Hybrid dissolvable plugs for sealing downhole casing strings

A plug deployable as part of a tool string into a wellbore having a casing string positioned therein, the plug comprising:

• an annular elastomeric sealing element comprising a radially outer sealing surface configured to extend outwardly from a central axis of the plug and sealingly press against an inner surface of the casing string when the plug is in a first deployed configuration;
• and
• a slip comprising at least one slip body formed from non-corrosive materials configured to resist corrosion when exposed to conditions in the wellbore, wherein the at least one slip body has a peripheral outer face oriented to face away from the central axis and towards the casing string, and one or more engagement members located on the outer face of the slip body wherein the one or more engagement members are configured to bite into the casing string when the plug is in the first deployed configuration to thereby resist axial movement of the slip relative to the casing string;
• an elongate mandrel having a first end, a second end longitudinally opposite the first end, and an outer surface extending from the first end to the second end, wherein the first end is configured to connect to a setting tool of the tool string for receiving an axially directed force transferrable through the mandrel and against the sealing element to force the sealing surface of the sealing element, which surrounds the mandrel, into sealing engagement with the casing string;
• wherein the plug comprises:
• a run-in configuration having a run-in maximum outer diameter configured to travel along and within the casing string;
• the first deployed configuration has a deployed maximum outer diameter that is greater than the run-in maximum outer diameter whereby an axially directed force applied through the mandrel causes radial expansion of the slip toward contact with the casing string so as to restrict relative rotation between the slip and the casing string, wherein the plug further comprises a lock ring having rachet teeth configured to engage with corresponding teeth formed on the mandrel so as to restrict relative movement between the mandrel and the lock ring, and wherein in the first deployed configuration relative rotation is restricted between the mandrel and the casing string via an intermediate connection formed between the mandrel and the rotationally locked slip;
• and
• a second deployed configuration in which the mandrel is dissolved but the slip remains in contact with the casing string restricting relative rotation therebetween.

A method for preparing a cased subterranean wellbore for the production of subterranean fluids, the method comprising:

• (a) deploying a tool string to a desired location within the casing string positioned in the wellbore, the tool string comprising one or more perforating guns, a setting tool, and a downhole-deployable plug in a run-in configuration having a central axis and a run-in maximum outer diameter configured to travel along and within the casing string, wherein the plug comprises an annular elastomeric sealing element, a slip comprising at least one non- corrosive slip body having a radially outer face, a nose comprising a corrosion-selected nose body located at a downhole end of the plug, an elongate mandrel having a first end coupled to the setting tool and a longitudinally opposed second end coupled to the nose, and one or more engagement members located on the outer face of the slip body;
• (b) actuating the setting tool with the tool string located at the desired location whereby the plug is actuated from the run-in configuration to a first deployed configuration having a deployed maximum outer diameter that is greater than the run-in maximum diameter and in which the one or more engagement members of the slip attach to the casing string and a radially outer sealing surface of the sealing element enters into sealing contact with the casing string such that fluid flow across the plug is restricted in at least one axial direction, wherein the plug further comprises a lock ring having rachet teeth configured to engage with corresponding teeth formed on the mandrel so as to restrict relative movement between the mandrel and the lock ring, wherein in the first deployed configuration relative rotation is restricted between the nose and the casing string via an intermediate connection formed between the nose and the rotationally locked slip;
• (c) activating the perforating gun of the tool string to form one or more perforations in the casing string at a location uphole from the plug;
• (d) pumping a completion fluid from the casing string, through the one or more perforations formed by the perforating gun, and into an earthen formation;
• (e) dissolving the corrosion-selected nose body of the plug following (d) in response to the nose being exposed to conditions in the wellbore following a predetermined delay period whereby the plug is shifted from the first deployed configuration to a second deployed configuration in which the mandrel and the nose are dissolved but the slip remains in contact with the casing string restricting relative rotation between the slip and the casing string;
• and
• (f) deploying a drill into the casing string and drilling out the attached non-corrosive slip body following the dissolving of the nose body to reduce an obstruction to fluid flow through the casing string formed by the attached slip.

A method for preparing a cased subterranean wellbore for the production of subterranean fluids, the method comprising:

• (a) performing multiple hydraulic fracturing operations in a progression moving from a downhole end of the wellbore toward an uphole end wherein each fracturing operation comprises:
• (i) deploying a unique tool string into the wellbore to a unique pre-determined location within the casing string located in the wellbore, the tool string comprising at least one perforating gun, a setting tool, and a hybrid frac plug in a run-in configuration having a run-in maximum outer diameter configured to travel along and within the casing string and located at a downhole end of the tool string wherein the hybrid frac plug includes a corrosion-selected nose, an annular elastomeric sealing element, an elongate mandrel having a first end coupled to the setting tool and a longitudinally opposed second end coupled to the nose, and at least one non-corrosive slip, between the ends of the hybrid frac plug is located the sealing element and the at least one non-corrosive slip where the sealing element extends continuously circumferentially around a central axis of the hybrid frac plug along an outer periphery of the hybrid frac plug;
• (ii) actuating the setting tool to impose axially directed forces against the sealing element of the hybrid frac plug to set the hybrid frac plug and transition the sealing element and the at least one non-corrosive slip from the run-in configuration to a sealing, first deployed configuration having a deployed maximum outer diameter that is greater than the run-in maximum diameter and where the at least one non-corrosive slip bites into the casing string resisting relative movement between the casing string and the hybrid frac plug while the sealing element extends towards and sealingly presses against an inner surface of the casing preventing fluid flow across the hybrid frac plug in at least a downhole direction, wherein the hybrid frac plug further comprises a lock ring having rachet teeth configured to engage with corresponding teeth formed on the mandrel so as to restrict relative movement between the mandrel and the lock ring, and wherein in the first deployed configuration relative rotation is restricted between the nose and the casing string via an intermediate connection formed between the nose and the rotationally locked slip;
• (iii) detaching the hybrid frac plug from the tool string;
• (iv) firing the at least one perforating gun to puncture perforations in the casing string;
• and
• (v) pressurizing the portion of the casing string located uphole from the hybrid frac plug with hydraulic fracturing fluid to fracture, expand and extend the perforations into a subterranean earthen formation surrounding the wellbore while the hybrid frac plug prevents the pressurized fracturing fluid from proceeding further through the casing string downhole from the hybrid frac plug;
• (b) dissolving the corrosion-selected nose of each of the hybrid frac plugs no sooner than six hours after each the hybrid frac plugs have been set while the at least one non-corrosive slip and the sealing element of each hybrid frac plug is preserved in place as set after each of the hybrid frac plugs have been set and whereby each of the hybrid frac plugs are shifted from the first deployed configuration to a second deployed configuration in which the mandrel and the nose are dissolved but the slip remains in contact with the casing string restricting relative rotation therebetween;
• (c) clearing the casing string of the at least one non-corrosive slip and the sealing element of each of the hybrid frac plugs with a drill system where the drill system whereby engagement between a drill bit of the drill system and the at least one non-corrosive slip and the sealing element of each hybrid frac plug is registered as an increase in resistance to the downhole progression of the drill bit through the casing string;
• (d) determining a position of each of the hybrid frac plugs estimated from the registered increase in resistance to the downhole progression of the drill bit;
• and
• (e) comparing the determined position of each of the hybrid frac plugs with a predetermined location of each of the hybrid frac plugs in the casing string to determine if any of the hybrid frac plugs have moved axially within the casing string after being transitioned to the first deployed configuration.