Abstract:
The present invention provides systems and methods for curing a leakage in a pipeline, the system including at least one gel pig and at least one sealant composition; wherein the at least one gel pig and the at least one sealant composition form a pig train, adapted to move along the pipeline to a region of the leakage and to seal the leakage.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to gel pigs for use in pipelines and methods for producing them, and more specifically to methods and apparatus for use in water pipelines. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many liquids are transported via subterranean/underwater pipelines. When a leakage crack or hole forms in the pipeline, the liquid leaks therefrom. Often, it takes a long time to detect a leakage and yet longer to locate the leakage site. Oil, gas and water transportation are thus subject to tremendous losses due to pipeline leakage. 
         [0003]    There is thus a need to maintain and seal subterranean/underwater pipelines quickly in situ. 
         [0004]    Several patent publications in the field include U.S. Pat. No. 3,523,826A which relates to a process for cleaning a piping system which is characterized by circulating in, and through said system a thixotropic emulsion having a hi.-h volume ratio of internal phase to external phase, the emulsion having an emulsifying agent, an emulsifiable oil and a non-oil, the emulsion being an oil-in-non-oil or a non-oil-in-oil emulsion, the internal phase of said emulsion being present in said emulsion in an amount of at least 80% by volume of the emulsion, said emulsion having the characteristics of a solid when at rest and the characteristics of a liquid when a force is exerted on it, said emulsion tending to be non-adhesive, said emulsion having a critical shear point sufficient to permit pumping at high rates, and said emulsion having an apparent rest viscosity greater than about 1000 cps. 
         [0005]    U.S. Pat. No. 4,216,026 describes a method for removing fluid and/or particulate debris from a pipeline, a Bingham plastic fluid plug is passed through a pipeline and the fluid and/or debris are collected by the plug. The plug is pushed through the pipeline with a scraper which in turn may be pushed by liquid or gas pressure. Where the fluid to be removed is water, the Bingham plastic fluid plug employed preferably is a composition of water and a xanthan gum, and the gum may be cross-linked with a multivalent metal. Where the fluid to be removed is a hydrocarbon, the Bingham plastic fluid plug employed preferably is a composition of a mineral oil and an organo-modified smectite, and may also include a particulate filler such as powdered coal. 
         [0006]    U.S. Pat. No. 4,252,465A describes a gel plug, which is employed during construction of an offshore pipeline to separate a gas-filled portion of the pipeline from a water-flooded portion, and to facilitate control and movement of the gas/gel plug/water interface as desired to assist in construction operations. 
         [0007]    U.S. Pat. No. 4,254,559A relates to an interior surface of a pipeline being dried by sequentially passing through the pipeline (a) an aqueous cross-linked gelled pig, (b) a fluid mobility buffer comprising a non-cross-linked gelled ankanol of from one to three carbon atoms, (c) a dessicating amount of a liquid ankanol from one to three carbon atoms. For example, a pipeline was dried by sequentially passing through it (a) a borate cross-linked hydroxypropyl guar gum pig, (b) a fluid mobility buffer comprising methanol thickened with hydroxypropyl cellulose, and (c) methanol. 
         [0008]    U.S. Pat. No. 4,379,722 discloses a gel plug of mineral oil, organo-modified smectite, and a particulate filler such as powdered coal, or a gel plug of mineral oil and organo-modified smectite is employed during construction of an off-shore pipeline to separate a gas-filled portion of the pipeline from a water-flooded portion, and to facilitate control and movement of a gas/gel plug/water interface as desired to assist in construction operations. 
         [0009]    U.S. Pat. No. 4,416,703 describes a method to remove particulate debris from a pipeline, a plug train including at least one gel plug having debris entraining characteristics and at least one pseudoplastic plug is passed through a pipeline and the debris is collected by the gel plug. The gel plug is pushed through the pipeline with a scraper which in turn may be pushed by liquid or gas pressure. 
         [0010]    U.S. Pat. No. 4,321,968A discloses gelled compositions comprising carboxymethylhydroxyethyl cellulose in aqueous brine solutions, which are gelled by the addition of an alkaline earth metal hydroxide such as calcium hydroxide. The gelled compositions have utility as water diversion agents, pusher fluids, fracturing fluids, drilling muds, work-over fluids, and completion fluids. 
         [0011]    U.S. Pat. No. 5,346,339A provides a method of cleaning a pipeline using a gel pig of a graft copolymer of a hydroxyalkyl cellulose prepared by a redox reaction with vinyl phosphonic acid. The gel pig is formed by hydrating the graft copolymer in an aqueous liquid. The gel pig is crosslinked by the addition of a Lewis base or Bronsted-Lowry base, to the gel in an amount sufficient to initiate crosslinking of the graft copolymer. Contaminants entrained in the crosslinked gel pig during the cleaning process may be separated by the addition of a pH reducing agent to the pig whereby the viscosity of the gel is caused to decrease. The gel may be used for further cleaning after contaminant separation by addition of an additional quantity of the Lewis base or Bronsted-Lowry base. 
         [0012]    US2003109385A provides a process for treating a hydrocarbon-bearing formation having at least one hydrocarbon bearing zone and at least one water bearing zone wherein the ratio of the permeability of the hydrocarbon bearing zone(s) to the permeability of the water bearing zone(s) is in the range of from 1:20 to 3:1 comprising: a) sequentially injecting into the formation: (i) an aqueous polymer solution comprising 0.01 to 0.5 weight percent of a water-soluble polymer having from 0.01 to 7.5 mole percent of crosslinkable carboxylate and/or phosphonate groups and a molecular weight in the range of 250,000 to 12,000,000; and (ii) an aqueous solution of a crosslinking agent; and b) back-producing the aqueous polymer solution over the crosslinking agent so that the polymer crosslinks within the formation to form a gel which is collapsible to allow hydrocarbon flow. 
         [0013]    US2008277112A discloses a method for treating a portion of a subterranean formation or a propellant pack is provided. In general, the method comprises the steps of: (A) forming or providing a treatment fluid comprising: (i) water; (ii) a chelating agent capable of forming a heterocyclic ring that contains a metal ion attached to at least two nonmetal ions; and (iii) a viscosity-increasing agent; and (B) introducing the treatment fluid into the wellbore under sufficient pressure to force the treatment fluid into the matrix of the formation or the propellant pack. 
         [0014]    WO2008081441 describes a method of repairing leakage in pipelines comprising the steps of forming a first and second openings in the pipeline upstream and downstream, respectively, of the leakage location, inserting through the first opening a first body, filling the space arrear of the first body (C 1 ) with a first viscous sealing material (M 1 ), inserting through the first opening a second body (C 2 ) arrear of the first viscous sealing material (M 1 ) compressing the first sealing material by applying a pressure against the first and the second bodies (C 1 , C 2 ) in opposite directions, causing the first and second bodies (C 1 , C 2 ) and the compressed first sealing material (M 1 ) to move in unison in the direction of the second opening, and retrieving the first and second bodies (C 1 , C 2 ). Preferably, the method is performed using three bodies (C 1 , C 2 , C 3 ) and two sealing materials (M 1 , M 2 ). 
         [0015]    However, there are still many types of pipeline leakages, which cannot be cured using the aforementioned prior art materials and methods. There thus remains an urgent need to develop systems and methods for curing pipeline leakages. 
       SUMMARY OF THE INVENTION 
       [0016]    It is an object of some aspects of the present invention to provide methods of forming gel pigs for use in systems and methods for sealing pipeline leakages. 
         [0017]    In preferred embodiments of the present invention, improved methods are provided for producing gel pigs. 
         [0018]    In other embodiments of the present invention, a method and system are provided for sealing water transport pipelines. 
         [0019]    The present invention provides systems and methods for curing a leakage in a pipeline, the system including at least one gel pig and at least one sealant composition; wherein the at least one gel pig and the at least one sealant composition form a pig train, adapted to move along the pipeline to a region of the leakage and to seal the leakage. 
         [0020]    There is thus provided according to an embodiment of the present invention, a system for curing at one leakage site in a pipeline, the system including;
       a) at least one gel pig; and   b) at least one sealant composition; wherein the at least one gel pig and the at least one sealant composition form a pig train, adapted to move along the pipeline to a region of the at least one leakage and to seal the at least one leakage.       
 
         [0023]    Additionally, according to an embodiment of the present invention, the at least one gel pig includes one gel pig and the at least one sealant composition includes one sealant composition. 
         [0024]    Furthermore, according to an embodiment of the present invention, the at least one gel pig includes two gel pigs and the at least one sealant composition includes one sealant composition. 
         [0025]    Further, according to an embodiment of the present invention, the at least one gel pig includes three gel pigs and the at least one sealant composition includes two sealant compositions. 
         [0026]    Moreover, according to an embodiment of the present invention, the pig train is adapted to move along the pipeline at a speed of 0.01 to 10 m/s. 
         [0027]    Additionally, according to an embodiment of the present invention, the at least one gel pig includes one rear pig. 
         [0028]    Furthermore, according to an embodiment of the present invention, the at least one of the two pigs has an average diameter of at least 5% less than an internal diameter of the pipeline. 
         [0029]    Additionally, according to an embodiment of the present invention, at least one of the two pigs has an average diameter of at least 10% less than an internal diameter of the pipeline. 
         [0030]    Additionally, according to an embodiment of the present invention, the at least one gel pig includes;
       a. a cellulosic polysaccharide;   b. a surfactant; and   c. water.       
 
         [0034]    Furthermore, according to an embodiment of the present invention, the at least one gel pig further includes;
       d. a filler; and   e. a metallic hydroxide.       
 
         [0037]    Additionally, according to an embodiment of the present invention, the at least one gel pig further includes an oil. 
         [0038]    Moreover, according to an embodiment of the present invention, the at least one gel pig includes a rear pig and a front pig of different compositions. 
         [0039]    Additionally, according to an embodiment of the present invention, the pig train is adapted to conform to an inner profile of the pipeline. 
         [0040]    Furthermore, according to an embodiment of the present invention, the inner profile of the pipeline is reduced in diameter in at least one section by at least 20%. 
         [0041]    Additionally, according to an embodiment of the present invention, the inner profile of the pipeline is reduced in diameter in at least one section by at least 50%. 
         [0042]    Further, according to an embodiment of the present invention, the inner profile of the pipeline is reduced in diameter in at least one section by at least 75%. 
         [0043]    Yet further, according to an embodiment of the present invention, the inner profile of the pipeline is further increased in the diameter in at least one section by at least 20%. 
         [0044]    Additionally, according to an embodiment of the present invention, the inner profile of the pipeline is increased in the diameter in at least one section by at least 50%. 
         [0045]    Importantly, according to an embodiment of the present invention, the inner profile of the pipeline is increased in the diameter in at least one section by at least 75%. 
         [0046]    Additionally, according to an embodiment of the present invention, A the system further includes a pressurized fluid for propelling the system from a first end thereof along the pipeline. 
         [0047]    Furthermore, according to an embodiment of the present invention, the pressurized fluid includes a liquid. 
         [0048]    Additionally, according to an embodiment of the present invention, the pressurized fluid includes a gas. 
         [0049]    Furthermore, according to an embodiment of the present invention, the pressurized fluid includes a tri-phase composition. 
         [0050]    Additionally, according to an embodiment of the present invention, the pressurized fluid is at a pressure of 1-150 bar. 
         [0051]    Moreover, according to an embodiment of the present invention, the pig train is adapted to prevent a bypass of a propelling product by of more than 30%. 
         [0052]    Additionally, according to an embodiment of the present invention, the pig train is adapted to be extracted from the pipeline via a conduit of less than two inch diameter at a pressure of less than 3 bar. 
         [0053]    Additionally, according to an embodiment of the present invention, the system further includes a counter pressurized fluid for counter-pressurizing the pig train from a second end thereof. 
         [0054]    Furthermore, according to an embodiment of the present invention, the counter pressurized fluid is for controlling velocity of movement of the pig train along the pipeline. 
         [0055]    Additionally, according to an embodiment of the present invention, the pig train can be launched from a pipe of a diameter of less than 75% of the pipeline. 
         [0056]    Further, according to an embodiment of the present invention, the pig train can be launched from a pipe of a diameter of less than 50% of the pipeline. 
         [0057]    Additionally, according to an embodiment of the present invention, herein the pig train can be launched from a pipe of a diameter of less than 75% of the pipeline. 
         [0058]    Additionally, according to an embodiment of the present invention, A the pig train can be launched from a pipe at an angle of greater than 30° to the pipeline. 
         [0059]    Further, according to an embodiment of the present invention, the pig train can be launched from a pipe at an angle of greater than 60° to the pipeline. 
         [0060]    Yet further, according to an embodiment of the present invention, the pig train can be launched from a pipe at an angle of greater than 80° to the pipeline. 
         [0061]    Additionally, according to an embodiment of the present invention, the pig train can be launched from a pipe at a pressure in the range of 2-15 bar. 
         [0062]    Moreover, according to an embodiment of the present invention, the pig train can be launched from a pipe at a pressure of 2-4 bar. 
         [0063]    Additionally, according to an embodiment of the present invention, the pig train is adapted to travel through an obstruction in the pipeline and to be operative thereafter. 
         [0064]    Further, according to an embodiment of the present invention, the obstruction selected from the group consisting of tuberculation, encrustation, a butterfly valve, a wedge, a nail, a screw, an obstructing element, an in-pipe meter, a service pipe ferrule, a baffle, a broomstick seal and combinations thereof. 
         [0065]    The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0066]    The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood. 
           [0067]    With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. 
           [0068]    In the drawings: 
           [0069]      FIG. 1A  is a simplified pictorial illustration showing a system for sealing a pipeline, in accordance with an embodiment of the present invention; 
           [0070]      FIG. 1B  is a simplified pictorial illustration showing another system for sealing a pipeline, in accordance with an embodiment of the present invention; 
           [0071]      FIG. 1C  is a simplified pictorial illustration showing another system for sealing a pipeline, in accordance with an embodiment of the present invention; 
           [0072]      FIG. 1D  is a simplified pictorial illustration showing another system for sealing a pipeline, in accordance with an embodiment of the present invention; 
           [0073]      FIG. 2  is a simplified flow chart of a method for sealing a pipeline, in accordance with an embodiment of the present invention; 
           [0074]      FIG. 3  is a simplified flow chart of another method for sealing a pipeline, in accordance with an embodiment of the present invention; 
           [0075]      FIG. 4  is a simplified flow chart of another method for sealing a pipeline, in accordance with an embodiment of the present invention; and 
           [0076]      FIG. 5  is a simplified pictorial illustration showing a system for sealing a pipeline, in accordance with an embodiment of the present invention. 
       
    
    
       [0077]    In all the figures similar reference numerals identify similar parts. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0078]    In the detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that these are specific embodiments and that the present invention may be practiced also in different ways that embody the characterizing features of the invention as described and claimed herein. 
         [0079]    Reference is now made to  FIG. 1A , which is a simplified pictorial illustration showing a system  100  for sealing a pipeline, in accordance with an embodiment of the present invention. 
         [0080]    System  100  is constructed and configured to seal a pipeline  106  comprising at least one leakage site  108 , such as a crack or hole. System  100  comprises a sealant composition  102  and a gel pig  104 . System  100  is adapted to travel along the pipeline using a first pressure force  110  to the rear of the gel pig and a counter force  112  upstream (lesser than force  110 ). Some non-limiting examples of the gel pig compositions appear in the examples hereinbelow. Some non-limiting examples of the sealant compositions are disclosed in Israel Patent No. 180474. 
         [0081]    A non-limiting example of composition  104  is:
       a) At least one organic or inorganic filler selected from carbon ash, aluminum hydroxide, calcium carbonate, calcium hydroxide, magnesium hydroxide, magnesium carbonate, titanium hydroxide, silica, similar fillers and combinations thereof in a weight ratio of 0.01-3% wt/wt.   b) At least one gelling agent selected from carrageenan, agar agar, hydroxymethylcelluose, hydroxyethyl cellulose, hydroxypropyl cellulose and combinations thereof in a weight ratio of 0 to 20% wt/wt.   c) A coloring agent selected from a water soluble dye, a water insoluble dye, a paint, an oxide, a metal oxide and combinations thereof in a weight ratio of 0 to 1% wt/wt.   d) At least one surfactant selected from an ionic surfactant, an anionic surfactant, a detergent, an edible oil, an inedible oil and combinations thereof in a weight ratio of 0.01 to 10% wt/wt.   e) At least one aqueous agent selected from sea water, tap water, distilled water, ice and combinations thereof in a weight ratio of 20 to 90% wt/wt.       
 
         [0087]      FIG. 1B  shows a simplified pictorial illustration showing another system  120  for sealing a pipeline, in accordance with an embodiment of the present invention. System  120  comprises two gel pigs  104 ,  106 . These gel pigs may be of identical or different compositions. These are termed herein a rear gel pig  104  and a front gel pig  106 . Dispersed between the two gel pigs is sealant composition  102 . Some non-limiting examples of the gel pig compositions appear in the examples hereinbelow. Some non-limiting examples of the sealant compositions are disclosed in Israel Patent No. 180474. 
         [0088]    There can be seen in  FIG. 1C  a simplified pictorial illustration showing another system  140  for sealing a pipeline, in accordance with an embodiment of the present invention. System  140  comprises three gel pigs  104 ,  114 ,  118  and two sealant compositions  102 ,  116 . These gel pigs may be of identical or different compositions. Likewise, sealant compositions  102 ,  116  may be identical or different. Some non-limiting examples of the gel pig compositions appear in the examples hereinbelow. Some non-limiting examples of the sealant compositions are disclosed in Israel Patent No. 180474. 
         [0089]    A non-limiting example of composition  114  is:
       a) At least one organic or inorganic filler selected from carbon ash, aluminum hydroxide, calcium carbonate, calcium hydroxide, magnesium hydroxide, magnesium carbonate, titanium hydroxide, silica, similar fillers and combinations thereof in a weight ratio of 0.01-10% wt/wt.   b) At least one gelling agent selected from carrageenan, agar agar, hydroxymethylcelluose, hydroxyethyl cellulose, hydroxypropyl cellulose and combinations thereof in a weight ratio of 0 to 30% wt/wt.   c) A coloring agent selected from a water soluble dye, a water insoluble dye, a paint, an oxide, a metal oxide and combinations thereof in a weight ratio of 0 to 1% wt/wt.   d) At least one surfactant selected from an ionic surfactant, an anionic surfactant, a detergent, an edible oil, an inedible oil and combinations thereof in a weight ratio of 0.01 to 20% wt/wt.   e) At least one aqueous agent selected from sea water, tap water, distilled water, ice and combinations thereof in a weight ratio of 20 to 85% wt/wt.       
 
         [0095]    A non-limiting example of composition  118  is:
       a) At least one organic or inorganic filler selected from carbon ash, aluminum hydroxide, calcium carbonate, calcium hydroxide, magnesium hydroxide, magnesium carbonate, titanium hydroxide, silica, similar fillers and combinations thereof in a weight ratio of 0.01-10% wt/wt.   b) At least one gelling agent selected from carrageenan, agar agar, hydroxymethylcelluose, hydroxyethyl cellulose, hydroxypropyl cellulose and combinations thereof in a weight ratio of 0 to 30% wt/wt.   c) A coloring agent selected from a water soluble dye, a water insoluble dye, a paint, an oxide, a metal oxide and combinations thereof in a weight ratio of 0 to 1% wt/wt.   d) At least one surfactant selected from an ionic surfactant, an anionic surfactant, a detergent, an edible oil, an inedible oil and combinations thereof in a weight ratio of 0.01 to 20% wt/wt.   e) At least one aqueous agent selected from sea water, tap water, distilled water, ice and combinations thereof in a weight ratio of 20 to 85% wt/wt.       
 
         [0101]      FIG. 1D  is a simplified pictorial illustration showing another system  160  for sealing a pipeline, in accordance with an embodiment of the present invention. System  160  comprises two gel pigs  114 ,  170  and a sealant composition  102  or  116  disposed therebetween. The front gel pig  114  may be similar or identical to those described herein. The rear gel pig  170  comprises at least two or three different compositions  122 ,  124 ,  126 , for introduction into a pipeline sequentially (first  122 , then  124  and thereafter  126 ). 
         [0102]    A non-limiting example of composition  122  or composition  124  or composition  126  is:
       a) At least one organic or inorganic filler selected from carbon ash, aluminum hydroxide, calcium carbonate, calcium hydroxide, magnesium hydroxide, magnesium carbonate, titanium hydroxide, silica, similar fillers and combinations thereof in a weight ratio of 0.01-3% wt/wt.   b) At least one gelling agent selected from carrageenan, agar agar, hydroxymethylcelluose, hydroxyethyl cellulose, hydroxypropyl cellulose and combinations thereof in a weight ratio of 0 to 20% wt/wt.   c) A coloring agent selected from a water soluble dye, a water insoluble dye, a paint, an oxide, a metal oxide and combinations thereof in a weight ratio of 0 to 1% wt/wt.   d) At least one surfactant selected from an ionic surfactant, an anionic surfactant, a detergent, an edible oil, an inedible oil and combinations thereof in a weight ratio of 0.01 to 10% wt/wt.   e) At least one aqueous agent selected from sea water, tap water, distilled water, ice and combinations thereof in a weight ratio of 20 to 90% wt/wt.       
 
         [0108]    Additionally or alternatively, the rear gel pig comprises four compositions, five compositions, six compositions, seven compositions, eight compositions or another multiplicity of compositions. A fourth composition  128  (not shown), a fifth composition  130  (not shown), a sixth composition  132  (not shown). 
         [0109]    When six compositions are applied the first composition (front to back) serves as a separator between the sealing composition and the second composition. It has a density of 1.0-1.5 g/cm 3 . The second composition, together with the third composition, forms a two (horizontal) layer sealant body preventing the bypass of the liquid propellant. The second composition has a density of 0.9-1.5 g/cm 3  and the third composition has a density of 0.8-1.2 g/cm 3 . The fourth and fifth compositions isolate the third composition from the propelling liquid. Respective densities are 1.0-1.8 g/cm 3  and 0.8-1.2 g/cm 3 . The sixth composition is a gel sealant, whose purpose is to temporarily seal the pig train from the rear upon launch. It has a density of 0.8-1.2 g/cm 3 . 
         [0110]    Reference is now made to  FIG. 2 , which is a simplified flow chart of a method  200  for sealing a pipeline, in accordance with an embodiment of the present invention, with reference to  FIG. 1A . A sealant composition, such as sealant composition  102  is introduced to pipeline  106  in a sealant composition introducing step  202 . This may be performed from one end of the pipe or from a manhole or vertical. 
         [0111]    Thereafter, gel pig  104  is introduced from the same end of the pipe as the sealant composition or from a manhole or vertical, in a gel pig composition introducing step  202 . 
         [0112]    The combination of the sealant composition  102  and gel pig  104  is termed herein a “pig train”. The pig train travels along the pipe in a travelling step  206  to site  108  of the leakage. The sealant composition is operative to seal the leakage in a sealing step  208 . It typically takes a few minutes to several hours until the seal is fully cured. 
         [0113]    Typically, gel pig  104  is of approximately the same diameter as the inner diameter of the pipe and is typically 0.5-10 diameters in length. The physical properties of the gel pig appear in Table 4. 
         [0114]    Reference is now made to  FIG. 3 , which is a simplified flow chart of another method  300  for sealing a pipeline, in accordance with an embodiment of the present invention, with reference to  FIG. 1 . 
         [0115]    A first gel pig  114  is introduced to the pipe in an introducing pig step  302 . The gel pig may be introduced from a fire hydrant, from a manhole, vertical, lateral pipe, communication pipe or from a branch pipe. 
         [0116]    A sealant composition, such as sealant composition  102  is introduced to pipeline  106 , from a fire hydrant, from a manhole, vertical, lateral pipe, communication pipe or from a branch pipe, in a sealant composition introducing step  304 . This may be performed from one end of the pipe or from a manhole or vertical. 
         [0117]    Thereafter, a second gel pig  104  is introduced from the same end of the pipe, from a fire hydrant, from a manhole, vertical, lateral pipe, communication pipe or from a branch pipe, as the sealant composition, in a second gel pig composition introducing step  306 . 
         [0118]    The combination of the sealants composition  102  and gel pigs  114 ,  104  is termed herein a “pig train”. The pig train travels along the pipe in a travelling step  308  to site  108  of the leakage. The sealant composition is operative to seal the leakage in a sealing step  310 . It typically takes a few minutes to several hours until the seal is fully cured. 
         [0119]    Typically, gel pigs  104 ,  114  are of approximately the same diameter as the inner diameter of the pipe and is typically 0.5-10 diameters in length. The physical properties of the front gel pig  114  appear in Table 5. 
         [0120]    The pig train is typically recovered from the pipeline in an exit pipe step  312 . 
         [0121]      FIG. 4  is a simplified flow chart of another method  400  for sealing a pipeline, in accordance with an embodiment of the present invention, with reference to  FIG. 1C . 
         [0122]    A first gel pig  118  is introduced to the pipe in a first introducing pig step  402 . The gel pig may be introduced from a fire hydrant, from a manhole, vertical, lateral pipe, communication pipe or from a branch pipe. 
         [0123]    A sealant composition, such as sealant composition  116  is introduced to pipeline  106  in a first sealant composition introducing step  404 . This may be performed from one end of the pipe or from a manhole from a fire hydrant, lateral pipe, communication pipe or from a branch pipe or vertical. 
         [0124]    Thereafter, a second gel pig  114  is introduced from the same end of the pipe as the first sealant composition or from a fire hydrant, from a manhole, vertical, lateral pipe, communication pipe or from a branch pipe, in a second gel pig composition introducing step  406 . 
         [0125]    A second sealant composition, such as sealant composition  102  is introduced to pipeline  106  from a fire hydrant, from a manhole, vertical, lateral pipe, communication pipe or from a branch pipe in a second sealant composition introducing step  408 . This may be performed from one end of the pipe or from a manhole or vertical. 
         [0126]    Thereafter, a third gel pig  104  is introduced from the same end of the pipe as the first and second sealant composition from a fire hydrant, from a manhole, vertical, lateral pipe, communication pipe or from a branch pipe, in a third gel pig composition introducing step  410 . 
         [0127]    The combination of the sealants compositions  102 ,  116  and gel pigs  118 ,  114  and  104  is termed herein a “pig train”. The pig train travels along the pipe in a travelling step  412  to site  108  of the leakage. The sealant composition(s) is/are operative to seal the leakage in a sealing step  414 . It typically takes a few minutes to several hours until the seal is fully cured. 
         [0128]    Typically, gel pigs  104 ,  114 ,  118  are of approximately the same diameter as the inner diameter of the pipe and is typically 0.5-10 diameters in length. The physical properties of the front/middle gel pig  118 / 114  appear in Table 5. 
         [0129]    The pig train is typically recovered from the pipeline in an exit pipe step  416 . In some cases, one or more of the gel pigs may be replaced with a polymer pig, such as polyurethane. 
         [0130]    Reference is now made to  FIG. 5 , which is a simplified pictorial illustration showing a system  500  for sealing a pipeline, in accordance with an embodiment of the present invention. 
         [0131]    System  500  comprises a front gel pig  114  and a real gel pig  104 . A sealant composition  102  is disposed between pigs  114  and  104 , forming a pig train  120 . A fluid  502  is inserted into a pipeline  501 , from a fire hydrant, from a manhole, vertical, lateral pipe, communication pipe or from a branch pipe, and a first pressure P 1    506  is applied to fluid  502 . Additionally a second counter-pressure P 2 ,  508  is applied to a second fluid  504 . Typically P 1  is much greater than P 2 . The average velocity of pig train  120  is determined by the fluid properties and a pressure difference (P 1 −P 2 ). 
         [0132]    Pressure P 1  is introduced by a pump  512 , pressure from an existing network or any other suitable pressure introducing means, known in the art. The pressure P 1  is typically regulated by control means, as are known in the art. 
         [0133]    Pressure P 2  may be introduced by any suitable passive means, such as a pressure relief valve  514 , a discharge valve, a pressure regulator or the like. 
         [0134]    The gel pigs of the present invention provide the following advantages:—
       1) Gel pigs are adapted to multi-dimensioned pipes-adaption to variable and changing diameters in situ.   2) Non-abrasive very non-abrasive (in contrast to poly pigs, which may get stuck in a pipeline, induce a reddening of water, induce a change of pH of the water, or may abrade tubicles.   3) Gel pigs of the present invention are to introduce into pipe and to remove from pips providing system flexibility.   4) Gel pigs of the present invention do not normally get stuck in the pipe (better than polymer (solid) pigs and due to their fluidity, can always be flushed out.   5) The rear pig does not compromise/dislodge disengage newly formed seals, in contrast to solid pigs.   6) Gel pigs of the present invention are fully flushable (in contrast, solid pigs leave debris).   7) A front pig of the present invention allows water to bypass and overtake-allows escape route to prevent/minimize sealant composition dilution.   8) In a two pig system, the rear pig acts differently to the front pig.   9) Pig receiver/retriever for solid pigs is not required for gel pigs.   10) The gel pigs of the present invention are biodegradable.   11) Gel pigs of the present invention require reduced transportation costs-here can be formulated at/near the site of use. Saving on transport costs.       
 
       EXAMPLES 
     Example 1 
       [0146]    A gel pig is formed according to the following method.
       1) Chemical constituents were obtained in accordance with table 1.   2) A gel pig mixture was made by mixing the components of table 1 in a stirred vessel for several (1-30) minutes at ambient temperature and pressure.   3) The resultant gel formed was stored in a closed container in the dark for 0-60 days at room temperature before use.       
 
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                 TABLE 1 
               
             
             
               
                   
               
               
                 Chemical composition of gel pig 
               
             
          
           
               
                   
                 Functional 
                 Example 
                   
               
               
                   
                 Component 
                 Constituent 
                 Weight percent [%] 
               
               
                   
                   
               
               
                   
                 Hygroscopic 
                 Cellulose, gum, 
                  1-10 
               
               
                   
                 component 
                 gelatin or other 
               
               
                   
                 surfactant 
                 Oil or other 
                 0-8 
               
               
                   
                 Base 
                 Aluminum 
                  0-20 
               
               
                   
                   
                 hydroxide 
               
               
                   
                 Particulate 
                 Silica 
                 0-2 
               
               
                   
                 Carrier fluid 
                 Water 
                 70-95 
               
               
                   
                   
                 Total 
                 100 
               
               
                   
                   
               
             
          
         
       
     
         [0150]    According to some embodiments, the physical properties of the gel pigs appear as in tables 2 and/or 3. 
         [0151]    According to one or more embodiments, hydrophobic solvents are liquid oils originating from vegetable, marine or animal sources. The canola oil exemplified may be replaced by any suitable liquid oil including saturated, unsaturated or polyunsaturated oils. By way of example, the unsaturated oil may be olive oil, corn oil, soybean oil, cottonseed oil, coconut oil, sesame oil, sunflower oil, borage seed oil,  syzigium aromaticum  oil, hempseed oil, herring oil, cod-liver oil, salmon oil, flaxseed oil, wheat germ oil, canola oil, evening primrose oils or mixtures thereof, in any proportion. 
         [0152]    According to one or more embodiments, the silica exemplified may be replaced by a) microsponges, b) silica, c) mineral bodies like zeolite, bentonite, (iii) graphite, including polymers, dendrimers and liposomes, or mixtures thereof, in any proportion. 
         [0153]    According to one or more embodiments, the aluminum hydroxide exemplified may be replaced by minerals such as aluminum phosphate and calcium phosphate or mixtures thereof, in any proportion. 
         [0154]    According to one or more embodiments, the hydroxyethyl cellulose exemplified may be replaced by any at least one polymeric additive selected from the group consisting of polysaccharides, natural polysaccharides, derivatives thereof, modified poysacharides, derivatives thereof, starch, dextrin, glycogen, cellulose and chitin, glycosaminoglycans (GAG&#39;s), chondroitin sulphate, dermatan sulphate, keratan sulphate, heparan sulphate, heparin, and hyaluronan, amylose and amylopectine, cellulose derivatives, xanthan gum, sodium CMC, methylcellulose, and hydroxyl propyl methyl cellulose or mixtures thereof, in any proportion. 
         [0155]    Specific non limiting examples of surfactants are an ionic surfactant, a non-ionic surfactant, a hydrophobic surfactant or mixtures thereof, in any proportion. 
         [0156]    Exemplary hygroscopic agents that can be used in accordance with one or more embodiments include, for example, naturally-occurring polymeric materials, such as locust bean gum, sodium alginate, sodium caseinate, egg albumin, gelatin agar, carrageenan gum, sodium alginate, xanthan gum, quince seed extract, tragacanth gum, guar gum, starch, chemically modified starches and the like, semi-synthetic polymeric materials such as cellulose ethers (e.g. hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxy propylmethyl cellulose), guar gum, hydroxypropyl guar gum, soluble starch, cationic celluloses, cationic guars, and the like, and synthetic polymeric materials, such as carboxyvinyl polymers, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid polymers, polymethacrylic acid polymers, polyvinyl acetate polymers, polyvinyl chloride polymers, polyvinylidene chloride polymers and the like. Mixtures of the above compounds are contemplated. 
         [0157]    According to some further embodiments, a base may be selected from sodium hydroxide, magnesium hydroxide, aluminum hydroxide, potassium hydroxide and combinations thereof. 
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                 TABLE 2 
               
             
             
               
                   
               
               
                 Physical and Chemical properties of rear gel pig 
               
             
          
           
               
                   
                 minimum 
                 maximum 
               
               
                   
                   
               
             
          
           
               
                   
                 Viscosity cPs 
                 5 
                 10000 
               
               
                   
                 Density g/cm 3   
                 0.8 
                 1.2 
               
               
                   
                   
               
             
          
         
       
     
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                 TABLE 3 
               
             
             
               
                   
               
               
                 Physical and Chemical properties of front gel pig 
               
             
          
           
               
                   
                 minimum 
                 maximum 
               
               
                   
                   
               
             
          
           
               
                   
                 Viscosity cPs 
                 5 
                 10000 
               
               
                   
                 Density g/cm 3   
                 0.8 
                 1.5 
               
               
                   
                   
               
             
          
         
       
     
         [0158]    The references cited herein teach many principles that are applicable to the present invention. Therefore the full contents of these publications are incorporated by reference herein where appropriate for teachings of additional or alternative details, features and/or technical background. 
         [0159]    It is to be understood that the invention is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope, defined in and by the appended claims.