Abstract:
This invention relates to a composition and use application of aqueous fluidized polymer suspensions of water soluble polysaccharides and/or polyvinyl alcohol (PVA) for use in oil field applications such completion fluids, drilling fluids, fracturing fluids and oil well cement slurries as rheology/viscosity modifier and fluid loss reducer for use where the affect on the marine environment is to be minimized.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/748,452 filed on Dec. 8, 2005, which is incorpora reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a composition and use application of solvent free fluidized polymer suspensions of cellulosic derivatives and/or polyvinyl alcohol (PVA) for use in oil field applications such completion fluids, drilling fluids and oil well cement slurries as rheology/viscosity modifier and fluid loss reducer. The slurry composition contains PLONOR (pose little or no risk to the environment) listed ingredients, particularly suitable for use in the North Sea sector.  
       BACKGROUND OF INVENTION  
       [0003]     Among a variety of additives, hydroxyethyl cellulose (HEC) is widely used in oilfield water-based fluids. While high viscosity types of HEC are generally used, in completion fluids, for rheology and fluid loss control properties, the low viscosity HEC is typically used, in oil-well cement slurries and drill-in-fluids, for filtration control properties. In some cases, both high viscosity and low viscosity HECs are used together to further optimize the overall properties, especially in cement slurries. While low weight average molecular weight (Mw) HECs are preferred fluid loss additives for medium temperature cementing, PVA is more preferred for low temperature conditions.  
         [0004]     For easy handling in oil and gas well rigs, oilfield operations, especially offshore, require the use of liquid substances/preparations whose discharge from offshore installations does not need to be strongly regulated. A variety of environmentally acceptable solvent based polymer suspensions have been used for the past a few years. These suspensions are based on either mineral oil or glycols. However, this type of suspensions still faces some use restrictions as none of them meets the entire regulatory requirements regarding the aquatic toxicity, biodegradability and bio-accumulation. Strict environmental regulations for the North Sea have required oil field service companies to reformulate their products so that their affect on the marine environment is minimized and that the components of the products comprise approved components.  
         [0005]     For use in the North Sea, chemical products are categorized into one of four (4) categories according to the ecotoxicological properties of its components. The four categories, each designated by color, are as follows: 
    Black: Forbidden to use or discharge;     Red: High priority for phasing out via substitution;     Yellow: Environmentally acceptable; and     Green: Only for chemicals listed on OSPAR Convention for the Protection of the Marine Environment of the North East Atlantic PLONAR (Pose Little Or No Risk) database.    
 
         [0010]     For oil and gas drilling operations in the North Sea, companies are required to phase out the use of Black and Red components in products and to use only new chemicals which are entirely composed of “Green” components.  
         [0011]     U.S. Pat. No. 5,268,466 to Burdick discloses that stable suspension of water soluble polysaccharides selected from the group of HEC, CMHEC, HM-HEC, HM-EHEC, MC, MHEC, MHPC, EC and Guar/Guar derivatives can be prepared in a solution of 12 to 40 wt. % dibasic potassium phosphate. The suspension includes 15-30 wt. % of said polysaccharide. The suspension further includes a stabilizing amount of xanthan gum. The industrial application of these stable suspensions was recited as for use in construction and coating materials such as joint compounds and latex paints.  
         [0012]     The need exists for liquid substances/preparations whose discharge from offshore installations do not pose a significant risk to the marine environment by virtue of the fact that the components of the liquid substances/preparations comprise approved PLONAR components while maintaining the functionality of these liquid substances/preparations in oilfield servicing fluids, such as drilling fluids, completion/workover fluids, fracturing fluids and oil well cementing fluids.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention is related to a suspension composition comprising an oil field servicing fluid selected from the group consisting of drilling fluids, completion/workover fluids, fracturing fluids and oil well cementing fluids, and a fluid polymer suspension comprising a water soluble polymer suspended in an aqueous solution of a potassium phosphate compound. The water soluble polymer is selected from the group consisting of water soluble polysaccharides and synthetic polymers. The water soluble polysaccharides may be selected from the group consisting of cellulose ethers, guar and guar derivatives. The synthetic polymer may be a polyvinyl alcohol. The cellulose ether can be hydroxyethyl cellulose (HEC), methyl cellulose (MC), hydroxypropyl cellulose (HPC), ethyl hydroxyethyl cellulose (EHEC), methyl hydroxyethyl cellulose (MHEC), hydrophobically modified hydroxyethyl cellulose (HMHEC), hydrophobically modified ethyl hydroxyethyl cellulose (HMEHEC), hydrophobically modified methyl hydroxyethyl cellulose (HMMHEC), ethyl cellulose (EC), methyl hydroxypropyl cellulose (MHPC), and carboxymethyl hydroxyethyl cellulose (CMHEC). The oilfield servicing fluids include drilling fluids, completion/workover fluids, fracturing fluids and oil well cementing fluids. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     It has been surprisingly found that a potassium phosphate compound that is environmentally friendly can be used in oilfield servicing fluids for providing efficient and superior results in oilfield usages. This invention provides an improved suspension of water soluble polymer in a concentrated aqueous salt solution of potassium phosphate based on the composition of matter described in the U.S. Pat. No. 5,268,466, the disclosure of which is incorporated herein by reference in its entirety. One benefit of the compositions of the present invention is that the entire suspension components may be selected from the OSPAR Convention for the Protection of the Marine Environment of the North East Atlantic PLONOR list of additives approved for use in the North Sea sector. It is noted that not all potassium phosphate salts are on the PLONOR list.  
         [0015]     It was discovered that suspensions of water soluble polymer, preferably water soluble polysaccharide, more preferably cellulose ethers, guar or guar derivatives, still more preferably the cellulose ethers selected from the group consisting of HEC, MC, HPC, EHEC, MHEC, HMHEC, HMEHEC, HMMHEC, EC, MHPC and CMHEC, still more preferably HEC in a concentrated aqueous potassium phosphate compound, preferably dibasic potassium phosphate anhydrous (CAS #7758-11-4), thereby providing a composition that is entirely composed of components listed as PLONOR substances. This composition may be stabilized with a minor amount of low molecular CMC, xanthan gum and/or sodium alginate.  
         [0016]     The potassium phosphate compound of use in the present invention may be selected from the group consisting of potassium phosphate, potassium phosphate dibasic (K 2 HPO 4 ), potassium phosphate tribasic (K 3 PO 4 ), potassium phosphate monobasic (KH 2 PO 4 ) and phosphoric acid potassium salt (2:1) (KH 5 (PO 4 ) 2 ) and mixtures thereof. The preferred potassium phosphate compound being potassium phosphate dibasic (K 2 HPO 4 ). One advantage of using potassium phosphate compounds in the suspension compositions of the present invention is that the suspension compositions become essentially self-preserving without the need for additional preservatives, which are typically not approved PLONAR materials.  
         [0017]     The suspension composition of this invention comprise the following components: water, potassium phosphate compound, preferably dibasic potassium phosphate anhydrous about 10-40 wt. % preferably about 20-30 wt %, more preferably about 25 wt % of the fluid polymer suspension and a water soluble polymer, preferably water soluble polysaccharide, more preferably a cellulose ether, still more preferably HEC. The suspension composition of the invention may additionally comprise an effective amount of a stabilizer which functions to stabilize the fluid polymer suspension with long term stability and to prevent settling of the components. The effective amount of stabilizer may be up to about 2 wt %, preferably up to about 1 wt %, still more preferably up to about 0.5 wt % of the fluid polymer suspension. The stabilizer may be a low molecular weight (Mw) sodium carboxymethylcellulose (CMC) such as for example Blanose® 7L1 sodium carboxymethylcellulose, available from Hercules Incorporated. Alternatively the stabilizer may be a xanthan gum, such as Rhodopol® 23 standard grade xanthan gum available from Rhodia USA or a sodium alginate. Alternatively, combinations of CMC and xanthan gum may be used. CMC and xanthan gum are added to the fluid polymer suspension to provide a long-term stability.  
         [0018]     It was discovered that in addition to water soluble polysaccharides, synthetic polymers such as polyvinyl alcohol (PVA) could also be suspended in such a fluid polymer suspension. Depending upon the type of water soluble polymer, stable and flowable fluidized polymer suspensions containing about 5-50 wt %, preferably about 10-40 wt % more preferably about 20-25 wt % water soluble polymer of the fluid polymer suspension can be prepared.  
         [0019]     The examples are presented to illustrate the invention, parts and percentages being by weight, unless otherwise indicated.  
       EXAMPLES  
       [0020]     Typical fluid polymer suspension and related long-term stability are given in Tables 1 and 2. No polymer settling was noticed after 6 weeks storage at room temperature. The fluid polymer suspensions were additionally tested for freeze/thaw stability (three cycles). The fluid polymer suspensions remained stable and flowable.  
                                                           TABLE 1                           Detailed Suspensions Composition            Ingredients   Suspension 1   Suspension 2   Suspension 3   Suspension 4                    DI water   53.09%   49.71%   53.09%   52.95%       Rhodopol ® 23 xanthan gum,   0.11%   0.10%   0.11%   0.13%       available from Rhodia USA       Blanose ® 7L1C1sodium   0.27%   0.25%   0.27%   0.45%       carboxymethyl cellulose,       available from Hercules       Incorporated       KH 2 PO4, Anhydrous,   26.54%   24.85%   26.54%   —       KH 2 PO4, 3H 2 O   —   —   —   26.47%       Natrosol ® 180 GXR hydroxyethyl   20.00%   —   —   —       cellulose, available from       Hercules Incorporated       Natrosol ® 250 LR hydroxyethyl   —   25.09%   —   —       cellulose, available from       Hercules Incorporated       Natrosol ® HIVIS hydroxyethyl   —   —   20.00%   — %       cellulose, available from       Hercules Incorporated       Celvol ® 540S polyvinyl alcohol,   —   —   —   20.00%       available from Celanese       Chemicals                  
 
         [0021]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
               
               
                 Long-term viscosity stability 
               
             
          
           
               
                 Brookfield 
                 Suspension 1 
                 Suspension 2 
                 Suspension 3 
                 Suspension 4 
               
               
                 Viscosity @ 
                 cPs 
                 cPs 
                 cPs 
                 cPs 
               
               
                   
               
               
                 T 0   
                 1570 
                 1660 
                 2040 
                 805 
               
               
                 1-wk 
                 1600 
                 1690 
                 2120 
                 — 
               
               
                 2-wk 
                 1560 
                 1690 
                 2140 
                 — 
               
               
                 3-wk 
                 1620 
                 1690 
                 2120 
                 — 
               
               
                 6-wk 
                 1620 
                 1690 
                 2140 
                 — 
               
               
                   
               
             
          
         
       
     
         [0022]     The following examples illustrate the typical performance of this type of suspensions of the present invention in completion fluids and low temperature oil-well cement slurry compositions.  
         [0000]     Application in Completion Fluids  
         [0023]     The thickening efficiency of Suspension No. 3 (Natrosol® HIVIS HEC suspension) was evaluated against its precursor by dissolving 2.8 lb/bbl (0.8 wt. %) equivalent dry HEC in NaCl saturated brine. The NaCl saturated brine was first prepared by dissolving 360 g NaCl in 1000 ml Deionized water. Then, 2.8 g dry HEC or 14.0 g as-is Suspension No. 3 was added into 420 g NaCl saturated water while mixing on Hamilton beach mixer (˜11,500 rpm). To speed up the hydration of the polymer, 1-ml 10% NaOH solution was added into the polymer solution to raise the pH. To reduce/eliminate excess foaming, a few drops of defoamer, (Advantage® A96 defoamer, available from Hercules Incorporated), were added. The solution was mixed for an elapsed time of 90 minutes. Measurement of both Fann rheology as well as fluid loss properties was then performed after 16 hours static ageing in a water bath at 25° C.  
         [0024]     Data in Table 3 indicates that suspension No. 3 (Example 2) performs slightly better than its dry precursor (Comparative Example 1) when used at a same active dosage in NaCl saturated water. Both Fann apparent viscosity and yield point properties are higher while the filtrate loss is lower (better) with the suspension.  
                                                                               TABLE 3                           Rheology and Fluid Loss properties of NaCl Saturated Brine                    Comparative                   Example 1   Example 2               Polymer   Type   Natrosol ®   HEC suspension               HIVIS HEC           Descritpion   Powder   Suspension N o  3           Active content   100%   20.00%           Concentration   2.8 lb/bbl   14.0 lb/bbl            Test temperature, ° C.   24.5   24.7            Fann Rheology,   600 rpm   159.5   165.3       DR   300 rpm   126.3   132.0           200 rpm   108.2   114.1           100 rpm   81.5   88.3            60 rpm   64.7   71.8            30 rpm   45.7   51.6            6 rpm   16.5   20.6            3 rpm   9.9   12.5            Apparent Viscosity, cPs   79.75   82.65       Plastic Viscosity, cPs   33.2   33.3       Yield Point, lb/100 ft 2     93.1   98.7       30′ API Fluid Loss, ml   82.3   68.3       pH   11.86   9.7                  
 
         [0025]     It can be seen from Table 3 that the aqueous suspension of HEC, subject of this invention, is an effective viscosifier and fluid loss reducer of completion/workover fluids.  
         [0000]     Application in Oil-well Cement Slurries  
         [0026]     The following examples illustrate the performance of HEC aqueous Suspensions (No. 1 &amp; 2, respectively) in a low temperature oil-well cement slurry composition. The performance of the suspensions was compared against their corresponding dry precursors at equivalent active content.  
         [0027]     The oil-well cement slurries were formulated using additives and mixing/formulation techniques commonly employed in the industry as recommended by the American Petroleum Institute (API). All concentrations of additives in the slurry compositions (Examples 3-6) are based on weight of cement (bwoc).  
         [0028]     The oil-well cement slurry was prepared by adding the cement dry mixture into the mix-water, eventually, containing the fluid loss additive (FLAC). The dry mixture consists of 600 g Cemoil G cement, 3.3 g Naphthalene Sulfonate Condensate Na Salt dispersant (Lomar® D cement dispersant available from Cognis)(0.55 wt. % bwoc) and 2.7 g dry FLAC (0.45 wt % bwoc). Because of its lower Mw, Natrosol®250 LR HEC was used at higher dosage (4.8 g or 0.80% bwoc). For the comparative experiment with the FLAC suspensions (Suspensions No. 1 &amp; 2), the polymer suspension was added into the mix-water prior to adding the dry mixture. In all preparations, a few drops of defoamer (Advantage® A96 defoamer, available from Hercules Incorporated) were added to reduce excessive foaming of the cement slurry.  
         [0029]     The performance testing of the oil-well cement slurries were conducted in terms of rheology and fluid loss control properties at relatively low temperature. Typically, the “mixing rheology” was measured with Fann type viscometer just after the slurry preparation at room temperature approximately 27° C. (˜80° F.), to simulate the mixing and pumping at the surface, while the “API rheology” was measured after conditioning the slurry at 27° C.(80° F.) for 20 minutes. The fluid loss control properties were measured at 27° C. (80° F.) after the slurry conditioning.  
         [0030]     Data in Table 4 shows that FLAC suspensions provide excellent fluid loss control properties. The filtrate volumes are equivalent to the corresponding dry precursor. It is interesting to see that Suspension No. 2, even at higher dosage, provides lower rheology with outstanding fluid loss control properties than Suspension No. 1.  
                                                                                                                                                     TABLE 4                           Comparative rheology and fluid loss properties of cement slurries                Comp. Example 3   Example 4   Comp. Example 5   Example 6            Ingredients   g   bwoc   g   bwoc   g   bwoc   g   bwoc                    Cemoil G cement   600   —   600   —   600   —   600   —       LOMAR D cement dispersant   3.3   0.55%   3.3   0.55%   3.3   0.55%   3.3   0.55%       HEC (Natrosol ® 180 GXR)   2.7   0.45%   —   —   —   —   —   —       Suspension N o  1   —   —   13.5   2.25%   —   —   —   —       HEC (Natrosol ® 250 LR)   —   —   —   —   4.8   0.80%   —   —       Suspension N o  2   —   —   —   —   —   —   19.20   3.20%       Demi-water   264     44%   256.85     44%   264     44%   254.40     44%       Fann Type Rheology   Mixing   API   Mixing   API   Mixing   API   Mixing   API           Rheology   Rheology   Rheology   Rheology   Rheology   Rheology   Rheology   Rheology       Test Temperature   25.9° C.   26.2° C.   25.9° C.   26.3° C.   25.7° C.   26.2° C.   25.8° C.   26.1° C.       300-rpm DR   303   258   289   254   159   141   194   172       200-rpm DR   224   187   212   186   116   101   141   126       100-rpm DR   133   108   126   108   67   56   88   73        6-rpm DR   27   15   27   17   17   8   57   15        3-rpm DR   21   11   21   12   14   6   50   12       P.V. (1.5xFx(300 DR —100 DR), cPs   255   225   244.5   219   138   127.5   159   148.5       Yv (Fx300 DR —PV), lb/100 ft 2     48   33   44.5   35   21   13.5   35   23.5            Filtrate collected under 1000 psi   Static Fluid Loss Cell   Static Fluid Loss Cell            Test Temperature   27° C.   27° C.   27° C.   27° C.       30′ API Fluid Loss, cc   34.8   36.8   22.0   22.4                  
 
         [0031]     It can be seen from Table 4 that the FLAC suspensions (Suspensions No. 1 &amp; 2), subject of this invention, are effective fluid loss control additives of oil-well cement slurries.  
         [0032]     While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.