US20180142528A1

US20180142528A1 - Wiper plug seal integrity system and method

Info

Publication number: US20180142528A1
Application number: US15/814,234
Authority: US
Inventors: Kevin R. George; Raymond C. Shaffer
Original assignee: Geodynamics Inc
Current assignee: Geodynamics Inc
Priority date: 2016-11-22
Filing date: 2017-11-15
Publication date: 2018-05-24
Also published as: CA2985943A1

Abstract

An efficient wiper plug seal integrity system and method for deviated/horizontal wellbore is disclosed. The system/method 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 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.

Description

FIELD OF THE INVENTION

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.

PRIOR ART AND BACKGROUND OF THE INVENTION

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.” FIG. 1 illustrates a wiper plug (0101) that is worn out on one side (0102 a) and transformed into a reduced diameter wiper plug (0102). The downfalls of having a wet shoe in a cemented wellbore casing include possible leak paths, lack of isolation, and no pressure integrity of the casing (10). Therefore, when a pressure casing integrity test fails, the cause of the failure is either a wet shoe or leak in the casing.
As generally seen in the flow chart of FIG. 2 (0200), a preferred exemplary wiper plug seal integrity method with an exemplary secondary sub integrated to a well casing may be generally described in terms of the following steps:

- (1) drilling a wellbore in a hydrocarbon formation (0201);
- (2) installing a wellbore casing in the wellbore along with a float collar and a shoe (0202);
- (3) pumping cement into the wellbore casing (0203);
- (4) pumping the wiper plug at a pumping rate into the wellbore casing (0204);
- (5) pumping water with inhibiting agents behind the wiper plug (0205);
- (6) slowing the pumping rate when the wiper plug approaches the float collar (0206); and
- (7) bumping the wiper plug against the float collar (0207).
  - The wiper plug worn on one side bumps against a float collar and causes water to flow past the plug. This may create a wet shoe condition.

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.

BRIEF SUMMARY OF THE INVENTION

System Overview

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:

- (1) drilling a wellbore in a hydrocarbon formation;
- (2) installing a wellbore casing in the wellbore along with the secondary engagement sub, a float collar and a shoe;
- (3) pumping cement into the wellbore casing;
- (4) pumping the wiper plug at a pumping rate into the wellbore casing;
- (5) pumping water with inhibiting agents behind the wiper plug;
- (6) slowing the pumping rate when the wiper plug approaches close to the secondary engagement sub;
- (7) providing an entry guide for the wiper plug into the secondary engagement sub;
- (8) centralizing and aligning the wiper plug in the secondary engagement sub; and
- (9) locking and latching the wiper plug into the float collar.

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.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 illustrates a prior art wiper plug and a worn wiper plug.

FIG. 2 shows a prior art method for sealing wiper plugs in a cemented wellbore casing.

FIG. 3 illustrates an exemplary system cross section of the secondary engagement sub deployed along with a wellbore casing according to a preferred embodiment of the present invention.

FIG. 4A illustrates an exemplary cross section of secondary engagement sub according to a preferred embodiment of the present invention.

FIG. 4B illustrates an exemplary perspective section of secondary engagement sub according to a preferred embodiment of the present invention.

FIG. 5 illustrates an exemplary flowchart method for wiper plug seal integrity with a secondary engagement sub according to a preferred embodiment of the present invention.

FIG. 6A illustrates an exemplary system cross section of a three stepped diameter wiper plug according to a preferred embodiment of the present invention.

FIG. 6B illustrates an exemplary perspective view of a three stepped diameter wiper plug according to a preferred embodiment of the present invention.

DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS

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 FIG. 3 (0300), wherein a secondary engagement sub (0303) is deployed along with a wellbore casing (0301) in a formation 20. The sub (0303) may be installed above or upstream of a float collar (0304). A shoe (0305) at the toe may be set by cement pumped into the casing. The casing may further be integrated with downhole tools (0302) such as restrictions, sliding sleeve valves, toe valves and the like. When a wiper plug is deployed into a well casing in front of pumped cement, the wiper plug wipes cement stringers off the casing at the same time the lateral length of the horizontal casing may erode or abrade the wiper plug on one side causing a reduction in the overall diameter of the plug. The reduced diameter on one side may enable fluids pumped behind the plug to bypass the plug and create a wet shoe.
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 5⁰to 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 FIG. 4A and FIG. 4B, a guide portion (0420) has a larger inner diameter so that a wiper plug may be guided and aligned into the toe sub end (0402).
As generally seen in the flow chart of FIG. 5 (0500), a wiper plug seal integrity method with an exemplary secondary sub integrated to a well casing may be generally described in terms of the following steps:

- (1) drilling a wellbore in a hydrocarbon formation (0501);
- (2) installing a wellbore casing in the wellbore along with the secondary engagement sub, a float collar and a shoe (0502);
- (3) pumping cement into the wellbore casing (0503);
- (4) pumping the wiper plug at a pumping rate into the wellbore casing (0504);
  - The pumping rate typically ranges from 3 barrels per minute to 15 barrels per minute;
- (5) pumping water with inhibiting agents behind the wiper plug (0505);
  - inhibiting agents may be pumped with water to inhibit premature setting of the cement;
- (6) slowing the pumping rate when the wiper plug approaches close to the secondary engagement sub (0506);
  - The pumping rate may be slowed down such that the worn wiper plug does bump into the sub or the float collar. The pumping rate may slow down to a range from 3 barrels per minute to 4 barrels per minute;
- (7) providing an entry guide for the wiper plug into the secondary engagement sub (0507);
  - 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 smaller diameter of the sub. The sub provides a tapered entry guide and seal sub directly above the float collar
- (8) centralizing and aligning the wiper plug in the secondary engagement sub (0508); and
  - 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 ensure it is properly latched into the locked position.
- (9) locking and latching the wiper plug into the float collar (0509).
  - The latching or sealing the worn wiper plug into a float collar or the secondary sub obstructs water from bypassing the plug and prevents a wet shoe. The secondary sub enables the cement to set without creating a wet shoe and furthermore enable a pressure integrity test to be performed without a leak in the toe of the casing.

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 FIG. 6A (0600) and FIG. 6B (0620). The second section (0602) may be attached or connected to the first section (0601) at an end (0604) of the first plug (0601) and said second section (0602) may extend outwards from the connected end (0604) of the first section (0601). The first section (0601) may have a diameter (0611) larger than a diameter (0612) of the second section (0602). As cement is pumped down in front of the stepped wiper plug, stringers or cement debris may be stuck to the inside of the casing and the inside of the downhole tools. The diameter (0611) of the first section (0601) is chosen such that the first section may wipe an inner or inside portion of the casing. For example, if the inner diameter of the casing is 4.67 inches, the diameter of the first section of the wiper plug may be chosen to be about 4.67 inches. According to a preferred exemplary embodiment the diameter the first section (0611) is substantially equal to an inner diameter of the casing. The diameter of the first section may range from 3 inches to 8 inches. The diameter (0612) of the second section (0602) may be designed to wipe inner portions of downhole tools in the casing. 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 second section may be chosen to be about 3.25 inches. According to another preferred exemplary embodiment, the diameter of the second section is substantially equal to the smallest inner diameter of all the downhole tools. The diameter (0612) of the second section may range from 1 inch to 6 inches. According to a preferred exemplary embodiment, when the stepped wiper plug (0600) enters a secondary sub in a toe end of the casing, the second section aligns into the sub and substantially obstructs fluid flow past the stepped wiper plug. According to another preferred exemplary embodiment the secondary sub is positioned upstream of a float collar in the casing. The secondary sub may be similar to the sub (0303) as illustrated in FIG. 3. According to a further preferred exemplary embodiment a ratio of the diameter (0611) of the first section (0601) to the diameter (0612) of the second section (0602) ranges from 0.4 to 0.9. According to yet another preferred exemplary embodiment the diameter of the second section is equal to an inside diameter of the secondary sub. An outer section of the second section is substantially not eroded when the second section wipes the downhole tools. The first section (0601) may wipe longer lateral distances in the casing that may range from 5,000 to 25,000 feet. The second section (0602) may wipe shorter distances inside of downhole tools and the distances may range from 500 to 2,000 feet. The first section and the second section may further comprise fins extending from an outer surface of the first section and the second section respectively. The fins may be elastomeric or rigid.
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.

Claims

What is claimed is:

1. An apparatus for sealing a casing with a wiper plug; said apparatus comprising

(a) a hollow tubular shaped secondary engagement sub having a toe sub end and a heel sub end; and

(b) an inner diameter surface having an entry guide portion near the heel sub end;

wherein said wiper plug enters said heel sub end and engages he inner diameter surface;

wherein said wiper plug produces a fluid seal with the secondary engagement sub.

2. The apparatus of claim 1 wherein the inner diameter surface of said secondary engagement sub is configured to enable substantially unobstructed entry of said wiper plug into said secondary engagement sub.

3. The apparatus of claim 1 further comprises:

(c) a float collar coupled to the toe sub end; and

(d) a wellbore casing coupled to the heel sub end of the secondary engagement sub.

4. The apparatus of claim 3 wherein said wellbore casing has an inner diameter and a ratio of said inner diameter of said secondary engagement sub to the inner diameter of said wellbore casing is less than 0.9.

5. The apparatus of claim 1 wherein an inner diameter of said toe sub end and an inner diameter of said heel sub end are equal.

6. The apparatus of claim 1 wherein an inner diameter of said toe sub end is smaller than an inner diameter of said heel sub end.

7. A wiper plug seal integrity method, said method operating in conjunction with a wiper plug seal integrity system in a wellbore casing comprising a secondary engagement sub;

said secondary engagement sub is a hollow tubular member that is positioned upstream of a float collar; said float collar is integrated at a toe end of said wellbore casing;

an inner diameter of said secondary engagement sub is configured to enable substantially unobstructed entry of said wiper plug; and

said secondary engagement sub is configured to latch said wiper plug thereon into a locked position when said wiper plug enters said secondary engagement sub;

wherein said method comprises the steps of:

(1) pumping cement into said wellbore casing;

(2) pumping said wiper plug at a pumping rate into said wellbore casing;

(3) pumping a fluid behind said wiper plug;

(4) slowing said pumping rate when said wiper plug approaches close to said secondary engagement sub;

(5) providing an entry guide portion for said wiper plug into said secondary engagement sub;

(6) centralizing and aligning said wiper plug in said secondary engagement sub; and

(7) locking and latching said wiper plug into said float collar.

8. The method of claim 7 wherein said inner diameter of said secondary engagement sub is configured to enable substantially unobstructed entry of said wiper plug into said secondary engagement sub.

9. The method of claim 7 wherein ratio of said inner diameter of said secondary engagement sub to an inner diameter of said wellbore casing is less than 0.9.

10. The method of claim 7 wherein said secondary engagement sub further comprises a toe sub end and a heel sub end; said toe sub end coupled to an end of said float collar; and said heel sub end coupled to said wellbore casing.

11. The method of claim 7 wherein an inner diameter of said toe sub end and an inner diameter of said heel sub end are equal.

12. The method of claim 7 wherein an inner diameter of said toe sub end is substantially smaller than an inner diameter of said heel sub end.

13. A stepped wiper plug for use in a wellbore casing; said stepped wiper plug comprising

(a) a hollow cylindrical shaped first section and

(b) a hollow cylindrical shaped second section attached to and extending from said first section;

wherein said first section has a diameter larger than a diameter of said second section; said first section configured to wipe an inner portion of said casing; said second section configured to wipe inner portions of downhole tools in said casing.

14. The stepped wiper plug of claim 13 wherein a ratio of said diameter of said first section to said diameter of said second section ranges from 0.4 to 0.9

15. The stepped wiper plug of claim 13 wherein said diameter of said second section is equal to a diameter of a secondary engagement sub.

16. The stepped wiper plug of claim 13 wherein said first section and said second section further comprises fins extending from an outer surface of said first section and said second section respectively.

17. The stepped wiper plug of claim 13 further comprises

(c) a third section that is attached and extending from an end of said second section.

18. The stepped wiper plug of claim 17 wherein a diameter said third section is less than an inner diameter of said downhole tools.

19. The stepped wiper plug of claim 17 wherein a ratio of said diameter of said second section to said diameter of said third section ranges from 0.2 to 0.9

20. The stepped wiper plug of claim 13 wherein said downhole tools are selected from a group comprising: sliding sleeve valves, restrictions, or toe valves.