Use of polyalphalolefin in downhole drilling

The composition of matter and application thereof in the present invention relates to the application of a synthetic hydrocarbon compound, a polyalphaolefin liquid, blended in various concentrations with chemical oil and water emulsifiers, thinners and oil and water surface tension reducers, the concentration of polyalphaolefin liquid to that of the remaining portion of the blend being no less than 5%; blending the polyalphaolefin liquid and the emulsifiers in a blending tank containing water base drilling mud; circulating the blend of polyalphaolefin liquid and emulsifier with the water base drilling mud down hole, so that the blend of polyalphaolefin liquid emulsifier and water base drilling mud lubricates the drill string or reduces the differential pressure between the wall of the borehole and the drill string so that the drill string is free to rotate and drilling may be undertaken with less drag or torque. In another application, the polyalphaolefin blended with the emulsifier serves as a spotting fluid in order to unstick drill pipe that has become stuck.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to downhole lubricants and spotting fluids. 
More particularly, the present invention relates to the use of a downhole 
drilling compound used as an additive in water-based drilling fluids to 
lubricate the drill pipe during the drilling process and to free the drill 
pipe that has become stuck during the drilling process. The present 
invention further relates to the use of a synthetic hydrocarbon fluid, in 
particular polyalphaolefin (PAO) liquid containing no more than 0.5% 
1-decene monomer, blended in a concentration range of at least 5% by 
volume with emulsifiers; sometimes referred to as the PAO/emulsifier 
blend. When introduced at a certain volume downhole, the compound performs 
as a lubricating agent, used particularly for preventing the drag and 
torque on drill pipe, and as a spotting fluid, for dislodging stuck drill 
pipe from the well bore. One distinct advantage of the invention over the 
previous art in this field, is that the PAO/emulsifier blend is non-toxic 
to marine life and does not produce a visible sheen when discharged into 
water bodies. 
2. General Background 
In the drilling of oil and/or gas wells, a drill bit at the end of a 
rotating drill string or at the end of a drill motor is used to penetrate 
through geologic formations. During this operation a drilling mud is 
circulated through the drill string, out of the bit and is returned to the 
surface via the annular space between the drill pipe and the formation. 
The drilling mud, a fluid, cools and lubricates the drill string and drill 
bit and is designed to counterbalance, through hydrostatic pressure, the 
encountered formation pressures while providing a washing action to remove 
the formation cuttings from the wellbore. The drilling mud also forms a 
friction reducing wall cake between the drill string and the wellbore. 
During the drilling of the well, the drill string may demonstrate a 
tendency to develop unacceptable rotational torque or in the worse case 
become stuck. At this point, the drill string cannot be raised, lowered 
and/or rotated. The common factors that can lead to this situation are (1) 
cuttings or slough buildup in the borehole; (2) an undergauge borehole; 
(3) irregular borehole development embedding a section of the drill pipe 
into the drilling mud wall cake; and (4) differential formation pressure 
unexpectedly encountered. 
In the case of differential sticking, the hydrostatic fluid pressure of the 
drilling mud is greater than the permeable pressure of the exposed 
formation causing the flow of drilling mud into that area of the formation 
thus lodging the drill pipe against the formation face. When this occurs, 
the contact area of the drill pipe and the formation is great enough to 
cause an increase in rotational torque such that it prevents further 
movement of the drill pipe without a risk of parting the drill pipe 
string. 
Previous publications concerning methods of preventing drill pipe from 
sticking and/or freeing stuck drill pipe have discussed the common method 
of using an oil mud or oil or water based surfactant composition, to 
reduce friction, permeate drilling mud wall cake, destroy binding wall 
cake and reduce differential pressure. 
There remains a serious need for chemical compositions which can better 
reduce frictional torque and release stuck drill pipe while demonstrating 
a low order of toxicity to marine life, more specifically a product to 
comply with NPDES permit GOM LC.sup.50 test, and not produce a surface 
sheen on the water body. In contrast to prior art developments which 
incorporated the use of refined crude oil, diesel, kerosene, mineral oil 
and most recently low polynuclear aromatic mineral oils (as described in 
International Pat No. WO 83,102,949), it has been discovered that 
synthetic oils, and iso-paraffinic oil with no aromatic content, in 
particular a class of synthetic oils known as polyalphaolefin, demonstrate 
the required fluid properties and provide the necessary low order of 
toxicity to comply with the NPDES permit GOM LC.sup.50 to function as the 
primary composition of downhole fluid additives, more specifically a 
lubricant and spotting fluid. 
Previous developments in this area deal with the application in oil based 
mud. This invention specifically pertains to the application of these 
polyalphaolefin compounds as an additive in water based drilling fluids. 
In contrast to the previous use of synthetic oils in lubricating engines, 
mills, etc., this invention does not deal with metal to metal, thin film 
type of lubrication. It is specifically the use of a polyalphaolefin 
liquid blended with emulsifiers used in a concentration of at least 0.25% 
by volume introduced as an additive into a water based drilling fluid to 
lubricate the drill pipe while rotating or pulling past a mud filter cake, 
hard or soft rock, or casing in a well bore, and to unstick drill pipe 
that has become differentially stuck. 
SUMMARY OF THE PRESENT INVENTION 
The composition of matter and application thereof in the present invention 
relates to the application of a synthetic hydrocarbon compound, a 
polyalphaolefin liquid, blended in various concentrations with chemical 
oil and water emulsifiers, thinners and oil and water surface tension 
reducers, the concentration of polyalphaolefin liquid to that of the 
remaining portion of the blend being no less than 5%; blending the 
polyalphaolefin liquid and the emulsifiers in a blending tank containing 
water base drilling mud in an amount of at least 0.25% by volume; 
circulating the blend of polyalphaolefin liquid and emulsifier with the 
water base drilling mud down hole, so that the blend of polyalphaolefin 
liquid emulsifier and water base drilling mud lubricates the drill string 
or reduces the rotational torque or drag between the wall of the borehole 
and the drill string so that the drill string is free to rotate and 
drilling may be undertaken with less drag or torque. In another 
application, the polyalphaolefin blended with the emulsifier serves as a 
spotting fluid in order to unstick drill pipe that has been stuck. In this 
method, the polyalphaolefin is blended with the emulsifiers in a 
concentration of at least 5% polyalphaolefin; the polyalphaolefin 
emulsifier blend is introduced into the borehole as a "pill"; the pill is 
circulated downhole in the mud system through the annulus to the depth at 
which the pipe is stuck; the polyalphaolefin emulsifier blend acts on the 
wall filter cake reducing the differential pressure bond. For purposes of 
this invention, the emulsifier, thinner and surface tension reducing 
additive can, in the case of the spotting fluid, be a blend of modified 
fatty acid and Amides. In the case of the drilling fluid lubricant, the 
additive can be described as a blend of sulfurized fatty acids and 
modified fatty acids. For purposes of this invention, the polyalphaolefin 
is a totally hydrogenated alpha-olefin oligomer produced from an 
alpha-olefin such as 1-decene. More particularly, the polyalphaolefin 
relates to an alpha-olefin oligomer comprised of dimer, trimer, tetramer 
and pentamer having a viscosity of approximately 2 centistokes at 210 
degrees Fahrenheit. 
Therefore, it is a principal object of the present invention to provide a 
synthetic hydrocarbon, more particularly, polyalphaolefin, utilized as a 
lubricant to be administered in downhole drilling operations for reducing 
the drag or torque on the drill string during drilling; 
It is a further object of the present invention to provide the application 
of a polyalphaolefin as a spotting fluid in order to unstick pipe that has 
been stuck downhole; 
It is a further object of the present invention to provide the application 
of a polyalphaolefin-emulsifier blend as a downhole lubricant which is 
non-toxic to marine life and does not produce a sheen on the water surface 
when dumped on the water body; 
It is still a further object of the present invention to provide a 
non-toxic base fluid that complies with NPDES-GOM-LC.sup.50 test, the 
polyalphaolefin liquid consisting of a low value (less than 0.5% 
concentration of 1-decene monomer).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment of the combination of matter and the system of 
application of same of the present invention would utilize a synthetic 
hydrocarbon fluid, in particular polyalphaolefin (PAO) liquid which would 
preferably contain no more than 0.5% 1-decene monomer, in a concentration 
range of at least 5% by volume with other liquid additives blended in 
various concentrations; additives such as chemical oil and water 
emulsifiers, thinners, and oil and water surface tension reducers. The 
concentration of the polyalphaolefin liquid to that of the remaining 
portion of the blend would be no less than 5% and function as a water base 
drilling mud lubricant or a water base drilling mud spotting fluid. When 
utilized as a water base drilling lubricant, the blend of polyalphaolefin 
liquid and additives, presently sold under the registered trademark 
"COASTALUBE", would have an optimum PAO liquid concentration of 70% to 95% 
and an optimum additive concentration of 30% to 5%. When utilized as a 
water base spotting fluid, the blend is sold under the registered 
trademark COASTAL SPOT; likewise, the polyalphaolefin liquid comprising an 
optimum percentage of 70% to 95% of the blend, and the optimum additive 
concentration comprising 30% to 5% of the blend. 
For purposes of this invention, in either case when the PAO liquid-additive 
blend is either serving as a drilling fluid lubricant, or as a spotting 
fluid, the emulsifier, thinner, surface tension reducing additives can be 
described as a blend of modified fatty acid and amides. The 
polyalphaolefin liquid is commercially prepared in a number of different 
methods, but for purposes of this invention the totally hydrogenated 
alpha-olefin oligomer is produced from an alpha-olefin such as 1-decene. 
More particularly, the PAO liquid is an alpha-olefin oligomer comprised of 
dimer, trimer, tetramer, and pentamer having a viscosity of approximately 
2 centistokes at 210 degrees Fahrenheit. Furthermore, in order to qualify 
as a non-toxic base fluid and comply with NPDES GOM LC.sup.50 test, the 
polyalphaolefin liquid must consist of a low value (less than 0.5% 
concentration) of 1-decene monomer. The various oligomer distributions 
were determined by gas chromotography. The important feature of the 
polyalphaolefin liquid application downhole and more particularly 
offshore, is the fact that it is non-toxic to marine life and does not 
produce a sheen on the water when the liquid is introduced into the sea 
water. 
Turning now to the manner in which the PAO blend is applied downhole, 
reference is made to the fact that in a water base drilling system, as was 
discussed earlier, the drill string may at one point demonstrate rotation 
through the formation under increased torque or drag, and lubrication of 
the drill string is critical. Therefore, one would introduce a lubricant 
into the water base mud system, in order to lubricate the drill string. 
This lubricant would comprise a polyalphaolefin liquid containing no more 
than 0.5% 1-decene monomer, at an optimum concentration range of between 
70% and 95% polyalphaolefin liquid to an optimum range of 30% to 5% 
additives, more particularly chemical, oil, and water emulsifiers, 
however, the percentage of of polyalphaolefin liquid would be no less than 
5% of the blend. This polyalphaolefin-additive blend would then be added 
to the water base mud system, for example by introduction of the 
polyalphaolefin-additive blend into the mud pit, so that the blend would 
be in a concentration of at least 0.25% to 6.0% by volume in the water 
base drilling mud system. The drilling mud, in the system, during the 
introduction of the PAO-additive blend, does not have to be interrupted, 
and the blend would then be mixed into the water base mud system and 
introduced downhole. Upon being introduced downhole, the PAO-additive 
blend would help to lubricate the surface between the wall of the drill 
pipe and the wall of the surrounding formation, so as to reduce the torque 
and drag on the drill string during downhole drilling. 
Due to the fact that the polyalphaolefin has a concentration of no more 
than 0.5% 1-decene monomer, the polyalphaolefin liquid is non-toxic to 
marine life, and therefore, can be maintained in the mud system during 
drilling, and the drill cuttings do not have to be recovered and may be 
discharged. In the previous state of the art, if an oil based lubricant 
was introduced into the mud system, the entire mud system would have toxic 
levels above acceptable limits as per the LC.sup.50 test and/or would 
produce a sheen on the water. In order to avoid the possibility of the 
spreading of the lubricant into the surrounding seawater, creating a 
hazard to marine life, the drilling fluid and cuttings would necessitate 
containment. The combination of matter in the present invention would 
overcome this likelihood and could be maintained in the water base mud 
system allowing normal discharge of drilling fluids and/or cuttings. 
In its second application, the polyalphaolefin liquid/additive blend, would 
be utilized in the same concentration, with the same additives such as 
emulsifiers, downhole in order to unstick the drill string that has become 
stuck to the wall of the formation due to various factors including 
differential pressure downhole. In this particular application of the 
invention, the normal circulation of the water base mud system would be 
altered to allow for a certain volume of the polyalphaolefin liquid/ 
additive blend to be introduced as a "pill" into the active mud system, 
which would therefore result in a greater combination of the 
polyalphaolefin liquid/additive blend being applied at a predetermined 
point downhole. Following the introduction of the blend into the the 
borehole, the blend would then be displaced into the annulus in the 
borehole at the estimated level that the drill string has become stuck, 
and the blend would serve as a spotting fluid in order to, for example, 
replace the water in the mud wall cake causing the sticking of the pipe 
against the wall mud cake due to differential pressure, and would relieve 
that pressure and rotational torque in order to allow the drill string to 
resume rotational and vertical movement. Again, in view of the fact that 
the polyalphaolefin liquid/additive blend is non-toxic to marine life, the 
pill could be maintained downhole and recirculated in the system, which 
thereafter it would function as a lubricant, and not have to be isolated 
and removed from the active mud system. At the present time, if an 
oil-base spotting fluid is introduced downhole as a pill, the EPA may 
require that 50 barrels of mud preceeding and following the pill be 
retrieved together with the pill in order to avoid contamination of the 
mud system by a toxic substance such as the state-of-art oil base spotting 
fluids. 
For purposes of clarification of the present invention, applicant is 
submitting herewith the following exhibits attached to this application 
and incorporated herein by reference, which provide evidence of the 
usefulness and non-toxicity of the present invention. 
EXHIBIT A 
Exhibit A attached hereto is a mixing chart of the polyalphaolefin 
liquid/additive blend being used as a spotting fluid, and the manner in 
which the composition would operate under various required densities. 
EXHIBIT B 
Exhibit B is a summary of the result of tests conducted for providing 
bio-assay data from Coastal Chemical Company on the drilling fluid 
containing 3% volume polyalphaolefin. 
EXHIBIT C 
Exhibit C is a test and the results of the tests for approximating 
LC.sup.50 of a base mud containing 10% of spotting fluid in the sample. 
Because many varying and different embodiments may be made within the scope 
of the inventive concept herein taught, and because many modifications may 
be made in the embodiments herein detailed in accordance with the 
descriptive requirement of the law, it is to be understood that the 
details herein are to be interpreted as illustrative and not in a limiting 
sense.