Workover fluid

The high temperature water loss property of alkaline well completion and well workover fluids is improved by the addition of an effective amount of a naphthalene sulfonate formaldehyde condensate in the form of its monovalent or bivalent metal salts.

FIELD OF INVENTION 
This invention relates to the drilling and servicing of wells and more 
particularly to aqueous well completion and workover fluids for use in 
drilling wells drilled into such formations. In accordance with another 
aspect, this invention is concerned with the addition of water loss 
additives to well workover and well completion fluids. 
In the servicing of wells drilled into subterranean formations, clear water 
and various brines and viscous aqueous solutions have been proposed as 
well completion and workover fluids. These fluids generally do not possess 
the requisite properties of density, viscosity, gel strength, stability 
and low fluid loss desired for these applications. Hence, need exists for 
a non-damaging well completion-workover fluid having said requisite 
properties for use in completing wells drilled through permeable strata 
and in conducting workover and similar operations in such wells but which 
will not result in any formation damage to said permeable strata. 
Accordingly, it is an object of this invention to provide improved well 
completion and well workover fluids. 
Another object of this invention is to provide substantially clay-free well 
completion and well workover fluids. 
Another object of this invention is to provide well completion and well 
workover fluids exhibiting low fluid loss properties. 
Other objects, aspects, as well as the several advantages of the invention 
will be apparent upon reading the specification and the appended claims. 
According to the invention, an effective amount of at least one naphthalene 
sulfonate formaldehyde condensate (NSFC) is added to packer and workover 
fluids to improve water loss control. 
In accordance with the invention, the high temperature water loss property 
of alkaline clay-free well workover and well completion fluids is improved 
by the addition of a water loss reducing amount of an additive selected 
from metal salts of naphthalene sulfonate formaldehyde condensates. 
In accordance with a specific embodiment of the invention, the high 
temperature water loss property of clay-free well workover and well 
completion fluids comprising water, an electrolyte, such as sodium 
chloride, an acid soluble weighting agent, such as calcium carbonate, an 
acid soluble suspending agent, such as asbestos, a polymeric viscosifier, 
such as carboxymethyl cellulose, and an alkaline reagent, such as Na.sub.2 
CO.sub.3, is improved by the addition of monovalent and bivalent metal 
salts of condensation products of naphthalenesulfonic acid with 
formaldehyde. 
In accordance with the invention, it has been found that the metal salts of 
naphthalene sulfonate formaldehyde condensates are effective high 
temperature water loss control additives for clay-free wellbore completion 
and workover fluids. 
The high temperature water loss control additives of the invention can be 
defined broadly as naphthalene sulfonate formaldehyde condensates. These 
are also known as sulfonated condenstion products of formaldehyde and 
naphthalene or salts thereof having molecular weights varying between 
about 300 and about 3,000. The additives of the invention are also known 
as metal salts of condensation products of naphthalenesulfonic acid with 
formaldehyde. Naphthaleneformaldehyde sulfonic acid can be prepared by 
reacting a mixture of naphthaleneformaldehyde condensate and sulfuric 
acid. The metal naphthaleneformaldehyde sulfonate can be prepared by 
reacting a metal oxide or other metal salt with an aqueous solution of 
naphthaleneformaldehyde sulfonic acid to obtain the desired metal. 
Presently preferred metal salts are the alkali metal salts. Mixtures of 
the additives can be used, if desired. 
Condensed naphthalene sulfonates suitable for use in the present invention 
are marketed by a number of companies under various trade names and the 
preparation of some of these are set forth, for example, in U.S. Pat. No. 
3,537,869; U.S. Pat. No. 3,686,133; U.S. Pat. No. 4,036,839; and U.S. Pat. 
No. 4,184,887; all of which are incorporated herein by reference. The 
naphthalene sulfonate formaldehyde condensate (NSFC) is commercially 
available as Lomar, CFR-2, Tamol, SM and TIC. Two of these, TIC and CFR-2, 
may contain an antifoaming agent (U.S. Pat. No. 3,820,602 and U.S. Pat. 
No. 3,804,174). In the case of CRF-2, the polyvinylpyrrolidone (PVP 
antifoaming agent) may also prevent the separation of free water from 
cement slurries (U.S. Pat. No. 3,359,225). Lomar is a tradename for 
unblended sodium NSFC. A letter suffix is used to designate viscosity 
grades. 
The amount of additive present in the instant compositions is an effective 
amount sufficient to reduce the water loss properties of well completion 
and well workover fluids. The use of naphthalene sulfonate formaldehyde 
condensates in the inventive compositions is effective at a concentration 
of at least 0.5 lb/bbl up to about 10 lb/bbl total composition. In 
compositions for high temperature water loss control, the amount of 
additive varies from about 0.5 to about 6 lb/bbl. 
The electrolyte can be a water soluble inorganic salt such as the halide 
and nitrate salts of sodium and potassium together with the ammonium salts 
including sodium chloride, potassium chloride, sodium bromide, potassium 
bromide, sodium nitrate, ammonium nitrate, ammonium chloride, ammonium 
bromide and the like and mixtures thereof. Saturated sodium chloride 
solution is presently preferred as the base fluid in the inventive 
compositions which exhibit densities in the range of about 10 to 14 lb/gal 
after the addition of selected acid soluble weighting agents. Sea water 
can be used for preparation of workover fluids with densities in the range 
of about 9 to 14 lb/gal. Thus, the instant invention is applicable to 
improving the water loss properties of workover fluids having densities in 
the range of about 9 to about 14 lb/gal. 
Weighting agents which are completely acid soluble such as CaCO.sub.3, 
BaCO.sub.3 and iron carbonate are used in the inventive compositions to 
give densities in the above recited ranges. These additives are completely 
acid soluble and can be dissolved and back flushed with acid from 
subterranean formations to prevent formation damage or plugging. 
Presumably such undesirable formation damage can occur with workover 
operations using fluids comprising non acid-soluble weighting agents such 
as barium sulfate. Ideally, a workover fluid should contain no solids, 
however, the addition of insoluble weighting agents is frequently 
necessary to raise fluid density to the desired level. The less preferred 
ferric and ferrous oxides can also be used as weighting agents in the 
inventive compositions. Ferrous oxide is preferred over ferric oxide 
because of the former's greater solubility in 15 percent HCl which is the 
fluid frequently used to correct formation damage. 
The amount of weighting agent employed can vary appreciably and will be 
sufficient to provide compositions having the desired densities. In 
general, the amount can range from about 15 lb/bbl to about 400 lb/bbl of 
fluid, preferably about 160 lb to about 380 lb/bbl of fluid. 
Suitable viscosity characteristics can be imparted to the inventive 
compositions by the use of viscosity additives comprising natural water 
dispersible polymers such as guar gum, cellulose ethers such as 
carboxymethyl cellulose, biopolymers and the like. Representative examples 
of suitable cellulose ethers and biopolymers that can be used are set 
forth in U.S. Pat. No. 3,785,437 which is incorporated herein by 
reference. With these viscosity additives the carrying capacity of the 
fluid will vary in the agitated and non-agitated states, thus, for 
example, in a non-agitated separating tank, the accumulated fluid loses 
its carrying capacity and sand, debris and the like drop out whereas the 
agitated fluid has sufficient carrying capacity to carry cuttings and the 
like to the surface should the fluids be used for such purposes. These 
viscosity-increasing additives exhibit effectiveness as water-loss agents 
in general, however, in the present compositions the overall high 
temperature water-loss property of the fluids is greatly improved by the 
addition of naphthalene sulfonate formaldehyde condensates. 
The amounts of polymeric viscosifier employed in completion and workover 
fluids can vary appreciably and are known in the art and generally range 
from about 0.25 lb to about 3 lb/bbl of fluid, preferably from about 0.75 
lb to about 2 lb/bbl. 
The aqueous well completion and workover fluids of the invention contain 
sufficient alkaline material to provide the desired alkalinity. The amount 
of alkaline material present in the fluids can vary depending upon the 
alkaline reagent added but will be sufficient to provide initially a pH of 
about 9, preferably 10 to 12. The amounts added ordinarily will range from 
about 0.1 to about 10 lb/bbl, preferably from about 2 to about 7 lb/bbl as 
for example when sodium carbonate is employed. In the working examples 
hereinbelow, initial pH values were on the order of 10. After thermal 
aging, pH values were in the range of 8 to 9. 
Suitable alkaline materials include ammonia, compounds of alkali metals 
such as hydroxides, carbonates, bicarbonates, orthosilicates, silicates, 
phosphates, and borates or other known alkaline materials. The carbonates, 
such as sodium carbonate, are often used for this purpose. 
Whereas asbestos is preferred as an acid soluble suspending agent for the 
weighting material in the inventive compositions other suspending agents 
such as ground paper can also be used. In this role asbestos is relatively 
inexpensive and the desirable flow characteristics (rheological 
properties) of the fluid systems are maintained. Of the various types of 
asbestos which are commercially available the asbestos derived from 
chrysotile is presently preferred. The chrysotile asbestos fibers provide 
maximum carrying or suspending properties with a minimum of asbestos. 
The amounts of suspending agents employed in completion and workover fluids 
are known in the art and generally range from about 1 lb to about 3 lb/bbl 
of fluid, preferably from about 1.5 lb to about 2.5 lb/bbl. 
The completion and workover fluid compositions of this invention are 
prepared by admixing the desired proportion of the various ingredients 
with water. All of the ingredients are fairly readily dissolved or 
dispersed in water by circulation through the conventional mixing 
equipment of a rotary drilling rig.

EXAMPLE I 
A base mud comprising saturated salt water, 2 lb/bbl carboxymethyl 
cellulose, 2 lb/bbl asbestos fiber, 5 lb/bbl sodium carbonate and weighted 
with 295 lb/bbl ground limestone was prepared. Two commercial grades of 
the naphthalene sulfonate formaldehyde condensate (NSFC): Lomar (an 
unblended material) and CFR-2 (a blend containing a polyvinylpyrrolidone 
anti-foaming agent), were mixed into aliquots of the base mud. The 
materials were run at concentrations of 1 and 5 lb/bbl. Test results are 
summarized in Table I. 
TABLE I 
__________________________________________________________________________ 
300 F. 
Run 
NSFC, 
Aging, 
Bleeding 
No. 
lb/bbl 
Days 
mL SS.sup.a 
PV/YP.sup.b 
Gels.sup.c 
WL.sup.d 
pH 
__________________________________________________________________________ 
1 -- 0 -- -- 80/16 
1/3 4.8 10.4 
0.6 8.6 140 
37/8 1/13 
30 8.9 
Part A: Lomar* 
2 1 0 -- -- 76/34 
2/3 4.0 10 
0.6 27 170 
45/16 
2/19 
16.8 
8.7 
3 5 0 -- -- TTTM.sup.e 
12/13 
2.0 10.1 
0.6 Too foamy to measure 
Part B: CFR-2** 
4 1 0 -- -- 78/25 
3/5 3.6 10.5 
0.6 15.5 80 
59/17 
3/9 16 8.9 
5 5 0 -- -- 78/22 
2/6 2.6 10.2 
0.6 30 220 
68/19 
2/20 
11 8.5 
__________________________________________________________________________ 
.sup.a Shear strength, lb/100 sq. ft. (shear strength and bleeding are no 
measured initially.) 
.sup.b Plastic viscosity, cp,/yield point, lb/100 sq. ft. 
.sup.c Gel strength, lb/100 sq. ft. (initial/10 minute) 
.sup.d Water loss, ml in 30 min. 
.sup.e Too thick to measure. 
*NSFC is not blended with an antifoaming agent. 
**NSFC is blended with polyvinylpyrrolidone (PVP) as an antifoaming agent 
 
Referring to the results in Table I, it is evident that for higher 
concentrations of NSFC an antifoaming agent such as polyvinylpyrrolidone 
(PVP), is necessary. Initially the fluid of run 3 with 5 lb/bbl of 
unblended NSFC (Lomar ST) had a viscosity too high to be measured with a 
Fann VG meter, model 35. This is because of the fine foam entrapped in the 
sample. The initial gel strength is high because of this foam. After this 
fluid had been aged overnight at 300 F., it was so foamy that none of the 
properties could be measured. The properties of the fluid in run 5 with 5 
lb/bbl of NSFC containing a polyvinylpyrrolidone defoamer (CFR-2) were 
normal and no foaming was experienced. There was only a small amount of 
foaming in run 2. The sample was sprayed with an aerosol defoamer before 
and after aging. This is a standard laboratory procedure. Since an 
antifoaming agent is desirable, although, at low concentrations, not a 
necessary component of the system, CFR-2 was used as the water loss 
control additive in the remainder of the examples. Again referring to the 
results in Table I and especially to the water loss value after thermal 
aging, it is evident that the CFR-2 improves high temperature water loss 
control, i.e., 30 (no additive in run 1) is significantly greater, 
respectively, than 16 (1 lb/bbl CFR-2 in run 4) and 11 (5 lb/bbl CFR-2 in 
run 5). The 5 lb/bbl loading of CFR-2 seems to be an over-treatment with 
respect to shear strength control which increased from 80 at the 1 lb/bbl 
level (run 4) to 220 at the 5 lb/bbl loading (run 5). The yield point (YP) 
values of runs 2-5 with NSFC are greater than those for the base mud. 
Referring to the same runs 1, 4 and 5 again after the thermal aging tests, 
a YP value of 7 in run 1 is significantly lower, respectively, than YP 
value of 17 and 19 in runs 4 and 5. When the amount of bleeding is 
considered, runs 4 and 5 with bleeding values of 15.5 and 30, 
respectively, show that NSFC in run 5 with PVP (CFR-2) increases bleeding 
compared to 8.6 in the base mud (run 1). The main value of the additive 
polyvinylpyrrolidone (PVP) in the workover fluids is as an antifoaming 
agent. Referring to the pH values in Table I, it is evident that all of 
the compositions were distinctly alkaline. 
The compositions of this invention are useful when a permeable subterranean 
formation is exposed as in the case of perforating or some workover 
operations or said formation has the potential of being exposed as in the 
case of a packer fluid. In its broadest application the process of this 
invention comprises circulating the aforesaid composition in a well to the 
zone in question and then returning the fluid or a major portion thereof 
to the surface either during the present operation or during subsequent 
future operations. The treatment can comprise a single temporary and 
selective step or it can be an integral part of a comprehensive process. 
The fluid compositions of this invention can be effectively used at 
elevated temperatures as well workover and well completion fluids in oil 
and gas wells. In workover applications, the fluid of the invention is 
circulated from the surface to a zone where remedial work is occurring and 
at least a portion of the fluid is returned to the surface. 
The following examples further demonstrate the operability of the instant 
compositions. 
EXAMPLE II 
The naphthalene sulfonate formaldehyde condensate (commercially available 
as CFR-2) was mixed into a base fluid comprising saturated salt water 
weighted with 295 lb/bbl ground limestone and also containing 2 lb/bbl 
carboxymethyl cellulose, 2 lb/bbl asbestos fiber and 5 lb/bbl sodium 
carbonate. The two inventive fluid samples (Runs 7 and 8) tested 
contained, respectively, 1 lb/bbl and 5 lb/bbl of said CFR-2. Test results 
are summarized in Table II. The designation CFR-2 represents the 
naphthalene sulfonate formaldehyde condensate additive in combination with 
polyvinylpyrrolidone (PVP). 
TABLE II 
______________________________________ 
300 
F. Water 
Ag- Loss.sup.d 
Run CFR-2 ing Shear.sup.a mL/30 
No. lb/bbl Days Strength 
PV/YP.sup.b Gels.sup.c 
min pH 
______________________________________ 
6 0 0 -- TTTM.sup.e 
43/59 4.0 10.0 
3 650 40/22 32/92 54.0 NM* 
7 1 0 -- TTTM.sup.e 
30/42 3.8 10.0 
3 -- 69/36 46/61 34.0 NM* 
8 5 0 -- TTTM.sup.e 
26/43 2.8 10.0 
______________________________________ 
.sup.a Shear strength, lb/100 sq. ft. (shear strength and bleeding are 
measured initially.) 
.sup.b Plastic viscosity, cp,/yield point, lb/100 sq. ft. 
.sup.c Gel strength, lb/100 sq. ft. (initial/10 minute) 
.sup.d Water loss, ml in 30 min. 
.sup.e Too thick to measure 
*NM represents "Not Measured". 
Referring to the initial properties in Runs 6, 7, and 8 it can be seen that 
the water loss was reduced from 4 to 3.8 to 2.8 on the addition of 1 
lb/bbl and 5 lb/bbl of the NSFC to the workover fluid. Referring to the 
thermal aging data in Runs 6 and 7, the addition of 1 lb/bbl NSFC lowered 
water loss from 54 to 34 and shear strength from 650 to 550 lb/100 
ft.sup.2. No thermal aging data were recorded in Run 8. Referring to the 
pH values of Table II, it is evident that all of the compositions were 
distinctly alkaline as formulated. 
EXAMPLE III 
The NSFC inventive additive was mixed into a base fluid comprising 
saturated salt water weighted with 295 lb/bbl ground limestone and also 
containing 2 lb/bbl carboxymethyl cellulose, 2 lb/bbl asbestos fiber and 5 
lb/bbl sodium carbonate. The three inventive fluid samples (Runs 10-12) 
tested contained, respectively, 1 lb/bbl, 2 lb/bbl and 3 lb/bbl of said 
NSFC additive. Test results are summarized in Table III. 
TABLE III 
______________________________________ 
300 
F. Water 
Ag- Loss.sup.d 
Run CFR-2 ing Shear.sup.a mL/30 
No. lb/bbl Days Strength 
PV/YP.sup.b Gels.sup.c 
min pH 
______________________________________ 
9 0 0.6 380 62/14 9/31 29.0 NM 
10 1 0.6 340 91/28 10/22 13.4 8.7 
11 2 0.6 300 110/50 14/38 10.0 8.6 
12 3 0.6 265 118/52 15/31 5.6 8.5 
______________________________________ 
.sup.a Shear strength, lb/100 sq. ft. (shear strength and bleeding are no 
measured initially.) 
.sup.b Plastic viscosity, cp,/yield point, lb/100 sq. ft. 
.sup.c Gel strength, lb/100 sq. ft. (initial/10 minute) 
.sup.d Water loss, ml in 30 min. 
Referring to the results in Table III it is evident that the addition of 
NSFC to the system reduced water loss progressively from 29 (see control 
run 9 with no NSFC) to 13.4, 10.0 and 5.6 at NSFC loadings, respectively, 
of 1 lb/bbl, 2 lb/bbl and 3 lb/bbl. This improved water loss control is 
unexpected because the naphthalene formaldehyde condensate is used as a 
dispersant in oil well cement rather than as a primary fluid loss control 
agent. It is also noteworthy that shear strengths were reduced as the NSFC 
loadings were increased and that the yield point values were increased. 
Referring to the pH values after thermal aging, it is apparent that all 
the compositions were still quite alkaline after the thermal aging tests. 
Referring to the general trend of yield points and gel strengths in Table 
III, it is evident that the high temperature water loss control additive, 
i.e., NSFC, is not functioning as a dispersant and/or thinning agent in 
the instant compositions. If the NSFC additive was functioning as a 
dispersant and/or thinning agent, the yield points (YP) and gel strengths 
(gels) would exhibit significantly decreased values as the NSFC loadings 
increased from 1 to 2 to 3 lb/bbl, respectively, in test numbers 10, 11 
and 12. 
EXAMPLE IV 
The NSFC (CFR-2) was mixed into a base fluid comprising saturated salt 
water weighted with 295 lb/bbl ground limestone and also containing 2 
lb/bbl carboxymethyl cellulose, 0.5 lb/bbl asbestos fiber and 5 lb/bbl 
sodium carbonate. The two inventive fluid samples (Runs 14 and 15) tested 
contained, respectively, 1 lb/bbl and 2 lb/bbl of said CFR-2 additive. 
Test results are summarized in Table IV. 
TABLE IV 
______________________________________ 
300 
F. Water 
Ag- Loss.sup.d 
Run CFR-2 ing Shear.sup.a mL/30 
No. lb/bbl Days Strength 
PV/YP.sup.b 
Gels.sup.c 
min pH 
______________________________________ 
13 0 0 -- 94/33 5/8 4.6 10.2 
3 750 46/39 32/46 64 8.1 
14 1 0 -- 84/28 4/8 4.0 10.0 
3 550 57/24 15/63 35 8.4 
15 2 0 -- 85/35 4/8 4.0 10.2 
3 400 64/26 7/32 25 8.3 
______________________________________ 
.sup.a Shear strength, lb/100 sq. ft. (shear strength and bleeding are no 
measured initially.) 
.sup.b Plastic viscosity, cp,/yield point, lb/100 sq. ft. 
.sup.c Gel strength, lb/100 sq. ft. (initial/10 minute) 
.sup.d Water loss, ml in 30 min. 
Referring to the results in Table IV and especially to the water loss 
values after thermal aging, it is evident that the CFR-B 2 improves water 
loss control, i.e., 64 (no additives in Run 13) is significantly greater 
than 35 (1 lb/bbl CFR-2 in Run 14) and 25 (2 lb/bbl CFR-2 in Run 15). 
Shear strengths are also progressively decreased from 750 to 550 to 400 as 
the additive loading of CFR-2 was increased from 0 lb/bbl to 1 lb/bbl to 2 
lb/bbl. A decrease in gel strength was also noted in this specific system. 
Referring to the pH values in Table IV, it is evident that the 
compositions were quite alkaline before and after the thermal aging tests. 
EXAMPLE V 
Comparison runs on a fluid similar to that in Example IV (Columns 7 & 8) of 
U.S. Pat. No. 4,304,300 were made to determine whether a fluid loss 
additive disclosed in the patent controlled the fluid loss of spacer fluid 
compositions disclosed in the patent. Spacer fluids ordinarily have a pH 
value of about 7 (neutral) because contact of an alkaline spacer fluid 
would be detrimental to cement. Consequently, the commonly used spacer 
fluids are usually characterized by pH values of about 7. Such spacer 
fluids are usually positioned between muds and cement in typical field 
applications. 
In the comparison runs, CMC was used instead of CMHEC and perlite instead 
of nut hulls. Cellulose and derivatives are disclosed in the '300 patent 
at Column 3, line 39 and perlite is specifically disclosed at Column 3, 
line 15. 
The test data are presented in Table V. 
TABLE V 
______________________________________ 
18% NaCl Brine Comprising 555.6 lb/1,000 gal 
Perlite and 4,000 lb/1,000 gal Barite 
and Other Materials as Noted 
WL 
Run CMC* HPG* LBG* CFR-2* ml/30 
No. lb/1,000 gal 
lb/1,000 gal 
lb/1,000 gal 
lb/1,000 gal 
min 
______________________________________ 
16 55.6 27.8 27.8 166.7 3.0 
17 -- 27.8 27.8 166.7 5.3 
18 55.6 27.8 27.8 -- 2.4 
19 -- -- -- 166.7 39.0** 
______________________________________ 
*CMC = Carboxymethyl cellulose 
HPG = Hydroxypropyl guar 
LBG = Locust bean gum 
CFR-2 = Mixture of 10% by volume polyvinyl pyrrolidone and 90% by volume 
sodium salt of naphthalene sulfonic acid condensed with formaldehyde 
**Settled 
In Run 16 all of the polymers recommended by the patentee were present in 
the comparison composition and the API water loss was 3 ml/30 min. 
Referring to Run 17, CMC was omitted from the composition and the water 
loss increased to 5.3 ml/30 min. In Run 18 the disclosed water loss 
additive was omitted and the water loss decreased to 2.4 from 3 in Run 16. 
The only polymer employed in Run 19 is the mixture of polyvinyl 
pyrrolidone and sodium salt of naphthalene sulfonate acid condensed with 
formaldehyde (CFR-2) and the water loss was 39 ml/30 min. 
These results clearly show that CFR-2 does not control the fluid loss of 
spacer fluids disclosed in U.S. Pat. No. 4,304,300. In fact, comparing the 
results of Run 18 with no CFR-2 with those of Run 16 where CFR-2 is 
present, the presence of CFR-2 is detrimental.