U.S. patent application number 15/475999 was filed with the patent office on 2017-10-05 for method for developing an oil bearing formation.
The applicant listed for this patent is SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Kreso Kurt Butula, Christopher Hopkins, Vladimir Viktorovich Malyshev, Vladimir Evgenievich Stashevsky, Sergei Vereschagin.
Application Number | 20170284179 15/475999 |
Document ID | / |
Family ID | 58452991 |
Filed Date | 2017-10-05 |
United States Patent
Application |
20170284179 |
Kind Code |
A1 |
Butula; Kreso Kurt ; et
al. |
October 5, 2017 |
METHOD FOR DEVELOPING AN OIL BEARING FORMATION
Abstract
Rows of horizontal production wells and rows of horizontal
injection wells are drilled and alternating in a formation. The
horizontal production wellbores and the horizontal injection
wellbores are placed in the direction of a minimum horizontal
stress in the formation. Within casing strings of the wells, at
least two hydraulic frac ports are installed and multi-stage
fracturing is performed through them in the production wells and in
the injection wells in such way that fractures are formed along
each production well and along each injection well in a direction
perpendicular to the horizontal wellbore, the hydraulic fractures
in the injection wells are offset from the hydraulic fractures in
the production wells. The production and the injection wells are
put into operation by injecting a fluid into the injection wells, a
flow rate and/or a volume of the injected fluid are controlled in
such a way that the injection pressure is below a fracturing
pressure.
Inventors: |
Butula; Kreso Kurt; (Moscow,
RU) ; Stashevsky; Vladimir Evgenievich; (Dubai,
AE) ; Malyshev; Vladimir Viktorovich; (Dubai, AE)
; Vereschagin; Sergei; (Tyumen, RU) ; Hopkins;
Christopher; (Paris, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHLUMBERGER TECHNOLOGY CORPORATION |
Sugar Land |
TX |
US |
|
|
Family ID: |
58452991 |
Appl. No.: |
15/475999 |
Filed: |
March 31, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 43/305 20130101;
E21B 43/26 20130101 |
International
Class: |
E21B 43/14 20060101
E21B043/14; E21B 43/16 20060101 E21B043/16; E21B 33/124 20060101
E21B033/124; E21B 34/06 20060101 E21B034/06; E21B 43/30 20060101
E21B043/30; E21B 43/26 20060101 E21B043/26 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2016 |
RU |
2016112172 |
Claims
1. A method for developing an oil bearing formation, the method
comprising: drilling within the formation alternating rows of
horizontal production wells and rows of horizontal injection wells,
the rows being placed at a first distance from each other, both
horizontal production wellbores and horizontal injection wellbores
are arranged in a direction of a minimum horizontal stress in the
formation so as to provide hydraulic fractures perpendicular to the
direction of the horizontal wellbores, providing at least two frac
ports at casing strings in the injection wells and in the
production wells, the frac ports being spaced at a second distance
from each other and providing fluid communication between the wells
and the formation, performing multi-stage hydraulic fracturing
through the frac ports in the production and the injection wells so
that multiple fractures are placed along each horizontal production
well and each injection well perpendicularly to the direction of
the horizontal wellbore, so that the hydraulic fractures of the
injection wells are offset from the hydraulic fractures of the
production wells by a third distance, putting the production and
the injection wells into operation by injecting a fluid into the
injector wells and controlling a fluid injection rate and/or a
fluid injection volume so that an injection pressure is maintained
below a fracturing pressure.
2. The method of claim 1, wherein the frac ports are capable of
repeated opening and closing, and the fluid injection rate and/or
the fluid injection volume are controlled by opening and closing
the frac ports.
3. The method of claim 1, wherein the hydraulic fractures of the
injection wells are offset from the hydraulic fractures of the
production wells by a half of the distance between the hydraulic
fractures.
4. The method of claim 1, wherein in case of an open hole completed
well each frac port is located between two frac packers is such way
that a distance between the frac packers is at least twenty times
less that the distance between the two neighboring frac ports.
5. The method of claim 2, wherein the frac ports are opened and
closed with a coiled tubing, rigid wire or/and a wireline tractor.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Russian Application No.
2016112172 filed Mar. 31, 2016, which is incorporated herein by
reference in its entirety.
BACKGROUND
[0002] This invention is related to oilfield industry and can find
use in secondary recovery methods such as water flooding (or other
methods of reservoir pressure support), where the field development
pattern design uses horizontal wells with multi stage fractures
(HWMSF) that are being drilled and completed in low to mid
permeability oil bearing reservoirs (k<100 md).
[0003] The completion design, including hydraulic fractures and the
wellbore hardware, the position, azimuthal orientation and spacing
of injector and producer wells are critical to the optimization of
hydrocarbon production and the recovery of reserves.
[0004] There are various current production-injection vertical well
pattern versions (5, 7, 9-spot) and modifications including
vertical wells, vertical fracture wells and horizontal production
wells with multi stage fractures (HWMSF).
[0005] The industry further evaluated a series of potential field
development patterns for fields under water flooding in relation to
the fracture propagation azimuth in order to achieve better
hydrocarbon recovery.
[0006] Thus, in SPE 162031 (I. S. Afanasiev et al., "Analysis of
multiple fracture horizontal well application of Priobskoe field"
ROGEPT Conference and Exhibition, Oct. 16-18, 2012) a direct line
drive pattern is described that has been designed with HWMSF placed
along the preferred fracture plane (wells and hydraulic fractures
are aligned to the maximum horizontal stress, .sigma..sub.max). The
HWMSF contains multiple longitudinal placed hydraulic fractures
spaced at a distance along the length of the horizontal well
section. Vertical water injection wells are drilled and
hydraulically fractured, in a row located at a distance from the
row of the production wells. The injection wells can be
intentionally hydraulically fractured or are fractured
unintentionally during water injection, when the water injection
occurs at formation face pressures above the fracture gradient.
[0007] Additional vertical production wells are located within the
injection row and hydraulically fractured, but later in the
production life of the reservoir will be converted to injection
wells.
[0008] The position of the fractures in the HWMSF and the injection
wells are not positively controlled and there are no specific
requirements on the exact spacing of the fractures. This is
particularly valid for open hole horizontal well completion systems
where the horizontal well section is not cemented. There are no
specific requirements for the open hole packers spaced between the
frac ports.
[0009] The lower the permeability of a formation under secondary
recovery mechanism (such as for example--water flooding) the well
of above described pattern type becomes less effective and initial
production rates are lower compared to HWMSF with perpendicularly
oriented fractures.
[0010] Also a pattern is known (N. A. Veremko "Optimization
formation production in Western Siberia using HW MSF" Lukoil SPE
Moscow Section Presentation, 7th February, 2012) consisting of
HWMSF that contains a number of perpendicularly placed multiple
hydraulic fractures spaced at a distance along the horizontal
wellbore length. The pattern contains further vertical injection
wells and any additional vertical production wells and vertical
hydraulically fractured production wells in the injection row at a
distance from the production well row.
[0011] This field development pattern is a regular approach of
changing the existing field development pattern with vertical
hydraulic fractured wells, to HWMSF pattern, where a row of
vertical fractured injection wells is spaced in-between HWMSF.
Between the injection wells vertical or vertical hydraulic
fractured production wells may remain until later stage of field
development when some or all of the production may be converted to
injection wells.
[0012] The position of the fractures in the HWMSF and the injection
wells are not positively controlled and there are no specific
requirements on the exact spacing of the fractures. This is
particularly valid for open hole horizontal well completion systems
where the horizontal well section is not cemented. There are no
specific requirements for the open hole packers spaced between the
frac ports.
[0013] As a result of the above development pattern a high initial
production rate is expected. The drawback of the pattern is that
the reservoir pressure maintenance is poorly supported, and the
reservoir pressure is declining rapidly, and such the later
production rates. A water breakthrough from the injection wells to
production wells is very likely, unless the injection rates are
maintained under fracturing pressure.
[0014] Another known development pattern perusing the knowledge of
mechanical rock properties and geomechanics is described in the RF
Patent No 22515628 C1. The method is based on the knowledge of the
state of stress in Western Siberia, where the horizontal in-situ
stresses have very low difference in magnitude
(.sigma..sub.Hmax-.sigma..sub.Hmin<3%), creating a low
anisotropy environment under initial reservoir conditions. The
method is using the condition of changing reservoir pressure under
production and injection to target the timing of placing wells
under injection to maximize the effect of hydrocarbon sweep with
the water from water injection.
[0015] The drawback of the method is the subsurface complexity and
the modeling of the same for realistic conditions, and the repeated
conditions injection wells injecting water above the fracturing
pressure of the formation.
[0016] For the few above and other analyzed patterns where HWMSF
completed wells are used in the field/sector development, the
difficulty is to optimize a total oil recovery when adjusting
initial and late production rate.
[0017] It is an object of the present disclosure to provide a
method and a pattern for developing oil bearing formations with the
use of HWMSF completions in which the aforementioned disadvantages
of existing patterns are avoided.
SUMMARY
[0018] The disclosure provides for maximum hydrocarbon recovery for
a field or a field sector at initial and subsequent stages by
providing best reservoir contact through vertical and lateral
coverage of low permeability hydrocarbon bearing zones, it also
provides for highest production/injection rates, in other words the
highest productivity index (PI), by providing the lowest draw-down
requirements (in production wells) and the lowest injection
pressure (in injection wells). The method also provides the lowest
risk of premature water breakthrough, an option to control a water
injection rate and an option for potential re-fracturing of the
initial completion in case such requirement arise in the process of
the well exploitation.
[0019] According to the disclosed method rows of horizontal
production wells and rows of horizontal injection wells are drilled
in an oil-bearing formation, both horizontal production wellbores
and horizontal injection wellbores are arranged in a direction of a
minimum horizontal stress in the formation. The rows of horizontal
production wells and the rows of horizontal injection wells are
alternating and are placed at a first distance from each other.
[0020] At casing strings in the injection wells and in the
production wells at least two frac ports are disposed, the frac
ports provide fluid communication between the wells and the
formation and are spaced at a second distance from each other.
[0021] Multi-stage hydraulic fracturing of the production wells and
the injection wells is performed through the frac ports so that
multiple fractures are placed along each horizontal production well
and each injection well perpendicularly to the direction of the
horizontal wellbores, the fractures are spaced at the second
distance from each other and the hydraulic fractures of the
injection wells are offset from the hydraulic fractures of the
production wells by a third distance.
[0022] Then the production and the injection wells are put into
operation by injecting a fluid into the injection wells and
controlling a fluid injection rate and/or a fluid injection volume
so that an injection pressure is maintained below a fracturing
pressure.
[0023] According one embodiment the frac ports are capable of
repeated opening and closing, and the fluid injection rate and/or
the fluid injection volume are controlled by opening and closing
the frac ports.
[0024] According to another embodiment of the disclosure the
injection fractures are offset from the production fractures by a
half of the distance between the fractures.
[0025] According to another embodiment of the invention in case of
an open hole completion each frac port is placed between two frac
packers so that a distance between the two frac packers is at least
twenty times smaller than the distance between the frac ports.
[0026] The frac ports can be opened and closed with a coiled
tubing, rigid wire or/and a wireline tractor.
BRIEF DESCRIPTION OF DRAWINGS
[0027] The disclosure is explained by the figures where FIG. 1
shows a field development pattern in accordance with one embodiment
of the disclosure; FIG. 2 shows an example of disposing frac ports
in an open hole horizontal wellbore; FIG. 3 shows an example of
disposing frac ports in a cemented cased hole horizontal wellbore;
and FIG. 4 shows an example of production profiles and water cut
for the HWMSF according to the disclosure and to the prior art
methods.
DETAILED DESCRIPTION
[0028] Hydraulic fracturing is a primary tool for enhancing well
productivity by creating highly permeable artificial fractures
between a wellbore and a reservoir. Conventional methods of
hydraulic fracturing in general case are divided into acid, in
which a permeable fracture is created by chemical etching, or
propped, in which permeability is maintained using proppants which
can be artificial (ceramic, bauxite, plastics or other materials)
or natural (quartz sand). The conductivity is achieved mainly by
selecting proppants having desired concentration, size and
qualitative characteristics or by creating almost infinite number
of channels between propped fracture pillars. The disclosed method
is applicable for all types of hydraulic fracturing.
[0029] The disclosure suggests a field development pattern that
embodies HWMSF completions. HWMSF are horizontal wellbores
containing multiple hydraulic fractures along a horizontal section
of the wells. The arrangement of the fractures depend on the
azimuth of a minimum horizontal stress and position of the
horizontal wellbore in relation to the minimum horizontal stress.
There is a multitude of the completion options ensuring creation of
hydraulic fractures in the formation. A distinction is generally
made between wells with an open hole wellbore and wells with a
cemented horizontal wellbore.
[0030] According to the disclosed method, rows of horizontal
production wells and rows of horizontal injection wells are drilled
in an oil bearing formation, horizontal wellbores of the production
wells and of the injection wells are arranged in a direction of a
minimum horizontal stress in the formation so as to provide
propagation of hydraulic fractures perpendicular to the direction
of horizontal wellbores.
[0031] The rows of the injection wells and the rows of the
production wells are alternating and are placed at a certain
distance (hereinafter referred to as the first) from each
other.
[0032] The horizontal wellbores of the injection and the production
wells are placed in the direction of the minimal horizontal stress
in the formation, i.e parallel to the minimum horizontal stress or
at angle close to it, so as to provide propagation of hydraulic
fractures perpendicular to the direction of the horizontal
wellbores. This placement ensures hydraulic fractures in the
production wells and the injection wells at the initial wellbore
completion with HSMSF in a perpendicular orientation to the
orientation of the horizontal wellbore, thus ensuring high initial
production rates and a high hydrocarbon recovery factor. The angle
between the direction of the minimum horizontal stress and the
direction of the rows of horizontal wellbores depends on properties
of rocks of the formation, formation pressure and thickness and is
an acute angle not more than 20.degree. to the direction of the
minimal horizontal stress.
[0033] Then, at least two frac ports spaced at a distance
(hereinafter referred to as a second distance) from each other are
created in casing strings disposed in the injection wells and in
the production wells. The frac ports provide fluid communication
between the wells and the formation and are capable of repeated
opening and closing. Multi-stage hydraulic fracturing of the
production wells and the injection wells is made through the frac
ports so that multiple fractures are created along each horizontal
production well and each injection well perpendicularly to the
direction of the horizontal wellbore.
[0034] A field development plan usually involves drilling wells in
a special arrangement, so-called pattern, for which a location and
a number of production and injection wells is selected in
accordance with an enhanced oil recovery project. The pattern is
generated based on the location of existing wells, reservoir size
and shape, rock properties, reservoir fluids, cost of new wells and
the recovery increase associated with the various possible
injection and production wells in a pattern.
[0035] A distance between the hydraulic fractures and accordingly
between the frac ports, and a number of fractures are selected
based on the formation properties (permeability and porosity), the
completion type (cemented or open hole) and a length of a well.
Usually seven to eight hydraulic fractures are created, for which
an appropriate number of frac ports are installed, but the number
of fractures may reach 15-20 and even more.
[0036] The distance between the rows of the injector and the
production wells is selected based on certain formation properties
(permeability and porosity), and characteristics of the hydraulic
fractures (fracture length and conductivity).
[0037] Common injection patterns are direct line drive, staggered
line drive, two-spot, three-spot, four-spot, five-spot, seven-spot
and nine-spot. The patterns are called normal or regular when they
include only one production well per pattern. Patterns are
described as inverted when they include only one injection well per
pattern.
[0038] FIG. 1 represents an embodiment of the disclosure with a
direct line drive pattern having two rows of production wells and
one row of injection wells disposed between the two rows of the
production wells.
[0039] Each production well 1 in the two rows of the production
wells has several perpendicular fractures of multiple hydraulic
fracturing (f.sub.1, f.sub.2. . . f.sub.n), each fracture has a
length 2. The fractures are located at a certain (second) distance
3 from each other along a length 4 of the horizontal wellbore.
[0040] Each injection well 5 in the row of the injection wells has
several perpendicular fractures of multiple hydraulic fracturing
(i.sub.1, i.sub.2. . . i.sub.n), each fracture has a length 6. The
length 6 of each fracture in the injection well is equal to the
length 2 of each fracture in the production well. The fractures are
spaced at a distance 7 along a length 8 of the horizontal wellbore,
the distance 7 is equal to the distance 3 between the fractures of
the production wells. The row of the injection wells 5 is located
at a distance 9 with respect to each row of the production wells
1.
[0041] The fractures in the injection wells 5 are offset from the
fractures in the production wells 1 by a distance 10 ensuring that
the injection and production fractures do not overlap.
[0042] This is achieved by:
[0043] cementing the wells and perforating/jet blasting openings
through the casing and cement into the formation at the exact
predetermined spot in the cemented horizontal wells or,
[0044] placing frac ports in an open hole completion system at the
casing string within the wellbore at the exact predetermined spot.
The frac ports are isolated from the remaining horizontal wellbore
by open hole packers spaced closely to the frac port.
[0045] Thus accurate placement of initiated and created fractures
in the horizontal wellbore is provided, and therefore a direct
connection of the fractures of the injection and the production
wells is excluded, which minimizes the risk of early water
breakthrough into the production well.
[0046] The length 2 of the hydraulic fractures, the distance 7
between the fractures and the distance 9 between the rows of the
wells are typically optimized based on a horizontal permeability.
The hydraulic fractures in the horizontal section of the injection
wells are offset from the hydraulic fractures in the horizontal
section of the production wells by approximately half of the
distance between the fractures in the wellbore. In the currently
used development patterns this is not controlled and therefore the
fractures from the injection wells may be at a small distance from
the fractures from the production wells and hence may connect with
them, resulting in early water breakthrough into the production
well.
[0047] Frac ports disposed in a wellbore are being used to create
hydraulic fractures. The frac ports used in accordance with one
embodiment of the disclosure allow for multiple closing and opening
as needed. Opening and closing of the frac ports are performed by
special tools delivered by a flexible pipe of a coiled tubing or by
a wireline tractor. Frac ports from various manufacturers are
described in literature (patent application USA No 20140332228;
patent application USA No 20110204273; IPTC-18104 <<Case
Study: A challenging Large-scale fracturing in Sichuan
basin>>, Yuan F. et al., December 2014 r.; SPE163935
<<Reducing Water Volume in Multistage Fracturing Using
sliding Sleeves and CT deployed resettable frac Isolation>>,
Schlosser D. et al., March 2013 r.; <<Hydraulic Fracturing
innovations target strategic fracture placement, re-fracturing of
existing wells for next bump in recovery>>, Katie Mazerov,
Drilling Contractor, Jan. 27, 2015, prospect Schlumberger
<<Reclosable frac Sleeve>>
http://www.slb.com/.about./media/Files/stimulation/product_sheets/broadba-
nd/broadband_reclosable_fracturing_sleeve_ps.pdf, 2014).
[0048] In other cases the frac ports can be closed by cementing,
installation of the plates on the casings or other known
methods.
[0049] In the case of open hole completions (FIG. 2) a frac port 11
is placed on a casing 13 between two external packers 12 to ensure
initiation of a hydraulic fracture at a certain point of the
horizontal wellbore and to control position of the fracture. The
ports in the injection and in the production wells are disposed in
such way that the fractures created in the injection wells are
offset from the fractures of the production wells by a third
distance.
[0050] A distance 14 between the packers located near the frac port
11, is relatively small (approximately 2-5 m) compared to a
distance 16 between the frac ports, and accordingly to a distance
15 to the next open hole packer at the next frac port
(approximately more then 100 m). The recommended distance between
the two packers is approximately twenty times less than the
distance between the neighboring frac ports. The distance 16
between the frac ports 11 defines the distance between the
hydraulic fractures 17 (f1 . . . fn) in the horizontal wellbore.
This also allows to select re-fracture position during the well
operation. The same is true for the injection wells and their frac
ports.
[0051] The frac ports are of the type that can be opened and closed
multiple times.
[0052] The closing and opening operations of the frac ports 11 can
be fulfilled with the use of a flexible tube of a coiled tubing and
(or) a wireline and (or) a rigid wire or a wireline tractor. On
FIG. 2 it is shown that the frac port 11 is open, through this port
a hydraulic fracture in the formation was created and water
injection 18 takes place. The other frac port 19 is closed after
the fracture was created, and water injection is not taking place.
In case of extreme water influx the frac port 19 can be closed not
only on the injection well, but also the similar opposite frac port
in the production well can be closed. In the event of increased
water cut in the production well, the water flow can be reduced by
closing the responsible frac port on the injector wellbore or the
watered out frac port in the production well. This ensures
controlled water injection 18 and active formation pressure
control, which reduces the risk of increased water cut in the
production of the well.
[0053] The wellhead injection pressure is determined by calculating
the hydrostatic pressure of the injection water column, corrected
for the pressure loss from the hydraulic friction pressure caused
by the flow from pumping water through the wellbore and through the
perforations/ports; the resulting wellhead pressure should be below
the breakdown pressure at the bottom of the well. (Rose, S. C.,
Buckwalter, J. F., and Woodhall, R. J. 1989. The Design Engineering
Aspects of Waterflooding, Vol. 11. Richardson, Tex.: monograph
series, SPE; Perkins, T. K. and Gonzalez, J. A. 1985. The Effect of
Thermoelastic Stresses on Injection Well Fracturing. SPE J. 25 (1):
78-88. SPE-11332-PA). The injection rate at each port or
perforation hole can be controlled by logging tools, for example
using spinners and other flowmeters, run on a coiled tubing or
wireline tractor, or using distributed thermometry obtained from a
fiber optic cable. Based on the information obtained, using coiled
tubing or wireline tractor, one can selectively close one or
several ports through which excessive water was pumped during the
injection period, while at the same time redistributing the
injection through other ports where the flow rate was lower. As a
result, the water front distribution between the injection well and
the production well is more uniform.
[0054] The pattern shown on FIG. 2 relates to the completion in an
open hole HWMSF wells, but is equally valid for cemented horizontal
wellbores 21 in HWMSF completed wells (FIG. 3) where position of
the frac ports 11 connecting the wellbore with the formation, and
the distance 16 between the ports and respectively between the
hydraulic fractures 17 should be selected taking into account not
only their position within the horizontal wellbore itself, but also
the position relative to the next row of the HWMSF.
[0055] The pattern created according to the disclosed method allows
to optimize the production profile from HWMSF completed wells. On
FIG. 4 it is represented with the curve A. The described pattern,
where the HWMSF are used as injection and production wells ensures
high initial production rates and high rates at later stages.
Current patterns can provide either high initial production rates
or high later rates, but do not ensure both high initial and later
production rates.
[0056] The curve B on FIG. 4 characterizes a production profile of
a well with a direct line drive pattern as described in SPE 162031
where drilling of horizontal wells is produced on the basis of the
longitudinal orientation of fractures along the horizontal
wellbore. This pattern has a lower production rates at the initial
stage because of the reduced drainage area, but provides a
sufficiently high and stable subsequent debit. Due to more uniform
formation pressure maintenance, the pattern also provides a smaller
content of the produced water in subsequent stages of operation of
the well, as shown by curve D.
[0057] The curve C describes the production profile of a well from
a pattern as described by G. A. Veremko where horizontal wellbores
of the production wells are drilled along the maximum stress and
the fractures are perpendicular to the horizontal wellbore. The
injection wells are vertical wells placed between the horizontal
wells. This pattern will provide higher production rates at the
initial because of a larger drainage area. The deficiency of the
pattern is an insufficient pressure support from the injector wells
which leads to a fast production decline. In addition, the
injection leads to an uncontrolled fracture extension into the
drainage area of the production wells and to the fast growth of the
content of formation water in the production from a certain moment
of operation of the wells, as demonstrated by the curve E.
[0058] Both patterns do not provide for the use of horizontal wells
with multi stage fracturing as injector wells, and the injector
wells are typically vertical, slanted or S-shaped wells with or
without hydraulic fractures completions. The injection is typically
done at a pressure above the fracturing pressure of the formation
rock using water/fluids which temperature may be lower than the
static formation temperature, which causes a hydraulic and/or
temperature fracturing. These fracturing is uncontrolled and not
always intentional. It is called an automatic frac (in English
literature--"auto-frac").
[0059] The curve A is characterized by the highest initial
production rates (compared to curve B and C) which results from the
large drainage area and best contact with the formation through
vertical and lateral coverage of the low permeability hydrocarbon
bearing zones by using HWMSF. The disclosed pattern using HWMSF
both for production and injection wells provides the highest
productivity along with an optimal pressure maintenance at the
maximum replacement ratio of the void volume. As a result, the
initial production rate is higher compared to curve C, and the
reduction in the production rate is slower compared to the curve
B.
[0060] Further, the pattern consists of HWMSF production and
injection wells. The injection wells are put into operation by
injecting water (or brine, or other liquid for pressure support)
with control of a fluid injection rate and/or a fluid injection
volume to maintain an injection pressure below a fracturing
pressure of the formation, the volumes injected are controlled by
opening and closing the frac ports.
[0061] Within the secondary recovery method, the HWMSF injection
wells are drilled and completed at the same time as the production
HWMSF, in order to maintain the reservoir pressure after the start
of production. For adequate volume replacement of produced oil
under matrix flow conditions a suitable secondary recovery method
of development is required. Regulation of the injection rate allows
to avoid exceeding the fracture gradient and consequently prevents
non-controlled fracture extension from the injection wells towards
the production wells. This prevents rapid water breakthrough from
the injection well into the production well, which is characterized
by the curve F.
* * * * *
References