Method And Composition For Treating High Pour Point Oils Under Low Ambient Temperature Conditions

Abstract

A low pour point additive composition comprising an admixture of about 1 to 20 weight percent of a copolymer of ethylene and a monoethylenically unsaturated ester, about 5 to 25 weight percent liquid monohydroxy phenols, and at least about 55 weight percent of a hydrocarbon solvent containing a substantial proportion of cyclic hydrocarbon compounds. A method for treating high pour point, wax-containing oil to inhibit the deposition of wax from the oil and to facilitate storage and pipeline transportation of the oil at ambient temperatures below the normal pour point of the wax-containing oil wherein the additive composition is admixed into the wax-containing oil to provide therein an effective concentration of the copolymer between about 5 to 10,000 ppm.

Description

This invention relates to the production, storage and transportation of high pour point, wax-containing crude petroleum and crude shale oil, and distillate and residual fractions of these oils, and more particularly relates to a low pour point additive composition and method for inhibiting the deposition of wax from wax-containing oils and for reducing the pour point and yield stress of a high pour point, wax-containing oil to facilitate storage and pipeline transport of the oil.

It is well known that when a crude petroleum or petroleum fraction or a shale oil or shale oil fraction containing paraffin wax is cooled below the solidification temperature of the wax, the wax solidifies and tends to deposit on the walls and other surfaces of equipment contacted by the cooled oil. The deposition and accumulation of wax-like substances on the walls and other surfaces of equipment contacted by wax-containing petroleum and shale oil is a major problem in the production, transfer, storage and processing of crude petroleum and shale oil, and distillate and residual fractions of these oils containing significant amounts of wax, since the wax deposits often restrict or completely stop flow through this equipment, requiring costly cleaning to maintain the equipment in operation. More specifically, it is well known that wax-like substances deposit and accumulate on the surfaces of conduits and flow passages of wells operated for the production of wax-containing crude petroleum and that this wax deposition causes plugging that progressively decreases the rate of production from the well. Also, the wax-like substances deposit in pipelines, vessels and storage tanks handling wax-containing oils which results in a serious problem of plugging and clogging this equipment. Furthermore, deposition and accumulation of wax can cause plugging in heat exchangers and malfunctioning of valves in pumps and other apparatus employed in the treating and transportation of wax-containing oil, and in the refining and distribution of such oil. The deposition and resulting accumulation of wax in well conduits and in transportation, storage and treating equipment reduces the efficiency and capacity of the equipment, often necessitating frequent cleaning to maintain the equipment operational.

Another problem is encountered in the transport of certain wax-containing oils that exhibit high pour points; i.e., pour points in the range of about 0.degree. F. to about 90.degree. F. These high pour point oils may be economically and efficiently transported through pipelines in conventional manner so long as the temperature of the oil being transported is maintained above its pour point. However, depending upon the geographical location of the pipeline, the season of the year, and whether the pipeline is buried beneath the earth, laid upon the bottom of a body of water, or exposed to the atmospheric environment, the oil being transported can be cooled to a temperature below its pour point. This cooling causes formation of a gel that is resistant to flow and increases the frictional losses in the pipeline. This phenomenon is particularly critical when the pipeline is shut down, since in order for flow to be restarted, sufficient force must be applied to the fluid in the pipeline to exceed the yield stress of the gel. In many applications, the pressure required to initiate flow of the gel exceeds the capacity of the pumps, and requires pressures exceeding the pressure rating of the pipeline and other equipment. Similar problems are encountered in storing these high pour point oils in bulk storage tanks. Heating of the oil in storage and transporting the heated oil through an insulated pipeline or an insulated and heated pipeline is expensive and often wholly impractical.

It is known that certain copolymers of ethylene and a monoethylenically unsaturated ester, such as copolymer ethylene and lower vinyl ester, added to a wax-containing oil in relative low concentrations are effective in inhibiting the deposition of wax on pipe and tank walls and other surfaces contacted by the oil, and that these agents are effective in reducing the pour point and yield strength of a high pour point, wax-containing oil. In use, the copolymer agent is generally dissolved in an organic solvent such as petroleum naphtha, kerosene, diesel oil, gas oil, light crude petroleum, or the like, and admixed into the oil to be treated in an amount sufficient to provide therein an effective concentration of the copolymer agent. In a typical application, the additive solution is prepared by dissolving or dispersing the copolymer agent in the solvent and the additive solution pumped or otherwise dispersed from a bulk storage tank, vessel or drum into the wax-containing oil. The additive solution can be injected into the wax-containing oil in a well, in a bulk storage tank, or the additive solution can be injected into a pipeline transporting the oil.

While the foregoing treatment is effective in many applications, difficulty has been experienced in injecting the additive solution into a well, tank, or pipeline under relatively cold ambient conditions as the additive solution has a high pour point and tends to freeze, thus necessitating that the additive solution storage vessel and injection piping be heated to prevent the solution from freezing during the injection operation. The additional heating step is both costly and an inconvenience. Thus, need exists for an ethylene/monoethylenically unsaturated ester composition that will remain liquid under the injection conditions normally encountered in field applications.

Accordingly, a primary object of this invention is to provide a copolymer ethylene/monoethylenically unsaturated ester composition useful as a wax deposition inhibitor and pour point depressant that remains liquid at relatively low ambient temperatures.

Another object of this invention is to provide a copolymer ethylene/monoethylenically unsaturated ester composition that has a pour point below about 25.degree. F.

Still another object of this invention is to provide a copolymer ethylene/lower vinyl ester composition that has a pour point below about 25.degree. F.

Yet another object of this invention is to provide a method for inhibiting the deposition of wax from a wax-containing oil onto metal surfaces contacted by the oil that can be practiced under low ambient temperature conditions.

A further object of this invention is to provide a method for transporting a high pour point, wax-containing oil by pipeline that can be practiced under low ambient temperature conditions.

Briefly, this invention contemplates an additive composition comprising an admixture of about 1 to 20 weight percent of a copolymer of ethylene and a monoethylenically unsaturated ester, about 5 to 25 weight percent of monohydroxy phenols, and at least about 55 weight percent of a liquid hydrocarbon solvent containing a substantial proportion of cyclic hydrocarbon compounds; and a method for treating a wax-containing oil to inhibit the deposition of wax on metal surfaces contacted by the oil and for treating a high pour point, wax-containing oil to reduce its pour point and yield stress at temperatures below the normal pour point of the oil. The additive composition exhibits a pour point substantially below that of a simple solution of the copolymer ethylene/monoethylenically unsaturated ester containing a comparable proportion of the copolymer. Because of its lower pour point, the additive composition can be employed under lower ambient temperature conditions than the simple solutions of the polymer.

The term "pour point" as employed herein means the lowest temperature at which oil is observed to flow under conditions prescribed by ASTM test method D 97-66 entitled "Standard Method of Test for Pour Point" ASTM Standards, American Society for Testing Materials, Part 17, Nov. 1971, pages 58-61, which procedure is herein incorporated by reference.

The term "yield stress" as employed herein means the shearing stress at the yield point, i.e., the point that a gel will flow under applied pressure, and the term "apparent yield stress" means that value of yield stress obtained by measurement with an apparatus comprised of a stationary cylindrical jacketed cup and a hollow, freely rotating cylindrical bob of somewhat smaller diameter suspended concentrically in the cup so as to form an annular chamber in which the oil to be tested is placed. Oil samples are introduced into the annular chamber through an inlet connection at the bottom of the cup. Temperature control is obtained by circulating coolant at the desired test temperature in series through both the bob and the jacket surrounding the cup. Measurement of the yield stress is accomplished with the aid of a force transducer mounted about the cup on a movable platform and connected, through a spring, to a vertical extension of the bob. During operation, the platform, and hence the transducer, is caused to rotate at some predetermined angular velocity. Then, since rotation of the bob is restrained in the solidified oil sample, an opposing torque is established in the spring and transmitted to the transducer. The shearing stress at the surface of the immersed portion of the bob increases linearly until the yield strength of the oil is exceeded, at which time the opposing torque abruptly decreases to some lower value.

The term "crude petroleum" as used herein is meant to include residual petroleum fractions obtained by removing lower boiling petroleum fractions from crude petroleum by distillation, such as for example topped crude petroleum and deasphalted topped crude petroleum; and the term "shale oil" is meant to include crude shale oil obtained by processing oil shale, distillate and residual shale oil fractions, and hydrotreated shale oil obtained by treating shale oil with hydrogen.

It is known that various copolymers of ethylene and a monoethylenically unsaturated ester are effective inhibiting the deposition of wax from wax-containing oils and in reducing the pour point and yield stress of high pour point, wax-containing oils. These polymeric additives are substantially linear addition polymers of ethylene and a monoethylenically unsaturated ester such as vinyl and allyl esters of saturated aliphatic carboxylic acids and the saturated aliphatic esters of monoethylenically unsaturated aliphatic carboxylic acids. The monoethylenically unsaturated esters that can be copolymerized with ethylene to produce the desired copolymers are characterized by the formula: ##SPC1##

wherein (1) R is hydrogen or an alkyl group containing from about 1 to 25 carbon atoms and R.sub.1 is a vinyl or allyl group, and preferably a vinyl group; or (2) R is an .alpha.,.beta.-unsaturated alkylene and R.sub.1 is an alkyl group containing from about 1 to 25 carbon atoms.

Exemplary monoethylenically unsaturated esters that are copolymerizable with ethylene to form the copolymers useful in treating wax-containing oils are the vinyl and allyl esters of formic, acetic, propionic, butyric, lauryic, palmitic and stearic acids; and the saturated aliphatic esters of acrylic acids such as methacrylic acid and the like. Also, ethylene can be copolymerized with a mixture of two or more of these esters to yield an ethylene/mixed ester copolymer.

Among the agents useful for inhibiting wax deposition and reducing the pour point and yield stress of high pour point crude petroleum and shale oils are copolymer ethylene/vinyl formate, copolymer ethylene/allyl formate, copolymer ethylene/vinyl acetate, copolymer ethylene/allyl acetate, copolymer ethylene/vinyl propionate, copolymer ethylene/allyl propionate, copolymer ethylene/vinyl butyrate, copolymer ethylene/allyl butyrate, copolymer ethylene/vinyl laurate, copolymer ethylene/allyl laurate, copolymer ethylene/vinyl palmate, copolymer ethylene/allyl palmate, copolymer ethylene/vinyl stearate, copolymer ethylene/allyl stearate, copolymer ethylene/methyl acrylate, copolymer ethylene/ethyl acrylate, copolymer ethylene/butyl acrylate, copolymer ethylene/isobutyl acrylate, copolymer ethylene/2-ethylhexyl acrylate, copolymer ethylene/methyl methacrylate, copolymer ethylene/ethyl methacrylate, copolymer ethylene/butyl methacrylate, copolymer ethylene/isobutyl methacrylate, copolymer ethylene/isodecyl methacrylate, copolymer ethylene/lauryl methacrylate, copolymer ethylene/tridecyl methacrylate, and copolymer ethylene/stearyl methacrylate.

The ethylene copolymerized with the ester tends to increase the oil solubility of the resulting copolymer. Thus, it is preferred that the copolymer contain a sufficiently high ethylene content to render it oil soluble or oil dispersible at the concentration employed. However, it has been found that increased ethylene content tends to reduce the effectiveness of the copolymer as a pour point and yield stress reducing agent. Accordingly, it is within the scope of this invention to employ as the active agent an ester polymer containing sufficient copolymerized ethylene to render the copolymer soluble or dispersible in oil.

Generally, it is preferred that the copolymer contain at least about 10 weight percent ester, and more preferably at least about 35 percent ester with the maximum ester content of the polymer not exceeding that amount which renders the agent insoluble or difficult to disperse in oil under the conditions of use. Also, it is generally preferred that the copolymer exhibit a melt index between about 1 and 600 grams per 10 minutes. The term "melt index" as employed herein is the flow rate reported as the rate of extrusion in grams per 10 minutes as determined by ASTM test method D1238-65T entitled "Measuring Flow Rates of Thermoplastics by Extrusion Plastometer" and performed under Standard Test Condition E, ASTM Standards, American Society for Testing Materials, Part 27, June 1969, pages 455-466, which procedure is herein incorporated by reference.

Of the foregoing ethylene/ester copolymers useful in the practice of the invention, the lower vinyl esters and the lower alkyl acrylates and methacrylates are preferred in many applications.

Preferred copolymer combinations having a special utility as wax deposition and pour point and yield stress reducing additives include copolymers of ethylene and vinyl acetate, ethyl acrylate and methyl methacrylate, i.e., copolymer ethylene/vinyl acetate, copolymer ethylene/ethyl acrylate and copolymer ethylene/methyl methacrylate.

One preferred class of agents particularly useful in the practice of this invention are ethylene/vinyl acetate copolymers containing from about 10 to 70 weight percent vinyl acetate, and more preferably containing about 35 to 55 weight percent vinyl acetate, and exhibiting a melt index between about 1 and 600 grams per 10 minutes.

A particularly preferred agent having a special utility as a wax deposition and pour point and yield stress reducing additive for high pour point crude petroleum and shale oils is an ethylene/vinyl acetate copolymer containing about 39 to 42 weight percent vinyl acetate and exhibiting a melt index between about 45 to 70 grams per 10 minutes. An ethylene/vinyl acetate copolymer of this type is marketed by the E. I. duPont de Nemours Company under the trademark ELVAX 40.

The ethylene/ester copolymers useful in the practice of this invention are prepared by generally known techniques such as by copolymerizing ethylene and the ester monomer by free radical reaction at elevated temperatures and pressures. Any of a wide variety of free radical initiators such as small quantities of molecular oxygen or other known sources of free radicals including various peroxide compounds such as benzoyl peroxide, t-butyl hydroperoxide and the like can be employed to initiate the free radical reaction. Also, the catalyst can be activated by the addition of a reducing agent such as sodium bisulfite or ferrous salts.

The monohydroxy phenols useful in the compositions of this invention are aryl and alkyl aryl monohydroxides and their halogenated derivatives having molecular weights up to about 300, such as for example phenol, the cresols, the xylenols and higher alkyl monohydroxy phenols and their halogenated derivatives. Specific agents useful in the compositions of this invention include phenol; o-cresol; m-cresol; p-cresol; 2,3-xylenol; 3,4-xylenol; 2,6-xylenol; 2,4-xylenol; 3,5-xylenol; 2,5-xylenol; 2-propylphenol; 3-propylphenol; the various isomeric butylphenols including especially 2-tert-butylphenol and 4-sec-butylphenol; the various isomeric dodecylphenols; the various isomeric benzylphenols; and the halogenated derivatives thereof such as for example 4-bromophenol; 2,benzyl-4-chlorophenol; and admixtures of these agents.

The monohydroxy phenols employed in the additive composition can be admixtures of various monohydroxy phenols such as for example phenol, the cresols, the zylenols and alkylphenols containing nine or more carbon atoms. Typical compositional ranges of these mixed monohydroxy phenols are:

Weight Percent ______________________________________ Phenol 0 - 90 o-Cresol 0 - 40 m-Cresol 0 - 65 p-Cresol 0 - 40 2,6-Xylenol 0 - 10 o-Ethylphenol 0 - 5 2,4-Xylenol 0 - 30 2,5-Xylenol 0 - 30 2,3-Xylenol 0 - 30 3,5-Xylenol 0 - 30 3,4-Xylenol 0 - 70 C9+Phenols 0 - 60 ______________________________________

A wide variety of mixed phenolic agents are available commercially, many of which have utility in the compositions of this invention.

A preferred mixture of monohydroxy phenols particularly useful in the compositions of this invention contains about 0 to 25 weight percent phenol, about 30 to 70 weight percent cresols, about 10 to 50 weight percent xylenols and ethylphenol, and from about 0 to 20 weight percent C9+ phenols.

The hydrocarbon solvent component of the compositions of this invention can be any of a wide variety of liquid cyclic hydrocarbon compounds or mixtures of liquid hydrocarbons containing a substantial proportion of cyclic compounds, i.e., at least about 20 weight percent cyclic compounds and preferably at least about 50 weight percent and more preferably at least about 70 weight percent cyclic compounds. Cyclic hydrocarbons useful in these compositions include both aromatic and saturated cyclic hydrocarbons, such as for example benzene, toluene, xylene and higher alkyl and polyalkyl benzenes, cyclopentane, cyclohexane and the various alkyl and polyalkyl cyclohexanes, and dipentene.

A suitable solvent is a liquid mixture of hydrocarbon compounds boiling generally within the range of about 100.degree. F. to about 700.degree. F. and containing a substantial proportion of cyclic compounds, i.e., at least about 20 weight percent cyclic compounds and preferably at least about 50 weight percent cyclic compounds. Suitable liquids of this type are produced from crude petroleum and by the destructive distillation of coal and oil shale. In applications where the additive composition is introduced into the annulus of a well having an elevated temperature, it has been found that the more volitale hydrocarbons evaporate before the additive is admixed into the reservoir of wax-containing oil in the well causing deposition of the less volatile constituents of the additive in the upper sections of the well. Thus, it is preferred that a higher boiling hydrocarbon solvent be employed in these applications, i.e., a hydrocarbon or hydrocarbon mixture boiling in the range of about 300.degree. F. to about 700.degree. F.

Preferred solvents include benzene, toluene, xylene, reformed naphtha obtained by the catalytic reforming of a distillate petroleum fraction, an Edeleanu extract obtained in the production of kerosene and turbine fuel, dipentene and aromatic mineral oils.

The low pour point additive compositions of this invention can be prepared by admixing the ingredients in the desired proportions and heating this admixture with gentle agitation to a temperature below the boiling point of the solvent, e.g., to a temperature of 150.degree. F. to 250.degree. F. for a period sufficient to dissolve the copolymer. Preferably, the copolymer is first dissolved in the solvent, then the monohydroxy phenol is added and admixed into this solution.

While the exact mechanism by which the additive compositions of this invention inhibit the deposition of wax is not completely understood, it is believed that they function by reducing agglomeration of the wax crystals so that they are more readily kept in suspension and exhibit less tendency to adhere to solid surfaces. Also, these agents may affect the deposition or attachment of the wax crystals to the metal surfaces which they contact. Thus, while it is believed that these inhibitors do not greatly affect the size and general appearance of individual wax crystals, they do affect the tendency of the crystals to agglomerate and to adhere to metal surfaces. However, although the exact mechanism by which the additive compositions of this invention inhibit wax deposition from a wax-containing oil may not be completely understood, it has nevertheless been conclusively demonstrated that low concentrations of these agents are effective in inhibiting the deposition of wax in well conduits, pipelines, tanks and like equipment handling wax-containing oil at a temperature below the solidification temperature of the wax. The term wax "deposition" is used herein to mean the precipitation and accumulation of wax and waxlike materials on the surfaces contacted by a wax-containing oil, and not merely the precipitation of wax crystals or particles that remain dispersed in the oil.

Also, it has been observed that the additive compositions of this invention not only inhibit the deposition of wax and wax-like materials on metal surfaces which they contact, but also will in at least some cases disperse previously accumulated deposits of wax. Accordingly, the additive compositions of this invention have utility both in inhibiting the deposition and accumulation of wax on surfaces contacted by a wax-containing oil and in removing previously deposited wax from such surfaces.

In practicing the method of this invention to inhibit the deposition of wax from a wax-containing oil, an effective amount of the aforementioned additive composition is incorporated into the wax-containing oil by any convenient mixing technique. It is to be recognized that the amount of copolymer agent required depends upon the properties of the particular crude petroleum or petroleum fraction, the amount and type of wax present in the oil, the temperature to which the oil is cooled, the particular type and physical arrangement of the equipment and the roughness of the interior surfaces contacted by the oil, the specific agent employed, and the degree to which it is desired to inhibit wax deposition. Thus, the optimum amount of copolymer agent required in any particular application will depend upon these factors, the cost of the additive composition, and the cost of cleaning and downtime due to wax plugging. Treatment at concentrations in excess of optimum is not only costly, but in some cases is less effective than the optimum concentration. The optimum treatment is best determined by actual field tests or by laboratory tests simulating field conditions.

Hence, broadly stated, this invention contemplates incorporating into a wax-containing crude petroleum, petroleum fraction, shale oil or other wax-containing oil an amount of the above-described additive composition sufficient to provide there an ethylene/ester copolymer concentration effective to inhibit the deposition of wax from the oil. While the exact amount of agent preferred in any particular application depends on the foregoing factors, nevertheless it has been found that the effective concentration of additive required to inhibit wax deposition is between about 5 and 10,000 ppm based on the weight of oil, and in many applications the effective concentration is between about 5 and 200 ppm, and preferably less than about 60 ppm. Thus, it is within the scope of this invention to incorporate in a wax-containing oil an effective amount of the inhibitor between about 5 and 10,000 ppm, and preferably between about 5 and 200 ppm.

While the additive composition can be intermittently admixed with the wax-containing oil, it is preferred, particularly in continuous operations such as in the production of oil from a producing oil well, or the flow of oil through a pipeline, that the additive be continuously added to the oil during the operation. However, where the additive is added for the purpose of periodically removing accumulated wax deposits from equipment, the additive composition can be effectively injected on an intermittant basis.

In a typical oil recovery operation, oil and other fluids flow from the producing earth formation into the well and accumulate in a reservoir therein, whereupon they are transported to the surface through production tubing, either under natural pressure or assisted by pumping or gas lift. Preferably, the additive composition is added to the reservoir of oil in the well before it cools to a temperature below the solidification temperature of the wax. Wax deposition in a producing oil well can be inhibited by adding the wax deposition inhibitor to the reservoir of oil in the well either by pumping the inhibitor down the well through a separate tubing string, such as a small diameter macaroni tubing, or by merely injecting the inhibitor into the annulus at the top of the well and allowing it to fall by gravity into the reservoir of oil in the well.

In practicing the method of this invention to reduce the pour point and yield stress of a high pour point wax-containing oil, the additive composition can be admixed with the high pour point oil to be treated prior to its introduction into a pipeline, such as by admixing the additive and the oil in a suitable tank, or the additive composition can be injected into the oil flowing through the pipeline at a location where the oil is at a temperature above its pour point, preferably on a continuous basis.

In a typical pipeline operation, high pour point wax-containing oil at a temperature above its pour point is pumped from a storage tank into the pipeline. Booster pumps are located at intervals along the pipeline to maintain pressure in the pipeline and to maintain the flow of the oil at a desired rate. The additive composition is injected into the oil flowing through the pipeline at a location where the oil is at a temperature above its pour point. The additive is admixed into the oil by the turbulence of the flowing oil. The oil can now be transported the length of the pipeline and stored in receiving tanks at the pipeline terminal at temperatures below the normal pour point of the oil without the oil becoming solidified. Also, the flow of oil through the pipeline can be stopped and then restarted without the high energy requirements experienced in the transport of untreated high point oil.

The method of this invention is generally applicable to the pipeline transportation of crude petroleum and shale oil having pour points above the ambient temperature to which they will be cooled during storage and transport operations. More specifically, the method is applicable to the storage and transport of crude petroleum and shale oils having pour points above about 0.degree. F., and even more specifically above about 30.degree. F., and most specifically above about 50.degree. F.

Thus, it is within the scope of this invention to add sufficient additive composition to a high pour point wax-containing oil to provide therein an ethylene/ester copolymer composition effective to reduce the pour point and yield stress of the oil a desired amount. While the exact amount of agent required in any particular application is dependent upon the characteristics of the oil being treated, its pour point, the particular additive employed, and the degree of pour point and yield stress reduction desired, nevertheless it has been found that the concentration of the copolymer agent required to reduce the pour point and yield stress a desired amount is between about 5 and 10,000 ppm, and more preferably between about 5 and 2,000 ppm.

The importance of reducing the yield stress of an oil to be transported through a pipeline at a temperature below its pour point can be illustrated by a consideration of the pressure required to initiate flow of the oil through the pipeline. The pressure drop per mile of pipeline required to initiate flow can be calculated by the relationship

.DELTA.P/L = 4 T.sub.y (5,280)/D(144)

where

.DELTA.P/L is the pressure gradient, psi/mile

T.sub.y is the yield stress, lb/ft.sup.2

D is the pipe diameter, ft.

Thus, in a typical pipeline operation wherein a 50 mile section of 12-inch diameter pipeline is filled with stagnant oil at a temperature below its pour point and having a yield stress of 0.7 lb/ft.sup.2, the pressure drop required to initiate flow is

.DELTA.P = [4(0.7)(5,280)/(1)(144)] (50)

.DELTA.P = 5,140 psi

The addition of sufficient additive to the oil to reduce its yield stress to 0.1 lb/ft.sup.2 will reduce the pressure drop required to initiate flow to about 735 psi, and the addition of sufficient additive to reduce the ultimate stress to 0 lb/ft.sup.2 will reduce the pressure drop required to initiate flow to 0 psi.

The optimum ultimate stress obtained by additive treatment is dependent upon the mechanical limitations of the pipeline and the pumping equipment and the cost of the additive treatment. In most cases, however, it is preferred to add sufficient additive to reduce the ultimate stress to less than 0.1 lb/ft.sup.2, and preferably to less than about 0.05 lb/ft.sup.2, and most preferably to less than about 0.01 lb/ft.sup.2. In most applications, the ultimate stress of the oil can be reduced to desired levels by the addition of about 5 to 10,000 ppm additive.

Not only does the reduction of the pour point and the yield stress of high pour point crude petroleum and shale oil facilitate pipeline transportation, but it also beneficially affects bulk storage of the oil and all other bulk handling operations downstream of the additive injection point.

In the practice of the methods of this invention to inhibit wax deposition from a wax-containing oil and to reduce the pour point and yield stress of a high pour point oil, it is preferred that the additive composition be added to the wax-containing oil before the oil has been cooled below the solidification temperature of the wax. While this temperature varies somewhat depending upon the particular waxes present in the wax-containing oil, it is generally preferred that the inhibitor be admixed into the wax-containing oil before the oil is cooled below a temperature of about 160.degree. F.

The invention is further described by the following examples which are illustrative of specific modes of practicing the invention and are not intended as limiting the scope of the invention defined by the appended claims.

EXAMPLES 1-13

Various additive compositions are prepared by admixing toluene, a selected monohydroxy phenol and an ethylene/vinyl acetate copolymer containing 39-42 weight percent vinyl acetate and exhibiting a melt index of 45 to 70 grams per 10 minutes marketed by the E. I. duPont de Nemours Company under the trademark ELVAX 40 in the proportions to yield a solution containing 10 weight percent copolymer, either 0, 5, 10, 15 or 20 weight percent monohydroxy phenol, and the balance toluene.

The monohydroxy phenols employed include o-cresol; m-cresol; p-cresol; 4-sec-butylphenol; dodecylphenol; 2-tert-butylphenol; 3,4-xylenol; 3,5-xylenol; 2-benzyl-4-chlorophenol; a mixed cresol containing approximately 54 weight percent m-cresol, 29 weight percent p-cresol and 17 weight percent other phenols marketed by Eastman Organic Chemicals under the trademark Cresol Technical Grade; and mixtures of monohydroxy phenols marketed by Productol Chemical Company under the trademarks Meta Para Cresol M-1 (Modified) and Cresylic Acid Grade 22. The compositions of the mixtures of monohydroxy phenols are reported in Table 1.

TABLE 1 __________________________________________________________________________ MIXED MONOHYDROXY PHENOL COMPOSITIONS __________________________________________________________________________ Meta Para Cresol Grade Cresylic Acid Cresylic Acid M-1(Modified) Grade 10 Grade 22 __________________________________________________________________________ Phenol 18.2 19.5 1.4 o-Cresol 4.8 18.7 37.9 m-Cresol 41.0 29.3 12.5 p-Cresol 16.4 Xylenols & Ethylphenol 19.6 29.3 43.5 C9+ Phenols -- 3.2 4.7 __________________________________________________________________________

Each mixture is heated to a temperature of 160.degree. to 200.degree. F. and mixed until all of the ingredients are in solution. Approximaterly 100 ml of the prepared sample is then placed in a 4-ounce bottle, stoppered and allowed to stand at a temperature of 35.degree. F. for 1 hour. At the end of 1 hour, the sample bottle is turned on its side and the fluid movement observed. The contents of the bottle is rated as either solid (no movement) or fluid (some movement). Apparent viscosity changes are disregarded. Those samples that appeared fluid were allowed to stand 24 hours or longer at the test temperature to confirm the result. The samples that are fluid at 35.degree. F. are then successively tested at temperatures of 25.degree. F., 15.degree. F., 8.degree. F., 0.degree. F., and -10.degree. F. until the sample appears solid.

An admixture containing 90 weight percent toluene and 10 weight percent copolymer is fluid at the test temperature of 25.degree. F. and solid at 15.degree. F. All of the compositions containing monohydroxy phenol are fluid at temperatures of 15.degree. F. or lower. The results of these tests are reported in Table 2.

TABLE 2 __________________________________________________________________________ Observed Appearance.sup.(1) at Conc. Various Temperatures, .degree. F. Example Monohydroxy Phenol Wt. % 35 25 15 8 0 -10 __________________________________________________________________________ Blank None 0 F F S -- -- -- 1 Cresol Technical Grade 5 F F F S -- -- do. 10 F F F F S -- do. 15 F F F F S -- do. 20 F F F F S -- 2 o-Cresol MP 29-31.degree. C. 5 F F F S -- -- do. 10 F F F F S -- do. 15 F F F F S -- do. 20 F F F F S -- 3 o-Cresol 10 F F F S -- -- do. 20 F F F S -- -- 4 p-Cresol 5 F F F S -- -- do. 15 F F F S -- -- do. 20 F F F F S -- 5 Meta Para Cresol Grade M-1 (Modified) 10 F F F S -- -- do. 20 F F F S -- -- 6 m-Cresol 5 F F F F S -- do. 10 F F F F S -- do. 15 F F F F F S do. 20 F F F F F S 7 Cresylic Acid Grade 22 10 F F F F S -- do. 20 F F F F S -- 8 4-Sec-butylphenol 20 F F F S -- -- 9 Dodecylphenol 20 F F F S -- -- 10 2-Tert-butylphenol 20 F F F F S -- 11 3,4-Xylenol 20 F F F S -- -- 12 3,5-Xylenol 20 F F F S -- -- 13 2-Benzyl-4-chlorophenol 20 F F F S -- -- __________________________________________________________________________ 1. The letter "F" indicates that the sample is fluid and the letter "S" indicates that the sample is solid at the test temperature.

EXAMPLES 14-22

Another series of additive compositions are prepared and tested in accordance with the procedure described in Examples 1-13 excepting that a relatively high-boiling aromatic oil marketed by the Mobil Oil Corporation under the trademark MZY-409 oil is substituted for the toluene. The MZY-409 oil is characterized as follows: Gravity, .degree.API 18.4 Viscosity, ssu at 100.degree. F. 37.5 Color Dark Flash, PMCC, .degree. F. 195 Distillation, .degree. F. i 411 10% 469 50% 541 90% 650 max 691 Aromatic content, wt. % above 50

The monohydroxy phenols employed in these compositions are p-cresol; m-cresol; 2-tert-butyl-phenol; 3,5-xylenol; 2-benzyl-4-chlorophenol; 4-sec-butyl-phenol; Meta Para Cresol Grade M-1 (Modified); Cresylic Acid Grade 22 and a mixture of monohydroxy phenols marketed by Productol Chemical Company under the trademark Cresylic Acid Grade 10. The composition of Cresylic Acid Grade 10 is reported in Table 1.

An admixture containing 90 weight percent MZY-409 oil and 10 percent copolymer is solid at 35.degree. F. All of the compositions containing monohydroxy phenol are fluid at temperatures of 25.degree. F. or lower. The results of these tests are reported in Table 3.

TABLE 3 __________________________________________________________________________ Conc. Various Temperatures, .degree. F. Example Monohydroxy Phenol Wt. % 35 25 15 8 0 __________________________________________________________________________ Blank None 0 S -- -- -- -- 14 m-Cresol 5 F S -- -- -- do. 10 F F S do. 15 F F F S -- do. 20 F F F S -- 15 Meta Para Cresol 5 F S -- -- -- Grade M-1 (Modified) do. 15 F S -- -- -- do. 20 F F S -- -- 16 Cresylic Acid Grade 10 20 F F F S -- 17 Cresylic Acid Grade 22 20 F F S -- -- 18 2-Tert-butylphenol 20 F F F F S 19 3,5-Xylenol 20 F F F S -- 20 2-Benzyl-4-chloro- phenol 20 F F F S -- 21 4-Sec-butylphenol 20 F F F S -- 22 p-Cresol 20 F F F S -- __________________________________________________________________________ 1. See footnote 1, Table 2.

EXAMPLES 23-31

This series of additive compositions are prepared and tested in accordance with the procedure described in Examples 1-13 excepting that a catalytically reformed naphtha is substituted for the toluene. The reformed naphtha is characterized as follows:

Gravity, .degree.API 39.4 Distillation, .degree.F., i 116 10% 270 50% 319 90% 365 Max. 411 Aromatic content, wt. % 65

The monohydroxy phenols employed in these compositions are o-cresol; m-cresol; p-cresol; 3,5-xylenol; 2-benzyl-4-phenol; 2-tert-butylphenol; 4-sec-butylphenol Cresol Technical Grade and 29-31.degree. F. melting point o-cresol. The compositions of the mixed phenols are listed in Table 1.

An admixture containing 90 weight percent reformed naphtha and 10 weight percent copolymer is fluid at the test temperature of 25.degree. F. and solid at 15.degree. F. All of the compositions containing monohydroxy phenols are fluid at temperatures of 15.degree. F. or lower. The results of these tests are reported in Table 4.

TABLE 4 __________________________________________________________________________ Observed Appearance.sup.(1) at Conc. Various Temperatures, .degree.F. Example Monohydroxy Phenol Wt. % 35 25 15 8 0 __________________________________________________________________________ Blank None 0 F F S -- -- 23 Cresol Technical Grade 10 F F F S -- do. 15 F F F F S do. 20 F F F F S 24 o-Cresol MP 29-31.degree. F. 10 F F F S -- do. 15 F F F F S do. 20 F F F F S 25 o-Cresol 10 F F F S -- do. 15 F F F S -- do. 20 F F F F S 26 p-Cresol 10 F F F S -- do. 15 F F F S -- do. 20 F F F S -- 27 m-Cresol 5 F F F S -- do. 10 F F F F S do. 15 F F F F S do. 20 F F F F S 28 3,5-Xylenol 20 F F F S -- 29 2-Benzyl-4-chlorophenol 20 F F F S -- 30 2-Tert-butylphenol 20 F F F F S 31 4-Sec-butylphenol 20 F F F S -- __________________________________________________________________________ 1. See footnote 1, Table 2.

EXAMPLE 32

This additive composition is an admixture of dipentene, ELVAX 40 and Meta Para Cresol M-1 (Modified) in the proportions of 10 weight percent copolymer, either 5, 10, 15 or 20 weight percent of the cresylic agent and the balance dipentene. The composition is prepared and tested in accordance with the procedure described in Examples 1-13. The composition of Meta Para Cresol M-1 (Modified) is listed in Table 1.

An admixture containing 90 weight percent dipentene and 10 weight percent copolymer is fluid at the test temperature of 25.degree. F. and solid at 15.degree. F. The compositions containing 15 and 20 weight percent Meta Para Cresol M-1 (Modified) are fluid at temperatures of 15.degree. F. and 8.degree. F. respectively. The results of these tests are summarized in Table 5.

TABLE 5 __________________________________________________________________________ Observed Appearance.sup.(1) at Concentration of Monohydroxy Various Temperatures, .degree. F. Phenol, Wt. % 35 25 15 8 0 -10 __________________________________________________________________________ 0 F F S -- -- -- 5 F F S -- -- -- 10 F F S -- -- -- 15 F F F S -- -- 20 F F F F S -- __________________________________________________________________________ 1. See footnote 1, Table 2.

EXAMPLE 33

These examples illustrate various low pour additive compositions prepared by admixing 5, 10, 15 and 20 weight percent of a selected ethylene/monoethylenically unsaturated ester copolymer; 0, 5, 10, 15, 20 and 25 weight percent of a Meta Para Cresol Grade M-1 (Modified): and the balance an aromatic hydrocarbon liquid boiling in the range of 400.degree. F. to 700.degree. F. The composition of Meta Para Cresol M-1 (Modified) is listed in Table 1. The various ethylene/monoethylenically unsaturated esters are listed in Table 6.

TABLE 6 ______________________________________ Melt Index, Ester Content, Copolymer Component Gms./10 min. Wt. % ______________________________________ Ethylene/ethyl acrylate 18 20 do. 18 30 Ethylene/vinyl acetate 335-465 17-19 do. 2.1-2.9 17-19 do. 0.7 18 do. 0.8 9.5 do. 300 10 ______________________________________

EXAMPLE 34

This example illustrates the practice of the invention in reducing the pour point and yield stress of a high pour point shale oil transported by pipeline from the retorting plant to a refinery located several hundred miles distant. The shale oil is a full range circle shale oil obtained by retorting Colorado oil shale and exhibits an additive-free pour point of about +65.degree. F. The product shale oil flows from the retort to a storage tank at a temperature of about 180.degree. F., from which it is pumped into the pipeline for transport to the refinery. The pipeline is buried along its entire length except for several river and road crossings.

The additive composition is admixed into the hot shale oil as it flows from the retort to the storage tank. The additive composition employed is an admixture of 10 weight percent of an ethylene/vinyl acetate copolymer containing about 45 weight percent vinyl acetate and exhibiting a melt index of about 50-60 grams per 10 minutes; 20 weight percent of mixed monoethylenically unsaturated phenols; and 70 weight percent of toluene.

The additive solution is added to the high pour point oil to provide an additive concentration in the oil sufficient to obtain a yield stress of about 0.05 lb/ft at the pipeline temperature expected for a particular season. The following copolymer concentrations are required at various temperatures to obtain a yield stress of about 0.05 lb/ft.sup.2 ;

Copolymer Temperature, .degree.F. Concentration, ppm ______________________________________ 65 0 55 30 45 65 35 110 ______________________________________

EXAMPLE 35

This example illustrates the practice of the invention in inhibiting wax deposition in a producing oil well and the associated surface production facilities handling a wax-containing East Texas crude oil. The well bottom hole temperature is approximately 130.degree. F., but the crude oil is cooled to about 110.degree. F. on reaching the surface. Wax deposition is experienced in the well and, to an even greater extent, in the surface production pipeline used for transporting the crude oil from the well. When the production pipeline is clean, a pressure of approximatly 55 psig is required at the well head to move the produced crude oil through the pipeline. However, after two or three weeks of operation wax deposition in the pipeline plugs it to the extent that the discharge pressure builds up to the maximum allowable pressure 300 psig, thus necessitating a costly cleaning operation.

Wax deposition in the crude oil is inhibited by adding a wax inhibitor composition to the well. The additive composition is an admixture of 10 weight percent ethylene/vinyl acetate copolymer containing about 39 to 42 weight percent vinyl acetate and exhibiting a melt index of between about 45 to 70 grams per 10 minutes, 20 weight percent of mixed monohydroxy phenols marketed by the Productol Chemical Company under the trademark Meta Para Cresol Grade M-1 (Modified), and 70 weight percent of an aromatic oil marketed by the Mobil Oil Company under the trademark MZY-409 oil. A concentrate is prepared at the well site by admixing two gallons of the additive solution and approximately one barrel of the produced crude oil. The well is treated by continuously pumping this concentrate into the well annulus at the rate of about one barrel per day so as to provide in the produced crude oil an additive concentration of about 40 ppm. The additive admixes with the oil in the well in a region where the oil is above the wax solidification temperature and is ultimately produced with the crude oil. The well is produced for a period of three months with no significant increase in well head pressure.

Various embodiments and modifications of this invention have been described in the foregoing description and examples, and further modifications will be apparent to those skilled in the art. Such modifications are included within the scope of this invention as defined by the following claims.

Claims

Having now described the invention, I claim:

1. An additive composition for use in treating wax containing oils, which comprises an admixture of about 1 to 20 weight percent of a copolymer of ethylene and a monoethylenically unsaturated ester characterized by the formula: ##SPC2##

wherein (1) R is hydrogen or an alkyl group containing from about 1 to 25 carbon atoms and R.sub.1 is a vinyl or allyl group, or (2) R is an .alpha., .beta. -unsaturated alkylene and R.sub.1 is an alkyl group containing about 1 to 25 carbon atoms, about 5 to 25 weight percent of monohydroxy phenols having molecular weights below about 300, and at least about 55 weight percent of liquid hydrocarbon solvent containing a substantial proportion of cyclic hydrocarbon compounds.

2. The composition defined in claim 1 wherein said copolymer is copolymer ethylene/vinyl acetate, copolymer ethylene/ethyl acrylate or copolymer ethylene/methyl methacrylate.

3. The composition defined in claim 1 wherein said copolymer is a copolymer of ethylene and vinyl acetate containing from about 10 to 70 weight percent vinyl acetate and exhibiting a melt index between about 1 and 600 grams per 10 minutes.

4. The composition defined in claim 1 wherein said copolymer is a copolymer of ethylene and vinyl acetate containing about 35 to 55 weight percent vinyl acetate and exhibiting a melt index between about 1 and 600 grams per 10 minutes.

5. The composition defined in claim 1 wherein said monohydroxy phenols comprise a mixture of monohydroxy phenols selected from the group consisting of phenol and alkyl and polyalkyl phenols in which each alkyl group contains from about 1 to 12 carbon atoms.

6. An additive composition for use in treating wax-containing oils, which comprises an admixture of (1) about 1 to 20 weight percent of a copolymer of ethylene and vinyl acetate containing from about 10 to 70 weight percent vinyl acetate and exhibiting a melt index between about 1 and 600 grams per 10 minutes, (2) about 5 to 25 weight percent of a mixture of monohydroxy phenols having molecular weights below about 300 selected from the group consisting of phenol and alkyl and polyalkyl phenols in which each alkyl group contains from about 1 to 12 carbon atoms, and (3) at least about 55 weight percent of liquid hydrocarbon solvent containing a substantial proportion of cyclic hydrocarbon compounds.

7. The composition defined in claim 6 wherein said copolymer of ethylene and vinyl acetate contains from about 35 to 55 weight percent vinyl acetate.

8. The composition defined in claim 6 wherein said liquid hydrocarbon is selected from the group consisting of benzene, toluene, xylene, hydrocarbon mixtures containing at least about 50 weight percent cyclic hydrocarbon compounds, and dipentene.

9. The composition defined in claim 8 wherein said liquid hydrocarbon solvent boils within the range of about 100.degree. F. to about 700.degree. F.

10. A method for inhibiting the deposition of wax from wax-containing oils and for depressing the pour point and yield stress of high pour point, wax-containing oils which comprises admixing into said oil a liquid admixture of about 1 to 20 weight percent of a copolymer of ethylene and a monoethylenically unsaturated ester characterized by the formula: ##SPC3##

wherein (1) R is hydrogen or an alkyl group containing from about 1 to 25 carbon atoms and R.sub.1 is a vinyl or allyl group, or (2) is an .alpha., .beta. - unsaturated alkylene and R.sub.1 is an alkyl group containing about 1 to 25 carbon atoms, about 5 to 25 weight percent of monohydroxy phenols having molecular weights below about 300, and at least about 55 weight percent of liquid hydrocarbon solvent containing a substantial proportion of cyclic hydrocarbon compounds, said liquid admixture having a pour point below about 25.degree.F.

11. The method defined in claim 10 wherein said copolymer is copolymer ethylene/vinyl acetate, copolymer ethylene/ethyl acrylate or copolymer ethylene/methyl methacrylate.

12. The method defined in claim 10 wherein said admixture is incorporated into said wax-containing oil at an oil temperature sufficiently high to maintain the wax dissolved in the oil, and wherein said oil is thereafter cooled to a temperature below the solidification temperature of the wax.

13. The method defined in claim 10 wherein said admixture is incorporated into said wax-containing oil in an amount to provide therein an effective concentration of said copolymer between about 5 and 10,000 ppm.

14. The method defined in claim 10 wherein said copolymer is a copolymer of ethylene and vinyl acetate containing from about 10 to 70 weight percent vinyl acetate and exhibiting a melt index between about 1 and 600 grams per 10 minutes.

15. The method defined in claim 10 wherein said copolymer is a copolymer of ethylene and vinyl acetate containing about 35 to 55 weight percent vinyl acetate and exhibiting a melt index between about 1 and 600 grams per 10 minutes.

16. The method defined in claim 10 wherein said monohydroxy phenols comprise a mixture of monohydroxy phenols selected from the group consisting of phenol and alkyl and polyalkyl phenols in which each alkyl group contains from about 1 to 12 carbon atoms.

17. A method for inhibiting the deposition of wax from wax-containing oils and for depressing the pour point and yield stress of high pour point, wax-containing oils which comprises admixing into said oil a liquid admixture of (1) about 1 to 20 weight percent of a copolymer of ethylene and vinyl acetate containing from about 10 to 70 weight percent vinyl acetate and exhibiting a melt index between about 1 and 600 grams per 10 minutes, (2) about 5 to 25 weight percent of a mixture of monohydroxy phenols having molecular weights below about 300 selected from the group consisting of phenol and alkyl and polyalkyl phenols in which each alkyl group contains from about 1 to 12 carbon atoms, and (3) at least about 55 weight percent of liquid hydrocarbon solvent containing a substantial proportion of cyclic hydrocarbon compounds said liquid admixture having a pour point below about 25.degree. F. and being added to said wax-containing oil in an amount to provide therein a concentration of between about 5 and 10,000 ppm of said copolymer.

18. The method defined in claim 17 wherein said copolymer of ethylene and vinyl acetate contains from about 35 to 55 weight percent vinyl acetate.

19. The method defined in claim 17 wherein said liquid hydrocarbon is selected from the group consisting of benzene, toluene, xylene, hydrocarbon mixtures containing at least about 50 weight percent cyclic hydrocarbon compounds, and dipentene.

20. The method defined in claim 17 wherein said liquid hydrocarbon solvent boils within the range of about 100.degree. F. to about 700.degree. F.

21. The method defined in claim 17 wherein an amount of said admixture is incorporated into said wax-containing oil effective to inhibit the deposition of wax from said wax-containing oil.

22. The method defined in claim 17 wherein an amount of said admixture is incorporated into said wax-containing oil effective to reduce the pour point and yield stress of said oil.