Title:
Method of cementing wells
United States Patent 2219325


Abstract:
The invention relates to methods of cementing wells and concerns an improved method of placing a cementitious sealing material behind a perforate liner in a well bore. It more particularly concerns an improved method of cementing perforate liners whereby cement or the like may be displaced...



Inventors:
Maness, Orie N.
Application Number:
US24984639A
Publication Date:
10/29/1940
Filing Date:
01/09/1939
Assignee:
DOW CHEMICAL CO
Primary Class:
Other Classes:
166/292, 166/295
International Classes:
C09K8/504
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Description:

The invention relates to methods of cementing wells and concerns an improved method of placing a cementitious sealing material behind a perforate liner in a well bore. It more particularly concerns an improved method of cementing perforate liners whereby cement or the like may be displaced from within a perforate liner into the annular space between it and the well bore at any desired level therein so as to seal off only a selected portion of the space behind the liner.

In wells, such as for example oil wells, having their producing zone or zones located in formations such as sands which are of a loose or unconsolidated nature, it is necessary in order to satisfactorily produce the well to line the well bore over a portion of its depth with a metal liner or screen. This metal liner is perforated or slotted in such -a manner as to prevent particles of the formation from being carried into the well along with the mineral fluids, for otherwise the particles entering the well cut or abrade the valves and other parts of the pump ordinarily used to lift the mineral fluid to the earth's surface. In addition to preventing particles from 2¶ entering the well and damaging the equipment therein, the perforate metal liner prevents the walls of the well bore from caving.

It oftentimes happens that as such wells are produced through the perforate liner, it becomes .1 desirable, and in some instances necessary, to seal off a zone or section of the formation at a point not necessarily at the bottom of the well in order to exclude undesirable fluids from the well. For example, water may be flowing into an oil well through the liner at a point some distance above the oil-producing stratum and it is usually desirable to exclude such water without shutting off the flow of oil into the well.

Although cement and similar materials have been used for various sealing operations in wells, their use in connection with sealing off a particular zone behind a perforate liner generally gives unsatisfactory results. This is because it is difficult, if not impossible, by any of the methods known in the art to effectively displace the sealing material from inside the liner and place it at the desired location in the well bore exterior of the metal liner. If cement grout or a similar material is to be used to seal off a particular stratum or section behind a perforate liner, it is necessary that the sealing material be introduced into the well inside the liner and be just displaced therefrom in such a manner as to completely fill the annular space between the per6U forate liner and the well bore over that section of the formation it is desired to seal, for otherwise an effective seal is not generally produced. In addition, if the sealing agent is not completely displaced, it may solidify inside the liner and must be drilled out before the well can be produced.

I have discovered that by first introducing into the well a non-penetrating liquid mixture in an amount sufficient to fill the well including the annular space between the liner and the well bore up to the level above which the seal is to be placed, introducing the sealing material, and thereafter introducing into the well on top of the sealing material a quantity of a non-penetrating liquid mixture containing a filler capable of preventing the non-penetrating liquid mixture from passing through the perforations in the metal liner and applying pressure thereto, the sealing material is readily displaced from the perforate metal liner into the space between it and the well bore. In those instances where it is desired to introduce the sealing agent behind the perforate liner adjacent the bottom of the well, the first step above mentioned may be omitted, the sealing material being first introduced and then displaced from inside the liner by use of a nonpenetrating liquid mixture containing a suitable filler.

The term "non-penetrating liquid mixture" used herein and in the appended claims means a 80 liquid mixture comprising a dispersion or solution in a liquid of a material which prevents the liquid from penetrating porous formations such as those traversed by a well bore but of sufficient fluidity to be introduced into the well and readily 85 withdrawn therefrom.

In the foregoing manner, cement grout or other similar sealing materials may be directed into the space between the liner and the well bore at any desired level in the well bore and in such a manner that the sealing material completely fills the space between the liner and the well bore over any desired section, thus forming a highly effective seal between liner and well bore.

The accompanying drawing, forming a part of this specification and which illustrates a mode of carrying out the invention, is a diagrammatic vertical view partly in section of an oil well.

In the drawing, the upper portion I of the well is cased and passes through non-productive earth and rock, the casing 2 being provided with casing seat 3 cemented in the rock stratum 4. The lower uncased portion 5 of the well passes through an impervious stratum 6, a gas stratum 7, a water-bearing stratum 8, and terminates in oil- 6. bearing stratum 9. The lower portion 5 of the well is shown provided with a slotted type of perforate metal liner 10, the slots being indicated by numerals 31. The liner extends over the entire uncased portion of the bore hole, 1. e., from the bottom 28 up into the casing 2 to a point II, for example. A releasable packer 12 of conventional type, such as a hook-wall packer, positioned for a treatment according to the invention is shown attached to the lower end of the tubing 13 from which the pump assembly has been removed. The packer 12 is shown seated at the lower level 17 of the gas-bearing stratum 7 sealing the annular space 29 between the liner 10 and tubing 13. The annular space 30 between the liner and the well bore below level 15 is shown filled with a non-penetrating liquid mixture. The lower portion of the well interiorly of the liner is shown filled with a non-penetrating liquid mixture 18 containing a filler up to a point 15, a short distance below the lower level of the water-bearing stratum 8. Cement grout 16 is shown displaced into the annular space outside the perforate liner and filling said annular space from level 15 up to a point 17 a short distance above the upper level of the water stratum 8.

Non-penetrating liquid mixture containing a filler and designated by numeral 18 is shown filling the space inside the liner above the level 15 and a portion of the tubing up to point 19. The remainder of the tubing above the level 19 is shown filled with a liquid such as oil 20 which is used as a pressuring medium on top of the non-penetrating liquid mixture containing the filler. Above the ground level the casing head 21, through which the tubing 13 extends into the well, is shown equipped with pipe 22 communicating with the casing, said pipe being provided with valve 23. To the tubing 13 above the casing head pipes 24 and 25 controlled by valves 26 and 27, respectively, are connected, suitably arranged for carrying out the method according to the invention and for producing the well.

In accordance with the invention, a sealing operation employing a neat cement slurry may be carried out in the following manner where it is desired that the sealing material be directed into only a certain zone or section of the annular space between the liner and the well bore such as, for example, the section opposite the water-bearing stratum 8. With the releasable packer 12 attached to the tubing 13 held in a seated position so as to form a seal between the tubing and liner at level II, a quantity of nonpenetrating liquid mixture designated by numeral 14 is introduced into the well through the tubing 13 in an amount sufficient to fill the annular space exterior of the liner up to a point 15 just below the lower level of the water-bearing stratum 8. The quantity of non-penetrating liquid mixture required may be readily calculated from a knowledge of the diameter of the liner, the size of the well bore, and the location of the water-bearing stratum. A quantity of non-penetrating liquid mixture containing a filler and designated by numeral 18 in an amount calculated to fill the interior of the liner up to a level 15 is then introduced Into the liner and pressure applied thereto displacing the non-penetrating liquid mixture first introduced into the annular space exteriorly of the liner into the'position shown in the figure. A quantity of a neat cement slurry in an amount sufficient to fill the annular space outside the liner between the TS levels 16 and 11 is introduced into the well and allowed to come to rest on top of the column of the non-penetrating liquid mixture containing the filler. Thereafter a quantity of a non-penetrating liquid mixture containing a filler is introduced into the well in an amount sufficient to fill the interior of the liner above the level 15 and a portion of the tubing and pressure applied thereto by pumping oil indicated by numeral 20 into the tubing 13. The non-penetrating liquid mixture containing the filler under the pressure thus applied thereto acts to displace the cement slurry through the perforate liner without itself passing through the same perforations because the filler in the mixture coats the perforations thus sealing them against the passage of fluid. An abrupt rise in the pressure applied to displace the cement slurry indicates that the cement is entirely displaced from the liner and that the filler contained in the non-penetrating liquid mixture has sealed the perforations. The ease and completeness with which the perforations or slots in the liner are sealed by the filler contained in the non-penetrating liquid mixture depends of course, upon the size of the perforations. In commercially available liners the diameter of the perforations, or in those cases where a slotted liner is used, the width of the slots generally varies from between about .005 to .04 inch, although liners having perforations or slots of other sizes may be employed. Pressure is preferably held upon the non-penetrating liquid mixture until the cement sets, after which the packer may be released, the well bailed or otherwise cleaned out, and returned to production. Although the method has been described with particular reference to placing a cementing material in a selected portion of the annular space between a well bore and a liner above the bottom of the well bore, it is to be understood that the mthod may be suitably used to displace a cementing material from other portions of the liner such as the lower portion of the liner by introducing the desired quantity of cementing material into the liner and thereafter displacing it therefrom by applying pressure upon a nonpenetrating liquid mixture containing a filler introduced into te ier the liner or top of the cementing material.

Various other modifications of the method just described may be employed. For example, instead of filling the lower portion of the well bore with a quantity of non-penetrating liquid mixture in order to control the level at which the sealing or cementing material is to be displaced, a packer of any conventional type, such as a cement retainer, may be set at the lower level at which it is desired to produce the seal, or the liner may be bridged over at the desired level In the conventional manner. In many instances the use of a packer attached to the tubing may be dispensed with and pressure applied directly on the top of a column of non-penetrating liquid mixture containing a filler. In some instances it may be desirable to insure against any of the cementing material returning through the perforations in the liner into the annular space between the liner and the tubing above the packer if such be used. To prevent such return of 70 the cementing material, a quantity of non-penetrating liquid mixture containing a filler may be introdced into the annular space between the tubing and liner above the packer and pressure applied thereto so as to prevent the return of sealing material into the interior of the liner above the packer while the sealing material is being displaced from the liner below the packer.

Among the non-penetrating liquid mixtures that are useful for keeping the cement slurry at Sthe proper lower level in the well are those liquid mixtures having non-penetrating characteristics and of substantially the same specific gravity as that of the cement slurry and capable of passing through the perforations in the liner. One type of non-penetrating liquid mixture consists of a solution or dispersion of an organic jellifying material in water. By an "organic jellifying material" is meant an organic material capable of being dispersed or dissolved in water to make a mobile liquid dispersion of solution, which liquid exhibits jellifying characteristics after a time. Suitable organic jellifying materials may be prepared from starches such as those of cassava or rice by mixing them with water to form a thin paste and boiling the mixture until the starch is hydrolyzed. The cooked starch is dried at about 800 C. and the dried material ground preferably to a fine powder. The powder so produced may be mixed with water in a concentartion of from about 1 to 8 per cent by weight to give a dispersion or solution which possesses suitable non-penetrating characteristics. Still another type of non-penetrating liquid mixture may be made by mixing a material such as bentonite with water in amounts of between about 1 to 5 per cent by weight. Such mixtures do not substantially penetrate into relatively porous formations, but readily pass through the perforations or slots in the metal liner and act to confine the sealing material to the desired level in the well bore.

Illustrative examples of fillers suitable to add to the above non-penetrating liquid mixtures to produce a mixture which is capable of displacing the cementing material through the relatively small perforations or slots in the liner without itself passing through the perforations ar( cellophane scraps, mica flakes, shredded photo. graphic film scraps, hemp fibers, and the like Cellophane scraps in the form of cofetti-likM4 particles are preferably used because reverse flow of fluids at moderate pressure through th, liner readily clears the perforations or slots s that permanent plugging of the slots does no occur. If desired, fillers having similar char acteristics and which may be readily remove by suitable solvents in case plugging does occu may be employed. Illustrative examples of solu ble fillers of a resin-like nature are styren scraps, ethyl cellulose scraps, and cellulose ace tate film scraps. Styrene and ethyl cellulose ai readily soluble in benzene or toluene, while ce lulose acetate is readily soluble in acetone. TI amount of such fillers to add to the non-pens trating liquid mixture to give the most sati factory results is from about 1 to 5 per cent more by weiglt, and preferably about 3 p cent.

Sealing agents which may be suitably us according to the method of the Invention a those of a fluid nature capable of passing throul the perforations in the liner which of themsel spontaneously solidify to form a strong sol mass. Although conventional neat cement sih ries are preferably used as sealing agents, ni bile resin-forming liquids of the type which E of themselves capable of transformation intc solid resin after a time by polymerization, ad, tion, condensation, or like chemical reaction ir be suitably employed in similar manner.

The following are illustrative examples of such resin-forming liqu'ds: Example 1 Mix together 70 parts of liquid vinylidene 5 chloride and 30 parts of hexachlordiphenyloxide.

When ready for use, add a catalyst mixture of benzoyl peroxide and lead tetraethyl, a suitable amount being 0.5 per cent of benzoYl peroxide and 0.5 per cent lead tetraethyl, based upon the volume of vinylidene chloride in the mixture.

This resin-forming liquid becomes non-fluid in 2 hours at 110* F. and solid in about 6 hours.

Mix together 80 parts of unpolymerized styrene, 20 parts of hexachlordiphenyloxide, and about 1.6 per cent stannic chloride, based on the volume of the styrene used. Such a mixture has a specific gravity of 1.15 and will polymer- 20 ize into a resinous solid in about 16 hours at 100o F.

Other sealing agents or materials having similar characteristics as regards their sealing action may also be employed, such as the gel- 25 forming liquid silicate mixtures. The following are illustrative examples of compositions and the methods of preparation of such silicate mix4xapt . A dilute solution of sodium silicate is prepared by diluting 40 per cent commercial sodium silicate (Na20-3.22SiO2) with water to a specific gravity of 1.171, giving a solution containing 19.1 per cent by weight of sodium silicate. The dilute solution of sodium silicate so prepared is then added with vigorous stirring to a dilute solution of hydrochloric acid prepared by adding water to concentrated (37 per cent by weight) hydrochloric acid in the follow- 40 ing proportions by volume: Per cent by volume Dilute solution of sodium silicate (19.1% by weight Na203.22SiO2) ----------- 10-75 45 Concentrated hydrochloric acid (37% by by weight) -------------------------- 12-70 Water ------------------------------ 12-70 Liquid silicate mixtures having a composition within the range of the above proportions spon- 50 taneously become solid gels in from % to 25 hours at 120° F. depending on the proportion of each ingredient.

Example 4 A dilute solution of sodium silicate is prepared by diluting 40 per cent sodium silicate Na20>3.22SiO2) with water to the specific gravity of 1.171, giv- 60 ing a solution containing 19.1 per cent by weight of sodium silicate. The dilute solution of sodium silicate so prepared is then added with stirring to a solution of ammonium bicarbonate, prepared by diluting with water a stock aque- 65 ous solution of ammonium bicarbonate containing 16.9 per cent by weight of the carbonate in the following proportions by volume: Per cent by volume 70 Dilute solution of sodium silicate (19.1% by weight Na2O-3.22SiO2) ------------ 5-85 Aqueous ammonium bicarbonate solution 5-85 Water ---------------------------- 85 Liquid silicate mixtures having a composition 7T CLLICiU· Example a within the range of the above proportions spontaneously become solid gels in from 1/2 to 15 hours at 120° F., depending upon the proportion of each ingredient.

Among the advantages of the invention are that a sealing material can be readily and completely displaced from the interior of a perforate liner, thus eliminating the possibility of forming a plug inside of the liner; that a sealing material can be displaced from the interior of a perforate liner in such a manner as to completely fill the annular space between the well bore and the liner, insuring an effective seal being formed; and that a sealing material can be directed into the annular space between the perforate liner and the well bore at any desired level so that the annular space between any two levels may be selectively sealed off.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed. I therefore particularly point out and distinctly claim as my invention: 1. In a method of producing a seal in the annular space between a well bore and a perforate liner therein, the steps which consist in introducing the sealing material into the perforate liner, then introducing into the perforate liner on top of the sealing material a non-penetrating liquid mixture containing a filler capable of preventing the non-penetrating liquid mixture from passing through the perforations in the liner, and applying pressure upon said non-penetrating liquid mixture so as to displace the sealing material from the perforate liner.

2. In a method of displacing a sealing material from a perforate liner or the like located in a well bore into a selected section of the annular space between the perforate liner and the well bore, the steps which consist in introducing into the perforate liner a quantity of non-penetrating liquid mixture in an amount sufficient to fill the annular space outside the perforate liner up to the lower level of the zone to be sealed, introducing into the liner a non-penetrating liquid mixture containing a filler in an amount equal to the volume of the liner between the bottom of the liner and the lower level of the zone to be sealed, introducing the sealing material into the perforate liner; introducing into the perforate liner a quantity of non-penetrating liquid mixture containing a filler capable of preventing the nonpenetrating liquid mixture from passing through the perforations in the perforate liner, and applying pressre upon the non-penetrating liquid mixture containing the filler, whereby the sealing material is just displaced from inside the perforate liner and confined in the annular space outside the perforate liner above the level of the non-penetrating liquid mixture in said annular space.

3. In a method of displacing a sealing material from a perforate liner or the like located in a well bore into a selected zone of the annular space between it and the perforate liner, the steps which consist in temporarily sealing off the interior of the liner at the lower level of the zone to be sealed, introducing a sealing material into the perforate liner, introducing into the perforate liner a quantity of non-penetrating liquid mixture containing a filler capable of preventing the nonpenetrating liquid mixture from passing through the perforations in the perforate liner, and applying pressure upon the non-penetrating liquid mixture containing the filler so as to displace the sealing material from the perforate liner.

4. In a method of displacing a sealing material from a perforate liner or the like located in a well bore into a selected zone of the annular space between the perforate liner and the well bore, the well being equipped with the usual casing and tubing, the steps which consist in temporarily sealing off the interior of the liner at the lower level of the zone to be sealed, setting a packer attached to the tubing above the upper level of the zone to be sealed so as to form a seal between the tubing and the perforate liner, introducing into the annular space between the tubing and the perforate liner a quantity of non-penetrating liquid mixture containing a filler, introducing a sealing material into the perforate liner, introducing Into the perforate liner a quantity of nonpenetrating liquid mixture containing a filler capable of preventing the non-penetrating liquid mixture from passing through the perforations in the liner, and applying pressure upon the nonpenetrating liquid mixtures containing the filler, whereby the sealing material is displaced from the perforate liner into the annular space exterior of the liner and confined in said space.

ORIE N. MANESS.