Cement mixing with vibrator

A casing string is cemented in a borehole of a well. The cement is prepared by introducing water and dry cement material into a mixing vessel. The water and dry cement material are mixed in the mixing vessel to form a cement slurry. The mixing is accomplished by agitating the slurry to cause the slurry to circulate within the vessel, and while agitating the slurry, transmitting vibrational energy into the slurry and thereby aiding in the wetting of the dry cement material in the slurry. This also aids in removing entrained air from the slurry. The slurry is then pumped into an annulus between the casing string and the boreholes.

BACKGROUND OF THE INVENTION 
1. Field Of The Invention 
The present invention relates generally to the mixing of cement slurries, 
and more particularly, but not by way of limitation, to the mixing of very 
high density, high viscosity, cement slurries to be pumped down a well to 
cement a casing string in a well bore. 
2. Description Of The Prior Art 
In the construction of oil wells, one necessary operation is the cementing 
of a casing string of the oil well in a bore hole. This is accomplished by 
pumping a cement slurry down the casing string, or down a smaller pipe 
located within the casing string, and then forcing the cement upward into 
an annular space between the casing string and the bore hole. 
For various reasons, it is sometimes desired to utilize cement slurries 
which are highly viscous and/or densified for this cementing operation. 
These slurries, which often contain saturated salt, large quantities of 
silica flour, gels or bentonite, and/or other thickening additives, are 
generally difficult to mix. They are difficult to mix because they have a 
tendency to entrain air, they are highly viscous, they have high surface 
area wetting requirements caused by large amounts of material such as 
silica flour, and because of chemical reactions taking place. A result is 
that often the slurries contain an excess of entrained air, e.g., greater 
than 3%. 
High viscosity makes it difficult to disperse the bulk materials to obtain 
a uniform slurry, and increases the problem of removing entrained air. The 
result is that entrained air often causes difficulty in measurement and 
control of slurry density and causes pump priming problems. Another 
difficulty is that high viscosity slurries sometimes require that mixing 
rates be slowed to as low as 11/2 barrels per minute. Additionally, high 
surface area materials such as silica flour are hard to wet, and tend to 
create unwetted lumps, thus the resultant slurry is likely not to be fully 
mixed or homogeneous. 
Prior art methods of mixing such slurries have relied solely upon 
mechanical agitation of the slurry such as with rotating blade-type 
agitators, recirculating pumps or the like to mix the dry cement material 
with water. 
Also, the prior art has included the use of vibrational energy to aid in 
placing cement downhole in a well. 
U.S. Pat. No. 4,736,794 to Bodine discloses a method for the sonic 
cementing of downhole well casings. While the cement is being flowed into 
the annulus surrounding the casing, sonic energy is transmitted to the 
bottom of the casing and operates to assure that cement fills the area 
around the casing in a uniform manner. 
Additionally, in more conventional construction operations such as the 
pouring of concrete structures, roadways, and the like, it is well known 
to utilize concrete vibrators to aid in placement of the concrete to make 
sure that it completely fills forms. These concrete vibrators can be 
hydraulically, pneumatically or electrically powered and typically include 
an elongated vibrator head either cylindrical or square in cross section 
having a cross-sectional dimension on the order of two to three inches, 
and having a length on the order of twelve to eighteen inches. 
In both the casing cementing operation of the Bodine '794 patent, and in 
the prior art use of concrete vibrators, the vibrational energy has been 
used for the purpose of placing concrete. 
SUMMARY OF THE INVENTION 
The present invention provides apparatus and methods utilizing vibrational 
energy to aid in the mixing of cement slurries before those slurries are 
placed at their final point of usage. 
As applied to the cementing of a casing string in a borehole of a well, the 
method includes steps of introducing water and dry cement material into a 
mixing vessel. The water and dry cement material are mixed in the vessel 
to form a cement slurry which typically includes lumps of dry cement 
material. This mixing includes steps of agitating the slurry to cause the 
slurry to circulate within the vessel, and while agitating the slurry, 
transmitting vibrational energy into the slurry to thereby aid in 
disintegration and subsequent wetting of the lumps of dry cement and other 
material in the slurry. 
The slurry produced in this manner is then pumped into the annulus between 
the casing string and the borehole to cement the casing string in place. 
By this technique, very high density cement slurries can be mixed much more 
thoroughly and much faster than they otherwise could be in the absence of 
the use of vibrational energy. The resulting slurries also have less 
entrained air than they otherwise would. The effect of the vibrational 
energy is to cause lumps of dry cement material to rapidly disintegrate so 
that a much more homogeneous cement slurry is produced than otherwise 
could be. 
Preferred apparatus for carrying out these methods are also disclosed. 
Numerous objects, features and advantages of the present invention will be 
readily apparent to those skilled in the art upon a reading of the 
following disclosure when taken in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, and particularly to FIG. 1, a well 10 is 
there schematically illustrated having a borehole 12, and a casing string 
14 which has been located in the borehole 12. 
A cement mixing apparatus 16 is generally illustrated. Apparatus 16 
includes a mixing tub or mixing vessel 18 and agitator means 20, 
associated with the mixing tub 18, for circulating a cement slurry 22 in 
the mixing tub 18 and for providing mixing energy. 
The tub 18 typically has a volume of from three to five barrels. 
The agitator means 20 illustrated includes both a rotating blade type 
agitator 21, and a recirculating pump 23. 
The rotating blade type agitator 21 includes a multi-bladed paddle 24, the 
blades of which have a diameter in the range of from about twelve inches 
to about twenty-four inches, and have a height on the order of four 
inches. The rotating blade agitator 21 is typically a relatively low speed 
agitator which typically would operate at approximately 250 rpm. 
The recirculating pump 23 draws slurry from tub 18 through a suction line 
25 and returns the slurry to the tub 18 through a discharge line 26. 
Located in the discharge line 26 above the open upper end of tub 18 is a 
mixing eductor 27. 
In the mixing educator 27, the slurry discharge line 26 is axially located. 
A water supply stream 28 is introduced into an annular area 29 surrounding 
an end 30 of discharge line 26. 
A stream 31 of dry cement material is supplied to mixing eductor 27 and is 
drawn into the mixing eductor 27 by the fresh water and recirculated 
slurry exiting annular area 29 and end 30 of discharge line 26, 
respectively. The recirculating slurry, clean water stream 28, and dry 
cement material 31 exit an outlet 32 of the mixing eductor into the tub 
18. 
As will be appreciated by those skilled in the art, the stream 31 of dry 
cement material will typically be conveyed by a pneumatic conveying system 
(not shown) in combination with the eductor 27 just described. The flow of 
the stream 31 of dry cement material is controlled by a throttling control 
valve 33. Other types of dry material feed systems, such as a screw type 
feeder or a gravity feed system could also be utilized. 
Also, it is noted that the general arrangement of the agitator 21, 
recirculating pump 23 and eductor 27 is only one possible form of the 
agitator means 20. Other combinations of agitating devices could also be 
used. 
The stream of water 28 and the stream of dry cement material 31 are 
introduced into the tub 18 through the mixing eductor 27. In the tub 18, 
the water and dry cement material, with other additives, are mixed by the 
agitator means 20, 21, 23 to form the slurry 22. When these materials are 
first introduced into the tub 18, the slurry 22 will typically include 
lumps of the dry cement material which are not completely wetted. When the 
term "lump" is utilized in this disclosure, it is being used only in a 
general sense to refer to a cluster of individual cement particles which 
initially stick together and are not completely wetted. The present 
invention is directed to systems for aiding in the disintegration and 
subsequent wetting of these lumps or clusters of dry cement material as 
the slurry 22 is circulated within or through the tub 18. This is 
accomplished by means of a vibrator 36. 
The vibrator 36 includes an elongated vibrator head 38 having flexible 
power supply lines 40 extending thereto. The power supply lines 40 are 
shown as being received within a resilient sheath 42 which may for example 
be a length of rubber tubing or the like. 
A support structure 44 including vertical members 46 and a cross member 48 
is connected to the tub 18 and extends above the tub 18. 
The vibrator head 38 of vibrator 36 is suspended in the slurry 22 within 
the mixing tub 18 from the support structure 44 by its power supply lines 
40 and the sheath 42. The sheath 42 is physically connected to the cross 
member 48 of support structure 44 by a U-bolt 50. In this manner, 
vibrational energy from the vibrator head 38 is substantially isolated 
from the mixing tub 18. 
The vibrator 36 may for example be a model HV-4-4 concrete vibrator 
manufactured by Minnich Manufacturing Company, Inc., of Mansfield, Ohio, 
as further described in the examples set forth below. 
While the slurry 22 is being agitated by the mechanical agitator means 20, 
the vibrator 36 is operated to transmit vibrational energy into the slurry 
22, thereby aiding in the disintegration and subsequent wetting of the 
lumps of dry cement material 34 contained in the slurry 22. 
Vibrational energy generated by vibrator 36 is relatively high frequency, 
and preferably is in a range of from about 7,000 to about 12,000 cycles 
per minute. Generally speaking, the vibrational energy can be described as 
preferably having a frequency of at least about 7,000 cycles per minute. 
As is shown by the examples set forth below, the cement slurry 22 can be 
thoroughly mixed much faster as a result of the use of the vibrator 36 as 
compared to a similar mixing process without the use of vibrational 
energy. Thus, the dry cement material 34 can be added to the tub 18 at a 
much higher rate than it could be added if vibration were not being used. 
Additionally, the slurry 22 can be mixed much more thoroughly as a result 
of the use of vibrational energy, thus resulting in much more homogeneous 
slurries 22. In addition to the observable disintegration of relatively 
large lumps of material, it is noted that even in a slurry that appears to 
be well mixed, there are macroscopic clusters of dry cement material which 
are not fully wetted. It is believed that these macroscopic clusters or 
lumps are further broken down by the use of vibrational energy to produce 
more homogeneous slurries. 
The advantages just described apply particularly to the viscous, harder to 
mix slurries. Not all slurries have difficulty in mixing, and the amount 
of benefit gained by vibration is slurry design specific. 
The use of vibrational energy is particularly advantageous for use with 
slurry designs which contain saturated salts, large quantities of silica 
flour, gels or bentonite, and/or other additives which contribute to 
mixing problems. 
The viscous slurries for which the present invention is most useful include 
two broad general categories. First, there are slurries which are very 
dense due to a high solids loading, and the viscosity of those slurries 
results in large part from the presence of high concentrations of solids 
materials. Such high density slurries may have densities in a range of 
from about 17 to about 19 lbs/gal. The second general category of slurries 
are those which are viscous because of the additives included in the 
slurries and because of chemical reactions in the slurries caused by those 
additives. This second group of slurries may or may not also be relatively 
high density slurries. 
The use of vibrational energy in mixing these very high density and/or high 
viscosity slurries aids in the removal of much of the entrained air which 
is typically contained in such slurries. 
After the cement slurry 22 is mixed in the tub 18, a high pressure pump 52 
takes the cement slurry from the tub 18 through a suction line 54 and the 
cement is pumped through a discharge line 56 down into the casing 14 as 
generally indicated by arrows 58. The cement slurry flows down the 
interior of the casing 14, or in many cases down a smaller pipe located 
concentrically within the casing 14, and then upward around the bottom of 
the casing 18 to fill an annular space 60 between the casing 14 and the 
borehole 12. Once this cement sets and cures within the annular space 60, 
it becomes an integral part of the well 10 holding the casing 14 in place 
within the borehole 12. 
Through the use of the present invention, cement slurries 22 having a 
higher quality, that is much more homogeneous slurries, can be mixed at 
higher rates than they could be with prior art techniques, thus providing 
improved cementing of the casing 14 within the borehole 12. This is 
particularly true where relatively high density and/or high viscosity 
cement slurries are desired. 
Also the removal of entrained air from the slurry is a significant 
advantage in that subsequent measurements of slurry density are made more 
accurate. These density measurements are made with a densometer, and the 
presence of entrained air causes the densometer to read light. 
APATUS AND PROCEDURES FOR EXAMPLES 1 THROUGH 4 
Examples 1 through 4 utilized a common laboratory apparatus and procedure 
which can be generally described with reference to FIG. 2. Two different 
slurry designs were tested in a batch tank 18A having approximately 
twenty-gallon capacity. The batch tank 18A had a low speed paddle agitator 
21A, and also included a high speed dispersator 62. In addition, one 
hydraulic-driven concrete vibrator 36 operating at approximately 8,000 rpm 
was operated in conjunction with the agitators. The dispersator 62 
operated at 10,000 rpm. The low speed agitator 21A had a six-inch diameter 
paddle one inch in height operated at 250 rpm, driven by a Servodyne D.C. 
motor which provides speed control and torque measurement. The vibrator 36 
was a hydraulic vibrator model HSV-4-4 manufactured by Minnich 
Manufacturing Co., which can produce up to 3.5 horsepower while operating 
from 8,000 to 10,000 rpm. The two slurries tested are generally referred 
to as a silica flour slurry and a saturated salt slurry. Each was mixed 
both with and without the vibrator. The time to fully mix all of the dry 
bulk material with the required water was recorded. 
EXAMPLE NO. 1 
Silica Flour Slurry (Without Vibrator) 
The silica flour slurry was prepared according to the specification shown 
in the following TABLE I: 
TABLE I 
______________________________________ 
SILICA FLOUR DESIGN 
Percent By Weight 
15 Gallon Batches 
______________________________________ 
Class "H" (API) 
100 102.0 lbs 
Cement 
SSA-1* (silica flour) 
60 61.4 
SSA-2* (Okla. No. 1 
40 40.9 
sand) 
Gas Stop* (additive to 
0.6 0.61 
prevent gas migration) 
CFR-3* (friction 
0.75 0.77 
reducer) 
Water 52 53.17 
______________________________________ 
*Indicates a trademark of Halliburton Services, Duncan, Oklahoma 
The slurry produced from the specifications of TABLE I had a density of 
17.26 lbs/gal. The formula yielded 1.84 cubic feet of slurry per 94-pound 
sack of cement. 
This slurry was first mixed without the use of vibration. The cement blend 
was added to the water as rapidly as possible while the paddle agitator 
21A and the dispersator 62 were operating. Cement addition was slowed or 
stopped if there was an appearance of too much dry material on the surface 
(material was not being incorporated). At approximately sixteen minutes, 
all of the material had been added and no further change to the appearance 
of the slurry seemed to occur with additional agitation. Therefore, the 
slurry was declared to be mixed (as best as possible with the existing 
agitation). The vibrator was then turned on. It immediately caused air to 
be expelled and eliminated the lumps in the slurry that had been 
previously mixed. 
EXAMPLE NO. 2 
Silica Flour Slurry (With Vibration) 
This test was conducted similar to Example No. 1, except that the vibrator 
was turned on initially as the bulk cement was added to the water. In this 
case, it took approximately 7.5 minutes to declare the slurry fully mixed 
and homogeneous. At 8.5 minutes, the vibrator was turned off. 
EXAMPLE NO. 3 
Saturated Salt Slurry (Without Vibration) 
The saturated salt slurry was prepared according to the specifications 
shown in the following TABLE II: 
TABLE II 
______________________________________ 
SATURATED SALT DESIGN 
Percent By Weight 
15 Gal Batches 
______________________________________ 
Class "H" API Cement 
100 117.3 lbs 
SSA-1* (silica flour) 
35 41.0 lbs 
Hi-Dense* #3 (heavy- 
10.64 12.5 lbs 
weight additive) 
Salt 20.74 24.3 
Halad* - 24 (fluid loss 
1.0 1.17 
additive) 
CFR-3* (friction reducer) 
0.75 0.88 
Fe-2* (fluid loss aid) 
0.22 0.26 
D-air* (entrained air 
0.25 0.29 
reducer) 
Diacel A* (cement 
6.0 7.04 
accelerator) 
Water 55.83 65.47 
______________________________________ 
*Indicates a trademark of Halliburton Services, Duncan, Oklahoma 
The slurry prepared according to the specification of TABLE II had a 
density of 16.38 lbs/gal. This recipe yielded 1.606 cubic feet of slurry 
per 94-pound sack of cement. 
The saturated salt slurry was first tested without vibration to determine 
the ability of the mixing system to mix and incorporate the bulk powder 
into the water without the use of a vibrator. It took approximately 6.75 
minutes. The surface of this batch had lumps of dry material and this 
condition did not appear to improve with time. At approximately 8.75 
minutes, the vibrator was turned on to see the effect of vibration on 
breaking up the lumps of dry material. This was very effective and almost 
immediately broke all of the visible lumps down and incorporated them into 
the slurry. The effect was to significantly increase the viscosity of the 
slurry. The paddle torque of agitator 21A was noticed to increase 
approximately 50% due to what is believed to be the incorporation of 
previously unwetted solids. 
EXAMPLE NO. 4 
Saturated Salt Slurry (With Vibration) 
This test was conducted similar to Example No. 3 except that the vibrator 
was turned on from the beginning of the test while the dry material was 
being added to the water. All of the material was incorporated within the 
water and the slurry was declared mixed without any lumps after 3.75 
minutes. The vibrator was left on until approximately test time of 9.5 
minutes. 
From the four tests set forth in Examples Nos. 1-4 above, it is clear that 
the vibrator 36 does allow or aid the incorporation of bulk material into 
water, particularly with the thicker fluids. The time to incorporate the 
bulk material into the water was cut approximately in half when the 
vibrator was used. Also where visible lumps of dry material were present 
while mixing without the vibrator, those lumps were quickly eliminated 
after the vibrator was turned on. 
EXAMPLE NO. 5 
Field Test 
One attempt has been made to test the present invention on an actual field 
job. A very high density slurry was prepared according to the 
specification shown in the following TABLE III: 
TABLE III 
______________________________________ 
Premium Cement 1135 sks 
SSA-1* (silica flour) 35% 
Salt 20.1 lb/sk 
Hi-Dense No. 3* (heavyweight additive) 
29.0 lb/sk 
HALAD 24* (fluid loss additive) 
0.8% 
CFR-3* (friction reducer) 
1.0% 
FE-2* (fluid loss aid) 0.2% 
D-Air-1* (entrained air reducer) 
0.25% 
Diacel "A"* (cement accelerator) 
9.0% 
______________________________________ 
*Indicates a trademark of Halliburton Services, Duncan, Oklahoma 
The slurry prepared according to the recipe of TABLE III had a density of 
17.6 lbs/gal. The recipe yielded 1.81 cubic feet of slurry per 94-pound 
sack of cement. 6.5 gallons of water were utilized per 94-pound sack of 
cement. 
The field equipment utilized a five-barrel capacity mixing tub 18. 
Conventional low speed rotating paddle agitators 21 were utilized in the 
tub. The vibrator utilized was a Model HSV-4-4 manufactured by Minnich 
Manufacturing Company. 
Although it was apparent that the vibrator had a very significant effect on 
the slurry, this particular slurry design was of such a high density that 
the use of the vibrator slowed the overall mixing process. This was 
believed to be due to the fact that the use of the vibrator caused a much 
faster incorporation of the bulk material into the slurry thus causing 
excessive viscosity. The vibrator did aid in reducing gel strength of the 
slurry so that it could be agitated by the conventional agitators. When 
the vibrator was turned off, the slurry was so thick that the agitators 
would not move the surface of the cement slurry in the tub. When the 
vibrator was restarted, the agitators were able to move and circulate the 
slurry. The conclusion is that the vibrator does aid significantly in the 
incorporation of bulk material into the liquid, but with this particular 
slurry design it had an adverse effect on overall mixing speed. It is 
believed that by redesign of the mixing system, the use of the vibrator 
can be advantageous even with the cement design of TABLE III which is very 
difficult to handle. 
Thus it is seen that the apparatus and methods of the present invention 
readily achieve the ends and advantages mentioned as well as those 
inherent therein. While certain preferred embodiments of the invention 
have been illustrated and described for purposes of the present 
disclosure, numerous changes in the arrangement and construction of parts 
and steps may be made by those skilled in the art, which changes are 
encompassed within the scope and spirit of the present invention as 
defined by the appended claims.