US2446640A

US2446640A - Well perforator

Info

Publication number: US2446640A
Application number: US684761A
Authority: US
Inventors: Robert F Davis
Original assignee: Well Surveys Inc
Current assignee: Well Surveys Inc
Priority date: 1946-07-19
Filing date: 1946-07-19
Publication date: 1948-08-10
Anticipated expiration: 1965-08-10

Description

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Patented Aug. 10, 1948 WELL PERFORATOR Robert F. Davis. Falls Church, Va., assgnor to Well Surveys, Incorporated, Tulsa, Okla., a corporation of Delaware Application July 19, 1946, Serial No. 684,761

4 Claims. (Cl. 164-05) This invention relates to an improved method and apparatus for firing a projectile into the wall of an oil well or other drill hole. More particularly it relates to a method and apparatus for ring a projectile through a steel well casing to provide an opening between the interior of the well casing and the surrounding geological strata.

Prior to this invention it has been an established practice to provide openings branching off from a well bore intermediate its ends by iiring projectiles radially from the well bore into the surrounding strata. In most instances, this is done to provide an opening through a steel well casing. but in some instances it may be done merely to provide an opening extending radially from an uncased well.

In most instances wells are illled with liquid and this necessitates the firing of the perforating projectile beneath the surface of the liquid which illls the well. In many instances it is desired to iire the perforating projectile into the wall of the drill hole at a distance several thousand feet from the surface of the earth and several thousand feet below the surface of the liquid in the drill hole.

Under such circumstances a maior diiculty is always encountered in that itis necessary for the projectile to move a certain amount of the surrounding liquid out of the way before it can reach and penetrate the wall of the drill hole. Since liquid is practically incompressible, this necessitates the movement of liquid all the way to the surface of the liquid in the drill hole. As this often means the movement oi' a considerable body of liquid, the inertia of the liquid due to its weight makes extremely ditilcult the rapid acceleration of the projectile. Hence. in normal operation, the projectile is very considerably slowed down by this phenomena and the penetration into the wall of the drill hole is not nearly so deep as it otherwise would be.

A further diiliculty is encountered whenother equipment is in the drill hole at the time the per-- foration is to be accomplished. For example, it is often highly desirable to lower a well exploring' unit with the perforator so as to locate the strata into Which it is desired to send the perforating projectile. Such an exploring device may be one of the type described in Technical Publication No. 193 of the American Institute of Mining vand Metallurgical Engineers (February 1945) and entitled Some practical aspects of radioactivity well logging, by Warren J. Jackson and John L P. Campbell.

When such a. device is lowered into a well along with a perforator and the perforator is then red,

2 a violent shock wave progresses through the liquid in the drill hole and is quite likely to damage the sensitive well logging instrument, particularly if it is anywhere near the perforator.

The purpose of the present invention, therefore. is to increase the effectiveness of perforating projectiles in perforating the well casing and the surrounding strata, and at the same time to avoid the eiects of a violent shock wave on nearby sensitive equipment.

Briefly the present' invention comprises burning a quantity of slow burning powder at a point adjacent the place where the 'projectile emerges from the barrel from which it is ired, and then before the gas formed by the burning ol the slow burning powder can leave the area. exploding the charge which propels the projectile, so that the projectile will not be forced to displace a large quantity of liquid and will not generate a shock wave extending throughout the uid in the drill hole.

Since the propellent charge for the projectile is normally ignited by electrical means, it is a relatively simple matter to ignite both the slow burning charge and the propellent charge by the same electrical means and to insert a time delay circuit in series with the igniter for the propellent charge so that there will be the necessary delay between the time the slow burning 'charge is ignited and the time that the propellent charge is ignited.

Further details and advantages of this invention will be apparent from the appended drawing, and the following detailed description thereof.

In the drawing, Figure 1 is a vertical crosssection of a part of a cased drill hole and a gun perforating device in which are embodied the principles of this invention; and

Figure 2 is a vertical cross-section of a part o! a cased drill hole in which is positioned a gun perforator and a well-exploring device in accordance with this invention.

As illustrated in Figure 1. the drill hole consists of a well casing l0 embedded Iin surrounding earth ii and containing a. gun perforating device i2 (shown only in part). Normally, such a. well casing will be illled with liquid to a level far above the point at which it is desired to peri'orate.

The gun perforator illustrated consists of an outer casing I3 in which is mounted a gun barrel 'I4 which in turn contains a perforating projectile I5 and a propellent charge I6, which when exploded will drive the perforating projectile IB through the well casing I 0 and into the surrounding strata.

In accordance with' this invention, a slow burnlng powder charge i1 is placed just ahead of the perforating projectile i5 and a detonator circuit I8 is connected so that upon operation it causes the slow burning powder charge l1 to be ignited. The propellent charge I6 is also connected to the detonating circuit I8 but instead of being connected directly, the propellent charge is connected through a time delay circuit I9 which has a time constant such' that the propellent charge i6 will not be red until sufficient time has elapsed for the slow burning charge I1 to burn and forma gas pocket adjacent the forward end of the projectile.

The slow burning powder or charge -can be oi. any desired material that will burn slowly and `produce a considerable volume of gas Without causing any abrupt pressure increase in the well or any appreciable shock wave. 'I'he time delay circuit -I9 may be of any desired type. the only requirement being thatv it produces sufcient delay between the ilring of the slow burning charge and ythe firing of the propellent charge. A slow burnlngpowder fuse may even be substituted for the time delay circuit to produce the same result.

The construction of the gun perforat-or casing, the gun barrel, the projectile and the propellent charge is conventional, except that it usuallyT is desirable to so form the gun barrel that an annular ring is formed around the propellent charge, which-ring serves to prevent the projectile from being forced backward against the propellent charge when the slow-burning powder charge is fired. This avoids any possibility of the pressure from the slow-burning powder charge being transmitted 'through the projectile and causing -detonation of the propellent charge sooner than desired` The 'slow burning powder` charge need not necessarily be placed in the gun barrel but may be placed in a separate chamber near the gun barrel an-d this chamber may be vented either intothe 4gun barrel or into the well at a point .near the gun barrel; It is desirable, but not essential, that the liquid in the gun barrel immediately ahead of: the projectile be blown out by .the slow burning. powder charge before the propeilent charge is ignited. The desirable result Vwill bep'ar-tially realizedA even if the gas formed .by the slow burning powder charge is at some little distance from the gun barrel, when the explosion occurs. -It is desirable, however, that the slow burning powder charge clear the barrel and the surrounding area and that all be clear of liq- .uid at the time the propellent charge is ignited.

i In many instances it is desirable to accurately I position the perforator by the use of a well surlveying instrument suspended on the same cable from the surface of the earth. In order to position vthe-periorator accurately itis desirable that ,the surveying instrument be positioned relatively close to the perforator.

. Following the principles of this invention and .as illustrated in Figure 2, a well surveying Ilnstrument 30 may conveniently. be suspended from the same cable 3| and positioned a short distance above a perforator 32. The gas formed by the slow burning powder charge will then act to absorb the shock wave produced by the explosion of the propellent charge and avoid damage to th surveying instrument.

A protecting disk may be placed between the slow-burning powder charge and theouter end of the gun barrel as shown in United States Patent 2,029,454, granted February 4, 1936, to Walter T. Wells.

What is claimed is:

1. A method of perforating the wail of a drill hole that comprises igniting a charge of slow burning powder in a drill hole adjacent the place where the wall is to be perforated and immediatelythereafter, before the gas formed by the slow burning powder has had a chance to leave the area, firing a projectile into the wall of the drill hole at the place where the drill hole is to be perforated.

2. A perf'ora-tor for the wall of a drill hole that comprises a capsule adapted to be lowered into a drill hole, a radially directed gun barrel in said capsule, a projectile in said gun barrel, a propellent charge behind said projectile, a slow burning powder charge adjacent the forward end of said projectile and means to detonate said slow burning powder charge and said propellent charge sequentially and at predetermined intervals of time.

3. Apparatus for perfora-ting the wall of a drill hole that comprises an exploring device and a gun -p-erforator suspended from a single cable one above the other, said gun perforator including a slow burning powder charge vented into the area surrounding the perf orator and means to re the slow burning powder charge at a predetermined interval of time prior to the iiring of the propellent charge for the projectile.

4. A gun perforator for perf-orating the wall of a drill hole that comprises a capsule adapted rto be lowered into a drill hole, a projectile in said capsule, a propellent charge arranged to propel the projectile into the surrounding strata,'a slow burning powder charge positioned adjacent the point where the projectile emerges from the capsule and means to electrically ignite lsaid slow burning charge and said propellent charge, said means including a time delay circuit connected to delay the ignition of the propellent charge until .a chance to burn.

the slow burning charge has been ignited and had ROBERT F. DAVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,029,478 Haines Feb. 4, 1936 2,246,542 Slnth June 24,-1941