Easy drill slip with degradable materials

Slip elements for a bridge plug include an inner body portion that is substantially formed of a material that is degradable by dissolution in response to a dissolving fluid and a hardened, resilient, radially outer contact portion. The outer contact portion includes a plurality of openings that function as stress risers. The inner body portion may be formed of magnesium powder.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the design of bridge plug slips.

2. Description of the Related Art

Bridge plugs are used to form closures in a flowbore. Typically, bridge plugs have a plug body with slip elements that can be selectively moved radially outwardly to bitingly engage a surrounding tubular member. One type of bridge plug is described in U.S. Pat. No. 6,167,963 issued to McMahan et al. That patent is owned by the assignee of the present application and is incorporated herein by reference.

Often, a bridge plug will need to be removed after it has been set, and this is usually done by milling through the plug. Unfortunately, milling through most conventional bridge plug designs leaves large pieces which may be difficult to circulate out of the flowbore.

SUMMARY OF THE INVENTION

The present invention provides a design for a bridge plug wherein the slip elements of the bridge plug include an inner body portion that is substantially formed of a material that is degradable by dissolution in response to a dissolving fluid and a hardened, resilient, radially outer contact portion. In described embodiments, the outer contact portion is substantially formed of a hardened material, such as cast iron, that is shaped to provide for biting into a surrounding tubular member. In described embodiments, the outer contact portion extends from the upper end of the slip element to the lower end of the slip element. Also in described embodiments, the outer contact portion includes a plurality of openings that function as stress risers.

In described embodiments, the inner body portion is substantially formed of a material that is dissolvable in response to a dissolving agent. In one current embodiment, the dissolvable material forming the inner body portion comprises magnesium powder. When the dissolvable material is magnesium powder, the dissolving agent may be potassium chloride (kcl).

As described, the slip inserts are cast within a surrounding molding to create a slip ring which can then be disposed onto the setting cone of the bridge plug. In described embodiments, the molding is a phenolic material which provides a laminate covering for the slip elements that protects the dissolvable material against premature dissolution.

In operation, the bridge plug is disposed into a flowbore and then set. When it is desired to remove the bridge plug from the flowbore, a milling device is used. During removal of the plug by milling, the molding of the slip ring is ruptured by the mill, which exposes the dissolvable material forming the inner body portions to wellbore fluid which contains the dissolving agent. The dissolving agent dissolves away the inner body portions, leaving the outer contact portions of the slip elements. The presence of openings disposed through the outer contact portions assists in disintegration of the outer contact portions into smaller component parts via operation of the milling device. The outer contact portions, or portions thereof, and other components of the bridge plug may be circulated out of the wellbore via fluid returns.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1depicts an exemplary bridge plug device10constructed in accordance with the present invention. It is noted that the term “bridge plug,” as used herein, is meant to refer expansively to a class of devices that use radially moveable slip elements to be mechanically set within a flowbore, including locks, plugs, and anchors. The bridge plug device10includes a setting cone12which is generally cylindrical. The outer radial surface14of the setting cone12includes a plurality of angled ramps16which are separated by guides18. A slip element20, constructed in accordance with the present invention, is located upon each of the ramps16.

In preferred embodiments, the slip elements20are cast within a surrounding molding21, which is best seen inFIG. 6. In particular embodiments, the molding21is formed of a phenolic resin and is cast in an annular ring shape having sheaths23. The sheaths23each encase one of the slip elements20. The molding21forms a slip ring which, asFIG. 1illustrates, is disposed onto the setting cone12to form the bridge plug10.

The slip elements20are moveable upon the ramps16of the setting cone12between the retracted, unset position shown inFIG. 1and a set position, wherein the slip elements20are moved upon the ramps16, in a manner known in the art, radially outwardly with respect to the setting cone12. In the set position, the slip elements20of the bridge plug10are brought into engagement with a surrounding tubular member.

The structure of the slip elements20is better appreciated with reference toFIGS. 2 and 3. AsFIG. 2shows, the slip element20has a slip body which includes a radially inner body portion22and an outer contact portion24. The inner body portion22is formed of a material that is substantially dissolvable in response to a dissolving agent. In a current embodiment, the inner body portion22is formed of magnesium-based composite powder compact.FIG. 4illustrates the inner body portion22apart from other components. The inner body portion22is generally wedge shaped. The inner body portion22may be formed by high-pressure compression at high temperatures. Thereafter, the part is shaped by known mechanical processes.

In the instance wherein the dissolvable material is magnesium-based composite-powder compact, the dissolving agent may comprise various brines or acids often used in an oil or gas well. The brines include, but are no limited to, potassium chloride (kcl), sodium chloride (NaCl) and calcium chloride/calcium bromine (Ca2Cl/CaBr2). The acids include, but are not limited to, hydrogen chloride, acetic acid and formic acid. In particular embodiments, the dissolving agent is a solution that includes from about 2% to about 5% potassium chloride. In a particularly preferred embodiment, the dissolving agent is a solution that includes about 3% potassium chloride.

Also in present embodiments, the inner body portions22are entirely covered by the phenolic material forming the molding21. AsFIG. 1illustrates, the contact surfaces26of the outer contact portions24may extend radially outside of the sheaths23. This material acts as a laminate that separates the dissolvable material forming the inner body portion22from surrounding fluids which might contain one of more agents capable of dissolving the body portion22.

FIG. 3depicts the outer contact portion24apart from the body portion22. The contact surface26of the contact portion preferably includes stepped wickers28formed thereupon to create a biting engagement with a surrounding tubular member.

In addition, openings30are preferably formed through the contact portion24. The openings30introduce points of weakness in the structure of the portion24. Thus, they serve as stress risers which assist the outer contact portion24in disintegration during removal of the bridge plug10by drilling.FIG. 6depicts an alternative embodiment for an outer contact portion24′ which has a similar construction to the outer contact portion24. However, the openings30′ are in the form of elongated slots.

The contact portion24(or24′) preferably extends from the upper end32to the lower end34of the slip element20. The outer contact portion24(or24′) is preferably affixed to the body portion22using a suitable adhesive.

In operation, the bridge plug device10is run into a flowbore and then moved from its unset position to a set position, in a manner known in the art. The outer contact portions24(or24′) of the slip elements20engagingly contact the surrounding tubular member.

When it is desired to remove the bridge plug device10from the flowbore, a drilling or milling device, of a type known in the art, contacts the bridge plug10and begins to destroy it by grinding action.FIG. 7illustrates the bridge plug10having been set within a surrounding tubular member36such that the wickers28of the slip elements20(one shown) are set into the interior surface38of the tubular member36in an engaging contact. A milling tool40is disposed within the tubular member36and moved in the direction of arrow42through flowbore44toward engagement with the upper end46of bridge plug10. AsFIG. 8shows, the milling tool40then engages and begins to mill away the upper end46of the bridge plug device10. The setting cone12is abraded away. As the milling tool40encounters the slip elements20, the phenolic material forming the slip ring molding21is milled through, as depicted, thereby exposing the inner body portions22to fluid within the flowbore44. Dissolving agent is present in the fluid within the flowbore44and acts to dissolve the inner body portions22within the wellbore fluid. It is noted that potassium chloride in solution is typically present in conventional drilling fluids. In addition, the milling tool40will mill away the outer contact portions24, and rupture the outer contact portions24into smaller component pieces due to the pattern of openings30which are disposed through the outer contact portions24. The design of the slip inserts20will permit the bridge plug device10to be rapidly removed from the flowbore44. In addition, a number of the components of the bridge plug device10can be more easily circulated out of the flowbore44.

Those of skill in the art will recognize that numerous modifications and changes may be made to the exemplary designs and embodiments described herein and that the invention is limited only by the claims that follow and any equivalents thereof.