Note: Descriptions are shown in the official language in which they were submitted.
F-4115 ~2~3~ S
GRAVEL PACK METHO~ AND DEVICE FOR HORIZONTAL WELLBORES
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This invention relates to -the control of particulate matter,
such as sand or fines via a fused porous refractory device when
producing subterranean resources, particularly hydrocarbonaceous
fluids in a loosely consolidated or unconsolidated formation. The
device comprises fluidly communicating sections of alternating
flexible tubing and fused porous refractory sections connected to a
productive tubing string assembly.
Recovery of formation resources such as petroleum from a
subterranean formation is frequently difficult when the subterranean
formation is comprised of one or more incompetent or unconsolidated
sand layers or zones. Sand particles in the incompetent or
unconsolidated sand zone move or migrate into a wellbore during the
recovery of formation fluids from that zone, or sand particles move
away from the wellbore during the injection of secondary or tertiary
recovery fluids into the formation. In the instance of recovering
the fluid from the formation, the movement of sand into the wellbore
can cause the wellbore to cease production of fluids. Also, small
sand particLes can plug small openings and porous masses formed
around the well~ore for the purpose of restraining the flow of sand,
such as screens or slotted liners which are frequently placed in
wells for this purpose. Not only can fluid production be reduced or
even stopped altogether, if sand particles flow through the well to
the surface, but also considerable mechanical problems can result from
passage of abrasive sand particles through pumps and other
mechanical devices.
Many techniques have been described in the prior art for
preventing or decreasing the flow of sand into a well during
petroleum production, including the use of sand screens, filters,
and perforated or slotted liners. These prior art attempts have
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been successful in some limited instances, but have nok always been
entirely satisfactory for a number of reasons. Mechanical devices
usually restrain only the larger particle sand and are not
completely effective for the purpose of restraining or preventing
the flow of fine particles from the formation into the well and
ultimately to the surface. Furthermore, the devices interfere with
various types of completions and workover operations. Additionally7
many of the devices were not able to withstand the combination of
high temperatures and high pH often encountered.
In addition to the problem areas mentioned above, use of
conventional gravel pack methods in a deviated or horizontal
wellbore are virtually impossible. This often occurs because the
angle of incidence is so severe that a conventianal gravel pack
cannot be made to turn through the angle formed by the vertical
tubing and the deviated tubing. Deviated or horizontal wellbores
extend the drainage capacity of a well.
Serious problems have been encountered in attempting to use
conventional production strings in conjunction with enhanced
recovery techniques involving steam injection, acidizing, or
workover fluids. Where the high temperature steam, acid, or hot
water under high flow rates contact the conventional string, it has
been found that such strings are quickly eroded away or dissolved
and must therefore be replaced at frequent intervals.
ûften formation fines and sand particles are difficult to
exclude by conventional production strings. Removal and replacement
of conventional production strings greatly increase the costs of
producing a well. These problems are exacerbated where the
production is utilized in a deviated or horizontal wellbore.
Therefore, what is needed is a production string which has a
section composed of a material which: (1) can withstand high
temperatures and pH environments, (2) can be cleared frequently
in-situ without erosion, (3) which can be placed in a deviated or
horizontal wellbore with minimum tooling and expense, and (4) which
can be "tailor-made" to the dictates of the formation
characteristics.
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This invention is directed to a process for controlling
formation fines during the production of resources, particularly
hydrocarbonaceous fluids from a formation where alternate flexible
and porous refrac-tory sections are affixed to a production tubing
string within a deviated or horizontal wellbore. To accomplish
this, at least one fused refractory section having a closed end is
formed. Other open ended sections can be interspersed therebetween
combined with sections of flexible tubing thereby increasing the
length and effectiveness of the refractory tubing. Each refractory
section is of a strength, composition, and porosity sufficient to
allow entry of li~uefied resources, particularly hydrocarbonaceous
~luids therethrough while excluding particulate matter, e.g.
formation fines or sand. The refractory tubing is formed to allow
entry into a wellbore and affixation to alternate sections of
flexible tubing where one end of a flexible tubing section is
affixed to and fluidly communicated with a production tubing string.
The refractory material from which said refractory section is
made is able to withstand high temperatures and pH conditions
encountered in the formation's environment. Each of the refractory
sections has affixed therearound a centralizer for proper placement
within the wellbore.
One refractory section is affixed to one end of a flexible
tubing section and the other end of the flexible tubing is affixed
to the vertical production string at a point sufficient to allow
placement of the refractory section adjacent to the formation's
productive interval. At least one flexible section should be
located substantially within the wellbore at the angle of incidence
formed by the deviated wellbore. A production string with
alternating flexible sections and fused refractory sections in place
is positioned within the wellbore so that the flexible section is
adjacent to the formation's production interval. The conbined
flexible and fused refractory sections culminate with a closed end
refractory section. Having obtained flexibility because of the
flexible sections the combined sections are able to turn through the
angle of incidence formed by the deviated or horizontal wellbore.
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Afterwards, resource liquids, hydrocarbonaceous fluids are produced
from the formation to the surface while particulate matter such as
formation fines and sand are excluded from khe flulds by the
combined sections.
The fused refractory section allows particulate matter, e.g.
accumulated fines or sand to be removed therefrom in-situ ~y acids
known to those skilled in the art. Hydrofluoric acid can be used to
remove formation fines from the flexible and fused refractory
sections. Solvents generally used for production, well completion,
and clean up can be used with minimum damage to the section. Also,
the flexible section can be used when steam is injected into the
wellbore, or into the formation when a steam flood is employed.
This section is able to withstand high formation temperatures and
pressures as well as steam temperatures.
The drawing depicts a cross-sectional view of alternate combined
flexible and fused refractory sections affixed to each other with
one flexible end affixed to a production tubing string within a
deviated or horizontal wellbore located in a formation's productive
interval.
In the practice of this invention, referring to Figure l,
formation lO contains a production interval which is penetrated by a
deviated or horizontal wellbore 12. Wellbore 12 contains
perforations 24 which are fluidly connected with the production
interval of formation 10. Production tubing string 14 is directed
into wellbore 12. Affixed to production tubing string assembly 14
is a flexible tubing 16 which is of a size, strength, and
composition sufficient to withstand the pressures and heat
encountered in a subterranean formation. Affixation can be by any
manner known to those skilled in the art such as screwing,
strapping, or the use of adhesives.
In one embodiment where only a small productive interval exists,
a fused refractory closed end section 22 can be affixed to a
flexible tubing section 16 and flexible tubing 16 can be located
subst.antially near the angle of incidence formed by wellbo~e 12.
Said end section 22 can be formed to allow fixation by methods
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similar to those above mentioned. Section 22 can be rnolded so that
a metal strap can be ~ittingly adapted ko fit over flexible section
16 to hold said flexible section 16 within a circumferential
depression near the open end of fused porous refractory section 22.
In order to keep fused porous refractory section 22 off the bottom
of wellbore 12 thereby decreasing its particulate matter removing
efficiency, refractory section 16 can also be formed to receive a
centralizer 20.
To keep fused refractory tubular sections 18 and 22 from lying
on the bottom of wellbore 12 thereby decreasing the particulate
matter removal efficiency of sections 18 and 22, a centralizing or
spacing means is required. A centralizer 20 which can be utilized
for centering or for circumferential space equalization within
wellbore 12 is shown in Figure 1. Spacing means 20 centers said
refractory sections 18 and 22 within wellbore 12. This centering
causes sections 18 and 22 to be lifted up and away from perforations
24 on the low side o~ inclined wellbore 12.
Centralizing or spacing means 20 can comprise a multiple
metallic lea~ spring means. Such sp~ing means can be made of a
metal suitable for use within the productive interval of wellbore
12. Of course, the spring means can be composed of any other
suitable material, e.g. thermoplastic materials, as is known to
those skilled in the art. As is preferred, at least two spring
means should be used to properly centralize fused refractory
sections 18 and 22. However, in order to provide greater stability
and rigidity, additional spring means can be employed.
In a pre~erred embodiment one or more refractory sections 18
having both ends open and having a flexible tubing 16 affixed
thereto can be affixed between flexible tubing 16 which is attached
to production string assembly 1~ and fused refractory section 22.
In this manner, combinations of flexible tubing 16 and refractory
section 18 can be made to any length desired for the removal of a
solubilized resource, particularly hydrocarbonaceous liquids,
depending upon the length of the productive interval in formation
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lO. As above-mentioned, a centralizer 20 can be placed onto each
refractory section 18. Each refractory section 18 should be made o~
a size, strength, composition, and porosity su~ficient to allow
entry therethrough of solubilized resources while excludiny
particulate matter.
Particulate matter as defined herein includes ~ormation fines,
sand fines, dirt, and other undesired materials commonly encountered
in solubilized resources as is known to those skilled in the art.
Exemplary resources comprise geothermal energy, iron, copper, and
uranium ores, shale oil, coal, tar sands, and hydrocarbonaceous
fluids such as oil.
Flexible tubing 16 can be made from any material suitable to
withstand the high temperatures, pressures and harsh environment
commonly encountered during the removal of resources from a
subterranean formation. Plastic flexible tubing is preferred for
fabricating section 16. A plastic tubing suitable for this purpose
is called Coflexip tubing ~hich is sold by Coflexip Corp. in
Houston, Texas. Flexible tubing 16 should comprise a material
sufficient to be flexed ~ithin the angle of incidence formed by the
deviated wellbore and the vertical production tubing string.
When the well 12 is produced, solubilized or liquefied resources
such as hydrocarbonaceous fluids leave formation lû via perforations
24 and enter fused refractory section 18 and 22 ~here particulate
matter, e.g. formation fines entrained in hydrocarbonaceous fluids
are removed. The fines are removed because pores in sections 18 and
22 are smaller than the particulate matter in the fluid.
Fused refractory sections 18 and 22 can be made by using silicon
carbide. A method can be used as disclosed in U.S. Patent No.
4,571,414 for molding silicon carbide sections 18 and 22.
Another method for molding tubing section 16 is discussed in
u.S. Patent No. 4,341,725 issued to Weaver et al. on
July 27, 1982.
Fused refractory sections 18 and 22 are constructed of silicon
carbide of a density sufficlent to exclude fines of a size
anticipated to be encountered in a formation. By utilizing this
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invention7 fused refractory sections 18 and 22 can be made of a
porosity sufficient for the formation where deployed. Generally,
the denslty will be abou-t 3.0 to about 3.6 gms. per cubic
centimeter. It can also be constructed of the desired porosity
while retaining the required thermal and chemlcal resistance
characteristics. Although the porosity will vary because of
differing envlronments within a formation, the pores in the
refractory tubing should be about 44 to about 500 microns in size.
Fused refractory sections 18 and 22 are preferably made of
ceramic which provides resistance to high temperatures encountered
which can be from about ambient up to about 6û0F while at the sarne
time providing for good heat transfer. Most ceramics have low
thermal conductivity with the exception of silicon carbide and
silicon nitride which are preferred for use in the present
invention. ûther ceramics can be used which have a thermal
conductivity of at least 3 BTU/hr/ft 2 /F./ft. Similar ceramics
are discussed in U.S. Patent No. 4,332,295 issued to LaHaye et al.
on June 1, 1982. For example, fused refractory sections 16 and 22
can be cast from a commercially available castable silicon carbide
such as"Carbofrax li, a product of the Carborundum Company of
Niagara Falls, New York. This product is typically mixed with water
and cast to a desired shape and then fired to temperatures over
180ûF to develop strength and good thermal conductivity. The
castable silicon carbide may also use a material such as
calcium-aluminate as a binder. This silicon carbide material may be
cast at room temperature and allowed to cure at room temperature.
It may then be preheated for a period of time and then first at
above 2100F for a period of about four hours.
Fused refractory sections 18 and 22 should be composed of a
ceramic material having a density preferably of about 65 to about
75% of the full density. The silicon carbide that is selected is
preferably of a density of in the order of about 3.0 grams per cubic
centimeter. Where silicon nitride is used, it similarly has a
density on the order of about 3.0 grams per cubic centimeter. It is
preferred that sections 18 and 20 have a density greater than about
65% of theoretical full density.
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Fused refractory sections 1~ and Z should be comprised ofmaterials to make it resistant to thermal shock and also resistant
to chemical attack at high temperatures. Alloys of silicon carbide,
silicon nitride, or other similar cerarnics can be used to construct
sections 18 and 22. U.5. Patent No. 4,332,295 issued to LaHaye et
al. discloses other ceramic compositions which can be used in
constructing sections 18 and 22.
Fused refractory sections 18 and 22 can be made sufficiently
porous to admit liquefied resources such as hydrocarbonaceous fluid
while excluding formation flnes. The desired porosity can be
obtained by varying the density of the ceramic material utilized.
Also the size, shape, diameter, chemical resistance, and thermal
resistance can be modified to conform to the dictates of the
particular formation where utilized. As is preferred, said
refractory sections 18 and 2û should have a wall thickness of about
5 to about 40 millimeters and sufficient to withstand pressures of
from about 1,000 to about 15,000 psig.
This invention, as disclosed below, can be utilized in many
applications. One such application is for facilitating the removal
of ores from a formation containing same. Sareen et al. in U.S.
Patent No. 3,896,879, disclose a method for increasing the
permeability of a subterranean formation penetrated by at least one
well which extends from the surface of the earth into the
formation. This method comprises the injection of an aqueous
hydrogen peroxide solution containing therein a stabilizing agent
through said well into the subterranean formation. After injection,
the solution diffuses into the fractures of the formation
surrounding the well. The stabilizing agent reacts with metal
values in the formation which allows the hydrogen peroxide to
decompose. Decomposition of hydrogen peroxide generates a gaseous
medium causing additional fracturing of the formation. Sareen et
al. were utilizing a method for increasing the fracture size to
obtain increased removal of copper ores from a formation.
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In addition to removing ores, particularly copper ores and iron
ores from a formation, the present invention can be used to recover
geothermal energy more efficiently. A method for recovering
geothermal energy is disclosed in U.S. Patent No. 3,86~,709 which
issued to Fitch on February ~, 1975. Disclosed
in this patent is a method and
system for recovering geothermal energy from a subterranean
geothermal formation having a preferred vertical fracture
orientation. At least two deviated wells are provided which extend
into the geothermal formation in a direction transversely of the
preferred vertical fracture orientation. A plurality of vertical
fractures are hydraulically formed to intersect -the deviated wells.
A fluid is thereafter injected via one well into the fractures to
absorb heat from the geothermal formation and the heated fluid is
recovered from the formation via another well.
The present invention can also be used to remove thermal energy
produced during in-situ combustion of coal. A method wherein
therrnal energy so produced by in-situ combustion of coal is
disclosed in U.S. Patent No. 4,û19,577 which issued to
Fitch et al. on April 26, 1977. Disclosed therein
is a method for recoverin~ thermal
energy from a coal formation which has a preferred vertical fracture
orientation. An injection well and a production well are provided
to extend into the coal formation and a vertical fracture is formed
by hydraulic fracturing techniques. These fractures are propagated
into the coal formation to communicate with both the wells. The
vertical fracture is propped in the lower portion only. Thereafter,
a combustion-supporting gas is injected into the propped portion of
the fracture and the coal is ignited. Injection of the
combustion-supporting qas is continued to propagate a combustion
zone along the propped portion of the fracture and hot production
gases generated at the combustion zone are produced to recover the
heat or thermal energy of the coal. Wate.r may also be injected into
the fracture to transport the heat resulting from the rombustion of
the coal to the production well for recovery therefrom. Both the
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injection and production wells can be deviated wells which penetrate
the coal ~ormation in a dlrection transversely of the preferred
fracture orientation.
Recovery of thermal energy from subterranean formations can also
be used to generate s-team. A method for such recovery is disclosed
in U.S. Patent No. 4,015,663 which issued to Strubhar on April 5,
1977.
Obviously, many other variations and modifications of this
invention, as previously set forth, may be made without departing
from the spirit and scope of this invention as those skilled in the
art readily understand. Such variations and modifications are
considered part of this invention and within the purview and scope
of the appended claims.
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