Patent Grant
9394767
Not applicable
It is generally recognized that many explosive tools have reduced performance when operating at higher wellbore pressures, particularly above 15,000 psi, when compared to when operating at lower wellbore pressures. The commercially available explosive cutters, for example, work reasonably well at lower hydrostatic pressure, say, below 15,000 psi, but are often marginal or ineffective above that pressure. See U.S. Pat. Nos. 7,146,913 and 6,644,099 to W. T. Bell. Explosive shaped charge cutters and severing tools are often used for critical situations where drill pipe is stuck and needs to be cut and pulled, while an expensive drilling rig is sitting idle, and this becomes more difficult at high pressure.
Perforating guns are also similarly affected by high hydrostatic pressure, as illustrated in
Higher pressure situations are becoming more frequent in the field and conventional approaches to design are limited in mitigating the effect. For cutters, for example, the traditional approach is to optimize the design by trial and error by increasing explosive, liner shape and density, initiation, which might squeeze out a marginal improvement in cutting at higher pressures. This effort is handicapped by the increased temperature requirements that typically accompany higher pressure, necessitating using an explosive which has inherently lower output, such as HNS. In addition, high pressure requires thicker walled and higher strength tubulars and drill pipe, as well as thicker walled housing for the explosive cutter, making a successful operation more difficult to achieve.
We recognize that if the hydrostatic pressure can be reduced temporarily during the short operating time required for an explosive cutter to initiate and complete the cut, that the cutter's performance could be increased, with an effectiveness that is comparable to operation in a lower pressure environment. One way to do this is to open a volume downhole prior to initiating the cutter. A volume opened quickly reduces the fluid pressure surrounding the cutter at the time of detonation, creating a temporary lower effective hydrostatic pressure for a better cut.
A similar situation occurs with perforating guns when operated at high hydrostatic pressures. The formation rock in these situations often has high compressive strength which can further reduce penetration. Shaped charge manufacturers can mitigate this somewhat with designs that are tailored to the high strength rock, but the wellbore pressure effect would still be present. Again, a temporary lowering of pressure in the wellbore surrounding the gun at the time that the gun initiates could increase the resulting penetration in the formation.
Conventional perforating gun systems sometimes use an empty chamber or gun volume that creates a dynamic underbalance. Although, sometimes effective in removing perforating damage through surge flow, the underbalance occurs too late to affect the penetration process itself: the shaped charge jet still has to penetrate through the high pressure fluid in the wellbore.
Perforating guns that have shaped charges with liners that contain reactive materials may be particularly susceptible to this same effect because the bulk of the reactive products are in the trailing slug and arrive inside the perforations at a later time than the jet that produces the perforation. See Bell, M. R. G., Hardesty, J. T., Clark, N. G. “Reactive Perforating: Conventional and Unconventional Applications, Learnings and Opportunities”, SPE122174, SPE European Formation Damage Conference, Netherlands, 27-29 May 2009. The effectiveness of these types of charges require that both the jet and the slug reach the perforation, meaning that there is more time for interference to occur and making the charge performance more susceptible to interference at high hydrostatic pressures.
The background above describes problems in performance of explosive devices at high hydrostatic wellbore pressure. Implicit in the understanding of the effect is that a lower hydrostatic pressure can alleviate some of the problem. Our invention couples explosive devices with existing implosion devices in a unique way to counter much of the wellbore pressure effect by a transient reduction of that pressure at the time of firing an explosive device. Our invention can also be used to control or modify the transient pressure at some remote position in the wellbore. Unregulated transient pressures from initiating an explosive device such as a perforating gun can upset plugs or packers, for example. By properly timed initiation of an auxiliary implosion or explosive device, the net transient pressure at a plug can be significantly reduced.
There are several applications for transient control of pressure down hole by opening a chamber to the surrounding fluid. One was suggested in the 1980s to create a controlled implosion for a downhole seismic application. See U.S. Pat. No. 4,805,726 to D. Thomas Taylor et al. Later, the idea was expanded to improve operations by inducing a dynamic underbalance during perforating, allowing better perforation cleanup by creating a favorable differential pressure between the formation and the wellbore for a short period of time. Later, this idea was incorporated into U.S. Pat. No. 6,598,682 to Ashley B. Johnson et al. In more recent years, implosion chambers have been used successfully to clean up existing scaly perforations by the surge created when a chamber is suddenly opened. See Harive, Kevin, Le, Cam, Khalek, Mohamed Abdel, “Service for Dynamic Scale Removal of Barium Sulfate in Perforation Tunnels,” SPE 143244, SPE European Formation Damage Conference, Netherlands, 7-10 Jun. 2011 and Busaidy, Adil Al, Zaouali, Zouhir, Baumann, Carlos Erik, Vegliante, Enzo, “Controlled Wellbore Implosions Show that Not All Damage is Bad—A New Technique to Increase Production from Damaged Wells,” SPE 144080, SPE European Formation Damage Conference, Netherlands, 7-10 Jun. 2011. When used with perforating guns for transient underbalance cleanup, these implosion chambers are typically initiated at the same time or within less than a millisecond of firing the perforating gun, all by firing a single detonator.
The invention we present here combines implosion and explosive devices by sequenced timing of the actuation of each device to create a favorable transient wellbore pressure that optimizes performance of an explosive cutter or formation perforator. In one embodiment, the ill effect of high wellbore pressure reducing formation penetration of a perforating gun or an explosive pipe, casing or tubing cutter is mitigated by the actuation of an implosion device several milliseconds before initiating the gun or cutter. Several control unit embodiments are described that determine the timed sequence of the initiations of the implosion and explosive device.
The advantages and further features of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout.
An “implosion device” as defined and used herein is a downhole tool that creates a net reduction in wellbore pressure when actuated by itself. It may be activated by initiating a small amount of propellant to open an empty tool volume to the surrounding wellbore such as by moving a tool sleeve. It can also be accomplished by using a number of small puncher charges to punch holes in the wall of an empty chamber thereby exposing the chamber to the wellbore.
An “explosive device” as defined herein is a downhole tool that creates a net increase in wellbore pressure when actuated by itself. Propellant guns used to create high pressure are one example; explosive cutters are another.
It should be noted that a perforating gun can be either an explosive device or an implosion device, depending on the magnitude of the wellbore pressure and the amount of explosive contained within the gun. If the wellbore pressure is higher than the resulting internal pressure from detonating the charges, the gun may be considered an implosion device, for example. And if the wellbore pressure is lower, then the gun may be considered an explosive device.
One embodiment of the invention is shown in
In the embodiment of
A typical dynamic response is shown in
A preferred embodiment of the time delay mechanism portion of the system contemplates usage with hot wire detonators, but those skilled in the art may conceive of similar designs for other detonator types, as well as variations on the circuitry disclosed here.
Operation of the circuit is described below:
A flow chart of
There are several approaches to effect a time delay between explosive events downhole. The one described above in
Other variations of the one described in
Another embodiment of the time delay mechanism, shown in
The embodiment consists of an electrical circuit that is attached to each detonator, where the circuit-detonators units are connected electrically in parallel. The circuit consists of a receiver, microprocessor, capacitor that is capable of firing the detonator when fully charged and a switch (typically a FET) that allows the charged capacitor to discharge into the detonator by command from a surface signal. The microprocessor is programmed to connect the detonator to the capacitor upon receipt of a special signal from the surface.
The capacitor is charged up by the application of DC voltage from a power supply at the surface that is connected to the wireline. Once the capacitor is fully charged, a signal is sent down the wireline that is received by each unit that starts an internal timer in each unit to then cause a timed discharge of the capacitor voltage through a FET to fire the unit's detonator. Each unit has a fully charged capacitor that allows the unit to fire independently of the firing of other units, obviating the problem of having one firing and preventing the firing of another by an electrical short.
Another application of having units with timing delays that can fire detonators independently without shorting is to increase the firing reliability of an explosive device by “double capping” the explosive initiation. For example, one unit with detonator can be attached to one end of the detonating cord in a perforating gun and another to the other end. Then both commanded to fire. The reliability for firing is therefore multiplied. The overall reliability of the detonators firing the gun is approximately the product of each firing (e.g., if the individual misfire rate of a single detonator is 1/100, the approximate reliability of firing of at least one of the two detonators, and thus firing the gun, is 1/10,000).
Although the invention disclosed herein has been described in terms of specified and presently preferred embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modifications of the invention are contemplated which may be made without departing from the spirit of the claimed invention.
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| Entry |
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| Number | Date | Country | |
|---|---|---|---|
| 20130220613 A1 | Aug 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61633268 | Feb 2012 | US |
