Note: Descriptions are shown in the official language in which they were submitted.
A Centrally Thermal Recovery Method for Excavating Oil from an Oil
Reservoir by Electrically Heating Edge-Bottom Water Layer with
Horizontal Wells
Technical Field
[1] This centrally thermal recovery method is applicable to oil reservoirs
with
edge-bottom water layers, such as heavy oil reservoirs and high pour-point oil
reservoirs, which can be thermally recovered in oil industry. This centrally
thermal recovery method resolves the problems of in-place oil with high
viscosity or high paraffin content, low thermal-recovery efficiency of huff
and
puff or steam flooding, short production plateau, high decline rate and low
oil
recovery.
Technical Background
[2] Huff and puff, steam flooding, hot-water flooding and in-situ combustion
are
examples of efficient technical methods in thermal recovery. However, with
increases in in-depth oil well development, more and more problems with these
methods are being exposed during production. Especially for the middle-deep
and super-deep reservoirs (depth 600-2300m), the contradiction during
production is gradually becoming more severe: (1) Because of long distance
transportation of the steam and hot water, huff and puff, steam flooding and
hot-water flooding have severe thermal loss and low thermal efficiency. Other
problems which impact final reservoir recovery include high water cut, low
production rate, and high decline rate in production well; (2) Although in-
situ
combustion is effective to production test some common-heavy oil fault blocks
and can satisfy the requirements of industry, it cannot be applied to most of
the
extra and super-heavy oil reservoirs. In addition, this development method is
destructive and is akin to draining the pond to catch all the fish or killing
the
goose that lays the golden eggs. Once the reservoir is destroyed, any advanced
thermal-recovery method invented in the future cannot be carried out. That is,
only in-situ combustion can be followed; (3) at present, electrically heating
method is confined to heating the pumping rod and borehole. Its purpose is to
improve the oil and gas lifting ability of the production well, and to reduce
oil
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viscosity and the phenomenon of paraffin precipitation near the wellbore; (4)
as
for the in-situ thermal-recovery method of hydraulic-fractured electrically
heating oil-shale by horizontal wells, it would be difficult, costly, and
severely
contaminative to apply it into heavy oil reservoirs; 5) At present, all
thermal-
recovery methods belong to a method of locally heating oil layers. In these
methods, oil layers are heated unevenly and there exists only a short thermal
effective time, low efficiency and high residual oil saturation, which is
mainly
located in thermal un-swept regions and low heat efficiency areas.
Summary of the Invention
According to an aspect of the invention, there is provided a method for
thermal recovery of oil from an oil reservoir said oil reservoir comprising an
upper edge-bottom water layer proximal to oil layers within the oil reservoir,
said
oil reservoir is at a first temperature and comprising a quantity of in-place
oil,
said method comprising:
providing several horizontal wells extending into the oil reservoir, each
horizontal well comprising an electric heater positioned in the upper edge-
bottom water layer of the oil reservoir;
electrically heating the edge-bottom water layer with the electric heaters
until the temperature of the oil reservoir increases such that all of the in-
place
oil becomes mobile and flows; and
recovering the mobilized oil.
According to another aspect of the invention, there is provided an electric
heater thermal recovery system, comprising,
an electric heater comprising an inner liner comprising an upper liner and a
lower liner;
several ferrite permanent magnet bars fixed at a top of the upper liner,
waterproof spring electrical heating bars in series connection in a middle
part of the upper liner; and
a heat insulation board set at a horizontal diameter of the inner liner;
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wherein the lower liner, in cooperation with the heat insulation board
insulates heat,
and is vacuum-sealed to reduce downward transmission of thermal energy.
According to another aspect of the invention, there is provided a method for
centrally thermal recovery of oil from an oil reservoir, said oil reservoir
comprising an
upper edge-bottom water layer proximal to oil layers within the oil reservoir,
said oil
reservoir is at a first temperature and comprises a quantity of in-place oil,
said method
comprising: providing several horizontal wells extending into the oil
reservoir, each
horizontal well comprising an electric heater thermal recovery system
comprising: an
electric heater comprising an inner liner comprising a slotted liner and a
vacuum-
sealed liner, said electric heater positioned in the upper edge-bottom water
layer of
the oil reservoir; several ferrite permanent magnet bars fixed at a top of the
slotted
liner to protect the electric heater from scaling; waterproof spring
electrical heating
bars in series connection in the slotted liner to generate heat; and a heat
insulation
board set in the inner liner; wherein the vacuum-sealed liner, in cooperation
with the
heat insulation board insulates heat, and is vacuum-sealed to reduce downward
transmission of thermal energy; centrally electrically heating the edge-bottom
water
layer with the electric heaters until the temperature of the whole oil
reservoir increases
such that all of the in-place oil becomes mobile and flows; and centrally
recovering the
mobilized oil.
According to another aspect of the invention, there is provided an electric
heater thermal recovery system, comprising, an electric heater comprising an
inner
liner comprising a slotted liner and a vacuum-sealed liner divided into two
parts by a
heat insulation board; the heat insulation board set in the inner liner;
waterproof spiral electrical heating bars in series connection provided on the
heat
insulation board in the slotted liner; several ferrite permanent magnet bars
fixed at a
top of the slotted liner, a sealing board provided on either side of the
vacuum-sealed
liner; wherein the vacuum-sealed liner, in cooperation with the heat
insulation board
insulates heat, and is vacuum-sealed by the sealing board and the heat
insulation
board to reduce downward transmission of thermal energy.
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Date Recue/Date Received 2020-04-17
Open Technical Problems about Invention
[3] Principle Foundation
[4] 1. Centrally heating
In cold, one gets heat by wearing a coat, and a family gets heat by having a
fire
in the house. For a large building, the best way of heating is central
heating. The most
economic, most effective, most convenient method among the three is central
heating. During the process of thermal recovery, huff and puff in a single
well is
similar to one person getting heat and the composite huff and puff is similar
to heating
a house. If the whole reservoir can be regarded as a unit and heated with
central
heating, the formation temperature can be raised as a whole so that the
thermal-
recovery problems within a single well can be solved as well.
[5] 2. "Immersion heater" is a common electric heater and can be used to boil
water,
heat milk, boil coffee, and so on, characterized in that a container is heated
from the
outside. Once the container is waterproofed, the benefits of saving time,
saving water,
saving electric power and saving effort can all be realized, and at the same
time it is
cheap, convenient and effective. For edge-bottom water reservoirs, water is
natural
resource which makes it possible to electrically heat the water layer. The
method is
economical, environmental, simple and highly efficient so that it can meet the
needs
of oil production.
[6] 3. Cooking buns with a steamer is one typical example of getting a thermal
effect
by heating bottom water in daily life. There's no problem of continuously
steaming as
long as there is enough bottom-water. The pressure and temperature in the
steamer
will be released when the steamed buns are taken out of the steamer.
Similarly, when
the edge-bottom water layer of a reservoir
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Date Recue/Date Received 2020-04-17
is heated, the heat will conduct upwards to the whole reservoir gradually. The
gradually accumulated reservoir pressure, which results from thermal
expansion of the formations and fluids, and the temperature will be released
with the oil production. Meanwhile, it is convenient to manage the extent of
the
temperature and the pressure rising up in the reservoir by controlling heating
time and heating temperature. When the temperature in the edge-bottom water
reservoir increases to the range of 80 C and 100 C, the in-place oil becomes
"movable" and can be thermally recovered.
[714. Gravity differentiation phenomenon of cold and hot water
When the ocean is heated by the Sun, the temperature of the top or surface
water is warmer than that of the water closer to the bottom. The cold and hot
water present a phenomenon of gravity differentiation if there's no effect of
the
ocean current. That is, the phenomenon of cold and hot water scrolling up-and-
down will not occur. Heat loss only behaves as the heat conduction between
cold and hot water. Therefore, the temperature of the whole reservoir can be
effectively improved by continuously electrically heating the top of the water
layer near the oil layer.
[8] Feasibility Demonstration:
[9] 1. As a petroleum system, the premise of oil and gas migration and
accumulation is that the formations have characteristics, such as fine
connection, well sealed overlying layers, high initial temperature and movable
in-place oil. It can be inferred from crude oil having unmovable status that
the
temperature of the formation has decreased to a temperature that is much lower
than the initial temperature. So, it can be realized that the oil in an
effective
channel can return to the movable state when the temperature is increased to
a certain degree. The pores where the oil and gas could reach are all
effective
flow channel and the heat conduction in the formation is faster than that in
the
surrounding mudstones. Heat can conduct gradually from the bottom to the top
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and be kept effectively by the surrounding mudstone so that the "centrally
heating" can be realized in the whole reservoir.
[10] 2.Reservoirs can be categorized into 10 types according to the
distribution
of oil, gas and water, such as block bottom-water oil reservoirs, layer-
structure
block bottom-water oil reservoirs, block edge-bottom and top-water oil
reservoirs, layer-structure edge-water oil reservoir, block gas-cap (bottom-
water) oil and gas reservoirs, block gas-cap and bottom-water oil and gas
reservoirs, layer-structure gas-cap and bottom-water oil and gas reservoirs,
layer-structure gas-cap oil and gas reservoirs, pure oil reservoirs, and pure
gas
reservoirs. Except for the pure oil reservoir, pure gas reservoir and layer-
structure gas-cap oil and gas reservoir, most of the reservoirs develop edge
and bottom water and contain adequate formation water resources, which
provides sufficient material for electrically heating edge-bottom water layers
with horizontal wells drilled in water layer.
[11] 3. Under the condition of a geothermal gradient between 2.5 C and
4.5 C/100m, the temperature of middle-deep layers and super-deep layers is
between 35 C and 103.5 C although it can also be higher. The temperature
difference is about 23.5-47.5 C for electrically heating the formation water
from
the initial formation temperature to the temperature of the reservoir at a
range
of 80-150 C under which in-place oil would be in a movable state. The deeper
the formation water layer is, the less electric energy is needed. The higher
the
power of the electric heater is, the faster the water temperature rises. On
the
other hand, several electric heaters could be used simultaneously so that the
formation temperature can be increased quickly;
[12] 4. Fora sealed reservoir heated as a whole, the characteristics of
formation
temperature and formation pressure rising is similar to that of a pressure
cooker
being heated. Under high pressure conditions, the boiling temperature of
formation water is higher than 100 C. The relationship between water melting
and boiling point and pressure demonstrates that when the formation pressure
is between 3MPa and 20MPa, the water boiling temperature ranges from 132.9 C
CA 2933277 2018-07-16
to 211.4 C. The higher the pressure is, the higher the boiling point is. When
the
temperature is below the boiling point, the temperature in the reservoir could
be raised up to the point at which the crude oil transitions to a movable
state.
Therefore, it is feasible to control the lifting range of formation water
temperature and pressure by keeping heating the formation water under high
temperature and high pressure, as long as the temperature and pressure test
is monitored reasonably in combination with of the blowdown of production well
and pressure release.
[13] 5. At present, all these techniques are relatively mature in pipeline
skin
effect current tracing system, borehole or pumping rod electrically heated
system, in which the temperature can be controlled and the material has high
temperature resistance, that can satisfy the long-distance transportation of
electrical energy, so that problems, such as heating the production oil, heat
dissipation of conductor, can be addressed and overcome.
[14] 6. When "immersion heater" is immersed in the liquid, heat energy can
conduct outside quickly through the liquid and the liquid can be heated
quickly,
and simultaneously the electric wire will not be burned, which is safe,
environmental, economical and effective.
[15] 7. The technique of electrically heating magnet descaling can effectively
solve the scaling problem arising during electrically heating. The scale
originates from hard water. Magnets can soften the water, which is
environmental, economical, convenient and safe. Ferrite permanent magnets
are widely used, and their components mainly include BaFe12019 and
SrFe12019. They are made by ceramic technology, and have the
characteristics of temperature resistance, moderate price and are suitable for
wide application.
Solutions for the Problems
Schemes of Technical Solutions
[16] 1) According to the size of the reservoir, horizontal wells are drilled
in the
upper water layer of the edge-bottom water reservoir, 20-30m away from the
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oil layer. An electric heater is installed in the sieve pipe of the horizontal
well to
conduct electric heat to the water layer.
[17] 2) the structure of the electric heater of the horizontal well is shown
in Fig.1. The
liner of the horizontal-well is divided into upper and lower parts by a heat
insulation
board. The upper part is slotted, in which several spiral electric heaters
with series
connection are set on the board which is set at the horizontal diameter of the
liner. In
the lower part, the liner is sealed in vacuum by a liner sealing board to
insulate heat
transferred downward in combination with the insulation board.
[18] 3) Several ferrite permanent magnet bars are fixed at the top of the
inner upper
limit to prevent scaling.
Beneficial Effect of the Invention
Beneficial Effect
[19] Middle deep¨super-deep heavy oil reservoirs and high pour-point oil
reservoirs
can be recovered safely, environmentally, economically and efficiently so that
the
development effect can be improved and the final recovery can be promoted.
This
method can be widely applied in thermal recovery of other similar types of
mineral
resources.
Brief description to the Figure
Figure Description
Figure 1 shows:
[20] 0 Upper slotted and lower vacuum-sealed liner;
[21] Ferrite permanent magnet bar;
[22] Waterproof spiral electric heating bar;
[23] Heat insulation board;
[24] Liner sealing board.
Best Example about Applying the Invention
Best Application Method about the Invention
[25] 1) According to the size of the reservoir, horizontal wells are drilled
in the
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Date Recue/Date Received 2020-04-17
7a
Best Example about Applying the Invention
Best Application Method about the Invention
[25] 1) According to the size of a reservoir, horizontal wells are drilled in
the
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upper water layer of the edge-bottom water reservoir, 20-30m away from the
oil layer, which can store enough thermal energy to raise the temperature of
the
whole oil layer and delay the formation fracture due to premature boiling of
the
formation water and overpressure.
[26] 2) The number, length and trend of horizontal well are determined by the
size of the water body and reservoir volume. Gravel packed open hole
completion works well.
[27] 3) If the horizontal well is sidetrack drilled from an oil production
well, the
conducting wire can be used as borehole or pumping rod electrical heater so
that the effect of cooling and heating can be realized; if the horizontal well
is
drilled individually, a skin heat tracing device needs to be applied to the
conducting wire. High temperature resistant materials should be optimized to
prevent the conducting wire from overheating in the borehole.
Application Example of the Invention
Application Method of the Invention
[28] Electric heaters are configured to be positioned in several horizontal
wells
drilled in an upper water layer of the reservoir, near the oil layers. The
electric
heaters heat the edge-bottom water layer of the reservoir so that the
temperature of the whole reservoir is increased. Several mechanisms are
applied to recover oil efficiently, such as, the effect of heat transfer, the
effect
of steam flooding produced by water soluble gas overflow, the thermal
expansion pressure from water formations and oil layers as well as the
viscosity-reduction effect / wax-precipitation effect of in-place oil under
high
temperature.
Industrial Applicability
[29] It can be applied to thermally recover heavy oil and high pour-point oil
reservoirs with edge-bottom water layers, especially for those heavy oil
reservoirs of middle-super deep depth which are difficult to recover.
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