Note: Descriptions are shown in the official language in which they were submitted.
TUC-~
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WATER SOLUBLE PERFORATION_ ACK
BACKGROUND OF THE INVENTION
This invention pertains to a r.ew process to minimize any decrease
in permeability oF the formation surrounding the perforations in a per-
forated well, i.e., to prevent or minimize any damage to the formationwhich would decrease the flow of oil or gas from the formation through
the perforations and hence into the well bore for transport to the
surface.
PRIOR ART
Various procedures have been developed and utilized to increase
the flow of hydrocarbons from hydrocarbon-containing subterranean for-
mations penetrated by well bores. For example, a commonly used technique
involves perforating the formation to provide flow channels therein through
which hydrocarbons flow from the formation to the well bore.
In such formation perforation procedures it is important to leave
the formation with maximum permeability or conductivity whereby hydro-
carbons contained in the formation flow to the well bore with the least
possible restriction. This can best be accomplished by: (1) preventing
the entry of solids into the formation, which entry results in a decrease
of the permeability of the formation, (2) utilizing well completion fluids
which do not tend to swell and/or disperse formation particles contacted
by the completion fluid, ~3) preventing the entry of formation particles
into the perforations, and (4) avoiding excessive fluid invasion into the
formation.
Sand production and its control is a major problem in almost all
fields that produce hydrocarbons from unconsolidated sandstone formations.
Sand influx into producing wells can cause reduced productivity, loss of
reserves, and added expense in combating equipment erosion and sand
accumulation problems. Consequently, there is a tremendous potential for
increasing profits through improved sand control.
Gravel packing inside casing is the most prevalent method of sand
control. A successful inside casing gravel pack require positive place-
ment of high permeability gravel within the critical perforation tunnels
through the casing and cement, and the prevention of permeability damage
within the formation around the perforation cavity beyond the cement.
Basic procedures for packing gravel (actually a fine graded sand) and
choasing the size of gravel to be packed are well known.
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~ ypical applications of completion fluids in sand control procedures
are in underreaming, perforating, perforation washing, as carrier fluids
to place gravel in perforations or behind screens and liners, and to
spot and displace acids or chemical treatments. Brine based fluids
S ranging from low density sea waters to very expensive commercial solutions
are widely used in sand control operat;ons. Four basic fluid properties
must be considered in selecting a brine Fluid for a particular application
These are: brine concentration -:to prevent clay swelling and dispersion;
fluid density - to provide formation pressure control; viscosity - to
achieve desired solids carrying capacity, and fluid loss control - to pre-
vent excessive whole fluid loss. The first two properties are selected
based on area experience and knowledge of well properties gained during
drilling. Minimum brine concentratio~ to prevent clay reactions in most
formations are generally considered to be 5 to 10% for sodium chloride,
and 1~ to 3% for calcium and potassium chloride brines. For well control,
industry commonly designs for an overbalance of 200 to 400 psi. Fluid
viscosity increases with brine concentration. It can be increased further
to desired levels for suspension o-f solids by addition of certain water
soluble polymers.
Fluid loss is controlled by the addition of polymers to "solids free"
brines to increase their viscosity, or by the addition of controlled-size,
solid particles. In conjunction with polymer viscosifiers, such particles
bridge on the formation face and form an extremely low permeability film
to prevent whole fluid loss. Materials commonly used are acid soluble
calcium carbonate, oil soluble resinsJ and water soluble salts such as
sodium chloride. The water soluble salts are used when the brine is
saturated with respect to the water soluble salt. See For example the
following U.S. patents to T.C. Mondshine: 4,175,042;
4 , 18 6 , 8 0 3 ; and 4 , 3 69 , 8 4 3 0
The primary advantage of fluid loss control is the ability to prevent
particle plugging of the critical near-well bore permeability by placing
the polymer-bridging particle "filter" on the formation face.
Cleaning perforations prior to any sand control process is important.
The permeability of the material in the perforation tunnel and cavity
greatly inf1uences productivity. Two techniques are well known and used
to clean out perforations prior to gravel packing: pressure washing and
backsurging. It is common practice to use filtered fluids for perforation
7~7
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washing despite evidence of severe plu~ging due to solids entering the
fluid a~ter filtration. Backwashing is a cleanout method in which
pr~ssuri~ed fluids do not contact the formation. The method uses a
sudden pressure underbalance to move fluids into the well bore and flush
debris ~rom perforation cavities and tunnels. Thus the potential for
plugging is less than with washing. Backsurging is generally preferred
to per~oration washing when reservoirs are low pressured and excessive
flu;d loss would occur.
After cleaning the perforations the perforations are packed with
selected sized sand. It is necessary to squeeze the fluid carrying the
sand into the ~ormation durin~ sand placement in order to fill the per-
foration tunnels with compacted sand. Only perforation tunnels through
which packing fluid flows are likely to be adequately packed.
During well completion and workover procedures there is occassionally
lS a need to temporarily seal the perforations to prevent the entry of fluid
and solids into the formation, if overbalanced, and to prevent the entry
of solids ~rom the formation into the perforations, if underbalanced.
This has been accomplished in the prior art by spotting a viscous polymer
pill in a solids-free brine across the perforations, or by placement of
a low permeability filter cake onto the formation face utilizing polymer
viscosifiers and bridging agents as noted previously. Considerable forma-
tion damage can result from these practices due to either incomplete re-
moval of the vis~ous polymer pill from the formation or incomplete removal
of the low permeability fil~er cake from the ~ormation/perforation channel
interface. In regards to the latter, even water soluble bridging solids
are difficult to remove in a reasonable period of time.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a new pro-
cess of temporarily sealing the perforations in a well completion process.
3n It is another object oF this invention to provide a ne~ process for
minimizing any decrease in permeability of the Formation surrounding per-
foration channels therein.
It is still another object of this invention to provide a process
for minimizing formation damage during perforated well completion operations.
3S These and other objects of the invention, which will be apparent to
one skilled-in-the-art upon reading this specification and the appended
claims, have been accomplished by the present invention which provides
for the placement of a slurry ~suspension) of specially sized salt particles
across the perforations to form a highly permeable salt pack within the
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perforations, and thereafter sealing the surface of the salt pack with
a low permeability film ("filter cake") utilizing a well completion
~luid having a low fluid loss,
While the invention is susceptible of various modifications and
alternative forms, specific embodiments thereof will hereinafter be
described in detail and shown by way of example. It should be under-
stood, however~ that it is not intended to limit the invention to the
particular forms disclosed, but~ on the contrary, the invention is to
cover all modifications and alternatives falling within the spirit and
scope of the invention as expressed in the appended claims.
The methods can comprise~ consist essentially of, or consist of
the stated steps with the materials.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In a typical well completion process, steel casing is cemented to
the sides of the borehole. Thereafter the casing is perforated with a
perforation tool, normally a jet perforator, to create cavities or chan-
nels through the casing and cement and into the formation surrounding
the borehole. As discussed herein, the perforations in an unconsolidated
sand are normally "gravel packed" by filling the perforation channels with
a specially sized s;lica sand ("gravel") to form a high permeability
gravel pack within the perforations. It is extremely important during
these perforation and gravel packing procedures to prevent or minimize
the entry of solids into the formation or the entry of solids into the
perforati~n channels from the formation surrounding the channels.
During well workover operations in low pressured formations, such as
in depleted s~nds, it is extremely important to prevent ~he entry of solids
and fluids into the formation which decrease the permeability of the forma-
tion. Because of the low pore pressure within the formation, the workover
~luid must be carefully designed to prevent an excessive pressure over-
balance into the formation as well as to prevent the entry of solids into
the formation.
The present invention prevents the entry of solids into the formation
surrounding the perforation channels and prevents the entry of solids from
the formation into the perforation channels subsequent to the well being
perforated. This is accomplished b~:
(a) pumping a treating fluid, hereinafter sometimes referred to
as a salt pack pill, into the well and contacting the per-
foration channels with this treating fluid, the treating
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fluid comprising a satur~ted aqueous saline solution
with at least one water soluble particulate sized salt
suspended therein which is substantially insoluble in
the treating fluid;
(b) filling the perforation channels with the water soluble
- particulate sized salt, the particle si~e range and dis-
tribution of the wàter soluble particulate sized salt being
such that a high permeability salt pack is formed within the
channels which is easily removed when desired by dissolving
the water soluble particulate sized salt in another treating
fluid which is non-saturated with respect to said ~ater
soluble particulate sized salt;
(c) forming a bridge and seal on the surface of the salt filled
perforation channels to bridge and seal off the filled per-
foration channels by contacting the filled perforation
channels with another treating fluid, hereinafter sometimes
referred to as a sealing pill, comprising a saturated aqueous
saline solution in which the water soluble particulate sized
salt within the perforation channels is substantially in-
soluble having at least one particulate sized bridging
material suspended therein, the bridging material having a
particle size range and distribution such that a low
permeability seal of the filled perforation channels is
obtained; and thereafter when desired;
(d) removing the low permeability seal from the surface of the
filled perforation channels, and
(e) removing the water soluble particulate sized salt from within
the perforation channels by dissolving the salt in still
another treating solution in which the salt is soluble.
Thereafter the perforation channels can be filled with sand -if desired.
The salt pack resulting from step (b) is readily dissolved and removed
from the perforation tunnel in step (e) due to its high permeability. The
treating fluid in step (e) can readily enter the salt pack and channeling
of this treating fluid is minimized by the high permeability of the salt
pack. Preferably the salt pack has a permeability higher than that of the
formation surrounding the perforation channels. ~
5~
The salt pack protects the perforation channels from damage by
preventing their collapse, and the low permeability film or filter cake
deposited on the surface of the salt pack prevents excess;Y~ invasion of
the formation with fluids or solids. The low permeability film, being on
the surface of the salt pack and not within the perforation channels, is
readily removed in step (d). Thus bv contacting the low permeability Film
with an appropriate fluid, or by mechanical means well known in the art,
the particulate sized bridging material is removed and the low permeability
film is destroyed.
The saturated aqueous saline solution utilized in steps (a) and (b)
is formed by dissolving a salt or mixture of salts in water and normally
the minim~m density of the saturated saline solu~ion is approximately at
least 10 pounds per gallon. In those situations where it is desirable to
employ the present invention with a density less than 10 pounds per gallon
the saturated saline solutlon can be diluted with some suitable substance
such as oil. In addition, the density of the saturated saline solution
can be increased by the addition of sand of the type subsequently to be
used to gravel pack the perforations when desired.
The saturated saline solution can be formed by dissblving any suitable
salt ~r mixture of salts in water to form the saturated saline solution.
Some salts that are generally available and which may be used include
potassium chloride, sodium chloride, calcium chloride, magnesium chloride,
sodium sulfate, sodium carbonate, sod;um bicarbonate, sodium bromide,
potassium bromide, calcium bromide and potassium carbonate.
Any water soluble salt which is substantially insoluble in the
saturated saline solution may be employed in steps (a) and (b). Some
which are generally available include potassium chlor;de, sodium chloride,
calcium chloride, magnesium chloride, sodium sulfate, sodium carbonate,
sodium bicarbonate, sodium bromide, potassium bromide, or calcium bromide
and potassium carbonate. In some instances, it may be ~esired to use a
mixture of these sal~s. The preferred particle size range of the water
soluble particulate sized salt to be suspended in the saturated saline solu-
tion is in a range from about 44 microns to about 1800 microns, preferably
from about 74 microns to about 300 microns. The particle size range and
particle distribution is such that a high permeability salt pack fills the
perforation channels. Such highly permeable salt packs are easily removed
by dissolving the salt in an aqueous liquid in which the salt is soluble.
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Typical salt packs obtained have a permeability from about 50 millidarcies
to about 5000 millidarcies, preferably frum about lOO to about 2000 milli-
darcies. Most preferably the salt pack within the perforation channels
will have a permeability greater than the permeability of the formation
surrounding the channels. The permeability of the salt pack can be cal-
culated ~rom the average particle size of the water soluble particulate
sized salt using the following formula:
Permeability, millidarcies = (Ave. Particle Size, ~)2tO.024)
The quant;ty of the water soluble particulate sized salt to be added
to the saturated saline solution may vary but is in a sufficient amount
to fill the perforations at the temperature conditions in the well.
Generally, from about 20 kg/m3 to about 600 kg/rn3 of the water soluble
particulate sized salt will be suspended in the saturated aqueous saline
solution, preferably from about 20 kg/m3 to about 150 kg/m3. When the
invention is employed in well bores which h~ve increased temperatures, the
water soluble particulate sized salt is added in a sufficient ~uantity so
that even though some of it may dissolve at higher temperatures, the amount
dissolved will not materially affect the ability of the water soluble
particulate sized salt to fill the perforation channels with a highly
permeable salt pack.
The saturated saline solution with the water soluble particulate
sized salt therein as described above may be employed with any suitable
viscosifier to provide the desired viscosity and suspension characteristics
to the treating fluid to retain the salt particles in suspension in the
saturated aqueous saline solution.
One suitable additive for obtaining desired viscosity and suspension
is hydroxyethyl cellulose. Hydroxyethyl cellulose is prepared by trea-ting
cellulose with caustic and then reacting the caustic treated cellulose with
about l to 3 moles of ethylene oxide for each anhydroglucose unit in the
cellulose molecule. The viscosity of an aqueous solution of hydroxyethyl
cellulose depends upon the concentration and molecular weight of the hydro-
xyethyl cellulose. Broadly, the hydroxyethyl cellulose employed in the
practice of th;s invention has about 1 to 3 moles of substituent ethylene
oxide per anhydroglucose unit and is characterized by a Brookfield viscosity
3~ of about 1,500 to 5,000 centipoises at 25C for a 1 weight percent solutionthereof. A preferred hydroxyethyl cellulose is marketed by Union Carbide
under the trademark Cellosize QP-lOO MH. Hydroxyethyl cellulose is employed
to increase the viscosity of the fluid and to increase the stability of the
dispersion.
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In general, most of the water soluble cellulose ethers can be used
as a viscosifier and to provide suspension for the sized salt particles
of th~ invention. Said cellulose ethers which can be used include, among
others: the various carboxyalkyl cellulose ethers, e.g., carboxyethyl
cellulose and carboxymethyl cellulose (CMC); mixed ethers such as carboxy-
alkyl hydroxyalkyl ethers, e.g., carboxymethyl hydroxyethyl cellulose
(CMHEC); hydroxyalkyl celluloses such as hydroxyethyl cellulose, and
hydroxypropyl cellulose; alkylhydroxyalkyl celluloses such as methyl-
hydroxypropyl cellulose; alkyl celluloses such as methyl cellulose, ethyl
10 cellulose, and propyl cellulose; alkylcarboxyalkyl celluloses such as
ethylcarboxymethyl cellulose; alkylalkyl celluloses such as methylethyl
cellulose, and hydroxyalkylalkyl celluloses such as hydroxyethylmethyl
cellulose, hydroxypropylmethyl cellulose; and the like. Many of said
cellulose ethers are available commercially in various grades. The
15 carboxy-substituted cellulose ethers are available as the alkali metal
salt, usually the sodium salt. However, the metal is seldom referred to
and they are commonly referred to as CMC, CMHEC, etc. For example, water
soluble CMC is available in various degrees of carboxylate substitution
ranging from about 0.3 up to the maximum degree of substitution of 3Ø
20 In general, CMC having a degree of substitution in the range of 0.65 to
0.95 is preFerred. CMC having a degree of substitution in the range of
0.85 to 0.95 is a more preferred cellulose ether. CMC having a degree of
substitution less than the above preferred ranges usually provides too low
a viscosity and is thus less desirable. Said degree of substitution of CMC
r 25 is commonly designated in practice as CMC-7, CMC-9, CMC-1~, etc., where the
7, 9, and 12 refer to a degree of substitution of 0.7, 0.9, and 1.2,
respectively. CMC having a degree o~ substitut;on of 0.7 through 0.9 serves
quite well and can be used with the saturated saline and salt particles.
For example, in CMHEC it is preferred that the carboxymethyl degree of sub-
30 stitution be at least 0.4. The degree o~ hydroxethyl substitution is less
important and can range widely, e.g., from about 0.1 or lower to about 4 or
higher.
Xanthan gum, which is used as a suspending agent, is also available
commercially. It is a hydrophilic colloid produced by bacteriurn of the
3~ species Xanthamonas campestris. The colloid is a polymer containing man-
nose, glucose, glucuronic acid salts such as potassium glucuronate, sodium
glucuronate, or the like, and acetyl radicals. Other Xanthamonas bacteria
have been found which produce the hydrophilic gum and any o~ the xanthan
gums and their derivatives can be used in this invent;on.
~2~
_ g
Xanthan gum is a high molecular weight linear polysaccharide that
is readily soluble in water to form a viscous fluid~ Examplary of the
xanthan gums that can be employed is an industrial grade of xanthan gum
marketed by the Kelco Company under the trademark Kelzan XC xanthan qum.
Xanthan gum increases the gel strength of the fluid without appreciably
increasing its viscosity.
Guar gums and their deri~atives can also be used. Guar gum is a non-
ionic naturally occurring, high molecular weight polysaccharide. For
example, hydroxypropyl guar gum and carboxymethyl hydroxypropyl guar~ and
quaternary ammonium guar gum may be used.
Other suitable viscosifiers and suspension agents can be employed
other than those specifically men~ioned above9 and I have found that any
one of such viscosifiers and suspension agents, or any combination Qf mix-
ture of suitable v;scosifier and suspension agents may be employed, including
those mentioned above in any amount as may be desired and preferably in
the range of about 0.5 kg/m3 to about 15 kg/m3 of saturated saline so1ution.
The treating fluid utilized in step (c) comprises a suspension of a
particulate sized bridging material suspended in a saturated aqueous saline
solution in which the water soluble particulate sized salt packed within
the perforation channels and the particulate sized bridging material are
substantially insoluble. Conveniently, and preferably, the saturated
aqueous saline solutions utilized in steps (a~, (b), and ~c) are the same,
and most preferably both comprise saturated sodium chloride solutions.
The particulate sized bridgin~ material may be water soluble, acid
soluble, or oil soluble. Examplary acid soluble materials are calcium
carbonate, dolomite, Colemanite (calcium borate, C2B6011-5H20), Ulexite
(a sodium calcium bora~e, NaCaB509-8H20), Probertite (a sodium calcium
borate, NaCaB509-5H20), and mixtures thereof. See for example Smithey
U.S. Patent No. 3,986,964, and PCT application No.
PCT/US83/01408 filed September 15, 1983, published as
International Publication No. WO85/01309 on March 28, 1985
(U.S. Patent No. 4,620,596 issued November 4, 1986).
Exemplary oil soluble materials are well known in the art,
such as waxes, resins and the like. See for example the
following U.S. Patents: Fisher et al 3,882,029; Jackson
et al. 3,878,141; and Jackson et al. 3,785,438.
Exemplary water soluble materials include the salts
disclosed hereinbefore for use in steps (a) and (b).
Their use in workover and completion
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fluids o,f the type utilized as the tr~ating fluid in step
(c) o~ the present invention is disclose~ in the following
U.S. Patents: Mondshine 4,175,042; Mondshine 4,186,803;
and Mondshine 4,369,~43.
The particulate sized brid~ing material must have a
particle size range and distribution which produces a low
permeability seal or film, i.e., a workover and completion
fluid which has a low fluid loss. This is well known in
the art. Fo~ example, the U.S. Patents and International
Publication referenced above disclose a particle size and
range which is effective for the bridging materials
disclosed ther ein.
Preferably the particulate sized bridging material comprises one or
more of the water soluble salts disclosed prev;ously including sodium
15 chloride, potassium chloride, calcium chloride, magnesium chloride, sodium
sulfate, sodium carbonate, sodium bicarbonate, potassium carbonate, cal
cium bromide, sodium bromide and potassium bromide. As disclosed in the
referenced Mondshine patents, these salts to be effective in producing a
low permeability film must have a particle size in the range from about
~0 S microns to about 800 microns wherein greater than about 5% of the
particles are larger than 44 microns; preferably greater than about 50%
of the particles are smaller than 30 microns. This is the preferred
particle size range and distribution for all particulate sized bridging
materials used. Generally the concentration of the bridging material will
25 be in the range ~rom about 10 kg/m3 to about 150 kg/m3.
The treating fluid containing the particulate sized bridging material
utilized in step (c) must contain a viscosifier to keep the bridging material
suspended therein. Any of the viscosifiers and the concentrations thereof
disclosed for use in the treating fluid of steps (a) and (b) can be used in
the treating fluid of step (c). Additionally, a fluid loss additive such
as calcium lignosulfonate can also be present in the treating fluid of
step (c) to further decrease the permeability of the film (i e., "filter
cake") formed on the surface of the salt pack, all as is well known in the
art.
The treating fluid utilized in step (e) may be any aqueous fluid in
which the water soluble particulate sized salt within the perforation
channels is soluble. Thus this treating fluid must be non-saturated with
respect to the water soluble particulate sized salt. Preferably this
treating fluid contains one or more additives which minimizes the swelling
and/or dispersion of any argillaceous materials in the subterranean formation
surrounding the perforation chann~ls, and beyond, such as potassium
chloride, zirconium compounds, titanium compounds, and the like~ all
as is well known in the art. Most preferably this treating fluid will
contain no particles which may reduce the permeability of the formation.
Conveniently the treating fluid utilized in step (e) may be the
carrier fluid containing the sized sand (gravel) to be packed into the
perforation channels. Thus as the ~ater soluble particulate sized salt
is dissolved in the carrier fluid,~ the perforation channel is opened and
the sand is deposited within the perforation channel.
The treating fluid utilized in steps (a) and (b) can conveniently
be present in the well bore during the perForation operations. In this
manner the water soluble particulate sized salt will help prevent the
entry of formation solids into the perforation channels, thus facilitating
clean up of the channels.
The low permeability seal or film on the surface of the salt pack is
readily removed in step (d) by either dissolving the particulate sized
bridging material in an appropriate fluid, thus destroying the low perme-
ability seal or by mechanical means. Thus if the bridging material is
water soluble, a non-saturated aqueous solution can be used. If the
bridging material is acid soluble, an acidic solution can be used. And
if the bridging material is oil soluble, an organic solvent can be used
Since the seal is on the outside of the perforations, it can be removed
by mechanical means well known in the art.
Gravel packing fluids are well known in the art. Thus such Fluids
contain a solids free carrier fluid, i.e., a filtered fluid, with a siz~d
sand suspended therein with a polymeric viscosifier of the type disclosed
herein.
The method of the invention may be practiced as follows:
The process of the invention may be applied to protect the perforations
in a well whenever the well must be killed and protected from solids intrusion
and excessive fluid and solids invasion into the formation. In a typical
example, prior to gravel packing, a well must be killed and controlled in
order to place a packer assembly and production screen in the well. In
the practice of this invention, the kill fluid is preceded by two pills.
The first pill contains the water soluble particulate sized salt suspended
in a saturated aqueous saline solution as disclosed hereinbefore to fill
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the perforations with a highly permeable pack of the water soluble
particulate sized salt. The second pill~ the sealing or bridging type
pill containing a particulate sized bridging material suspended therein
as disclosed hereinbefore, follows irnmediately behind the salt pack pill.
Both pills are pumped downhole by the kill fluid. Placement of the pills
is accomplished by either bull heading or by circulating to kill the well.
The fluids can be pumped down the tubing or down the tubing casing annulus
depending on the tool assembly and downhole requirements.
The volume of each pill depends upon the placement procedure, the
hole size, the downhole assembly, and tubing-casing capacity. Generally
the volume requirement of each pill is estimated to adequately fill the
rat-hole and then cover the perforated interval. Normally from about
0.5 m3 to about 1.0 m3 of the salt pack (first) pill is used, followed by
a 1.5 m3 to about 3.0 m3 volume of the sealing type (second) pill. The
~5 second or sealing pill must fill the annulus of the perforation interval
whereas the salt pack pill need only fill the perforations. Consequently,
a much smaller volume of the salt pack pill is needed.
Once the pills have been placed and the well is killed, suitable
tools can then be run into the hole and gravel placement techniques can
be applied to prepare the well for production. Thereafter when desired,
but before packing the perforation channels with gravel if gravel packiny
is desired, the sealing cake on the surface of the perforations is removed
either mechanically or chemically as by dissolving the particulate sized
bridg;ng material, or a combination of these methods. Any fluid circulated
across the face of the perforations will erode and mechanically remove the
sealing cake by hydraulic action. Preferably the fluid is a -fluid in which
the particulate sized bridging material is soluble. After the sealing cake
is removed from the surface of the salt pack within the perforation channels,
the salt pack (i.e., the water soluble particulate sized salt) is removed
by contacting the perforations with an aqueous fluid which is non-saturated
with respect to the water soluble particulate sized salt. If the perfora-
tions are to be filled with gravel, the gravel carrier fluid can be formu-
lated to dissolve the water soluble particulate sized salt and thus allow
the gravel to fill the opened perforation channels.
The method can also be utilized in non-gravel pack completions or
workovers. Thus a perforated well within a depleted pressure zone is highly
susceptible to excessive fluid loss. The well must be controlled by
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temporarily sealing the perforations. The method of this invention
protects the perforations and assures a subsequent effective clean-up
of the perforations. The method of application is similar to the
technique previously described. In this case usually a larger volume
of the sealing pill may be used, such as from about 1.5 m3 to about
5 m3. A~ter placement of the salt pack pill and the sealing type pill,
well workover operations as desired may be conducted. Thereafter, the
- sealing cake, and water soluble particulate sized salt within the per-
forations, are removed as discussed hereinabove. In some cases, the
well can be cleaned-up for production by swabbing or by pressure under-
balance and may not require washing.
The composition of the salt pack pill requires a saturated saline
solution, a viscosifier, and suspended water soluble particulate sized
salt particles. A typical pill contains about 1.5-3.0 kg/m3 of a water
soluble polymer, preferably Xanthamonas campestris biopolymer, and about
70 kg/m3 o~ 74 to 300 microns particulate sized salt in a saturated
aqueous salt solution. Standard drilling or workover rig equipment and
procedures are used to prepare the pill. ~t least 20 kg/m3 of a water
soluble particulate sized salt must be present to insure that all of the
suspended salt does not dissolve at downhole temperatures. Other water
soluble polymers as disclosed herein can be used in place o~, or in com-
bination with, the biopolymer, such as hydroxyethylcellulose, guar gum
and derivatives thereof, etc.
The composition of the sealing pill requires a saturated saline
solution in which the water soluble particulate sized salt within the
perforation channels is substantially insoluble, a viscosifier, and sus-
pended particulate sized bridging materials. A typical pill contains about
5 kg/m3 of a water soluble polymer, such as Xanthamonas campestris bio-
polymer, hydroxyethylcellulose, carboxymethylcellulose, hydroxypropyl guar
gum, and the like, and about 50 kg/m3 of a parkiculate sized bridging
material having a particle size in the range from about 5 microns to about
800 microns wherein at least 5% of the particles have a particle size
greater than 44 microns and wherein at least 50% of the particles have a
particle s;ze less than about 30 microns in a saturated aqueous saline
solution. Standard drilling or workover rig equipment and procedures are
used to prepare this sealing pill.
