DOWNHOLE PLUGS HAVING SINGLE ANCHORING MECHANISMS AND METHODS THEREOF

Abstract

Downhole plugs having single anchoring mechanisms and methods thereof are disclosed. The plug comprises of inner mandrel with proximal portion and distal portion, outer assembly and one or more retaining members. The outer assembly comprises of support element, elastomeric element for sealing the gap between the plug and casing, anchoring mechanism at the distal portion for anchoring the plug to the casing and nose element. The elastomeric element is retained in a compressed state at the downhole end by the anchoring mechanism and at the up hole end by the retaining members. In some embodiments, the retaining members are snap rings that are pushed down from step portions at the proximal portion when the plug is mobilized to a set position thereby retaining the elastomeric element. In some embodiments, the retaining members are ratcheted open rings that ratchet over the proximal portion thus retaining the elastomeric element.

Description

RELATED APPLICATION AND PRIORITY CLAIM

The present disclosure claims priority from pending U.S. Provisional Patent application No. 62/352,019 filed on: 20 Jun. 2016, the pending application being incorporated in its entirety into the present application, to the extent not inconsistent with the disclosure herein.

TECHNICAL FIELD

The present disclosure generally relates to tools used for isolation in well bores. More particularly, the present disclosure relates to downhole plugs having single anchoring mechanisms and methods thereof.

BACKGROUND

Technological innovations in the oil and gas industry are primarily focused on the exploration and production business. Due to low permeability in the shale rocks and tight sands deep under the ground, it is extremely difficult to drill and stimulate production of crude oil otherwise popularly known as “black gold”. Hence the unconventional directional drilling associated with the Plug and Perf operations and the hydraulic fracturing process has been getting popularity from the wildcat wells to promising drill pads. Hydraulic fracturing has been of late getting lots of interests in the gas exploration and production process. It is a gas well stimulation and extraction technique designed for areas underlain by large shale formations found a mile or more below the ground surface.

Composite materials have replaced metals in various engineering applications owing to their numerous advantages, like high strength/weight ratio and other better physical properties. Due to these advantages, there has been an increasing demand for use of these materials in manufacturing frac and bridge plugs. Though composite plugs have the advantages of having lesser weight, being deployable downhole at a faster speed and being millable within a shorter duration as compared with conventional plugs, it would be desirable to have plugs that are even shorter than the existing ones with a lesser milling duration.

The present invention discloses shorter downhole plugs with a single anchoring mechanism. The plugs are set downhole in the same manner as conventional plugs. During the setting process, the elastomer in the plug seals a gap between the plug and the casing and the slips anchor the plug to the casing. Then, fluid pumped into the well will cause the frac ball to seat on the frac seat in case of frac plugs, sealing the through hole of the composite mandrel. Once the ball is seated and perforation is carried out resulting in mild and tiny cracks around the explosion zone, the pumping of sand, water and chemical additives into the well at very high pressures of about 10,000 PSI results in further cracking/fracturing of the initially perforated fissures. Once all the fracking stages are performed, the plugs will be milled out to tiny pieces with a cutting tool such as bit, thereby opening the bore for the production.

The overall length of the plugs disclosed herein is about half the length of many conventional plugs. This reduced length is favored by oil operators as it proffers many advantages including a shorter milling time.

For a plug to completely set in a casing, two things need to happen: (i) the teeth on the slips should bite into the external casing and anchor the plug in place, preventing it from moving under the influence of external pressures, and (ii) the compressed and energized elastomer should be held in place and prevented to relax and return to its initial state. Conventional plugs have slips on either side of the elastomer that prevent the compressed elastomer from relaxing. The novel plug disclosed herein has only a single slip system at the down hole end of the elastomer and meets the two requirements for the setting process in the following manner:

In theory, a frac plug only ever experiences external pressures from the up hole end during fracking. Any pressure from the downhole side unseats the frac ball and the fluid is allowed to pass across the plug through the internal diameter. So, this would mean that the frac plug only needs to be anchored against the casing in one direction. The novel frac plug uses only a single slip system at the down hole end of the elastomer with teeth facing the downhole direction for anchoring to the casing against up hole differential pressures.

The second requirement of holding the compressed elastomer in its energized state is achieved as described herein. At the downhole end, the lower and only slip system prevents the elastomer from relaxing, as in any other conventional plug. The novel design in this plug comes in the manner in which the elastomer element is held compressed from the up hole end in the absence of a second slip. This is achieved by using retaining members such as snap rings for retaining the elastomer in a compressed state from the up hole end thus negating the need for a second slip system at the up hole end of the elastomer element thus reducing the length and milling time of this novel plug.

SUMMARY

The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key/critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

Exemplary embodiments of the present disclosure are directed towards downhole plugs having single anchoring mechanism. The plug comprises of a substantially cylindrical hollow inner mandrel, a substantially cylindrical hollow outer assembly and one or more retaining members. The mandrel has a proximal portion configured to be oriented up hole and a distal portion configured to be oriented downhole. The outer assembly is disposed circumferentially around the mandrel and comprises of a support element that is disposed at the proximal portion, an elastomeric element, an anchoring mechanism and a nose element that engages the distal portion. The elastomeric element is disposed between the support element and the anchoring mechanism and is configured for sealing a gap between the plug and a casing. The elastomeric element has an up hole end contacting the support element and a downhole end contacting the anchoring mechanism. The anchoring mechanism is configured for securely anchoring the plug to the casing and for retaining the elastomeric element in a compressed state from the downhole end after the plug is mobilised to a set position. The retaining members are housed within the support element and are configured for being pushed in a unidirectional manner towards the downhole direction during setting of the plug. The retaining members are further configured for retaining the elastomeric element in a compressed state from the up hole end by preventing the support element from backing off after the plug is mobilized to the set position. In some embodiments, the retaining members are snap rings that are pushed down from step portions at the proximal portion when the plug is mobilized to a set position thereby retaining the elastomeric element. In some embodiments, the retaining members are ratcheted open rings that ratchet over the proximal portion thus retaining the elastomeric element.

Other exemplary embodiments of the present subject matter are directed towards methods for isolating a well bore by using a downhole plug having a single anchoring mechanism. The method begins with the step of providing a plug as described in the previous paragraph followed by deploying the plug into the well bore to a predetermined location. The plug is then mobilized from an unset position to a set position, wherein the anchoring mechanism anchors the plug to the casing, the elastomeric element seals the gap between the plug and the casing and the retaining member is pushed in a unidirectional manner towards the downhole direction. The last step is releasing the plug form the setting tool, wherein the anchoring mechanism retains the elastomeric element in a compressed state from the downhole end and the retaining member retains the elastomeric element in a compressed state from the up hole end by preventing the support element from backing off.

It is an object of the present invention to disclose shorter plugs that are easier to handle, transport and use.

It is another object of the present invention to disclose shorter plugs with reduced milling time thereby reducing downtime and lowering expenses on drilling fluid.

The two slip systems of conventional plugs are made of cast iron and hence those plugs have a longer milling time. It is another object of the present invention to disclose plugs with a single slip system that result in reduced milling time.

It is another object of the present invention to disclose plugs with retaining members at up hole end that ensure a failsafe locking method to prevent the elastomer from relaxing and also ensures that the elastomer is always compressed and energized leading to a perfect seal.

Furthermore, the objects and advantages of this invention will become apparent from the following description and the accompanying annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, in conjunction with the accompanying drawings, wherein like reference numerals have been used to designate like elements, and wherein:

FIG. 1 is a schematic representation of an isometric view of a frac plug, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 2 is a schematic representation of an exploded view of a frac plug, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 3A is a schematic representation of a longitudinal section of a frac plug having a single step and multiple snap rings in an unset position, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 3B is a schematic representation of a sectional view of a portion of a frac plug having a single step and multiple snap rings in a set position, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 4A is a schematic representation of a longitudinal section of a frac plug having multiple steps and a single snap ring in an unset position, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 4B is a schematic representation of a sectional view of a portion of a frac plug having multiple steps and a single snap ring in a set position, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 5 is a schematic representation of an isometric view of an inner mandrel having multiple steps, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 6A is a schematic representation of a longitudinal section of a frac plug having an open ring mounted over an inner mandrel with ratchet threads in an unset position, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 6B is a schematic representation of a sectional view of a portion of a frac plug having an open ring mounted over an inner mandrel with ratchet threads in a set position, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 7 is a schematic representation of an isometric view of an open ring showing the ratchet threads on an inner surface, in accordance with a non limiting exemplary embodiment of the present disclosure.

FIG. 8 is a schematic representation of a side view of an inner mandrel having ratchet threads, in accordance with a non limiting exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The present disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

The use of “including”, “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. Further, the use of terms “first”, “second”, and “third”, and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another.

According to different non limiting exemplary embodiments of the present disclosure, downhole plugs having single anchoring mechanisms are disclosed.

In accordance to different non limiting exemplary embodiments of the present disclosure, methods for isolating well bores by using downhole plugs having single anchoring mechanisms are disclosed.

Referring to FIGS. 1 and 2, they depict a frac plug 100 comprising a substantially cylindrical hollow inner mandrel 102, a substantially cylindrical hollow outer assembly 104 and multiple retaining members. The mandrel 102 has a proximal portion 120 configured to be oriented up hole and a distal portion 122 configured to be oriented downhole. The outer assembly 104 is disposed circumferentially around the mandrel 102 and comprises of a top element 106 that engages the proximal portion 120, a support element 108 that is positioned adjacent to the top element 106 at the proximal portion, an elastomeric element 110, an anchoring mechanism and a nose element 116 that engages the distal portion.

The elastomeric element 110 is disposed between the support element 108 and the anchoring mechanism and is configured for sealing a gap between the plug 100 and a casing. The elastomeric element 110 has an up hole end 124 contacting the support element 108 and a downhole end 126 contacting the anchoring mechanism.

The anchoring mechanism is configured for securely anchoring the plug 100 to the casing and for retaining the elastomeric element 110 in a compressed state from the downhole end 126 after the plug 100 is mobilised to a set position. In this particular embodiment, the anchoring mechanism comprises of a slip system 114 having teeth facing a downhole direction and a conical ring element 112 contacting the downhole end 126 of the elastomeric element 110. When the plug 100 is mobilized into the set position, the slip system 114 rides over the conical ring element 112 thereby breaking and expanding outward followed by biting into the casing and anchoring the plug 100 to the casing. Other than the anchoring mechanism disclosed herein, any other anchoring mechanism known in the art that can efficiently anchor the plug to the casing can be used without limiting the scope of the present disclosure.

The retaining members are housed within the support element 108 and are configured for being pushed in a unidirectional manner towards the downhole direction during setting of the plug 100. The retaining members are further configured for retaining the elastomeric element 110 in a compressed state from the up hole end 124 by preventing the support element 108 from backing off after the plug 100 is mobilized to the set position. In different embodiments, the retaining members are expanding rings that are flexible, semi-flexible and/or resilient. In different embodiments, the expanding rings can be closed, nearly closed or open rings without limiting the scope of the present disclosure. In different embodiments, the expanding rings can be retaining rings such as snap rings, split rings, circlips, spiral rings, wave rings or any other retaining ring known in the art without limiting the scope of the present disclosure. The expanding rings can be circular or non-circular without limiting the scope of the present disclosure. The retaining members can be one or more in number depending on specific applications without limiting the scope of the pre sent disclosure.

Referring specifically to FIG. 1, the outer components of the frac plug are shown. The mandrel 102 is the inner central part over which all the other components of the plug are assembled. These include, the top element 106 which is pushed on by a setting sleeve and setting tool during the plug setting process, the support element 108 which houses a set of snap rings (not shown here) on its inner side and also adds support to the elastomeric element 110 that seals against the casing to hold pressure once the plug 100 is set. Supporting the elastomeric element 110 the other end is the conical ring element 112 which has a tapered profile at one end. The metal slip 114 rides up on this tapered surface of the conical ring element 112 by breaking and expanding outward after which it bites into the casing anchoring the frac plug 100 in place. All of these outer components are held in place by a nose element 116 which is screwed onto the threads on the lower end of the mandrel 102. This frac plug 100 also includes a set of three anti-preset screws 118 which are screwed into the top element 106 and sit in a groove on the mandrel 102.

Referring specifically to the exploded view of the frac plug in FIG. 2, the outer assembly components and their sequence of arrangement over the mandrel 102 can be seen clearly. In this particular embodiment, the proximal portion 120 of the mandrel 102 has a circumferential retaining step portion 128 over which three snap rings 130 are expanded and assembled. The support element 108 goes over the snap rings 130 and supports the elastomeric element 110 from its up hole end 124. The remaining parts work in a manner similar to any conventional frac plug and are well known in the art.

The circumferential step portion 128 is significant to the invention and design of this plug. In different embodiments, the number and dimensions of the circumferential step portions could vary depending on specific applications and the type and number of the retaining member(s) that are used without limiting the scope of the present disclosure.

Referring to FIGS. 3A and 3B, they depict a frac plug 100, having a single step and multiple snap rings, in an unset position and a set position respectively. The frac plug 100 components, namely the mandrel 102 with the step portion 128, the top element 106, the support element 108, snap rings 130, elastomeric element 110, conical ring element 112, slip system 114, nose element 116 and anti-preset screws 118 as well as the arrangement of the components with each other can be seen clearly. The anti-preset screws 118 prevent the accidental setting of the plug 100, commonly known as presetting. In this way, for the setting process to begin, the anti-preset screws 118 must shear against the wall of the groove 119 on the mandrel 102 inside which they sit. These are low strength screws and shear first to begin the process of setting the plug. In this particular embodiment, three snap rings 130 serve as retaining members. These snap rings 130 mimic the function of the second slip of the conventional frac plugs by retaining the elastomeric element 110 in its energized or compressed state and preventing it from relaxing. It is important to note here that when the plug 100 is in an unset position, the snap rings 130 mounted over the mandrel are not in their free and relaxed state but are in a radially expanded state. In this state, they act as a spring ready to relax and snap back into place. When the plug 100 is mobilized to the set position, one or more of the snap rings 130 are pushed down from the step portion 128 to a step base 132 and the snap rings 130 change into a relaxed state in the step base 132, as shown in FIG. 3B, thus retaining the elastomeric element 110 in a compressed state.

Conventional frac plugs usually have two slips on either end of the elastomeric element for anchoring the plug to the casing and to retain the elastomeric element in an energized or compressed state. Since this plug is only a ball drop frac plug, it sees pressures only from the up hole end and none from the downhole end. The slips at the distal portion anchor the plug to the casing against this up hole pressure. The only purpose of a conventional second metal slip at the proximal portion would be to prevent the element from relaxing. This purpose is served by the snap rings in this plug. When the setting process begins, the setting tool applies force on the top element. This pushes the support element and the snap rings inside it towards the downhole direction over the mandrel. Once the snap rings cross the step in the mandrel, they snap back to their relaxed and smaller state and sit on the step base where the outer diameter of the mandrel is lesser than that of the step portion. One by one, the snap rings snap down into their relaxed state on the mandrel. Once the plug is set, the energized elastomeric element pushes back onto the support element which transfers the force to the snap rings. The snap rings cannot be pushed further back towards the up hole direction because of the step in the mandrel. Hence these rings now serve the purpose of a conventional second metal slip at the proximal portion and retain the elastomeric element in a compressed state by preventing the support element from backing off.

Referring to FIGS. 4A and 4B, they depict a frac plug 400, having multiple steps and a single snap ring, in an unset position and a set position respectively. Referring to FIG. 5, the proximal portion of the mandrel 402 has a series of circumferential retaining step portions 428 with the outer diameter of the proximal portion 420 increasing progressively from the lowermost step portion to the uppermost step portion 428. The retaining member in this embodiment is a snap ring 430 that is mounted over the uppermost step portion 428 of the mandrel 402. When the plug 400 is in an unset position, the snap ring 430 is in a radially expanded state over the uppermost step portion 428. When the plug 400 is mobilized to a set position, the top element 406 is pushed in a downhole direction by a setting sleeve of the setting tool which in turn pushes the snap ring 430 down the series of steps. In some embodiments, the frac plugs 400 have multiple steps and multiple snap rings for retaining the elastomeric element 410. The snap rings 430 that are pushed to a lower step change into a partially relaxed state and those that are pushed down to the step base 432 change into a completely relaxed state. The snap rings 430 at the partially or completely relaxed state pushes against the steps of the mandrel 402 and cannot move back in the up hole direction thus preventing the support element 408 from backing off. This ensures that the elastomeric element 410 is retained in a compressed state and prevents its relaxation thus negating the need for a conventional second slip at the proximal portion 420 the frac plug 400.

Referring to FIGS. 6A and 6B, they depict a frac plug 600, having an open ring mounted over an inner mandrel with ratchet thread, in an unset position and a set position respectively. The retaining member in this particular embodiment is an open metal ring 630 having ratchet threads 640 on its inner surface 644 as shown in FIG. 7. Referring to FIG. 8, it shows the mandrel 602, wherein an outer surface 642 of the proximal portion 620 is partially threaded with ratchet threads 638. The ratchet threads 640 on the inner surface 644 of the open ring 630 has corresponding dimensions with the ratchet threads 638 of the mandrel 602 thus enabling the open ring 630 to ratchet over the mandrel 602 in a unidirectional manner when the plug 600 is mobilized to the set position. Here, the elastomeric element 610 is retained in a compressed state by the open ring 630 that prevents the support element 608 from backing off.

The downhole plugs disclosed herein specifically pertain to frac plugs, though other plugs used for isolation in well bores such as bridge plugs are also within the scope of the present invention. This design minimizes the length and the milling time of the plug. In some embodiments, the length of the frac plug is about 12 inches. The plug is preferably made of fiber composite material though metal plugs or plugs made partly of metal and partly of composite are also within the scope of the pre sent disclosure.

In accordance with a non limiting exemplary embodiment of the present subject matter, a method for isolating a well bore by using a downhole plug having a single anchoring mechanism is disclosed. The method begins with the step of providing a plug as described above followed by deploying the plug into the well bore to a predetermined location. The plug is then mobilized from an unset position to a set position, wherein the anchoring mechanism anchors the plug to the casing, the elastomeric element seals the gap between the plug and the casing and the retaining member is pushed in a unidirectional manner towards the downhole direction. The last step is releasing the plug form the setting tool, wherein the anchoring mechanism retains the elastomeric element in a compressed state from the downhole end and the retaining member retains the elastomeric element in a compressed state from the up hole end by preventing the support element from backing off.

Although the present disclosure has been described in terms of certain preferred embodiments and illustrations thereof, other embodiments and modifications to preferred embodiments may be possible that are within the principles and spirit of the invention. The above descriptions and figures are therefore to be regarded as illustrative and not restrictive.

Thus the scope of the present disclosure is defined by the appended claims and includes both combinations and sub combinations of the various features described herein above as well as variations and modifications thereof, which would occur to persons skilled in the art upon reading the foregoing description.

Claims

1. A downhole plug having a single anchoring mechanism, the plug thereof comprising:

a) a substantially cylindrical hollow inner mandrel, the mandrel thereof having a proximal portion configured to be oriented up hole and a distal portion configured to be oriented downhole;

b) a substantially cylindrical hollow outer assembly being disposed circumferentially around the mandrel, the outer assembly thereof comprising a support element, an elastomeric element, an anchoring mechanism and a nose element, the support element thereof being disposed at the proximal portion, the elastomeric element being disposed between the support element and the anchoring mechanism, the elastomeric element thereof being configured for sealing a gap between the plug and a casing, the elastomeric element thereof having an up hole end contacting the support element and a downhole end contacting the anchoring mechanism, the anchoring mechanism thereof being configured for securely anchoring the plug to the casing, the anchoring mechanism further being configured for retaining the elastomeric element in a compressed state from the down hole end after the plug is mobilized to a set position and the nose element thereof engaging the distal portion; and

c) at least one of a retaining member, the retaining member being housed within the support element, the retaining member thereof being configured for being pushed in a unidirectional manner towards a downhole direction during setting of the plug, the retaining member thereof further being configured for retaining the elastomeric element in a compressed state from the up hole end by preventing the support element from backing off after the plug is mobilized to the set position.

2. The plug as claimed in claim 1, wherein the proximal portion has a circumferential retaining step portion, wherein the retaining member is an expanding ring, the expanding ring thereof being mounted over the step portion, the expanding ring thereof being in a radially expanded state when the plug is in an unset position, at least one of the expanding ring being configured to be pushed down from the step portion to a step base when the plug is mobilized to the set position, the expanding ring that is pushed down from the step portion changing into a relaxed state over the step base thereby retaining the elastomeric element in a compressed state.

3. The plug as claimed in claim 2, wherein the expanding rings are three in number.

4. The plug as claimed in claim 2, wherein the expanding ring is an open ring.

5. The plug as claimed in claim 4, wherein the open ring is a snap ring.

6. The plug as claimed in claim 1, wherein the proximal portion has a series of circumferential retaining step portions, the proximal portion thereof having an outer diameter associated therewith, the proximal portion thereof progressively increasing in the outer diameter from the lowermost step portion to the uppermost step portion, wherein the retaining member is an expanding ring, the expanding ring thereof being mounted over the uppermost step portion, the expanding ring thereof being in a radially expanded state when the plug is in an unset position, at least one of the expanding ring configured for being pushed down from the uppermost step portion to a lower position when the plug is mobilized to the set position, the expanding ring that is pushed down from the uppermost step portion changing into a relatively relaxed state at the lower position thereby retaining the elastomeric element in a compressed state.

7. The plug as claimed in claim 6, wherein the lower position is a step base.

8. The plug as claimed in claim 6, wherein the expanding ring is an open ring.

9. The plug as claimed in claim 8, wherein the open ring is a snap ring.

10. The plug as claimed in claim 1, wherein an outer surface of the proximal portion is partially threaded with ratchet threads, wherein the retaining member is an expanding ring having ratchet threads on an inner surface, wherein the ratchet threads of the expanding ring have corresponding dimensions with the ratchet threads of the proximal portion to enable the expanding ring to ratchet over the proximal portion from an up hole direction towards the downhole direction when the plug is mobilized from an unset position to the set position thereby retaining the elastomeric element in a compressed state.

11. The plug as claimed in claim 10, wherein the expanding ring is an open ring.

12. The plug as claimed in claim 1, wherein the anchoring mechanism comprises of a slip system having teeth facing the downhole direction and a conical ring element, the conical ring element thereof contacting the downhole end of the elastomeric element, the slip system thereof being configured for riding over the conical ring element when the plug is mobilized into the set position thereby breaking and expanding outward followed by biting into the casing and anchoring the plug to the casing.

13. The plug as claimed in claim 1, wherein the plug is a frac plug.

14. The plug as claimed in claim 1, wherein the plug is substantially made of composite material.

15. The plug as claimed in claim 1, wherein the plug has a length of about 12 inches.

16. A method for isolating a well bore by using a downhole plug having a single anchoring mechanism, the method thereof comprising:

a) providing a downhole plug, the plug thereof comprising:

a substantially cylindrical hollow inner mandrel, the mandrel thereof having a proximal portion configured to be oriented up hole and a distal portion configured to be oriented downhole;

a substantially cylindrical hollow outer assembly being disposed circumferentially around the mandrel, the outer assembly thereof comprising a support element, an elastomeric element, an anchoring mechanism and a nose element, the support element thereof being disposed at the proximal portion, the elastomeric element being disposed between the support element and the anchoring mechanism, the elastomeric element thereof being configured for sealing a gap between the plug and a casing, the elastomeric element thereof having an up hole end contacting the support element and a downhole end contacting the anchoring mechanism, the anchoring mechanism thereof being configured for securely anchoring the plug to the casing, the anchoring mechanism further being configured for retaining the elastomeric element in a compressed state from the down hole end after the plug is mobilized to a set position and the nose element thereof engaging the distal portion; and

at least one of a retaining member, the retaining member being housed within the support element, the retaining member thereof being configured for being pushed in a unidirectional manner towards a downhole direction during setting of the plug, the retaining member further being configured to retain the elastomeric element in a compressed state from the up hole end by preventing the support element from backing off after the plug is mobilized to the set position;

b) deploying the plug into a well bore to a predetermined location;

c) mobilizing the plug from an unset position to the set position, the anchoring mechanism thereof anchoring the plug to the casing, the elastomeric element thereof sealing the gap between the plug and the casing and the retaining member thereof being pushed in a unidirectional manner towards the downhole direction; and

d) releasing the plug from a setting tool, the anchoring mechanism thereof retaining the elastomeric element in a compressed state from the downhole end and the retaining member thereof retaining the elastomeric element in a compressed state from the up hole end by preventing the support element from backing off.

17. The method as claimed in claim 16, wherein the proximal portion has a circumferential retaining step portion, wherein the retaining member is an expanding ring, the expanding ring thereof being mounted over the step portion, the expanding ring thereof being in a radially expanded state when the plug is in the unset position, at least one of the expanding ring being pushed down from the step portion to a step base when the plug is mobilized to the set position, the expanding ring that is pushed down from the step portion changing into a relaxed state over the step base thereby retaining the elastomeric element in a compressed state.

18. The method as claimed in claim 17, wherein the expanding rings are three in number.

19. The method as claimed in claim 17, wherein the expanding ring is an open ring.

20. The method as claimed in claim 19, wherein the open ring is a snap ring.

21. The method as claimed in claim 16, wherein the proximal portion has a series of circumferential retaining step portions, the proximal portion thereof having an outer diameter associated therewith, the proximal portion thereof progressively increasing in the outer diameter from the lowermost step portion to the uppermost step portion, wherein the retaining member is an expanding ring, the expanding ring thereof being mounted over the uppermost step portion, the expanding ring thereof being in a radially expanded state when the plug is in the unset position, at least one of the expanding ring being pushed down from the uppermost step portion to a lower position when the plug is mobilized to the set position, the expanding ring that is pushed down from the uppermost step portion changing into a relatively relaxed state at the lower position thereby retaining the elastomeric element in a compressed state.

22. The method as claimed in claim 21, wherein the lower position is a step base.

23. The method as claimed in claim 21, wherein the expanding ring is an open ring.

24. The method as claimed in claim 23, wherein the open ring is a snap ring.

25. The method as claimed in claim 16, wherein an outer surface of the proximal portion is partially threaded with ratchet threads, wherein the retaining member is an expanding ring having ratchet threads on an inner surface, wherein the ratchet threads of the expanding ring have corresponding dimensions with the ratchet threads of the proximal portion, the expanding ring thereof ratcheting over the proximal portion from an up hole direction towards the downhole direction when the plug is mobilized from the unset position to the set position thereby retaining the elastomeric element in a compressed state.

26. The method as claimed in claim 25, wherein the expanding ring is an open ring.

27. The method as claimed in claim 16, wherein the plug is a frac plug.