The field of the invention is perforating guns and more particularly the design of connectors for guns attached to each other so as to control the fluid flow from the formation and to prevent housing deformation in the connector which can lead to guns stuck in the well.
Perforating guns feature an inner tube that supports the shaped charges and the detonating cord that is connected to the shaped charges. A surrounding housing has machined recesses that are aligned with the shaped charges so that when the gun is set off the released energy exits through the housing recesses and creates perforation tunnels beyond the surrounding tubular that now has been perforated, and creates perforation tunnels through the casing and into the reservoir formation. In the perforation process, the result is often a spike in wellbore pressure as the charges are detonated, and is sometimes followed by a rapid decline in pressure which can cause formation fluids rush into the gun that is now hollow where the charges used to be. This rush of formation fluid is often desired to a point to assist in removing any damage or debris in the perforation tunnel to increase the flow capability from the reservoir. However, too much inflow or pressure reduction in the wellbore can also produce undesirable formation sand or even cause a casing collapse.
It is common practice when perforating multiple intervals of the well that perforating gun assemblies that are loaded with perforating charges are often separated by perforating guns that are not loaded. These non-loaded perforators are referred to as “blanks” or “spacer guns”.
Prior designs of connectors between or among guns have had the design shown in
What can also happen due to rapid pressure swings and shockwave interactions as the guns are shot and the formation fluids rush in is that the housing tubulars 20 or 22 of the blank spacers can be collapsed causing effectively an increased diameter so that retrieval of the guns becomes a problem. The blank spacer housings could also become sheared-off, separating the housing from the other perforating assemblies. The dimensional change due to pressure differential can lead to guns stuck in the well and cause the need for an expensive milling operation. Assemblies that are separated and left in the well require time-consuming “fishing” operations to retrieve the assemblies left in the wellbore.
It is therefore desirable to configure the connectors with a smaller inner tube that can better handle the differential pressures during firing of the guns and to further limit the potential volume in the gun for the formation fluid to fill after the guns are shot. An outer tube that is in pressure balance can because it has a series of holes conforms to the shape of the remaining connector components so that even if the pressurized inner tube is distorted the guns will not be stuck at the connectors since any distortion will not reach the outer tube. This pressure-balanced outer tube maintains the ability as a load-bearing member and provides the rigidity and strength required to convey the perforating assembly into the wellbore. Since this outer tube is pressure balanced, materials having a higher D/t ratio (i.e. “thinner wall”) can be employed.
Alternative embodiments such as boring out a rod for the detonation cord or altering the wall thickness of housing tubulars such as 20 or 22 to make them more resistant to deformation while at the same time controlling the volume of the chambers such as 16 and 18 are also contemplated.
The following patents reveal the state of the art for gun design that uses an inner tube to mount the detonating cord and the shots and an outer tube that is perforated in alignment with the shot pattern. These designs do not address the connector design for connectors that are disposed between the guns: U.S. Pat. No. 7,621,342 (FIG. 5); U.S. Pat. No. 6,865,978 (FIG. 8); U.S. Pat. No. 7,246,548 (FIG. 1b); U.S. Pat. No. 7,055,421 (FIGS. 2 and 2A) and U.S. Pat. No. 5,054,564 (FIG. 5).
Perforating gun connectors are provided with a small diameter inner tube to house the detonating cord and an outer tube that is ported to be in pressure balance prior to firing the perforating guns. The inner tube controls the volume in the gun for the well fluids to enter after the guns are fired and the initial pressure surge dissipates. The smaller diameter also increases pressure rating and diminishes the chance of plastic deformation. Since the inner tube is inset even some deformation is tolerated without distorting the outer tube due to the space between the tubes.
Alternative embodiments with a bored rod as a housing member or with a layered single outer wall effect are also contemplated.
Additional benefit of this invention is realized in high-pressure well environments having formation properties like unconsolidated sandstones that may be prone to producing formation sand during perforation., which can cause the assembly to become stuck in the wellbore. Having this ported outer housing and inner tube configuration allows use of high-pressure spacer gun assemblies with essentially the same outer diameter as the loaded perforating guns. By keeping the effective diameters across the assembly essentially the same, the risk of influx sand gathering in any regions where significant diameter change occurs is eliminated. This further reduces the likelihood of becoming sand-stuck.
Referring to
The reduction in diameter of the inner tubes 32 and 34 as compared to the larger housing tubes 20 and 22 of the prior art
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
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