Method For Cleaning Wells

Abstract

A combination of repeated mild explosions and a series of pressure pulsations provides both repetitive shock and repetitive sustained fluid pulsations. The shock is required to break up and loosen various formations and materials formed in the well casing perforations and interstices of surrounding formation. The pulsations achieve repeated flow of the well fluid back and forth through the casing perforations and surrounding formation to thereby remove particles of plugging material that are loosened by the shock waves. A series of explosive caps, explosive power of which is enhanced by surrounding layers of plastic sheet explosive, are individually interposed between a number of gas pulsation producing modules. Each module is arranged to effect burning of a combustible in a series of pulses to produce the desired fluctuating pressure pulses and fluid surging. The entire assembly of gas producing modules and explosive caps is interconnected in a string and arranged so that the burning or explosion of one element of the string will, itself, initiate the burning or explosion of the succeeding element, thus eliminating the need for multiple control lines for the desired sequential ignition.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the enhancement of operation of fluid wells and more particularly concerns methods and apparatus for cleaning well casings and the immediately surrounding formations.

Increasingly large numbers of oil, gas and water wells that produce fluids through perforated casings and/or well screens via porous productive formations, including sand, gravel, or shale are confronted with the problem of accelerating reduction of production. Casing perforations commonly used throughout fluid bearing strata in oil, gas or water wells tend to become clogged with various incrustations, asphaltum, paraffin, alkali or other material that may be deposited upon or within the casing perforations and upon or within the interstices of formations immediately surrounding the casing. Mineral, bacteria or algae-like growths gradually deposit on passage surfaces reducing the area, or in some cases, completely blocking some passages. Fine sand or silt material is drawn into and deposited within the relatively small passages that form a part of the porous formation whereby the flow of fluid through such formations and into the well casing or screening is significantly reduced.

The problem of clogged interstices and well casing perforations is emphasized in those wells that employ water injection to enhance production. The water itself includes additional chemicals that may not be naturally occurring in the area of the productive formation. Such chemicals introduce still other well-clogging deposits within the casing, its perforations, or within the gravel pack that is sometimes emplaced between the casing and the surrounding productive formation. Further, with velocity increases that may occur as the result of water injection, additional fine silt-like materials will be drawn into and deposited in the relatively narrow passages, thus further accelerating degradation of the well flow characteristics.

2. Description of Prior Art

When production from such a well decreases materially due to clogging conditions as described above, washing and/or cleaning operations are undertaken. Washing operations of the swabbing type employ a piston-like element that is inserted into the well, substantially extending across the entire internal area of a portion of the well casing, and arranged to be reciprocated within the well to cause the fluid therein to surge back and forth through well perforations and the surrounding formations. Swabbing is ineffectual when the perforations are clogged because surging action alone will not loosen relatively hard incrustations. Moreover, where the casing to be cleaned is several hundred feet in length, the task of inserting and operating such a device is difficult, expensive, and time consuming.

Various chemicals, heat, or sustained pressures have also been employed in cleaning, all without significant success since scale and other clogging materials are not readily removed by such methods.

In order to break up and loosen hard scale deposits, various types of explosive cleaning arrangements have been suggested. For example, U. S. Pat. No. 2,414,349 to Alexander suggests a single line of exceedingly high velocity explosive to provide a shock wave substantially simultaneously along a significant length of the well casing. Greene, in U. S. Pat. No. 2,650,539, suggests that explosive cleaning charge be supplemented with either heat or a continuous pressure. Other workers in the field such as Ebaugh, U. S. Pat. No. 2,756,826 and McCloud, U. S. Pat. No. 2,790,388, suggest plural or sequential detonation of explosive charges either with or without chemical treatment. Where a number of explosive charges are lumped at vertically spaced points within the casing, the operator is faced with an almost insurmountable task of striking a suitable compromise between the use of charges light enough to avoid damaging or rupturing the casing, and charges heavy enough to assure actual cleaning of the casing at all points between the charges. With charges of strength adequate to break up clogging deposits in the casing perforations, there is the inevitable consequence of the development of relatively intensive pressure waves that travel longitudinally of the casing. Such traveling pressure waves may build up cumulative peak pressures at localized points between charges to thereby greatly complicate the problem of obtaining a group of charges of sufficient strength to perform an optimum cleaning operation without doing serious damage to the casing.

In any event, whether a single explosive charge is employed or a sequence of such charges are employed, and presuming that the problem of selecting optimum charge strength has been solved, the explosively created shock waves are of substantially instantaneous duration and at best, will break or loosen clogging deposits. Such deposits, after termination of the explosion or explosions, will tend to remain in place although broken and loosened and thus the desired cleaning is only partially accomplished, at most. Furthermore, clogging materials that remain in place even though loosened will form the basis for a much more rapid rebuilding of the clogging materials, whereby the well will soon experience a return of decreased production.

Accordingly, it is an object of the present invention to provide a method and apparatus for well cleaning that will both break up and loosen clogging materials and will also tend to remove such materials from the fluid flow passages.

SUMMARY OF THE INVENTION

In carrying out the principles of the present invention in accordance with a preferred embodiment thereof, a fluid well is cleaned by producing within the well a sequence of explosive shocks of relatively high intensity and short duration and following at least one of such explosive shocks by a sequence of pressure pulses of relatively long duration and lesser intensity. The lesser intensity pressure pulses, although providing a relatively sustained pressure increase, are not continuous to thereby provide a pulsating flow of fluid that travels through the casing perforations and surrounding formations with a rapidly fluctuating velocity whereby improved washing and flushing action is achieved.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an elevation view of a well casing having inserted therein apparatus (shown enlarged relative to the casing) for performing the combined shock and flushing operation of this invention,

FIG. 2 shows a section of a portion of the well casing and apparatus therein of FIG. 1, showing the upper portion of the casing inserted apparatus,

FIG. 3 illustrates a section of the well casing containing the lower end of the apparatus (also enlarged) inserted therein,

FIG. 4 is an enlarged view of one portion of the apparatus of FIGS. 1 through 3 illustrating certain details of construction and modes of connection of the several elements,

FIGS. 5 and 6 are cross-sections of the apparatus shown in FIG. 4,

FIG. 7 shows a modification of the apparatus of FIGS. 1-6, and

FIG. 8 illustrates another modification.

DETAILED DESCRIPTION

In order to properly clean a relatively long section of a well by both shock wave and flushing action, the present invention contemplates, in a preferred embodiment, the provision of an explosively generated shock wave followed by a sequence of relatively sustained but substantially discrete pressure pulses of relatively lower intensity. Such combination of pressure pulses and shock waves provides adequate cleaning for a given length of the well and, accordingly, for cleaning a significant extent of the well, the combination of explosion or shock wave followed by sustained discrete pressure pulses is repeated. Thus, the apparatus for producing the desired effect within the well casing may extend for a considerable length of the casing. Sequentially timed operations are required to be carried out in the desired sequence at points that may extend many hundreds of feet from the surface. For multiple shock waves and multiple pressure pulses, individual control of timing or ignition from apparatus on the surface becomes impractical, if not impossible, because of the large number of control lines that would be required.

In accordance with one aspect of the present invention, the apparatus is arranged so that each group of a single shock wave and a plurality of sustained pressure pulses is connected to the following group to actually trigger the operation of such following group upon completion of the operation of the preceding group. Not only does the operation of one full group initiate operation of the following group, but within each group, each explosion or pressure pulse itself triggers the next operation of the group. That is, the explosion or shock wave that occurs first within a group, will initiate a first one of the sustained pressure pulses. The latter, upon its termination, thereupon initiates the succeeding one of the sustained pressure pulses of the group. Termination of the final pressure pulse of one group will itself cause initiation of the explosion of the following group. The latter, in turn, initiates the first sustained pressure pulse of its group and so on down the entire length of the string. Thus, timing and sequence of operation of shock waves and sustained pressure pulses are all inherent within the apparatus which accordingly needs but one control line to start the entire sequence.

As illustrated in FIG. 1, for cleaning a well casing 10, there is inserted into the casing, and positioned at the portion of the casing that is to be cleaned, a string of pressure producing devices comprising a series of combinations of an explosive cap and a gas pulsation generator. The uppermost one of such combinations comprises an explosive cap 12 and a pulsation generator 14. The second such combination includes an explosive cap 16 and pulsation generator 22. The particular number of combinations of explosive cap and pulsation generator may vary from two to as many as fifty or more in a single interconnected string and it is within the concept of the present invention to employ but one combination of explosive cap and pulsation generator.

A cable or wire 28 is suitably secured to the entire string as by a substantially continuous spiral wrapping of tape (not shown). A thin polyethylene or vinyl adhesive coated tape has been found to be satisfactory. The cable is secured at its upper end (not shown) to suitable apparatus such as a power winch or the like and is looped at its lower end and secured to a weight 30 for lowering the assembly for emplacement at the desired portion of the well casing. All that is required to withstand shock action and heat of the gas generated is a light weight steel wire, for example, of from 0.05 to 0.08 inches in diameter.

The parts of each combination of explosive cap and gas pulsation generator are held together by connecting sleeves 32, 34, 36 and like sleeves for additional assemblies or groups (not shown). The several groups are interconnected by insertion of the elongated gas pulsation generators into enlarged upper ends of the several explosive caps. As more particularly illustrated in FIG. 2, the first explosive cap 12 is a conventional electrically detonated cap such as, for example, the Instantaneous SF Electric Blasting Caps manufactured by Atlas Chemical Industries, Inc. of Wilmington Del., having electrical leads 38, 40. Conveniently, the electrically conductive supporting cable 28 may be connected to one of the electrical leads 40 to provide a ground therefor, the other lead 38 being continued to the surface for selective completion of the electrical circuit between the leads for initiation of the action of the explosive cap 12. To controllably enhance the explosive force of cap 12, one or more layers 42 of a plastic sheet explosive is wound around and affixed to the cap by a standard adhesive. An example of sheet material suitable for this use is the EL-506 series of flexible sheet explosive manufactured by E. I. duPont deNemours & Co., Inc. of Wilmington, Del. The sleeve 32 has an upper portion 44, (between the sheet explosive and the cap), an intermediate portion 46 and a lower enlarged portion 48.

Snugly secured to and within the lower enlarged portion 48 of the sleeve 32 is the upper end portion 50 of the first of the gas pulsation generators 14. The gas generator 14, which is substantially identical to each of the other gas generators, such as those indicated at 18 and 22 of FIG. 1, is formed of a solid body 52 of a suitable plastic material such as, for example, polyethylene or polyvinyl chloride which may be readily molded to the desired shape. The body 52 of gas generator 14 has formed therein a plurality of combustion chambers of which those indicated at 54, 56, 58, 60 and 62 are illustrated in FIG. 2. Of the series of chambers in gas generator 14, the uppermost chamber 54 of the group and the lowermost chamber 62 are open at the respective upper and lower ends of the generator. Within each gas generator and between and communicating with adjacent chambers are necked down or restricted conduits or passages such as indicated at 64, 66, 68, and 70 in FIG. 2.

Snugly mounted within the intermediate portion 46 of each malleable metal containing sleeve 32, 34, 36, etc., is a spark producer comprising a cylinder 72 (FIG. 4) having its exterior grooved to enhance its connection to and within the sleeve when the latter is crimped thereon. Each spark producer has an internal conical surface 74 upon which is coated a spark producing compound 76 such as the conventional phosphorous trisulphide commonly employed on matchheads. The larger upper end of the conical surface 76 is open to the bottom of the adjacent explosive cap 12 and the lower, smaller end is open to the open upper end of the uppermost chamber 54 of the gas pulsation generator 14.

The second combination of explosive cap and gas generator in the string is substantially identical to the first as are all of the succeeding combinations of explosive caps and gas generators with one significant exception. The explosive cap of all succeeding combinations is not electrically detonated but is arranged to be combustion detonated and, further, is deformed to provide the connection with the immediately preceding gas generator. Thus, for example, the second explosive cap 16 (FIG. 2) of the second group of cap and gas generator has the upper end thereof enlarged as at 78 to snugly receive the lower end of the first gas pulsation generator 14 to which it is crimped to enhance the rigidity of the connection. The lower portion of cap 16 contains the explosive charge and, in accordance with the illustrated embodiment of the present invention, has the explosive power thereof controllably enhanced by one or more layers of sheet explosive 80 which surround the cap just as described in connection with the electrically initiated explosive cap 12. No sheet explosive need be used in some applications wherein the explosive charge of the cap is itself deemed adequate. The connecting sleeve 34 has the upper end thereof snugly receiving and secured to the lower body of the cap and, as described in connection with the electric cap 12, extends between the body of the cap and the circumscribing sheet explosive 80. Also secured within the intermediate portion of sleeve 34 is a second spark producing cylinder 82, substantially identical to the spark producer 72, having the lower smaller end opening into and in communication with the upper end of the uppermost chamber of the connected gas pulsation generator. The latter has the upper end thereof snugly secured to and within the lower end of the malleable metal connecting sleeve 34.

Subsequent assemblies of explosive cap, spark producer, and gas pulsation generator are all constructed and arranged just as the combination previously described and the several assemblies are connected in a string in end to end relation by the above-described connecting arrangements.

Portions of the lowermost of the gas pulsation generators and the end of the string are illustrated in FIG. 3 which indicates that this gas pulsation generator is cut to the desired length within the length of any given chamber. Thereafter its terminal portion is suitably sealed against fluid and pressure by any one of a number of conventional means such as, for example, simply immersing the end in a plastic coating and sealing compound 84.

Each of the chambers of the gas pulsation generators and also each of the restricted necks or passages thereof are completely filled with a suitable combustible or propellant that generates the gas pressure upon deflagration. The combustible mixture contained within the chambers and conduits of the gas pulsation generators preferably has a relatively slow burning rate as compared with the detonation rate of the explosive within the standard caps 12, 16, etc., and the sheet explosive 42, that is attached thereto. Preferably the combustible comprises fuel such as a standard black powder, ball powder, or other deflagrating mixture, and may include significant percentages of aluminum or magnesium powder to increase the expansion rate of the gases generated by the combustion. More specifically the black powder may be mixed with aluminum powder in the ratio of 40 percent aluminum powder to 60 percent black powder in order to increase the expansion rate. A high rate of expansion, of as much as 3,000 to 1, is desired for optimum operation. Alternate formulations of suitable combustible mixture include the conventional ball powder and various standard igniter mixes such as employed, for example, in electric blasting caps of Atlas Chemical Industries, Inc. The function of the combustible is to provide a continuous deflagration (as distinguished from the detonation of the explosive caps) that assures a rapid expansion of generated gaseous combustion products.

Where the gas pulsation generator is made in two halves separated along a longitudinal plane, the combustible is mixed with a suitable solvent to provide a mixture having a consistency of a heavy paste or light putty so that it may be readily spread or emplaced within the chambers and necks of the gas pulsation generator body. The latter is molded in longitudinally split halves (FIG. 6) and the several chambers and necked passages are then filled with the paste or putty-like combustible mixture of fuel and oxidizer to ensure a continuous body of combustible throughout the length of the gas pulsation generator. The two halves, with the combustible contained therein are then mated and fixedly secured to each other by conventional adhesive. For improved bonding of relatively long sections of gas pulsation generator, the body portion is molded in longitudinally split 1 foot long sections. After filling the chambers and passages with propellant the mating surfaces are covered with adhesive. The propellant is temporarily masked during application of the adhesive to avoid contamination. The one foot half sections are assembled to provide gas pulsation generators in lengths of from 18 to 60 inches or more. Obviously, other lengths of half sections and lesser or greater assembly lengths may be employed. The length of the gas generator will determine the number of long duration pressure pulsations between successive explosions. In assembly, opposite half sections may be staggered longitudinally so as to avoid butt joints that extend entirely across the body.

In assembly of the explosive cap, spark producer and gas pulsation generator, the spark producer is first placed within the intermediate portion of the associated malleable sleeve such as sleeve 32, the latter is then crimped to securely engage with the grooves in the exterior of the spark producer, the explosive cap is then snugly inserted into the upper portion of the sleeve and the latter crimped if deemed necessary or desirable to ensure positioning of the cap. Thereafter the gas pulsation generator has the upper end inserted in the lower enlarged portion 48 of the malleable connecting sleeve and the latter then is crimped to ensure the connection. The sheet explosive is then emplaced upon and secured to the portion of the connecting sleeve extending about the explosive cap if enhancement of explosive force is desired. A number of such assemblies of explosive cap, spark producer, and gas pulsation generators are assembled with the first one of such assemblies having an electrically initiated explosive cap and each of the other assemblies having a combustion initiated cap of which the upper end thereof is enlarged to a diameter sufficient to snugly receive the lower end of the body of the gas pulsation generator. Thereafter, several of the assemblies are interconnected to form a string of assemblies simply by inserting the end of one of the gas pulsation generators into the end of the explosive cap of the next assembly and crimping the latter into place. The final gas pulsation generator of the string of assemblies is suitably sealed as indicated previously. The cable 28 is taped to the string of assemblies. The string may then be coiled, with a coil diameter of as little as 16 inches, for transport. Prior to emplacement and use the electrical leads of the first of the explosive caps are connected as illustrated, the weight is attached, and the entire string of assemblies lowered to the desired position at the desired depth within the well casing.

The assembly as previously indicated is emplaced within the well casing 10 which has a number of perforations such as indicated at 86 that are to be cleared of obstructions, deposits, growths, and the like that block these perforations. The blocking material extends as indicated at 88 (FIG. 2) to coat the interior or exterior of the casing closely adjacent the various perforations. After proper emplacement of the string of assemblies, the electrical lead 38 and the electrically conductive cable 28 connected to lead 40 are connected to the terminals of a suitable power source so as to initiate detonation of the explosive cap 12 which, in turn, effects detonation of the circumscribing sheet explosive 42. Thus, a first high intensity pressure pulse or shock of very short duration is created to break and loosen the various hard scale-like deposits on the interior of the casing, within its perforations and within and on the interstices and walls of the surrounding porous formation. The magnitude of this initial explosion and of each of the other explosions is readily varied during assembly of the apparatus by control of the type, longitudinal extent, thickness and number of layers of sheet explosive 42 affixed to the explosive cap. The magnitude or intensity of the explosion employed is considerably less than that required in prior art arrangements that employ solely explosives because the explosion is to be followed by a sequence of sustained pressure pulses as will be described. Upon detonation of the explosive cap, fragments of the metallic case thereof are forcibly expelled into and upon the conical internal surface of the spark producer 72 to impinge upon the spark-producing coating thereof, producing a flame that is ejected from the small end of the conical opening within the spark producer. This flame contacts the combustible with which all of the combustion chambers of the gas pulsation are filled, and thereby initiates its deflagration.

Each of the combustible filled chambers is approximately three-quarters of an inch in length and five-sixteenths of an inch in diameter. The outer diameter of the body 52 of the molded gas pulsation generator is slightly larger than the diameter of the chamber whereby the wall of the combustion chamber, indicated at 90 and 92 in FIG. 4, has a total thickness of approximately thirty-thousandths of an inch. Accordingly, with appropriately chosen propellant mixtures as described above, combustion will occur within the mixture contained in a single chamber of the indicated dimensions in a period of approximately 16 to 17 milliseconds. With the heat generated by this mixture and the relatively thin combustion chamber walls, the latter soften and are breached almost immediately to release the gaseous combustion products into the immediately surrounding well fluids. The released gases create a pressure pulse of an intensity considerably less than the intensity of the pressure produced upon explosion of the cap and sheet explosive, but of a sustained duration, a duration considerably greater than the duration of the explosion. The sustained pressure pulse causes a relatively rapid surge of well fluid outwardly through the casing perforations and through the interstices of the immediately surrounding producing formations.

When the combustible mixture in a given chamber, such as chamber 54, burns down to the lower end thereof it thereupon begins to burn within the relatively narrow necked down passage 64. Thus, combustion is sustained within the passage and will thereafter progress along the passage until the propellant within the adjacent chamber begins to deflagrate. However, during the time that the deflagration is taking place within the combustible mixture of the conduit 64, the pressure pulse is terminated and the pressure within and applied to the fluid within the well is considerably diminished as compared to the pressure existing during the burning of the combustible mixture within any one of the enlarged chambers. With diminution of pressure, well fluid surges inwardly to return through the casing perforations.

Each of the conduits or neck passages 64, 66, etc., has a length of about half the length of one of the chambers, that is, a length of about three-eighths of an inch, and has a diameter of approximately thirty-thousandths of an inch, whereby the portions of the body of the gas pulsation generators adjacent to the necked down passages are considerably heavier as indicated at 94 in FIG. 4. Thus, the gaseous products of combustion within the passage are considerably smaller in quantity and furthermore are partially restricted in their radially outward propagation to thereby achieve a considerably diminished pressure during this portion of the burning. When deflagration has propagated completely through the combustible in the necked down portion, combustion begins in the adjoining chamber to produce a second sustained pressure pulse. Termination of the second pulse initiates sustaining deflagration of combustible within the following necked down passage. Thus the operation continues through alternate ones of successive chambers and passages until the completion of combustion of propellant within the final chamber, such as chamber 62 of the first gas pulsation generator 14. Thus there is achieved a pulse-delay-pulse-delay cyclical operation that causes the surging of the well fluid.

When combustion of the material in chamber 62 reaches the lower end thereof, it causes ignition and denotation of the explosive cap 16 and the circumscribing sheet explosive 80. Fragments of the cap thereupon strike the spark-producing compound coating the conical surface of spark-producer 82 which thereby initiates combustion of the propellant in the first of the combustion chambers of the following gas pulsation generator 18.

It will be seen that the described arrangement provides a sequence of groups of pressure pulses wherein the pressure pulses of each group comprise a first explosively produced pulse of high intensity and short duration followed by a number of discrete, sustained pressure pulses each of considerably lesser intensity, but of greater duration than the first explosively produced pulse. Further, the last of the series of the sustained lower intensity pulses of each group itself initiates the first high intensity short duration explosive pressure pulse of the following group. Thus, in this embodiment there is no need for a large number of individual control lines, cables, or electrical leads since the sequence, once initiated by the single electrically triggered explosive cap, is self-sustaining and each of the pulses, in turn, initiates the succeeding pressure pulse.

Improved well cleaning is achieved by following each of the explosions with a series of pressure pulsations that cause the fluid within and about the well and casing to surge back and forth through the casing perforations and formation, and through the formation interstices. In effect, there is provided a combination of explosive and swabbing action. Each explosion is followed by a number of relatively sustained and relatively gentle pulsations of well fluid through the perforations and formations.

It will be seen that completion of firing leaves a minimum of residue suspended in the well liquid. Metallic parts settle to the bottom, plastic parts are consumed, and the cable is withdrawn.

The specific size, length and number of gas pulsation generators, explosive caps, or chambers in any one or numbers of assemblies may be varied as deemed necessary or desirable. In an embodiment employing dimensions described above as typical for a particular application, the arrangement is such that about one-half second elapses between successive detonations of the explosive caps. In such an arrangement employing combustion chambers of three-quarters of an inch in length, between which are interposed passages of three-eighths of an inch in length, a gas pulsation generator body of approximately 18 inches in length includes 20 combustion chambers such as those indicated at 54, 56, etc., in FIG. 2. Accordingly, each group of pulses will comprise a single high intensity short duration shock caused by the explosion of the cap, followed by 20 pressure pulses each of about 16 milliseconds duration and each following the immediately previous sustained pressure pulse by about 8 milliseconds, which is the time required for the deflagration to traverse the entire length of the three-eighths inch long necked passage. Assemblies of explosive caps, spark producers, and the gas pulsation generators may be interconnected in a single string with the number thereof limited only by economics and facility of handling of the assembly. Total lengths of assembly of from 3 to 60 feet have been found to be most convenient for handling.

Results obtained with the described method of sequential explosions each followed by pressure pulses are considerably improved as compared with previously known arrangements. For example, in application to a coastal oil well drilled at about a 69.degree. angle under the ocean floor, it was determined that cleaning was required when well production had been degraded to 400 barrels gross and 114 barrels of oil net per day. The arrangement described above was employed to clean approximately 180 feet of the well producing zone. This was achieved by cleaning different sixty foot sections at three successive times. After such cleaning, production of the well was found to be 1,100 barrels per day gross and 214 barrels of oil per day net. The described arrangement can be used in casings of varying sizes such as oil well casings having an inside diameter of as little as 3 inches or less through sizes including 26 inch diameter water well casing.

Illustrated in FIG. 7 is a portion of an embodiment that is preferred for improved precision, controllable operation and greater simplicity of manufacture. Improved back and forth surging of well fluid is also provided. In this embodiment, the overall arrangement of a string of assemblies of explosive caps each followed by a spark producer and a length of gas pulsation generator is the same as that described in the previous embodiment. The arrangement of caps, layers of sheet explosives and spark producer are exactly the same as previously described and successive sub-assemblies are similarly held together by malleable sleeves and portions of the caps which need little or no enlargement in this arrangement. In the form shown in FIG. 7, the gas pulsation generator is modified to facilitate manufacture, although as modified, it will perform almost the identical function performed by the gas pulsation generator described above in connection with FIGS. 1 through 6. As illustrated in FIG. 7, the modified gas pulsation generator includes a thin walled tube, preferably of polyvinyl chloride, having an outside diameter of approximately five-sixteenths of an inch. The thin walled tube 150 has alternate longitudinal sections thereof, filled with combustible mixture 154 (preferably in powder form) of the type previously described, alternating with cylindrical delay tubes or separators 164 which perform a function equivalent to that of the necked down portions 64 of FIGS. 1 through 6. The delay tubes 164 are solid cylinders, one-quarter inch diameter, fitting snugly but slidably within the tube 150 and having a total length of three-quarters of an inch with an elongated central aperture or conduit 167 therein of approximately one-sixteenth of an inch in diameter. The elongated aperture or restricted passage 167 is countersunk at each end of the cylinder as indicated, for example, at 169.

The aperture or passage 167 of the delay tubes 164 may be filled with the same combustible mixture as included in the gas producing chambers 154. It is found preferable, in the embodiment of FIG. 7, to fill the aperture 167 with a delay mix used in standard delay type electric blasting caps such as those manufactured by duPont, Atlas, Olin and others. A mixture of selenium, barium peroxide and sulphur, for example, is a well known delay mix. The countersinking of apertures 167 may be convenient in manufacture, although it is found in practice that it is not necessary since the ends of the cylindrical delay tubes 164 may be cut in a plane normal to the cylinder axis and still have contact with the combustible 154 sufficient to ensure continuity of the deflagration such as from one combustible chamber through the delay tube to the next chamber.

In assembly of the gas pulsation generator of FIG. 7, the first step after the selection of a length of tubing 150 is to form the apertures in delay tube cylinders 164 and fill these with the delay mix. One of the delay tubes 164 then is inserted into a length of tubing 150 that is selected to be of the desired length of the gas pulsation generator and the delay tube is located substantially in the center of the tube 150. Predetermined amounts of the combustible powder are inserted in measured quantities into the tube on either side of the first delay tube 164 to extend for a length that will determine the time of generation of the gas pressure pulse. This combustible powder is compacted to the desired degree, increased compaction effecting a decrease in deflagration rate as well known. Second and third delay tubes 164 are then inserted into opposite ends of the tube and pressed down onto the free surface of the combustible powder and measured amounts of combustible are again added. Thus the gas pulsation generator is built up from the center toward either end, from the first inserted delay tube outwardly toward each end of the tube.

When the desired total length of gas pulsation generator has been achieved, as for example, a length in the order of 5 feet, one end of the tube with chambers of combustible 154 alternating with delay tubes 164 is then inserted into the upper portion 178 of the conventional explosive cap 144 just as described in connection with the embodiment of FIGS. 1 through 6. In this arrangement, in order to secure the end of the cap 144 to the tube 150, a suitable adhesive has been found adequate although crimping will insure improved sealing.

A malleable metal sleeve 132 functionally equivalent to the sleeve 32 or 34 of FIGS. 2 and 4 is fixedly secured as by crimping and/or adhesive to the lower end of the cap 144 and one or more layers of sheet explosive 142 are wrapped around the lower end of the cap with the malleable sleeve 132 between the explosive and cap. The explosive 142 increases the explosive power just as described in connection with the previous embodiment of FIGS. 1 through 6.

A spark producer 172, having a spark producing compound 176 coated on an internal conical surface thereof is securely affixed to and within the intermediate portion of the malleable metal sleeve 132 as by crimping or adhesive or both, just as previously described. A second gas pulsation generator 151, having a first or uppermost combustible containing chamber 154 followed by the first of a number of delay tubes 164 has the upper end thereof suitably secured as by adhesive, or crimping or both, to and within the lower end of the malleable sleeve 132 in sealing engagement therewith. Accordingly in the assembly, after the production of two or more of the gas pulsation generators, each has the lower end thereof inserted in an upper portion of one of the explosive caps 144, one of the sleeves 132 is affixed to the cap, sheet explosive 142 is wrapped around the sleeve at the lower end of the explosive cap, a spark producer is inserted into the intermediate portion of the sleeve, if it has not already been inserted prior to the assembly of the cap and the sleeve, and then the upper end of a second one of the gas pulsation generators such as that indicated at 151 is inserted upwardly into the lower portion of the malleable sleeve 132 and secured and sealed thereto.

It will be understood that, just as described in connection with FIG. 2, the upper end of the first of the series of gas pulsation generators 150 is secured in a malleable sleeve having in addition to a spark producer, an electrically initiated cap instead of the combustion initiated cap, whereby the entire sequence of explosions and gas pulsations may be triggered by a single electrical signal. The lowermost end of the last of the gas pulsation generators of the series is sealed as by a plastic cap (not shown in FIG. 7) or the like just as described in connection with the previous embodiment.

In those situations, such as water wells for example, where some metallic debris may be tolerated, all of the explosive caps of an entire string, such as caps 12, 16 and 20 of the string FIGS. 1 and 2 and caps 144 of the string of FIG. 7 may be electrically initiated. Although it is possible to sequentially detonate a series of such caps by connecting separate trigger wires and circuits to each, it is preferable, for such a system, to employ a group of delayed caps all electrically initiated by a single signal on a single wire. As described, for example, in U. S. Pat. No. 2,756,826 the several caps are each provided with different time delay values. Thus, electrical energization of the single circuit and single electrical wire will energize each of the delayed caps, but because of the different delay times, the explosive charges of the second and subsequent caps will detonate a predetermined time after detonation of the preceding cap. The time interval between successive cap detonations may be varied within wide limits. It is preferred that no two caps be detonated simultaneously, to prevent mutual reinforcing of shock waves.

In a preferred arrangement for delayed electrical detonation of all caps, some nine to 15 caps may be employed, each cap connected in the described assembly of cap, spark producer and gas pulsation generator. For example, as illustrated schematically in FIG. 8, the caps (and associated spark producer and gas generator assemblies) may be arranged in three groups, designated A, B and C, of three caps each, designated 1, 2 and 3. Group A and cap 1 thereof may be located at the lower end of the string with caps 2 and 3 of Group A positioned at successively higher locations. Groups B and C and the caps 1, 2, and 3 thereof are likewise positioned successively higher. In such arrangement, the delay times of the several caps are selected so that cap 1 of Group A is detonated first, followed at intervals by successive detonations of each cap 1 of each of the other groups. Following detonation of cap 1 of the last or highest positioned group (Group C in FIG. 8) by about one to two seconds, each cap 2 of all groups are similarly successively detonated at selected intervals, from the lowest positioned group to the highest.

After another one to two second interval, each cap 3 of all groups are successively detonated at similar millisecond intervals. In the exemplary illustration of FIG. 8 the order of cap detonation, as determined by the chosen delays as A1, B1, C1, A2, B2, C2, A3, B3, C3.

Just as previously described, detonation of each cap, via its associated spark producer, initiates deflagration of the associated gas pulsation generator. Accordingly in this all electrically detonated arrangement, a number of the latter may be operating simultaneously although at spaced locations along the string of assemblies.

There has been described an improved method and apparatus for well cleaning employing both explosive and pressure pulsation principles. Novel assemblies have been described to create groups of pressure pulses comprising a first high intensity pulse of short duration followed by a number of relatively low intensity pulses of long duration. For some applications the arrangement is self-triggering to provide the desired sequence in response to but a single initiating signal.

The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.

Claims

I claim:

1. The method of cleaning a fluid well comprising the step of

creating within said well a plurality of groups of pressure pulses, said groups being initiated at successive times and respectively at different points along the extent of said well, said step comprising

creating each said group as a series of at least three pressure pulses initiated at successive times and respectively at different points along the extent of said well, at least one pressure pulse of each group being explosively initiated and having a magnitude substantially greater than the other pressure pulses of such group.

2. The method of enhancing operation of a fluid well comprising the steps of

sequentially detonating a plurality of explosions within the well, and

upon occurrence of said detonations, generating a sequence of pressure pulses each having a duration considerably greater than the duration of said explosions.

3. The method of claim 2 wherein said step of generating a sequence of pressure pulses includes the steps of

burning a combustible within the well, and

releasing gases of said burning at a rate that fluctuates to produce pressure pulses of released gas.

4. The method of cleaning a fluid well comprising the steps of initiating an explosive shock within the well, and after initiating said explosive shock, initiating a chronologically spaced series of pressure pulses of relatively lesser intensity than said shock, said step of initiating pressure pulses comprising initiating deflagration of a series of discrete quantities of combustible that burns at a rate that is less than the rate of said explosive shock.

5. The method of cleaning a fluid well comprising the steps of

initiating a chronologically spaced series of explosions within the well, and

during an interval between at least two of said explosions, initiating a chronologically spaced series of pressure pulses each having a duration considerably greater than the duration of said explosions.

6. The method of cleaning a fluid well comprising the steps of

initiating a chronologically spaced series of explosions within the well, and

during an interval between at least two of said explosions, initiating a chronologically spaced series of pressure pulses each having a magnitude substantially smaller than the magnitude of pressure due to said explosions.

7. The method of claim 6 wherein each of said pressure pulses and explosions, except the first of said explosions, in initiated by the immediately preceding pressure pulse or explosion.

8. The method of cleaning a fluid well comprising the step of

creating within said well a plurality of groups of pressure pulses, said groups being initiated at successive times and respectively at different points along the extent of said well, said step comprising

creating said group as a series of pressure pulses initiated at successive times and respectively at different points along the extent of said well, one pressure pulse of each group having a magnitude substantially greater than the other pressure pulses of such group and each of said pulses except the first being initiated by the immediately preceding pulse.

9. The method of cleaning a fluid well comprising the step of

creating within said well a plurality of groups of pressure pulses, said groups being initiated at successive times and respectively at different points along the extent of said well, said step comprising,

creating said group as a series of pressure pulses initiated at successive times and respectively at different points along the extent of said well, one pressure pulse of each group having a magnitude substantially greater than the other pressure pulses of such group, and having a duration considerably less than the duration of the other pressure pulses of the group.

10. The method of cleaning a fluid well comprising the steps of

forming a pulsation generator having an elongated body with a plurality of mutually spaced chambers interconnected by restricted passages,

loading said passages and chambers with combustible material,

placing said pulsation generator within a well to be cleaned,

placing an explosive device within said well,

detonating said explosive device, and causing detonation of said explosive device to ignite said combustible material.

11. The method of cleaning a well comprising the steps of

forming a plurality of chambers interconnected to provide an elongated string of chambers,

loading said chambers with a combustible that burns at less than explosive rate,

inserting said string of loaded chambers into a well to be cleaned,

initiating combustion of the combustible in a first one of said chambers,

initiating combustion of the combustible in each of the other of said chambers in succession, each in response to combustion in an adjacent chamber, and

including the step of detonating an explosive device within said well.

12. The method of claim 11 including the step of causing detonation of said explosive device to effect said step of initiating combustion of combustible in said first chamber.