Abstract:
The present invention relates to and uses, in order to prevent crude oil from “congealing” in a transportation line, a controlled-crosslinking thermal insulation gel, i.e. relatively fluid at the start and developing in-situ gelation in lines only under certain conditions, temperature conditions among other things. In order to obtain controlled crosslinking, it is possible to carry out 1) Physical crosslinkings, i.e. physical bonds between polymers—completely reversible bonds by thermal effect and/or mechanical shear—and 2) Chemical crosslinkings: monomers or polymers having functions allowing chemical bonds to be established between polymers.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     The present invention relates to the technical field of thermal insulation of oil transportation lines whose operating conditions in production wells are of the order of 60 to 120° C. as regards temperature and about 300 bars as regards pressure; the crude oil is then liquid and pumpable. The pressure and the temperature fall continuously along these lines and congealing of the crude oil is the major drawback.  
         [0002]     The application relates more particularly to offshore as well as onshore drilling where the temperatures are very low or even negative.  
       TECHNICAL PROBLEM  
       [0003]     In offshore development, the production well is provided with a production wellhead that rests on the sea bottom. The crude oil then has to be carried to tankers, storage barges or storage and/or pumping platforms, by means of complex systems of risers, pipelines and similar means, referred to hereafter as lines or flowlines.  
         [0004]     Under deep and very deep offshore drilling conditions, the environment of the risers is water at 0-10° C., the pressure decreases and the crude therefore congeals because of the deposition of hydrates, paraffin,          black mud         , etc.  
         [0005]     These lines can be about twenty km long and, in case of production stop due to congealing of the crude, the maintenance and servicing operations are extremely expensive. Congealing of the crude oil therefore has to be prevented in particular.  
         [0006]     Current Solutions: 
        Heating of the lines by means of hot water or resistors     Thermal insulation of the lines with insulating material sheaths such as glass wool, rock wool, insulating foam . . . 
 
 The drawbacks are: 
    difficult to implement 1)     efficiency loss in case of breakage and in the presence of water 2)     high cost 3)              Pipe in pipe          technique (concentric lines) with the annulus evacuated or filled with a rare gas (argon, xenon . . . ), which are good thermal insulants. 
 
 Drawbacks: Points 1)+3) 
    Syntactic foam: system where hollow glass marbles are embedded in a thermosetting resin matrix as described in patent U.S. Pat. No. 5,575,871 (Takeda Chemical Ind./1999) 
 
 Drawbacks: Points 1)+2)+3) 
    Gel based on ethylene glycol and water.        
 
         [0018]     Prior Art: 
    1) U.S. Pat. No. 5,290,768 Merck &amp; Co/1994): Polysaccharide thickener of Welan™ type in ethylene glycol and with EDTA (ethylene diamine tetra-acetic acid) as rust complexing agent.     2) U.S. Pat. No. 5,876,619 (Montsanto/1999): Polysaccharide thickener of scleroglucane type in glycerin and water. 
 
 Drawbacks: 
        sensitive to bacteria pollution     sensitive to rust     heavy (ballast product).     Gel based on petroleum products (gas oil, kerosine, mineral oils): 
 
 1) U.S. Pat. No. 5,177,193 (Ravchem Corp/1993): various polymer gels in a mineral base with chemical crosslinking 
 
 Drawback: Point 1) 
 
 2) U.S. Pat. No. 5,858,489 (Elf Aquitaine Production): Aerogels 
 
 Drawback: Point 1) extremely difficult to implement 
 
 3) U.S. Pat. Nos. 5,871,034 and 60,092,557 (G. R. Summer 1999 and 2000): Mixture of bitumens with thermoplastic polymers and mineral fillers. 
 
 Drawbacks: Point 1) and soft product under high pressure and high temperature. 
 
 4) U.S. Pat. No. 4,941,773 (Smit Offshore Contractors, 1990): The base and kerosine thickened by thermosetting resins based on polyols and aldehydes. 
   
       
 
         [0033]     Among all these solutions, gels currently represent the most advantageous technique as regards its cost, material selection flexibility and ease of use. They essentially consist of a base and of a thickener: 
        base: the most thermally insulating possible base is selected, generally petroleum or chemical products or glycol derivatives     thickener: used to congeal the base and thus to prevent thermal convection phenomena.        
 
         [0036]     General Drawbacks of the Existing Techniques:  
         [0037]     Apart from gels, the solutions are immediately solid insulants that are difficult to use.  
         [0038]     The current gels are          pasty          system that are less difficult to use than solid insulants, but they remain difficult and excluded in lines with complex configurations such as bundles. These are tubes attached to one another comprising for example two production tubes and three smaller lines or tubes used to carry other fluids, the assembly being embedded in a common external sheath filled with thermally insulating gels.  
         [0039]     Many pressure losses occur during filling of these bundles, without it being possible to use high-pressure pumping means (&gt;100 bars for example) because of the low mechanical strength of the outer walls, and air pockets or air bubbles inevitably appear. This can pose problems of collapse of the external sheath under high pressure (150 bars) under deep sea conditions.  
       SUMMARY OF THE INVENTION  
       [0040]     The present invention relates to and uses, in order to prevent the crude oil from          congealing          in a line, a controlled-crosslinking thermal insulation gel, i.e. a relatively fluid gel in the beginning, gelation occuring in-situ in the lines only under certain conditions, temperature conditions among other things. The gels obtained are mechanically and thermally stable at high and low temperature, and especially in very weakly solvent bases such as pure linear paraffins, pure isoparaffins . . . and also especially with bases of the same type exhibiting phase changes such as crystallization. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     According to the invention, controlled crosslinking can be obtained by carrying out: 
    1) Physical crosslinking: i.e. by establishing physical bonds between polymers, notably with the following means:     a) Diblock or triblock sequential polymers: crosslinking nodes by affinity, then phase segregation     b) Polymers having functions allowing physical bonds (hydrogen, Van der Waals, dipole-dipole, etc.), for example polar functions such as alcohols, acids, amines, ethers, esters . . . and similar functions, generally functions with heteroatoms of O, N, S, Cl type.     2) Chemical crosslinking: Monomers or polymers having functions allowing to achieve chemical bonds between polymers.    
 
         [0046]     The advantages are as follows: 
        Ease of use (pumping, setting, complex systems)     Homogeneous gel, without          air bubbles or pockets              No thermal convection     Stable at high temperature between 80-150° C.     Great durability     Pressure resistant     Thermal insulant     Light gel (density&lt;0.8)     Physical gel: specifications flexibility, i.e. reversible or irreversible, pseudoplastic or thixotropic     Products more economical than syntactic foams.        
 
         [0057]     Chemical systems usable according to the invention: the following instances are given by way of non limitative example, and the man skilled in the art can complete them according to his general knowledge and possibly to some routine tests.  
         [0058]     1) Bases: 
        petroleum products: light cuts or others, according to the application considered, such as kerosine, gas oil, cut referred to as petroleum spirit; type 60 (S or NS) mineral bases up to paraffins, bitumens and similar products,     petroleum products with transformation: linear paraffins or isoparaffins . . . , hydroisomerized bases, . . . ,     chemical derivatives of glycol, of monoethylene glycol, monopropylene glycol, diethylene glycol and similar types,     water→insulants+ballast,     vegetable oils such as rapeseed, sunflower, soybean, palm oil, etc., extracted from seeds, plants, barks, fruit, . . .     synthetic bases such as polyalphaolefins (PAO), polyisobutylenes (PIB), polyalkyleneglycols (PAG), polyinternal olefins (PIO), fatty esters, fatty alcohols, fatty ethers.        
 
         [0065]     Among these bases, 2 categories can be distinguished: 
        (1) the bases, light (of very low viscosity) or not, which do not crystallize at positive temperatures,     (2) the bases that crystallize at positive temperatures.        
 
         [0068]     The latter bases are particularly interesting when this crystallization is exothermic and when this energy is used to compensate for the heat waste at low temperature of the sea bottom It is well-known that the more linear and the longer the hydrocarbon chains, the more they tend to crystallize at increasingly high temperatures. Examples of linear paraffins are Linpar® 13-14, 14, 14-17, 16-18 type paraffins, fatty esters, fatty alcohols, for example Nacol® 12, 14, 16, 18, 20 or 22 . . . Nafol® 12-14, 12-18, 16-18, or simply mineral bases with a high paraffin content.  
         [0069]     These phase-change bases form with conventional thickeners often loose and unstable gels when they are subjected to thermal cycles.  
         [0070]     2) Physical Gelling Agent: 
    a) Diblock or triblock or radial sequential polymers:    
 
         [0072]     Any diblock or triblock or radial sequential polymer. This very particular structure type is mainly obtained by ionic (anionic or cationic) polymerization.  
         [0073]     A non-limitative example is the range of products known under the tradename KRATON® and marketed by Shell™. These products are distinguished by: 
        the number of sequences (blocks): two or three or radial     an elastomeric sequence of polybutadiene or polyisoprene type, as it is (D series) or hydrogenated (G series),     a sequence of polystyrene type (which forms the crosslinking phase),     the composition (% styrene),     the molecular mass,     in the case of a triblock or radial polymer, the styrene phases generally          surround          the elastomeric phase.        
 
         [0080]     The mechanical properties of the gel depend on the nature of the base used, the grade of the Kraton™ used, the percentage. According to the desired application, a very          firm         , rubbery, extremely resistant and stable towards thermal or mechanical stresses, or a very          loose          gel, on the verge of flowing, reversible, thixotropic and pseudoplastic is obtained.  
         [0081]     Standard thickeners of polyisoprene, polybutadiene, natural rubber, polyisobutylene, ethylene-propylene copolymers type are also advantageously associated with these physical gelling agents.  
         [0082]     Several Kraton™ grades can also be used together according to the desired performances.  
         [0083]     This first category of sequential-structure physical gelling agents whose crosslinking nodes are the phase segregation zones preferably include, by way of non limitative example, the Kraton® products range marketed by Shell™ etc.  
         [0084]     The bases preferably used in the following non-limitative examples, as described above, are: a rapeseed methyl ester, a linear paraffin (Linpar C 10 ®),          light          cut and          heavy          cut (Linpar C16-C18®), an isoparaffin (Isopar™ M), a standard gas oil, petroleum spirit, etc.  
         [0085]     The tests carried out to evaluate the gelation kinetics, the various mechanical properties, the compatibility of the gel with the base, are as follows: 
        A composition is prepared under the conditions mentioned in the examples hereafter, in a glass bottle provided with a metallic screw cover to obtain a gel or not.     A composition is fluid at the observation temperature if it flows when the bottle is inclined (or tilted at 180°). In the opposite case, a gel is obtained.     The gel time is the time required for a composition to change from the fluid state to the state of gel at the temperature of the experiment.     Mechanical strength test: A steel ball of about 10 g is dropped at a height of about 20 cm above the surface of the gel. The gel is loose if the ball penetrates the gel with or without bounce. In the opposite case, the gel is firm, mechanically stable at the testing temperature.     Test intended to evaluate the compatibility and the thermal stability of the gel with the base under the conditions of a thermal cycle; the gel is subjected to 2 thermal cycles: 
            (1) Cycle 1: 10 h at 80° C./14 h at 20° C./10 h at 80° C./14 h at 20° C.     (2) Cycle 2: 10 h at 80° C./14 h at 0° C./10 h at 80° C./14 h at 0° C.    
               
 
         [0093]     At the end of the thermal cycle, the gel must remain firm (no mechanical properties loss) without          releasing          the base, i.e. existence of 2 phases, a liquid phase and a gel phase. This phenomenon is known as syneresis or bleeding.  
         [0094]     This phenomenon is particularly marked in bases with phase changes, for example Linpar® C 18 -C 20 , which crystallizes from 30° C. and which, besides the fact that it is a very bad solvent for conventional polar thickeners, separates from the gel once crystallized.  
         [0095]     The physical gelling agents selected according to the invention are perfectly stable with these bases, even bases with          phase change         .  
         [0096]     The range of Kraton® thermoplastic polymers finds applications as additives in adhesives, bitumens, mixtures of thermoplastics, mastics, elastomers, etc.  
         [0097]     In the present invention, the Kraton® products described above can be more or less suitable according to the specific needs and to the bases used. The following examples illustrate this feature in a non limitative way:  
         [0098]     It is also possible to incorporate one or more mineral fillers in order to optimize the cost of the product, its mechanical or physical properties, to weight it or on the contrary to lighten it. The man skilled in the art knows in these fields fillers such as clays, bentonite, barite, calcium carbonates, and examples of lightening agents are, in particular, glass microballs such as those marketed by the 3M™ company, which are microballs of about 10 to 150 microns, with an average dimension of about 30 microns, and a double function of product lightening and thermal insulation improvement.  
         [0099]     The man skilled in the art will be able to envisage all the fillers and filler combinations of this type.  
       EXAMPLE 1  
     Comparative Test with a Conventional Thickener  
       [0100]    
       
         
           
              Base=Linear paraffin Linpar® C 18 -C 20    
              Gelling agent=Kraton G 1651 E vs. bentone (Thixogel® VP)  
              Testing temperature=Cycles 1 and 2  
           
         
       
     
         [0103]     The percentages in the examples hereunder are expressed in mass of active substance.  
                                           TABLE 1                           Characteristics of the gels            Percen-               tage   Kraton ® G 1651 E   Thixogel ® VP                    4   &lt;&lt; Firm &gt;&gt; gel. No bleeding.   Fluid solution           Thermal cycle stability       8   &lt;&lt; Firm &gt;&gt; gel. No bleeding.   Fluid solution           Thermal cycle stability       10       &lt;&lt; Loose &gt;&gt; gel. Bleeding.               Thermal cycle instability       12       &lt;&lt; Loose &gt;&gt; gel. No bleeding.               Thermal cycle stability       15       &lt;&lt; Firm &gt;&gt; gel. No bleeding.               Thermal cycle stability                  
 
         [0104]     The example given above clearly shows the advantage afforded by physical gelling agents in relation to conventional thickeners for a given base, much lower proportion of material used, higher gel quality and stability.  
       EXAMPLE 2  
     Manufacturing Process and Direct Use  
       [0105]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
               
               
                 Manufacture and use of the products 
               
             
          
           
               
                   
                 Kraton ® G 1651 
                 Thixogel ® VP 
               
               
                   
                   
               
             
          
           
               
                 Manufac- 
                 Dispersion of the powdered 
                 Manufacture of a bentone- 
               
               
                 ture 
                 polymer at 40° C. if the base 
                 based grease followed by 
               
               
                   
                 has to be melted, or at ambient 
                 crushing, deaeration 
               
               
                   
                 temperature (20° C.) in the 
                 Gel having a certain 
               
               
                   
                 presence or not of other 
                 consistency 
               
               
                   
                 polymers or dispersants 
               
               
                   
                 Liquid dispersion of 
               
               
                   
                 &lt;&lt; swollen &gt;&gt; polymer powders 
               
               
                 Use in 
                 Filling with the fluid liquid 
                 Filling by pumping under 
               
               
                 the lines 
                 dispersion from the bottom 
                 pressure (150 bars) and 
               
               
                   
                 In-situ gelation with 
                 &lt;&lt; vacuum draining &gt;&gt; 
               
               
                   
                 temperature (example: at 80° C. 
                 throughout the line 
               
               
                   
                 gel at 4% gel time = 4 h) or 
                 Risk of &lt;&lt; air pockets or 
               
               
                   
                 others 
                 bubbles &gt;&gt; 
               
               
                   
               
             
          
         
       
     
         [0106]     This example shows the ease and flexibility of use of a physical gel with in-situ crosslinking and controlled initiation, for example by temperature.  
       EXAMPLE 3  
     Product Conditioning Process in Case of no Direct Use  
       [0107]    
       
         
               
               
               
               
               
             
           
               
                   
               
               
                   
               
               
                   
                 Temper- 
                   
                   
                   
               
               
                 Bases 
                 ature 
                 Composition 
                 Aspect 
                 Pot life 
               
               
                   
               
             
             
               
                 Linpar 
                 20° C. 
                 8% Kraton G 
                 Heterogeneous 
                 3 to 6 
               
               
                 C10 
                   
                 1651 
                 swollen powders 
                 months 
               
               
                   
                   
                   
                 dispersion 
               
               
                 Linpar 
                 20° C. 
                 6% Kraton G 
                 Homogeneous 
                 3 to 6 
               
               
                 C10 
                   
                 1651 
                 dispersion 
                 months 
               
               
                   
                   
                 2% Kraton G 
               
               
                   
                   
                 1702 
               
               
                 Linpar 
                     40° C.(1) 
                 8% Kraton G 
                 Heterogeneous 
                 3 to 6 
               
               
                 C18-20 
                   
                 1651 
                 swollen powders 
                 months 
               
               
                   
                   
                   
                 dispersion 
               
               
                 Linpar 
                     40° C.(1) 
                 6% Kraton G 
                 Homogeneous 
                 3 to 6 
               
               
                 C18-20 
                   
                 1651 
                 dispersion 
                 months 
               
               
                   
                   
                 2% Kraton G 
               
               
                   
                   
                 1702 
               
               
                   
               
               
                   (1)It is recommended to keep these products or to bring them to a temperature of 40° C. prior to use (crystallization temperature 28° C.).    
               
             
          
         
       
     
         [0108]     It appears that, in cases where the product is not directly used from the conditioner, incorporation of another polymer allows the homogeneity, the stability and the pumpability of the product to be improved.  
       EXAMPLE 4  
     Effect of the Base, of the Temperature, of the Nature and of the Concentration of the Physical Gelling Agent: Comparative Tests with Conventional Polymeric Thickeners  
       [0109]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
               
               
                 Formation conditions of a stable gel at 20 or 80° C. 
               
             
          
           
               
                   
                 Linpar ™ 
                 Linpar ™ 
                   
                   
               
               
                   
                 C18-20 
                 C10 
                 Gas oil 
                 Isopar ™ M 
               
               
                   
                   
               
             
          
           
               
                 Poly- 
                 Fluid 
                 Fluid 
                 Fluid 
                 Fluid 
               
               
                 isoprene 
                 solution 
                 solution 
                 solution 
                 solution 
               
               
                   
                 any temp. 
                 any temp. 
                 any temp. 
                 any temp. 
               
               
                   
                 up to 20% 
                 up to 20% 
                 up to 20% 
                 up to 20% 
               
               
                 Kraton ™ G 
                 8% firm 
                 8% firm 
                 8% firm 
                 8% firm 
               
               
                 1651 
                 gel &gt;= 
                 gel &gt;= 
                 gel &lt;= 
                 gel &gt;= 
               
               
                   
                 100° C. 
                 80° C. 
                 20° C. 
                 80° C. 
               
               
                 Kraton G 
                 10% firm 
                 Fluid 
                 Fluid 
                 Not studied 
               
               
                 1652 
                 gel &lt;= 
               
               
                   
                 20° C. 
               
               
                 Kraton D 
                 8% loose gel 
                 Fluid 
                 Fluid 
                 Not studied 
               
               
                 1111 
                 at 80° C. 
               
               
                 Kraton D 
                 Fluid 
                 Fluid 
                 Fluid 
                 Not studied 
               
               
                 1101 
               
               
                 Kraton D 
                 Fluid 
                 Fluid 
                 Fluid 
                 Not studied 
               
               
                 1161 
               
               
                 Kraton G 
                 8% loose gel 
                 15% loose 
                 8% firm gel 
                 Not studied 
               
               
                 1701 
                 at 80° C. 
                 gel at 
                 at 20° C. 
               
               
                   
                   
                 80° C. 
               
               
                 Kraton G 
                 8% firm gel 
                 8% loose gel 
                 8% firm gel 
                 Not studied 
               
               
                 1654 
                 at 100° C. 
                 at &gt;20° C. 
                 at 20° C. 
               
               
                 Kraton 
                 8% firm 
                 8% firm gel 
                   
                 Not studied 
               
               
                 GRP 6917 
                 gel &gt;= 
                 at 80° C. 
               
               
                   
                 100° C. 
               
               
                   
               
             
          
         
       
     
         [0110]     This example shows that, according to the conditions of the application (temperature, base, etc.), the nature of the suitable physical gelling agent and its concentration can be selected.  
         [0111]     As described above, these polymers occur as diblocks or triblocks or radial polymer, preferably as triblocks with ethylene-propylene sequences or butadiene or isoprene, preferably ethylene-propylene with styrene sequences with a styrene composition ranging from 10 to 40%, preferably from 20 to 35%, with weight average molecular weights characterized in the manufacturer&#39;s data sheet by high, average and low, preferentially high weight average molecular weight. The percentage of use of these physical gelling agents depends on the bases used, but it generally ranges between 1 and 30%, preferably between 2 and 20%.  
       EXAMPLE 5  
     Reversible Gel by Shear and Temperature Effect  
       [0112]     Another advantage of these physical gelling agents is that it is possible to reversibly destroy these crosslinking nodes of the three-dimensional network which are the styrene phases by temperature rise and/or mechanical stirring, the latter re-forming as soon as these two effects stop.  
                                 TABLE 4                           Effect of temperature and stirring: perfect reversibility of the gel                    Heating at 130° C.               Heating   and stirring with a           at 130° C.   dispersing device at   2-h rest       Initial state   for 1 h   1500 rpm for 1 h   at 80° C.               Firm gel with 4%   Loose gel   Fluid   Firm and       Kraton G 1651 in           stable gel       Linpar C18-20       stable at 80° C.                  
 
         [0113]     This reversibility is particularly interesting for use in bundles of complex geometry.  
       EXAMPLE 6  
     Characteristics of Physical Gels with Kraton® G 1651 (8%)  
       [0114]    
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                   
               
               
                 Properties of the gels 
               
             
          
           
               
                   
                 Linpar C 18-20   
                 Linpar C 10   
               
               
                   
                   
               
             
          
           
               
                   
                 50° C. 
                 0.774 
                 0.755 
               
               
                   
                 density 
               
               
                   
                 20° C. 
               
               
                   
                 Thermal convection (1) 
                 No 
                 No 
               
               
                   
                 Thermal conduction (2) at 
                 0.16 
                 0.14 
               
               
                   
                 80° C. (W · m −1 ,  0 K −1 ) 
               
               
                   
                   
               
             
          
         
       
       
          (1) The thermal conductivity is measured at different angles of rotation; if it is the same everywhere, there is no convection.  
          (2) ISO 8894-2 
 
 b)          Associative          Polymers: 
 
       
     
         [0118]     Certain          associative          polymers give great interactions in certain solvents, which result in a thixotropic (variation of the viscosity as a function of time) and pseudoplastic gel.  
         [0119]     There is a series of resins which, once dispersed in a solvent, develop highly thixotropic gels. Examples of such resins are ALKYDE, ACRYLIC, URETHANE resins, etc. These resins are extremely complex as regards their formula, and their selection and association require a certain expertise. Without being limitative, the present description will focus on Alkyd resins, which are the most important ones in this application. 
        These Alkyd resins result from an addition reaction between a polyol and a polyacid. They can be long or short in oil, modified or not, for example with amide, urethane, isocyanate functions.     They are often used in synergy with other resins or polymers of polyurea, polyamide, polyurethane type, etc.        
 
         [0122]     In relation to the above physical gelling agent family, the latter rather represent a          loose         , thixotropic and pseudoplastic gel. In the first case, gelation is initiated by the temperature and, in the second case, it occurs practically at the end of the mixing operation and with time.  
       EXAMPLE 7  
     Examples of Thixotropic Physical Gels Based on Associative Polymers  
       [0123]     a) Petroleum Spirit Base:  
                                                       Alkyd resin Lixol ™   27%           Resin Super Gelkyd ™ 391W   30%           Dowanol ™ PM   1.5%            Petroleum spirit   41.5%                        
 
         [0124]     b) Linpar C 10 ™ Base:  
         [0125]     The petroleum spirit of example a) is replaced by Linpar C 10 .  
         [0126]     c) Gas Oil Base:  
         [0127]     The petroleum spirit of example a) is replaced by gas oil.  
         [0128]     d) Rapeseed Methyl Ester Base:  
         [0129]     The petroleum spirit of example a) is replaced by rapeseed methyl ester.  
         [0130]     These gels are prepared according to a protocol determined by each manufacturer&#39;s expertise.  
         [0131]     All these gels are          loose          gels, perfectly thixotropic and pseudoplastic. The ease of use is the same as for physical gels: the compositions are fluid under heavy mechanical stirring (or at a temperature&gt;40° C.) and gelation occurs at rest with time inside the flow lines.  
         [0132]     The gels are stable towards the thermal cycles and in time.  
         [0133]     The gel based on petroleum spirit was evaluated as regards thermal convection; no thermal convection and no thermal conductivity could be observed: λ=0.14 W.m −1 , °K −1 .  
         [0134]     The general compositions of these physical gels based on associative polymers are between 10-40% alkyd resin, preferably about 35%, possibly with a polar solvent derived from glycol between 0.5 and 10%, preferably 1 to 3%, the rest consisting of the base.  
         [0135]     Physical gels are particularly easy to use: 
        The polymer(s) are dispersed in the selected base the reaction does not start.     According to the application, the temperature and/or stirring is used to completely solubilize the macromolecular chains: the reaction starts.     According to products, gelation (congealing) is more or less fast and occurs with time through physical bonds or segregation phases.        
 
         [0139]     According to the application requirements, a          loose         , mechanically reversible physical gel may be preferred, i.e. a pseudoplastic and thixotropic gel (fluid through shearing), which becomes thermally fluid (fluid through temperature increase).  
         [0140]     3) Chemical Gelling Agent:  
         [0141]     In the case of a chemical gelling agent, two mechanisms can be considered: 
    a) the initial mixture is a mixture of reactive monomers which, under the effect of radical initiators or not, will initiate the polymerization (or polyaddition) or crosslinking (polyfunctional monomers) reaction in the presence or not of catalysts, under predetermined temperature and stirring conditions.     b) the initial mixture is a mixture of polymers having reactive functions that react with each other or by means of a monofunctional or polyfunctional monomer. The latter plays the same crosslinking agent role as in the first case. This reaction can also start with radical initiators or not, in the presence or not of catalysts and under predetermined temperature and stirring conditions.    
 
         [0144]     In the first case, the following non limitative examples can be mentioned: 
        polymerization (radical crosslinking): the monomers have an unsaturated bond (double bond) which, under the effect of a radical initiator, will start the reaction. Examples of monomers are alkyl methacrylate or alkyl acrylate monomers, vinyl esters, vinyl chlorides, etc.; examples of polyfunctional monomers are a neopentylglycol dimethacrylate or divinylbenzene; examples of radical initiators are peroxides (for example benzoyl peroxide) or diazoic compounds (for example AIBN: 2,2′azobisisobutyronitrile);     polyaddition (or polycondensation) reaction: polyurethanes (the polyols reacting with the polyisocyanates), polyureas (the polyamines reacting with the polyisocyanates), polyesters (the polyacids with the polyalcohols), polyamides (the polyamines with the polyacids), thermosetting resins of epoxy resin type, polyimides, etc.        
 
         [0147]     The reactive monomers and the compounds necessary to the reaction are mixed in the selected base and the crosslinking polymerization reaction is generally initiated by a temperature increase. The gel time must be controlled according to the implementation process.  
         [0148]     In the second case, the following non limitative examples can be mentioned: 
        polymers soluble in the selected base having reaction functions or double bonds capable of crosslinking the polymers with each other. Examples thereof are polyisoprenes, hydrogenated or not, polybutadienes, hydrogenated or not, ethylene-propylene-diene monomers (EPDM), styrene-butadiene rubbers (SBR), functionalized polyisobutylenes (with an anhydride, carboxylic or amine function for example), and more preferably esters referred to as alkyd resins, resulting for example from an addition between a polyol and unsaturated fatty acids.     In the case of radical crosslinking, initiators such as peroxide type initiators, for example benzoyl peroxide, etc., or nitrogen-containing, for example 2,2′azobisisobutyronitrile, with or without difunctional monomers of neopentylglycol dimethacrylate or divinylbenzene type are suitable.        
 
         [0151]     The gel time must also be controlled according to the process requirements.  
       EXAMPLE 8  
     Chemical Gel  
       [0152]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                   
               
             
             
               
                   
                 Alkyd resin Lixol 
                 20% 
               
               
                   
                 Synolac 6883 
                 20% 
               
               
                   
                 Coporob 2526 
                 20% 
               
               
                   
                 BYK 411 
                  1% 
               
               
                   
                 Monomers and crosslinking agents 
                  2% 
               
               
                   
                 Radical initiators 
                  1% 
               
               
                   
                 Catalysts 
                 0.8%  
               
               
                   
                 Linpar C10 
                 35.2%   
               
               
                   
                   
               
             
          
         
       
     
         [0153]     The composition gives a firm gel after about 4 h at 80° C.  
         [0154]     The example is given only by way of illustration of the concept of chemical gel in this application.  
         [0155]     The advantages that all these chemical systems of the invention have in common are: 
        a compound that can be fluid to relatively viscous, but perfectly pumpable and posing no filling problems in lines of complex geometry and configuration such as bundles, or air pocket or aeration problems if the compound is too          consistent         ,     gelation of the system starts either very progressively in time, or it is initiated by an external factor (temperature, energy supply),     the gel is thermally perfectly stable from 0° C. to 100° C., resistant to biological pollution and stable in time,     according to needs, the gel is perfectly compact, supple and pressure-resistant,     for certain bases with crystallization between 0 and 50° C., the gel remains always stable towards thermal cycles between 0 and 1100° C.,     the gels are totally incompatible with sea water, they cannot          fade         , with a density &lt;or =0.8 and therefore relatively easy to recover in case of an accident. Under certain conditions, these gels can be non toxic to the marine environment and to man (vegetable oils, esters, 100% linear paraffin or isoparaffin base).        
 
         [0162]     Validation of the Application  
         [heading-0163]     1.1 Description of the Measuring Model:  
         [0164]     (the measuring model is shown in the accompanying sole FIGURE)  
         [0165]     The models consist of a 27-mm diameter and 50-cm long steel hub (M) (L&gt;&gt;d so as to limit edge effects) filled with oil maintained at constant temperature by a direct current-fed heater band.  
         [0166]     This steel tube is arranged in a 100-mm diameter Plexiglas™ tube (1) and kept in position by means of polystyrene insulating centering plugs (2). The cavity (3) thus formed is filled with INSULATING GEL in the most homogeneous way possible. Heating resistors (4) are arranged in the centre.  
         [0167]     The assembly is immersed in a container comprising water maintained at 30° C. by an immersion heater.  
         [0168]     The models are equipped with 6 thermocouples T: 
        1 on the steel wall     1 on the Plexiglas™ wall,     4 in the paraffin layer at various depths.        
 
         [0172]     They all have the same angular position.  
         [0173]     The object of the measurement is: 
        to check the absence of thermal convection by measuring the temperature field which must remain constant in the three different angular positions 0, 90 and 1800,     to have an average thermal conductivity of the insulant.        
 
         [0176]     This model was filled with a gel based on conventional bentonite in Linpar C18-20 in comparison with a loose gel based on associative polymers:  
         [0177]     In the first case, a particular assembly is used: 
        Conditioner heated and stirred at 80° C./1 h. Placed under vacuum for          dearation          purposes.     Device connecting the conditioner to the model with vacuum downstream and pressure upstream from the conditioner, with a feed pump to prevent air pockets or bubbles.        
 
         [0180]     In the second case, it is sufficient to mechanically shear the gel based on petroleum spirit which becomes fluid, to feed the model, to place under vacuum for dearation and to let the gel recover its consistency at ambient temperature after about 4 hours.  
         [0181]     The results obtained are as follows:  
                                                                 Gel: 15% Bentone in   Gel: petroleum           Linpar C18-20 (Ex. 1)   spirit (Ex. 6)                                    Thermal loss (W/°K*m2)   8.19   9.01       Thermal field   Constant   Constant       At different angles   (&lt;1/10°)   (&lt;1/10°)       Thermal conductivity   0.174   0.147/0.141/0.134       (W/m*°K)                  
 
         [0182]     It can be seen that these are very good thermal insulants where thermal convection phenomena are entirely blocked even in the case of loose gels in petroleum spirit.