Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
This invention relates to a process for producing a solid
foaming agent body and to a process of using said body for the removal
of water from a gas well borehole by foam generation.
When a gas well is flooded, a column of water forms in the
borehole which reduces the flow of the gas from the well. Several
methods exist to remove the water from the borehole. For example, the
water may be pu~ped to the surfacei however, this is both time and
energy consuming. Liqu;d foaming agents are available which may be pumped
to the bottom of the column of water to attain efficient foam generation,
but they involve the expense of servicing the well. A preferred
alternative is to drop a solid foaming agent down the borehole. As the
solid dissolves, gas from the producing zone passing through the column
of water generates foam which allows the water to be blown out of the well.
In principle, any water soluable surface active agent with
foaming capabilities could be used to remove water from boreholes by
foam generation. However, when it is desirable to use a solid foaming
agent, cèrtain classes of surfactants are preferred. In particular,
some members of the class of polyethyoxylated nonionic surfactants,
being hard waxes at ambient temperatures, can be readily melted and cast
into molds for use as solid foaming agents. Inorganic salts may be
added to increase the bulk density of such compositions. An example of
thi`s type of foami`ng agent is disclosed in U~ S. Patent No. 3,251,~17
to Holman et al.
These solid foaming agents are usually molded into long cylin-
drical sticks approximately 3 cm in diameter and 30 to 50 cm in length.
During warm weather these products tend to become soft and waxy and are
difficwlt to drop down the well borehole.
A more serious problem of these prior art compositions is
their low rate of solubility. ~n order to generate foam in a reasonably
short period of time an excessive quantity of the solid foaming agent
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is added to the well. Even in large amounts, these foaming agents often -take
in the order of 3 to ~ hours to expel water from the well. After most
of the water has blown out of the well, the foaming agent continues to
slowly dissolve in the residual water. The foam thus genenated becomes
;ncorporated in the gas production, which is undesirable.
It is known in the field of surfactant chemistry to combine
liqu1d surfactants or detergents with urea to form solid urea adducts.
The adducts decompose in water to release urea and the uncomplexed sur-
factant. It has generally been found that urea adducts can be formed
lO with many straight chained hydrocarbons, fatty acids and alcohols,
whereas highly branched hydrocarbons remain substantially uncombined with
urea. Urea forms a helical structure in which the surfactant is trapped
or held. Apparently strai'ght chai'n hydrocarbons, or those with a low
degree of branching or ri'`ng formation can more easily fit into the
15 helical structure and thus form the urea adducts.
To our knowledge no one has yet attempted to utilize these
urea adducts in the removal of water from well boreholes~
''SUMMARY OF THE INVENTION
The present ;'nvent;on provides a process for removing water
from a gas well and involves util;`zing a solid foaming agent formed
by combining a water-soluable surfactant with urea to obtain a solid urea
adduct. The solid adduct is dropped into the column of water ;n the well.
The urea rapidly~dissolves, releasing the surfactant which acts to foam
the watèr,as gas ;`s produced through the columnO The gas flow gradually
removes the foam from the ~ell.'
In a preferred form of the inventi'on, the sol;d foam;ng agent
;5 provided by first mix;ng urea with a water-soluable non-ionic
polyethoxylated' surfactant to form the adduct and then compressing the
adduct under h~;gh pressure ;nto a shape of sufficient size and density
to enable ;t to drop through the well bore to the bottom of the water
column. By this size and densi`ty crite~ia i5 meant that the foami'ng
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agent is in a form which fits into the gas borehole, and has a density
suff;ciently greater than water to permit it to drop through the flooded
borehole.
In a more preFerred form, the urea is combined with the
surfactant in a ratio in the range of about 1:1 to 9:1 by weight
respectively.
In another preferred feature of the invention, a lubricant
is added to the urea adduct to assist in the compression operation. A
polyethylene glycol having a molecular weight of about 400 to 6000 is
satisfactory for this purpose~
DESCRIPTION OF THE PREFERREn EMBODI~ENT
The surfactant used in the formati`on of the solid foaming
agent i:s a non-ioni`c water-saluble polyethyoxylated compound having the
general formula
R - (:OCH2CH2)nOH
where R is a lipophilic group and n is a whole number.
Three factors generally restrict the type of surfactant which
can be used. The surfactant must have a structure whi:ch enables it to form
a solid adduct ~;th urea, and must also be sufficiently water soluble20 to give the desirable rapi:d foami:ng acti.on. Further, the rate of water
solubility should be suffici:ently fast to gi:ve a rapi:d foaming capabili.ty
to the foaming agent.
The lower value of n is limi:ted to that value which will confer
water solubility to the lipophilic m~iety. For this purpose n must usually
25 be at least 6. I:ncreasing the value of n, i:n general, allows the
phys;cal form of the non-ionic surfactant to vary from a li.quid (n= 9 to 14),
to a semi-solid (:n - 12 to 14), -to a hard wax (n = 20 to 150). These
ranges vary wi:th the particular lipophili:c groupO
Suitable li:pophi:li:c groups i:nclude mono or dialkyl phenols,
30 fatty carboxylic acids, and fatty alcohol residues.
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The urea used in the process of the present invention isusually provided in the form of granules or pellets which are crushed
to a fine powder prior to mixing with the surfactant. This step has
been found to greatly influence the efficiency of adduct formations; in
general, the finer the particle size of the urea the more rapid and
complete the adduct formation.
The urea is combined with the surfactant in a ratio in the
range of about 9:1 to 1:1 by weight respectively~ This range is not
critical to the product formed, however, it is found to be a practical
working range. With greater amounts of surfactants, the product formed
tends to be waxy, slower to solidify, and slower dissolving in water~ while
with lower amounts of surfactant, the urea is merely diluting the surfactant
beyond practical limits. The most desirable compositions, that is those
which solidify within a few days to form a urea adduct that is water
soluble, result from using a urea to surfactant ratio of about 9:1 to 3:1
by weight respectively.
A urea-surfactant mixture derived from a liquid or semi-solid
surfactant initially appears as a moist composition which solidifies
- gradually as the urea adduct is formed to take on a dry appearance. This
provides a simple visual assurance of complete adduct formation. The
solid surfactants, on the other hand, are melted prior to combining with
the urea. As the latter compositions solidify it is more difficult to
ascertain whether, in fact, a urea adduct has formed, or the solid surfac-
tant has merely resalidified unreacted.
- 25 To increase the lubricity of the urea-surfactant adduct
during the compression step, a lubricant can be used. Incorporating with
the adduct about 1 - 30% by ~eïght of a polyethylene glycol with an aver-
age molecular weight between ~00 and 60QO has been found to facilitate in
the compression of many of the drier compositions. These drier forms
of the adduct result from using large amounts of the urea. Often, when
lower amounts of urea are included in the adduct, the surfactant itself
acts as a lubricant for the compres~ion. Other lubricants familiar to
the art of tablet-pressing may be suitable.
The foaming agent is prepared by adding the liquid surfactant
slowly with thorough mixing to the powdered urea, and lubricant if re-
quired. If a solid or semi-solid surfactant is being used it is melted
and added to the mixed urea-lubricant mixture. The resulting moist
composition is allowed to s-olidify For 24 to 48 hours to form a dry,
solid urea adduct. Often the adduct exists in hard clumps which are
crushed in a suitable grinder. The adduct is then compressed at
high pressures into a shape of size and density sufficient to enable
it to be dropped to the bottom of a column oF water existing in a
well borehole. Typically, the adduct is pressed into a cylindrical
stick about 1.25" in diameter and 4.5" in length having a weight of about
4 ouncès.
The size and shape of the compressed foaming agent are re-
stricted by the physical limitations of the well borehole. Usually thereis a 2 in. valve at the well head through which the compressed product must
pass. The density of the foaming agent, once compressed, must be suf-
ficiently greater than water to enable the product to drop through the
- flooded borehole. Typically a density greater than 102 g/cm is suf-
ficient for this purpose.
The compressed foaming agent when dropped into a flooded gas
borehole, dissolves to lower the surface tension of the water. The
reduced gas flow through th;s water causes foam generation, which foam is
blown out of the well. If the flow oF gas in the gas well has been stopped
by large quantities of water, an external source of compressed air is
required to generate the foam.
The quantity of foaming agent required to remove the water
necessarily vary with the depth,pressure and amount of water in the parti-
cular well.
The 1ollowing example is illustrative of the present invention.
EXAMPLE 1
A urea adduct was formed by combining in the following
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weighted am~unts:
20% polyethoxylated C12 - C15 linear alcohol containing 69%
ethylene oxide, or 20% polye-thoxylated C1O - C12 linear
alcohol containing 60% ethyleneoxide;
75~ powdered ureai and
5% polyethylene glycol of molecular weight 4000.
The powdered urea and the polyèthylene glycol 4000 were
intimately mixed. The polyethoxylated compound was melted at 35C
and added over 15 min. with m;xing to the urea-lubricant mixture.
After 3Q minutes of m;xing, the free flowing granular composition was
run out and stored 24 to 48 hours to form a dry, granular urea adduct.
The adduct was compressed to 6000 psig into 4 ounce, 1.25
in. x 4 in. cylindrical sticks with the use of a hydraulic press. The
product thus formed had a density of about 1.25 g/cm3.
The foaming agent thus formed was tested in a number of
shallow gas wells having relatively low pressures and located in the
Med;cine Hat and Milk River areas of Southern Alberta. The wells had an
average depth of about 150Q to 3Q00 feet and a ~ottom hole pressure of
about 400 to 50Q psi.
- 20 With the variation in depth, pressure and amount of water to
be displaced in the wells, varying quantities of the foaming agent were
used. Usually 1 to 4 sticks were dropped into the well and water unloading
occurred within 7 to 25 minutes.
FEATURES AND ADVANTAGES
The following features and advantages are achieved by the
preferred embodiment of the present invention.
(1) Ihe solub;lity rate in ~ater of the polyethoxylated non-
ionic surfactant is improved due to the dispersed and
finely divided state which is achieved in ~he urea
adducts. This ult;~mately increases the speed at which
foam can be generated in the water flo~ded well.
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(2) Solidification of the surfactants with urea improves
the temperature stability of the solid foaming agents.
Whereas many of -the prior art foaming agents were subject
to melting at ambient temperatures.
(3) A large range of suitable surfactants can be utilized since
both liquid and solid surfactants will form solid urea
adducts.
(4) The density of the solid ~oaming agent is increased with
the use of urea. Urea has a density of 1.34 g/cm3 so,
when combined with the surfactant,results in a product
which can be compressed to a density sufficient to enable
it to drop through the water flooded borehole.
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