Process comprising a reversible forming composition

Details Process comprising a reversible forming composition Process comprising a reversible forming composition

1999-12-20

2001-09-11

Suchfield, George (Department: 3672)

Wells

Processes

Producing foam or gas in well by foaming or gas producing...

C166S312000, C175S069000, C507S102000, C507S120000, C507S203000, C507S225000, C507S925000

Reexamination Certificate

active

06286601

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a process and to a system for implementing the process in underground development wells for drilling, cleaning or bringing in of these wells in the case of a producing reservoir. In the process, a foaming fluid is circulated between the ground surface, the well bottom and back to the surface from a string of pipes lowered in the well. The foam is generally injected inside the pipes and returns through the annular space defined by the outside of the pipes and the well walls. The fluid in form of foam carries the cuttings along to the surface, thus cleaning the working face. This technique, referred to as foam drilling, is well-known and notably affords the advantage of not leading to too high a bottomhole hydrostatic pressure thanks to the low density of the foam. However, the drawback of this technique is that it does not allow easy recycling of the foaming solution, considering the products initially brought into solution to stabilize the foam after stirring and gas injection. “Breaking” of the foam is thus a troublesome problem for an application where it is desired to recover most of the foaming products for repeated use, or if the environmental conditions do not allow spreading of the volume of foam back from the well.
BACKGROUND OF THE INVENTION
Document WO-94/17,154 describes using an amphoteric foaming agent combined with other surfactants as a base for a stable foaming composition. The foam is broken by suitable variation of the pH value of the foam If the foam is basic, the foam is broken by lowering the pH value to at least below 4, if the foam is acidic, the foam is broken by raising the pH value to at least above 9.5.
SUMMARY OF THE INVENTION
The present invention relates to a foam drilling process using a foaming solution consisting of a combination of at least one surfactant, cationic or anionic, used as the foaming agent, whose charge hardly depends on the pH value and of a polyampholytic polymer whose global charge depends on the pH value. The polymer according to the invention has no foaming property. For a determined pH value of the present foaming solution, the foaming function thereof is optimized by adjusting the respective quantities of ampholytic polymer and of surfactant (anionic or cationic according to the sign of the charges of the polymer under these determined pH conditions), by taking into account the respective charges of the polymer and of the surfactant. Changing the pH value of the foam thus modifies the charges of the ampholytic polymer. As a result, the interactions of the charges between the polymer and the surfactant are modified so that the foam can be destabilized and possibly even broken. It is thus possible to envisage re-using the foaming composition for a new injection.
The process and the composition according to the invention can be advantageously applied to oil well drilling, servicing or completion operations requiring a well fluid having a density below 1, such as a foam.
The polyampholytic polymers of the process or of the foaming composition according to the present invention are preferably selected from the group consisting of:
a) the polymers having the following general formula (I):
 where A denotes a group resulting from copolymerization of an ethylene-unsaturated monomer and carrying an anionic group —COO
−
,
X
+
is a cation resulting from neutralization of the anionic groups —COO
−
by an inorganic or organic base,
B is a group resulting from copolymerization of at least one hydrophilic ethylene-unsaturated monomer, preferably acrylamide,
C is a group resulting from copolymerization of an ethylene-unsaturated monomer and carrying a cationic group E
+
such that
 wherein R1, R2 and R3, identical or different, are hydrogen, a C1-C22 alkyl group, linear, branched or cyclic (cycloaliphatic or aromatic),
Y denotes an anion resulting from neutralization of groups E by an inorganic or organic acid or from quaternization of groups E,
x1, x2 and y respectively denote the percentages by moles for groups A, B and C, with x1 greater than or equal to x2, and x1+x2+y=1;
b) the betainic polymers having the following formula:
 wherein R4, R6 and R7, identical or different, denote hydrogen or a C1-C4 alkyl, linear or branched,
F denotes NH or O or forms, with group R5, a C5-C7 aromatic or non-aromatic cycle or heterocycle,
R5 and R8 denote, independently of each other, a divalent hydrocarbon group, in particular a group —(CH2)n— with n an integer ranging from 1 to 4,
R5 can form a C5-C7 heterocycle with R6 and R7,
B is a group resulting from copolymerization of at least one hydrophilic ethylene-unsaturated monomer, preferably acrylamide,
z and t are the percentages by moles of the groups, such that z+t=1,
p is 0 or 1 and q is 1.
In the general formula (I) defined above, the monomers leading after copolymerization to units having the following structure:
are selected from the salts of carboxylic acids, linear, branched or cyclic (cycloaliphatic or aromatic), such as crotonic acid, acrylic acid, metacrylic acid, vinylbenzoic acid salts; carboxylic diacid salts such as maleic, fumaric or itaconic acid salts, as well as their monoesters and monoacids,
the counterion X
+
associated with COO
−
generally results from neutralization of the group. COO
−
by an inorganic base such as NaOH or KOH or an organic base such as an amine or an aminoalcohol.
In general formula (I), the monomers leading to the structural units —B— are selected from the hydrophilic ethylene-unsaturated monomers and are so selected that the final polymer is water-soluble.
In general formula (I), the monomers leading to units having the following structure:
are preferably selected from acrylic, vinylic, allylic or diallylic type monomers comprising a tertiary amine function quaternized by an alkyl halide or a dialkyl sulfate.
Examples thereof are:
dimethylaminoethylacrylate,
diethylaiminoethylacrylate,
dimethylaminopropylacrylate,
dimethylaminopropylacrylamide,
2-vinylpyridine,
4-vinylpyridine,
dimethylallylamine,
quaternized by an alkyl halide or a dialkyl sulfate.
The polyampholytes of formula (I) preferably used are selected from sodium acrylate, acrylamide and acryloxyethyltrimethylamnnonium copolymers.
The molecular weights of the polyampholytes according to the invention can range from 5000 to 10,000,000 and they preferably range between 100,000 and 2,000,000.
All the conventional anionic surfactants can be used in the present invention as surfactants combined with the polyampholytic polymer, such as the anionic function, i.e.:
sulfonates:
alkylbenzene sulfonates,
paraffin sulfonates,
&agr;-olefin sulfonates,
petroleum sulfonates,
lignosulfonates,
sulfosuccinic derivatives,
polynaphtylmethane sulfonates,
alkyltaurides,
sulfates:
alkylsulfates,
alkylethersulfates,
phosphates:
monoalkyl phosphates,
dialkyl phosphates,
phosphonates.
Examples of cationic surfactants are:
quaternary ammonium salts, whose nitrogen:
comprises a fatty chain, for example alkyltrimethyl or triethyl ammonium derivatives, alkyldimethyl benzylammonium derivatives,
comprises two fatty chains,
belongs to a heterocycle, for example pyridinium, imidazolinium, quinolinium, piperidinium, morpholinium derivatives.


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