Novel Perforating Tool with Dynamic Underbalance Mitigation and Related Methods

This application claims the benefit of U.S. Patent Application No. 63/642,278 filed May 3, 2024, and entitled “Novel Perforating Tool with Dynamic Underbalance Mitigation and Related Methods,” the disclosure of which is herein incorporated by reference.

The present disclosure relates to an apparatus and method for completing a well and, more particularly, to a perforating tool and method for perforating a subterranean formation that is intersected by a wellbore.

Hydrocarbons, such as oil and gas, are produced from cased wellbores intersecting one or more hydrocarbon reservoirs in a formation. These hydrocarbons flow into the wellbore through perforations in the cased wellbore. Perforations are usually made using a perforating gun loaded with shaped charges. The gun is lowered into the wellbore on an electric wireline, slickline, tubing, coiled tubing, or other conveyance device until it is adjacent to the hydrocarbon producing formation. Thereafter, a surface signal actuates a firing head associated with the perforating gun, which then detonates the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to create perforations, thereby allowing formation fluids to flow through the perforations and into a production string.

Referring to, there is shown a prior art perforating tooldisposed in a wellboredrilled in a hydrocarbon bearing formation. The wellboremay be lined with a wellbore tubular, such as casing, and contain one or more wellbore fluids. As used herein, the term “fluid” is inclusive of liquids and gases and may refer to a single fluid or a mixture of fluids (e.g., two different types of liquid, a mixture of a liquid and a gas, etc.).

A wellbore-formation pressure differential may exist between the wellboreand the formationand, more particularly, between the wellbore fluidsin the wellboreand formation fluidsin the formation. Where the pressure exerted by the wellbore fluidson the formation(the “wellbore fluid pressure” or “hydrostatic pressure”) is below the internal pressure from the formation fluidsin the formation(the “formation fluid pressure”), the wellbore-formation pressure differential is termed an “underbalanced condition” or “underbalance”. On the other hand, where the wellbore fluid pressure exceeds the formation fluid pressure, the wellbore-formation pressure differential is termed an “overbalanced condition” or “overbalance”. During drilling operations, underbalance and overbalance may be used strategically to control the flow of formation fluids. In a state of underbalance, formation fluidsflow from the formationinto the wellbore, where they may be produced to the surface. Overbalance, by contrast, may be used to prevent formation fluidsfrom entering the wellboreor to cause wellbore fluidsto enter the formation. Where no wellbore-formation pressure differential exists (i.e., the wellbore fluid pressure is equal to the formation fluid pressure), the system is in “balance.”

Turning back to, the perforating toolincludes one or more shaped chargesdisposed in an interiorof a carrier. Conventionally, the interioris at or near atmospheric pressure. As depicted, the interioris sealed such that the wellbore fluidsin the wellborecannot enter the interior.

When the shaped chargesare detonated, the detonation creates a transient overbalanced condition between the wellboreand the formation(a “dynamic overbalance”). More particularly, when the shaped chargesdetonate, pressure is introduced to the wellborethat causes the wellbore fluid pressure to exceed the formation fluid pressure briefly. Referring to, detonation of the shaped chargesalso forms tunnelsthat extend through the carrier, through the wellbore tubular, and a limited distance into the formation.

It will be appreciated that a carrier-wellbore pressure differential may exist between the perforating tooland the surrounding wellbore. For example, a carrier-wellbore pressure differential occurs when the interiorof the carrierincludes a volume of empty space such that pressure within the interioris lower than the wellbore fluid pressure. Upon detonation of the shaped charges, the carrier-wellbore pressure differential is herein termed a “dynamic underbalance event” or “dynamic underbalance”. Dynamic underbalance between the perforating tooland the wellborecauses the wellbore fluidsto flow rapidly from the wellboreinto the interiorof the carrier. The rapid outflow of wellbore fluidsfrom the wellborereduces the wellbore fluid pressure, thereby triggering an underbalanced condition between the wellboreand the formation. As a result of this underbalanced condition, formation fluidsmay flow rapidly into the wellbore. If the flow of formation fluidsinto the wellboreis too rapid, damage may result to the formation, the tunnels, or both.

Referring to, there is shown a graph illustrating an exemplary dynamic underbalance event associated with perforating a formationusing the perforating toolof. The horizontal axis is time (T) in seconds and the vertical axis is pressure (P) in psi. The hydrostatic pressure of the wellbore fluidis about 9,000 psi. At the time of firing the perforating tool, the pressure P spikes to above 12,000 psi (see T1). As wellbore fluidsrush into the interiorof the carrier, the wellbore fluid pressure in the wellborerapidly falls to about 4,500 psi (see T2) in less than about 0.05 seconds. Thereafter, the wellbore fluid pressure in the wellboregradually returns to 9,000 psi after about 0.5 seconds from the firing of the perforating tool. Thus, the dynamic underbalance event between the perforating tooland the wellbore—and the resulting underbalanced condition between the wellboreand the formation—dissipated within about 0.5 seconds. Although this exemplary underbalance event was transient and lasted less than one second, this short timeframe would be sufficient to damage some formation types.

A need exists, therefore, for perforating tools that mitigate dynamic underbalance events that may occur while perforating a formation. The present disclosure is directed to these and other deficiencies in the prior art.

In aspects, the present disclosure provides a perforating tool for perforating a subterranean formation intersected by a wellbore. The perforating tool may include a carrier having an interior; at least one shaped charge disposed in the interior; and a pressure applicator disposed in the interior. The pressure applicator may be configured to release a gas simultaneous with detonation of the at least one shaped charge.

In aspects, the present disclosure provides a related method for perforating a subterranean formation intersected by a wellbore. The method may include the step of positioning a pressure applicator within the wellbore, where the perforating tool includes a carrier having an interior, at least one shaped charge disposed in the interior, and a pressure applicator disposed in the interior and configured to release a gas. The method may also include the steps detonating the at least one shaped charge and releasing the gas simultaneous with the step of detonating the at least one shaped charge.

In aspects, the present disclosure provides a related method for perforating a subterranean formation intersected by a wellbore. The method may include a stop of positioning a perforating tool within the wellbore, where the perforating tool includes a carrier having an interior, a shaped charge disposed in the interior, and a pressure applicator disposed in the interior, where the pressure applicator is configured to release a gas. The method may also include a step of detonating the shaped charge, where the detonation creates an overbalanced pressure difference between hydrostatic pressure in the wellbore and formation fluid pressure in the subterranean formation, and a step of releasing the gas to generate a gas pressure simultaneous with the step of detonating the shaped charge.

The above-recited examples of features of the disclosure have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the disclosure that will be described hereinafter and which will form the subject of the claims appended hereto.

In aspects, the present disclosure provides devices and related methods for mitigating an underbalanced condition that may occur while perforating a well. The present disclosure is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present disclosure with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein.

Referring to, a perforating toolis schematically illustrated in accordance with one embodiment of the present disclosure. The perforating toolis disposed in a wellborethat is drilled in a subterranean formationcontaining formation fluids(e.g., liquid hydrocarbons). The wellborecontains wellbore fluidssuch as engineered fluids (e.g., drilling fluids), water, formation fluids, or combinations of the same.

As depicted, the perforating toolincludes a carrierhaving an interior. The interiormay be sealed such that overall pressure within the interioris lower than pressure at a location that is exterior to the carrier(e.g., the wellbore fluid pressure in the annular spacebetween the carrierand the walls of the wellbore). For example, the interiormay be at or near atmospheric pressure. Disposed within the interiorare one or more shaped chargesand one or more pressure applicators. In various embodiments, the perforating toolincludes an equal number of shaped chargesand pressure applicators, more shaped chargesthan pressure applicators, or fewer shaped chargesthan pressure applicators. In some embodiments, the shaped chargesand pressure applicatorsare arranged in an alternating configuration (e.g., a first shaped chargefollowed by a first pressure applicator, followed by a second shaped charge, followed by a second pressure applicator, followed by a third shaped charge).

Each of the shaped chargesmay be of any conventional design. Upon detonation, the shaped chargesform one or more tunnelsthat extend through the carrierand the wellboreinto the subterranean formation. In exemplary embodiments, when the shaped chargesare detonated, the detonation briefly creates a dynamic overbalance between the wellboreand the subterranean formation. In this transient state, an overbalanced pressure difference exists temporarily between the hydrostatic pressure in the wellboreand formation fluid pressure in the subterranean formation. As used herein, the term “overbalanced pressure difference” refers to the difference (e.g., in units of psi) between the hydrostatic pressure and the formation fluid pressure. In exemplary embodiments, detonation of the shaped chargesalso creates a dynamic underbalance in which the pressure in the interiorof the carrieris lower than the hydrostatic pressure in the wellbore. This dynamic underbalance event may cause wellbore fluidto flow from the wellboreinto the interiorof the carrier. As the fluid flows from the wellbore, an underbalanced condition may be created between the wellboreand the subterranean formation, resulting in damage to the subterranean formation, the tunnels, or both.

To mitigate formation and/or tunnel damage, the pressure applicatoris configured to release a high-pressure gas simultaneous with the detonation of the shaped charges. As used herein, the term “simultaneous” means within a range from 1 second before the detonation of a shaped chargeto 1 second after the detonation of a shaped charge. If more than one shaped chargeis used, then the detonation defining the range may be the detonation of the first shaped chargeto detonate, the detonation of the last shaped chargeto detonate, or any intermediate detonation of a shaped charge.

The high-pressure gas, when released by the pressure applicator, generates a gas pressure that increases pressure within the interiorof the carrier. The increased pressure within the carrier reduces the carrier-wellbore pressure differential and resists the rapid rush of wellbore fluidsinto the interior, thus mitigating the dynamic underbalance between the perforating tooland the wellbore. By mitigating the dynamic underbalance, the release of high-pressure gas also indirectly mitigates the underbalanced condition between the wellboreand the subterranean formation. It will be appreciated that “mitigation” is accomplished where the applicable pressure differential (e.g., the carrier-wellbore pressure differential, the wellbore-formation pressure differential) is within a range that does not constitute an underbalance or overbalance condition capable of damaging the subterranean formation, the perforation tunnels, or both. It will be appreciated that the range of suitable pressure differentials for mitigation will vary based on the type of subterranean formation. Some formation types, such as unconsolidated formations, include soils, rocks, and other solids which may be more susceptible to damage from an underbalance or overbalance condition than other formation types and, thus, require a smaller range of pressure differentials for mitigation.

Referring to, there is shown a graph illustrating a dynamic underbalance associated with perforating a formationusing the underbalance mitigation techniques according to the present disclosure. As in, the horizontal axis is time (T) in seconds, the vertical axis is pressure (P) in psi, and the hydrostatic pressure is about 9,000 psi. At the firing of the perforating tool, the pressure P spikes to about 12,000 psi (see T3) with detonation of the shaped charges. Simultaneous with this detonation, the pressure applicatorreleases high-pressure gas that increases the pressure within the interior. As a result of this gas release, the rate of flow of wellbore fluidsinto the interiorof the carrierslows such that the wellboreencounters only a relatively small drop in pressure of less than 500 psi (see T4).

For theperforating scenario, it should be noted that the pressure applicatorreleased the high-pressure gas for only a relatively short time (less than 0.03 seconds) to achieve the depicted results. In various non-limiting embodiments, the pressure applicatoris configured to release the gas for a pressure application interval ranging from 0.01 seconds to 2 seconds, more particularly from 0.02 seconds to 1.9 seconds, more particularly from 0.03 seconds to 1.8 seconds, more particularly from 0.04 seconds to 1.7 seconds, more particularly from 0.05 seconds to 1.6 seconds, more particularly from 0.1 seconds to 1.5 seconds, more particularly from 0.2 seconds to 1.4 seconds, more particularly from 0.3 seconds to 1.3 seconds, more particularly from 0.4 seconds to 1.2 seconds, more particularly from 0.5 seconds to 1.1 seconds, more particularly 1 second.

As discussed above, the pressure application interval begins at a starting point that is within a range from 1 second before to 1 second after detonation of a shaped charge(i.e., the high-pressure gas is released simultaneous with the detonation). In various embodiments, the starting point of the pressure application interval is determined as a function of an estimated peak pressure duration. As used herein, the phrase “estimated peak pressure duration” refers to an estimated time interval during which pressure will be at its highest point due to detonation of the shaped charge. The pressure application interval may begin, for example, at a starting point that falls between 10% and 50% of the estimated peak pressure duration. In a non-limiting exemplary embodiment, the shaped chargedetonates at time=0, and the estimated peak pressure duration is pre-calculated to last for 0.03 seconds (i.e., until time=0.03); the pressure application interval begins between 0.003 and 0.015 seconds from the moment of detonation (i.e., the starting point is between time=0.003 and time=0.015). In another non-limiting embodiment, the estimated peak pressure duration is pre-calculated to last for 0.02 seconds (i.e., until time=0.02), and the pressure application interval therefore begins between 0.002 and 0.01 seconds from the moment of detonation (i.e., the starting point is between time=0.002 and time=0.01). In yet another non-limiting embodiment, the estimated peak pressure duration is pre-calculated to last for 0.01 seconds (i.e., until time=0.01), and the pressure application interval therefore begins between 0.001 seconds and 0.005 seconds from the moment of detonation (i.e., the starting point is between time=0.001 and time=0.005).

In various embodiments, the endpoint of the pressure application interval is determined as a function of an estimated underbalanced condition duration. As used herein, the phrase “estimated underbalanced condition duration” refers to an estimated time interval during which an underbalanced condition will exist between the wellboreand the formationabsent mitigation. The pressure application interval may end, for example, at an endpoint that falls between 50% and 200% of the estimated underbalanced condition duration. In a non-limiting exemplary embodiment, the shaped chargedetonates at time=0, and the estimated underbalanced condition duration is pre-calculated to last for 0.5 seconds (i.e., until time=0.5); the pressure application interval ends between 0.25 and 1 seconds from the moment of detonation (i.e., the endpoint is between time=0.25 and time=1). In another non-limiting embodiment, the estimated underbalanced condition duration is pre-calculated to last for 0.4 seconds (i.e., until time=0.4), and the pressure application interval ends between 0.2 and 0.8 seconds from the moment of detonation (i.e., the endpoint is between time=0.2 and time=0.8). In yet another non-limiting embodiment, the estimated underbalanced condition duration is pre-calculated to last for 0.3 seconds (i.e., until time=0.3), and the pressure application interval ends between 0.15 and 0.6 seconds from the moment of detonation (i.e., the endpoint is between time=0.15 and time=0.6).

In various embodiments, the pressure applicatoris configured to release the gas in accordance with a predetermined gas parameter. Suitable predetermined gas parameters include, but are not limited to, pre-specified gas pressure, release volume, flow rate, and combinations of the same. For example, the pressure applicatormay be configured to release the gas with a pre-specified gas pressure between 250 psi and 5,000 psi, more particularly between 500 psi and 2,500 psi. With reference to release volume, the pressure applicatormay be configured to release between 50 inand 1,000 inof the gas. Regarding flow rate, the pressure applicatormay be configured to release the gas at a rate of between 0.1 m/s and 10 m/s.

In various embodiments, the predetermined gas parameters are determined with reference to the characteristics of the formation fluids, the subterranean formation, or both. Applicable characteristics of the formation fluidsmay include the formation fluid pressure, chemical composition, and phases; characteristics of the subterranean formationmay include formation type (e.g., consolidated or unconsolidated), permeability, and rock strength.

One or more predetermined gas parameters may be selected with reference to lithological properties such as an anticipated fracture threshold for the subterranean formation. As used herein, the term “fracture threshold” refers to the magnitude of pressure applied to the subterranean formationthat must be exceeded for a fracture to form therein. The gas pressure generated by the gas that is released by the pressure applicatorand the pressure associated with detonation of the shaped chargesmay, in combination, apply a “combined pressure” to the subterranean formation. To avoid unwanted fracturing, the anticipated fracture threshold for the subterranean formationmay be determined before detonation of the shaped charges. Based on the anticipated fracture threshold, one or more predetermined gas parameters may be selected to generate a gas pressure that is below the anticipated fracture threshold and will not independently fracture the subterranean formation. In other embodiments, the predetermined gas parameter(s) may be selected to generate a gas pressure that will not, in combination with an anticipated detonation pressure, result in a combined pressure that exceeds the anticipated fracture threshold. In another example, the predetermined gas parameter(s) may be selected such that the combined pressure does not exceed ninety percent of the fracture threshold of the subterranean formation.

In various embodiments, the gas pressure is generated with reference to the overbalanced pressure difference that occurs during the brief dynamic overbalance when the shaped chargesare detonated. Before detonation, an anticipated overbalanced pressure difference may be determined, and the predetermined gas parameter(s) may be selected such that the gas pressure will not exceed the overbalanced pressure difference. In other embodiments, the predetermined gas parameter(s) are selected such that the gas pressure will be between 10% and 120% of the overbalanced pressure difference. It will be understood that, as used herein, a range of X % to Y % will be interpreted to include the disclosure of each discrete integer value between X and Y (e.g., X, X+1, X+2 . . . Y−1, Y).

In some embodiments, the pressure applicatorincludes one or more canisters that are filled with the gas in a highly pressurized compressed form.

In other embodiments, the pressure applicatorincludes a plurality of pellets that each include a gas-generating material (e.g., a propellant). As depicted in the perforating toolof, each pellet may be interposed between two shaped charges. In some embodiments, the gas-generating material is a solid oxidizer. Suitable gas-generating materials include, but are not limited to, nitro compounds such as hexanenitroethane, 1,2-dicyanotetranitroethane (TENDE), fluorotrinitromethane, hexanitrostilbene (HNS), and ammonium picrate; nitramines such as cyclotetramethylenetetranitramine (HMX) and cyclotrimethylene trinitramine (RDX); nitrates such as pentaerythritol tetranitrate (PETN), potassium nitrate (BKNO3), ammonium nitrate, nitroglycerin, and polyglycidyl nitrate; tetrazoles such as diammonium bitetrazole; tetrazines such as dihydrazinium 3,6-bis(5-tetrazolyl) dihydrotetrazine; perchlorates such as ammonium perchlorate; fuel-oxidizer mixtures such as thermites and black powder; synthetic polymers such as polytetrafluoroethylene (PTFE), hydroxyl-terminated polybutadiene (HTPB), polybutadiene acrylonitrile (PBAN), and polyurethane; metals (e.g., aluminum); and metalloids (e.g., boron). It will be appreciated that the formulation selected for the gas-generating material may be used to achieve the desired predetermined gas parameters (e.g., pre-specified gas pressure, release volume, flow rate).

The perforating toolmay also include an initiator that is configured to apply kinetic energy, thermal energy, electrical energy, or a combination of the same to initiate the gas-generating material. As used herein, the term “initiate” refers to applying a stimulus (e.g., kinetic, thermal, or electrical energy) that is sufficient to cause a release of energy from the gas-generating material. In non-limiting embodiments, the release of energy is obtained by igniting the gas-generating material, combusting (e.g., burning) the gas-generating material, detonating the gas-generating material, or initiating a chemical reaction with the gas-generating material.

As depicted in, the initiator is a detonating cordthat is used to detonate the shaped charges, thereby initiating the gas-generating material. The energy released by the detonated shaped chargescauses the pellets from the pressure applicatorto break open and gas-generating material therein to burn rapidly, thereby generating the gas.

In other embodiments, the pressure applicatoris initiated by a designated initiator. The initiatormay include energetic materials or any other suitable arrangement to initiate the pressure applicator.

The present invention may suitably comprise, consist of, or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “about” in reference to a given parameter is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the given parameter). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

The foregoing description is directed to particular embodiments of the present disclosure for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope of the disclosure. Thus, it is intended that the following claims be interpreted to embrace all such modifications and changes.