Abstract:
Compounds of the formula H(CH 2 ) Z COO—[C 2 H 4 O] X C Y H 2Y+1  where z is 0-2, x is an integer from 1 to 5 and y is an integer from 4-9 are used as emulsion breakers and defoamers in formation treatment fluids in the recovery of hydrocarbons from subterranean formations. A preferred material has the formula HCOO—[C 2 H 4 O] 3 C 6 H 7 .

Description:
RELATED APPLICATION  
       [0001]    This application claims the full benefit of provisional application No. 60/313,606 filed Aug. 20, 2001. 
     
    
     
       TECHNICAL FIELD  
         [0002]    Alkyl ether organic acid esters are included in drilling and other formation treatment fluids used in hydrocarbon production to provide a demulsifying and defoaming action on foams and emulsions in the producing formation. The action of the compositions is time and temperature dependent and therefore their action can be controlled in situ.  
         BACKGROUND OF THE INVENTION  
         [0003]    In the production of hydrocarbons from the earth, drilling fluids and formation fracturing fluids are well known and come in many varieties. Where surfactants are included with the fluids, foaming is likely to occur, and frequently surfactants are added to generate foam to assist in removing the particulate products of drilling, or for other purposes. Emulsions may be added deliberately, but also they may be generated due to the pressure and mixing of the fluids with the target hydrocarbons. In most cases it is not desirable for emulsions to be formed in the formation with the hydrocarbons to be produced, since the emulsion will have to be broken after recovery in a separate, time-consuming step. Whether the emulsions are deliberately added or formed in situ, they may migrate under pressure into the pores of the subterranean formation, where they tend to seal the hydrocarbons which are the object of the production process.  
           [0004]    A well-controlled method of breaking foams and emulsions in the formation is needed to produce hydrocarbons more efficiently.  
         SUMMARY OF THE INVENTION  
         [0005]    We have developed compositions and methods for breaking both emulsions and foams in a subterranean hydrocarbon-bearing formation or a wellbore penetrating such a formation. The method comprises including with a drilling fluid or fracturing fluid (that is, a well treatment fluid) an alkyl ether organic ester of the formula H(CH 2 ) Z COO—[C 2 H 4 O] X C Y H 2Y+1  where z is 0-2, x is 1-5 and y is 4-9, preferably where z is 0-1, x is 2-4, and y is 5-7, and most preferably where z is 0, x is 3, and y is 6—that is, most preferably where the compound is an alkyl ether formate of the formula HCOO—[C 2 H 4 O] 3 C 6 H 7 . The formation should have a temperature of at least 100° F. At temperatures of 100 degrees F. or over, the alkyl ether organic acid ester will hydrolyze to the organic acid and the ethoxylated alkyl alcohol, and act to reduce the foaming tendencies of the surfactants, at least partially by reducing the pH. It will also tend to break emulsions present through the action of the alcohol group on the etherified alkyl. Alternatively, the alkyl ether organic acid ester may be injected into the formation after the fracturing fluid. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0006]    Compounds of the formula H(CH 2 ) Z COO—[C 2 H 4 O] X C Y H 2Y+1  where z is 0-2, x is 1-5 and y is 4-9 are believed to be novel compounds. They may be made by the simple esterification reaction of the corresponding hydroxy ethoxylated alkyl and organic acid. For example, the preferred compound HCOO—[C 2 H 4 O] 3 C 6 H 7  may be made by the reaction of formic acid with C 6 H 7 OCH 2 CH 2 OCH 2 CH 2 OCH 2 CH 2 OH. Preferably the reactants are heated and a slight excess of formic acid is used.  
         [0007]    Our compositions and methods are not only effective for defoaming and demulsifying, but the dissociation products (particularly the ethoxylated alkyl alcohol) are more environmentally acceptable than a simple alcohol demulsifier. As a general rule, the demulsifying action is accelerated in time as Y is reduced in value in the above formula, but this tends to result in a product that may not be as environmentally benign as the larger alkyl groups. As the number of carbons is increased in the alkyl group (Y), the product becomes less soluble in water, adversely affecting the defoaming action. When we use the term “alkyl ether organic acid ester compound,” and/or where we use the term “C6,” it should be understood that we may substitute saturated and unsaturated (i.e. phenyl) cyclic moieties.  
         [0008]    The following description of laboratory tests will illustrate the invention. For comparison, an emulsion was made utilizing 10% oil, 89% fresh water, and 1% of a commercial foamer/emulsifier comprising an amine oxide and an anionic surfactant. This was treated with a proposed emulsion breaker comprising octyl formate that is, a compound of the formula HCOOC 8 H 9 , in concentrations ranging, in increments of 0.25% by weight, from 0.25% to 1% and at temperatures ranging, in increments of 25° F., from 100° F. to 200° F. Each sample was observed at 1,2,3,4,5 and 24 hours. A conclusion was drawn that the proposed breaker was generally ineffective at lower temperatures, lower concentrations and shorter times, and only moderately effective at the higher temperatures, higher concentrations and longer times. A similar series of tests was performed for the preferred breaker of the invention, having the formula HCOO—[C 2 H 4 O] 3 C 6 H 7 . At 100, 125, 150, 175 and 200° F., the emulsion broke on contact for the 0.50%, 0.75% and 1.0% solutions of breaker. The 0.25% breaker solution was effective but somewhat less efficient.  
         [0009]    Also as a general rule, our alkyl ether organic acid ester compounds are effective when used in about a 1:1 molar ratio to the surfactants present in the fracturing or other well treatment fluid either as foaming or emulsifying agents. However, our alkyl ether organic acid ester compounds may be used in very small amounts, i.e. 1% of the content of the foaming agent, emulsifier, or surfactant in the formation fluid; they may be expected to be effective roughly to a corresponding degree. Amounts or concentrations of our material in excess of molar 1:1 may also be used, to very high multiples, but results will not be commensurate with the increased concentrations. We prefer not to use more than about three times the amount of surfactant, foaming agent, or emulsifier in the drilling or other well treatment fluid. A preferred amount of our novel well treatment compound will be in a molar ratio to surfactant in the formation fluid of 2:1 to 1:2. Likewise, it should be understood that our invention may be effective at formation temperatures lower than 100 degrees Fahrenheit, at a correspondingly retarded rate and effectiveness. The process is not recommended at temperatures below 90° F. for any variation of our composition. Temperatures may be considerably higher than 100° F., however. We are not aware of a subterranean temperature above which our compositions will be ineffective for the purposes described.  
         [0010]    Our invention is especially useful where the hydrocarbons to be removed from the subterranean formation contain more than about 0.01% by weight paraffins or waxes containing more than 19 carbon atoms, particularly in the lower temperature ranges.