BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improving the flow properties of heavy crude petroleum, more specifically, heavy crude petroleum products having an API gravity of about 6 to about 20.
2. Background of the Invention
There are huge reserves of heavy and extra heavy crude oil and natural bitumen in Venezuela, Canada, and elsewhere. A variety of enhanced oil recovery techniques permit the recovery of such heavy crude oils from otherwise unproductive wells by such known means as steam flooding, carbon dioxide flooding, and fire flooding.
The transportation and movement of heavy crude petroleum is difficult because of its high viscosity. At ambient conditions, heavy crude petroleum, such as Hamaca crude found in Venezuela, has an API gravity of about 8, and exists in a semi-solid state such that its viscosity cannot be measured.
Heavy crude petroleum oil usually contains significant amounts of high molecular weight materials such as asphaltenes and resins. The molecular weight of asphaltene can vary from about one thousand to two million. Asphaltenes are the major constituent of heavy crude petroleum oil and are present in amounts that vary from about 2 weight % to about 40 weight %, and more commonly from about 10 weight % to about 30 weight %.
- SUMMARY OF THE INVENTION
Asphaltenes contribute to the high viscosity of crude petroleum and can adversely influence the transportation and processing of heavy crude petroleum due to the tendency of asphaltenes to agglomerate and precipitate. This can impede the efficient and effective transport of crude petroleum through a pipeline and in the most serious cases lead to clogging and blockage of the pipelines.
BRIEF DESCRIPTION OF THE DRAWING
The flow properties of crude petroleum having an API gravity varying from about 6 to 12 are improved by heating the crude petroleum to a temperature of about 35° C. to 200° C. and, in the presence of a suitable viscosity reducing additive, shearing the heated crude petroleum with a high shearing force sufficient to reduce the viscosity of the crude petroleum to a range of about 250 centipoise (cP) to about 1000 cP. Suitable viscosity reducing additives include gasoline, naphtha, butanol, petroleum ether, diesel fuel, citrus oil based cleansers and degreasers, and mixtures thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a graphical plot of viscosity versus time and shear rate data for processed and raw petroleum sludge.
It has been found that the viscosity of heavy crude petroleum having an API gravity that ranges from about 6 to about 20 can be significantly reduced by exposing the crude petroleum to high rates of shear in conjunction with heat. An example of such heavy crude petroleum is Hamaca crude found in Venezuela. The combined heating and shearing of the crude petroleum in the presence of suitable viscosity reducing additives can reduce its viscosity to a level where it can be conveniently transported through pipelines. Suitable pipeline viscosities range from about 400 cP to about 1000 cP.
The reduction of viscosity obtained from the application of heat alone is not long lasting. The reduced viscosity attained through heating alone will revert to its original viscosity after the heat has been removed from the crude petroleum and it has been allowed to cool to ambient temperature.
The application of high shearing forces to the crude petroleum has been found to significantly reduce its viscosity. The crude petroleum is preferably heated to a temperature of about 35° C. to about 200° C. and preferably about 50° C. to about 150° C. in a contained or sealed vessel to prevent volatile components, commonly referred to as “light ends”, from escaping by vaporizing at the heating temperature. Light ends include naphthas and other light distillate materials. The sealed heating vessel should be able to maintain pressures of about 100 psig to retain the light ends in the crude petroleum.
Although shearing action alone will contribute heat to the crude petroleum mass and increase its temperature, it is preferable to externally heat the petroleum crude to the desired temperature range of about 35° C. to about 200° C. and then contact the heated petroleum crude with a sufficient high rate of shear while it is at this elevated temperature range.
The extent of viscosity reduction with shearing and heating depends on the time/duration/type of shearing device used. The effect of viscosity reduction from shearing has been found to remain for at least 5 days after shearing is stopped. This should allow for sufficient time to transport the crude petroleum. However, the beneficial effect of viscosity reduction from shearing can last for up to 6 months or even one year.
Shearing is accomplished with a high shear device containing a rotor stator mechanism, wherein the tip speed of the rotor varies from about 500 revolutions per minute (rpm) to about 25,000 rpm, and preferably from about 5,000 rpm to about 25,000 rpm. Other high shearing devices can also be used wherein the rotor stator peripheral tip speeds vary from about 500 feet per minute (fpm) to about 18,000 f/m.
Shearing devices, such as those made by Charles Ross & Sons, Inc. of Happague, New York, or Smith Meters are suitable to reduce the viscosity of the crude petroleum. The shearing devices can be utilized either above ground or below ground to facilitate the transportation and removal of the petroleum crude. Ultrasonic devices can also accomplish the shearing effect by means of ultrasound.
It has also been found that lighter components of petroleum, such as gasoline, naphtha, butanol, petroleum ether, diesel fuel, and mixtures thereof function as excellent viscosity reducing additives for the crude petroleum. Other substances such as citrus oil based degreasers and cleansers including d-Lemonene™ (Herbert Environmental Inc.) and Orange Clean™ (Orange Glo International) are also suitable. The viscosity reducing additives can be added to the crude petroleum in either a sheared or unsheared state.
The addition of the viscosity reducing additives to the crude petroleum can be accomplished by simple hand mixing with a paddle or impeller or at relatively low mixing speeds for about 30 seconds to about five minutes, preferably for about one to about three minutes. The mixing speeds are less than 1000 rpm, preferably less than 500 rpm and most preferably about 1 to 100 rpm.
A particular benefit of using naphtha and gasoline as viscosity reducing additives is that each are relatively easy to separate from the crude petroleum because of their volatility. This enables the naphtha and gasoline to be easily recovered from the petroleum and reused as viscosity reducing additives, which is an economical advantage of this invention.
In general, the amount of viscosity reducing additive can vary from about 15 weight % to about 50 weight %, and preferably about 20 weight % to 35 weight %, of the petroleum crude. About 20 weight % to 35 weight % of gasoline and/or light naphtha is sufficient to reduce the viscosity of the petroleum crude to less than about 600 cP to less than about 400 cP at 35° C.
A typical assay of heavy crude Hamaca petroleum appears in Table 1.
|TABLE 1 |
|Assay of Hamaca Crude Petroleum |
|Property ||Value ||Test Method |
|API Gravity @ 60° F. ||9.0 ||ASTM D-287 |
|Specific Gravity @ 60° F. ||1.0071 ||ASTM D-70 |
|Total Sulfur, wt % ||3.947 ||ASTM D-2622 |
|Mercaptan Sulfur, wppm ||Too Heavy ||ASTM D-3227 |
|Total Nitrogen, wppm ||5,640 ||ASTM D-4629 |
|Reid Vapor Pressure, psi ||Nil ||ASTM D-5482 |
|Pour Point, ° F. ||21 ||ASTM D-5840 |
|Viscosity, CST @ 40° C. ||— ||ASTM D-445 |
|Viscosity, CST @ 100° C. ||337.6 ||ASTM D-445 |
|Neutralization Number, ||3.29 ||D-664 |
|mg KOH/g oil |
|Micro Carbon Residue, wt % ||15.02 ||ASTM D-4530 |
|Salt content, gms/bbl ||5.58 ||X-Ray Fluorescence |
|BS&W, LV % ||— ||ASTM D-1796 |
|Vanadium, wppm ||388 ||X-Ray Fluorescence |
|Nickel, wppm ||94 ||X-Ray Fluorescence |
|Iron, wppm ||16 ||X-Ray Fluorescence |
|1000° F. Resid, wt % ||53.3 ||ASTM D-1160 |
|1000° F. Resid, LV % ||51.6 ||ASTM D-1160 |
|H2S Content, wppm ||Too Heavy ||ASTM D-3227 |
|Ethane & Lighter, LV % ||0.0 ||Gas Chromatography |
|Propane, LV % ||0.0 ||Gas Chromatography |
|iso-Butane, LV % ||0.0 ||Gas Chromatography |
|n-Butane, LV % ||0.0 ||Gas Chromatography |
|iso-Pentane, LV % ||0.0 ||Gas Chromatography |
|n-Pentane, LV % ||0.0 ||Gas Chromatography |
|C6's & Heavier ||100.00 ||Gas Chromatography |
- EXAMPLE 1
The following examples are illustrative of the present invention. All parts and percentages are by weight unless otherwise noted.
- EXAMPLE 2
Raw Hamaca crude petroleum having the analysis shown in Table 1 and an initial viscosity of 21,000-22,000 cP was heated to 50° C. The crude petroleum was sheared for periods of 2, 4, and 6 minutes using an IKA Lab Ultra-Turrax T-50 unit at 7000 nominal rpm. The viscosity was measured at relatively low shear rates varying from 0.14-0.185 seconds−1 using a Bohlin Rheometer Model No. CVS 120 (Bohlin Inc.). At two minutes the viscosity was 19,000 cP. At four minutes the viscosity was 17,500 cP. At six minutes the viscosity was 16,500 cP. The results show that viscosity decreased with increased shear rate and time. The viscosity of the crude petroleum continued to decrease as the shear rate increased from 0.14-0.185 seconds−1 during viscosity measurement. A reduction in the viscosity of the crude petroleum by as much as 20% was achieved by shearing.
- EXAMPLE 3
The viscosity of a sample of raw Hamaca crude petroleum was measured over a period of 200 seconds at ambient conditions and varied from 20,000-21,000 cP. A second sample of raw Hamaca crude petroleum was also sheared for 200 seconds using an IKA Lab Ultra-Turrax T-50 unit at 7000 nominal rpm. The viscosity dropped from 17,500 cP to 16,500 cP indicating that the viscosity of crude petroleum exposed to a constant shear rate diminished over time.
- EXAMPLE 4
A 75-gallon quantity of raw Hamaca crude petroleum having the analysis of Table 1 was heated to 90° for one hour and sheared in a Ross Model 425 shearing device operating at 5 horsepower. Using a Bohlin Rheometer, the viscosity of the unsheared crude was 20,000 cP. The viscosity of the sheared crude measured at one second−1 was 9000 cP. The viscosity of the crude petroleum was significantly reduced as a result of shearing.
Several substances were tested to evaluate their effectiveness as viscosity reducing additives for Hamaca crude petroleum. These additives included gasoline (87 octane, unleaded), butanol, petroleum ether (Alfa Chemical Co.), d-Lemonene™, a commercial cleanser (Herbert Environmental Inc.), Orange Clean™, a commercial degreaser made of pure orange oil with strong cleaning agents (item 659270, Orange Glo International, Littleton, Colo.), and diesel fuel. The additives were contacted with the Hamaca crude petroleum by simple hand mixing with a paddle or by shearing with an IKA Lab Ultra-Turrax T-50 unit at 7000 nominal rpm. The results are tabulated in Table 2.
|TABLE 2 |
|Effect of Shearing, Additive and Mode |
|of Mixing on Viscosity of Hamaca Crude |
| ||Temp, || || |
|Additive Weight % ||° C. ||Mode of Mixing ||Viscosity, cP |
|Raw Hamaca-100% (none) ||50 ||none ||22,000 |
|Sheared Hamaca-100% (none) ||50 ||Ross Emulsifier ||10,000 |
|Gasoline 20% ||25 ||HD 2 min ||650 |
|Gasoline 15% ||35 ||HD 2 min ||1200 |
|Gasoline 20% ||35 ||HD 2 min ||300 |
|Gasoline 25% ||35 ||HD 2 min ||250 |
|d-Lemonene 1% ||50 ||HD 2 min ||12,000 |
|d-Lemonene 2% ||50 ||HD 2 min ||12,000 |
|d-Lemonene 3% ||50 ||HD 2 min ||7500 |
|d-Lemonene 5% ||50 ||HD 2 min ||4800 |
|d-Lemonene 10% ||35 ||Shear 30 sec ||5100 |
|d-Lemonene 15% ||35 ||Shear 30 sec ||2200 |
|d-Lemonene 20% ||35 ||HD 2 min ||700 |
|d-Lemonene 20% ||35 ||Shear 30 sec ||800 |
|d-Lemonene 25% ||35 ||HD 2 min ||460 |
| 5% d-lemonene + 15% gas ||25 ||HD 2 min ||600 |
| 5% d-lemonene + 15% gas ||35 ||HD 2 min ||350 |
|10% d-lemonene + 10% gas ||25 ||HD 2 min ||550 |
|12% d-lemonene + 8% gas ||25 ||HD 2 min ||1300 |
|15% d-lemonene + 5% gas ||25 ||HD 2 min ||1100 |
|15% d-lemonene + 5% gas ||35 ||HD 2 min ||900 |
|Pet Ether 20% ||35 ||HD 2 min ||350 |
|(100 F.-140 F.)* |
|Pet Ether 20% ||35 ||HD 2 min ||450 |
|(140 F.-170 F.)* |
| 5% butanol ||35 ||HD 2 min ||10,000 |
|20% butanol ||35 ||HD 2 min ||1000 |
|20% diesel fuel ||35 ||HD 2 min ||5690 |
|25% diesel fuel ||35 ||HD 2 min ||2000 |
|Orange Clean 20% ||35 ||HD 2 min ||2000 |
- EXAMPLE 5
The commercial cleanser, d-Lemonene™ although more expensive than gasoline and was not able to reduce viscosity to the same extent as gasoline. Mixtures of d-Lemonene™ and gasoline also provided viscosity reduction greater than d-Lemonene™ alone, but not greater than gasoline alone. Petroleum ether was comparable to gasoline in performance but is not as readily available and is more expensive than gasoline.
The viscosity of raw crude oil and sheared crude oil, with and without gasoline as a viscosity reducing additive, was measured. The viscosity of the crude oil was determined with a Brookfield Digital Viscometer, spindle 34. The results appear below in Table 3:
|TABLE 3 |
|Sample ||Viscosity, cP ||Temp. ° C. |
|Raw crude oil ||22000 ||50.0 |
|Sheared crude oil ||12700 ||50.0 |
|Raw crude oil with 20% gasoline ||522 ||35.0 |
|Sheared crude oil with 20% gasoline ||331 ||35.0 |
- EXAMPLE 6
The data in Table 3 shows that shearing the crude oil decreases the viscosity of the crude oil by about half, and the addition of gasoline to both the raw and sheared crude oil further reduced the viscosity significantly.
- EXAMPLE 7
This example shows the effect of pretreatment by shearing on the viscosity of petroleum sludge. Petroleum sludge is primarily asphaltenic material. A raw heavy fraction of petroleum sludge was pretreated by shearing with a Ross Series shearing device at a nominal shearing rate of 7,500 rpm and initial temperature of 50° C. This pretreatment converted the raw petroleum sludge to a processed petroleum sludge with an initial viscosity of 200 cP. The processed petroleum sludge and a second sample of raw petroleum sludge having an initial viscosity of about 1240 cP were each separately passed through a Bohlin Rheometer at 25° C. at an increasing shear rate of 100 seconds−1 to 600 seconds−1. The shear rate versus viscosity data has been plotted in FIG. 1.
Light naphtha and diesel fuel were added in amounts of 20 weight % to heavy Hamaca crude petroleum before heating. Each additive was added to the Hamaca crude in a separate container. The Hamaca crude was then heated to about 90° C. for 2 hours. At the end of the heating period essentially all of the light naphtha was removed and recovered while only 3-5% of the diesel fuel was removed from the Hamaca crude during the heating period. This shows that naphtha is easier to separate from heavy crude Hamaca petroleum than diesel fuel.
Although this invention has been discussed in the context of improving the flow properties of heavy crude petroleum, the teachings contained herein are also applicable to heavy petroleum fractions and waste petroleum sludge having an API gravity of about 6 to about 20.