CROSS-REFERENCE TO RELATED APPLICATIONS

See Application Data Sheet.

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STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to isolating zones in a wellbore. More particularly, the present invention relates a frac plug system that sets in position and sets a seal for isolating zones in a wellbore. Even more particularly, the present invention relates to a frac plug system with a pre-set seal, while setting in position in multiple stages.

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98

Within a wellbore, the hydrocarbons are located at particular depths within a rock formation. These depths can be organized into production zones so that the delivery of production fluids can be targeted to the location of the hydrocarbons. The production fluids facilitate the recovery of the hydrocarbons from the wellbore. Other depth levels do not contain hydrocarbons, which can be called “non-productive zones”. There is no need to waste production fluids on non-productive zones without hydrocarbons. Thus, the productive zones are isolated from the non-productive zones for the recovery of hydrocarbons from the wellbore.

There are known downhole tools to separate a production zone from a non-productive zone so that the production fluids can be delivered to the production zone and not the non-productive zone. Examples of downhole tools to isolate zones include a plug, a packer or other tool with an isolation valve.

In the conventional process, the frac plug device is run to a downhole location. When located in the correct place, the setting tool that traveled with the frac plug device will set the packer, i.e. expand the frac plug against the walls of the borehole. Then, the settling tool is removed. The frac plug still must be activated in order seal the zone. The frac plug is sealed to the borehole, but fluid still flows through the packer. Conventionally, a frac ball is dropped into the borehole. The frac ball travels to the downhole location to sit on a ball seat, which triggers the actual seal across the frac plug. Fracking can commence with the actual seal across the packer. The frac fluids are only delivered to the isolated zone, and production fluids are only harvested from the isolated zone.

There also frac plug devices that do not require a frac ball. U.S. Pat. No. 3,298,437, issued on 1967 Jan. 17 to Conrad, discloses background information for setting a plug. The mandrel is solid, and there is not even a ball seat or other trigger. The seal is formed when the plug is set. U.S. Pat. No. 4,784,226, issued on 1988 Nov. 15 to Wyatt, and U.S. Pat. No. 7,424,909, issued on 2008 Sep. 16 to Roberts et al also disclose the conventional setting of a plug to create the sealed borehole as soon as set. U.S. Pat. No. 6,796,376, issued on 2004 Sep. 28 to Frazier discloses the conventional sealed plug as setting with the shearing at the end of the mandrel. This type of frac plug is a pre-set frac plug because the frac plug is already sealed when set in position.

There are also versions of a pre-set frac plug system with a frac ball. U.S. Pat. No. 2,627,317, issued on 1953 Feb. 3 to Baker, discloses a well tester with pre-set frac ball. The tester is run in with the frac ball in place. The tester is triggered to seal against the borehole wall. The ball member and ball valve can be actuated by pressure to open the tester at the bottom. The frac ball is deployed in place with the frac plug, so that the frac plug forms the actual seal across the frac plug as soon as the setting tool is used.

The problem with the pre-set frac plug is the risk of accidentally triggering a pre-set frac plug. Boreholes are not straight and smooth. There are bumps and turns. When a conventional frac plug is accidentally triggered or accidentally set in position at the wrong downhole location, strong acid is pumped into the borehole to dissolve the plug. There is no frac ball, so there can be fluid injection to remove the accidentally triggered frac plug. However, with a pre-set frac plug in the wrong downhole location, there is no pumping because the accidentally triggered pre-set frac plug already has a pre-set seal across the frac plug. Thus, pre-set frac plug are very risky.

There are frac plugs and packers with flow bypass systems for delivery of fluids pasta frac plug or packer in a wellbore. U.S. Pat. No. 2,143,251, issued on 1939 Jan. 10 to Savitz, discloses a tool with a circulating valve that actuates from a run-in position to a set position. The mandrel moves the openings from a sealed position to a flow position. U.S. Pat. No. 4,286,661, issued on 1981 Sep. 1 to Gazda, shows another equalizing valve with a run in position and a set position. The open flow position can be actuated by movement of the slit openings into a spaced window and lower than the spaced window. U.S. patent Ser. No. 10/400,540, issued on 2019 Sep. 3 to Williamson et al shows flow restriction channels along the exterior of a mandrel that are selectively opened.

It is an object of the present invention to provide a frac plug system to isolate zones in a wellbore.

It is an object of the present invention to provide a frac plug system to be easily removed, if accidentally triggered in the wellbore.

It is an object of the present invention to provide a frac plug system with multiple stages for isolating a zone in a wellbore.

It is another object of the present invention to provide a frac plug system having a setting mandrel with fluid bypass slots and a sleeve member.

It is an object of the present invention to provide a frac plug system with multiple stages for isolating a zone with fluid pressure variation.

It is an object of the present invention to provide a frac plug system that is removeable during different stages of the process of isolating a zone.

It is another object of the present invention to provide a frac plug system that is removeable by injecting a strong acid.

These and other objectives and advantages of the present invention will become apparent from a reading of the attached specification, drawings and claims.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention include a frac plug system with a pre-set seal. Once the frac plug system is set in position within a wellbore, there is no need for a frac ball or other operation to form the seal at the position within the wellbore. The frac plug system of the present invention has components so that setting in position is split into multiple stages, which allows quick removal if the trigger to start the setting in position was wrong or accidental.

The present invention is a frac plug system comprising a setting mandrel, a sleeve member, a sealing member, a cone assembly, and a slip device. The setting mandrel includes a mandrel body, a plurality of fluid bypass slots, and a sealing shoulder surface. The fluid bypass slots extend longitudinally along the mandrel body. Each slot has an opened end and a closed end. In some embodiments, the setting mandrel can have O-ring grooves for O-rings in sliding engagement between the sleeve member and the setting mandrel. the sleeve member includes a sleeve body with an outer sleeve surface, an abutment end and a free end. The setting mandrel has a first configuration without fluid flow through the packer system because the closed ends of the slots are covered by the sleeve member. The setting mandrel has a second configuration with the closed ends of each slot open and fluid connection through the frac plug system.

In embodiments of the present invention, the abutment end of the sleeve member is mechanically engaged with a seal end of the setting mandrel. The mechanical engagement includes direct contact, like being adjacent, or other connection so as to exert force on each other. In one embodiment, the abutment end is a conical wedge cooperative with a sealing shoulder surface of the setting mandrel.

Embodiments of the sealing member, cone assembly, and slip device of the present invention include conventional components of a frac plug to set the frac plug system in position in the wellbore. The slip device anchors to the wellbore. The sealing member seals against the wellbore so that there is no fluid flow around the frac plug system. The cone assembly slides into the slip device to press the slip device into the wellbore. The sealing member has an extended position and an expanded position with a diameter for sealing against the wellbore larger than the diameter of the extended position.

In the present invention, the second configuration of the setting mandrel only corresponds to the sealing member in the expanded position at the first setting stage. The first configuration of the setting mandrel corresponds to both the sealing member in the expanded position at the second setting stage and the sealing member in the extended position, while being run-in before any setting stages.

Embodiments of the present invention include the method for isolating a zone in a wellbore. The method includes running a frac plug system in a borehole with a setting tool. The setting mandrel is in the first configuration, and the sealing member is in the extended position. Next, the frac plug system is placed in a location in the wellbore, which can include breaking the setting mandrel with the setting tool.

The method now includes transitioning the sealing member in the extended position to the sealing member in the expanded position at the location and moving the setting mandrel from the first configuration to the second configuration so as to form a fluid connection through the fluid bypass slots in a first setting stage of setting in position. In some embodiment, fluid pressure is applied to exert force on the abutment end of the sleeve member, which compresses the sealing member and moves the sleeve member along the setting mandrel to the second configuration of the setting mandrel. The fluid bypass slots are now in fluid connection through the frac plug system. The closed ends of the slots allow fluid flow and pumping through the frac plug system.

Next, the method includes moving the setting mandrel from the second configuration to the first configuration so as to seal the fluid connection in a second setting stage. The pre-set seal at the seal end of the sleeve member is finally moved into place. In the embodiments with fluid pressure, additional fluid pressure is applied to the seal end to exert force on the setting mandrel. With the sleeve member anchored by the sealing member and slip device, the setting mandrel now moves toward the sleeve member. The setting mandrel returns back to the first configuration, closing the fluid bypass slots in the second setting stage. In the second setting stage, the setting in position is completed so that the pre-set seal can form a seal across the frac plug system to isolate a zone.

Alternative embodiments of the method of the present invention include the step of injecting fluids to remove the frac plug system. If the frac plug system is in the wrong place by accident or unintentionally, strong acid can be injected to dissolve the frac plug system or at least components of the frac plug system so that the frac plug system is removed from the wrong place in the wellbore. The fluid bypass slots allow pumping acid or other additives to be delivered to the frac plug system.

The present invention provides a frac plug system with multiple stages to isolate zones in a wellbore. The frac plug system is pre-set because no additional stage is needed to set the seal. A frac ball and related ball seat are no longer needed. The present invention includes components for multiple stages for setting in position to isolate the wellbore.

