U.S. patent application number 12/815001 was filed with the patent office on 2010-12-30 for pattern steamflooding with horizontal wells.
This patent application is currently assigned to CONOCOPHILLIPS COMPANY. Invention is credited to Wendell Peter MENARD.
Application Number | 20100326656 12/815001 |
Document ID | / |
Family ID | 43379461 |
Filed Date | 2010-12-30 |
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United States Patent
Application |
20100326656 |
Kind Code |
A1 |
MENARD; Wendell Peter |
December 30, 2010 |
PATTERN STEAMFLOODING WITH HORIZONTAL WELLS
Abstract
Processes and systems comprising a five-spot pattern of multiple
horizontal wells for increasing the efficiency of heated
vapor-assisted hydrocarbon recovery from subterranean viscous
hydrocarbon formations.
Inventors: |
MENARD; Wendell Peter;
(Katy, TX) |
Correspondence
Address: |
ConocoPhillips Company - IP Services Group;Attention: DOCKETING
600 N. Dairy Ashford, Bldg. MA-1135
Houston
TX
77079
US
|
Assignee: |
CONOCOPHILLIPS COMPANY
Houston
TX
|
Family ID: |
43379461 |
Appl. No.: |
12/815001 |
Filed: |
June 14, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61220731 |
Jun 26, 2009 |
|
|
|
Current U.S.
Class: |
166/272.3 ;
166/57 |
Current CPC
Class: |
E21B 43/086 20130101;
E21B 43/305 20130101; E21B 43/24 20130101 |
Class at
Publication: |
166/272.3 ;
166/57 |
International
Class: |
E21B 43/24 20060101
E21B043/24 |
Claims
1. A process for recovering viscous hydrocarbons from an
underground hydrocarbon formation, comprising the following steps:
a) drilling a "production unit" comprising three separate and
adjacent wellbores into an underground formation containing viscous
hydrocarbons; b) extending each of the three wellbores through said
formation in a substantially horizontal direction for a distance
greater than thirty meters; said horizontal portion of each
wellbore being substantially parallel to the other two wellbores in
both horizontal and vertical planes; c) inserting a tubular liner
into each well comprising periodic sections of liner containing one
or more orifices, separated by multiple sections of liner without
orifices; d) inserting tubing with a closed end into each wellbore
inside of the liner, wherein the tubing contains periodic orifices,
and wherein the annular space between the outer wall of the tubing
and the inner wall of the liner on either side of each periodic
tubular orifice is isolated from the remainder of the wellbore by a
device that restricts flow through the annular space; e) injecting
heated vapor into the tubing present in the first and third
wellbores, such that the vapor enters the formation and reduces the
viscosity of the viscous hydrocarbons contained therein; f)
collecting hydrocarbons exiting the formation via periodic orifices
in the tubular liner present in the second wellbore, wherein the
second wellbore utilized for hydrocarbon production is centrally
located between injection wellbores one and three when viewed from
above, and wherein the second wellbore is approximately equidistant
to the two adjacent injection wellbores.
2. The process of claim 1, wherein the periodic orifices in the
tubular liners of the three adjacent wellbores comprising a
production unit are positioned relative to each other such that
when viewed from above, a five-spot pattern is formed, with each
collection orifice in the tubular liner of wellbore two being
encircled by four substantially equidistant steam injection
orifices consisting of two orifices in the tubular liner of
wellbore one and two orifices in the tubular liner of wellbore
three.
3. The process of claim 2, wherein the three adjacent wellbores
comprising a production unit are located in a substantially
horizontal plane.
4. The process of claim 2, wherein the third well of a first
production unit serves as the first well of a second, adjacent
production unit.
5. The process of claim 4, wherein multiple, adjacent production
units are drilled to cover the width of an entire formation
containing viscous hydrocarbons.
6. The process of claim 2, wherein the multiple periodic liner
orifices utilized for either injection of heated vapor or for the
production of hydrocarbons comprise a member of the group
consisting of mesh screens, wire-wrap screens, perforations or
slots.
7. The process of claim 2, wherein prior to production from
wellbore two, heated vapor is first injected simultaneously into
all wellbores until the viscous hydrocarbons present in the
underground formation reach a temperature where recovery of the
hydrocarbons as a liquid is possible.
8. The process of claim 2, where the distance between injection
points in the five-spot pattern is between 10 and 500 meters.
9. The process of claim 2, where the distance between injection
points in the five-spot pattern is between 25 and 300 meters.
10. A system for injecting heated vapor into a formation containing
viscous hydrocarbons, and recovering hydrocarbons from the same
formation, comprising: a) a "production unit" of three separate and
adjacent wellbores drilled into an underground formation containing
viscous hydrocarbons; i. wherein each of the three wellbores is
drilled through said formation in a substantially horizontal
direction for a distance greater than 30 meters; said horizontal
portion of each wellbore drilled substantially parallel to the
other two wellbores in both horizontal and vertical planes; ii. and
wherein the substantially horizontal section of each wellbore is
uncased; iii. and wherein the second wellbore is utilized for
hydrocarbon production and centrally located between the first and
third wellbores when viewed from above; iv. and wherein the first
and third wellbores are utilized for injection of steam into the
formation; b) tubing with a closed end inserted into each wellbore,
wherein said tubing contains periodic orifices, said orifices being
selected from the group consisting of slots, perforations, or
wire-wrap screens, or wire mesh screens; c) a device that regulates
the flow of heated vapor through the annulus formed between the
injection tubing and the liner wall on either side of each periodic
injection orifice; d) a device for regulating the flow of
hydrocarbons through the annulus formed between the production
tubing and the liner wall on either side of each periodic
production orifice.
11. The system of claim 10, wherein said device for regulating the
flow of hydrocarbons comprises a device selected from the group
consisting of mechanically-set packers, hydraulically-set packers,
inflatable packers or seals.
12. The system of claim 10, wherein the periodic orifices of the
three adjacent wellbores comprising a production unit are
positioned relative to each other such that when viewed from above,
a five-spot pattern is formed, with each collection orifice in the
liner of wellbore two being encircled by four substantially
equidistant steam injection orifices consisting of two orifices in
the liner of wellbore one and two orifices in the liner of wellbore
three.
13. The system of claim 12, wherein the three adjacent wellbores
comprising a production unit are located in a substantially
horizontal plane.
14. The system of claim 12, wherein the third well of a first
production unit serves as the first well of a second, adjacent
production unit.
15. The system of claim 14, wherein multiple, adjacent production
units are drilled to cover the width of an entire formation
containing viscous hydrocarbons.
16. The system of claim 12, wherein the multiple periodic liner
orifices in each well utilized for either the injection of heated
vapor or the production of viscous hydrocarbons comprise mesh
screens, wire-wrap screens, perforations, or slots.
17. The system of claim 12, wherein prior to production from
wellbore two, heated vapor is first injected simultaneously into
all wellbores until the viscous hydrocarbons present in the
underground formation reach a temperature where recovery of the
hydrocarbons as a liquid is possible.
18. The system of claim 12, where the distance between injection
points in the five-spot pattern is between 10 and 500 meters.
19. The system of claim 12, where the distance between injection
points in the five-spot pattern is between 25 and 300 meters.
Description
FIELD OF THE DISCLOSURE
[0001] The invention generally relates to improved methods and
apparatus for the recovery of viscious hydrocarbons from
underground formations. More specifically, it relates to methods
and apparatus for enhancing the recovery of viscous hydrocarbons
from a subterranean formation by steamflooding utilizing multiple
horizontal wells.
BACKGROUND
[0002] Steam and combustion processes have often been employed to
heat underground formations containing viscous hydrocarbon
deposits, thereby lowering the viscosity of the petroleum contained
within and providing a driving force to produce these viscous
hydrocarbons from a well. Steam injection methodology was
originally conducted using vertical wells. U.S. Pat. No. 5,014,784
describes a series of vertical injection wells in conjunction with
adjacent vertical production wells. U.S. Pat. Nos. 4,598,770,
4,727,937 and 5,957,202 describe multiple vertical injection wells
in conjunction with adjacent horizontal production wells. However,
viscous hydrocarbon recovery using vertical wells requires a high
well density (or number of wells per unit area), to effectively
recover the hydrocarbons in a timely and efficient manner. Vertical
well densities of 640 wells per square mile or more have been used
in the recovery of viscous hydrocarbons in California.
[0003] The use of horizontal drilling technology for viscous
hydrocarbon recovery is now well-established. An increased area of
contact between the wellbore and the formation can be achieved by
drilling wells with a substantially horizontal component
(typically, 300 to 2,000 meters, compared to 5-30 meters for a
typical vertical well). This large contact area allows viscous
hydrocarbon formations to be developed and recovered by far fewer
horizontal wells than are required in a vertical well development.
The final result is higher oil production rates from fewer wells.
Similarly, in a steam injection process, a single horizontal
injection well can deliver more steam over a wider area of the
viscous oil reservoir than many vertical wells, thereby heating the
reservoir more efficiently.
[0004] Some older viscous hydrocarbon recovery methods involve
injection of steam through either orifices in the casing or the
tubing, such as multiple sections of tubing containing multiple,
parallel slots (known as slotted liners), with single horizontal
wellbores serving as both the injection and production well. This
is commonly known as the "huff and puff" technique. Unfortunately,
these single wellbore techniques do not allow simultaneous steam
injection and hydrocarbon production. Consequently, more recently
developed methodologies involve the use of multiple horizontal
wells. U.S. Pat. No. 4,574,884 describes a method for drilling
multiple substantially parallel horizontal wells, where fluid
communication is established between the wells and injection of
steam into one well provides the driving force for production of
hydrocarbons from an adjacent well. U.S. Pat. No. 4,700,779
describes a more elaborate method for drilling at least four
substantially parallel horizontal wells, followed by injection
and/or production from different wells within the group. What is
lacking in these methods is a way to effectively control the entry
of steam into the formation, thereby maximizing the overall
percentage of hydrocarbons recovered.
[0005] As the viscous hydrocarbons within a formation are heated,
gravity generally causes the downward flow of these heated
hydrocarbons within the formation. Some methodologies for
recovering viscous hydrocarbons incorporate this phenomenon, known
as "steam-assisted gravity drainage" (SAGD). U.S. Pat. No.
4,577,691 describes drilling a series of parallel horizontal wells
that are vertically-spaced, with each well designed such that it is
simultaneously possible to both inject steam and produce
hydrocarbons. Initially, steam is injected through one or more
upper wells, and heated viscous hydrocarbons are recovered from
progressively lower wells. U.S. Pat. No. 5,244,041 and U.S. Pat.
App. 2007/0295499A1 describe methods that utilize SAGD by drilling
multiple pairs of horizontal wells, with each pair spaced
vertically. These references also describe the injection of steam
to induce lateral flow of viscous hydrocarbons between adjacent
well pairs. Similarly, U.S. Pat. No. 6,257,334 describes a pair of
vertically-spaced horizontal wells, along with a single, laterally
offset horizontal well used for injection. U.S. Pat. Nos. 4,850,429
and 5,803,171 describe methods that utilize SAGD by drilling a
group of parallel horizontal wells, with adjacent wells alternating
between higher and lower depths within the hydrocarbon-bearing
formation. Steam is initially injected into the upper wells, and
production initiated in the lower, adjacent wells.
[0006] Premature breakthrough of steam is a problem that has
plagued multiple well steam injection methodologies since their
inception. While this problem is a nuisance in vertical well
pattern steam flooding, it can be catastrophic in horizontal well
steamflooding. In the case of vertical well steam flooding, there
are many wells (injection wells and production wells), and the flow
rate of each well can be controlled independently at the well head,
so as to balance the patterns and achieve maximum oil production
with minimum of steam production. This level of control at the
surface is not usually possible in the case of horizontal well
steam flooding, where each horizontal well is akin to a line of
many vertical wells with only one common well head. This makes it
highly desirable to control both the rate and distribution of steam
injection along horizontal injector well bores, as well as
production distribution of viscous hydrocarbons along horizontal
producer well bores. Consider pair of 1000-meter long horizontal
wells, one serving as a production well and the other an injection
well. If steam from the injection well breaks through to the
production well prematurely, (i.e., early in the viscous
hydrocarbon recovery effort) it is likely that the majority of the
viscous hydrocarbons between the two wells will remain unrecovered
because the steam would continue to flow preferentially along this
same path, leaving the majority of the formation unexposed to the
steam, and therefore unheated (FIG. 1A). U.S. Pat. No. 5,141,054
discusses a method to promote uniform steam injection distribution
along the length of a horizontal steam injection well using a
limited number of perforations. Spacing a limited number of
perforations along the injection well bore limits the amount of
steam that can be injected in any one location along the well
bore--the perforation acts as a choke that limits the flow to the
path of least resistance, thereby allowing the steam to exit other
perforations along the wellbore instead of all exiting in one
place. However, while this method addresses the uniform
distribution of steam into the formation from an injection well, it
does not address regulating the entry of mobilized viscous
hydrocarbons into the production well. This is an important
additional consideration if the efficiency of viscous hydrocarbon
recovery is to be maximized (FIG. 1B).
[0007] Concern over the environmental impact of subterranean
hydrocarbon recovery has grown recently, especially in regards to
fragile biomes such as the north slope region of Alaska. Thus,
there is an increased societal demand for drilling and recovery
methodologies that minimize impact on the environment. U.S. Pat.
No. 5,014,784 discusses methods for recovering viscous oil through
the use of multiple wells. The methods involve drilling multiple
vertical steam injection wells, then producing viscous hydrocarbons
from adjacent vertical wells. U.S. Pat. No. 4,598,770 combines the
use of vertical wells for steam injection with recovery from
multiple adjacent horizontal production wells. The end result of
these strategies is a relatively large land surface "footprint"
required for drilling and recovery of hydrocarbons, which is often
considered unsightly and overly damaging to the local ecosystem.
Any reduction in the surface "footprint" required for hydrocarbon
drilling and recovery operations would certainly be of benefit to
the environment and may facilitate the exploration for hydrocarbons
in areas of the Earth where the local ecosystem might be deemed too
fragile to explore using conventional techniques.
[0008] What is needed are methods that maximize recovery of viscous
hydrocarbons from underground formations by simultaneously
promoting an even, regulated distribution of steam into a given
viscous hydrocarbon-producing reservoir and an even, regulated
distribution of produced fluids from the same reservoir.
Simultaneously, these methods must minimize the environmental
impact of land-based oil drilling and production operations, given
the fragile nature of the natural environment where a significant
percentage of this activity currently takes place.
BRIEF DESCRIPTION
[0009] The present invention describes a method for maximizing the
recovery of viscous hydrocarbons from an underground formation
using steam injection. A "production unit" comprising at least
three adjacent horizontal wellbores is drilled into a formation
containing viscous hydrocarbons. In certain embodiments, said three
wells all contain a substantially horizontal component extending
for at least 30 meters, In certain embodiments, the three wells are
substantially parallel to each other when viewed from above. In
certain embodiments, the three wells are located near the bottom of
the hydrocarbon-producing formation. In certain embodiments, the
central production well is located in substantially the same
horizontal plane as the two outer steam injection wells.
[0010] In certain embodiments of the current invention, pressurized
steam is passed directly into the formation via periodic orifices
in the liner of the two injection wells. On either side of each
periodic orifice within the wellbore, a device is placed that can
restrict steam flow through the annular space between the tubing
and the wellbore wall. These flow restriction devices may comprise
mechanical or hydraulically-actuated packers, inflatable packers,
or other types of seals that can effectively restrict the point of
steam entry into the formation to relatively small periodic regions
comprising less than twenty-five percent of the length of the
entire wellbore.
[0011] The injected steam enters the formation and transfers heat
to the viscous hydrocarbons in the formation, lowering the
viscosity of the hydrocarbons and providing a force to cause
migration of the hydrocarbons in a generally lateral and/or
downward direction towards the periodic inlet orifices in the
central production well located between the two injection wells
(when viewed from above). In certain embodiments, the periodic
orifices in the injection and production wells are spaced in a
five-spot pattern comprising a central production orifice,
surrounded by four injection orifices (two orifices provided by
each adjacent injection well) that are approximately equidistant
from the central production orifice. In preferred embodiments, the
four injection orifices are also approximately equidistant from
each other. This five-spot pattern arrangement is designed to
maximize the time that steam injection into the formation can
continue before steam breakthrough to the production well.
[0012] The disclosure provided herein describes a method for
recovering viscous hydrocarbons from a subsurface formation that
increases the efficiency of hydrocarbon recovery while also
minimizing environmental impact. In certain preferred embodiments,
the production process described herein requires far fewer wells
than a viscous hydrocarbon recovery process utilizing vertical
wells for periodic steam injection. Thus, the ground surface
"footprint" required for hydrocarbon recovery is minimized, as well
as the resultant environmental impact.
[0013] For the purposes of this disclosure, the term "liner"
describes a cylindrical pipe inserted into a wellbore for
maintaining wellbore integrity, and controlling production of sand
and sediment along with the produced hydrocarbons; "Liner" also
facilitates the selective distribution of steam into the formation,
and selective recovery of hydrocarbons via periodic orifices in the
liner.
[0014] For the purposes of this disclosure, the term "tubing" is
defined as a cylindrical tubing that is inserted inside of the
liner and either facilitates transport of steam into the formation,
or transport of hydrocarbons out of the well.
[0015] For the purposes of this disclosure, the term "wellbore" is
synonymous with "well", as both terms describe a hole drilled into
the earth at any angle using conventional drilling equipment.
[0016] For purposes of this disclosure, the terms "uncased well" or
"openhole completion" are defined as a wellbore in which the
portion of the wellbore utilized for production is not protected by
a conventional well casing. In most horizontal wells, this area
represents the substantially horizontal section of the well that
penetrates the formation containing recoverable hydrocarbons.
[0017] For the purposes of this disclosure, the terms "steamflood"
or "steamflooding" are synonymous with "steam injection", as all of
these terms describe a technique by which steam is injected into an
underground formation to cause increased flow of viscous
hydrocarbons.
[0018] For the purposes of this disclosure, the term "five-spot
pattern" is synonymous with any pattern which when viewed from
above, has five distinct points, with a central point surrounded by
four points that are approximately equidistant from the central
point, and approximately equidistant from each other.
[0019] For the purposes of the current disclosure, the term
"substantially" is defined as a being as close to the desired
outcome as is feasible utilizing currently available
technology.
[0020] For purposes of the current disclosure, the term "viscous
hydrocarbon" is synonymous with the terms "heavy oil", "bitumen",
"tar", "tar sands" or "asphaltic substance".
[0021] For purposes of the current disclosure, the term
"hydrocarbon-bearing formation" is synonymous with any underground
formation containing hydrocarbons, including viscous oil.
[0022] For purposes of the current disclosure, the term "horizontal
well" is synonymous with any well that extends underground and has
a substantially horizontal component extending greater than 30
meters.
[0023] In certain embodiments, the current disclosure describes a
process for recovering viscous hydrocarbons from an underground
hydrocarbon formation, comprising the steps of: a) drilling a
"production unit" comprising three separate and adjacent wellbores
into an underground formation containing viscous hydrocarbons; b)
extending each of the three wellbores through said formation in a
substantially horizontal direction for a distance greater than
thirty meters; said horizontal portion of each wellbore being
substantially parallel to the other two wellbores in both
horizontal and vertical planes; c) inserting a tubular liner into
each well comprising periodic sections of liner containing one or
more orifices, separated by multiple sections of liner without
orifices; d) inserting tubing with a closed end into each wellbore
inside of the liner, wherein the tubing contains periodic orifices,
and wherein the annular space between the outer wall of the tubing
and the inner wall of the liner on either side of each periodic
tubular orifice is isolated from the remainder of the wellbore by a
device that restricts flow through the annular space; e) injecting
heated vapor into the tubing present in the first and third
wellbores, such that the vapor enters the formation and reduces the
viscosity of the viscous hydrocarbons contained therein; and f)
collecting hydrocarbons exiting the formation via periodic orifices
in the tubular liner present in the second wellbore, wherein the
second wellbore utilized for hydrocarbon production is centrally
located between injection wellbores one and three when viewed from
above, and wherein the second wellbore is approximately equidistant
to the two adjacent injection wellbores. In certain embodiments,
the three adjacent wellbores comprising a production unit may be
placed in a substantially horizontal plane.
[0024] The current disclosure also describes a system for injecting
steam into a formation containing viscous hydrocarbons, and
recovering hydrocarbons from the same formation, comprising: a) a
"production unit" of three separate and adjacent wellbores drilled
into an underground formation containing viscous hydrocarbons;
wherein each of the three wellbores is drilled through said
formation in a substantially horizontal direction for a distance
greater than 30 meters; said horizontal portion of each wellbore
drilled substantially parallel to the other two wellbores in both
horizontal and vertical planes; and wherein the substantially
horizontal section of each wellbore is uncased; and wherein the
second wellbore is utilized for hydrocarbon production and
centrally located between the first and third wellbores when viewed
from above; and wherein the first and third wellbores are utilized
for injection of steam into the formation; b) tubing with a closed
end inserted into each wellbore, wherein said tubing contains
periodic orifices, said orifices being selected from the group
consisting of slots, perforations, or wire-wrap screens, or wire
mesh screens; c) a device that regulates the flow of steam through
the annulus formed between the injection tubing and the liner wall
on either side of each periodic injection orifice; d) a device for
restricting the flow of hydrocarbons through the annulus formed
between the production tubing and the liner wall on either side of
each periodic production orifice.
[0025] In certain embodiments of both the process and system, the
periodic orifices in the tubular liners of the three adjacent
wellbores comprising a production unit are positioned relative to
each other such that when viewed from above, a five-spot pattern is
formed, with each collection orifice in the tubular liner of
wellbore two being encircled by four substantially equidistant
steam injection orifices consisting of two orifices in the tubular
liner of wellbore one and two orifices in the tubular liner of
wellbore three. In certain embodiments of the process and system,
the three adjacent wellbores comprising a production unit are
placed in a substantially horizontal plane.
[0026] In certain embodiments of both the process and system, the
distance between the periodic orifices in the five-spot pattern is
between 10 and 500 meters, and may be between 25 and 300 meters. In
certain embodiments of the process and system, the third well of a
first production unit serves as the first well of a second,
adjacent production unit, and multiple adjacent production units
are drilled to cover the width of an entire formation containing
viscous hydrocarbons.
[0027] In certain embodiments of both the process and system, the
periodic liner orifices in each tubular liner utilized for the
injection of vapor may comprise a member of the group consisting of
mesh screens, wire-wrap screens, perforations or slots. Similarly,
the periodic liner orifices in the second well utilized for
production of hydrocarbons may comprise a member of the group
consisting of mesh screens, wire-wrap screens, perforations or
slots. In certain embodiments of the method and system, steam is
first injected simultaneously into all wellbores prior to
production from wellbore two, until the viscous hydrocarbons
present in the underground formation reach a temperature where
recovery of the hydrocarbons as a liquid is possible.
[0028] In certain embodiments of the process, the annular space
between the outer wall of the tubing and the inner wall of the
liner on either side of each periodic orifice in the liner is
isolated from the remainder of the wellbore by a device that
restricts flow through the annular space. The device may comprise a
member of the group consisting of mechanically-set packers,
hydraulically-set packers, inflatable packers, or seals. In
injection wells, the device serves to restrict the flow of heated
vapor down the annulus, while in production wells, the device
serves to restrict the flow of recovered heated viscous
hydrocarbons down the annulus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Advantages of the present invention will become apparent to
those skilled in the art with the benefit of the following
description and upon reference to the accompanying drawings.
[0030] FIG. 1A shows a typical result of an uncontrolled
steamflooding process utilizing multiple adjacent horizontal wells.
The unregulated entry of steam into the formation via the injector
wells (top and bottom) often results in premature breakthrough of
steam to the production well (central), thereby limiting recovery
of the remaining heavy oil located between the wells. FIG. 1B shows
an expected drainage of heavy oil from a formation utilizing an
embodiment of the current invention. Regulated, periodic entry of
steam into the formation and regulated periodic recovery points
function together to maximize the recovery of heavy oil prior to
steam breakthrough at the production well.
[0031] FIG. 2 shows examples of conventional steam injection
methodologies, wherein vertical injection wells are combined with
vertical production wells (FIG. 2A), vertical injection wells are
combined with horizontal production wells (FIG. 2B), or horizontal
injection wells are combined with established vertical production
wells (FIG. 2C).
[0032] FIG. 3A is a schematic overhead view of an embodiment of the
current invention, illustrating a "production unit" comprising
three adjacent horizontal wells, and showing the five-spot pattern
established between each orifice in a production well and the
surrounding four injection points supplied by the adjacent
injection wells. FIG. 3B is a schematic cross-sectional end view of
an embodiment of the current invention showing the positioning of
the adjacent horizontal wells of a "production unit" at different
depths within the hydrocarbon-bearing formation. FIG. 3C is a
schematic end-view showing the positioning of the adjacent
horizontal wells of a "production unit" in substantially the same
horizontal plane within the hydrocarbon-bearing formation.
[0033] FIG. 4 is a schematic view of an embodiment of the current
invention, showing adjacent, overlapping "production units" wherein
the third well of the first "production unit" simultaneously serves
as the first well of the second "production unit".
[0034] FIG. 5 is a close-up schematic view of an embodiment of the
current invention, wherein steam is distributed downhole via a
segment of perforated liner (FIG. 5A), slotted liner (FIG. 5B),
mesh screen (FIG. 5C), or wire-wrap screen (FIG. 5D), wherein the
annular space between the outer wall of the tubing and the inner
wall of the liner on either side of each periodic tubular orifice
is isolated by a device that restricts flow through the annular
space (packers are shown).
[0035] FIG. 6 is a close-up schematic view of an embodiment of the
current invention, wherein hydrocarbons are collected at an orifice
in the liner of a production well via a segment of perforated liner
(FIG. 6A), slotted liner (FIG. 6B), mesh screen (FIG. 6C), or liner
with a wire-wrap screen (FIG. 6D), wherein the annular space
between the outer wall of the tubing and the inner wall of the
liner on either side of each periodic tubular orifice is isolated
by a device that restricts flow through the annular space (packers
are shown).
[0036] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof are shown by
way of example in the drawings. The drawings may not be to scale.
It should be understood that the drawings and their accompanying
detailed descriptions are not intended to limit the scope of the
invention to the particular forms or embodiments depicted, but
rather, the intention is to cover all modifications, equivalents
and alternatives falling within the spirit and scope of the present
invention as defined by the appended claims.
DETAILED DESCRIPTION
[0037] A typical, uncontrolled steamflooding process utilizing
multiple adjacent horizontal wells is depicted in FIG. 1A. The
unregulated entry of steam into the formation via the injector
wells (10, 11) often results in premature breakthrough of steam to
the central production well (12), thereby limiting recovery of the
heavy oil located between the wells (13). FIG. 1B shows a
hypothetical drainage pattern of heavy oil from a formation
utilizing an embodiment of the current invention. Regulated,
periodic entry of steam into the formation (15) and regulated
periodic recovery points (16) function together to maximize the
recovery of heavy oil prior to steam breakthrough at the production
well.
[0038] FIG. 2 depicts examples of conventional steam injection
methodologies. In FIG. 2A vertical injection wells (black
triangles) are combined with vertical production wells (open
circles). In FIG. 2B, vertical injection wells (open triangles) are
combined with horizontal production wells (solid black lines).
Finally, in FIG. 2C, a horizontal injection well (solid black line)
is combined with two established vertical production wells (open
circles).
[0039] The disclosure provided herein comprises a process and
system for heated vapor-assisted recovery of viscous hydrocarbons
from a subsurface formation. FIG. 3A depicts an embodiment of the
current invention from an overhead view, and illustrates a
"production unit" consisting of three adjacent, parallel, and
substantially co-extensive horizontal wells. Each well has a well
head (17) and is drilled downward through the overburden and into a
formation containing viscous hydrocarbons, whereupon the direction
of the drilling is altered using established directional drilling
technology until the direction of drilling is substantially
horizontal. The wellbores are extended in a substantially
horizontal direction through the hydrocarbon-bearing formation for
a distance of between 30 and 5,000 meters. The periodic orifices in
the liner of the injection and production wells are preferably
spaced in a five-spot pattern that centers around each inlet
orifice in the production well. The perimeter of the "five-spot"
pattern is outlined by a dashed line (18), and comprises a central
production orifice (19) surrounded by four injection orifices (20)
(i.e., two orifices present in the liner of each adjacent injection
well [20]) that are approximately equidistant from the central
production well orifice (19). In certain preferred embodiments,
these four surrounding injection orifices are also approximately
equidistant from each other.
[0040] In certain embodiments, pressurized steam is passed directly
into the formation via periodic orifices in the liner of the two
outer wells of the "production unit". The injected steam enters the
formation and transfers heat to the viscous hydrocarbons in the
formation, lowering the viscosity of the hydrocarbons and providing
a force to cause migration of the hydrocarbons in a generally
lateral and/or downward direction towards the periodic inlet
orifices in the central production well located between the two
injection wells. The five-spot pattern arrangement, in combination
with the restricted entry of steam from the injection orifices into
the formation, is designed to maximize the time that steam
injection into the formation can continue before steam breaks
through to an orifice on the production well.
[0041] In certain embodiments, the distance between wells in the
five-spot pattern may range between 10-500 meters, in other
embodiments may range between 25-300 meters, and in still other
embodiments may range between 50-200 meters. In general, the
relationship of the distance between injection orifices and the
central production orifice is defined by the Pythagorean theorem.
For example, if the distance between injection wells is set at 100
meters, the distance between each injection well and the central
production well is equal to the length of the hypotenuse of a right
triangle with two sides, each 50 meters in length. In this example,
the length of the hypotenuse equals the square root of
(50.sup.2+50.sup.2), or 70.71 meters.
[0042] FIG. 3B depicts a cross-sectional end view of one embodiment
of the current invention, wherein the central production well (21)
of the "production unit" is located at a lower depth than the
adjacent injection wells (22). FIG. 3C depicts a cross-sectional
end view of one embodiment of the current invention, wherein the
central production well (23) of the "production unit" is located at
substantially the same depth in the formation as the adjacent
injection wells (24).
[0043] In certain embodiments, a "production unit" consisting of
three wells may effectively overlap with an adjacent production
unit. FIG. 4 illustrates that the third well of a first production
unit (25) may simultaneously serve as the first injection well of
an adjacent production unit. Subsequent additional production units
may be extended laterally from a first production unit in this
overlapping manner in order to cover an entire formation containing
viscous hydrocarbons, thereby increasing the efficiency of
hydrocarbon recovery.
[0044] The first and third wells of the "production unit" are
injection wells, utilized for injecting steam under pressure into
the formation (FIG. 5). Liner containing periodic orifices is
inserted into the injection wellbores (26), followed by the
insertion of tubing (27) containing periodic orifices that are
placed in sufficiently close proximity to the periodic orifices in
the liner to facilitate the passage of steam (28). The steam is
injected down the tubing, exiting at least one flow regulator (29),
then entering the formation via one or more adjacent periodic liner
orifices located in close proximity to the flow regulator (29). In
certain embodiments, these sections of liner containing one or more
orifices are placed between multiple sections of liner without any
openings (i.e., blank pipe), so as to regulate the injection of
steam into the formation in such a way as to prevent steam
breakthrough to the production well. In certain embodiments where
wells traverse stable formations, the periodic orifices in the
liner may comprise perforations (30) (FIG. 5A) instead of slotted
liner (31) (FIG. 5B). In certain embodiments where infiltration of
sediment and sand from the formation may interfere with injection,
the periodic liner orifices may comprise wire-mesh screens (32)
(FIG. 5C) or wire-wrapped screens (33) (FIG. 5D).
[0045] Adjacent to each flow regulator and one (or more) periodic
liner orifice(s), the annular space between the outer wall of the
tubing and the inner wall of the liner on either side of each
periodic tubular orifice is isolated from the remainder of the
wellbore by a device that restricts flow through the annular space
(34) (FIGS. 5A-D) to prevent unregulated flow of heated vapor down
the annulus. These devices may comprise mechanically or
hydraulically-actuated packers, inflatable packers, or other types
of seals that can largely prevent the unregulated passage of heated
vapor down the annulus. This system acts to restrict the entry of
steam into the formation to specific periodic openings in the
liner.
[0046] The second well of each "production unit" is a production
well (FIG. 6), utilized for recovery of hydrocarbons mobilized as a
consequence of heated vapor entering the formation through
injection wells one and three. Liner containing periodic orifices
is inserted into the production wellbore (35) followed by the
insertion of tubing (36) containing periodic orifices that are
placed in sufficiently close proximity to the periodic orifices in
the liner to facilitate the passage of mobilized viscous
hydrocarbons (37) first into the liner, then into a periodic
orifice in the tubing (38) for recovery. On either side of each
periodic tubing orifice, a device is placed to restrict steam flow
through the annular space between the tubing and the liner wall
(39). These flow restriction devices may comprise mechanically or
hydraulically-actuated packers, inflatable packers, or other types
of seals that restrict the passage of steam down the annulus. This
system restricts hydrocarbon recovery from the formation to
specific periodic openings in the liner, thereby increasing the
percentage of total hydrocarbons recovered from the formation prior
to breakthrough of injected, heated vapor at the production well
(35).
[0047] In certain embodiments, the sections of liner in a
production well containing one or more periodic orifices are placed
between multiple sections of liner without any openings (i.e.,
blank pipe), so as to regulate the recovery of hydrocarbons from
the formation. In certain embodiments where wells traverse stable
formations, the periodic orifices in the liner may comprise
perforations (40) (FIG. 6A) instead of slotted liner (41) (FIG.
6B). In certain embodiments where infiltration of sediment and sand
from the formation may interfere with injection, the periodic liner
orifices may comprise wire-mesh screens (42) (FIG. 6C) or
wire-wrapped screens (43) (FIG. 6D).
[0048] In certain embodiments of the current invention, pressurized
steam is passed into an underground formation containing viscous
hydrocarbons via periodic orifices in the liner of the injection
wells. The injected steam enters the formation and transfers heat
to the viscous hydrocarbons in the formation, thereby lowering the
viscosity of the hydrocarbons and also providing a force to assist
migration of mobilized hydrocarbons in a generally lateral and/or
downward direction towards the periodic inlet orifices in the
central production well. The quality and quantity of steam to be
injected is based upon both the relative porosity of the formation
and the relative viscosity of the hydrocarbons contained within the
formation. These variables also affect the optimal spacing between
the orifices comprising the five-spot pattern. The optimal spacing
of orifices and quantity of steam to be injected depends on several
factors related to the hydrocarbons (mainly its viscosity), the
hydrocarbon-bearing formation (its thickness, porosity,
permeability, temperature, and mechanical properties), the wells
(length, diameter, completion, and artificial lift equipment), and
the facilities (rate, temperature, and pressure limitations). In
general, to maintain the five-spot pattern as described, the
distance between periodic orifices in the liner of a given well
would be approximately the same as the distance between adjacent
horizontal wells in the "production unit".
[0049] The process described herein recovers viscous hydrocarbons
from a subsurface formation with increased efficiency while also
minimizing environmental impact. The overall land "footprint"
required by the current invention would be much smaller than
methods that utilize a exclusively vertical wells, or a combination
of vertical injection and horizontal production wells. In certain
preferred embodiments, the production process described herein
requires far fewer wells since each horizontal well can replace
multiple vertical wells for either injection or recovery. Thus, the
ground surface "footprint" required for hydrocarbon recovery is
minimized, as well as the resultant environmental impact.
[0050] In further embodiments, features from specific embodiments
may be combined with features from other embodiments. For example,
features from one embodiment may be combined with features from any
of the other embodiments. Additional features may be added to the
specific embodiments described herein without departing from the
spirit of the invention as described herein. Other embodiments of
the first through thirteenth widget sub-part may also be made
and/or used as is otherwise described herein.
[0051] Further modifications and alternative embodiments of various
aspects of the invention will be apparent to those skilled in the
art in view of this description. Accordingly, this description is
to be construed as illustrative only and is for the purpose of
teaching those skilled in the art the general manner of carrying
out the invention. It is to be understood that the forms of the
invention shown and described herein are to be taken as examples of
embodiments. Elements and materials may be substituted for those
illustrated and described herein, parts and processes may be
reversed and certain features of the invention may be utilized
independently, all as would be apparent to one skilled in the art
after having the benefit of this description of the invention.
Changes may be made in the elements described herein without
departing from the spirit and scope of the invention as described
in the following claims.
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