US2650539A - Cleaning of well perforations - Google Patents

Description

Sept. 1, 1953 H. M. GREENE CLEANING oF WELL PERFORATIONS Filed Aug. 23, 1947 'Patented Sept. l, 1953 CLEANING F WELL PERFORATION S Haskell M. Greene, Whittier, Calif.

Application August 23, 1947, Serial N o. 7 70,238

1 Claim.

This invention has to do with improved methods and equipment for clearing apertures in the wall of an oil well bore, as for example the removal of bodies restricting or closing the apertures of a perforated casing or liner.

The invention particularly is directed to improvements in aperture or perforation clearing by explosive force, and specifically where such force is created substantially simultaneously and uniformly along a vertically extended length of the bore wall. This general practice heretofore has been employed by lowering within the zone to be cleaned, a string-like high velocity explosive of the type variously known as detonating or explosive cord, and Primacord as manufactured by the Ensign-Bickford Company. Such cord is characterized by its capacity, as indicated, for practically simultaneous and uniform explosion throughout the length of the string, and for creating an instantaneous or shock-like explosive force which is transmitted radially to the apertured bore wall.

One of my major objects is to supplement the effect of the explosive force so generated, in respects creating other conditions which enhance greatly the effectiveness with which the apertures may be cleared. For example, it is found that by generating heat in addition to the heat of explosion, many well regions are more thoroughly cleared of clogging bodies such as asphaltic and paranic accumulations, by reason of the capacity of the additionally generated heat to melt and uidize them. Also it is found that for best results, the clogging bodies may not be dislodged most effectively by an explosive force of instantaneous duration, as compared with an explosion-created force followed by a continuing Epressure generating effect which `adds a sustaning quality to the applied pressure, and corresponding tendency for fluid displacement through the apertures.

Accordingly, the invention contemplates igniting upon explosion of the string, a metallic mix- 'ture capable of generating considerable heat,

and distributed longitudinally of the zone to be cleared in a manner resulting in uniform heat generation to an intensity which may be predetermined as will later appear. Prolonged pressure generation may be accomplished by supplementing the relatively instantaneous explosion of the string, which results in relatively little gas generation, with the burning of a powder or charge characterized by its slower burning properties and capacity for gas generation in quantities sufficient to convert the otherwise shocklike explosive effect of the string to a sustained pressure surge creating an effective washing displacement of the well fluid out through the perforations.

The invention further aims to supplement the washing action of uid displacement under explosive force, by the impact and clearing effects of solid particles projected at extremely high velocity by the explosion force. To serve this purpose, I may place at the outside of the string a mass of small, hard abrasive particles which are projected against the bore wall and into the apertures to physically strike and dislodge the clogging bodies by a sand blast-like action. As later explained, the heat generating metals and abrasive particles may be assembled together, or placed as a mixture, about the string, so that upon its explosion the thermal and particle projection effects emanate radially and uniformly from the string in all directions.

structurally, the invention contemplates lowering the explosive string alongside a wire or other stronger line weighted to assure maintenance of proper elongation of the string under whatever conditions encountered in the hole. Preferably the string is placed within a protective sheath or tubular container which may serve the several purposes of isolating the string from attack by acidic fluids in the well, heat insulating the string, and accommodating the abovementioned heat generating metals and abrasive particles.

All the abovementioned as Well as additional features and objects of the invention will be understood most readily from the following detailed description of an illustrative embodiment shown by the accompanying drawing, in which:

Fig. l is a sectional View illustratingthe equipment positioned within vertically extended section of a perforated casing or liner to be cleared;

Fig. 2 is an enlarged cross-section on line 2-2 of Fig. 1; and

Fig. 3 is a fragmentary enlarged section on line 3 3 of Fig. 2.

Referring first to the general showing of Fig. 1, it may be assumed that the apertured or perforated inedium to be cleared consists of a vertically extended length or section of perforated casing or liner I0 set in the well bore I I containing, as usual, a hydrostatic column providing the liquid medium displaceable, as will later appear, by washing action through the perforations I2. Though I have thus typically represented the perforated medium as comprising a casing 0r liner, it will of course be obvious that the -device may be employed to clear apertures in any perforated element or in the well bore itself. Consequently, I dene the invention in the claim as apparatus for opening apertures in the wall of an extended length of a well bore, meaning by the term well bore" any medium in which apertures are to be cleared. The explosive string assembly, generally indicated at I3, is lowered on an electric cable I4 connected as at I5 with a wire line I6 suitably weighted at its lower end so that the line, and string carried thereby, at all times remain in straight distended condition. The lower end of the wire line preferably is connected with a non-magnetic, e. g. copper, shell Il containing -a variable mass, such as metal shot I8, the quantity of which may be adjusted in accordance with the length of the line and string to maintain proper tension. The shell Il and also the wire line near its upper end, may carry spring guides 19 which center the equipment in the hole.

The wire line I8 carries a non-conductor water proof sheath preferably in the form of a straight organic plastic tube 2| which may be substantially coextensive with the zone to be cleared and of appropriate size, e. g. ve-eighths of an inch I. D., to accommodate the later described materials. The tube 2l may be taped or otherwise secured to the wire line at intervals 22 sufficiently close to enable the wire line to laterally7 support the tube in straight condition.

The tube 2l contains one or more high velocity explosive strings 23 of the character hereinabove described, the string or strings extending centrally throughout the length of the zone to be cleared, which as will be understood, may range from relatively short distances to sections several hundred feet in length. Referring to Fig. 3, the upper end of the string 2.3 terminates at a detonating cap 24 4contained within a sleeve 25 and sealed within the top of the tube 2| by suitable fluid impervious sealing material 20. The `detonator 24 is electrically connected by conductors 2 with the suspension line I4. Being closed also at its lower end, the plastic tube 2l affords a iiuid-tight, acid and alkali resistant sheath preventing injury to the string 23 by any fluid conditions existing in the well, the tube further, and particularly by reason of its spaced relation from the string, .serving to thermally insulate the latter from high temperature conditions which otherwise might affect the string.

The tube .2l contains a mixture 28 of abrasive particles and pulverulent metals of the composition adapted to burn with the production of intense heat. 'Ihe abradant may be of any suitable hard, nely divided composition, such as tungsten particles or flakes, or siliceous material such as fine sand. The heat producting metals may comprise a mixture of powdered aluminum and ferric oxide, with or without antimony sulphide. To assure effective ignition of the metallic mixture, it may be desirable to rst coat or dust the string 23 with aluminum powder. It isto be understood that the quantities, or relative proportions, of the abradant and powdered metal mixture, may be varied as desired and depending upon conditions existing in -any particular job. In some instances, greater amounts of abrasive may be required because of the particular conditions causing scaling, corrosion, or clogging of the screen apertures. Likewise, where heavy paraffin or asphalt accumulations exist in the screen, 'greater quantities of the metallic mixture may be required to generate the heat necessary to melt or 'soften such bodies.

Reference previously has been made to the -desirability `of supplementing the high velocity and shock-like explosive vforce of the string 23, with gas generation at a slower rate which will have the effect of creating a more prolonged outward pressure surge through the perforations. For this purpose I may place in the tube 2l a powder or explosive having the desired burning characteristics and gas generating properties, to so supplement the string explosion and its lesser gas generation. Preferably the supplement-ary gas generating charge is distributed longitudinally of the string, as by placing quantities 29 of explosive powder, for example gun powder or black powder, at uniformly spaced intervals of say around three feet, longitudinally of the string.

In considering the operation, assume the equipment to be lowered into the well in the condition shown in Fig. 1. By .electrically firing the detonator 24, the string 23 is detonated substantially simultaneously throughout its length to create a relatively high velocity or more instantaneous shock explosion uniformly throughout its length. The force of the explosion projects the abrasive particles contained in the mass 28, at high velocity radially and uniformly in all directions against the casing l0 and into the perforations, the result being essentially a sand blasting effect which descales the pipe and tends to dislodge vclogging bodies from its perforations. The explosion heat ignites the metal mixture, causing the latter to burn with suicient heat generation to soften meltable bodies on-the pipe and within its apertures. Ignition of the powder bodies 29 results in generation of gas in quantities and at a pressure such as to continue and extend the pressure surge initiated in the well fluid by explosion of the string 23. The end result is that a substantially extended surge of fluid occurs from within the well pipe, outwardly through its perforatons, the quantity and period of the fluid displacement being such as to create an effective washing action through the perforations. When the out surge is spent, the hydrostatic column pressure outside the pipe creates a reverse or inward washing surge through the perforations, with consequent additional cleansing action. Thus the reciprocating of the hydrostatic columns inside and outside the pipe, may continue until equilibrium is reached.

I claim:

Apparatus for opening apertures in the wall of an extended length o f well bore, comprising an elongated string of high velocity kexplosive to be lowered into the well bore and to extend coextensively with said length thereof, said string being adapted to explode ysubstantially simultaneously along its entire length, a plurality `of bodies of relatively low velocity explosive powder extending about said string at locations spaced longitudinally therealong and adapted to supplement the explosion of said string by gas generation over a relatively extended period .of time, a plurality of bodies containing a mixture of hard abrasive particles and high temperature burning metallic powder and extending about said string between said bodes of explosive powder, a liquid impervious tube extending about said bodies and said string, said explosive powder and metallic powder being adapted for ignition by explosion of said string, and means for detonating said string.

HASKELL M. GREENE.

References Cited in the flle of this patent UNITED .STATES PATENTS Number Name Date 86,691 Roberts Feb. 9, 1869 203,034 Haus Apr. 30, 1878 905,336 Lheure Dec. 1, 1908 1,406,844 Gelm Feb. 14, 1922 1,510,926 De Kaiser et al. Oct. 7, 1924 1,628,401 Haber May 10, 1927 1,762,044 Bedient June 3, 1930 2,067,408 Morris Jan. 12, 1937 2,362,829 Kinley Nov. 14, 1944 2,414,349 Alexander Jan. 14, 1947 2,455,556 Burch Dec. 7, 1948 FOREIGN PATENTS Number Country Date 615,552 Great Britain Jan. 7. 1949

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