Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. As a result, over the years well architecture has become more sophisticated where appropriate in order to help enhance access to underground hydrocarbon reserves. For example, as opposed to wells of limited depth, it is not uncommon to find hydrocarbon wells exceeding 30,000 feet in depth. Furthermore, as opposed to remaining entirely vertical, today's hydrocarbon wells often include deviated or horizontal sections aimed at targeting particular underground reserves.
While such well depths and architecture may increase the likelihood of accessing underground hydrocarbons, other challenges are presented in terms of well management and the maximization of hydrocarbon recovery from such wells. For example, during the life of a well, a variety of well access applications may be performed within the well with a host of different tools or measurement devices. However, providing downhole access to wells of such challenging architecture may require more than simply dropping a wireline into the well with the applicable tool located at the end thereof Indeed, a variety of isolating, perforating and stimulating applications may be employed in conjunction with completions operations.
In the case of perforating, different zones of the well may be outfitted with packers and other hardware, in part for sake of zonal isolation. Thus, wireline or other conveyance may be directed to a given zone and a perforating gun employed to create perforation tunnels through the well casing. As a result, perforations may be formed into the surrounding formation, ultimately enhancing recovery therefrom.
The described manner of perforating can be accompanied by a significant degree of ‘gun shock’, particularly in higher pressure wells. That is, in conjunction with firing of perforating gun, a problematic pressure wave may arise from differential pressure which then results in undesired movement of the gun and associated equipment inside the wellbore. This may result in damage to the well and surrounding hardware. For example, the perforating shaped charges are initially held within a carrier of the gun that is of a given ambient pressure which is isolated from the pressure of the well. Once the gun is fired, the detonation pressure forms inside the gun carrier while the shape charge jets emerge from the carrier in a manner that creates holes within the wall of the carrier. The differential between the post-detonation pressure within the carrier and that of the well can lead to a sudden rush of wellbore fluids into (or a sudden rush of detonation gas products out of) the carrier depending on whether the detonation pressure inside the gun carrier is smaller or larger than the wellbore pressure. Strong pressure waves may be induced by this rapid fluid motion. Thus, gunshock results. A large magnitude of the pressure wave can damage the downhole equipment.
As well environments continue to become harsher and depths continue to increase, the degree of gunshock may be quite significant. For example, while the gun and carrier are sealed at surface, the pressure at the high pressure well zone at issue may be anywhere from 10,000 to 25,000 PSI. Thus, a dramatic degree of gunshock may follow a firing perforating application. This may damage surrounding hardware at the zone and require follow-on remediation. Ultimately, the loss of operational time and cost of hardware repair or replacement may run in the hundreds of thousands of dollars if not more.
So as to help avoid such significant expense, efforts have been undertaken as a means of addressing the issue of gunshock. For example, metal-based filler may be distributed throughout the inner volume of the carrier. As a result, once perforating takes place and the carrier is exposed to the surrounding well pressure, the degree of gunshock may be minimized due to the small amount of lower pressure space actually exposed. Of course, this also results in a heavier and more expensive gun.
As an alternative to the heavier metal-filled carrier housing, measures may be undertaken which address the nature of underlying perforating application reactions themselves. For example, perforating by firing a series of shaped charges as noted above are detonated by detonation cord. Thus, the detonation of each charge leads the high speed jet that creates the perforation. In order to address gunshock as noted above, the charges may alternatively include propellant to increase gas production after the firing. In theory, the slower reacting propellant would lead to pressure increase inside perforating gun following the detonation of shaped charge,
Unfortunately, propellants which might theoretically be of limited effectiveness in this manner often fall short in the reality of the well environment. That is, these propellants are not particularly well suited to withstand high temperature environments which are often high pressure as described hereinabove. Thus, a more effective technique is needed to mitigate the gun shock damage.
A charge for use with downhole tools such as a perforating gun is disclosed. The charge may be located within a carrier housing of the tool and equipped with different types of explosives. For example, a first type of explosive may be incorporated into the charge for carrying out an application in a well such as perforating. However, a second type of explosive such as reactive metal powder may be incorporated into the charge for adjusting (or controlling) a pressure differential between the well and the carrier housing immediately after the application.
Embodiments are described with reference to certain perforating applications directed at high pressure well environments. In particular, wireline deployed perforating gun applications are detailed. However, other forms of deployment and application types may take advantage of pressure inducing charge embodiments as detailed herein. Regardless, pressure inducing charge assemblies are described which include a metal reactive powder material for minimizing a pressure differential between the assembly and surrounding well pressure at the time of the application.
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A detonation cord 140 is provided to each of the indicated shaped charges 125 to allow for detonation or firing during a perforating application (e.g. such as within the well 180 depicted in
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The above described embodiments include holders 100 which may be self-contained devices that provide structural support for accommodation of a material 190 therein which may be in the form of a reactive metal powder. Alternatively, the reactive metal powder may be incorporated into the case 195 or elsewhere. As described further below, the reactive metal powder material may be a powder mixture of heat and gas generating constituents of a generally slower reaction rate than that of the high energy explosive in conventional shaped charge. For example, the detonation cord 140 may initially set off high energy explosives in the shaped charge 125 for sake of perforating. However, this may in turn lead to initiating a reaction of reactive metal powder of material types as detailed further below. This subsequent reaction of reactive metal powders may take place at a rate thousands to millions of times slower than the initial reaction of high energy explosive. Yet, by taking place in this sequential and subsequent manner, heat and gas buildup emerges in a manner to diminish the above detailed pressure differential.
The particular construction of the shaped charges 125 may be configured in light of likely exposure to higher temperature and pressure environments. Further, apart from driving a perforating shaped charge jet as described below, a shaped charge 125 as detailed herein may additionally or alternatively drive the generation of heat and/or gas sufficient to diminish pressure differentials. In fact, with such capacity provided to the gun assembly 101, it may be effectively employed in even higher pressure wells without undue concern over downhole architectural damage as a result of extensive gunshock. Indeed, substantial gunshock related damage may be avoided through use of embodiments as described herein, even in circumstances where the targeted downhole location of the well 180 exceeds about 20,000 PSI.
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Upon firing of the high energy explosive that makes up the material 190 as described above, a secondary reaction may also be initiated. More specifically, the case 195 itself may be constructed of a reactive metal powder having a comparatively slower reaction rate as noted hereinabove. Thus, in conjunction with the initial high energy explosive reaction, a subsequent gas forming reaction is ignited which takes place over a longer period of time so as to increase pressure in the depicted void space 130. As such, gunshock inducing pressure differentials may be minimized.
In one embodiment, the heat and gas forming reaction of the material may be one that is fuelled by a mixture of at least about 5% of each of a metal, a metal oxide or/and metal nitrate, a metal carbonate. That is, the case 195 may be constructed of a powder form of such materials, compressed into a durable form so as to make up the structure of the case 195. With added reference to more specific material choices below, in one embodiment, the case 195 may be constructed of a mixture of Al, Fe2O3, CaCO3, and Ca(NO3)2. Thus, during this subsequent or extended reaction a generation of carbon oxide and nitrate gases may ensue so as to mitigate the pressure differential and any measurable degree of gunshock. Once more, this mitigation may take place over a longer period of time as compared to the initial primary reaction, thereby provided an added degree of mitigation.
The particular reactive metal powder material of the case 195 may be any of, or a combination of, aluminum, beryllium, titanium, tantalum, yttrium, and/or zirconium. As for metal oxides, bismuth, cobalt, chromium, copper, iron, iodine, manganese, nickel, lead, strontium, and tungsten-based oxides may be utilized. Metal carbonates of barium, calcium, magnesium, potassium, lithium and/or a strontium-base may be employed which, during reaction may degenerate to carbon dioxide gas. Similarly, the metal nitrate may lead to the generation of a gas. Candidates of this nature may include a nitrogen-oxide based barium, calcium, lithium, potassium magnesium and/or strontium.
In another embodiment, the material types of the case 195 and internal material 190 may be reversed. That is, the case 195 may be constructed of the high energy explosive for fueling the perforating, whereas the internal material 190 may be of an extended reacting, reactive metal powder form. Indeed, for that matter, a liner 201 of reactive metal powder, may also be provided to further fuel the appropriate reaction.
In yet another embodiment, the entire charge 125 may be filled with an internal material 190 of only the reactive metal powder. That is, with added reference to
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In spite of the exposure of the assembly interior to the well and potentially high pressures therein, well damaging gunshock may be substantially avoided. This is due to the above noted reactive metal powders which may raise in-gun pressure at the aforementioned interior as noted at 575. Indeed, as indicated at 595, an elevated in-gun pressure is achieved and may even be maintained for a period that exceeds the relevant triggering and/or application timeframe of high pressure explosive application. Thus, measurable gunshock related damage to the well as a result of the application may be rendered even less likely.
Embodiments described hereinabove include charge assemblies for use in downhole environments in a manner that substantially avoids gunshock induced damage in the well. This may be achieved in a manner that avoids sole reliance on propellants. Thus, an effective technique for carrying out applications such as using reactive shaped charges in perforating operation may be undertaken in high differential pressure environments without a significant likelihood of follow-on high cost remedial action.
In another embodiment, the disclosed technique is used in perforating for hydraulic fracturing operations. Thus, a substantial increase in gun pressure may be obtained such that the wellbore pressure will also be substantially increased. This leads to creating fractures in the formation near the wellbore region when at least one perforation exists on the casing 480 near the perforating gun assembly 101.
The preceding description has been presented with reference to presently preferred embodiments. Persons skilled in the art and technology to which these embodiments pertain will appreciate that alterations and changes in the described structures and methods of operation may be practiced without meaningfully departing from the principle, and scope of these embodiments. For example, techniques detailed herein may be utilized in open-hole environments, or as a manner by which to enhance perforating depth and character irrespective of gunshock minimization. Furthermore, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.