Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
METHOD FOR COMMUNICATION OF DUAL HORIZONTAL WELLS
Technical Field
The present invention relates to the oil and gas development field,
particularly to a
method for communication of dual horizontal wells.
Background of the Invention
Exploitation of super heavy oil in shallow reservoirs adopting Steam Assisted
Gravity
Drainage (SAGD) with dual horizontal wells is successful in Canada, and is
commercially available, and therefore such an exploitation approach has also
been
gradually appreciated in our country accordingly. In the SAGD startup stage,
an oil
reservoir has a low initial temperature, crude oil has a high viscosity, an
effective
communication is difficultly established between dual horizontal wells with
traditional 5 meters well spacing, thus the heavy oil having a flowing
capacity cannot
.. flow downwards after peripheries of the steam-injection wells are heated, a
vapor
chamber also cannot be expanded, and therefore it seems quite significant to
establish
an effective fluid communication. In addition, an inter-well thermal
communication is
also of vital importance, thermal losses occur in the heavy oil heated at the
top in the
process of slow seepage to the production wells at the bottom, so that the
temperature
drops and the viscosity increases, thereby making it difficult to flow crude
oil between
wells, and impossible to complete the drainage process successfully.
Summary of the Invention
In order to overcome the above-mentioned drawbacks of the prior art, the
technical
problem to be solved by the embodiments of the present invention is to provide
a
method for communication of dual horizontal wells, which can effectively
enhance a
degree of uniformity of communication between dual horizontal wells, shorten
communication time between the dual horizontal wells.
The concrete technical solutions of the embodiments of the present invention
are
provided as follows:
A method for communication of dual horizontal wells comprising steam-injection
horizontal wells and production horizontal wells, the method comprising the
following steps:
testing the steam-injection horizontal wells and the production horizontal
wells to
obtain a minimum principal stress of the steam-injection horizontal wells, a
fracture-initiation pressure of the steam-injection horizontal wells, a
minimum
principal stress of the production horizontal wells and a fracture-initiation
pressure of
the production horizontal wells;
injecting solvents into the steam-injection horizontal wells and the
production
horizontal wells respectively;
injecting water into the steam-injection horizontal wells via wellbores of the
steam-injection horizontal wells, injecting water into the production
horizontal wells
via wellbores of the production horizontal wells, so that the solvents in the
wellbores
1
CA 3012371 2018-07-25
of the steam-injection horizontal wells and the production horizontal wells
are
displaced in oil reservoirs;
continuously injecting water into the steam-injection wells and the production
horizontal wells respectively, improving water-injection pressure of the
steam-injection horizontal wells to between the minimum principal stress of
the
steam-injection horizontal wells and the fracture-initiation pressure of the
steam-injection horizontal wells, and improving the water-injection pressure
of the
production horizontal wells to between the minimum principal stress of the
production horizontal wells and the fracture-initiation pressure of the
production
horizontal wells;
after a high water-cut region is formed in the respective solvent area of the
steam-injection horizontal wells and the production horizontal wells; after
closing the
steam-injection horizontal wells and the production horizontal wells meets a
first
preset condition, injecting gas into the steam-injection horizontal wells and
the
production horizontal wells respectively, so that underground water flows back
to
ground, and
after the underground water flows back to the ground, injecting isobaric steam
into the
steam-injection horizontal wells and the production horizontal wells to meet a
second
preset condition.
In a preferred embodiment, continuously injecting the water into the steam-
injection
wells and the production horizontal wells respectively, improving the water-
injection
pressure of the steam-injection horizontal wells to between the minimum
principal
stress of the steam-injection horizontal wells and the fracture-initiation
pressure of the
steam-injection horizontal wells, and improving the water-injection pressure
of the
production horizontal wells to between the minimum principal stress of the
production horizontal wells and the fracture-initiation pressure of the
production
horizontal wells, so that one high water-cut region centered on wellbores is
formed in
the solvent area of the steam-injection horizontal wells and the production
horizontal
wells respectively, and the high water-cut region of the steam-injection
horizontal
wells is not in communication with the high water-cut region of the production
horizontal wells.
In a preferred embodiment, the method for communication of dual horizontal
wells
further comprises the following steps
injecting water with pressure into the steam-injection horizontal wells and
the
production horizontal wells respectively, in order to determine development of
underground fractures.
In a preferred embodiment, the method for communication of dual horizontal
wells
further comprises the following steps:
Cyclically injecting water into the steam-injection horizontal wells and the
production
horizontal wells respectively, in order to clean up wellbore walls.
2
CA 3012371 2018-07-25
In a preferred embodiment, the method for communication of dual horizontal
wells
further comprises the following steps:
before said step of injecting water into the steam-injection horizontal wells
via the
wellbores of the steam-injection horizontal wells, injecting water into the
production
horizontal wells via the wellbores of the production horizontal wells, so that
the
solvents in the wellbores of the steam-injection horizontal wells and the
production
horizontal wells are displaced in oil reservoirs, injecting a soluble gum of
slugs into a
wellbore annulus of the steam-injection horizontal wells and the production
horizontal
wells respectively.
In a preferred embodiment, providing a first pipe string and a second pipe
string
longer than the first pipe string in the steam-injection horizontal wells,
providing a
third pipe string and a fourth pipe string longer than the third pipe string
in the
production horizontal wells, in said step of after closing the steam-injection
horizontal
wells and the production horizontal wells meets a first preset condition,
injecting gas
into the steam-injection horizontal wells and the production horizontal wells
respectively, so that underground water flows back to ground, injecting gas
into a well
annulus of the steam-injection horizontal wells and the production horizontal
wells
respectively, so that the underground water of the steam-injection horizontal
wells
flows back from the first or second pipe string to the ground, the underground
water
of the production horizontal wells flows back from the third or fourth pipe
string to
the ground.
In a preferred embodiment, in said step of injecting gas into the well annulus
of the
steam-injection horizontal wells and the production horizontal wells, so that
the
underground water of the steam-injection horizontal wells flows back from the
first or
second pipe string to the ground, the underground water of the production
horizontal
wells flows back from the third or fourth pipe string to the ground, gradually
reducing
down-hole pressure, so as to promote the underground water to flow back to the
ground.
In a preferred embodiment, the first preset condition is that closing time of
the
steam-injection horizontal wells and the production horizontal wells is
greater than or
equal to 24 hours.
In a preferred embodiment, the second preset condition is that the time of
injection of
the isobaric steam into the steam-injection horizontal wells and the
production
horizontal wells is greater than or equal to 2 months.
In a preferred embodiment, in said step of injecting the solvents into the
steam-injection horizontal wells and the production horizontal wells
respectively, so
that the wellbores of the steam-injection horizontal wells and the wellbores
of the
production horizontal wells are filled up with the solvents, adjusting flow
rate and
pressure of the solvents injected by injection pressure, when the wellbores of
the
3
CA 3012371 2018-07-25
steam-injection horizontal wells and the wellbores of the production
horizontal wells
are filled up with the solvents.
In a preferred embodiment, the steam-injection horizontal wells and the
production
horizontal wells meet the following conditions: there exists no inter-well
interlayer
between the steam-injection horizontal wells and the production horizontal
wells; the
oil reservoir where the steam-injection horizontal wells and the production
horizontal
wells are located belongs to a Group III of oil reservoir; there exists no
natural
fracture in an oil reservoir region where the steam-injection horizontal wells
and the
production horizontal wells are located; and there exists no edge-bottom water
in the
oil reservoir region where the steam-injection horizontal wells and the
production
horizontal wells are located.
In a preferred embodithent, the solvents and heavy oil can be miscible with
each other,
and asphaltene is not precipitated out.
In a preferred embodiment, the viscosity of the solvents at room temperature
ranges
between 1mPa.S and 100mPa.S, and the density ranges between 0.7g/cm3 and
1 .2 giem3.
In a preferred embodiment, the solvents have viscosity-reduction properties at
the oil
reservoir temperature, and viscosity of mixtures containing the solvents of
which
mass fraction is 20% and crude oil should be less than 5,000mPaS.
In a preferred embodiment, the solvents include at least one of benzene,
toluene, =
xylene, kerosene, diesel oil, petroleum ether and light crude oil.
In a preferred embodiment, in said step of after closing the steam-injection
horizontal
wells and the production horizontal wells meets a first preset condition,
injecting gas
into the steam-injection horizontal wells and the production horizontal wells
respectively, so that underground water flows back to ground, the gas is
nitrogen.
In a preferred embodiment, injecting the solvents into the steam-injection
horizontal
wells and the production horizontal wells respectively, so that the wellbores
of the
steam-injection horizontal wells and the wellbores of the production
horizontal wells
are filled up with the solvents.
The technical solutions of the present invention have the following remarkable
advantageous effects:
the method for communication of dual horizontal wells in this application
comprises
said steps of: injecting solvents into dual horizontal wells, next, injecting
water to
displace the mixture formed of solvents and heavy oil, thus gradually forming
a high
water-cut region centered on wellbores, and then injecting steam into the dual
horizontal wells for circulation. Since the high water-cut region enlarges a
radius of a
4
CA 3012371 2020-02-25
linear heat source, heat transfer distances between the dual horizontal wells
are
declined to a great extent, so that a rate of rise in temperature is
substantially
increased between the dual horizontal wells, as a result, this method can
significantly
shorten communication time between the dual horizontal wells, so as to save a
large
amount of steam; in addition, a degree of uniformity of communication can also
be
enhanced dramatically between the dual horizontal wells.
Brief description of the drawings
The drawings described herein are for illustration purposes only and are not
intent to
limit the scope of the present disclosure in any way. In addition, shapes and
proportional dimensions of components in the drawings are only schematic to
facilitate an understanding of the present invention, and are not intent to
concretely
define the shapes and proportional dimensions of components of the present
invention.
Under the teachings of the present invention, those skilled in the. art can
select various
possible shapes and proportional dimensions to implement the present invention
in
dependence on the specific circumstances.
FIG. I is a sectional view along the direction of horizontal wells under
routine SAGD
productions;
FIG. 2 is a schematic diagram illustrating a temperature field under unsteady-
state
heat transfer of double heat sources with 5 meters well spacing under routine
SAGD
productions;
FIG. 3 is a schematic diagram illustrating unsteady-state heat conduction by
conventional steam injection circulation in thermal communication with the
double
heat sources;
FIG. 4 is a schematic diagram illustrating steps of the method for
communication of
dual horizontal wells in the embodiments of the present application;
FIG. 5 is an effect graph illustrating fingering formed by injecting water
after solvents
are injected in the embodiments of the present application; and _
FIG. 6 is a relationship graph illustrating a midpoint temperature of dual
horizontal
wells where steam is circulated changes over time under conditions of
different
heating radius in the embodiments of the present application.
The reference numerals of the figures mentioned above:
CA 3012371 2020-02-25
1. steam-injection horizontal wells; 11. first pipe string; 12. second pipe
string; 2.
production horizontal wells; 21. third pipe string; 22. fourth pipe string; 3.
central line
of dual horizontal wells.
Detailed description of the Invention
Details of the invention will become more apparent in the light of the
description of
the accompanying drawings and the embodiments of the present invention.
However,
the embodiments of invention described herein are provided only for the
purpose of
illustration and are not to be construed as limiting the scope of the
invention in any
.. way. Under the teachings of the present invention, any possible deformation
can be
devised by those skilled in the art based on the present invention and these
should be
contemplated as being within the scope of the invention. It will be understood
that
when an element is referred to as being "disposed on" another element, it can
be
directly on another element or intervening elements may also be present. When
an
element is referred to as being "connected" to another element, it can be
directly
connected to another element or intervening elements may also be present. The
terms
"mounted", "interconnected" and "connected" are to be understood broadly,
e.g.,
either electrical or mechanical connections, or interior communications of two
elements, or direct connections, or indirect connections through
intermediaries, the
specific meanings of those terms can be understood by those skilled in the art
depending on the specific circumstances. The terms "perpendicular",
"horizontal",
"upper", "lower", "left", "right" and the like as used herein are for
illustrative purposes
only, and not intent to represent the only embodiment.
Unless otherwise defined, all technical and scientific terms used herein have
the same
meaning as commonly understood by those skilled in the technical field to
which this
application belongs. The terminology used in the Description of the present
application herein is only used for purposes of describing specific
embodiments, and
is not intent to limit the present application. As used herein, the term
"and/or" includes
any and all combinations of one or more of the associated listed items.
FIG. 1 is a sectional view along the direction of horizontal wells under
routine SAGD
productions. As shown in FIG 1, the current mainstream operating technique is
arranging a dual tubing pipe string structure at steam-injection wells at the
top and
production wells at the bottom, performing an isobaric steam-injection
circulation
preheating for the steam-injection wells and the production wells
simultaneously, to
form a stable high-temperature region in the vicinity of wellbores, then
transferring
heat to depth of a reservoir in a form of heat conduction in dependence on
temperature difference, so as to slowly heat the oil reservoirs between
injection-production wells. FIG 2 is a schematic diagram illustrating a
temperature
field under unsteady-state heat transfer of double heat sources with 5 meters
well
spacing under routine SAGD productions; FIG. 3 is a schematic diagram
illustrating
unsteady-state heat conduction by conventional steam-injection circulation in
thermal
communication with the double heat sources. As shown in FIGS. 2 and 3, it is
6
CA 3012371 2018-07-25
analyzed from the perspective of heat transfer theory that the above-mentioned
method has the following intrinsic drawbacks: 1. there exists a low-
temperature
bottleneck zone in a portion of the region between the steam-injection
horizontal
wells 1 and the production horizontal wells 2, and the low-temperature
bottleneck
zone easily leads to nonuniformity of communication between the steam-
injection
horizontal wells 1 and the production horizontal wells 2 in a later period; 2.
an invalid
heating zone can be formed due to the heat conduction below the production
wells,
where heat utilization efficiency is not high; 3. the fixed double heat
sources have a
slow heat-transfer rate, and a high energy consumption; and 4. well killing
for cooling
is desired when switching to SAGD and repairing pumps, thus a large amount of
heat-energy losses can be caused within the wells.
For the horizontal wells buried about 350 meters deep, steam-injection
temperature is
about 260 degrees Celsius, pressure is 4.5MPa, and length of the horizontal
wells is
400 meters or so with an openhole diameter of 9.186 inch or so, and steam-
injection
flowrate is about 70M3/d. At present, main heat sources are steam boilers
using
natural gas, and it is calculated based on such a flow rate that the natural
gas cost of a
single well group is namely more than 10,000 CNY in a single day. In general,
the
circulating and preheating process at least needs to last about 4 months to
ensure
effective communications between the wells, so that normal SAGD production
phases
can be switched to. However, impacts of a plurality of unfavorable factors,
such as
high water saturation of oil reservoirs, poor thermo-physical properties, poor
control
of drilling tracks, deep burying, thin oil layer, low quality of injection
steam, unequal
underground heating, arise during inter-well communications, the above-
mentioned
factors may result in poor effects on circulating and pre-heating, and time-
consuming,
the duration of circulating and pre-heating may take nearly 1 year or so if
serious, thus
the overall oil-gas ratio, economic efficiency of SAGD exploitations will be
significantly affected. In addition, in the SAGD startup stage, if the
previous
circulating and pre-heating effect is poor, it often leads to a low producing
degree of
the horizontal wells after switching to SAGD, the oil production rate does not
reach
the expected rate designed by solutions, then even if measurements are taken
subsequently to improve the producing degree of the horizontal wells, the
effects after
the producing degree is improved are also extremely limited, thus the
communication
effects between the wells in the initial startup stage are in a poorer state,
which will
-- significantly affect the development effects of SAGD.
In order to effectively enhance communication effects between dual horizontal
wells,
shorten communication time between the dual horizontal wells, the present
application proposes a method for communication of dual horizontal wells,
where the
dual horizontal wells comprise: steam-injection horizontal wells 1 and
production
horizontal wells 2, the steam-injection horizontal wells 1 can be provided
with a first
pipe string 11 and a second pipe string 12 longer than the first pipe string
11, the
production horizontal wells 2 can be provided with a third pipe string 21 and
a fourth
pipe string 22 longer than the third pipe string 21, a central line 3 of dual
horizontal
7
CA 3012371 2018-07-25
wells is provided between the steam-injection horizontal wells 1 and the
production
horizontal wells 2, at the same time, the steam-injection horizontal wells 1
and the
production horizontal wells 2 meet the following conditions: there exists no
inter-well
interlayer between the steam-injection horizontal wells 1 and the production
horizontal wells 2; the oil reservoir where the steam-injection horizontal
wells 1 and
the production horizontal wells 2 are located belongs to a Group III of oil
reservoir;
there exists no natural fracture in an oil reservoir region where the steam-
injection
horizontal wells 1 and the production horizontal wells 2 are located; and
there exists
no edge-bottom water in the oil reservoir region where the steam-injection
horizontal
wells 1 and the production horizontal wells 2 are located. Certainly, when the
method
in the present application is applied to the steam-injection horizontal wells
1 and the
production horizontal wells 2, test data of ground stress of the wells
adjacent to the
block where the steam-injection horizontal wells 1 and the production
horizontal
wells 2 are located and other related data, e.g., physical property parameters
of
reservoirs and crude oil, such as porosity, permeability, formation water
salinity, oil
saturation, crude oil viscosity, etc., should be obtained in advance, so as to
implement
the corresponding data support provided in this method. FIG. 4 is a schematic
diagram
illustrating steps of the method for communication of dual horizontal wells in
the
embodiments of the present application, and the method for communication of
dual
horizontal wells comprises the following steps:
S101: injecting water with pressure into the steam-injection horizontal wells
1 and the
production horizontal wells 2 respectively, in order to determine development
of
underground fractures. In this step, the water with pressure can be injected
into the
steam-injection horizontal wells 1 and the production horizontal wells 2
respectively,
so as to determine whether there exist underground natural fractures and
development
states of underground fractures. If information on the underground natural
fractures
and development states of underground fractures of the steam-injection
horizontal
wells 1 and the production horizontal wells 2 mentioned above has already been
known, this step can be omitted.
S102: cyclically injecting water into the steam-injection horizontal wells 1
and the
production horizontal wells 2 respectively, in order to clean up wellbore
walls. In this
step, water can be injected into wellbores of the steam injection wells 1 or
the first
pipe string 11 or the second pipe string 12, so as to clean the mud on the
wall of the
wellbores of the steam-injection horizontal wells 1, the waste water after
cleaning can
flow back to ground from the corresponding wellbore or the first pipe string
11 or the
second pipe string 12. For example, water is injected into the wellbores of
the
steam-injection horizontal wells 1, then the waste water after cleaning can
flow back
to the ground from the first pipe string 11 or the second pipe string 12.
Likewise,
water can be injected into the wellbores of the production horizontal wells 2
or the
third pipe string 21 or the fourth pipe string 22, so as to clean the mud on
the wall of
the wellbores of the production horizontal wells 2, the waste water after
cleaning can
flow back to the ground from the corresponding wellbore or the third pipe
string 21 or
8
CA 3012371 2018-07-25
the fourth pipe string 22. If the wellbore walls of the steam-injection
horizontal wells
1 and the production horizontal wells 2 meet the requirements, this step
cannot be
implemented.
S103: testing the steam-injection horizontal wells 1 and the production
horizontal
wells 2 to obtain a minimum principal stress of the steam-injection horizontal
wells 1,
a fracture-initiation pressure of the steam-injection horizontal wells 1, a
minimum
principal stress of the production horizontal wells 2 and a fracture-
initiation pressure
of the production horizontal wells 2. In general, that test can be a
microfracture test.
S104: injecting solvents into the steam-injection horizontal wells 1 and the
production
horizontal wells 2 respectively, so as to inject the solvents into the
wellbores of the
steam-injection horizontal wells 1 and the wellbores of the production
horizontal
wells 2. In this step, when injecting the solvents into the wellbores of the
steam-injection horizontal wells 1 and the wellbores of the production
horizontal
wells 2, adjusting flow rate and down-hole pressure of the solvents injected
by
injection pressure. When the down-hole pressure increases to the minimum
principal
stress, the flow rate of the injected solvents is reduced, that is, decreasing
the injection
pressure; and when the down-hole pressure decreases continuously, the flow
rate of
the injected solvents can be properly increased, that is, improving the
injection
pressure. Meanwhile, the down-hole gas can be first emptied, then the
wellbores of
the steam-injection horizontal wells 1 and the wellbores of the production
horizontal
wells 2 are filled up completely as quickly as possible.
When the solvents are injected into the steam-injection horizontal wells and
the
production horizontal wells respectively, the solvent injection pressure is
consistently
less than the minimum principal stress. The step S104 is pressurizing and
squeezing
the solvents, and solvent fingering can form a low viscous solvent fingering
area, and
the subsequent water injection displaces the solvent fingering area, thereby
forming
.. high water-cut regions that are centered on wellbores of the injection and
production
horizontal wells respectively; both of the high water-cut regions require
tight control
over size, so as not to allow for its local priority communication.
The injected solvents have no effects of fracture and dilatation, and no pore
space
communicated between wells is created by fracture and dilatation. Also, after
the
solvents reduce viscosity of crude oil in near bore zones, the pore space that
the crude
oil leaves and stays is carried.
In this embodiment, types of the solvents can be diversified, e.g., the
solvents can be
made of either a single component, or a mixture, as long as it meets the
following
conditions: the solvents and heavy oil can be miscible with each other, and
asphaltene
is not precipitated out; the viscosity of the solvents at room temperature
ranges
between 1mPa.S and 100mPa.S, and the density ranges between 0.7g/cm3 and
1.2g/cm3; the solvents have viscosity-reduction properties at the oil
reservoir
9
CA 3012371 2018-07-25
temperature, and the viscosity of mixtures containing the solvents of which
mass
fraction is 20% and crude oil should be less than 5,000mPaS. When steam is
subsequently injected into the steam-injection horizontal wells 1 and the
production
horizontal wells 2, the solvents can be in either liquid phase or gas phase
under the
.. influence of high temperature steam. For example, the solvents can at least
include
one of benzene, toluene, xylene, kerosene, diesel oil, petroleum ether and
light crude
oil.
The injection rate at which the solvents are injected into the steam-injection
horizontal
.. wells 1 and the production horizontal wells 2 varies with types of the
solvents.
Generally, for a solvent chamber having a radius of 1 meter formed with centre
at the
wellbores at an injection rate of 400 meters or so as a target horizontal
well, an
optimal injection rate ranges between 78 cubic meters and 144 cubic meters.
.. After the wellbores of the steam-injection horizontal wells 1 and the
wellbores of the
production horizontal wells 2 are filled up with the solvents, the solvents
carrying the
heavy oil viscosity-reduced partially in the wells go deep into the reservoir
along
radial directions of the wells, so that one columnar solvent area centered on
wellbores
can be formed.
S105: injecting a soluble gum of slugs into a wellbore annulus of the steam-
injection
horizontal wells 1 and the production horizontal wells 2 respectively. To
enable
injection of water into the steam-injection horizontal wells 1 and the
production
horizontal wells 2 in the later stage and separation of water from the
solvents
.. previously injected, forming a displacement process, since organic solvents
have a
lower density than water, the soluble gum of slugs can be injected into
wellbore
annulus at this moment, thus subsequently, the solvents in the wellbores can
be
pressed into the formation as much as possible. Such a soluble gum can be
dissolved
at high temperature, and therefore when steam is injected into the steam-
injection
horizontal wells 1 and the production horizontal wells 2 in the later stage,
the soluble
gum can be dissolved under the influence of steam heating, so as to avoid it
from
influencing fluid communications and thermal communications between the
steam-injection horizontal wells 1 and the production horizontal wells 2.
S106: injecting water into the steam-injection horizontal wells 1 via the
wellbores of
the steam-injection horizontal wells 1, injecting water into the production
horizontal
wells 2 via the wellbores of the production horizontal wells 2, so that the
solvents in
the wellbores of the steam-injection horizontal wells 1 and the production
horizontal
wells 2 are displaced in oil reservoirs. In this step, injecting water into
the
steam-injection horizontal wells 1 and the production horizontal wells 2 via
the
wellbores, the injected water displaces the original solvents of horizontal
and vertical
sections of the steam-injection horizontal wells 1 and the production
horizontal wells
2 in oil reservoirs.
lo
CA 3012371 2018-07-25
S107: continuously injecting water into the steam injection wells 1 and the
production
horizontal wells 2 respectively, improving water-injection pressure of the
steam-injection horizontal wells 1 to between the minimum principal stress of
the
steam-injection horizontal wells 1 and the fracture-initiation pressure of the
steam-injection horizontal wells 1, and improving the water-injection pressure
of
production horizontal wells 2 to between the minimum principal stress of the
production horizontal wells 2 and the fracture-initiation pressure of the
production
horizontal wells 2.
In this step, continuously injecting water into the steam-injection wells 1
and the
production horizontal wells 2, improving water-injection pressure, and
improving the
water-injection pressure of the steam-injection horizontal wells 1 to between
the
minimum principal stress of the steam-injection horizontal wells 1 and the
fracture-initiation pressure of the steam-injection horizontal wells 1, so
that mobile oil
in the solvent area of the steam-injection horizontal wells 1 is displaced by
water to
the deeper inside of the oil reservoirs, in this way, a high water-cut region
centered on
wellbores is formed inside and in the vicinity of the solvent area of the
steam-injection horizontal wells 1. Similarly, improving the water-injection
pressure
of the production horizontal wells 2 to between the minimum principal stress
of the
production horizontal wells 2 and the fracture-initiation pressure of the
production
horizontal wells 2, so that mobile oil in the solvent area of the production
horizontal
wells 2 is displaced by water to the deeper inside of the oil reservoirs, in
this way, a
high water-cut region centered on wellbores is formed inside and in the
vicinity of the
solvent area of the production horizontal wells 2. Meanwhile, the high water-
cut
region of the steam-injection horizontal wells 1 is not in communication with
the high
water-cut region of the production horizontal wells 2. FIG. 5 is an effect
graph
illustrating fingering formed by injecting water after solvents are injected
in the
embodiments of the present application. As shown in FIG 5, two black circles
indicate the steam-injection horizontal wells 1 and the production horizontal
wells 2
respectively; it indicates in turn outward from the start of the black
circles, the
wellbores (the black circles), the high water-cut area centered on wellbores,
the
solvent-affected area, and the original oil reservoirs. A part of the crude
oil can reduce
viscosity in near bore zones by this step, and the crude oil is displaced by
water into
stratum depths, a high water-cut saturation area is formed in the near bore
zones after
the crude oil is displaced by water, the following objectives can be realized
using the
high water-cut saturation area: 1. a heat transfer by convection mode with
high heat
transfer efficiency is mainly adopted in the high water-cut saturation area,
corresponding to increasing a diameter of a horizontal hole, shortening a
distance
between wells where heat is transferred inefficiently, so as to shorten steam
circulation time and accelerate communication process, and also save
consumption of
steam. 2. Since the high water-cut saturation areas respectively centered on
the
steam-injection horizontal wells 1 and the production horizontal wells 2 are
not in full
communication, which avoids a local priority communication during subsequent
steam circulation, as a result, the section temperature at a part of the
horizontal section
CA 3012371 2018-07-25
is significantly increased, and the part of the horizontal section cannot be
effectively
heated, i.e., the problem of non-uniform communication of the dual horizontal
wells.
S108: closing the steam-injection horizontal wells 1 and the production
horizontal
wells 2 meets a first preset condition, injecting gas into the steam-injection
horizontal
wells 1 and the production horizontal wells 2 respectively, so that
underground water
flows back to ground, after the high water-cut region is formed in the
respective
solvent area of the steam-injection horizontal wells and the production
horizontal
wells. In this step, first closing the first steam-injection horizontal wells
1 and the
production horizontal wells 2 meets the first preset condition, where the
first preset
condition is a length of time, under which, a more stable high water-cut
region is
formed inside and in the vicinity of the solvent area of the steam-injection
horizontal
wells 1 and the production horizontal wells 2. In general, the first preset
condition is
that closing time of the steam-injection horizontal wells 1 and the production
horizontal wells 2 is greater than or equal to 24 hours. Then injecting gas
into the
steam-injection horizontal wells 1 and the production horizontal wells 2
respectively,
so that the underground water flows back to the ground, the gas can be a safe
gas
insoluble in water that can be flushed into underground, for example,
nitrogen. In a
feasible embodiment, injecting gas into a well annulus of the steam-injection
horizontal wells 1 and the production horizontal wells 2 respectively, so that
the
underground water of the steam-injection horizontal wells 1 flows back from
the first
pipe string 11 or the second pipe string 12 to the ground, the underground
water of the
production horizontal wells 2 flows back from the third pipe string 21 or the
fourth
pipe string 22 to the ground. In the above process, down-hole pressure can be
gradually reduced to promote underground water to flow back to the ground, so
as to
reduce the contents of underground fluid having a high specific heat capacity
to water,
for the sake of quickly raising the temperature in the near bore zones and
using latent
heat of steam more effectively in next step.
S109: after the underground water flows back to the ground, injecting isobaric
steam
into the steam-injection horizontal wells 1 and the production horizontal
wells 2 meets
a second preset condition. In this step, steam can be injected into the second
pipe
string 12 of the steam-injection horizontal wells 1, the liquid returns via
the first pipe
string 11 of the steam-injection horizontal wells 1 for circulation;
similarly, steam can
be injected into the fourth pipe string 22 of the production horizontal wells
2, the
liquid returns via the third pipe string 21 of the production horizontal wells
2 for
circulation. Since a high water-cut region is formed inside and in the
vicinity of the
steam-injection horizontal wells 1 and the production horizontal wells 2, the
temperature of this high water-cut region is raised quickly due to convection
heat
transfer of mobile water. In the steam-injection phase, its temperature can
rise up
close to a saturated-steam temperature, accordingly, with respect to the
effective
heating radius being originally equal to the radius length of a horizontal
well wellbore,
in this case, the effective heating radius is enlarged. That is, the radius of
the original
linear heat source is a radius length of a horizontal well wellbore, the
radius of the
12
CA 3012371 2018-07-25
present linear heat source is slightly less than a radius length of the high
water-cut
region, and thus the radius of the linear heat source is effectively enlarged.
When
injecting the isobaric steam into the steam-injection horizontal wells 1 and
the
production horizontal wells 2 for heating between the wells, because the
increase in
radius of the linear heat source of the steam-injection horizontal wells 1 and
the
production horizontal wells 2 results in a decrease in heat transfer distances
between
the steam-injection horizontal wells 1 and the production horizontal wells 2,
therefore,
the rate at which the temperature between the wells rises in the heating
process can be
substantially increased, so on the premise that an inter-well distance is
unchanged,
effective communications can be achieved between two wells, and time of
communication is significantly shortened between two wells; typically, the
second
preset condition is that the time of injection of isobaric steam into the
steam-injection
horizontal wells 1 and the production horizontal wells 2 can be shortened to 2
months
or more. Shortening the time of communication between two wells can save
substantial amounts of injected steam, and substantially reduce the
communication
cost. This method can achieve an effective communication between the two
wells, and
therefore the track requirements can be reduced for well-drilling wellholes,
the even
producing degree of the horizontal section is improved when oil reservoirs are
exploited, which gives full play to advantages of gravity drainage in
horizontal wells.
In this embodiment, heat transfer occurs only in a manner of convection of
heat in a
high water-cut band (equivalent to an effect of enlarging a radius of a
wellbore), and
the final communication between wells still relies on steam-injection
circulation, in
other words, it is completed by heat conduction, wherein characteristics of
the heat
conduction are that uniformity is preferable. FIG. 6 is a relationship graph
illustrating
a midpoint temperature of dual horizontal wells where steam is circulated
changes
over time under conditions of different heating radius in the embodiments of
the
present application. As shown in FIG. 6, in one embodiment, steam-injection
temperature is 250 degrees Celsius, steam-injection flowrate is 75 cubic
meters/day, a
relation of a midpoint temperature of dual horizontal wells against steam
circulation
preheating time when effective radii of wellbores are calculated as 0.11 meter
and
1.11 meters respectively is obtained according to an unsteady-state heat
transfer
model when dual linear heat sources have an infinite radius, where 0.11m can
be a
radius of the horizontal hole, and 1.1Im can be a radius of the high water-cut
area
formed after solvents is injected, followed by water; in the steam circulation
process,
equivalent to that the radius of the wellbore is enlarged to 1.11m. It can be
appreciated
from the relation of the midpoint temperature calculated based on different
heating
radii (radii of linear heat source) with time that after the radius is
increased to 1.11m,
it is only necessary to increase the inter-well midpoint temperature (i.e.,
2.5m when a
drilling trajectory is idealized) up to more than 100 C in 30 days. And the
heating
radius (the radius of linear heat source) in a conventional method is only
0.11m, it
needs to take more than 100 days of steam circulation time for increase in
inter-well
midpoint temperature up to 100 C. Thus it can be appreciated by contrast that
after the
heating radius (the radius of linear heat source) is enlarged, the rate at
which the
interwell temperature rises is substantially increased, and the steam-
injection time
13
CA 3012371 2018-07-25
required by crude oil that possesses flowing capacity is also significantly
shortened,
from the viewpoint of this embodiment, the steam-injection time is about 1/3
of that
of the conventional solution. Since the steam-injection time is significantly
shortened,
substantial amounts of steam cost can be saved, while the water processing
cost can
also be greatly decreased, so the solution has a preferable economic benefit.
The following is an example that the method for communication of dual
horizontal
wells in the present application is applied in some specific oil reservoir.
The oil reservoir is a heavy oil reservoir buried at 440m depth, where a
degassed
crude oil has a viscosity of 106,000mPa.S at 50 C, the oil reservoir has a
porosity of
30%, and a permeability of 1,400md, an oil saturation of 85%, a reservoir
thickness of
25m. The minimum principal stress obtained by field testing is 6.3MPa, and the
fracture-initiation pressure is 8.5MPa. A length of the horizontal section of
the dual
horizontal wells in the oil reservoir is provided at 400 meters, with wellhole
diameter
of 8.5in, 5 meters well spacing of the dual horizontal wells, and production
horizontal
wells are located 1 meter above the basement rock at the bottom. 80 cubic
meters of
xylene is injected into the dual horizontal wells respectively, and
subsequently, 117
cubic meters of water is injected into each of the dual horizontal wells in 5
days in
total, then nitrogen is injected from the respective well annulus of the dual
horizontal
wells, the water is drained from the pipe strings in wells, the well annulus
pressure is
progressively reduced, and finally, steam is injected from the respective long
pipe
string of the dual horizontal wells, the returned liquid is circulated in the
short pipe
strings, where the steam-injection pressure is 4MPa, underground steam flow
rate is
75 cubic meter/day, steam quality is 95% at wellhead, and it determines after
the
circulation in 2 months that good communications occur between the dual
horizontal
wells, the effective production rate of the horizontal section of the dual
horizontal
wells reaches 90%, normal SAGD productions are switched after switching to
half
SAGD transition. Relative to other neighboring well groups using a
conventional
method, the circulation preheating time is shortened by nearly 10 months.
The method for communication of dual horizontal wells in the present
application is
injecting solvents into dual horizontal wells, next, injecting water to
displace the
mixture formed of solvents and heavy oil, thus gradually forming a high water-
cut
region centered on wellbores, and then injecting steam into the dual
horizontal wells
for circulation. Since the high water-cut region enlarges a radius of a linear
heat
source, heat transfer distances between the dual horizontal wells are declined
to a
great extent, so that a rate of rise in temperature is substantially increased
between the
dual horizontal wells, as a result, the method in the application can
significantly
shorten communication time between the dual horizontal wells, so as to save a
large
amount of steam, in addition, a degree of uniformity of communication can also
be
enhanced dramatically between the dual horizontal wells.
14
CA 3012371 2018-07-25
At the same time, the method for communication of dual horizontal wells in
this
embodiment avoids a risk of a local priority communication of horizontal wells
by
strictly controlling the down-hole pressure to be less than the minimum
principal
stress, inter-well non-differential pressure operations, pressurized soaking
of the
solvents, sizes of the solvent fingering area and high water-cut regions, so
as to
enhance a degree of uniformity of communication.
In addition, finally, the method for communication of dual horizontal wells
provided
in this embodiment also implements the steam circulation preheating for a
predetermined time period (e.g., 3 months or so), which thus helps development
of
steam cavity and reservations of heat after switching to SAGD. Since the
solvents
injected in the early stage form a solvent fingering, the temperature rises
due to
conduction of heat in the later stage, both the solvents and the heat reduce
the
viscosity of crude oil above the steam-injection well in a collaborative
manner, which
facilitates development of a steam chamber after switching to SAGD and
improvement of production rate.
All disclosed articles and references, including patent applications and
publications,
are hereby incorporated by reference for all purposes. The term "consisting
essentially
of' to describe a combination shall include the element, ingredient, component
or step
that is being determined and other elements, ingredients, components or steps
that do
not essentially affect basic novel characteristics of the combination. Use of
the term
"comprising" or "including" to describe a combination of elements,
ingredients,
components or steps herein also contemplates embodiments that are
substantially
composed of those elements, ingredients, components or steps. Any property
described to demonstrate that a term "may" includes is selectable by use of
the term
"may" herein. A plurality of elements, ingredients, components or steps can be
provided by a single integrated element, ingredient, component or step.
Alternatively,
the single integrated element, ingredient, component, or step may be divided
into a
plurality of separated elements, ingredients, components, or steps. The
disclosure of
"a" or "an" to describe an element, an ingredient, a component, or a step is
not
intended to exclude other elements, ingredients, components, or steps.
The embodiments in the Description are described in a progressive manner, and
the
embodiments highlight the differences from another embodiment, referring to
the
identical or similar part between the embodiments mutually. The above
embodiments
are merely intent to illustrate the technical concept and characteristics of
the present
invention, and aim to allow for those skilled in the art to understand the
disclosure
contained in the present invention and implement the present invention based
thereon,
and it is not intent to limit the protection scope of the present invention.
Any
equivalent change or modification in accordance with the spirit of the
invention is
intent to be covered by the protection scope of the present invention.
CA 3012371 2018-07-25
