wet shoe conditions.
While these objectives should not be understood to limit the teachings of the present invention, in general these objectives are achieved in part or in whole by the disclosed invention that is discussed in the following sections. One skilled in the art will no doubt be able to select aspects of the present invention as disclosed to affect any combination of the objectives described above.
The present invention may be seen in more detail as generally illustrated in
According to a preferred embodiment, an apparatus for sealing a horizontal wellbore casing (0301) with a wiper plug comprises a hollow tubular shaped secondary engagement sub (0303) positioned upstream of a float collar (0304) in the wellbore casing; wherein when the wiper plug enters the secondary engagement sub, the secondary engagement sub centralizes the wiper plug such that said wiper plug aligns into the float collar and substantially obstructs fluid flow past the wiper plug. Cement sets in the toe (0305) when fluids are not bypassed. The exemplary secondary sub (0303) obstructs the fluids from bypassing and therefore cement may be set without causing a potential wet shoe. According to a preferred exemplary embodiment, an inner diameter of the secondary engagement sub is configured to enable substantially unobstructed entry of the wiper plug into the secondary engagement sub. For example, a casing with a 4.67 inch inner diameter may be integrated with a sub with a 4.25 inner diameter so that a wiper plug with a diameter of 4.67 inch may be guided and aligned into the sub even with a lower diameter after eroding inside the casing. The lower diameter of the sub may enable an eroded wiper plug to be centralized and latched or engaged in a float collar.
In one embodiment, the secondary engagement sub (0400) has an inner diameter surface 410, a ratio of the inner diameter of the secondary engagement sub to an inner diameter of the wellbore casing is less than 0.9. According to another embodiment the secondary engagement sub further comprises a toe sub end (0402) and a heel sub end (0401). The toe sub end may be mechanically coupled to an end of the float collar. The heel sub end may be mechanically coupled to the wellbore casing. The heel sub end (0401) may be configured to be threaded or attached by other means to the well casing. Similarly, the toe sub end (0402) may be configured to be threaded or attached by other means to the float collar. According to another embodiment the inner diameter of the toe sub end and inner diameter of the heel sub end are equal. In another embodiment the inner diameter surface (0410) tube in the sub is tapered. The inner diameter of the toe sub end is substantially smaller than the inner diameter of the heel sub end. For example, the diameter of the toe sub end may be 4.25 inches and the diameter of the heel sub end may be 4.67 inches. The sub may be tapered gently to allow for the wiper plug to gradually enter the sub without bumping into the sub or the float collar as the pumping rate is slowed down. The angle of the taper may range from 50 to 450. A ratio of the inner diameter of the heel sub end (0401) to an inner diameter of the toe sub end (0402) may range from 0.2 to 0.5. As illustrated in both
As generally seen in the flow chart of
The horizontal wellbores present a more challenging trajectory for the equipment due to the extended casing length and concentrated friction on only one side of the wiper plug. As a consequence, the elastomeric fins can become worn on one side and rendered incapable of sealing properly in the dimensions of the conventional shoe joint. According to a preferred exemplary embodiment, a secondary sub provides an improved seal configuration that will provide a reduced internal seal bore into which the fins of the wiper plug can fully and properly seat. The secondary sub may reduce the number of wet shoes by properly aligning the wiper plug into the float collar and by the improved seal integrity.
The secondary sub may be adapted to many styles of wiper plugs to achieve a seal integrity with a variety of wiper plugs including but not limited to chevron stacks or a certain number of wiper fins that are undersized to the actual casing while being optimized to seal within the specific seal sub.
According to another preferred exemplary embodiment, a stepped wiper plug (0600) for use in a horizontal wellbore casing may comprise a hollow cylindrical shaped first plug section (first section) (0601) and a hollow cylindrical shaped second plug section (second section) (0602) as illustrated in
According to a preferred exemplary embodiment, the stepped wiper plug may further comprise a third plug section (third section) (0603) that is attached and extending from an end (0605) of the second section (0602). The end (0605) is away from the end (0604) attached to the first section (0601). The third section may be a chevron stack or the like. According to another preferred exemplary embodiment the diameter (0613) the third section (0603) is substantially less than the smallest inner diameter of all the downhole tools. For example, if the smallest inside diameter of the downhole tools such as a sliding sleeve valve is 3.25 inches, the diameter of the third section may be chosen to be less than 3.25 inches. The diameter of the third section may range from 1 to 3 inches. The third section may be a hollow cylindrical element or a solid piece extending from the end (0605) of the second section. According to a preferred exemplary embodiment a ratio of the diameter (0612) of the second section (0602) to the diameter (0613) of the third section (0603) ranges from 0.2 to 0.9. According to another preferred exemplary embodiment the diameter of the third section is configured to fit into the secondary sub. The diameter of the third section and the diameter of the sub are chosen such that the third section latches into place while obstructing fluid flow past the plug. The latching of the third section into the sub creates a seal and may further avoid creation of wet shoe in the toe of the casing. The smaller diameter of third section enables an outer section of the third section to substantially be not touched or eroded when the stepped wiper plug wipes the downhole tools and the casing. The third section (0603) may further comprise fins extending from an outer surface of the third section. According to another preferred exemplary embodiment wherein the downhole tools are selected from a group comprising: sliding sleeve valves, restrictions, or toe valves.
An alternate preferred embodiment is a spiral wiper plug configured with a spiral tail attached to an upstream end such that the tail rotates in the casing while wiping the cement. The rotation of the wiper plug with the spiral tail enables the wiper plug to be worn equally on all sides. An equally worn wiper plug may fit into a conventional float collar with a reduced diameter and provide a tight seal and obstruct fluid bypass into the shoe of the casing. The spiral tail may further comprise a rudder to steer and rotate the wiper plug. The spiral tail may comprise fins that rotate about a longitudinal axis along the casing.
This general method summary may be augmented by the various elements described herein to produce a wide variety of invention embodiments consistent with this overall design description. The present invention anticipates a wide variety of variations in the basic theme of oil and gas extraction. The examples presented previously do not represent the entire scope of possible usages. This basic system and method may be augmented with a variety of ancillary embodiments. For example, in one alternative, an inner diameter of the secondary engagement sub is configured to enable substantially unobstructed entry of the wiper plug into the secondary engagement sub. In another embodiment, the ratio of inner diameter of the secondary engagement sub to inner diameter of the wellbore casing is less than 0.9. In another embodiment, the secondary engagement sub further comprises a toe sub end and a heel sub end; the toe sub end mechanically coupled to an end of the float collar; and the heel sub end mechanically coupled to the wellbore casing.
Further, in another embodiment, the inner diameter of the toe sub end and inner diameter of the heel sub end are equal. In another embodiment, the hollow tube is tapered; inner diameter of the toe sub end is smaller than the inner diameter of the heel sub end. An embodiment wherein the secondary sub is positioned upstream of a float collar in the casing. An embodiment wherein the diameter of the first section is substantially equal to an inner diameter of the casing. An embodiment wherein the diameter of the second section is substantially equal to the smallest inner diameter of all the downhole tools. An embodiment wherein a ratio of the diameter of the first section to the diameter of the second section ranges from 0.4 to 0.9. An embodiment wherein the diameter of the second section is equal to a diameter of the secondary sub. An embodiment wherein an outer section of the second section is substantially not eroded when the second section wipes the downhole tools. An embodiment wherein the first section and the second section further comprises fins extending from an outer surface of the first section and the second section respectively.
An alternative embodiment further comprises a third plug section that is attached and extending from an end of the second section; the end away from the end attached to the first section. In this embodiment, the diameter of the third section is substantially less than the smallest inner diameter of all the downhole tools. A ratio of the diameter of the second section to the diameter of the third section ranges from 0.2 to 0.9. In this embodiment the diameter of the third section is configured to fit into the secondary sub. Further, an outer section of the third section is substantially not touched when the stepped wiper plug wipes the downhole tools and the casing.
| Number | Date | Country | |
|---|---|---|---|
| 62425509 | Nov 2016 | US |
