Patent Grant
7775279
The invention generally relates to the field of oilfield exploration, production, and testing, and more specifically, to the use of materials designed to create debris-free perforating apparatus and techniques for enhanced hydrocarbon recovery.
For purposes of enhancing fluid communication between wellbore and geological rock formation containing hydrocarbons, holes are punched from the wellbore to the rock formation during operations, known in the oilfields as perforating operations. More specifically, during these operations a long and tubular device called a perforating gun is run into the wellbore in preparation for production. After the perforating gun has been deployed at its appropriate position downhole, perforating charges (shaped charges, for example) contained within the perforating gun are fired. As a result of firing these shaped charges, extremely high-pressure jets capable of opening perforation tunnels through both casing and liner (if the wellbore is cased) are produced, and a skin of the surrounding rock formation is then made more permeable for releasing its hydrocarbons.
The shaped charges are designed so that a cavity-effect explosive reaction is produced and focused in a high-pressure and high-velocity jet that can force materials, such as steel (casing), cement and rock formations, to fracture and then flow plastically around the jet and effectively open a perforation tunnel. Shaped charges may be classified according to the tunnel depth their perforation jet forms and the tunnel cross-sectional diameter (called the “hole size”) at its entrance. One type of shaped charge, referred as a “big hole” shaped charge, produces a relatively large-diameter hole in the casing and has a relatively shallow penetration depth into the rock formation. Such “big hole” shaped charges are commonly employed in sand control applications. Another type of popular shaped charge is a “deep penetrating charge.” Such a shaped charge leaves a relatively smaller-diameter hole in the well casing but has the advantage of penetrating relatively farther into the geological rock formation. The greater penetration depth associated to these charges is hugely beneficial to extend well fluid communication past any damage zone (caused by drilling of the wellbore), and it also tends to significantly enhance well productivity. Deep penetrating charges are employed in natural completion applications.
The shaped charges may be contained either inside a tubular member as part of a hollow carrier perforating gun or may be individually encapsulated. In order to prevent deteriorating the explosives contained within the shaped charges due to inadvertent contact with well fluids, each shaped charge is sealed by a corresponding cap. By being more massive, the encapsulated shaped charges tends to produce significantly more debris than the same size charges that are carried by a hollow carrier perforating gun. The encapsulated charges also tend to generate larger diameter holes in the casing that extend deeper into the geological rock formation.
The firing of the perforating gun results in debris from both the shaped charges and other parts of the gun located in close proximity to the explosives. Though the debris is largely contained within the perforating gun and the wellbore, some debris is inescapably introduced into the rock formation. In situations where significant debris (in particular from the shaped charge liner) reaches the rock formation, the productivity of the well may be hindered, resulting in a problem often referred as “skin damage”. To mitigate the detrimental consequences of debris left in the perforating tunnel, perforating is generally conducted underbalanced (i.e., in conditions wherein the wellbore possesses a lower pressure than the formation pressure) since a higher formation pressure causes debris to evacuate with the formation fluids surged into the well. Today, other methods of stimulation such as acidizing and propellent fracturing are often used for purposes of overcoming this damage and bringing the well up to its full potential. If not property conducted, perforating debris may induce significant losses with regard to time and cost operating the well. As example, an extra intervention may be needed in the well to remove debris from a fractured zone. Of considerable concern to a field operator, the debris may cause additional damage to the well, such as damage caused to a packer elastomer seal or damage due to the clogging of a downhole choke, for example.
Thus, there is a continuing need for new and/or improved solutions to minimize the amount of debris in a well and therefore, offer new and improved perforating operations.
In an embodiment of the invention, an apparatus that is usable with a well includes a perforating system that is adapted to be fired downhole in the well. The perforating system includes a component that incorporates an alloy having a negative corrosion potential and being unable to passivate, and the component adapted to disintegrate to form substantially no debris in response to the firing of the perforating system.
In another embodiment of the invention, a method that is usable with a well includes providing a perforating system downhole in the well and firing at least one perforating charge of the perforating system. In response to the firing of the perforating charge(s), a component of the perforating system, which has an alloy with a negative corrosion potential and having the inability to passivate is disintegrated.
Advantages and other features of the invention will become apparent from the following drawing, description and claims.
In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible.
As used here, the terms “above” and “below”; “up” and “down”; “upper” and “lower”; “upwardly” and “downwardly”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or diagonal relationship as appropriate.
Referring to
The perforating system, in accordance with some embodiments of the invention, includes a perforating gun 50 (depicted in
Among its other features, the string 30 may include, as an example, a packer 40 for purposes of sealing off an annulus 42 between the tubular string 30 and the casing string 20 prior to the firing of the perforating gun 50.
In general, the perforating gun 50 may include a firing head 52, which is constructed to respond to stimuli communicated from the surface of the well for purposes of directing the firing of perforating charges, such as shaped charges 56, of the perforating gun 50. More specifically, the stimuli may be in the form of an annulus pressure, a tubing pressure, an electrical signal, pressure pulses, an electromagnetic signal, an acoustic signal. Regardless of its particular form, the stimuli may be communicated downhole and detected by the firing head 52 for purposes of causing the firing head 52 to ignite the shaped charges 56 and thus, fire the perforating gun 50.
As an example, in response to a detected fire command, the firing head 52 may initiate a detonation wave on a detonating cord (not depicted in
The perforating gun 50 is depicted in
For example, referring to
Regardless of the particular form of the perforating system that is used, the perforating system includes components that are designed to leave substantially zero debris in the well after the firing of the system. More specifically, in accordance with embodiments of the invention, these components contain materials that may be characterized as being anodic with respect to common engineering materials and immune to building a passive, long-lasting, and protective film.
In the context of this application, an “anodic” material is a material that possesses a corrosion potential lower than that of common engineering materials, for instances commercial steels and aluminum alloys. Therefore, when the anodic material is electrically connected to such steels and aluminum alloys while exposed to an aqueous environment the anodic material degrades providing the absence of corrosion inhibitors. The byproduct of this degradation may be characterized as non-metallic (e.g. hydroxides, oxides though containing ionically bound metallic elements)
By being anodic, the materials described herein are intrinsically metallic in nature and may also be characterized as being reactive. In this context, the term “reactive” extends beyond the metals in the two first rows of the periodic table, namely the alkaline and alkaline-earth metals. For instance, aluminum and possibly iron (the fundamental ingredient in steels), once properly alloyed and processed, may be also considered to be “reactive”. With proper alloying, such metals may be designed to avoid forming any stable (durable) protective oxide, hydroxide, and other like protective non-metallic films, as conventional commercial alloys do, and may furthermore develop intra-galvanic cells that self-consume the material, even in a benign environment such as neutral water (i.e. without addition of one or several acids so that pH is about 7.0).
In the presence of water, including neutral water, the anodic materials that are described herein degrade at various rates. The rate of degradation depends upon intrinsic thermodynamic variables such as temperature and pressure, as well as other variables, including the fluid to which the material is exposed, its composition, and often more important the chemical composition and internal structure (developed in particular by processing, for instance heat treatment) of the material, as well as the presence of an electrical link to a more cathodic material (e.g. a steel). Materials are described herein that, in accordance with some embodiments of the invention, are designed to avoid forming a passive (protective) layer, even in a very benign environment like distilled (e.g. halide-free) neutral water. In accordance with embodiments described herein, the materials are therefore such that they do not protect themselves effectively against their surrounding. Commercial alloys of aluminum, iron (e.g. steels, stainless steels), nickel, and so on rapidly develop stable (durable) oxides, hydroxides or other semi-metallic like layers that impede them from further degradation. The materials that are disclosed herein are considerably different because they are not capable of developing such immunity that commercial alloys are required to acquire, when for instance exposed to a fluid as friendly as water. Additionally, as described herein, the materials, although designed to form zero debris, may be further improved in strength, density and apparent elastic moduli: three important material properties that in perforating primarily affect jet formation and penetration depth, and thus, performance of a perforating operation.
Because the materials that are described herein are either anodic by nature, or intentionally made more anodic by design, in aqueous fluids hydrogen gas normally evolves and may be expected even under the high pressure and high temperature seen downhole a hydrocarbon well. It also follows that metallic components that are galvanically coupled to the anodic materials described herein may potentially be at risk of being cathodically (hydrogen) charged and therefore, may subsequently crack under applied or residual tensile stresses, if countermeasures are not properly planned; for instance, electrically insulating the anodic materials from other metallic tools using insulating plastics, elastomers, or ceramics. However, in accordance with embodiments of the invention, for purposes of preventing this type of cracking, the materials are selected to create basic and alkaline environments.
More specifically, when the anodic materials that are described herein degrade (dissolves) in an aqueous environment, the pH of this environment increases, possibly reaching values culminating nearby 10 or 11 in environments that are for instance contained (e.g. like in stagnant fluids). As more of the materials degrade and cause this environment to gradually become saturated and eventually supersaturated, the precipitation of hydroxides follows at pH values closer to 10 or 11. Practically, this means that the gradual degradation (dissolution) of the materials removes hydrogen (protons and gas) from the aqueous environment. Even if hydrogen charging is to proceed on the cathodic side of an established galvanic circuit, given the life expectancy of the zero debris and anodic material and the relatively high downhole temperature (which makes hydrogen particularly diffusible in downhole alloys), proper conditions for cracking the downhole alloys can hardly be established. Furthermore, when also exposed to environments that have low concentrations of chloride ions, are anaerobic (de-aerated), and non-stagnant (flowing conditions), the anodic materials that are described herein present no risk to the alloys of the permanent downhole completion.
Turning to the more specific details, in accordance with embodiments of the invention, three types of materials (that are hereinafter referred to as “debris free anodic materials”) may be used with the intent to produce substantially zero perforating debris: 1.) an alloy designed with a negative corrosion potential that is also not capable of forming a durable passive layer (i.e., the material is not able to self-protect); 2.) a metal-matrix composite designed with a matrix that comprises a metal or alloy of negative corrosion potential that also does not possess the ability to passivate (self-protect); and 3.) a ceramic-matrix composite designed with a main additive that contains a metal or alloy of negative corrosion potential that also does not possess the ability to passivate (self-protect). The debris free anodic materials are described in greater details below.
Referring to
In accordance with some embodiments of the invention, the debris free anodic material is an alloy that has a negative corrosion potential and the inability to passivate (self-protect). For example, the alloy may have a corrosion potential that is comparable with or less than that of aluminum, in accordance with some embodiments of the invention.
A table 160 that is depicted in
As additional example in accordance with some embodiments of the invention, the debris free anodic materials may include materials such as calcium alloys as well as materials that incorporate calcium or any other alkaline element or phase that compares to calcium in hazard ranking (safety). Table 180 in
As additional examples, other materials that have negative corrosion potentials and may be also considered debris-free include magnesium-lithium type alloys (e.g. LA141, LZ145, LA91 for instance). Other materials may also include transition-metal alloys like ferrous alloys. Such materials or alloys must be intentionally alloyed (enriched with alloying elements) and processed to not passivate, or protect themselves from the well environments. Such materials or alloys may be useful in situations where other combinations of strengths, toughness, and especially degradation rates are demanded. In that aspect, these other alloys may be seen as complementary to the calcium alloys and the degradable aluminum alloys previously described. When ferrous alloys are intentionally made degradable, they should exclude alloying elements such as chromium, molybdenum, and nickel. Like the calcium and the aluminum alloys previously listed, these ferrous alloys may be produced by casting, powder-metallurgy routes, or other near-net shape manufacturing processes. Heat-treating may also be employed to optimize specific properties of the alloys, depending upon conditions of use.
In accordance with some embodiments of the invention, the debris free anodic material may be a metal-matrix composite or a so-called “cermet” (i.e., a ceramic-metal composite wherein the metal serves as binder or matrix, while the ceramic serves as reinforcement), wherein the matrix is composed of a metal or alloy characterized by having both a negative corrosion potential and the inability to passivate (self-protect). As examples, the matrix of the composite may contain some of the alloys previously described, such as, in particular, aluminum, calcium, or other degradable alloys. By being a composite, the material also contains additives, in particular discontinuous phases such as powder and particulates that are intentionally added to impart certain properties to the composite material. If, for example, the density of the debris free anodic material is to be controllably raised, as needed by certain perforating applications, a heavy transition metal like tungsten or tantalum, and/or semi-metallic phases or compounds of such heavy-transition metal elements like carbides, nitrides, carbo-nitrides, and/or oxides (e.g. tungsten nitride) may be incorporated at the appropriate proportions to an aluminum-gallium or calcium alloy for instance.
Types of composites include functionally-graded materials, such as layered composites of alloys for instance, as well as the more traditional composites where the additives are uniformly distributed with a matrix. Types of additives for metal-matrix composites include continuous fibers, discontinuous fibers, particulates, powders, etc. Another advantage of the metal-matrix composites and cermets in aqueous environments is that the composite may readily form intragalvanic cells. Such cells may further accelerate the full degradation of the composite, leading to shorter degradation time than if the material of the matrix were used without additives. Such intragalvanic cells are formed in-situ an electrically conductive fluid environment by the presence of at least two phases that have different corrosion potentials. Examples of such composite is the tungsten aluminum composite earlier discussed. In that example, the aluminum phase is anodic and thus degrades while the tungsten is cathodic.
Another example of debris-free anodic material in accordance with embodiments of the invention is a ceramic-matrix composite (compositionally similar to a cermet, but the ceramic here acts as matrix, or binder), where the main additive includes a metal or alloy that has a negative corrosion potential and is unable to passivate (self-protect). As examples, the ceramic-matrix composite in accordance with embodiments of the invention, may include alkalines, alkaline-earth oxides, nitrides, etc. In general, ceramics shatter upon detonation due to their inherently poor toughness (or high brittleness). In order to minimize debris size, the ceramic material may be interrupted by the presence of an alloy that has a negative corrosion potential and is unable to passivate (self-protect). This alloy may be used to toughen the formed ceramic composite and expand its application range.
In accordance with some embodiments of the invention, the alloy may be designed to exhibit a poor toughness and thus exhibit a brittle-like behavior upon overloading/impact loading so that upon firing of the perforating system parts made of the alloy shatters in small and harmless debris. Over time the debris then fully degrades in the downhole environment, eventually leaving zero debris. In order to respond to dynamic loads, the alloy may incorporate unusually high fractions of brittle intermetallic phases. Suitable intermetallic phases may be generally recognized on equilibrium phase diagrams by their narrow composition ranges and high melting temperatures. From a thermodynamic standpoint, these intermetallic phases are the result of negative enthalpy of mixing, meaning that heat is spontaneously generated when these intermetallic phases form (i.e., exothermic reactions occur). Examples of brittle intermetallic phases may be found in aluminum—copper or aluminum calcium phase diagrams for instance.
In other embodiments of the invention, the debris free anodic material may be relatively strong prior to firing of the perforating system. However, once the charges are ignited and consequently temperature rapidly raises while a pressure spike is momentarily produced, phase transformations may occur within the material, thereby causing the material to weaken and fragment into fine (i.e. with large surface-to-volume ratios) debris in the terminal stages of perforating; i.e. after the jet has formed. The fragmentation of such brittle material into debris is also enhanced by the fact that the phases forming immediately after firing are brittle intermetallic phases that also have lattice parameters and/or volume expansions/contractions widely differing from the initial phases. In the presence of rapidly changing temperatures and stress (pressure) fields, the cracking, as assisted by the formation of new phases, may be useful, most specifically if this cracking originates fine debris that subsequently degrade in the fluid environment. In some embodiments of the invention, nano-materials (pure and unreacted copper nanoparticles in an aluminum matrix, as an example) may be used to produce secondary exothermic reactions giving rise to highly brittle materials. Thus, many variations are contemplated and are within the scope of the appended claims.
The debris free anodic materials may be used in one or more components of a shaped charge in accordance with some embodiments of the invention.
It is noted that the shaped charge may be an encapsulated shaped charge, such as an encapsulated shaped charge 250 that is depicted for purposes of example in
In accordance with some embodiments of the invention, the zero debris material may be an essential building block to fabricate a zero debris shaped charge case. Therefore, due to this design, after detonation of the shaped charge, the debris is substantially totally degraded and leaves practically no residue inside the gun or wellbore. A higher density may be desired for the case for purposes of allowing the case to contain pressure longer and deliver more energy to the perforation jet to therefore enhance charge performance. To increase case density, a high density material, such as tungsten, may be added to a degradable material, thus forming a metal-matrix composite wherein the matrix or bonding agent is the degradable material. After the detonation, the bonding material degrades and the additive material is left in fine powder form, which does not cause any detrimental effects to subsequent well operations.
In accordance with some embodiments of the invention, the zero debris material may be used for a shaped charge liner. By using a high-density material in the liner, the perforation jet is enabled to reach deeper in the rock formation. In order to increase liner density, additives like tungsten powder may be incorporated to the liner. Because the material in the liner is degradable and is said to be zero-debris, the residual material that is often deposited in the bottom of the perforating tunnel is eliminated. If an additive, such as a fine tungsten power is used, the leftover powder has a relatively good permeability and may be flushed out of the tunnel.
The zero debris material, in accordance with embodiments of the invention, may likewise be employed in components of an encapsulated shaped charge, such as in the case, cap and/or liner. The benefits described above apply to using the material in one or more components of the encapsulated charge.
The zero debris material may be used as a supplementary heat source for purposes of increasing the perforation jet energy, in accordance with some embodiments of the invention. More specifically, in some embodiments of the invention, all of the components of the shaped charge, such as the case, liner, cap (if the charge is encapsulated) and even part of the explosive(s) may be made from the zero debris material for purposes of increasing the perforation jet energy. The zero debris material reacts quickly and affects the pressure power of the liner, which increases the perforation jet energy. In order to create a high level of exothermicity, transition metals and their semi-metallic phases may be added. A degradable aluminum gallium alloys incorporating fine and homogeneously distributed iron oxide may be used to produce thermite-like reactions for instance. Other additives may include metallic elements that once in contact with aluminum and gallium for instance would react exothermically. Examples of such elements are iron, titanium, nickel as well as copper. It is noted that nanoparticle size may be used for this effect, in accordance with some embodiments of the invention. Furthermore, by increasing the perforation jet energy, pressure inside the perforating gun, the wellbore and ultimately, the perforating tunnel may all be beneficially effective, thereby leading to superior charge performance and enhanced well productivity.
Components of the perforating system other than the shaped charge and its subcomponents may be formed from the zero debris material in accordance with embodiments of the invention. For example, the zero debris material may be used as a plug material on a gun/firing head housing that is exposed to the well fluid. In this regard, referring to
The pressure inside the firing head housing 300 is equalized if a sufficiently high pressure exists inside the perforating gun. In this regard, sometimes, a loaded gun string may stay downhole at elevated temperatures for a significantly long time period, which exceeds the time duration specification for the perforating gun. When this occurs, the explosive inside the perforating gun partially or completely degrades, and the pressure inside the gun becomes significantly high. At this point, the perforating gun may malfunction, and even if the gun is fired, the perforating charge holes in the gun may be plugged and high pressure gas may be trapped inside the gun. Thus, via the port 304 and associated plug 310, any trapped high pressure gas inside the perforating gun is relieved before the gun is brought the surface to prevent a hazardous situation from occurring. After the plug 310 dissolves to establish communication between the interior space of the firing head housing 300 and the wellbore (via the port 304), the wellbore pressure may be controllably increased for purposes of, for example, firing the perforating gun.
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
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