Note: Descriptions are shown in the official language in which they were submitted.
Docket No. DF-673 (DP 50 6-1041
ACCE~ERATING SET OF RETARDED CEMEN~
SPECIFICATION
Field of the Invention
This invention relates to cementing oil and ~as
wells. More particularly, this invention relates to
accelerating set of cement that is highly retarded:
such as, retarding drilling 1uid converted to cement:
or retarded con~entional cement~, including cement
slurries that mi~ht commingle with a drilling fluid or
otherwis~ become conta~inated with a retarding
chemical.
Back~round of ~he Inven-tiQn
The prior art i5 replete with a wide variety o~
both inorganic and organic cQment accelerators. In a
co-pending application, Docket DP-50-~-980~, serial
number 07/131,878, entitled 'tCEMENTING OIL AND GAS
~ELLS USING CONV~RTED D~ILLING FLUI~" o~ Whlch the
present co-inventors are co-inven~or~ and having the
same assignee, there was discus~ed ~he completion o~
oil and gas well~ by convertin~ of a drilling ~luid, or
"mud", to a cement, and several patents were cited
therein Which disclose compositions for accomplishing
thi~.
In that application it was noted that ef~orts to
convert drilling fluid containing cementitious
materials have posed problems such as increased
viscosi~y due to ~loccula~ion as cementitious material
is added to the drilling mud, and subsequently pumped
into the wellbore. Therein was ci~ed U.S. 3,499,~91,
,'~", ~ ,JJ .
which describes di~ficulties with yelling
characteristics and, particularly, temperaturP
sensitivity.
In both primary and remedial applications, it is
also sometimPs desirable to set retarded cement
formulations more rapidly. Typically cement is
retarded for pumping into wellbore annuli or
perforations where it is desirable to have a contxolled
viscosity and set ti~e to permit safe cement slurry
placement, but also desirable to have the slurry set
rapidly after placement. For example, to allow ample
time for placement of c~ment formulations before set,
retarders are ~requently added to prevent the
development of high viscosities or premature setting of
cement slurry during the pumping and ~queezing into the
annular ~oids or perforations. Yet, these retarders
can also delay the setting of the cement for long
periods o~ time after placement even under in situ
conditions. Excessive set times contribute to high
operational costs due to rig ~ime ~tandby. Thus, ik is
desirable that a compatible accelerator be employed in
some fashion to greatly reduce the set time fsr the
cement.
The same i6 krue when setting cement in the form
o~ plugs in the wellbore. This may be ~or pluggillg the
well; form~tion pack of~, or seal ofP between
productive fo~mations or otherwise; and/or or wellbore
deviation. Fre~uantly, gravity or other ~actors cause
the cement plug to intermin~le or become contaminated
with the drilling fluid. The drilling fluid is an
e~ective cement ~et r~tarder and prevents or de].ays
the set of the cement plug. In any event, it is
sometimes desirable th~t an over wash be provided to
accelerate the set of the cement strength development
without adversely af~ecting pumping time.
Summary of the Inventio~
Accordingly, it is an objec~ o~ the present
invention to provide improved composition and method
that will increase the rate of set of retarded cem~nt
regardless of what application it is employed in.
It is a specific object of this invention to
provide a composition in which the drilling fluid can
be converted to a cement which will ~et up within a
desirable time after the cementitious material i5 added
thereto.
These and other objects will become apparent from
the descriptive matter which follows.
In a broad aspect of this invention, there is
provided a compatible accelerator for accelerating the
set strength development rate of a retarded cement in
any application.
In accordance with one aspect of this inventio~,
there i8 provided a method of accelerating the set of
highly retarded cementi by overwa~hing a r~tarded
cement composition with a compatible accelerator that
will decrease the setting tim~ for the cement in
annular voids or perforations and/or in a plug in a
wellbore.
In accordance wlth another aspect of th:is
invention, there i8 provided a cement composition for
cementing any design~ted section o~ a wellbore wherein
the space in the wellbore i~ occupied by a drilllng
fluid. The composition comprises a quantity of the
drilling ~luid containing YiSCoSity control agents
which ~erve as re~arder~ when the cementitious ~aterial
is added; a dry cement material, a dispersant, and an
accelerator that is compatible.
By compatible accelerators i~ meant an accelerator
that contains a material that will fo~n ~o~n~te ions
without a violent reaction with basic cement slurry
constituents in the cement slurry. We have obtained
excellent results with formamide and know that it works
regardless o~ whether or not the theory reyarding
formate ion is correct. Other sources of formate ion
in cement slurry are salts of formic acid and esters of
formic acid. For example, it is known that the first
four carbon ester~ of formic acid will react
satisfactorily ~ast to give good results. These esters
include the methyl ester of ~ormic acid, sometimes
called methyl formate; the ethyl ester of formic acid,
sometimes called ethyl formate; the propyl, both iso-
and normal-propyl estsr of for~ic acid, sometimes
called, respectively, iso-propyl formate or normal-
propyl formate; and the butyl, iso-, normal-, or
tertiary-butyl ester of ormic acid, sometimes called
iso-, normal- or t-butyl fo~ate. Whether or not the
theory of hydrolysis i5 correct, we do obtain excellent
results with the~e fir~t ~our carbon esters o~ formic
acid and know that they worX regardless of whether or
not ~he theory ia correct~
In another aspect, this invention provides
method ~or treating a well in which the suhterrarlean
formation about the well may or ~ay not be ~ractured
and a retarded cement slurry is applied to seal o~
annular voids and per~orations~ There is also provided
the method for improvement o~ washing over th~ cement
with a solution o~ a compatible organic accelerator
such as the material that w~ll yield formate ions, as
delinea ed hereinbefore.
In another aspect of thi~ invention there is
provided a method for accelerating a cement plug in a
well completed in a subterranean ~ormation where cement
is pumped into the well and allowed to set to fo~n a
plug therewithin~ The improvement comprises either
washing over the cement plug with a ~olution o~ a
compatible organic accelerator or pumping the plug into
~ ~J
an interval of the well previously filled with the
compatible organic accelerator. The compatible oryanic
accelerator is khe material that will yield formate
ions in the cement slurry, as d~lineated hereinbe~ore.
These compatible organic accelerators can be
employed alone or in combination with o~her known
accelerators, such as but not limited to those
inorganic accelerator~ like silicates (sodium
metasilicate, sodium silicate, or potassium silicate)
or chlorid2s (sodium chloride, potassium chloride, or
calcium chloride).
Description of Pxeferred ~mbodiments
The cunversion of ~ell drilling fluids lnto cement
slurries for th~ purposes of cementing in wellbores to
casing annulus, and/or performing other wellbore
cementing applications i~ attractive for several
reasons; one of which would be that a major portion o~
the drilling fluid would not be ~ubject to waste
disposal regulations. Moreover, the conversion o~
drilling flùid to a cement ~lurry minimizes the
handling o~ drilling ~luid a~ter completion of the
well, and minimizes the cement expense, and the mud
cement will ef~ect a ~ore nearly compl.ete dl~placement
o~ the drllling ~luid.
The convQr~ion oP drilling fluid, or "mud" to a
cement slurry is not without some operational problems
and undesirable compo~itional changes~ For example,
the addition vf cementitious mat~rial such a~ mixtures
of lime, ~ilica, alu~ina or lime and magne~ia, silica
and alu~ina and iron oxid~, or cement materials such as
calcium sulfate and Portland cement to aqueous drilling
fluids can substantially increa6e the Visc08ity 0~ the
fluid ~ixture and cause ~evere ~locculakion. E~forts
to circulate such mixture~ through a wellbore can
result in highly unsati~factory circulation rates,
;
restricting flow in the wellbore annulus, increasing
pressures, resulting in breakdown of the earth
formations in the vicinity of the wellbore. In
addition, excessive viscosity contributes to failure of
the surface operations to mix the cement slurry
proparly. Certain dispersants have been developed for
use in these drilling fluids during the drilling
operations. These include lignite, ligno-sulfonates,
and polyacrylates. Other disper~ants have been used:
particularly, in the situation where it is desired to
convert a drilling mud to a set cement. These other
dispersants are discus~ed in co-pending application DP
50 6-980A, now serial numb~r 07/131,878.
It is well recognized by those ~killed in the ar~
that these normal constituents of drilling mud also act
as retarders, which inhibit the setting of cement
slurries. Specifically, it may take a week or longer
~or such converted drilling mud cement~ to set, and it
i8 de irable to horten thl~ time.
It is believed helpful to discuss this conversion
of drilling mud to cement ln greater detail b0fore
looking at other embodiment~ ~or which this inv4ntion
is useful. The process for converting a drilling mud
to a cement 61urry for cementing a well is di~cu~sed in
the above-re~erenc~d serial number 07/131,878, and does
not require detailed explanation herein. Details o~
that application are included herein by re~erence.
Expressed otherwise, the operation simply comprises a
casing that iB extended into a portion of the formation
Prom a wellhead with a ~econd casing extending into the
formation further as a wellbore is deepened to form an
annulus which may include washouts or void areas behind
the casing. The casing is adapted to be in
commun~cation with the pump ~or circulating drilling
Pluid through the interior of the casing, up the
annulu~ and through a return conduit to a storage tank
~J~7,~ J1~,7~
or pit and is recirculated khrough the pump in normal
drilling operations. Conventional drilling fluid
conditioning devices such as shale shakers, sand
separators and related equipment may be employed; but
are normally not shown in schematic illustrations in
the interest o~ clarity. One method for converting a
drilling fluid into a cementitious slurry is the
addition o~ premixed quantities from storage of dry
blended cement formulation for conduction to a slurry
mixing operation. The ~ormulation is added ~o a slurry
and mixe~ into the drilling fluid which is thereby
converted into a cementitious slurry. It is at this
point that it is convenient to add accelerators or the
like to at least neutralize the 6et retarding effects
of the varlous dispersants that may have ~een present
in the drilling fluid, or added to the drilling fluid
in the cement conversion process.
As described hereinbefore, compatible accelerators
comprise the materials which will yield the formate
ions without the violent reaction. We know ~rom
experimental data that for~amide will provide excellent
results and that th~ ~lrst ~our carbon esters oE formic
acid will provide qood result~.
These material~ ar~ di~cussed in Haakh'3 Chemical
Dictionary and do not re~uire ~urther description
herein.
In thia invention, a compatible accelerator is
employed when a concentration range of from 0.05 to
about 2.5 gallons per ~arrel of original drilling fluid
is present. A better concentration is a range of 0.3 -
1.2 gallons per ~arrel of cement ~lurry employed7 The
concentration may vary from this for a specific
application. For most applications khe optimum
concentration is about 0.6 gallons per barrel of cement
slurry. This will result of a setting time for the
cementitiou3 slurry of approximately twenty-~our hours,
which is substantially ~horter than the prior art
retarded cements.
When employed in an over wash, the compatible
accelerator is in a concentration within the range of 5
percent by weight to 100 percent by weight, the
remaindert if any, being water.
As indicated, this invention is useful also when
an over wash is employed a~ter squeezing cement through
perforations or in casing cracks. A highly retarded
cement may be emplaced and then wa~hed over with a
solution containing the compatible accelerator; for
example, the first four carbon esters of formic acid.
The differential pressure extended from the wellbore
into the formation will ~orce the liquid that is
employed as the over wash solution containing the
cement accelerator into the permeable cement matrix.
Normally, such an over pressure i~ ln the range of from
200 500 pound~ per 6quare inch ( psi) greater in the
well than it i5 in the form~tion so it tends to e~fect
flushing of the over wa~h solution containing the
ce~ent accelerator through t~e hydrating cement matrix.
The compatible accelerator can be employed to
mitigate adverse e~ect~ of contamlnation ~rom in situ
mixing with ~luids, ~uch as drilling ~luids, in any
application. Speciiically, i~ too much ret~rder is pu~
into a cement slurry, an e~ective amount of compatible
accelerator can be employed to neutralize the retarder
and get it back into the desired range.
In another operation, the ~olution containing the
accelerator may be 6potted below a cement to be placed
in a well ~o form a plug. Thereafter a spot of liquid
containing the cement accel~rator may be positioned
above the cement. A ~urfactant may be employed in a
small concentration o~ about 0.1 ~1.0 percent (~), if
des~red, in th~ preflush~ cement ~lurry, or overflush,
l~ /S;
to decrease the interfacial tension and help the
surrounding fluids to penetrate into the cement matrix.
The accelerators have the property o~ accelerating
the set o~ the cement and have the potential for
immediate application in the conversion of mud to
cement and as an over wash additive, or Por washing an
acceleratiny solution from both above and/or below to
produce acceleration of cement nodes in remedial
squeeze operations, cement plugs in plugback, kicko~f,
whipstock procedures, or cement at the top of liners
after liner cementing operations.
EXAMPLE
The ~ollowing example illustrates both a control
without this invention and laboratory experiments
performed to ~imulate field conditions and show
e~fectiveness o~ the accelerator.
EXAMPL~ I
Xn thls exampl~ from 350 cubic c:entimet~ri (cc's),
serving as an experimental one barrel quantlty, o~
10.45 pounds (lb~.) per gallon (ppg) Rapid Mud (a
trademark o~ Baroid Corp) wa~ employed with 175 cc's
serving as 0.5 barrel of water, and 300 lbs. per barrel
(coarse grind) Raiser Cement in a quant~ty of 300 grams
was employed wikh 2.25 lbs. per barrel (2.25 gram SSMA,
which is ~ul~onated styrene ~aleic anhydride
copolymer). The result was a retarded cement having a
density o~ 12.3 pounds per gallon. This served as a
base ~or comparison and had 0 psi compressive strength
and had not even begun to ~et up after 4 days, but
after 4.6 day~ it gave a compressive strength o~ 50 psi
and a~ter 11 day~ gave a compressive strength of 500
``` ~,;~i i"! ,/1
psi but the pumping time was still about 48~ hours at
94 degrees Fahrenheit.
In contrast, 350 cc's of 10.45 ppg Rapid Mud in
175 cc's water, giving 300 lbs. per barrel ~coarse
grind) Xaiser Cement with 3 gms. (lbs. per barrel) SSMA
and 2.4 gal/bbl, or 20 ml., of formamide, gave a
compressive strength of 50 psi ~pounds per square inch)
after only 18 hours; 460 psi after 4 days and 562 psi
after 11 day~. The pumping time remained unchanged at
48+ hours at 94 degrees Fahrenheit.
Although this invention has been described with a
certain degree of particularity, it is understood that
the present di~closure i8 made only by way of example
and that numerous changes in the details of
; construction and the combination and arrangement of
part~ may be resorted to without departing fro~ the
spirit and the scope of the invention, re~erence being
had for the latter purpose to the appended claims.
