WO1992018151A1

WO1992018151A1 - Ablating gelatin pig and method for use in tubulars

Info

Publication number: WO1992018151A1
Application number: PCT/US1992/002885
Authority: WO
Inventors: Frank E. Lowther; Alden W. Olsen
Original assignee: Atlantic Richfield Company
Priority date: 1991-04-10
Filing date: 1992-04-09
Publication date: 1992-10-29
Also published as: NO933568L; EP0579788A1; EP0579788A4; CA2104298A1; NO933568D0

Abstract

An ablating pig (20) comprised of a mass of gelatin for use in treating tubulars (15). The pig will ablate as it passes through the tubular thereby depositing a treatment layer (21) onto the wall of the tubular. The pig can be molded outside the tubular or it can be formed in situ. The pig is formed by mixing common (i.e. technical) gelatin of the type derived from collagen with a heated liquid and a treating solution (e.g. corrosion inhibitor, drag reducer, etc.). In one aspect, magnetic particles (13) are entrained in the mass. The mass can be integral or it can be made up of individual components of gelatin. A slug of the treating solution can also be passed through the pipeline between two ablating gelatin pigs. For high temperatures applications, a hardener may be used to increase the melting temperature of the gelatin.

Description

ABLATING GELATIN PIG AND METHOD FOR USE IN TUBULARS

DESCRIPTION

1. Technical Field

The present invention relates to a compliant, ablating gelatin pig for use in tubulars and in one of its aspects relates to a compliant pig which is comprised of a mass of gelatin which preferably contains a treating solution, e.g. corrosion inhibitor, drag reducer, etc., and /or magnetic particles, wherein the pig will ablate as it passes through a tubular to thereby deposit a treatment layer onto the wall of the tubular.

2.Background Art

Most tubulars which carry fluids must be treated periodically to extend their operational life and/or to improve and maintain their operating efficiencies. For example, well tubing and casing strings, pipelines, and the like used for transporting crude oil and/or natural gas which contain even small amounts of water routinely experience severe corrosion problems which, if not timely treated, can result in early failure of the line. Also, the interior surfaces of the tubulars have a substantial "roughness" even when new which increases with scaling, pitting, etc. during use. As this roughness increases, the friction or "drag" between the tubular wall and the fluids flowing therethrough increases thereby substantially reducing the flowrate through the tubular.

In most known corrosion and drag reduction treatments of tubulars, a layer or film of an appropriate treating solution, i.e. corrosion inhibitor or drag reducer, is deposited onto the interior surface or wall of the tubular. In corrosion treatment, the film of corrosion inhibitor protects the wall from contact with water or other electrolytes or oxidizing agents while in drag reduction, the film of drag reducer fills pits, etc. to "smooth" out the wall surface to reduce the friction between the flowing fluids and the tubular wall. In still other instances, tubulars may be treated for other problems, e.g. bacteria buildup, etc. wherein different treating solutions are used, e.g. biocides, herbicides, etc..

There have been several techniques proposed for providing a film of treating solution onto the wall of a tubular. Probably the most commonly-used technique for treating pipelines involves merely adding the treating solution to the fluids flowing through the pipeline and/or periodically flowing a separate slug of the liquid treating solution through the line. Due to the properties of treating solution, it migrates outward against the pipe wall and adheres thereto; hopefully forming a relatively uniform layer or thin film on the entire surface of the wall. Of course, insuring that such a uniform layer of solution will actually be deposited and remain on the wall is extremely difficult, if possible at all.

Further, the amount of treating solution that must be added to the fluids flowing through the line is several magnitudes greater than is required to form the desired thin layer of film on the pipe wall. Accordingly, large volumes of solution are wasted with no benefits being derived therefrom. As can be imagined, the large volumes of excess solution required makes this technique very expensive. Still further, this excess treating solution has been found to "coat" any particulates, e.g. sand, entrained in the flowing fluids which seriously affects the processing of the fluids once they have reached their destination since it extremely difficult to separate the coated particles from the fluids with standard equipment.

Other techniques for treating tubulars involve flowing slugs of treating solution between substantially rigid plugs or "pigs" (i.e. members that move freely in the pipeline and act as pistons) or dispensing the solution directly onto the wall from specially-designed pigs as they move through the pipeline. In addition to the costs involved in the use of excess solution and the uncertainty of providing a uniform layer of solution on the wall, there are several other drawbacks involved in using rigid pigs in the treatment of tubulars. For example, special pig "launchers" and "catchers" have to be built and installed into the pipeline which adds substantially to the cost and handling problems. Also, since these pigs are substantially rigid and have a constant, fixed diameter, it is difficult, if possible at all, for the pig to negotiate bends in the pipeline and pass through restricted diameters (e.g. chokes) in the line.

One tubular treating technique which overcomes many of the drawbacks associated with the above-discussed prior art methods is one which uses a compliant "gelled" pig or pigs, see Canadian Patent 957,910. The pig is comprised of an integral mass which is formed by gelling a liquid hydrocarbon with a gelling agent, e.g. alkyl orthophosphate ester, and an activator, e.g. sodium aluminate. This compliant pig, which may also contain a corrosion inhibitor, is forced through the pipeline by either a liquid or a gas to deposit a corrosion-protective layer on the pipe wall. This technique is attractive since compliant pigs have several advantages over rigid pigs, e.g. gelled pigs resiliently deform to (1) pass through tubulars of differing diameters; (2) pass through line restrictions such as chokes; and (3) expand radially as they are pumped through the tubular thereby remaining in contact with the wall of the pipe over long distances.

SUMMARY OF THE INVENTION

The present invention provides an ablating gelatin pig for use in tubulars which is capable of undergoing large deformations as it passes through the tubular and then quickly and forcibly returning substantially to its original configuration. This allows the pig to easily negotiate the bends, restrictions, obstacles, etc. which may be encountered by the pig as it moves through the tubular. Due to the properties of gelatin, the temperature in the tubular and/or the heat generated by the pig moving along in contact with the interior wall of the tubular will cause the pig to ablate to thereby deposit a layer of gelatin (and treating solution if present in the pig) the wall. The pig can be molded and inserted into the tubular through a simple inlet conduit or it can be formed in situ so there is no need for an expensive and cumbersome pig "launcher" at the upstream end of the tubular. Further, the pig can be sized so that it will be substantially used up by the time it reaches its destination, so there is no need for a pig "catcher" at the downstream end of the tubular.

More specifically, the ablating gelatin pig of the present invention is comprised of a mass of "gelatin" which is adapted to be continuously compressed longitudinally by the fluids flowing through a tubular, e.g. pipeline, so that it will expand radially to contact the interior wall of the pipeline as the mass moves therethrough. The mass of gelatin is formed by mixing technical gelatin of the type derived from collagen (e.g. commercial grade A or B gelatin) with a heated liquid (e.g. about 170° F.) and then preferably allowing the mixture to cool to ambient temperature (less than about 100^β F.).

The mixture may be cooled in a mold before inserting the pig into the pipeline or it can be formed in situ within the pipeline, itself. Preferably, the liquid used to form the mixture includes a treating solution, e.g. corrosion inhibitor, drag reducer, biocide, herbicide, etc.) which is to be used to treat the pipeline and may also include magnetic particles entrained in the mass. The mass may be integral or it may be formed of individual components of gelatin which are then accumulated together to form the pig.

In some applications, a slug of the treating solution can be passed through the pipeline between the pig and a second ablating gelatin pig to supply additional treating solution onto the wall of the pipeline if needed or desired. When temperatures in the pipeline are high enough to adversely effect the layer on the wall, a hardener, e.g. an aldahyde, may be added to the gelatin to increase the temperature at which the gelatin will melt and/or a slug of hardener is passed through the pipeline between two ablating gelatin pigs to react with and harden the treatment layer which has been deposited on the wall by the front pig. BRIEP DESCRIPTION OF THE DRAWINGS

The actual construction, operation, and apparent advantages of the present invention will be better understood by referring to the drawings in which like numerals refer to like parts and in which:

FIG. 1 is an idealized representation of technical gelatin molecules in a cooled aqueous solution;

FIG. 2 is an idealized representation of the gelatin molecules of FIG. 1 in a heated state;

FIG. 3 is an idealized representation of the heated gelatin molecules of FIG. 2 with magnetic particles and molecules of a treated solution blended therein;

FIG. 4 is an idealized representation of the gelatin, magnetic particles, and treating solution molecules of FIG. 3 after cooling;

FIG. 5 is an elevational view, partly in section, of a gelatin mass within a tubular;

FIG. 6 is an elevational view, partly in section, of the mass of FIG. 5 after it has partially passed through the tubular;

FIG. 7 is an elevational view, partly in section, of another embodiment of an ablating gelatin pig being formed in a pipeline;

FIG. 8 is an elevational view of a tubular treating method using two ablating gelatin pigs;

FIG. 9 is an elevational view, partly in section, of the method of FIG.8 after the pigs have partially passed through a pipeline; FIG. 10 is a representative graph plotting the length of pig required to provide a protective layer against the lengths of different diameter tubulars;

FIG. 11 is an elevational view, partly in section, of apparatus used in forming a compliant pig wherein the pig is formed of a mass of "spaghetti" strings of a gelled material;

FIG. 12 is a sectioned view taken along lines 12-12 of FIG. 11;

FIG. 13 is an elevational view, partly in section, of an apparatus used for forming a single string of gelled material which , in turn is used to form a compliant, pig;

FIG. 14A and 14B are illustrations of different configurations of strings of gelled material which can be used to form compliant pigs;

FIG. 15 is an elevational view, partly in section, of an apparatus used for forming spun strands of a gelled material which, in turn, is used to from a compliant, pig;

FIG. 16 is an elevational view, partly in section, of a compliant pig within a pipeline which is formed by individual modules of a gelled material;

FIG. 17 is an elevational view of another configuration of a compliant pig;

FIG. 18 is an elevational view of the pig of FIG. 17 when positioned within a tubular;

FIG. 19 is a sectional view, partly broken away, of a well having a mass of gelatin within the upper end of a tubing string; and

FIG. 20 is a sectional view similarly to FIG. 19 with the mass of gelatin near the lower end of the tubing string.

BEST KNOWN MODE FOR CARRYING OPT INVENTION

In accordance with the present invention, a compliant "pig" is provided for treating tubulars wherein a relatively thin film or layer of a treating solution is deposited onto the wall of the tubular by the pig as it passes through the tubular. As used herein, "tubular" is intended to include any pipe or conduit through which fluids (i.e. liquids and gases) and solids (i.e. particulates) are flowed. While the present invention will be described primarily in relation to a substantially horizontal pipeline which carries crude oil, natural gas, and/or other products, it should be understood that it equally applies in treating substantially vertical and/or horizontal tubulars such as well casings and tubings, flowlines in refineries, water or other conduits, etc..

The compliant pig of the present invention is comprised of a mass of "gelatin". Gelatin is a material which is capable of recovering from large deformations quickly and forcibly which allows the pig to easily negotiate bends, constrictions, and the like in the pipeline. Due to the ambient heat in the pipeline and flowing fluids and/or the heat generated by the moving pig against the wall of the pipe, the gelatin pig "ablates" to deposit a treatment layer onto the wall.

As is well known, "gelatins" are high molecular weight polypeptides derived from collagen which, in turn, is the primary protein component of animal connective tissue (e.g. bones, skin, hides, tendons, etc.). Gelatin, which is commonly used in foods, glues, photographic and other products, does not exist in nature and is a hydrolysis product obtained by hot water extraction from the collageous raw material after it has been processed with acid, alkaline, or lime. The viscosity of aqueous gelatin solutions increases with increasing concentrations and decreasing temperatures. For a more complete description and discussion of gelatin, its compositions and properties, see ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Kirk- Othmer, 3rd Edition, Vol. 11, J.Wiley & Sons, N.Y., pps. 711 et sec.

While gelatin, itself, effectively adheres to the tubular walls in most applications, in one aspect of the present invention, this adhesion is reinforced by the magnetic particles which are thoroughly mixed and entrained in the mass of gelatin and which are deposited along with the gelatin onto the wall of the tubular. The latent magnetism of these particles provide a magnetic force which attract each other and to the wall of a magnetic tubular, e.g. steel. The magnetic particles are comprised of magnetized, micro-sized particles of a supermagnetic material (e.g. iron oxide) of the type commonly used in printer inks, toners, etc., (e.g. magnetic particles commercially-available from Wright Industries, Inc. , Brooklyn, N.Y. such as Type 4000 (0.05 micron diameter particles); Type 012672 (0.3 microns); Type 041183 (12 microns) etc..

The gelatin, itself, acts a treating agent (e.g. as a corrosion inhibitor and/or a drag reducer) when deposited onto the tubular wall. Preferably, however, a separate treating solution is incorporated into the gelatin mixture either with or without the magnetic particles. Referring to the drawings, FIG. 1 is a highly idealized representation of an aqueous solution of gelatin molecules 11 as they appear in a cooled state while FIG. 2 represents the molecules as they appear when heated (e.g. above 180° F.). Molecules of a treating solution 12 and micromagnetic particles 13, preferably of different diameters (e.g. from about 0.02 to about 12 microns) are blended into the hot gelatin mixture (FIG. 3) and become entrained within the gelatin molecules 11 as the gelatin mixture is cooled back to room temperature (FIG. 4).

In corrosion treatments, the treating solution can be almost any known corrosion inhibitor of the type used to treat tubulars. Examples of good corrosion inhibitors are (1) an aqueous blend of fatty acid imidazoline quaternary compound and alcohol, e.g. commercially-available as NALCO 3554 INHIBITOR; (2) an alkylamide polyamide fatty acid sulfonic acid salt in a hydrocarbon solvent, e.g. VISCO 945 CORROSION INHIBITOR; (3) an imidazoline fatty acid, e.g. OFC C-2364 CORROSION INHIBITOR. For examples of other corrosion inhibitors, see U.S. Patent 5,020,561, issued June 4, 1991.

In drag reduction treatments, any known drag reducer of the type used to reduce drag in tubulars can be incorporated into the compliant pig. For example, many of the above-identified corrosion inhibitors are also good drag reducers thereby producing the combined benefits of reducing drag and inhibiting corrosion. Also, high molecular weight (e.g. 10 ) homopolymers, e.g. polyethylene oxide, are good drag reducers in that the high weight molecules at least partially "fill" any indentations in the pipewall to "smooth" out the roughness of the wall thereby reducing drag between the pipewall and the flowing fluids. Further, other treating solutions such as biocides, herbicides, etc. can be incorporated into the ablating gelatin pig if desired for a particular treatment.

When formulating gelatin mixtures, it has been found that the hardness (i.e. firmness of the cooled gelatin) is primarily dependent on the amount of gelatin in the mixture and is relatively independent on the composition of the water/treating solution used with in the mixture. For example, a gelatin mass formed with approximately 17% gelatin and a liquid comprised of 30% water and 70% treating solution (e.g. NALCO 3554 INHIBITOR) has substantially the same hardness as that of a mass formed with the same amount of gelatin and a liquid comprised of 70% water and 30% treating solution (NALCO 3554). While it should be recognized that the exact formulation of a particular gelatin mixture may vary with the actual components used, the environoment in which a gelatin pig is to be used, the treatment to be carried out, etc., the following example illustrates a typical composition of a gelatin mixture which can be used to form the present compliant pigs: 100 parts of a treating solution (e.g. NALCO 3554) is mixed thoroughly with 100 parts by weight of hot water (180° F) . 60 parts by weight of technical gelatin is blended into the hot liquid mixture. The temperature of the gelatin-liquid mixture at this point should be at least 170° F. The gelatin-liquid mixture is allowed to cool to ambient temperature (e.g. room temperature) to thereby form the mass of gelatin which becomes the pig, as will be described in detail below. When magnetic particles are incorporated into the mass, a typical mixture can be comprised of thirty-six percent (36%) by weight of a treating solution (e.g. NALCO 3554) mixed thoroughly with an equal amount of hot water (180° F.). Fourteen point four percent (14.4 %) by weight of gelatin is blended into the hot liquid mixture along with thirteen and one-half percent (13.5 %) of magnetic particles (e.g. magnetized iron oxide. The warm gelatin mixture may be poured into an external mold where it is allowed to cool to form an integral mass of gelatin basically in the shape of the mold. Preferably, however, it is molded in situ inside the tubular, itself.

Referring again to the drawings, FIG. 5 discloses a tubular (pipeline 15) having a valve 16 therein. A gelatin-hot liquid mixture 17 is flowed into the pipeline and up against the closed valve through an inlet conduit 18 having a valve 19. The gelatin-liquid mixture builds up in the pipeline and is allowed to cool to form the gelatin pig 20. Valve 19 is then closed and valve 16 is opened. Flow is then established in the pipeline behind pig 20 to force it through open valve 16 and on through pipeline 15. Pig 20 will deform as it passes through the restrictive diameter of valve 16a and then will substantially return to its original configuration.

While it is preferable to allow the gelatin mass to cool to form a gelled pig, it should be recognized that the mass may also be flowed through tubular 15 in an ungelled state as a slug, if desired, to deposit the protective layer onto the inner wall of the pipe.. In either case, the mass of gelatin 20 ablates as it is forced through tubular 15 by fluid flowing behind the mass of gelatin 20 to thereby deposit a treatment layer 21 onto the wall of the tubular (FIG. 6).

FIG. 7 illustrates still another technique for forming pig 20. Pig 20 can be formed in situ completely within inlet 18a or it can be formed in situ partially within inlet 18a and partially within pipeline 15 whereby it will have an angle "x" (FIG. 7) along its length when cooled. Since the gelatin pig is easily deformable to conform to the diameter of pipeline 15, it can easily be pushed into the pipeline 15 by piston 25 or the like even if the pig is formed with an angle therein. Further, the diameter of inlet 18a may actually be larger or smaller than the diameter of the pipeline. If the diameter of the pig is larger, it will be compressed upon entering pipeline 15 thereby providing additional outward pressure which aids in forcing the periphery of the pig against the wall of the pipeline as it moves therethrough.

The pressure from the fluids being pushed ahead of pig 20 will act on the leading face of the pig while the pressure of the fluids pushing the pig will act on its rear face. These opposed pressures will radially- compress pig 20 along its longitudinal axis thereby continuously forcing the periphery of pig 20 into contact with the pipewall at all times, even as the material in the pig ablates against the wall. This is true regardless whether the diameter of the pig is smaller, larger, or approximately the same as the diameter of the pipeline. The temperature of the pipeline 15 and/or the heat generated by pig 20 as it moves along in contact with the interior wall of the pipeline causes the gelatin pig to ablate thereby depositing a layer 21 (FIG. 6) of combined gelatin and treating solution onto the pipewall. The temperature at which a typical gelatin pig ablates is around 100° F.

Pig 20 is sized so that it effectively will be consumed by ablation when its reaches its final destination in the pipeline 15 so there is no need to install a pig "catcher" in the pipeline. The size of a particular pig can be determined from basic geometrical calculations based on the diameter of the tubular to be treated, the rate of ablation, the thickness of layer 21, etc. FIG. 10 shows a graph which is representative of the length of a typical ablating gelatin pig that would be required to produce a layer 21 having a thickness of 3000 microinches over a specified length of different diameter pipelines. As seen from the graph, the required length of some pigs will be substantial (e.g. 100 feet). However, it should be understood that the such pigs do not need to formed as a single integral unit. That is, the pig may be molded or formed in several, individual sections of shorter lengths and then positioned one behind the other whereby the sections effectively function as an integral unit during operation. The sections do not have to be physically joined or connected since all will abut and be pushed through the pipe by the flowing fluids as if they formed an integral unit.

In some treatments, it may be desirable or necessary to treat the tubular with treating solution in addition to that contained in the pig. For example, as illustrated in FIGS. 8 and 9, a slug 22 of treating solution is positioned in pipeline 15 between two ablating gelatin pigs 20 wherein solution from the slug 22 is deposited onto the pipewall as it is carried through the pipeline between the pigs 20. Again, pigs 22 are sized so that they will be substantially co sumed by ablation by the time they reach their destination (FIG. 9) so there is no need to recover the pigs from the pipeline.

In another aspect of the present invention, the compliant pig is not formed as an integral mass but instead, is formed of components or modules of the gelled material, e.g. gelatin, which are then accumulated into a mass which functions in the same way as if the mass was integral. A pig formed of a mass of individual components or modules is normally more compliant thereby improving its ability to negotiate any curves, bends, constrictions, etc.. Also, the ability of the pig to remain in contact with the wall of the tubular is improved, even as the pig is being continuously ablated.

One technique for forming a compliant pig of individual components is illustrated in FIGS. 11 and 12. A tubular to be treated, e.g. pipeline 30, has an inlet conduit 31 mounted thereon which, in turn, has a jacket 32 positioned around a portion thereof. Jacket 32 has a fluid inlet 33 and an outlet 34 whereby a cooling fluid or refrigerant can be flowed through the annulus between the jacket and the conduit to cool conduit 31 and its contents. A plate 35 having a plurality of openings 36 (FIG. 12) therethrough is positioned across conduit 31 at the lower end of jacket 32.

A warm, gelatin mixture is flowed through conduit 31 and is cooled as it passes through the jacketed section 32. As the gelatin cools, it sets or "gels" and is forced through openings 36 in plate 35 to form a plurality of "spaghetti" strings 37. As the strings 37 flow into pipeline 30, they fold back upon themselves and accumulate in a tangled or disoriented mass to form pig 20a. When enough of the gelatin strings are accumulated to form a pig of desired size, the flow of warm gelatin is ceased and the pig 20a (accumulated mass of gelatin "spaghetti" strings 37) is forced through tubular 30 by commencing flow in the tubular.

As with an integral pig, the opposed pressures across the mass of components causes the pig to compact and to expand radially along its longitudinal axis thereby continuously forcing the periphery of pig 20a into contact with the pipewall even as the material in the pig ablates against the wall. The radial expansion of the mass of components also compacts the mass thereby making it effectively impermeable to the flow of fluids therethrough. Accordingly, pig 20a acts basically in the same manner as if it was formed of an integral mass. As described above, pig 20a is sized so that it effectively will be consumed by ablation by the time its reaches its final destination in the pipeline 20a so there is no need to install a pig "catcher" in the pipeline.

FIG. 13 illustrates another apparatus for forming a compliant pig. Apparatus 41 is similar to that disclosed in FIGS. 11 and 12 except it produces only a single string of gelatin which is formed by forcing a warm, gelatin mixture from a feed conduit 42 through a reduced- diameter tubing 43 which, in turn, has a portion 44 submerged in a cooling bath 45 or the like. A substantially continuous string 46 of gelled gelatin exits tubing 43 downstream of bath 45 and folds back on itself to accumulates to form pig 46. Pig may be formed either in situ inside a tubular or externally and then inserted into the tubular.

Tubing 43 can be shaped so that a string of gelatin may be produced which has different configurations, e.g. coiled-shaped string 46A (FIG. 14A), serpentine-shaped string 46B (FIG. 14B), etc.. The individual string or strings (i.e. should the continuous string break) of these different configurations may be accumulated into a mass which forms a compliant pig similar to that discussed above. As used throughout the present specification and claims, the term "components", although plural, is intended to include a continuous string of material such as described above. Again, the accumulated mass of components, i.e. string(s), will function basically as if it were an integral mass when in operation within a tubular except it will be more compliant.

Further, components having configurations different from the string-like elements described above can also be used to form compliant pigs. For example, a plurality of individual spheres 50 (FIG. 16) or other shaped modules of gelatin can be molded and then positioned in a tubular to form a compliant pig 51 which will function the same manner as an integral mass when in operation.

FIG. 15 illustrates still another apparatus which can be used to make a compliant pig in accordance with the present invention. Apparatus 60 is basically a "cotton- candy" making machine, e.g. Model 3017, Gold Medal Products Co., Cincinnati, OH, and is comprised of a rotating head 61 which is mounted in a dish or tub 62. Heated gelatin mixture is fed through slots 63 in head 61 and the head rotates. The mixture is flung into the air within the tub which cools the gelatin mixture which then gels into fiber¬ like strands having extremely small diameters, e.g. around 10 microns. The spun strands of gelatin (not shown) collect and accumulate within tub 62 much in the same way that a sugar solution forms cotton candy. The strands are then removed and loosely compacted to form a pig which, in turn, is passed through a tubular in the same manner as described above.

Further, a compliant pig may be molded or formed in several, individual sections of shorter lengths and then positioned one behind the other whereby the sections effectively function as an integral unit during operation. The sections do not have to be physically joined or connected since all will abut and be pushed through the pipe by the flowing fluids in the tubular. One configuration for such sections is illustrated in FIG. 17 wherein a mass 70 of gelatin is molded in a serpentine configuration which has a diameter"d" substantially equal to the diameter of the tubular to be treated. When the serpentine section(s) are inserted into a tubular 71 (FIG. 18), they will deform against their inherent resiliency or elasticity to substantially conform to the tubular wall. This inherent resiliency or elasticity of mass provides a force which tends to bias the perphery of the mass outward into engagement with the tubular wall.

A gelatin pig such as described above can also be used to treat tubulars in producing wells and the like. Referring again to the drawings, FIGS. 19 amd 20) illustrate a well 80 (e.g. an hydrocarbon-producing well) having a casing 81 secured in the borehole by cement 83, both of which have perforations 84 therethrough adjacent production and/or injection formation 85. A string of tubing 86 extends from a wellhead at the surface 88 to a point adjacent perforations 84 and forms an annulus 89 with casing 81.

The well is shut-in and a mass of gelatin 20b is positioned into tubing 86 through line 90. While it is preferable to allow the gelatin-hot liquid mixture to cool to form a gelled pig, it should be recognized that the gelatin-hot liquid mixture may also be flowed through tubing 86 in an ungelled state, if desired, to deposit a protective layer onto the inner wall of the tubing. In either case, the mass of gelatin is passed downward in tubing 86, preferably by flowing fluid (e.g. production or injection fluids) through tubing 86 behind gelatin 20b. The fluids in the tubing below mass 20 will be pushed ahead of the gelatin and will either be forced through perforations 84 into formation 85 or returns can be taken through annulus 89 and line 82 at the surface. As the mass of gelatin 20b passes through tubing 86, it will deposit a treatment layer 93 (FIG.20) onto the inner wall of the tubing.

Due to the possibility of damage to the formation, it is desirable to prevent any treating fluid, e.g. corrosion inhibitor, in the mass of gelatin 20b from entering into formation 84. Accordingly, pumping of fluid through tubing 86 behind the mass 20b is halted before the mass 20 passes completely through the tubular (e.g. as it nears the bottom of tubing 86 - FIG. 20) and the circulation of fluids is reversed by pumping fluids down annulus 89 and taking returns through the tubing. If the production or injection interval is normally packed off by a tubing packer, the packer is released to allow circulation through the annulus. If the tubing is normally landed in a tubing seating nipple (dotted lines 95 in FIGS 19 and 20) or the like, the tubing is raised above same to allow circulation through the annulus. Reverse circulation results in forcing mass 20b back up through the tubing thereby depositing additional gelatin onto the wall of tubing 86. The mass 20b is preferably sized so that it will effectively be used up before it again reaches the surface.

In some treatments, the ambient temperature in the tubular may be high enough (e.g. substantially above 100 ° F.) to seriously affect the ability of a gelatin layer to adhere to and remain on the tubular wall after it has been deposited thereon. That is, excessive temperatures may cause the gelatin in the layer to "melt" and be swept away by the fluids flowing in the pipeline. Accordingly, a "hardener" may be used to react with the gelatin to protect the gelatin against softening or melting at the operating temperatures. The hardener also toughens the gelatin in the layer and makes it resistant to abrasion. Examples of such hardeners (e.g. formaldehydes) are those used to harden gelatin in photography applications, see THE THEORY OF THE PHOTOGRAPHIC PROCESS, Third Edition, The Macmillan Co., N.Y. Chapter 3, pps. 45-60. The hardener may be added to the gelatin-hot liquid mixture during the formation of the pig to contol the melting or ablating point of the pig, itself, or the hardener can be positioned between two pigs, as shown in FIG. 8, whereby it comes into contact with the gelatin after layer 21 has been deposited onto the pipewall.

Claims

CLAIMSWhat is claimed is:

1. An ablating, gelatin pig for use in tubulars, said pig comprising: a mass adapted to contact the interior wall of said tubular as said mass passes therethrough to ablate and deposit a treatment layer onto the wall of said tubular, said mass formed from a mixture of technical gelatin of the type derived from collagen.

2. The ablating, gelatin pig of claim 1 wherein said gelatin mixture is mixed in said tubular and allowed to cool therein to form said pig in situ in said tubular.

3. The ablating, gelatin pig of claim 2 including: a hardener added to said gelatin mixture for increasing the temperature at which the mass of gelatin will melt.

4. The ablating, gelatin pig of claim 3 wherein said hardener comprises: an aldehyde.

5. The ablating, gelatin pig of claim 1 wherein said mixture includes a treating solution.

6. The ablating, gelatin pig of claim 5 wherein said treating solution comprises: a corrosion inhibitor.

7. The ablating, gelatin pig of claim 5 wherein said treating solution comprises: a drag reducer.

8. The ablating, gelatin pig of claim 1 wherein said pig is formed by allowing the gelatin mixture to cool in a mold before inserting it into the tubular.

9.The ablating, gelatin pig of claim 1 wherein said mass of gelatin contains magnetic particles entrained in said gelatin.

10. The ablating, gelatin pig of claim 9 wherein said magnetic particles comprise: micro particles of a magnetized material.

11. The ablating, gelatin pig of claim 9 wherein said magnetized material comprises: iron oxide.

12. The ablating, gelatin pig of claim 9 wherein said particles of magnetized material have effective diameters of from about 0.02 to about 12 microns.

13. The ablating, gelatin pig of claim 1 wherein said mass of gelatin is formed of individual components of technical gelatin, said components then being accumulated into a non-consolidated mass of a size adapted to contact the interior wall of said tubular as said mass moves therethrough.

14. The ablating, gelatin pig of claim 13 wherein said components comprise: a plurality of spaghetti-like strings of said gelatin.

15. The ablating, gelatin pig of claim 13 wherein said components comprise: a plurality of coil-shaped strings of said gelatin.

16. The ablating, gelatin pig of claim 13 wherein said components comprise: a plurality of serpentine-shaped strings of said gelatin.

17. The ablating, gelatin pig of claim 13 wherein said components comprise: a continuous string of said gelatin.

18. The ablating, gelatin pig of claim 13 wherein said components comprise: a plurality of substantially spherically- shaped modules of said gelatin.

19. The ablating, gelatin pig of claim 13 wherein said components comprise: fibrous strands of said gelatin.

20. A method for treating a tubular comprising: passing an ablating pig formed of a mass of gelatin through said tubular wherein said pig contacts the interior wall of said tubular and ablates to deposit a treatment layer on said wall, onto the wall of said tubular, said mass of gelatin being formed from a mixture of technical gelatin of the type derived from collagen.

21. The method of claim 20 wherein said mixture includes a treating solution.

22. The method of claim 21 wherein said treating solution comprises: a corrosion inhibitor.

23. The method of claim 21 wherein said treating solution comprises: a drag reducer.

24. The method of claim 20 wherein said gelatin mixture is mixed in said tubular and allowed to cool therein to form said pig in situ in said tubular.

25. The method of claim 20 including: adding a hardener to said gelatin mixture for increasing the temperature at which the mass of gelatin will ablate.

26. The method of claim 20 including; passing a solution containing a hardener through said tubular behind said pig to react with said layer on said wall to increase the temperature at which said layer will melt.

27. The method of claim 20 wherein said gelatin mass has magnetic particles entrained therein.

28. The method of claim 20 including: passing a slug of treating solution through said tubular between said mass of gelatin and a second mass of gelled gelatin.

29. The method of claim 20 wherein said tubular to be treated is well tubular and wherein said method includes: passing said mass of gelatin downward through said tubular to deposit a treatment layer on said wall; and stopping said mass of gelatin before it travels completely through said tubular; and passing any remains of said mass of gelatin upward in said well tubular toward the surface.