U.S. patent application number 12/582307 was filed with the patent office on 2010-06-24 for method and apparatus for sealing wells in co2 sequestration projects.
Invention is credited to HOMER L. SPENCER.
Application Number | 20100155085 12/582307 |
Document ID | / |
Family ID | 42122707 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100155085 |
Kind Code |
A1 |
SPENCER; HOMER L. |
June 24, 2010 |
METHOD AND APPARATUS FOR SEALING WELLS IN CO2 SEQUESTRATION
PROJECTS
Abstract
Method for forming a downhole plug within an abandoned well
casing for preventing the flow of gas through the plug and reaching
the surface, particularly for CO2 sequestration projects. A milling
tool mills out a longitudinal section of the perimeter of the well
casing and surrounding cement and detritus to expose the well bore.
A heater containing solid metallic alloy is lowered into the casing
and the alloy is melted so that it fills the milled out area and
flows into the face of the well bore. The heater is removed to
allow the alloy to solidify. The upper casing acts to restrain any
movement of the plug following solidification of the alloy.
Inventors: |
SPENCER; HOMER L.; (Calgary,
CA) |
Correspondence
Address: |
JOHN RUSSELL UREN
2431 Simpson Road
Richmond
BC
V6X 2R2
CA
|
Family ID: |
42122707 |
Appl. No.: |
12/582307 |
Filed: |
October 20, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61106936 |
Oct 20, 2008 |
|
|
|
Current U.S.
Class: |
166/386 ;
166/192 |
Current CPC
Class: |
E21B 41/0064 20130101;
E21B 33/134 20130101; Y02C 20/40 20200801; E21B 33/12 20130101;
Y02C 10/14 20130101 |
Class at
Publication: |
166/386 ;
166/192 |
International
Class: |
E21B 33/12 20060101
E21B033/12 |
Claims
1. A method of forming a metal alloy plug within the well casing of
a well bore of an abandoned oil or gas well to prevent the flow of
gas through said metal alloy plug comprising the steps of dropping
a casing milling tool down said well casing to a predetermined
depth within said well casing, said well casing having a plug below
said predetermined depth, milling out a longitudinal section of
said well casing and the well cement and detritus surrounding said
well casing and above said plug so as to expose the wall of said
well bore while leaving the upper portion of said well casing above
said milled out area and while leaving the bottom portion of said
well casing below said milled out area, removing said casing
milling tool and dropping a heater into said well casing to said
predetermined depth, said heater carrying a solid metallic alloy
plugging material, increasing the temperature of said heater to
melt said metallic alloy and maintaining said increased temperature
until said melted metallic alloy has flowed from said heater and
permeated said well bore to a desired depth, removing said heater
from said well casing and allowing said melted metallic alloy to
solidify within said well bore, said casing and said milled out
area.
2. Method as in claim 1 and further comprising applying pressure on
said liquid metallic alloy following said melting of said solid
metallic alloy and allowing said pressure to assist said melted
alloy to flow from said heater.
3. Method as in claim 2 wherein said metallic alloy comprises
bismuth as a principal component.
4. Method as in claim 1 wherein the quantity of melted metallic
alloy is sufficient to entirely fill said milled out area between
said upper and lower portions of said well casing, said upper well
casing restraining movement of said metal alloy plug following said
solidification of said metal alloy within said milled out area.
5. Apparatus used to form a metallic alloy plug within a well
casing, said apparatus comprising a milling tool used to mill out a
longitudinal section of a well casing at a predetermined depth
within said well casing and leaving the upper and lower portions of
said well casing above and below said milled out area and a heating
tool operable to carry solid metallic alloy billets, to melt said
billets at an elevated temperature of said heating tool to form
liquid alloy and to maintain said elevated temperature of said
heating tool until said liquid alloy flows into said milled out
area for a desired time period, said heating tool having a
connected power cable to supply power to said heating tool and to
lower and raise said heating tool within said well casing.
6. Apparatus as in claim 5 and further comprising means to apply
pressure on said liquid alloy to assist flow of said liquid alloy
from said heating tool and into said milled out area.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from provisional
application Ser. No. 61/106,936 filed Oct. 20, 2008 and entitled
METHOD AND APPARATUS FOR SEALING WELLS IN CO2 SEQUESTRATION
PROJECTS.
INTRODUCTION
[0002] This invention relates to a method and apparatus for the
sequestration of carbon dioxide and, more particularly, to the
sequestration of carbon dioxide from large fossil fuel burning
facilities.
BACKGROUND OF THE INVENTION
[0003] To prevent carbon dioxide (CO2) from entering the atmosphere
when large fossil fuel burning facilities are used, a proposed
solution is to capture the CO2, concentrate and compress it and
transport it to a depleted oil or gas field which is then used as a
storage vessel facility. The compressed CO2 is injected into the
depleted and depressurized geologic formation previously holding
oil or gas. The process is capital intensive and time consuming and
it clearly is only of value if the storage is permanent and there
is no leakage from the reservoir where the CO2 is injected. Fields
that may be satisfactory to hold the CO2 have defining
characteristics which include being closed and with no natural
fractures or permeable cap rock. These depleted fields also contain
numerous wells that have been abandoned following depletion. The
usual procedure of dealing with such abandoned wells includes
plugging the wells with cement and capping the well casings near
the surface with a sealed steel plate. The wells will have been
drilled through the cap rock of the storage reservoir so they too
must be permanently sealed or they will become conduits for the
injected CO2 to lead to the atmosphere which is undesirable.
[0004] The use of cement which is commonly used in the completion
of wells and sealing them when they are subsequently abandoned is
not a reliable procedure to prevent leakage of gas under pressure.
This is so particularly with older wells which have used cement
with less sophisticated cement formulations than those formulations
presently available. The unreliability of such abandonment
procedures has let to a proposed change in well abandonment
procedure being mandated by the Alberta Energy Resources
Conservation Board. This proposed change now requires that
abandoned well caps not be sealed so as to avoid the safety
problems resulting from accidental damage of a abandoned well
casings and the inadvertent release of flammable natural gas which
has accumulated below the well cap as a result of gas diffusion
through sealing cement which has become permeable over time. The
cement further does not form a particularly tight seal against the
steel wall of the well casing and cracks can develop from a variety
of causes that then act as conduits for gas flow through towards
the surface. Well cement in contact with CO2 and water or brine is
also vulnerable to damage and deterioration through chemical
reaction.
[0005] Yet a further disadvantage with the use of cement plugs in
well abandonments relates to long term degradation of the steel
well casing. Over time, corrosion of the steel casing is likely
occur within a certain period. The corrosion can again allow
undesirable gas defusion to the surface. To prevent this
possibility, it has been suggested that the steel casing be removed
following well abandonment and that a reliable gas seal be deployed
within the open well bore.
SUMMARY OF THE INVENTION
[0006] According to one aspect of the invention, there is provided
a method of forming a metal alloy plug within the well casing of a
well bore of an abandoned oil or gas well to prevent the flow of
gas through said metal alloy plug comprising the steps of dropping
a casing milling tool down said well casing to a predetermined
depth within said well casing, said well casing having a plug below
said predetermined depth, milling out a longitudinal section of
said well casing and the well cement and detritus surrounding said
well casing and above said plug so as to expose the wall of said
well bore while leaving the upper portion of said well casing above
said milled out area and while leaving the bottom portion of said
well casing below said milled out area, removing said casing
milling tool and dropping a heater into said well casing to said
predetermined depth, said heater carrying a solid metallic alloy
plugging material, increasing the temperature of said heater to
melt said metallic alloy and maintaining said increased temperature
until said melted metallic alloy has flowed from said heater and
permeated said well bore to a desired depth, removing said heater
from said well casing and allowing said melted metallic alloy to
solidify within said well bore, said casing and said milled out
area.
[0007] According to a further aspect of the invention, there is
provided apparatus used to form a metallic alloy plug within a well
casing, said apparatus comprising a milling tool used to mill out a
longitudinal section of a well casing at a predetermined depth
within said well casing and leaving the upper and lower portions of
said well casing above and below said milled out area and a heating
tool operable to carry solid metallic alloy billets, to melt said
billets at an elevated temperature of said heating tool to form
liquid alloy and to maintain said elevated temperature of said
heating tool until said liquid alloy flows into said milled out
area for a desired time period, said heating tool having a
connected power cable to supply power to said heating tool and to
lower and raise said heating tool within said well casing.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0008] Specific embodiments of the invention will now be described,
by way of example only, with the use of drawings in which:
[0009] FIG. 1 is a diagrammatic side cross-sectional view of a
cement plugged well with a window milled through the casing and the
cement sheath surrounding the casing;
[0010] FIG. 2 is a diagrammatic side cross-sectional view of a
fusible alloy heater lowered within the well to the milled
window;
[0011] FIG. 3 is a diagrammatic side cross-sectional view of the
molten alloy following heating which extends through the milled
window and into the formation; and
[0012] FIG. 4 is a diagrammatic side-cross sectional view of the
solidified alloy plug extending through the window and into the
formation with the alloy heating tool withdrawn from the well.
DESCRIPTION OF SPECIFIC EMBODIMENT
[0013] It is useful to select an interval for forming the gas
sealing plugs in the abandoned wells. Several sites for forming the
gas sealing plugs may be selected with several plugs set. The
formation of only one such plug will be described herein, it being
understood that such a process can apply to several other sites
that may be considered favorable for the sealing process.
[0014] Conveniently, a favorable site for a sealing plug within a
well 105 will be in an area adjacent a permeable stratum atop an
impermeable stratum such as cap rock such as that site generally
illustrated at 100 in FIG. 1. The cap rock 101 will seal the top of
the reservoir into which the CO2 is injected.
[0015] A section of the casing 102, conveniently less than one (1)
meter in length, is milled from the casing string 103. The annulus
surrounding the casing is cleaned of cement 104 and other foreign
material such that the face 110 of the well bore is exposed. FIG. 1
illustrates the condition of the target well at this stage of the
procedure. Generally, such a well 105 will have cement plugging
material 111 within the well casing 102 at the bottom of the milled
section 102. In the event, however, that there is no such cement
below the milled section, a bridge plug (not illustrated) is set
just below the bottom of the milled section 102 as is known.
[0016] A heating tool 112 (FIG. 2) is attached to the end of an
electrically conducting cable 113 and is lowered from the surface
down the well casing 103 to the top of the plugged casing. The
heating tool 112 is cylindrical and hollow with a retaining flange
114 near its bottom. Electrical heating elements (not shown) are
embedded within the wall of the tool 112 and are connected to an
electrical power source 120 on the surface by the electrical
conducting cable 113. Billets 121 of solid fusible alloy are
inserted within the hollow heating tool 112 before it is lowered
down the well 105 which will be normally filled with water, brine
or drilling mud to the ground surface. Such a heating tool is
disclosed in our U.S. Pat. No. 7,065,607, the contents of which are
herein incorporated by reference.
[0017] When the heating tool 112 reaches the top of the plugged
casing adjacent the milled window 102, electrical power is applied
through the power cable 113 to the heating elements within the tool
112. The temperature of the elements rises above the melting point
of the contained fusible alloy and the molten metal flows out of
the bottom of the heating tool 112 and into the well bore 110 and
casing 103 as seen in FIG. 3. For a predetermined period, power
continues to be applied to the heating elements to raise the
temperature of the well bore 110 and the surrounding formation
material above the melting point of the metal alloy. Pressure is
then applied to the fluid column within the well bore 110 above the
level of the molten alloy. The pressure assists in forcing the
molten alloy into the porosity of the geologic stratum.
[0018] The power is then shut off to the heating tool 112 and the
tool 112 is lifted from the well bore 105 and removed as seen in
FIG. 4. The molten alloy cools by conduction of heat to the
surrounding earth and the alloy solidifies. The alloy plug 122 that
remains fills the milled section 102 of casing 103, covers the end
of the production casing 103 and its cement sheath 104 and renders
the surrounding geologic formation impermeable to gas flow by
virtue of the solid alloy that fills its porosity to a depth to
effect a seal against gas flowing upward from below. By filling the
entire milled section 102 of the casing 103 with solidified fusible
alloy 122, the alloy plug 122 butts against the edge of the well
casing 123 above and cannot move as long as the casing 123 remains
competent. The well above the alloy plug 122 may be filled with
cement or some other suitable material (not shown) as ballast to
over balance against any subsequent pressure from below that
otherwise might cause a creeping movement of the alloy plug 122.
The above described alloy plugging procedure may be repeated as
many times as desired in different permeable geologic strata in the
open well bore in order to increase the assurance that a permanent
gas seal has been assured.
[0019] In respect of the alloy intended to be used as the alloy
plug 122 for the plugging procedure, certain properties are
conveniently exploited to make the procedure more efficacious.
First, the alloy must conveniently expand volumetrically upon
solidification from the liquid phase sufficiently to form an
effective gas seal against corroded, oily, and dirty steel casing
103 as well as within the confined space of the well annulus
exposed by the milling of the casing section; secondly, in the
liquid state, the alloy must conveniently have a sufficiently low
viscosity and surface tension in order to be successfully pressured
into the permeable geologic stratum; third, the alloy must
conveniently have a specific gravity high enough to displace
efficiently any fluid material present such as water, brine, or
drilling mud; fourth, the alloy must not chemically corrode
significantly in contact with CO2 or other acid gas and saltwater;
fifth, the alloy must not itself corrode significantly, nor can it
cause significant corrosion of the steel well casing due to
galvanic action; and, sixth, the solidified alloy should be
impermeable to gas flow under pressures common to gas sequestration
operations.
[0020] There are further desirable properties associated with the
alloy. First, it is preferred if the alloy is comprised of
component metallic elements that are not toxic if the sealing plug
122 may have the possibility of contact with fresh ground water;
second, the alloy is conveniently a eutectic mixture such that the
alloy melts and solidifies at a single characteristic temperature;
and, third, the melting point temperature of the alloy should be
low enough to allow efficient melting with a heater 112 deployed
within the well without causing damage to the well bore face 110
within which the molten alloy flows at the pressure applied.
[0021] There are four known substances that expand volumetrically
upon solidification from the liquid to the solid phase. The
substances are water, and the metallic elements bismuth, antimony,
and gallium. To be useful as a component in a well sealing plug, a
substance must be solid at temperatures existing in wells. This
eliminates water and gallium. Gallium melts at 29.6.degree. C. and
is also corrosively attacked by inorganic acids. Antimony is
possibly useful as an alloy component but it is disadvantageous in
that it is toxic.
[0022] Bismuth is not toxic and a number of its alloys expand
volumetrically upon solidification from the liquid phase. Some
bismuth alloys are eutectic mixtures that melt at temperatures
convenient for in situ formation of plugs in wells. Bismuth and its
alloys generally have low liquid phase viscosities and surface
tensions and specific gravities high enough to efficiently displace
fluids likely to be present in wells. Bismuth alloys are
furthermore impermeable to gas flow under pressure conditions of
CO.sub.2 injection wells.
[0023] While there are several bismuth alloys which may be useful
to form well plugs, an alloy known as CERROTRU (Trademark) has been
shown to be most desirable under many well conditions of pressure
and temperature. It is comprised of bismuth and tin, neither of
which are toxic. It is also a eutectic mixture which melts and
solidifies at a temperature of 137 deg. C. Tests have shown that
the CERROTRU alloy of bismuth and tin does not itself corrode
significantly under the physical and chemical conditions of oil,
natural gas, and CO.sub.2 injection wells. In addition, the
presence of this alloy in contact with well fluids and steel well
casing does not cause corrosion of the casing steel. Bismuth is
essentially inert under well conditions, and the behavior of
CERROTRU alloy approximates that of elemental tin. Under acidic
conditions, tin passivates and does not corrode. Under the
anaerobic well environment, the passivated tin galvanic couple with
steel causes the steel to passivate also and no increased corrosion
of the steel results.
[0024] Many modifications will readily occur to those skilled in
the art to which the invention relates and the particular
embodiments described herein should be taken as illustrative of the
invention only and not as limiting its scope as defined in
accordance with the accompanying claims.
* * * * *