Note: Descriptions are shown in the official language in which they were submitted.
CA 02279876 1999-07-29
OIL PRODUCTION METHOD
The invention is referred to oil production, in particular to methods of oil
production
from heterogeneous reservoirs with conformance control to level out
injectivity profile of
injection wells and decrease water inflow of production wells. The method
includes
simultaneous or consequent injection of solutions of two or more gel or
sediment forming
agents.
The essence of the invention: avoidance of premature chemical reaction and
adsorption of
agents in the process of injecting their water solutions into the reservoir
and raising the
efficiency of blocking water flushed intervals and reservoir fractures due to
forming
viscous elastic gel directly in such areas with the use of polyacrylamide
(PAA) water
solutions and salts of polyvalence ration or forming a stable non soluble
sediment when
injecting water solutions of salts of polybasic acid such as sodium silicate
and alkaline-
earth metal, such as calcium chloride. The method is applied through injection
of water
solution of two or more gel or sediment forming agents into the reservoir as
an aggregate
stable water-in-oil emulsion in low viscosity hydrocarbon solvent (benzene,
kerosene
etc). 5-20% of mass of porphirine and asphaltene-resin oil components are
dissolved in
the hydrocarbon solvent prior to that. For every applied water agent solution
first 50%
(volume) of aggregate stable water-in-oil emulsion is prepared separately with
the size of
particles (globules of emulsified water agent solution) comparable to the size
of pores of
high permeability sections of the reservoir. Then previously prepared
emulsions of gel or
sediment forming agents are blended in equal volumes prior to injection. After
injection
of a blended emulsion for its destruction and foaming a water blocking barrier
in the high
permeability sections of the reservoir a hydrocarbon solution of demulsifier
of a water-in-
oil emulsion is injected into the reservoir in a form of viscous elastic gel
(or non-soluble
sediment) in the amount sufficient for destruction of injected volume of the
aggregate
stable water-in-oil emulsion
There exist oil production blocking methods through leveling out injectivity
profile of a
heterogeneous reservoir. They involve simultaneous or consequent injection of
a water
PAA solution with a cross linking agent (water solution of a polyvalence
ration salt) into
the reservoir where to decrease polymer volume and control velocity of the
chemical
reaction of gel forming (linking) a pH of water PAA solution and the linking
agent is kept
at the level of 3-4 after blending and after injection it reaches 7-10 (a.c.
SU 1128573 A, C
08 L33/26 and C 08 K 3/24, E 21 B 43/22 and SU 1627678 Al, E21 B./43, 33/138).
However these methods do not prevent a change in the concentration of injected
agents in
reservoir conditions and have a limited application due to complications in
reaching the
pH of 7-10 of injected water solutions in the reservoir. Besides, using an
inorganic acid to
control the time of linking does not prevent chemical destruction of the PAA
molecules
and in general is not applicable to control velocity of the chemical reaction
of residue
forming agents.
In the oil production method (Patent RU 2086757 C1, 6E 21 B 43/22) to control
the time
of gel forming (linking) and decrease mechanical and chemical (salt)
destruction of the
CA 02279876 1999-07-29
PAA water solutions of PAA and cross linking agent (aluminum salt) are
consequently
injected into the reservoir and fresh water is injected between them. With
this method
there is a possibility that water PAA solution, fresh water and water based
cross linking
agent being low viscosity systems will flow into both high and low
permeability sections
of the reservoir. This in its turn will inevitably result in unnecessary high
volumes of
applied agents. Besides, this method is not ei~ective at consequent injection
of water
based salt forming agents into the reservoir due to a sharp decrease in the
velocity of the
chemical reaction when these solutions are diluted with fresh water.
The closest to the proposed method in its technical essence is the method of
injecting
solution of polybasic acid salt emulsified in hydrocarbon fluid (for example,
sodium
silicate, sodium phosphate or sodium carbonate) into the reservoir (Patent RU
2101486 C
1, 6 E21 B 43/22). As a compound containing alkaline-earth metal salt a water
solution of
an alkaline-earth metal is used (for example, calcium chloride, magnesium
chloride or
barium chloride) or its emulsion in a hydrocarbon fluid (for example, in oil,
diesel fuel,
kerosene). As an emulsion stabilizer low soluble surfactants are used:
Emultal,
Neftechim, Neftenol, Neonol, AF9-4, AF9-6, OP-4, sodium salts of SZHK
(Translator's
note: unclear abbreviation) etc.
The major disadvantage of this method selected as a prototype of the invention
is low
aggregate stability of water-in-oil emulsions stabilized by the aforementioned
low soluble
surfactants which leads to their destruction (water phase separation) at a
short depth of
penetration (filtration) of the water-in-oil emulsion into the reservoir. This
circumstance
shows that it is impossible to ei~ectively apply this method at blending and
simultaneous
injection into the reservoir of two or more water solutions of sediment
forming agents as
a water-in-oil emulsion as the chance of emulsion separation and forming non
soluble
sediment in the near well bore area is high. Therefore this method can only be
applied
through consequent injection of water solution of a salt of polybasic acid
emulsified in
hydrocarbon fluid in the presence of a low soluble surfactant and then water
solution
containing a alkaline-earth metal salt or an emulsion of this solution in a
hydrocarbon
solvent, also in the presence of a low soluble surfactant.
The method is applied as follows. An estimated volume of aggregate stable (50%
of
volume) water-in-oil emulsions in low viscosity hydrocarbon solvent (for
example,
kerosene containing prior dissolved 5-20% (mass) of asphaltene-resin and
porphirin
(ARP) compounds - natural stabilizers of water-in-oil emulsions) is prepared
for each of
the used water solutions of gel or sediment forming agents. This is performed
at the well
selected for blocking methods taking into view geophysical and physical
parameters of
the reservoir and current development parameters. The intensity and time of
blending for
each of applied water solutions of agents with specified concentration and
hydrocarbon
solvent containing specified amount of natural stabilizers of the water-in-oil
emulsion
should be such that finally for applied water solution of gel or sediment
forming agent a
thinly dispersed (the dimensions of water globules should be comparable to the
dimensions of flushed highly permeable sections of the reservoir) aggregate
stable (not
coalescenting while settling and being treated in a centrifugal filed) water-
in-oil emulsion
CA 02279876 1999-07-29
would result. These properties of formed water-in-oil emulsions are easily
controlled in
practice with the use of a common microscope and vile centrifuge with 6,000
RPMs.
Prior to injecting water-in-oil emulsions of two or more gel or sediment
forming agents
into the reservoir for each selected composition water-in-oil emulsions are
blended in
equal volumes, i.e. in each instance both with gel forming and sediment
forming
compositions water blends of the aforementioned agents are injected into the
reservoir as
a thinly dispersed aggregate stable water-in-oil emulsion in low viscosity
hydrocarbon
solvent. The drops (globules) of this or that injected agent water solution
are isolated
from one another by a strong armored film of natural stabilizers which do not
only
prevent early chemical reaction between injected compounds but also prevent
adsorption
of injected agents on active hard areas of the reservoir which allows to
drastically
decrease volumes of applied compounds and reach expected results. Aggregate
stable
blend of water-in-oil emulsions are injected in volumes sufficient to form
highly viscous
emulsion "plugs" in flushed and permeable sections which in reality is traced
through the
change (excess) of injection pressure of the injected into the reservoir
system. Then a
specified volume of hydrocarbon (mainly in an aromatic solvent) solution of a
demulsifier is injected into the well in the amount sufficient to destroy
injected aggregate
stable water-in-oil emulsion. The well is then allowed 12-36 hours for a
reaction. Within
this time a destruction (coalescence) of injected into the reservoir water-in-
oil emulsion
and blending of formed water solutions of gel or sediment forming agents takes
places as
well as their chemical reaction the result of which is forming water blocking
barriers in
flushed and highly permeable sections. The barriers are made of highly viscous
cross-
linking polymer compositions (CLPC) or sediment that is strong and not
destructed by
water.
The objective of the proposed method is to raise the efficiency of oil
production due to
avoiding premature chemical reaction and adsorption of two or more applied gel
or
sediment forming agents in the process of simultaneous injection of their
water solutions
into the reservoir.
The objective is achieved though the fact that in the proposed method of oil
production
water solutions of applied agents are injected into the reservoir as an
aggregate stable
water-in-oil emulsion in a low viscosity hydrocarbon solvent (benzene,
kerosene etc.) in
which 5-20% (mass) of porphirin and asphaltene-resin oil components are
dissolved prior
to it, porphirin and asphaltene-resin oil components being the major most
capable natural
stabilizers of water-in-oil emulsions ("Stabilization and Destruction of Oil
Emulsions" by
G.N. Pozdnyshev, M. "Nedra", 1982, page 221 ).
Another distinction of the proposed method is that for each water agent a 50%
(volume)
aggregate stable water-in-oil emulsion is prepared separately prior to
injection with the
dimensions of the particles (globules of emulsified agent solution) comparable
to the
dimensions of flushed highly permeable reservoir sections and later prior to
injection
aggregate stable emulsions of gel or sediment forming agents are blended in
equal
volumes. At the time of injection of such a blend of aggregate stable
emulsions i.e.
emulsions which are not destroyed while filtering through the porous reservoir
rock, the
CA 02279876 1999-07-29
4
emulsion is concentrated (packed) in the most permeable and fracture sections
of the
reservoir up to formation of highly viscous emulsion "plugs' containing 90-95%
(volume) of blended globules of water solutions of gel or sediment forming
agents. Thus
without free water phase separation (separation of the injected agents' water
solutions)
not only is adsorption of applied agents on the hard reservoir rock surface
avoided, but a
chemical reaction of the applied agents does not take place.
The process of forming highly viscous concentrated "plugs" of blended water-in-
oil
emulsions from aggregate stable globules of agents' water solutions (not
reacting with
one another) in highly permeable and fracture reservoir sections has great
importance as a
water blocking barrier. The fact that such a barrier is formed can be easily
traced through
the increase of injection pressure (at constant injection volumes) or through
decrease in
injection volumes at constant injection pressure.
Another distinction of the developed technical approach is a possibility to
make the
barrier stronger due to injection of a demulsifier in volumes sufficient to
separate injected
aggregate stable water-in-oil emulsion and a chemical reaction between gel and
sediment
forming agents forming cross-linking polymer systems (CLPS) or sediment
forming salt
compounds.
Parameters which make the proposed technical approach distinct from the
prototype were
not traced in other technical approaches and as a result the proposed method
complies
with "sufficient distinction" category.
The following chemicals and brands containing them are applied in the method:
~ As gel forming agents: 0.01-5.0% water solutions of anion polymer i.e.
polyacrylamid, carboxyl methyl cellulose etc. and as a cross linking agent
water
solution (0.003-0.2%) of polyvalence ration salts, i.e. chrome acetate etc.
~ As sediment forming agents: water solutions of salts of polybasic acids,
i.e. water
solution (10-20%) of sodium silicate (liquid glass), ammonium sulphate etc and
water
solutions (10-30%) of salts of alkaline-earth metals i.e. calcium chloride,
barium
chloride etc.
When 50% water-in-oil emulsions are formed the above water solutions disperse
in low
viscous hydrocarbon solvent i.e. kerosene (or gas benzene) where 5-20%
concentrated
ARP compounds are dissolved prior to that, such as OPA (TU 2458-001-21166006-
97).
To prepare water solutions in the field process or produced water is used. The
major
requirement to water is the absence of a water-in-oil emulsion demulsifier.
To destroy injected water-in-oil emulsions a 0.01-0.1% solution of a water-in-
oil
emulsion demulsifier in an aromatic solvent is used, i.e. Dissolvan 4411, 4490
etc.
The effectiveness of the developed method and the prototype method was
evaluated in
laboratory conditions based on the change in the velocity of fluid filtration
in core
CA 02279876 1999-07-29
samples of various permeability and an increase in oil displacement rate which
were
calculated accordingly based on the change in production rates and watercut of
the
produced oil. Incremental oil and fluid production rate were determined on the
model for
chemical oil displacement processes in porous media, a modified I11PK model.
Preparation of the reservoir model and fluids prior to testing was performed
according
STP 0148070-013-91 "Methods of Laboratory Tests".
All tests were performed on the reservoir model that consisted of two
intervals with
different permeability in the form of two filled columns 40 cm long and 3.7 cm
in
diameter. The intervals were consequently saturated by produced water and then
oil.
Later oil was displaced by produced water to 100% of product watercut. Then
gel or
sediment forming composition was injected according to the proposed method (in
the
form of a blend of water-in-oil emulsions with later injection of a 0.01%
demulsifier in
toluene for their destruction. The prototype method was also performed.
As per Table 1, gel forming polymer compositions, proposed method allows to
decrease
velocity of water filtration in high permeability sections of the reservoir
and thus provide
a considerable (2.5-4.5%) increase of oil displacement rate at much lower (2-
2.5 times)
volumes of expensive chemicals (water soluble PAA and cross-linking agent -
chrome
acetate) in correlation to the prototype. As per Table 2, the application of
the proposed
method of treatment of highly permeable sections of the reservoir with
sediment forming
compositions in correlation to the prototype allows to achieve a higher water
isolation
effect which is reflected in a 2-2.5 fold decrease of watercut in product 13.
Table 1
Effectiveness of redistribution of filtration flows and oil displacement with
the proposed
method and prototype, gel forming (cross linking) polymer compositions.
# Reservoir Oil Method i'iltration Oil
by velocity
model water correlation displace-
displace meat
meat increase,
rate,
ChemicalWater Prior After
to
solution chemicalchemical
concentrationinjectioninjection
maSB
Pro
sect
method
1 heterogeneous47.4 PAA 0.25 4.0 3.6 2.5
Chrome
acetate 0.01
Proto
a
method
2 heterogeneous47.4 PAA 0.25 4.0 3.9 0.5
Chrome
acetate 0.01
Pro
sect
method
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3 heterogeneous50.5 PAA 0.25 5.5 2.4 3.5
Chrome
acetate 0.01
Proto
a
method
4 heterogeneous50.5 PAA 0.25 4.5 3.4 1.5
Chrome
acetate 0.01
heterogeneous49.7 PAA 1.0 5.0 1.1 4.5
Chrome
acetate 0.08
heterogeneous50.3 PAA 1.0 5.0 3.0 2.0
Chrome
acetate 0.08
Table 2
Effectiveness of filtration flow redistribution and oil displacement with the
proposed
method and prototype, sediment forming compositions.
# Reser CorrelMethod Filtration Watercut
velocity, in product,
voir anon milesJhour
model of Chemical Water Prior After Prior After
to to
perme solutionchgmicalchemicalchemicalchemical
ability concentra-injectioninjectioninjectioninjection
tlOn
maS9
Pro
Method
1 Hetero-13.5 Na2Si03 15 5.5 0.4 91.7 19.4
eneous CaCl2 13
Pinto
Method
2 Hetero-12.3 Na2Si03 15 5.4 1.5 92.3 39.5
eneous CaCl2 13
Pro
sed
Method
3 Hetero-14.3 (NH4)250420 5.0 0.2 93.7 15.3
eneous BaCl2 30
Pro
Method
4 Hetero-13.7 (NH4)250420 5.1 2.1 92.7 49.4
I I I
geneous BaCl2 30
OIL PRODUCTION METHOD
Invention formula
The method of oil production creating water isolation barriers in flushed high
permeability sections of the pay zone as a result of simultaneous or
consequent injection
of water solutions of two or more gel or sediment forming agents is unique due
to the fact
that to improve efficiency of the process of reservoir treatment and avoid
premature
chemical reaction of the applied agents in the injection process water
solution of gel or
sediment forming agents are injected into the reservoir as an aggregate stable
water-in-oil
emulsion in low viscosity hydrocarbon solvent (benzene, kerosene etc). S-20%
of mass of
