Abstract:
Lipophilic fibers are effective media for cleaning non-aqueous fluids out of a subterranean wellbore. The fibers are preferably added to a drilling fluid, a spacer fluid, a chemical wash, a cement slurry or combinations thereof. Non-aqueous fluids, such as an oil-base mud or a water-in-oil emulsion mud, are attracted to the fibers as they circulate in the wellbore.

Description:
CROSS REFERENCED APPLICATIONS 
       [0001]    This application claims the benefit of the disclosure of European patent application number 11306087.5 filed on Aug. 31, 2011 incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    This disclosure relates to compositions and methods for removing non-aqueous fluids from a subterranean wellbore. 
         [0004]    During the construction of subterranean wells, it is common, during and after drilling, to place a tubular body in the wellbore. The tubular body may comprise drillpipe, casing, liner, coiled tubing or combinations thereof. The purpose of the tubular body is to act as a conduit through which desirable fluids from the well may travel and be collected. The tubular body is normally secured in the well by a cement sheath. The cement sheath provides mechanical support and hydraulic isolation between the zones or layers that the well penetrates. The latter function is important because it prevents hydraulic communication between zones that may result in contamination. For example, the cement sheath blocks fluids from oil or gas zones from entering the water table and polluting drinking water. In addition, to optimize a well&#39;s production efficiency, it may be desirable to isolate, for example, a gas-producing zone from an oil-producing zone. The cement sheath achieves hydraulic isolation because of its low permeability. In addition, intimate bonding between the cement sheath and both the tubular body and borehole is necessary to prevent leaks. 
         [0005]    The cement sheath is usually placed in the annular region between the outside of the tubular body and the subterranean borehole wall by pumping the cement slurry down the interior of the tubular body, out the bottom and up into the annulus. The cement slurry may also be placed by the “reverse cementing” method, whereby the slurry is pumped directly down into the annular space. During the cementing process, the cement slurry is frequently preceded by a spacer fluid or chemical wash to prevent commingling with drilling fluid in the wellbore. These fluids also help clean the tubular-body and formation surfaces, promoting better cement bonding and zonal isolation. The cement slurry may also be followed by a displacement fluid such as water or a brine. This fluid usually resides inside the tubular body after the cementing process is complete. A complete description of the cementing process and the use of spacer fluids and chemical washes is presented in the following publications. Piot B and Cuvillier G: “Primary Cementing Techniques,” in Nelson E B and Guillot D:  Well Cementing -2 nd Edition,  Houston, Schlumberger (2006) 459-501. Daccord G, Guillot D and Nilsson F: “Mud Removal,” in in Nelson E B and Guillot D:  Well Cementing -2 nd Edition,  Houston, Schlumberger (2006) 143-189. 
         [0006]    Drilling-fluid removal and wellbore cleaning may be challenging when the well has been drilled with non-aqueous fluids. In the art of well cementing, non-aqueous fluids may be oil-base muds or water-in-oil emulsions. Conventionally, operators employ water-base spacer fluids or chemical washes comprising surfactants that render the fluids compatible with non-aqueous fluids. In the context of well cementing, fluids are compatible when no negative rheological effects such as gelation occur upon their commingling. Such effects may hinder proper fluid displacement, leaving gelled fluid in the wellbore and reducing the likelihood of achieving proper zonal isolation. Ideally, the spacer fluid, chemical wash or both will completely remove the non-aqueous fluid and leave casing and formation surfaces in the annulus water wet. Water-wet surfaces may promote intimate bonding between the cement sheath and casing and formation surfaces. 
         [0007]    Many of the surfactants commonly used in the art to impart compatibility of spacer fluids and chemical washes with non-aqueous fluids may not be suitable for use in regions where governmental regulations restrict their use, disposal, or both. Therefore, despite the valuable contributions of the prior art, it remains desirable to have materials and methods by which non-aqueous fluids may be removed from a wellbore, yet comply with governmental regulations. 
       SUMMARY 
       [0008]    The present disclosure describes such improvements. Aqueous fluid including (but not limited to) spacer fluids, chemical washes, drilling fluids and cement slurries are provided that are compatible with non-aqueous fluids and have the ability to remove them from a wellbore during a cementing treatment. In an aspect, embodiments relate to methods for cleaning surfaces coated with a non-aqueous fluid. In a further aspect, embodiments relate to methods for cementing a subterranean well. 
         [0009]    This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a diagram illustrating the ability of lipophilic fibers to remove non-aqueous fluids from casing and formation surfaces in a wellbore. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The description and examples are presented solely for the purpose of illustrating the preferred embodiments should not be construed as a limitation to the scope and applicability of the disclosed embodiments. While the compositions of the present disclosure are described herein as comprising certain materials, it should be understood that the composition could optionally comprise two or more chemically different materials. In addition, the composition can also comprise some components other than the ones already cited. 
         [0012]    The Applicants have determined that aqueous treatment fluids comprising lipophilic fibers may clean surfaces that are coated with a non-aqueous fluid. 
         [0013]    Embodiments relate to methods for cleaning surfaces coated with a non-aqueous fluid. Such surfaces comprise a borehole in a subterranean well whose surfaces are coated with a non-aqueous fluid. An aqueous treatment fluid is provided that comprises lipophilic fibers. The aqueous treatment fluid may comprise (but would not be limited to) a drilling fluid, a spacer fluid, a chemical wash, or a cement slurry, or combinations thereof. 
         [0014]    The fibers may comprise polypropylene-isotactic, polypropylene-atactic, polypropylene-syndiotactic, polyester, polydimethylsiloxane, polytetrafluoroethylene, polytrifluoroethylene, polyhexylmethacrylate, polyvinylidene fluoride, poly(t-butylmethacrylate), polychlorotrifluoroethylene, polyisobutylmethacrylate, polybutylmethacrylate, polytetramethylene oxide, polytetrahydrofurane, polyisobutylene, polycarbonate, polyethylene-branched, polyethylene-linear, polyethylmethacrylate, polyvinylacetate, polyvinyl fluoride, polyethylacrylate, poly-a-methyl styrene, polyvinyltoluene, polystyrene, polyamide-12, polymethylacrylate, polymethylmethacrylate, polyvinylchloride, polyetheretherketone, polyethylene oxide, polyethyleneterephthalate, polyvinylidine chloride, or polyamide-6,6, and combinations thereof. The fiber length may be between about 5 mm and 50 mm. The fiber geometry may be cylindrical, trilobal, ribbon like, or grooved, and combinations thereof. An example of a grooved fiber is 4DG™ fibers from Fiber Innovation Technology, Inc., Johnson City, Tenn. 37604, USA. The fibers may be further coated with a hydrophilic material, or sizing, to promote dispersion in the aqueous medium. Suitable coatings may include (but would not be limited to) starch, xanthan polymers, diutan, scleroglucan, guar, guar derivatives, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, polyvinyl alcohols, or water-soluble acrylates and combinations thereof. 
         [0015]    The solid surface energy of the fibers may be less than the surface tension of water, or between about 20 mN/m and 40 mN/m. For efficiency, the fibers are selected such that they may absorb between about 10 times to about 60 times their weight of non-aqueous fluid. 
         [0016]    The surfaces coated with non-aqueous fluid are placed in contact with the treatment fluid. In a wellbore, the treatment fluid may be circulated, for example in the annular space between the casing (or other tubular body) and the subterranean formation wall. The circulation of the treatment fluid may remove the non-aqueous fluid, filter cake or both from the casing and formation surfaces, leaving them water wet. The treatment fluid is then removed from the wellbore. The treatment fluid may further comprise a surfactant. Suitable surfactants may include (but would not be limited to) alkylammonium compounds, dodecyl benzene sulfonate, derivatives of oxyethylated esters of fatty acids and polyglycol esters of alkyl phenols. 
         [0017]    The treatment fluid is then removed from the wellbore, leaving the tubular-body and formation surfaces water wet. 
         [0018]    One example of the method is illustrated in  FIG. 1 . Casing  101  is present in the wellbore, and a non-aqueous coating  104  is deposited on its surface. On the other side of the annular space, a non-aqueous coating  104  also is attached to the formation wall  102 . The treatment fluid comprising lipophilic fibers  105  is flowing upward  103  in the annular space. The lipophilic nature of the fibers causes the non-aqueous coating to be removed from the casing and formation surfaces as they travel up the annulus. 
         [0019]    Embodiments relate to methods for cementing a subterranean well. An aqueous treatment fluid is provided that comprises lipophilic fibers. The aqueous treatment fluid may comprise a drilling fluid, a spacer fluid, a chemical wash, or a cement slurry, or combinations thereof. 
         [0020]    The fibers may comprise polypropylene-isotactic, polypropylene-atactic, polypropylene-syndiotactic, polyester, polydimethylsiloxane, polytetrafluoroethylene, polytrifluoroethylene, polyhexylmethacrylate, polyvinylidene fluoride, poly(t-butylmethacrylate), polychlorotrifluoroethylene, polyisobutylmethacrylate, polybutylmethacrylate, polytetramethylene oxide, polytetrahydrofurane, polyisobutylene, polycarbonate, polyethylene-branched, polyethylene-linear, polyethylmethacrylate, polyvinylacetate, polyvinyl fluoride, polyethylacrylate, poly-a-methyl styrene, polyvinyltoluene, polystyrene, polyamide-12, polymethylacrylate, polymethylmethacrylate, polyvinylchloride, polyetheretherketone, polyethylene oxide, polyethyleneterephthalate, polyvinylidine chloride, or polyamide-6,6, and combinations thereof. The fiber length may be between about 5 mm and 50 mm. The fiber geometry may be cylindrical, trilobal, ribbon like, or grooved, and combinations thereof. An example of a grooved fiber is 4DG™ fibers from Fiber Innovation Technology, Inc., Johnson City, Tenn. 37604, USA. The fibers may be further coated with a hydrophilic material, or sizing, to promote dispersion in the aqueous medium. Suitable coatings may include (but would not be limited to) starch, xanthan polymers diutan, scleroglucan, guar, guar derivatives, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, polyvinyl alcohols, or water-soluble acrylates and combinations thereof. 
         [0021]    The solid surface energy of the fibers is may be less than the surface tension of water, or between about 20 mN/m and 40 mN/m. For efficiency, the fibers are selected such that they may absorb between about 10 times to about 60 times their weight of non-aqueous fluid. 
         [0022]    The treatment fluid is circulated in the wellbore, for example in the annular space between the casing (or other tubular body) and the subterranean formation wall. The circulation of the treatment fluid may remove the non-aqueous fluid, filter cake or both from the casing and formation surfaces, leaving them water wet. The treatment fluid is then removed from the wellbore. The treatment fluid may further comprise a surfactant. Suitable surfactants may include (but would not be limited to) alkylammonium compounds, dodecyl benzene sulfonate, derivatives of oxyethylated esters of fatty acids and polyglycol esters of alkyl phenols. 
         [0023]    The treatment fluid is then removed from the wellbore, leaving the tubular-body and formation surfaces water wet. 
         [0024]    A cement slurry is then provided and placed in the annular space between the tubular body and the subterranean-formation wall. 
       EXAMPLE 
       [0025]    The following example serves to further illustrate the invention. 
         [0026]    40 mL of water containing 0.25 wt % polyolefin fibers, with a length of 18-20 mm and a diameter less than about 0.03 mm, were placed in a 50-mL glass vial with a cap. 0.2 mL of an water-in-oil emulsion drilling fluid from MI SWACO, Houston, Tex. USA were added to the vial. After capping the vial, the mixture was shaken. The drilling fluid was attracted to the fibers, allowing the fluid to be removed from the vial with the fibers. Clear water was left in the vial. 
         [0027]    Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.