OA10040A

OA10040A - The use of polyalphaolefin in downhole drilling

Info

Publication number: OA10040A
Application number: OA59720A
Authority: OA
Inventors: David O Trahan; Michael B Faulk
Original assignee: Coastal Mud Inc
Priority date: 1988-01-19
Filing date: 1990-01-03
Publication date: 1996-10-14
Also published as: NO893712L; AU619253B2; NO893712D0; AU3049689A

Description

-1- 10040

THE ÜSE OF POLYALPHALOLEFIN INDOWNHOLE DRILLING

SPECIFICATION

BACKGROOND OF THE INVENTION 1. Fleld of the Invention

The présent invention relates to downholelubricants and spotting fluide. More particularly, the 5 présent invention relates to the use of a downhole drilling compound used as an additive in water-baseddrilling fluids to lubricate the drill pipe during thedrilling process and to free the drill pipe that hasbecome stuck during the drilling process. The présent 10 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 volumewith emulsifiers; sometimes referred to as the 15 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 ondrill pipe, and as a spotting fluid, for dislodging stuckdrill pipe from the well bore. One distinct advantage of 20 the invention over the previous art in this field, is that the PAO/emulsifier blend is non-toxic to marine life anddoes not produce a visible sheen when discharged intowater bodies. ί 00 40 -2- 2. General Background

In the drilling of oil and/or gas wells, a drill bitat the end of a rotating drill string or at the end of adrill motor is used to penetrate through géologieformations. During this operation a drilling mud iscirculated through the drill string, out of the bit and isreturned to the surface via the annular space between thedrill pipe and the formation. The drilling mud, a fluid,cools and lubricates the drill string and drill bit and isdesigned to counterbalance, through hydrostatic pressure,the encouritered formation pressures while providing awashing action to remove the formation cuttings from thewellbore. The drilling mud also forros a friction reducingwall cake between the drill string and the wellbore.

During the drilling of the well, the drill string maydémonstrate a tendency to develop unacceptable rotationaltorque or in the worse case become stuck. At this point,the drill string cannot be raised, lowered and rotated.The most common factors that can lead to this situationare (1) cuttings or slough buildup in the borehole; (2) anundergauge borehole; (3) irregular borehole developmentembedding a section of the drill pipe into the drillingmud wall cake; and (4) differential formation pressureunexpectedly encountered.

In the case of differential sticking, the hydrostaticfluid pressure of the drilling mud is greater than thepermeable pressure of the exposed formation causing theflow of drilling mud into that area of the formation thuslodging the drill pipe against the formation face. Whenthis occurs, the contact area of the drill pipe and theformation is great enough to cause an increase inrotational torque such that it prevents further movementof the drill pipe without a risk of parting the drill pipestring.

Previous publications concerning methods ofpreventing drill pipe from sticking and/or freeing stuckdrill pipe hâve discussed the common method of using an FF ./ 1 0040 -3- 10 15 20 25 30 oil mud or oil or water based surfactant composition, toreduce friction, permeate drilling mud wall cake, destroybinding wall cake and reduce differential pressure.Applicant is attaching hereto a statement of the art whichis pertinent to the présent invention.

There remains a serious need for Chemicalcompositions which can better reduce frictional torque andrelease stuck drill pipe while demonstrating a low orderof toxicity to marine life, more specifically a product tocomply with NPDES permit GOM LC5® test, and not produce asurface sheen on the water body. In contrast to prior artdevelopments which incorporated the use of refined crudeoil, diesel, kerosene, minerai oil and most recently lowpolynuclear aromatic minerai oils (as described inInternational Pat No. WO 83,102,949), it has beendiscovered that synthetic oils, an iso-paraffinie oil withno aromatic content, in particular a class of syntheticoils known as polyalphaolefin, demonstrate the requiredfluid properties and provide the necessary low order oftoxicity to comply with the NPDES permit GOM LC5® tofunction as the primary composition of downhole fluidadditives, more specifically a lubricant and spottingfluid.

Previous developments in this area deal with theapplication in oil based mud. This invention specificallypertains to the application of these polyalphaolefincompounds as an additive in water based drilling fluids.In contrast to the previous use of synthetic oils inlubricating engines, mills, etc., this invention does notdeal with métal to métal, thin film type of lubrication.It is specifically the use of a polyalphaolef in liquidblended with emulsifiers used in a concentration of atleast .25% by volume introduced as an additive into awater based drilling fluid to lubricate the drill pipewhile rotating or pulling past a mud filter cake, hard orsoft rock, or casing in a well bore, and to unstick drillpipe that has become differentially stuck. 35 1 0040 -4-

SÜMMARY OF THE PRESENT INVENTION

The composition of matter and application thereof in the présent invention relates to the application of asynthetic hydrocarbon compound, a polyalphaolefin liquid,blended in various concentrations with Chemical oil andwater emulsifiers, thinners and oil and water surfacetension reducers, the concentration of polyalphaolefinliquid to that of the remaining portion of the blend beingno less than 51; blending the polyalphaolef in liquid andthe emulsifiers in a blending tank containing water basedrilling roud in an amount of at least .25% by volume;circulating the blend of polyalphaolefin liquid andemulsifier with the water base drilling mud down hole, sothat the blend of polyalphaolefin liquid emulsifier andwater base drilling mud lubricates the drill string orreduces the rotational torque or drag between the wall ofthe borehole and the drill string so that the drill stringis free to rotate and drilling may be undertaken with lessdrag or torque. In another application, thepolyalphaolefin blended with the emulsifier serves as aspotting fluid in order to unstick drill pipe that hasbeen stuck. In this method, the polyalphaolefin isblended with the emulsifiers in a concentration of atleast 5% polyalphaolefin; the polyalphaolefin emulsifierblend is introduced into the borehole as a "pill"; thepill is circulated downhole in the mud System through theannulus to the depth at which the pipe 13 stuck; thepolyalphaolefin emulsifier blend acts on the wall filtercake reducing the differential pressure bond. Forpurposes of this invention, the emulsifier, thinner andsurface tension reducing additive can, in the case of thespotting fluid, be a blend of modified fatty acid andAmides. In the case of the drilling fluid lubricant, theadditive can be described as a blend of sulfurized fattyacids and modified fatty acids. For purposes of this invention, the polyalphaolefin is a totally hydrogenatedalpha-olefin oligomer produced from an alpha-olefin such î 0040 -5- as l-decene. More particularly, the polyalphaolefinrelates to an alpha-olefin oligomer comprised of dimer,trimer, tetramer and pentamer having a viscosity ofapproximately 2 centistokes at 210 degrees Fahrenheit. 5 Therefore, it is a principal object of the présent invention to provide a synthetic hydrocarbon, moreparticularly, polyalphaolefin, utilized as a lubricant tobe administered in downhole drilling operations forreducing the drag or torque on the drill string duringdrilling;

It is a further object of the présent invention toprovide the application of a polyalphaolefin as a spottingfluid in order to unstick pipe that has been stuck downhole; 15

It is a further object of the présent invention toprovide the application of a polyalphaolefin - emulsifierblend as a downhole lubricant which is non-toxic to marinelife and does not produce a sheen on the water surface 2® when dumped on the water body;

It is still a further object of the présent inventionto provide a non-toxic base fluid that compiles with NPDES- GOM - LC^O test, the polyalphaolefin liquid consistingof a low value (less than .5% concentration of 1 - decene ' r monomer). 25

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the combination of matterand the system of application of same of the présentinvention would utilize a synthetic hydrocarbon fluid, in30 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 withother liquid additives blended in various concentrations;additives such as Chemical oil and water emulsifiers,thinners, and oil and water surface tension reducers. Theconcentration of the polyalphaolefin liquid to that of theremaining portion of the blend would be no less than 5% 35 -6- 10040 and furiction as a water base drilling mud lubricant or awater base drilling mud spotting fluid. When utilized asa water base drilling lubricant, the blend ofpolyalphaolefin liquid and additives, presently sold underthe registered trademark "COASTALUBE", would hâve anoptimum PAO liquid concentration of 70% to 95% and anoptimum additive concentration of 30% to 5%. Whenutilized as a water base spotting fluid, the blend is soldunder the registered trademark COASTAL SPOT; likewise, thepolyalphaolefin liquid comprising an optimum percentage of70% to 95% of the blend, and the optimum additiveconcentration comprising 30% to 5% of the blend.

For purposes of this invention, in either case whenthe PAO liquid - additive blend is either serving as adrilling fluid lubricant, or as a spotting fluid, theemulsifier, thinner, surface tension reducing additivescan be described as a blend of modified fatty acid andamides. The polyalphaolefin liquid is commerciallyprepared in a number of different methods, but forpurposes of this invention the totally hydrogenatedalpha-olefin oligomer is produced from an alpha-olefinsuch as 1 - decene. More particularly, the PAO liquid isan alpha-olefin oligomer comprised of dimer, trimer,tetramer, and pentamer having a viscosity of approximately2 centistokes at 210 degrees Fahrenheit. Furthermore, inorder to qualify as a non-toxic base fluid and comply withNPDES GOM LC^° test, the polyalphaolefin liquid mustconsist of a low value (less than .5% concentration) of 1- decene monomer. The various oligomer distributions weredetermined by gas chromotography. The important featureof the polyalphaolefin liquid application downhole andmore particularly offshore, is the fact that it isnon-toxic to marine life and does not produce a sheen onthe water when the liquid is introduced into the seawater.

Turning now to the manner in which the PAO blend isapplied downhole, reference is made to the fact that in a î 0040 -7- water base drilling System, as was discussed earlier, thedrill string may at one point demonstrate rotation throughthe formation under increased torque or drag, andlubrication of the drill string is critical. Therefore,one would introduce a lubricant into the water base mudSystem, in order to lubricant the drill string. Thislubricant would comprise a . polyalphaolefin liquidcontaining no more than .5% 1 - decene monomer, at anoptimum concentration range of between 70% and 95%polyalphaolef in liquid to an optimum range of 30% to 5%additives, more particularly Chemical, oil, and wateremulsifiers, however, the percentage of of polyalphaolefinliquid would be no less than 5% of the blend. Thispolyalphaolefin - additive blend would then be added tothe water base mud System, for example by introduction ofthe polyalphaolefin - additive blend into the mud pit, sothat the blend would be in a concentration of at least.25% to 6.0% by volume in the water base drilling mudSystem. The drilling mud, in the system, during theintroduction of the PAO - additive blend, does not hâve tobe interrupted, and the blend would then be mixed into thewater base mud System and introduced downhole. Upon beingintroduced downhole, the PAO - additive blend would helpto lubricate the surface between the wall of the drillpipe and the wall of the surrounding formation, so as toreduce the torque and drag on the drill string duringdownhole drilling.

Due to the fact that the polyalphaolefin has aconcentration of no more than .5% 1 - decene monomer, thepolyalphaolefin liquid is non-toxic to marine life, andtherefore, can be maintained in the mud system duringdrilling, and the drill cuttings do not hâve to berecovered and may be discharged. In the previous State ofthe art, if an oil based lubricant was introduced into themud system, the entire mud system would hâve toxic levelsabove acceptable limite as per the LC^® test and/or wouldproduce a sheen on the water. In order to avoid the 1 00 40 -8- possibility of the spreading of the lubricant into thesurrounding seawater, creating a hazard to marine life,the drilling fluid and cuttings would necessitatecontainment. The combination of matter in the présentinvention would overcome this likelihood and could bemaintained in the water base mud System allowing normaldischarge of drilling fluids and/or cuttings.

In its second application, the polyalphaolefinliquid/ additive blend, would be utilized in the sameconcentration, with the same additives such asemulsifiers, downhole in order to unstick the drill stringthat has become stuck to the wall of the formation due tovarious factors including differential pressure downhole.In this particular application of the invention, thenormal circulationof the water base mud System would bealtered to allow for a certain volume of thepolyalphaolefin liquid/ additive blend to be introduced asa "pill" into the active mud system, which would thereforeresuit in a greater' combination of the polyalphaolefinliquid/additive blend being applied at a predeterminedpoint downhole. Following the introduction of the blendinto the the borehole, the blend would then be displacedinto the annulus in the borehole at the estimated levelthat the drill string has become stuck, and the blendwould serve as a spottîng fluid in order to, for example,replace the water in the mud causing the sticking of thepipe against the wall mud cake due to differentialpressure, and would relieve that pressure and rotationaltorque in order to allow the drill string to résumérotational and vertical movement. Again, in view of thefact that the polyalphaolefin liquid/additive blend isnon-toxic to marine life, the pill could be maintaineddownhole and recirculated in the system, which thereafterit would function as a lubricant, and not hâve to beisolated and removed from the active mud system. At theprésent time, if an oil-base lubricant mud is introduceddownhole as a pill, the EPA may require that 50 barrels of -9- 1 0040 mud preceeding and following the pill be retrievedtogether with the pill in order to avoid contamination ofthe mud System by a toxic substance such as thestate-of-art oil base spotting fluids.

For purposes of clarification of the présentinvention, applicant is submitting herewith the followingappendixes attached to this application and incorporatedherein by reference, which provide evidence of theusefulness and non-toxicity of the présent invention.

APPENDIX A

Appendix A attached hereto is a mixing chart ofthe polyalphaolefin liquid/additive blend being used as aspotting fluid, and the manner in which the compositionwould operate under various required densities.

APPENDIX B

Appendix B is a summary of the resuit of testsconducted for providing bio-assay data from CoastalChemical Company on the drilling fluid containing 3%volume polyalphaolefin.

APPENDIX C

Appendix C is a test and the results of thetests for approximating LC50 of a base mud containing 10%of spotting fluid in the sample.

Because many varying and different embodiments may bemade within the scope of the inventive concept hereintaught, and because many modifications may be made in theembodiments herein detailed in accordance with thedescriptive requirement of the law, it is to be understoodthat the details herein are to be interpreted asillustrative and not in a limiting sense.

What is claimed as invention is:

Claims

-10- mu ÇLAIMS

1. A drilling fluid compound for lubricating drillpipe in a water base mud System during the drillingprocess, the compound comprising: a) a polyalphaolefin liquid at a concentrationof at least 5% of the drilling fluid compound; b) an emulsifier additive added to thepolyalphaolef in liquid, in a range of 30% to 5%concentration; and c) the drilling fluid compound introduced intothe water base mud system in a liquid volume concentrationof 0.25% to 6.0% of the water base drilling mud forserving as a lubricant in the water base drilling mudsystem.
2. The drilling fluid compound in Claim 1, whereinthe polyalphaolef in would contain no more than .5 % 1 -decene monomer.
3. The drilling fluid compound in Claim 1, whereinthe optimum percentage of polyalphaolefin in the drillingfluid compound would be 90%.
4. The drilling fluid compound in Claim 1, whereinthe optimum percentage of emulsifier additives in thedrilling fluid compound would be 10%.
5. The drilling fluid compound in Claim 1, whereinthe drilling fluid compound is non-toxic to marine lifeand may be a permanent addition to the water base mudsystem.
6. In a process for drilling oil wells, wherein thedrill string is rotated in a formation utilizing a waterbase mud system, the process comprising the followingsteps; a) combining a liquid polyalphaolefin in aconcentration of at least 5% by volume of thepolyalphaolefin to an emulsifier; b) introducing a volume of the polyalphaolefin- emulsifier combination into the volume of water base mudat a concentration of 0.25% to 6.0% percent of 100 40 -11- polyalphaolef in - emulsifier; c) circulating the mud containing the polyalphaolefin - emulsifier combination down the boreholesufficient to lubricate the pipe to reduce the frictionbetween the wall of the drill pipe and the formation asthe drill pipe is rotated.
7. The process in Claim 6, wherein thepolyalphaolefin - emulsifier contains 90% polyalphaolefinand 10% emulsifier.
8. The process in Claim 6, wherein thepolyalphaolefin - emulsifier combination is non-toxic tomarine life in its application downhole.
9. A process for unsticking drill pipe in a waterbase mud System, where the drill pipe has becomedifferentially stuck against the formation, the processcomprising the following steps: a) locating the point downhole where the drillpipe has become stuck against the formation; b, blending a polyalphaolefin in aconcentration of at least 5% by volume with an emulsifier;and c) introducing a certain volume of thepolyalphaolefin - emulsifier downhole as a spotting fluidto the depth of the point of the stuck pipe and in aquantity sufficient to displace the water-based mud overthe entire stuck interval to unstick the pipe.
10. The process in Claim 9, wherein thepolyalphaolefin-emulsifier blend is introduced into themud System as a "pill" separated from the mud in theSystem.
11. The process in Claim 9, wherein thepolyalphaolefin emulsifier blend displaces the water inthe formation at the point the pipe is stuck against theformation and lubricates the pipe and wellbore so thatrotation and vertical movement of the drill pipe can bereestablished.