U.S. patent number 3,782,466 [Application Number 05/273,082] was granted by the patent office on 1974-01-01 for bonding casing with syntactic epoxy resin.
This patent grant is currently assigned to Shell Oil Company. Invention is credited to Jimmie Brown Lawson, Edwin A. Richardson, George O. Suman.
United States Patent |
3,782,466 |
Lawson , et al. |
January 1, 1974 |
BONDING CASING WITH SYNTACTIC EPOXY RESIN
Abstract
In a well in which a movement of earth formation material is apt
to collapse a casing, an improved bond between the casing and the
sur-rounding earth formations is formed by a syntactic epoxy resin
foam that collapses progressively and has a compressive strength
slightly less than that of the casing.
Inventors: |
Lawson; Jimmie Brown (Houston,
TX), Richardson; Edwin A. (Houston, TX), Suman; George
O. (Houston, TX) |
Assignee: |
Shell Oil Company (Houston,
TX)
|
Family
ID: |
23042472 |
Appl.
No.: |
05/273,082 |
Filed: |
July 19, 1972 |
Current U.S.
Class: |
166/295 |
Current CPC
Class: |
E21B
33/14 (20130101); C09K 8/42 (20130101) |
Current International
Class: |
E21B
33/13 (20060101); E21B 33/14 (20060101); C09K
8/42 (20060101); E21b 033/14 () |
Field of
Search: |
;166/295,294,292,254 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Novosad; Stephen J.
Attorney, Agent or Firm: Harold L. Denkler et al.
Claims
We claim:
1. In completing a well by forming a fluid-tight and mechanically
strong bond between a casing string and adjacent earth formations,
an improved process for increasing the endurance of such bond in a
region that contains subterranean faults, which improved process
comprises:
determining the depth of a fault zone encountered by the borehole
of the well;
positioning within the borehole of a well a casing string that has
a known compressive strength at each depth;
adjusting the composition of a liquid self-curing syntactic epoxy
resin foam formulation to the extent required to cause it to
produce a cured resin having a compressive strength slightly less
than the compressive strength of the portion of the casing strength
that is positioned adjacent to said fault zone;
forming a bond between the casing string and adjacent earth
formations in said fault zone by emplacing and curing the
strength-adjusted resin foam formulation along the portion of said
fault zone encountered by the well and emplacing; and
forming a bond between the casing string and adjacent earth
formations in other portions of the well by emplacing and curing
cement in those portions.
2. The process of claim 1 in which said resin formulation is a
diafoam resin formulation.
Description
BACKGROUND OF THE INVENTION
This invention relates to casing the borehole of a well. More
particularly, it relates to bonding a well casing to the
surrounding earth formations at a depth at which the casing is apt
to be collapsed by a movement of earth formation material toward
the interior of the borehole, for example, in a permafrost zone or
in a zone of fault crossing, or the like.
Well casings comprise pipe strings that are relatively long, large
and expensive. In completing a well, a casing program is designed
to line the borehole with a casing having at each depth a strength
that is adequate but not excessive. The well casing is
conventionally bonded to the adjacent earth formations by pumping a
slurry of cement into the space between the casing and the earth
formation ad allowing the cement to harden. In many situations, it
is important that the casing to earth formation bond be both
mechanically strong, to cause stresses applied to the casing to be
transmitted to the earth formation, and fluid-tight, to prevent any
flow of fluid between the casing and the earth formation. The
conventional well cements form bonds that are mechanically strong
and fluid tight, but also relatively rigid and brittle. If earth
formations move toward the interior of the borehole, the cement
tends to be cracked and pushed into deformations in the casing. A
cracking of the cement may be caused by a slight movement of earth
formation material toward the borehole interior and a casing
collapse may be caused by any additional movement.
The present invention is, at least in part, premised on a discovery
that (1) a mechanically strong syntactic epoxy resin foam
formulation can be cured in the space between a well casing and the
surrounding earth formation to form a solid resinous foam that
collapses progressively and has a compressive strength that is near
but slightly less than that of the adjacent section of casing and
(2) such a syntactic resin-foam casing-bonding procedure provides
results that are unobviously advantageous. In a permafrost zone,
the endurance of a fluid-tight and mechanically strong bond between
a fully open section of casing and adjacent earth formations is
extended, by the cooperation between the progressive crushing,
resiliency and thermal insulating properties of a syntactic epoxy
resin foam. In a fault zone the endurance of such a bond is
extended by the progressive crushing and resiliency properties of
such a foam. A syntactic epoxy resin foam is one in which gas
bubbles are dispersed in an epoxy resin and at least some of the
bubbles are gas-filled, or hollow, microspheres, or micro-bubbles,
such as socium silicate or high strength glass micro-bubbles.
SUMMARY OF THE INVENTION
The invention relates to an improved process for casing a well. A
casing string having a strength that is adequate, but not excessive
for each depth location within the well, is suspended within the
borehole. At at least one depth of possible casing crushing due to
a movement of earth formation material toward the interior of the
borehole, a self-curing liquid syntactic epoxy resin foam
formulation is flowed into the space between the casing and the
earth formation. The resin formulation is adjusted to the extent
required to produce a resin having a compressive strength slightly
less than that of the adjacent portion of casing. The resin
formulation is cured in situ to form a syntactic epoxy resin foam.
At least one other portion of the string, in a different location
within the well borehole is, preferably, bonded to the adjacent
earth formations by a conventional grouting material such as
cement.
DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1C are schematic partially cross-sectional
illustrations of a portion of well casing bonded to an earth
formation in accordance with this invention.
FIGS. 2A to 2C are similar illustrations of an analagous structure
in which the bonding material is cement.
FIGS. 3A and 3B are similar illustrations of a portion of well
casing bonded in accordance with the present invention in a zone of
fault crossing.
DESCRIPTION OF THE INVENTION
The invention can be practiced by employing known materials and
techniques. Known casing program and casing string design
techniques can be used to fabricate the casings to be bonded. Known
well logging, or the like techniques, can be used to determine
possible casing-crushing depths at which material in the earth
formations encountered by the well is apt to move toward the
interior of the borehole. Known compositions and techniques can be
used to formulate, emplace and cure a liquid syntactic epoxy resin
foam formulation that forms a resin having a compressive strength
slightly less than that of the adjacent portion of casing. Suitable
compositions and techniques for forming and curing syntactic epoxy
resin foams are described in publications such as the American
Chemical Society Epoxy Resins Advance in Chemistry Series 92, (from
Symposium 155, of the ACS Meeting, 1968) the textbooks "Plastic
Foams" by Calvin J. Benning, Wiley Inter Science Division of John
Wiley and Sons, 1969, and the like.
The present utilization of a syntactic epoxy resin foam in a well
is distinctly different from prior uses in well of syntactic or
other types of resin foams. For example, U.S. Pat. No. 3,379,253
describes the plugging of a zone of lost circulation within an
earth formation around a borehole by effecting an in situ foaming
and curing of a polystyrene, polyurethane, or the like, resin foam
within the borehole and the zone of lost circulation. The
compression strength of such a foamed resin is not adjusted
relative to that of the well casing, since the resin is used only
to plug the pores of the earth formation. U.S. Pat. No. 3,456,735
describes a use of a foamed resin as a thermal insulating material
installed in the annular space between a production tubing string
and the next larger casing string. The compressive strength of the
foamed resin is not adjusted relative to that of the well casing,
since the resin is placed inside of the casing and is used only as
an insulation.
In the drawing, FIGS. 1A to 1C show a casing 1 in a borehole 2
within an earth formation 3 in a permafrost zone. The casing to
earth formation bond is formed by a syntactic epoxy resin bonding
material 4 having a compressive strength slightly less than that of
the adjacent portion of casing. FIGS. 1A and 1B show the tendency
for the earth formation to subside and cause a redistribution into
a disturbed earth formation material 5, around the casing string
and bonding material. FIG. 1C illustrates the movement of earth
formation material 6 that is caused by a refreezing of the
permafrost. Such material may comprise ice or other frozen
materials and/or rock particles of debris and portions of it are
apt to move toward the interior of the borehole. Some or all of the
mechanical strength and fluid permeability of the casing to earth
formation bond is retained by the ability of the resin bonding
material 4 to collapse progressively while resiliently pressing
against the portions of earth formation material 6 that have moved
into the borehole. The compressive strength of a resin foam bonding
material such as material 4 is preferably from about 75 to 95
percent of the casing compressive strength of the adjacent portion
of casing.
FIGS. 2A to 2C show an analagous situation in which the casing
bonding material is a conventional sheath of cement 7. In this
case, in the refrozen stage shown in FIG. 2C, the incursion of
earth formation material 6 tends to form fractures 8 within the
cement sheath 7 and to collapse the casing wall by pushing cement
fragments inward to form the indentations 9 in the casing.
FIG. 3A shows a casing 11 in a borehole 12 in the zone of the
crossing of a fault 13 in earth formation 14. Above and below the
fault crossing zone, the casing is bonded to the adjacent portions
of the earth formation with a conventional cement bonding material
16 and 16a. Within the fault-crossing zone, the casing is bonded to
the adjacent earth formation with a strength-tailored syntactic
epoxy resin foam bonding material 18, such as that described in
connection with FIGS. 1A to 1C. As shown in FIG. 3B, such an earth
formation fault is susceptible to shifting in a manner that forms
an S curve, such as curve 11a, in the well casing while moving
encroaching portions, such as portion 14a, of the adjacent earth
formation towards a portion of the interior of the borehole.
As indicated in FIGS. 1C and 3B, where the casing to earth
formation bonding material is a progressively compressible
syntactic epoxy resin foam having a compressive strength slightly
less than that of the adjoining well casing, movements of earth
formation material toward the interior of the borehole tend to
compress the bonding material without disrupting the fluid-tight
integrity of that material or diminishing the size of the
passageway within the well casing.
In completing a well that extends through a permafrost zone, in a
preferred embodiment of the present invention, the well casing
program is designed to include a multiplicity of casing strings,
such as a conductor pipe, a permafrost string, a surface casing
string, and an intermediate production string, etc. In bonding the
outermost casing strings to the earth formations, each portion that
is bonded to an earth formation within the permafrost zone, (i.e.,
in a zone of possible casing collapse) is bonded by means of a
syntactic epoxy resin foam of tailored compressive strength. For
example, in installing a conductor pipe having a compressive
strength, such as 1,000 psi, the pipe is suspended within the
borehole while a liquid syntactic epoxy resin foam formulation is
pumped into the space between the pipe and the earth formation.
Such a resin formulation may comprise a slurry of microspheres
(available from Emerson and Curning, Inc., amount to about 60
percent by volume of the slurry in liquid comprising a mixture of
about 1 part by volume Epon 828 (Shell Chemical Company) per 1 part
by volume Versamide (General Mills) and 0.1 percent by weight of a
blowing agent such as ammonium carbonate. Such a resin formulation
reacts in situ to form a syntactic epoxy resin diafoam (one
containing macro cells, formed in situ by the blowing agent, in
addition to the hollow microspheres) having a compressive strength
of about 500 to 1,000 psi. Each smaller casing string that has a
portion exposed to earth formations within the permafrost zone is
preferably also bonded to the earth formation by means of such a
syntactic epoxy resin foam, with the resin foam being extended from
that depth to the surface, in order to enhance the benefits
provided by the thermal insulating properties of such a foam by
extending the foam into the space between the larger and smaller
casings.
In completing a well in which a portion of the borehole extends
across a fault, such as the fault 13 of FIG. 3A, a syntactic epoxy
resin foam bonding material is preferably emplaced as shown in FIG.
3A. The positioning of portions of conventional cement 16 and 16a
above and below the fault zone can readily be accomplished by known
techniques such as staged cementing techniques. For example, casing
11 can be perforated at the depth of the top of the lower portion
of cement 16a, a tubing string can be lowered within the casing and
packed-off near the bottom and used to displace cement up the
annulus between the casing and the earth formation to the depth of
the perforations. After curing the element, a bridge plug can be
set near the top of the cement, the casing can be perforated near
the top of the depth selected for the resin foam bonding material
and the latter can be injected by a procedure similar to that
described above. After curing the resin the bridge plug can be
moved to the top of the resin-bonded section and the
above-described selective injection operations can be repeated, in
order to emplace the upper portion of cement 16.
* * * * *