Method of using a well treating fluid

The instant invention is directed to shear thickening fluids which comprise a water-swellable material (clay), present in a sufficient concentration so as to be capable of forming a stiff paste upon interaction with the water used, and water wherein the clay and water are kept separated by an intervening hydrocarbon-surfactant composition. The intervening oil phase prevents the interaction between the water and the clay phases and results in a stable, nonreacting, pumpable composite until such time as the oil envelope is ruptured by application of a sufficiently high shear force. Upon such rupture, the materials interact rapidly forming a semi-rigid stiff paste. Various well-control problems, such as oil and gas with blowouts, can be controlled by use of the above-described composite. The composite is pumped down the well pipe. Exiting the orifices of the drill bit or a nozzle supplies the shear force needed to rupture the oil envelope thereby permitting the interaction between the clay and the water resulting in the formation of a stiff paste which can stop or prevent unwanted flow in or near the wellbore.

BRIEF DESCRIPTION OF THE INVENTION 
The instant invention is directed to well treating fluids, particularly 
blowout control fluids, which are shear thickening fluids. The fluid 
composites comprise a water swellable material phase (clay for short) 
present in sufficient quantity so as to form a stiff paste upon 
interaction with the water used, which can constitute any of the known 
hydratable clays such as bentonite or attapulgite, a nonaqueous 
hydrophobic phase (oil for short) which comprises a hydrocarbonaceous 
component and a surfactant-strengthening agent component, and water which, 
when permitted to interact with the clay, results in a semi-rigid high 
strength paste. 
In one particular embodiment, the clay is encapsulated in the oil phase and 
this encapsulated clay is suspended in the water resulting in a composite 
which is identified as a clay in oil in aqueous phase material, an aqueous 
continuous phase system. 
Alternatively, the water can itself be encapsulated as discrete droplets in 
the oil phase whereby the oil phase becomes the continuous phase, the 
system being identified as an oil continuous system. 
In either embodiment, the clay and the water are kept separate from each 
other by the intervening oil phase until such time as their interaction is 
desired. Such interaction is effected by rupturing the oil phase envelope 
by the application of a shear-force sufficient to rip apart the oil phase 
envelope and thereby mix the clay and water components. 
In drilling operations, this fluid is pumped down the drill pipe only when 
necessary for the specific purpose of blocking unwanted flow channels 
either in or immediately adjacent to the wellbore. This material is not to 
be confused with typical well circulation-drilling fluids containing clay 
and water components. 
The material of the instant invention is stable to the forces exerted upon 
it during pumping down the well pipe. Exiting the orifices of the drill 
bit, however, applies a sufficient force to rupture the oil envelope and 
mix the clay and water components in a semi-rigid, high strength gel 
capable of, for example, plugging a wellbore to stop a blowout or sealing 
a lost circulation zone. 
A particular achievement of the instant invention is its ability to stop 
pre-existing unwanted flows provided that the paste is injected into the 
unwanted flow at an approximately high rate and provided that the unwanted 
flow is exiting through a flow channel long enough for a paste plug to be 
formed. 
The exact placement of a paste plug in or near a wellbore will depend on 
the problem to be treated. For example, if unwanted fluid was entering the 
wellbore at the bottom and flowing uphole, the paste plug would be formed 
as close to the bottom of the hole as possible. On the other hand, if 
fluid was flowing downhole from and departing the wellbore undesireably 
into a thief formation, the composite would be pumped into the wellbore 
just above the thief zone so that the paste would be formed at the flow 
channels in that zone and plug them. Other possible uses of the present 
invention can also be envisioned, such as blocking channels in cement 
behind casing, repairing leaks in casing or tubing, placing temporary plug 
in various places, etc. 
BACKGROUND OF THE INVENTION 
During drilling, or production of an oil or gas well, there are 
occasionally unwanted fluid flows in or near the wellbore, and there are 
also occasionally unwanted channels open downhole where unwanted flow 
could take place. On these occasions, it may be necessary to introduce 
fluids into the well to kill the well, or at the very least, terminate the 
unwanted flow or seal the unwanted channels. Examples of these problems 
are: 
Unwanted influx of formation fluid into the wellbore (blowout). 
Loss of drilling fluid into fractures or vugs in the formation (lost 
circulation). 
Channels in cement behind casing. 
Holes in casing. 
Improperly sealing linear hangers. 
A typical scenerio involves formation fluid influx which cannot be 
contained by closing the blowout preventers or by circulating the high 
density, drilling mud. For example, when an unusually high pressure 
formation is encountered, it may be necessary to empty drilling mud at 
such high weight that a formation above the high pressure zone is 
fractured. This fractured zone then becomes a "lost zone" into which mud 
flows at such a high rate that "lost circulation" occurs. The lost 
circulation may be so severe that it ultimately becomes impossible to 
maintain a column of mud above the high pressure zone sufficient to impart 
the necessary hydrostatic head to offset the high pressures in the high 
pressure zone. As this occurs, the well becomes increasingly susceptible 
to blowout into the lost zone or to the surface. 
There are a number of techniques which have been employed when one or 
another of these problems are encountered. A common solution is to force a 
cement slurry into the unwanted flow channel. This procedure is often 
successful, although sometimes multiple treatments are necessary, as long 
as there is no significant flow present in the unwanted channel. Cement is 
useless against a pre-established flow because cement has almost no flow 
resistance until it is set. Thus it is always necessary to stop the flow 
before using cement to plug the flow channel. 
The hydrostatic head of various fluids is often employed to prevent or stop 
unwanted movement of fluids up the wellbore. In particular, most blowouts 
involve the uncontrolled flow of formation fluids into the wellbore and 
then upwards in the wellbore. This type of blowout can be controlled by 
injecting fluid at the proper density and rate into the wellbore at or 
near the point of influx. In practice, the required density and rate may 
be difficult to obtain. 
One technique involves placing a high density barite slurry (barium 
sulfate) in the annulus adjacent the high pressure zone to provide the 
extra hydrostatic head needed to stop or prevent formation fluid influx. 
If the barite slurry remains deflocculated after placement at the bottom 
of the well and relatively undisturbed, the barite settles uniformly to 
form a hard plug. One problem with using barite to form a plug is that the 
barite's ability to form a plug varies greatly depending upon the 
formation temperature, the operating conditions, and the quality of barite 
used. For example, it is sometimes difficult to plug a well in the 
presence of a significant flow movement in the wellbore. If the fluid 
influx is not killed immediately by the hydrostatic head of the barite 
slurry, the settling barite will usually not stop the unwanted flow. 
The unwanted loss of fluids from the wellbore is often treated by injecting 
a slurry of fiberous, lumpy, or flakey material into the wellbore at the 
region of the loss. These "lost circulation materials" are intended to 
plug or form a mat over the channels through which the fluid is entering 
the rock. 
A pasty material known as "gunk" is sometimes used as a lost circulation 
material and occasionally to form temporary plugs in the wellbore. Gunk is 
a slurry of dry powdered bentonite in diesel oil. A typical gunk recipe is 
350 lb. of bentonite in of bbl of diesel oil. This slurry is quite fluid 
when mixed and remains fluid as long as it is kept anhydrous. Mixing gunk 
slurry with an approximately equal volume of water causes the clay to 
hydrate into a stiff paste. If formed at the right time and at the right 
place, this gunk paste is an effective lost circulation and plugging 
material. However, since the gunk slurry will hydrate and thicken 
immediately upon contacting water, it must be kept dry until it has been 
pumped downhole to the place where a plug is desired. The mixing of the 
gunk slurry with water takes place downhole as the two fluids are 
commingled. In some cases, there is some control over the ratio of gunk 
slurry to water; in other cases, even this control cannot be achieved. 
Since gunk only achieves adequate flow resistance to form a plug within a 
certain range of gunk/water ratios, the performance of gunk as a plugging 
agent has been erratic. In particular, gunk is seldom useful for blowout 
control because the requirement of having the proper gunk/water ratio is 
difficult to satisfy.

The composites of the instant invention solve a multitude of well control 
problems, in particular, the problems of thief zone control and blowout 
control or prevention. A low viscosity material, stable to pumping, is 
pumped down a well pipe and forced through the orifices of the drill bit 
or out a nozzle. Upon exiting the drill bit or nozzle or being subjected 
to any other perturbation sufficient to generate a high enough applied 
shear, the oil envelope separating the clay from the water is ruptured, 
permitting the clay and water to mix and set up into a high strength part 
at the point in the well at which such a paste is required. 
The shear thickening well treating fluids of the instant invention are a 
multi-component composite comprising a water swellable material, present 
in sufficient quantity to react with the water used and set up into a high 
strength paste, (for the purposes of this specification, the term "clay" 
shall be employed) preferably a bentonite or attapulgite clay, which can 
broadly be described as any layered or chair configuration material which, 
in the presence of water, swells into a high viscosity solid mass; a 
hydrophobic phase comprising a hydrocarbonaceous component and a 
surfactant component and water, preferably fresh water, but any water is 
satisfactory so long as it does not contain any materials in a high enough 
concentration to interfere with the gelling of the water swellable 
material. 
In general, the hydrophobic phase comprises a liquid oil, preferably any 
low aromatic content oil, typically mineral oil, paraffinic oils of from 6 
to 1000 carbons (provided they are liquid at the temperature at which they 
are employed) motor oils such as diesel fuel or kerosene, substituted 
paraffinic oils wherein the substituents are selected from the group 
consisting of halogens, amines, sulfates, nitrates, carboxylates, 
hydroxyls, etc. Preferred oils are the C.sub.6 -C.sub.200 liquid paraffin. 
These hydrophobic nonaqueous materials are preferably mixed with oil 
soluble surfactants so as to enhance their hydrophobicity. A wide variety 
of surfactants can be used in the process of the instant invention. These 
surfactants include anionic, cationic, nonionic and ampholytic 
surfactants. These surfactants are described in the book Surface Active 
Agents and Detergents by Schwartz, Perry and Beich, Interscience 
Publishers, Inc., New York, New York. 
The only requirement which must be met by the surfactant is that it be able 
to stabilize the water droplets and clay particles in the oil phase 
sufficiently to protect the mixture from premature gelling under low shear 
mixing conditions. 
Anionic surfactants include carboxylic acids, i.e., fatty acids, resin 
acids, tall oil acids and acids from paraffin oxidation products. Also 
included among the anionic surfactants are alkyl sulfonates, alkylaryl 
sulfonates, mohogany and petroleum sulfonates, phosphates and lignin. 
Cationic surfactants include quaternary ammonium compounds, e.g., salts of 
long chain primary, secondary and tertiary amines as well as quaternary 
amine salts with 7 to 40 carbon atoms. Styrene copolymers containing 
pendant quaternary ammonium groups including derivatives of trimethylamine 
or dimethylethanolamine are also useful cationic surfactants. 
Unprotonated amines fall into the class of non-ionic surfactants. A 
preferred group of amines have the general formula: 
##STR1## 
wherein R, R.sub.1 and R.sub.2 may be independently selected from the 
group consisting of hydrogen, C.sub.1 to C.sub.20 alkyl, C.sub.6 to 
C.sub.20 aryl and C.sub.7 to C.sub.20 alkylaryl radicals. 
Various polyamine derivatives are useful within the scope of the instant 
invention. The preferred polyamine derivatives are those having the 
general formula: 
##STR2## 
wherein R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, R.sub.8, R.sub.9 and 
y are chosen from the group consisting of hydrogen, C.sub.1 to C.sub.20 
alkyl, C.sub.6 to C.sub.20 aryl, C.sub.7 to C.sub.20 alkaryl radicals and 
substituted derivatives thereof, and x is an integer of from 1 to 100. The 
substituted derivatives are preferably selected from the group consisting 
of oxygen, nitrogen, sulfur, phosphorus and halogen containing derivative. 
The most preferred material is: 
EQU H.sub.2 N(CH.sub.2 CH.sub.2 NH).sub.3 CH.sub.2 CH.sub.2 NH.sub.2 
In general, the preferred surfactants are the products obtained by the 
reaction of the polyamine described above with various polyalkyl succinic 
anhydrides, such as polyisobutylene succinic anhydride, polypropenyl 
succinic an hydride and polyisobutenyl succinic anhydride. 
A preferred polyamine derivative, formed by reacting together an alkyl 
succinic radical, and the polyamine has the general formula: 
##STR3## 
wherein n varies from 10 to 60, preferably 10 to 30, most preferably 
15-17, x varies from 1 to 100, preferably 3 to 10, R.sub.5, R.sub.6, 
R.sub.7, R.sub.8 and R.sub.9 are hydrogen C.sub.1 to C.sub.20 alkyl, 
C.sub.6 to C.sub.20 aryl, C.sub.7 to C.sub.20 alkaryl radical and 
substituted derivatives thereof, preferably hydrogen and y is selected 
from the group consisting of hydrogen and oxygen containing hydrocarbyl 
radicals having up to 10 carbons, e.g., acetyl. Typically, the surfactants 
have a molecular weight on the order of about 1000. 
Nonionic systems include the polyethenoxy surfactants, i.e., polyethoxy 
ethers of alkyl phenols, polyethoxy ethers of alcohols, etc. The 
polyethenoxy ethers are especially useful in the invention as their 
solubility may be varied according to the weight of ethylene oxide added 
to the alkyl phenol starting material. Another non-ionic surfactant which 
is particularly useful is sorbitan monooleate which is known in the trade 
by the name of Span-80 and manufactured by the Atlas Chemical Company. 
Ampholytic surfactants contain both an acidic and a basic function in 
their structure and therefore will be cationic or anionic according to the 
pH of the solution in which they are dissolved. 
The final component of the shear sensitive fluids of the instant invention 
is water, preferably fresh water, but as previously stated, any water may 
be employed so long as it does not contain any material or pollutant in 
high enough concentration to interfere with the gelling of the water 
swellable material. 
The composite made up of the above recited ingredients can assume a number 
of physical conditions all of which are included within the scope of the 
instant invention and all of which will function as shear thickening 
fluids. 
In one embodiment, the clay component will be encapsulated in the 
previously defined oil phase (hydrocarbonaceous component and surfactant) 
and this encapsulated clay will in turn be suspended in the water wherein 
the water will exist as the continuous phase. 
In an alternative embodiment, the clay as discrete particles will be 
encapsulated in the oil phase while discrete droplets of water will also 
be encapsulated in the oil phase (the discrete clay particles and water 
droplets existing as separate entities, separated by the oil phase) which 
oil phase in this embodiment is the continuous phase. 
In either embodiment, the clay and the water are kept separate until such 
time as their mixing is deliberately desired, and this is accomplished by 
subjecting the composite to a shear force, as by passage through the 
nozzle of a drill bit, of sufficient intensity to rupture the oilphase 
envelope. Sufficient shear can also be generated by pumping the composite 
through the pipe at such a rate that a sufficient pressure drop is created 
to rupture the oil envelope. 
In a preferred embodiment, the clay is a bentonite clay, the hydrocarbon 
oil is S100N, a C.sub.30 paraffinic liquid oil, and the surfactant is 
chosen from the group of materials having formula corresponding to 
Compound A, previously defined. Most preferably, polyamines of the formula 
A.sub.1 or A.sub.2 below are employed: 
##STR4## 
Polyamine A.sub.1 is available as Paranox 100 from Exxon Chemical Co., 
while Polyamine A.sub.2 is available as Paranox 106 from Exxon Chemical 
Co. 
In addition, the composition may have included in it, either in the oil 
phase or in the water, preferably the oil phase, a fiberous material such 
as fiberglass, asbestos, wood fiber, cellulose, shreaded paper, cotton 
seed hulls, sugar cane bagasse, peanut shells, shreaded old tires, etc., 
which is substantially impervious to the action of the water and to the 
oil phase. These added materials serve the purpose of imparting increased 
mechanical strength and rigidity to the gel paste which sets up, upon 
rupture of the oil envelope, when the clay and water phases interact. 
The shear thickening fluid may also have added to it materials such as 
barite, hematite, galena, ilmenite, etc., which are commonly used for 
increasing the density and drilling fluids. These weighting agents are not 
water-swellable and will not participate in the shear-thickening effect of 
the instant invention but would be added if higher density formulations 
were particularly desired. If used, the weighting agents will absorb some 
of the surfactant, especially if the agent is finely powdered. 
With the one proviso that the clay and the water are never mixed before 
their introduction into the hydrocarbonaceous phase, the composites of the 
instant invention, whether water continuous or oil continuous, are 
prepared by mixing the components in any order. In general, the oil 
surfactant and clay are mixed together employing any convenient mixing 
apparatus. The clay can be added to premixed oil and surfactant, or clay 
can be added to the surfactant and then the oil added or vice-versa. 
Alternatively, the oil can be added to the clay and then the surfactant 
added, or the oil-surfactant combination can be added to the clay. Any 
technique is acceptable so long as the clay becomes encapsulated by the 
oil-surfactant phase. 
The composite of the instant invention has its components present in the 
following ranges (expressed in parts by weight): 
Clay 100 
Water 150 to 400 
Oil 50 to 150 
Surfactant 5 to 50 
The effectiveness of the liquid-membrane well control fluid is illustrated 
clearly in the following examples, summerized in Table I. 
When 10% bentonite was mixed with 90% water, a thick gel was formed with a 
viscosity of 2200 cp. When bentonite was encapsulated by liquid membrane 
No. 1 (3% polyamine A 97% S100N) and then mixed with water at a 1/9 
ratio, the mixture had only a viscosity of 350 cp. When a second 
formulation was used for encapsulation of the bentonite clay particles (LM 
No. 2, 5% polyamine A 95% S100N), the viscosities of the mixture of the 
encapsulated bentonite and water (1/9 to 1/24 ratio encapsulated clay to 
water) were in the range of 4 to 5 cp, indicating that the encapsulation 
was indeed very effective and that the mixture was almost as fluid as 
water (viscosity of 1 cp) and therefore would be easily pumpable down the 
well. The last experiment shows that when the above mixture is subjected 
to a strong shear in a Waring blender similar to that as would be 
encountered upon being pumped through drilling bit nozzles, the membranes 
were ruptured, exposing the bentonite particles to the surrounding water, 
a thick gel was found which had a viscosity of 2085 cp. In an actual 
operation, this would mean that the gel would be formed after the mixture 
was pumped through the drilling bit nozzles, which would presumably plug 
the well and prevent the flow of the unwanted fluids in or near the well 
bore or generate a paste at the precise locaion desired to seal off lost 
circulation zones or channels in cement behind casings or holes in casings 
or improperly sealed liner hangers, etc., in other words, generate a paste 
capable of effecting the desired control in the well. 
TABLE 1 
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ENCAPSULATION OF BENTONITE 
TO FORM A WELL CONTROL FLUID 
Temperature = 25.degree. C. 
Viscosity* (cp) 
______________________________________ 
1. 10% bentonite dispersed in water 
2200 
2. Bentonite encapsulated by LM No. 1 (poor 
encapsulation) mixed with water at 1/9 wt. 
ratio in a beaker with stirrer 
350 
3. Bentonite encapsulated by LM No. 2 (good 
encapsulation) mixed with water at 1/9 wt. 
ratio in a beaker with stirrer 
5 
4. Bentonite encapsulated by LM No. 2 (good 
encapsulation) mixed with water at 1/24 wt. 
ratio in a beaker with stirrer 
4 
5. Bentonite encapsulated by LM No. 2 (good 
encapsulation) mixed with water at 1/9 wt. 
ratio in a Waring blender 
2085 
______________________________________ 
LM No. 1: 3% Paranox 100 (polyamine), 97% S100N (isoparaffin C.sub.35) 
LM No. 2: 5% Paranox 100, 95% S100N 
*Viscosities were measured in a Fann Viscometer Model 35 at 3 RPM bob 
spinning speed, 10 minutes after mixing was stopped. 
Samples 2, 3, 4 and 5 contained 50 grams Bentonite in 75 grams of LM.