Abstract:
Methods and compositions are provided that may comprise cement, a stabilizing additive, latex, and water. An embodiment of the present invention includes a method of cementing in a subterranean formation. The method may include introducing a cement composition into the subterranean formation, wherein the cement composition comprises cement, a stabilizing additive, latex, and water. Another embodiment of the present invention include a cement composition. The cement composition may comprise cement, a stabilizing additive, latex, and water.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/949,202 that was filed on Mar. 6, 2014. 
     
    
     FIELD OF INVENTION 
       [0002]    Embodiments of the present invention generally relate to latex cement systems for downhole operation. More particularly, the invention relates to methods and apparatuses for controlling separation in cements incorporating latex. 
       BACKGROUND 
       [0003]    In cementing a well many cement compositions are commonly utilized. For instance, during drilling, a pipe string such as casing or liners may be run into a well bore and cemented in place using a cement. In a typical cementing operation, cement may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe string disposed therein. The cement sets in the annular space, forming an annular sheath of hardened, substantially impermeable cement that supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the subterranean formation. Among other things, the annular sheath of cement surrounding the pipe string functions to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Cement may also be used in remedial cementing methods, such as squeeze cementing and the placement of cement plugs. 
         [0004]    In many instances, the cement in the annular space between the well bore and the pipe string often suffers structural failure due to pipe movements which cause shear stresses to be exerted on the set cement. Such stress conditions are commonly the result of relatively high fluid pressures and/or temperatures inside the cemented pipe string during testing, perforating, fluid injection or fluid production. High internal pipe pressure or temperature can result in the expansion of the pipe string, both radially and longitudinally, which places stresses on the cement sheath causing the cement bond between the exterior surfaces of the pipe or the well bore walls to fail and thus allow leakage of formation fluids and so forth. In such instances it may be desirable for the cement slurry used to cement a pipe string into the well bore to develop high strength after setting and to have sufficient resiliency (e.g., elasticity and ductility) to resist loss of the cement bond between the exterior surfaces of the pipe or the well bore walls, or both. Also, it may be desirable for the cement composition to be able to resist cracking and/or shattering that may result from other forces on the cement sheath. For example, it may be desirable for the cement sheath to include structural characteristics that protect its structural integrity from forces associated with formation shifting, overburden pressure, subsidence, tectonic creep, pipe movements, impacts and shocks subsequently generated by drilling and other well operations. 
         [0005]    Typically latex has been included in cement compositions for use in subterranean formations to improve various properties of the compositions. The usual ratios of cement to latex, where the latex displaces a portion of the water, are anywhere from ½ gallon of latex per 94 pound bag of cement up to 2½ gallons of latex per 94 pound bag of cement. 
         [0006]    Latex may be included in a cement composition for fluid loss control, to provide resiliency to the set cement, and/or to reduce the issues associated with gas channeling. In general, latex used in cement compositions may be provided as a water-in-oil emulsion containing high quantities of natural or synthetic rubber such as styrene-butadiene rubber. However there are temperature limitations to the latex slurries. Typically when using latex slurries at high temperatures, the viscosity of the latex cement slurry increases, increasing the amount of power required to pump the cement, in certain instances the viscosity of the cement may increase to the point where it will no longer pump at all, as well as reducing the ability of the cement to bond to the tubular and to the formation. Additionally, the styrene-butadiene may invert so that the styrene and butadiene disassociate allowing the cement precipitate out of the mixture leaving the styrene and butadiene segregated from the cement such that there are pockets of styrene, pockets of butadiene, and pockets of cement such that the cement job will not bond with the formation or the tubular and therefore will not seal the annular region between the pipe in the formation. 
       SUMMARY 
       [0007]    The present invention relates to an additive that tends to stabilize the latex cement slurry and allows the use of latex cement slurry when the temperature exceeds 350° F. 
         [0008]    Typically the stabilizing additive is generally comprised of salts of polycarboxylates with lipophilic increments, such as copolymers of maleic acid and olefines, such as polyethylene, polypropylene or polyisobutylene. The water soluble and anionic polyelectrolytic nature of the invention, coats onto the latex particles to achieve a better dispersion and homogenous distribution in a slurry by a mechanism of electrostatic repulsion which then helps to prevent separation of particles and prevents separation of the latex-cement emulsion in high temperature environments. 
         [0009]    The stabilizing additive also prevents particles settling in high pressure, high temperature spacers at temperatures exceeding 350° F. It uses the same mechanism as described above to prevent separation and fall-out of the high density material. It works well in suspending barite and other weighting agents in high density spacers having weights from about 14.5 pounds per gallon to about 18.5 pounds per gallon. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0011]      FIG. 1  depicts a graph of the viscosity of the latex cement slurry with the stabilizing additive as the temperature increases. 
           [0012]      FIG. 2  depicts a graph of the viscosity of the latex cement slurry without the stabilizing additive as the temperature increases. 
           [0013]      FIG. 3  depicts a graph of a second test of the viscosity of the latex cement slurry with the stabilizing additive as the temperature increases. 
           [0014]      FIG. 4  depicts a picture of a cylinder of latex cement slurry with a stabilizing additive after being mixed and heated. 
           [0015]      FIG. 5  depicts a picture of a cylinder of latex cement slurry without a stabilizing additive after being mixed and heated. 
           [0016]      FIG. 6  depicts the results of a dynamic stability test of a latex cement slurry with a stabilizing additive after being mixed and heated. 
           [0017]      FIG. 7  depicts the results of a dynamic stability test of a latex cement slurry without a stabilizing additive after being mixed and heated. 
           [0018]      FIG. 8  depicts the results of a dynamic stability test of a spacer system with a stabilizing additive after being mixed and heated. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The description that follows includes exemplary apparatus, methods, techniques, and instruction sequences that embody techniques of the inventive subject matter. 
         [0020]      FIG. 1  depicts a graph of the consistency  12 , in Bearden units corresponding to scale  17 , of the latex cement slurry with the stabilizing additive as the temperature  14 , corresponding to scale  13 , and pressure  16 , corresponding to scale  15 , are increased. In this instance the latex cement slurry was created by adding 1 gallon of latex to a single 94 pound sack of portland cement. The latex was 65% styrene and 35% butadiene. The stabilizing additive, a salt of polycarboxylates with a lipophilic increment, was added in a ratio of about 0.4% of stabilizing additive to the cement slurry by weight. The stabilizing additive may be effective in ratios from as low as about 0.2% by weight of stabilizing additive to the cement slurry to as high as 2.5% by weight of stabilizing additive to the cement slurry. In practice ratios from about 0.5% to about 0.8% by weight of stabilizing additive to the cement slurry are better while the ratio of about 0.4% by weight of stabilizing additive to the cement slurry is preferred. 
         [0021]      FIG. 1  shows us a latex cement slurry with the stabilizing additive after the slurry has been mixed but remains at about room temperature of about 75° F. After about an hour the pressure  16  and temperature  14  of the latex cement slurry was increased to about 6800 pounds per square inch (“PSI”) and to about 300° F. over a period of 1 hour. As can be seen the consistency  12  of the latex cement slurry remain constant until about 7 hours 45 minutes when the latex cement set thereby driving its consistency or viscosity  12  off the scale. 
         [0022]      FIG. 2  depicts a graph of the consistency  22 , in Bearden units, corresponding to scale  27  of the latex cement slurry without the stabilizing additive as the temperature  24 , corresponding to scale  23 , and pressure  26 , corresponding to scale  25 , are increased.  FIG. 2  shows us a latex cement slurry without the stabilizing additive after the slurry has been mixed but remains at about room temperature of about 75° F. After about an hour the pressure  16  and temperature  14  of the latex cement slurry was increased to about 7000 PSI and to about 300° F. over a period of 1 hour. As can be seen the consistency  22  of the latex cement slurry becomes unstable at about 1 hour 24 minutes into the test or as the temperature reached about 150° due to the styrene butadiene rubber inverting. 
         [0023]      FIG. 3  depicts a graph of a second test of the consistency  32 , in Bearden units, corresponding to scale  37 , of the latex cement slurry without the stabilizing additive as the temperature  34 , corresponding to scale  33 , and pressure  36 , corresponding to scale  35 , are increased.  FIG. 3  shows us a latex cement slurry without the stabilizing additive. In this instance almost as the temperature  34  began to approach 230° F. the consistency  32  of the latex cement slurry begins a dramatic rise becoming unstable within minutes. Once the latex cement slurry became unstable the latex cement slurry was allowed to cool to room temperature of about 75° F. 
         [0024]      FIG. 4  is a picture of a graduated slurry containing a latex cement slurry with the stabilizing additive. The latex cement slurry has been subjected to a stability test where it was mixed with the stability additive and heated to 300° for 2 hours. The latex cement slurry with the stability additive was then cooled down and poured into a graduated cylinder and then placed in an oven at 180° F. until the cement either sets or the styrene butadiene rubber inverts. As can be seen in  FIG. 4  the sample with the stabilizing additive did not invert. 
         [0025]      FIG. 5  is a picture of a graduated slurry containing a latex cement slurry without the stabilizing additive. The latex cement slurry has been subjected to the same stability test criteria as the sample in  FIG. 4  where the latex cement slurry without the stabilizing additive was mixed and heated to 300° for 2 hours. The latex cement slurry without the stability additive was then cooled down and poured into a graduated cylinder and then placed in an oven at 180° F. until the cement either sets or the styrene butadiene rubber inverts. As can be seen in  FIG. 5  the latex cement slurry has channeling  55  indicating that the styrene butadiene did invert. 
         [0026]      FIG. 6  is an image of the cone height obtained from the Dr. Beirute dynamic settling test where latex cement slurry with the stabilizing additive, after being mixed and heated to 300° F. for 2 hours then cooled, was tested. The dynamic settling test simulates the settling of solids in a downhole conditions. In the dynamic settling test the solids that remain on the top of the lower paddle blade  62 , referred to as the cone height, are measured from the lower paddle blade to the top of the solids  64 . A cone height of ½ inch in a cement slurry test indicates a failure meaning that solids that are settling out of the slurry. In  FIG. 6  the latex cement slurry was created by adding 1 gallon of latex to a single 94 pound sack of portland cement. The latex was 65% styrene and 35% butadiene and 0.4% by weight of stabilizing additive was used. In this test the cone height was % inch thereby passing the test. 
         [0027]      FIG. 6  is an image of the cone height obtained from the Dr. Beirute dynamic settling test where latex cement slurry without the stabilizing additive, after being mixed and heated to 300° F. for 2 hours then cooled, was tested. In this instance the cone height  72  is about 1¼ inches as indicated on the ruler  74  as measured from the bottom of the paddle  76 . The cone height of 1¼ inch indicates a failure in that solids are settling out of the slurry. As before the latex cement slurry was created by adding 1 gallon of latex to a single 94 pound sack of portland cement. The latex was 65% styrene and 35% butadiene and 0.4% by weight of stabilizing additive was used. 
         [0028]    In many instances prior to pumping the latex cement slurry into the well a spacer is first pumped in order to separate the drilling mud or other fluids from the latex cement slurry. Typically the spacer is a mixture of a suspending agent such as a guar or an absorbent clay such as montmorillonite or bentonite, a high density material such as magnetite, hematite, or barite, water, and a surfactant. Typically such heavy weight spacers will have spacer density of from about 14.5 pounds per gallon to about 18.5 pounds per gallon. It has been found that the stabilizing additive preferably in an amount of about 1 pound of stabilizing additive per 42 gallons of spacer fluid. In practice it has been found that the use of about ½ pound to 3 pounds of stabilizing additive per 42 gallons of spacer fluid is effective to keep the high density material in suspension although using about ½ pound to 2 pounds of stabilizing additive per 42 gallons of stabilizing fluid is better at keeping the high density material in suspension.  FIG. 8  shows a dynamic settling test of test spacer fluid having a density of about 16 pounds per gallon with a stabilizing additive added at a ratio of about 1 pound per 42 gallons of spacer fluid. A cone height of 1.0 inches or greater in a spacer test indicates a failure meaning that solids that are settling out of the slurry. In this instance the cone height  84  is about ½ inches as indicated on the ruler  82  as measured from the bottom of the paddle  86 . The cone height of ½ indicates a spacer that passes such that solids are not settling out of the slurry at too rapid a rate. 
         [0029]    Bottom, lower, or downward denotes the end of the well or device away from the surface, including movement away from the surface. Top, upwards, raised, or higher denotes the end of the well or the device towards the surface, including movement towards the surface. While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible. 
         [0030]    Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter. 
         [0031]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.