FRAC plug having reduced length and reduced setting force

A frac plug having a mandrel body, a cap coupled to an upper end of the mandrel body and an outer housing coupled to a lower end of the mandrel body. A guide shoe is coupled to the outer housing. A single slip assembly is positioned between the cap and the guide shoe and surrounds the mandrel body. A sealing element is positioned between the cap and the single slip assembly and surrounds the mandrel body.

BACKGROUND

Field

Embodiments disclosed herein relate to non-retrievable plugs that may be used to isolate a portion of a well in the production of oil and gas.

Description of the Related Art

Fracturing plugs or “frac plugs” are designed to set, seal, and isolate inside of a wellbore casing to divide the well into one or more zones. After the frac plug is set, it acts as a one way valve that allows fluid flow in one direction and not the other. This allows the casing to hold tremendous pressure above the frac plug, but when the pressure is released, the well returns to equilibrium. The casing is then perforated in one of the zones, and the formation surrounding the perforation is fractured using hydraulic pressure that is supplied through the casing to stimulate the formation. After the pressure is released and the stimulation is complete, the perforations in the casing and fractures in the formation allow the flow of oil and gas to enter the annulus of the casing and be recovered to the surface. After the fracturing and stimulation operation is complete, the frac plug is drilled out to allow access to the full bore of the casing for subsequent operations.

Frac plugs create a seal inside of the wellbore casing by axially squeezing an “element package” having a seal element located between two members on a body of the frac plug. One drawback of conventional frac plugs is that they require a large axial setting force to “squeeze” the element package, which results in the seal element projecting radially outside the outside diameter of the frac plug to contact the casing. Another drawback is that conventional frac plugs have long axial lengths, which increases the amount of drilling that is needed to drill out the frac plugs to have access to the full bore of the casing as described above.

Therefore, there exists a need for new and/or improved frac plugs.

SUMMARY

Embodiments disclosed herein relate to non-retrievable frac plugs that may be used to isolate a portion of a well in the production of oil and gas.

In one embodiment, a frac plug is disclosed which includes a mandrel body, a cap coupled to an upper end of the mandrel body, wherein the cap has an angled surface, an outer housing coupled to a lower end of the mandrel body, a guide shoe coupled to the outer housing, a single slip assembly positioned between the cap and the guide shoe and surrounding the mandrel body, and a sealing element positioned between the cap and the single slip assembly and surrounding the mandrel body. The sealing element is movable along the angled surface to force the sealing element radially outward into contact with a surrounding wellbore.

In one embodiment, a frac plug is disclosed which includes a mandrel body, a cap coupled to an upper end of the mandrel body, an outer housing coupled to a lower end of the mandrel body, a guide shoe coupled to the outer housing, a single slip assembly positioned between the cap and the guide shoe and surrounding the mandrel body, and a sealing element positioned between the cap and the single slip assembly and surrounding the mandrel body. The length of the frac plug when in a set position is shorter than the length of the frac plug when in an unset position.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized with other embodiments without specific recitation.

DETAILED DESCRIPTION

Embodiments disclosed herein relate to non-retrievable fracturing plugs or “frac plugs” that may be used to isolate a portion of a well in the production of oil and gas. Conventional frac plugs require a large axial setting force to be set and are relatively long in length. Embodiments of the frac plug disclosed herein require a setting force that is about 90% less than the setting force of conventional frac plugs. Embodiments of the frac plug disclosed herein are shorter in length than conventional frac plugs, which reduces the amount of time needed to drill out the frac plug from a well.

FIG. 1is an isometric bottom view of a frac-plug100according to one embodiment.FIG. 2is an isometric top view of the frac-plug100.FIG. 3is a bottom view of the frac-plug100.FIG. 4is a side view of the frac-plug100along lines4-4ofFIG. 3.

The frac-plug100includes a mandrel body200coupled to a guide shoe110. A cap105, having a lower angled surface107, is disposed about an outer surface of the mandrel body200. The cap105includes a shoulder170on opposing sides thereof. The shoulders170may include a flat227(shown inFIG. 2) milled in or on opposing sides thereof. The flats227of the shoulders170are configured as a contact point for an outer mandrel of a setting tool. An upper portion of the cap105is configured as a setting tool interface for the frac-plug100.

The mandrel body200includes an inner diameter220forming a flow bore through which fluid can flow through when the frac-plug is in an unset position and a set position as further described below. The mandrel body200also includes a ball seat225sized to receive a ball300(shown inFIG. 2), which may be made from a composite material and dropped onto the ball seat225to prevent fluid from flowing through the flow bore of the mandrel body200. The inner diameter220allows fluid to flow through the frac-plug100when the ball300is not seated in the ball seat225. The inner diameter220is sized to receive an inner mandrel of a setting tool as shown and described in more detail inFIGS. 5A and 5B.

A sealing element115and a single slip assembly120are also disposed about the outer surface of the mandrel body200. The frac-plug100has a length202(shown inFIG. 4) that is less than conventional frac plugs, which often include two sets of slip assemblies. Additionally, the number of parts in the frac-plug100is less than conventional frac plugs, which reduces manufacture time and costs.

The sealing element115is disposed between cap105and the single slip assembly120. The sealing element115includes a biasing member215(shown inFIG. 4) disposed within the sealing element115material. The biasing member215is a metallic member that biases the sealing element115radially inward toward the outer surface of the mandrel body200. The biasing member215may be a spring or spring-like element that surrounds the mandrel body200.

The single slip assembly120includes a cone125, slips130, and pins135disposed about the outer surface of the mandrel body200. The pins135are positioned at least partially between the slips130. The pins135also are disposed at least partially through the cone125. The slips130are positioned above an outer housing140. A lower portion of the outer housing140is received in a reduced diameter shoulder210(shown inFIG. 4) of an upper portion of the guide shoe110.

A shear cap145is positioned in an inner region of the guide shoe110. The shear cap145is held in place by a plurality of shear pins150(shown inFIGS. 3 and 4) that are disposed through the guide shoe110. The shear cap145includes a central opening155sized to receive an inner mandrel of a setting tool as shown and described in more detail inFIGS. 5A and 5B. When setting the frac-plug100, the shear pins150are sheared after the frac-plug100is set which may free the shear cap145. The shear cap145is maintained within the frac-plug100by a pin160coupled to a bottom portion of the guide shoe110. As shown inFIGS. 5A and 5B, one or more set screws165may be used to secure the cone125to the mandrel body200, as well as to secure the outer housing140to the mandrel body200. The pin160may be utilized to prevent a ball from seating in the guide shoe110(thereby preventing the frac-plug100from becoming a bridge plug).

The frac-plug100is made from drillable materials such as composite materials, plastics, rubbers, and fiberglass, as well as cast iron, brass, and fiberglass. Composite material may include a carbon fiber reinforced material or other material that has high strength yet is easily drillable. The mandrel body200, the cap105, the cone125, the outer housing140, the guide shoe110, and the shear cap145may be made of a composite material. The slips130may be made of cast iron. The biasing member215may be made of light gauge spring steel that is easily drilled. The shear pins150may be made of carbon steel. The set screws165may be made of brass. The pin160and the pins135may be made of fiberglass.

The sealing element115may be made of a rubber that can withstand high temperatures, such as hydrogenated nitrile butadiene rubber (HNBR), or other suitable polymeric material. In one embodiment, the sealing element115has a hardness of about 80 on the Shore D scale, and withstands temperatures of about 300 degrees Fahrenheit.

FIGS. 5A and 5Bare side, sectional views of the frac-plug100along lines5-5ofFIG. 3illustrating a setting procedure. The frac-plug100is shown positioned in a wellbore400inFIGS. 5A and 5B.FIG. 5Ashows an unset position whileFIG. 5Bshows a set position. A wellbore400includes a casing405into which the frac-plug100is lowered and set to form a seal. A setting tool, only a portion of which is shown inFIGS. 5A and 5B, includes an inner mandrel410, an outer mandrel415, and an adapter420which is configured to engage the upper end and shoulder170of the cap105, as well as the upper end of the mandrel body200.

The inner mandrel410is disposed through the frac-plug100and is coupled to the guide shoe110and the shear cap145by the shear pins150. An axial pull force, also referred to as a setting force, is applied by the inner mandrel410while the outer mandrel415and the adapter420remain static to set the frac-plug100. The axial pull force applied by the inner mandrel410applies an upward force to the guide shoe110which is transmitted to the outer housing140, the slips130, the cone125, and the sealing element115.

The guide shoe110, the outer housing140, the slips130, the cone125, and the sealing element115all move upward together relative to the mandrel body200and the cap105, which are held in place by the outer mandrel415and the adapter420of the setting tool. The sealing element115is moved upward along the angled surface107of the cap105and forced radially outward into contact with the inner surface of the casing405to form a seal with the casing405. The cone125is at least partially held in place by the expanded sealing element115and such that the slips130move up along the cone125, which causes the slips130to extend radially outward into contact with the inner diameter of the casing405. The setting force applied to the frac-plug100is decreased by about 90% due to pulling the sealing element115up along the angled surface107to form the seal, when compared to the setting force required to set conventional frac plugs which require compressing or “squeezing” a sealing element between two bodies.

As shown inFIG. 5B, the frac-plug100is set within the casing405, and the sealing element115forms a seal between the frac-plug100and the casing405. The axial pull force is continued to be applied by the inner mandrel410until the shear pins150shear, as shown inFIG. 5B, which releases the inner mandrel410from the frac-plug100. The setting tool can then be removed from the wellbore400and fluid can still flow through the frac-plug100when set. When needed, the ball300(shown inFIG. 2) can be dropped onto the ball seat225of the mandrel body200to close fluid flow through the frac-plug100. Pressure within the casing405above the frac-plug100can be increased to conduct a fracturing and/or stimulation operation as known in the art.

The frac-plug100is held in the set position by a friction or interference-fit interface425, which includes a surface to surface contact between an outer surface of the mandrel body200and an inner surface of the outer housing140. The friction or interference-fit interface425may be used to allow movement in one direction and prevents or minimizes movement in the opposite direction. In particular, the sealing element115, the slip assembly120, the outer housing140, and the guide shoe110can all move upward relative to the mandrel body200but downward movement relative to the mandrel body200is minimized by the friction or interference-fit interface425between the outer surface of the mandrel body200and the inner surface of the outer housing140. Other types of directional control mechanisms known in the art can be used in addition to or as an alternative to the friction or interference-fit interface425.

The length of the frac-plug100when in a set position is shorter than the length202of the frac-plug100when in an unset position as shown inFIG. 4. A pre-set gap length435(as shown inFIG. 5A) formed between the mandrel body200and the guide shoe110transitions to a set gap length440(as shown inFIG. 5B) after setting, the set gap length440being less than the pre-set gap length435. In one example, the length202is about 13.5 inches in the unset position and shortens by about 2 inches or 2.5 inches in the set position. This shortened length results in less time needed to drill out the frac-plug100to have full bore access to the casing405when desired, such as after the completion of a fracturing and/or stimulation operation as known in the art.

While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure thus may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.