Note: Descriptions are shown in the official language in which they were submitted.
~0"6768
STARTING HYDROCARBON FLUID PRODUCTION BY
INJECTING NITROGEN-GENERATING LIQUID
The invention relates to treating a liquid-containing well
by passing a nitrogen gas-generating solution into the well to
cause a gas-effected displacement of liquid from the well. More
particularly, it relates to "kicking off" or initiating pro-
duction from a well which is "dead" due to hydrostatic pressureof the liquid it contains; without the necessity of swabbing the
well, or injecting nitrogen or other gas which has been com-
pressed at a surface location.
The process according to the invention for treating a well
communicating with a hydrocarbon fluid-containing formation from
which production is prevented by the hydrostatic pressure of
liquid contained within the well, comprises displacing sufficient
liquid from the well to reduce the hydrostatic pressure to less
than the reservoir fluid pressure by means of gas generated from
at least one aqueous liquid solution which forms or contains a
nitrogen gas-forming mixture of (a) at least one water-soluble
compound which contains at least one nitrogen atom to which at
least one hydrogen atom is attached and is capable of reacting
within an aqueous medium to yield nitrogen gas and by-products
which are substantially inert to the components of the well
and reservoir formation, (b) at least one oxidizing agent which
is capable of reacting with said nitrogen-containing compound
to form said gas and by-products, and (c) an aqueous liquid
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which is capable of dissolving or homogeneously dispersing said nitrogen-
containing compound, the oxidizing agent and the by-products of the nitrogen
gas-producing reaction.
In one embodiment of the invention the nitrogen gas-forming mixture
is injected into a production tubing string at a rate such that the gas is
formed within and accumulated at the top of the tubing string. The gas is
subsequently released to initiate the production of fluids from the well and
reservoir. In another embodiment of the invention, the composition of the
gas-forming mixture and its rate of injection can be adjusted so that at
least some of the gas is formed within the porés of the reservoir formation.
In still another embodiment, an aqueous solution or dispersion of a foam-
forming surfactant is injected, before, during of after the injection of the
nitrogen gas-forming mixture, so that a release of gas from the well induces
foaming and a foam-transporting of liquid out of the well.
Water-soluble amino nitrogen compounds, which contain at least one
nitrogen atom to which at least one hydrogen atom is attached and are capable
of reacting with an oxidizing agent to yield nitrogen gas within an aqueous
medium, which are suitable for use in the present invention can comprise sub-
stantially any water-soluble ammonium salts of organic or inorganic acids,
amines, amides and/or nitrogen-linked hydrocarbon-radical substituted homo-
logues of such compounds as long as the substituted compounds react in a man-
ner substantially equivalent to the parent compounds with respect to the
production of nitrogen gas and by-products which are liquid or dissolve to
form aqueous liquid which are substantially inert relative to the well con-
duits and reservoir formation. Examples of such compounds include ammonium
chloride, ammonium nitrate, ammonium acetate, ammonium formate, ethylene
diamine, formamide, acetamide, urea, benzyl urea, butyl urea, hydrazine,
phenylhydrazine, phenylhydrazine hydrochloride, and the like. Such ammonium
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salts, e.g., ammonium chloride, ammonium formate or ammonium acetate are
particularly suitable.
Oxidizing agents suitable for use in the present process can com-
prise substantially any water-soluble oxidizing agents capable of reacting
with a water-soluble nitrogen-containing compound such as an ammonium salt
or a urea or hydrazine compound as described above to produce nitrogen gas
and the indicated types of by-products. Examples of such oxidizing agents
include alkali metal hypochlorites (which can, of course, be formed by in-
jecting chlorine gas into a stream of alkaline liquid being injected into
the well), alkali metal or ammonium salts of nitrous acid, such as sodium or
potassium or ammonium nitrite and the like. The alkali metal or ammonium
nitrites are particularly suitable for use with nitrogen-containing compounds
such as the ammonium salts.
Aqueous liquids suitable for use in the present invention can com-
prise substantially any relatively soft fresh water or brine. Such aqueous
liquid solutions preferably have a total dissolved salt content of from about
1 to 100 ppm, and a total hardness in terms of calcium ion equivalents of no
more than about 50 ppm.
Foam-forming surfactants suitable for use in the present invention
can comprise substantially any which are capable of being dissolved or dis-
persed in an aqueous liquid solution containing the nitrogen-containing com-
pound and oxidizing agent and remaining substantially inert during the nit-
rogen gas-producing reaction between the nitrogen-containing compounds and
the oxidizing agent. Examples of suitable surfactants comprise non-ionic and
anionic surfactants, commercially available sodium dodecylbenzene sulphonates,
e.g., SIPONATE DS-10 (trade name), mixtures of the Siponate or similar sul-
phonate surfactants with sulphated polyoxyalkylated alcohol surfactants,
e.g., the NEODOL (trade name) sulphate surfactants; sulphonate sulphate
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surfactant mixtures; petroleum sulphonates; BRYTON (trade name) sulphonates;
PETRONATES and PYRO~ATES (trade names); fatty acid and tall oil acid soaps,
e.g., ACTYNOL HEADS (trade name); non-ionic surfactants, e.g., TRITON X100
(trade name), and the like surfactant materials which are soluble or dis-
persible in aqueous liquids.
To increase the viscosity of the aqueous solution to an extent
enhancing the effectiveness of the gas in the gas-lifting liquid of the
present process, water-thickening agents may be added to the liquid, such
agents comprising substantially any water-soluble polymer or gel capable of
dissolving in an aqueous liquid solution containing the nitrogen-containing
compound and oxidizing agent and remaining substantially inert during the
nitrogen gas-producing reaction between them.
Examples of suitable water-thickening agents include Xanthan gum
polymer solutions such as marketed under the trade names KELZAN or XANFLOOD;
hydroxyethyl cellulose, carboxymethyl cellulose, guar gum and the like
thickening agents. Such thickening agents are particularly effective within
a well conduit. They retard the rising velocity of gas bubbles so that more
liquid is removed by the rising gas, and thus such thickening agents are par-
ticularly effective in treatments in which most of the nitrogen gas is gen-
erated within the well.
The composition of the nitrogen gas-forming mixture should be cor-
related with the pressure, temperature and volume properties of the reservoir
and well components. In general, the rate of gas formation tends to increase
with increasing temperature and inceasing concentration of reactants. With
certain reactants the amount of gas production tends to be limited where the
pressure is particularly high. By means of calculations and/or tests, the
composition of the gas-forming mixture can be adjusted so that the volume of
the liquid which contains or forms that mixture need to be no more than about
1~196768
the volume of the tubing string plus the volume of the annular space between
the tubing string and the casing in order to generate an amount of gas that
will displace enough liquid to reduce the hydrostatic pressure to less than
the fluid pressure in the adjacent portion of the reservoir. Such a liquid
can be circulated within the borehole by flowing it into the tubing string
while flowing fluid out of the casing without injecting into the reservoir.
Alternatively, in certain situations, it is advantageous to cause
a significant amount of flow of gaseous fluid from the reservoir to the well.
In such situations the composition of the nitrogen gas-forming mixture can
be adjusted relative to the ambient temperature and the pressure and temper-
ature of the reservoir so that the rate of gas generation is slow enough to
allow a significant portion of the gas-forming mixture to be displaced into
the reservoir. The generation of gas within the reservoir tends to increase
the fluid pressure adjacent to the well and, when gas is released from the
well, to ensure a relatively large inflow of gaseous fluid into the well.
By way of example, reference is now made to a procedure for cor-
relating the composition of the nitrogen gas-forming mixture with the res-
ervoir properties and the selected duration of the treatment, wherein use is
made of an amino nitrogen compound which is a salt of ammonia and an oxidizing
agent which is an alkali metal or ammonium salt of nitrous acid as the gas-
generating reactants. Such composition has a slower reaction rate than, for
example, the composition comprising urea and hypochloride as reactants, and
thus can be used in place of the latter to provide (a) a slower reaction rate
at a given temperature and concentration or (b) a similar rate of reaction at
a higher temperature or concentration. Such reactants can also form relat-
ively concentrated solutions which minimize the amount of water that must be
injected to induce the gas generation in the selected location. In addition,
since their reaction rate increases with increasing pH, the nitrogen gas-
-- 5 --
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generating reaction rate of a solution of them can be buffered (a) at a
relatively high pH at which the rate is relatively slow at the reservoir
temperature by adding, for example, sodium acetate or other compatible buf-
fer providing a near neutral or slightly alkaline solution; or (b) at a rel-
atively low pH at which the rate is relatively fast at the reservoir tem-
perature by adding, for example, a mixture of acidic acid and sodium acetate
or other compatible buffer providing a slightly acidic solution.
In addition to being useful for initiating a sustained production
of fluids from a dead well, such as a gas well or an oil well, the present
process can also be used to displace a slug of treating liquid into a reser-
voir and then produce it back out of the reservoir without a need for employ-
ing swabbing equipment or gas which has been highly pressurized at a surface
location. Such a treatment could comprise, injecting one or more fluids such
as an oil solvent and/or acid, or scale-dissolving liquid with which it is
desired to wash the perforations and/or near well zone by injecting and sub-
sequently backflowing.
The injecting and subsequent backflowing of the treating liquid may
be conducted as follows. A sequence of one or more slugs of treating liquid
is arranged to precede a slug or volume of the present gas-generating liquid
which, if desired, may be followed by a slug or volume of inert aqueous
liquid. Then, the sequence of liquids is spotted within or near the bottom
of the well being treated; for example, by injecting the liquids sequentially
into the well through a tubing string (and/or an annulus around it) so that
the liquid already in the well is displaced into the reservoir and continuing
the injection until the frontal portion of the treatment liquid is at or near
the bottom of the well. Alternatively, the sequence can be such that the
liquids are sequentially included within a stream of fluid which is being
circulated into the well (through the annulus or tubing string) and terminat-
lQ9676~
ing the fluid cirulation when the frontal portion of the treating liquid isat or near the bottom of the well. The wellhead is then closed so that gas
generated by the gas-generating liquid accumulates above the liquid within
the well while it displaces the treating liquid into the reservoir. At
least a portion of the so-accumulated nitrogen gas is then released in order .
to initiate a back-flowing of the treating liquid from the reservoir into
the well.
As will be apparent to those skilled in the art, where the well
depth and/or tubing size is sufficient to accommodate a significant portion
of the nitrogen gas-forming mixture, the composition of such a mixture can
be adjusted so that a significant volume of pressurized gas will be formed.
The injecting and producing of the treating liquid slug can be repeated a
plurality of times, by closing the wellhead so that the accumulating gas
injects the treating liquid slug and releasing gas so that the treating
liquid flows back; and, then again closing the wellhead so that the dis-
placement of treating liquid slug into the reservoir is repeated.
In an alternative procedure for initiating a sustained flow of
production fluid from a well in which production has been prevented by the
hydrostatic pressure of liquid in the well, gas generated by the gas-gener-
ating mixture is allowed to collect in at least one of the upper ends of theproduction tubing or the annulus. In one embodiment, fluid is circulated
into the top of one well conduit and out the top of the other until a slug
of the gas-generating liquid is present within at least one of the conduits.
The top of the conduit containing the gas-generating liquid is then closed
while the top of the other is left open. As the gas is generated it ini-
tially accumulates above the liquid in the so-closed conduit while displac-
ing liquid down through the bottom of that conduit and out through the open
top of the other conduit. Where the vo ume of the so-generated gas is suf-
~L0~768
ficient and/or where the gas-generating liquid is injected within both of
the conduits, at least some portions of the liquid are displaced by a gas-
lifting type action of the generated gas. While the gas-generating liquid
is present within both of such conduits the tops of both may be left open.
In another alternative procedure for initiating a fluid flow from
a well (such as a flow of hydrocarbon gas, or a flow of hydrocarbon liquids,
or a flow of hydrocarbon liquids and gas), a composition of a gas-generating
liquid is correlated with the temperature and injectivity properties of the
reservoir and injected into the reservoir in a manner such that a significant
proportion of the gas is generated within the reservoir formation. Where
desirable, a pair of well conduits such as a tubing string and the annulus
between it and a surrounding pipe string can be utilized to relatively
rapidly circulate a slug of the treatment liquid to the bottom of the well
and then displace that liquid into the reservoir formation in a way which
reduces the overall time for which the gas-generating liquid is exposed to
the reservoir temperature before it has entered the reservoir formation. A
particularly suitable gas-generating liquid for use in such a procedure is
one in which the nitrogen-containing reactant is an ammonium salt and oxidiz-
ing reactant is an alkali metal or ammonium nitrite.
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