US2336168A - Method and apparatus for completing wells - Google Patents

Description

Dec. 7, 1943. J. E. ECKEL 2,336,163

METHOD AND Arrmuus ron commune wms Filed April 9, 1942 2 Sheds-Sheet 1 i n6 v 'r'oR.

ATTORN EY 3' J. E. ECKEL METHOD AND PPLRATUS FOR COHPLETING' B11115 Filed April 9,1942 2 Sheets-Sheet 2 ffllllll f/lf- I)- i ATTOJRNEY 20 M hi2 BY meme Dec. 7, 1943 METHOD AND APPARATUS FOR COMPLETXNG WELLS John E. Ecltel, Houston, Tex, asslgnor to Standard Oil Development Company, a corporation of Delaware Application April 9, 1942, Serial No. 438,243 9 Claims. (Cl. 166-5) The present invention relates to a method and equipment for completing an oil well.

For many years it has been known that the productivity of an oil well can be improved by depositing a gravel pack adjacent the exposed face of the producing formation.

Ordinarily in such a completion the producing formation is underreamed to enlarge the surface exposed and the cavity so formed is filled with gravel in which may be embedded a screen carried at the lower end of the producing string. In such completion operations the gravel is usually.deposited in loose discrete form. The movement 'of the lumps of gravel relative to each other exercises a sort of abrading action which causes the producing formation to be'worn away withthe resultthat formation material becomes mixed wtih the gravel and decreases its efficiency. To avoid this difficulty it has been suggested in the past to mix the gravel with a binder of relatively dense plastic material which will prevent formation material from mixing with.

the gravel until the binder is removed after the gravel is in place.

In addition to gravel packs deposited in reamed-out cavities, as described above, the art has used prepacked liners which are concentric perforated cylinders of different diameters having the annular spaces between them packed with gravel or other aggregate. These liners are lowered into the well opposite the producing formation at the end of the producing string of tubing. Since the gravel in such liner is put in place at the surface and is held stationary until the liner is located in its final position, the-possibility of this gravel mixing with formation material is eliminated. Nevertheless, in a great many instances it has been found that after the prepacked liner has been put in place opposite the producing formation it was impossible to effect a passage of formation fluid through the liner.

The present invention is based on the realization that such prepacked liners become plugged in transit from the surface to the producing formation by virtue of the fact that they pass through mud which contains colloidal clay which deposits around thegravel particle and forms a seal, the removal of which is practically impossible. Accordingly, it is'the principal object of the present invention to protect the gravel during its transit through the mudcolumn from contamination with the mud. This may be done by mixing with the gravel any filler which' will exclude the mud and which may be removed by the application of heat or a suitable solvent after the liner has been placed opposite the producing formation.

Another object of the present invention is the provision of a mud excluder for a prepacked liner which will not require any special operation for its removal after the liner is in place but will be removed automatically during the completion operations. This objective is achieved by mixing with the gravel a substance which at ordinary temperature is solid or semi-solid andpreferably water insoluble or immiscible and which at the temperature at the depth of the producing formation becomes a mobile or viscous liquid which may be removed when it is subjected to a pressure differential. Among materials suitable for this purpose may be mentioned greases, waxes,

such as paraiiin wax, asphalts and tars, certain natural-gums and resins and the like.

In a completion operation, in accordance with the preferred embodiment of the present invention, a liner is packed with gravelmixed with a suitable mud excluder, such as cup grease. The

liner is of such construction that during its pas-- sage downwardly through the mud'collimn the pressure on both sides of the pack is the same. When this condition is observed it is not of great moment that the cup grease may become sufficiently mobile to flow during the travel of the liner downwardly since even if this happens it will not flow because it is immiscible with the aqueous fluid and is not subjected to a pressure difierential, When the liner is in place opposite the formation, its lower portion is sealed off by a suitable packer from the upper portion of the hole and the fluid above the liner either in the producing string or in the entire hole is removed by swabbing. This immediately results in having one side of the liner subjected to the pressure of the producing formation while the other side is subjected to atmospheric pressure or a substantially reduced pressure. At the temperature prevailing at the depth of the producing formation the cup grease will be of suiflciently low viscosity to flow and willbe forced out of the gravel pack by the pressure diiferential so created. The oil passing through the filter pack will be miscible with the cup grease and will upon the institution of flow wash out the grease completely from the gravel pack. g

' The same action occurs when any other mud excluder which undergoes a change of viscosity with temperature is employed. Instead of a material of this type, there is contemplated for the practice of the present invention the use of a gela given period of time.

which is consumed or deteriorated bacterially over in U. S. Patent No. 1,998,756. In this patent it is proposed to form such gels in situ in a bore hole and then permit them to be removed bacterially. -When such gels are used in the prac- Such gels are described tice or the'presentinvention, they are formed at the surface in the gravel packed liner before the latter is introduced into the well and they have incorporated with them suitable bacteria in sum- .,cient amount to liquefy the gel within the de-' sired period of time.

. the'lower end of which is secured to the liner in a known manner, and the upper end of which is connected to a sleeve 27 slidably mounted on the liner and having an internal shoulder 28 In the practice of the present invention there is also contemplated an operation in which the avoidance of pressure differential on opposite sides of the filter ack until it is properly located need not be observed. For example, in utilizing a mud excluder which has a viscosity which varies with temperature, the temperature of the fluid in the bore hole can be regulated by continuous or periodical circulation so that it will not go below the melting point of the mud excluder until the liner is located adjacent the stopped. Again it is contemplated that the prepacked liner containing the mud excluder may be provided with a solid refrigerant which'will keep the mud excluder solid until the refrigerant producing formation and fluid circulation has is consumed. A suitable'refrigerant is dry ice which may be packed into the inner cylinder of the prepacked liner,'the latter in this case having its ends sealed off to prevent the aqueous fluid in the well from coming into contact with the dry ice. Y

The nature and objects of the present inven- 2,338,168 r I n right to disengage the threads is irom the head i The lower up of a plurality of joints, in one of which is a coupling sleeve 23 having peripherally spaced vertical slots 24,.in each of which is pivoted a pawl 25 normally spring-pressed outwardly. I

The upper end of the liner carries a packer 28,

adapted to receive the pawls 25.

With the parts in the position shown, the assembly is lowered into the bore hole to the position shown in Fig. 1. In this position both sides of the liner are subjected to the same fluid pressure so that there is no pressure differential across the annular space. Thus, even though the filler be one which may tend to become mobile at the bottom hole temperature, such as cup grease, parafiin,;or the like,.it will not ordinarily become fluid enough to flow out of the annular space and there will be no pressure differential to move it out. At this point, water is forced down the tubing to wash out the drilling mud with which the hole has been filled. fiushing with water also serves to remove the mud sheath from the producingjormation and the outside of the liner. In; this connection, it is helpful to use chemicals such as acids and deflocculating agents, in the wash water, particularly wheresubstances decomposable by acid such as lime have been used in the drilling mud. 4 When tion may be better understood from the following detailed description of the accompanying I drawings in which Fig. 1 is a vertical section in diagrammatic form showing a liner packed according to the present invention being lowered into place;

Fig. 2 is a similar view showing the parts in position for the establishment of a pressure differential across the liner; and

Fig. 3 is a similarview withthe parts in producing position.

the returns, show clear, the head II is set on the bottom and the tubingi is rotated to the right,

thereby disengaging threads I 8 and-screwing down cup it until it isseated on the seat l3.

- When the cap I1 is disengaged from the head I H,- the tubing is raised until the pawls 25 clear the shoulder28 of sleeve 21. Then the tubing is again set down whereupon the'pawls push down the sleeve 21 and press the packer 26 against 1 the casing. This serves to seal off the outside 01' Referring to the drawings in detail, numeral I designates a bore hole, lined with casing 2 which extends to the surface from the producing formation 3 and is cemented'in place by cement '4. Suspendedin the bore hole is a string of tubing 5 which has at its lower end a liner made up of an outside cylinder 6 and an inside cylinder I. These liners are concentric and of diflerent diameters whereby there is an annular space bethe liner from the fluid column in the hole and leave it exposed to formation pressure. The formation pressure will then build up outside the liner, 'thereby creating a pressure differential across the gravel pack which forces the filler out tween them filled with aggregate 8 mixed with a filler 8. Both cylinders are provided with pet'- forations l0.

The cylinders carry at their lower end a head H which has a central passage l2 in one portion of which there is.a seat llfor a valve I. This valve is in the form of a cup having a central cavity l5 of polygonal shape adapted to receive a head 16 of the same shape carried at the "end ofthe producing string as an integral part of a cap l1 provided with exterior left-hand threads 18. The cup vll is also provided with ex-. terior right-hand threads I! and with radial pasunderstood that the setting tool at the end of the tubingneed not be left in the well since the sages 2') connecting the cavity IS with a spacef 2| immediately above the seat It and below the flange 22 which is threaded to receive threads I9.

As will be observed, the cup "is also spaced from, the seat I! as to permit ilow of tubing 5 through the central passage l2 and to be seated on I! when thet'ubingis turned to the fluid from the of the pack. This pressure dlfierential can be en'-' 'hanced by swabbing the tubing and it will 'usually be advisable to perform the swabbing oper-* ation in the, tubing in order to start the well new- The parts are shown in Fig. 3 in the positionthey occupy when the well is flowing. It will be setting string can be pulled out, and the well produced through the casing or through a separate producing string introduced for that purpose.

As haspreviously been indicated,'the apparatus invention. Fillers other than those specifically.

named maybe employed and theuse of these end of the producing string is made" flllers may require completion operations in addition to or instead of those specifically described. While such various operations are contemplated, the present invention is preferably practiced by the use of a filler which may be removed by the creation of a pressure diflerential across the packed annular space.

The nature and objects orthe present invention having been thus described and illustrated, what is claimed as new. and useful and is desired to be secured by Letters Patent is:

1. A method for completing an oil well which comprises lowering into the well a prefabricated pack of aggregate embedded in a filler immiscible with an aqueous fluid, disposing said pack opposite the producing formation' between the latter and the producing string, removing the filler from the pack and flowing the well.

2. A method according to claim 1 in which the filler is a plastic material, the viscosity or which decreases with an increase in temperature and is sufliciently lowat the temperature of the producing formation to permit it to be moved by a pressure difierential across the pack of aggregate.

3. A method according to claim 1 in which the filler is a gel containing bacteria which causes the gel to liquefy after a predetermined period of time.

4. A method according to claim 1 in which the filler is a petroleum grease.

5. A method for completing an oil well which comprises lowering into the well filled with drilling fluid a prefabricated pack of aggregate embedded in a filler immiscible with an aqueous fluid, disposing said pack opposite the producing formation between the latter and the producing string while maintaining an equal pressure on either side of the ,pack, establishing a pressure differential across the pack sufficient to remove the filler therefrom, and flowing the well.

6. A method for completing an oil well which comprises lowering into the well filled with a drilling mud a prefabricated annular pack of gregate embedded in a filler immiscible with an aqueous fluid, locating said pack opposite the producing formation between the latter and the producing string, flushing the mud out of said well from the space between said pack and said formation, sealing oil the exterior or the pack from the remainder of the bore hole, establishing a pressure diflerential between the exterior of the pack and the interior thereof, and flowing the well.

7. A method according to claim 6 in which the pressure differential is created by swabbing the producing string.

8. A method according to claim 6 in which the filler is a grease immiscible with water and having a viscosity which, at the temperature of the producing formation, is such as to permit the grease to be moved by a pressure differential across the pack.

9. A prepacked liner for wells comprising an 0 annular chamber, a filling therefor comprising JOHN E. ECKEL.

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