Method for improving the transportability of heavy crude oil

Abstract

The invention relates to a method for improving the transportability of heavy crude oil. Proceeding from the disadvantages of the known prior art a method is to be provided, in which an additive can be used which is producible from a byproduct arising during mineral oil production. The method is to be performable with low expenditure and without any special safety precautions. Further the additive shall lead to an increased yield of conventional petroleum during subsequent refining. According to the invention, an aqueous hydrocarbon mixture having a chain length of predominantly C4 to C12 which does not contain any oxygen-containing hydrocarbon compounds is utilized. This is produced in the area of a mineral oil field from natural gas arising as by-product and/or mineral oil-associated gas. Thereby from the heavy crude oil a crude oil which is light in quality and transportable is obtained. During the subsequent refining of the light crude oil to give conventional petroleum, the amount of petroleum produced is increased by the amount of hydrocarbons present in the aqueous hydrocarbon mixture.

Claims

1. A method for improving the transportability of heavy crude oil from a mineral oil field to a refinery, wherein a viscosity-reducing agent is added to the heavy crude oil, characterized in that the viscosity-reducing agent is an aqueous hydrocarbon mixture having a chain length of predominantly C4 to C12, which does not contain any oxygen-containing hydrocarbon compounds, and is produced on the site of the mineral oil field from arising natural gas and/or mineral oil-associated gas using the following method steps: a) conversion of the natural gas and/or mineral oil-associated gas into a methanol/water mixture, b) processing of the methanol-water mixture by distillation to form a distillate having a high water and alcohol content of above 90%, c) catalytic conversion of the distillate into a dimethyl ether/methanol/water mixture, d) conversion of the dimethyl ether/methanol/water mixture by dehydration into the aqueous hydrocarbon mixture having a chain length of predominantly C4 to C12; and the hydrocarbon mixture obtained according to method steps a) to d) is added either untreated or after degassing and/or dewatering to the heavy crude oil, as a result of which, from the heavy crude oil, a crude oil light in quality is obtained which is transported via lines to a refinery and during the subsequent refining of the light crude oil to give conventional petroleum, the amount of petroleum produced is increased by the hydrocarbons present in the aqueous hydrocarbon mixture.

2. The method as claimed in claim 1, characterized in that the conversion of the natural gas and/or mineral oil-associated gas into a methanol-water mixture is performed on the site of the mineral oil field with the following method steps: desulfurization; saturation with process condensate and steam; pre-cracking into a gas mixture of methane, carbon dioxide and carbon monoxide; then, the pre-cracked gas mixture is catalytically converted into synthesis gas at elevated temperature and a pressure of at least 50 bar in an autothermal reactor with addition of preheated oxygen, which synthesis gas is cooled and compressed by means of a compressor, and then, therefrom, by catalytic conversion in the context of a two-stage methanol synthesis in a water-cooled and in a gas-cooled reactor, methanol is produced and by subsequent multi-stage condensation crude methanol (methanol-water mixture) is obtained.

3. The method as claimed in claim 1, characterized in that the conversion of the natural gas and/or mineral oil-associated gas into a methanol-water mixture is performed on the site of the mineral oil field by means of the following method steps: desulfurization; saturation with process condensate and steam; subsequent diverting of a substream of water-saturated process gas which is precracked into a gas mixture of methane, hydrogen, carbon dioxide and carbon monoxide; this gas mixture is converted in a steam reformer into a first synthesis gas, a mixture of hydrogen, carbon dioxide and carbon monoxide, which is reintroduced to the water-saturated process gas stream and mixed therewith; then, the process gas stream is catalytically converted at elevated temperature and a pressure of at least 50 bar in an autothermal reactor with addition of preheated oxygen into a second synthesis gas which is cooled and compressed by means of a compressor, and then, therefrom, by catalytic conversion in the context of a two-stage methanol synthesis, in a water-cooled and in a gas-cooled reactor, methanol is produced and by subsequent multi-stage condensation, crude methanol (methanol-water mixture) is obtained.

4. The method as claimed in claim 3, characterized in that the water-saturated process gas, after the pre-reformer, is divided into two substreams, wherein the one substream is run to the steam reformer and the other substream is run to the autothermal reformer.

5. The method as claimed in claim 4, characterized in that the methanol-water mixture (crude methanol) obtained is subjected to a two-stage distillation, wherein, in the first stage, low-boiling compounds are separated off, and in the second stage higher-boiling compounds are separated off, and a distillate having a high water and alcohol content is formed, which is then catalytically converted in a fixed-bed reactor into a dimethyl ether/methanol/water mixture which is then converted in further adiabatically operating reactors in the temperature range from 300 to 450 C. into the aqueous hydrocarbon mixture as end product.

6. The method as claimed in claim 5, characterized in that a methanol having a residual water content of at least 4%, and an alcohol content of 0.1%, is formed as intermediate product.

7. The method as claimed in claim 6, characterized in that the dimethyl ether/methanol/water mixture arising in the fixed-bed reactor is admixed with recycled gas for temperature adjustment.

8. The method as claimed in claim 7, characterized in that a first subquantity of synthesis gas is diverted, run in a cycle, and during this compressed to the required operating pressure.

9. The method as claimed in claim 8, characterized in that a second subquantity of synthesis gas is diverted, hydrogen is separated off in a pressure-swing appliance, which hydrogen is introduced into the synthesis gas stream on the suction side of the compressor.

10. The method as claimed in claim 9, characterized in that the hydrocarbon mixture formed is fed directly on the site of the mineral oil field either to the heavy crude oil already produced and/or via the borehole to the heavy crude oil still stored under ground.

11. The method as claimed in claim 10, characterized in that the hydrocarbon mixture formed is introduced into the borehole via a purge tube.

12. The method as claimed in claim 10, characterized in that the hydrocarbon mixture formed is dewatered and degassed before it is contacted with the heavy crude oil.

13. The method as claimed in claim 12, characterized in that treated hydrocarbon mixture that is dewatered and degassed is added to the heavy crude oil before or after the central oil processing facility.

14. The method as claimed in claim 12 characterized in that non-treated hydrocarbon mixture is added to the heavy crude oil before the central oil processing facility.

15. The method as claimed in claim 14, characterized in that, after separating off water and oil-associated gas from the crude oil, a further amount of treated hydrocarbon mixture is added to the crude oil, which, depending on the viscosity of the heavy oil, is metered in such a manner that a light crude oil is formed.

16. The method as claimed in claim 15, characterized in that treated hydrocarbon mixture is fed on the suction side of the pump used for the transport of the crude oil.

17. The method as claimed in claim 16, characterized in that the viscosity of the extracted heavy crude oil is measured, and, depending on the current measurement result, the amount of hydrocarbon mixture is added in a metered manner in order to obtain light crude oil.

18. The method as claimed in claim 17, characterized in that treated hydrocarbon mixture and heavy crude oil are mixed in a separate mixing arrangement.

Description

(1) In the associated drawing,

(2) FIG. 1 shows a first variant embodiment as a flowchart and

(3) FIG. 2 shows a second variant embodiment as a flowchart.

(4) In a mineral oil field, 1088 t/h of heavy crude oil (API 23) are extracted which has the following composition:

(5) TABLE-US-00001 hydrocarbons 818 t water 240 t and gaseous components 30 t.

(6) In a central oil processing facility 1, the crude oil originating from differing boreholes 2 is combined, mixed, and then fed to a separating arrangement, in which the aqueous phase and the gaseous components are separated off. The separating arrangement is a component of the central oil processing facility 1. In FIGS. 1 and 2, three boreholes 2 are shown symbolically.

(7) In connection with mineral oil extraction, natural gas/mineral oil-associated gas arises having the following composition:

(8) TABLE-US-00002 nitrogen 1.5% methane 92% ethane 3.5% propane 1.5% higher hydrocarbons 1% sulfur 50 ppm.

(9) The natural gas/oil-associated gas (350 000 m.sup.3 (standard cubic meters)/h) is converted as follows into a hydrocarbon mixture in a chemical plant erected on the site of the mineral oil field.

EXAMPLE 1

(10) As shown in FIG. 1, natural gas/oil-associated gas 3 is first desulfurized at a pressure of 70 bar at a temperature of 375 C. over a zinc oxide bed (desulfurization unit 4), thereafter saturated with process condensate and steam (saturator 5) and after establishing a steam/carbon ratio of 1.0 in the prereformer 6, an adiabatically operating catalytic reactor, is precracked at 480 C. into a mixture of methane, carbon dioxide and carbon monoxide.

(11) After further heating to 630 to 650 C., the precracked gas is fed to an autothermal reformer 7. In this catalytic reactor, by addition of oxygen 9 that is preheated to 230 C. and which is obtained in an air separation unit 8, a synthesis gas 10 is generated at 1030 C., which synthesis gas consists of hydrogen, carbon monoxide and carbon dioxide, and contains only a very small amount of uncracked methane. This synthesis gas is cooled in a waste-heat system 11.

(12) Via various stages which are used for steam generation and/or heating of various gas/product streams, the now cooled synthesis gas at 55 bar is compressed by a compressor 12 to 75 bar. Then in a dual system, consisting of a water-cooled and a gas-cooled reactor 13, synthesis gas is catalytically converted in the temperature range from 220 to 260 C. to methanol and by condensation a crude methanol 14 having the following composition is obtained:

(13) TABLE-US-00003 methanol 83% by weight carbon dioxide 3.6% by weight water 11.7% by weight methane 1.5% by weight higher hydrocarbons 0.1% by weight higher alcohols 0.1%.

(14) During the methanol synthesis, a subquantity of synthesis gas is run in a cycle via a circuit line 15 and during this, by means of a further compressor 16, brought to the required pressure. On account of the impurities present in the synthesis gas, a subquantity of synthesis gas is diverted as purge gas 17 and run via a pressure-swing arrangement (PSA) 18. To this PSA a synthesis gas substream 19 is also fed at high pressure, which synthesis gas substream 19 is branched off after the pressure elevation by means of the compressor 12. The hydrogen 20 generated in the PSA 18 is returned to the synthesis gas stream on the suction side of the synthesis gas compressor 12.

(15) The crude methanol 14 that is condensed in a plurality of stages after the methanol synthesis is first degassed in a distillation unit 21 downstream from the methanol synthesis and then purified to remove low-boiling products and finally higher-boiling products. Compared with the classical three-stage distillation for producing marketable methanol, the distillation is carried out in the temperature range from 70 to 140 C. in only two columns, and a residual water content of 4% in the methanol generated is established. Overall, after the distillation, 435 t/h of crude methanol arise, which contain 17 t of water.

(16) The methanol distilled to 4% water content is then catalytically converted into a DME (dimethyl ether)/methanol/water mixture in a fixed bed reactor 22 (DME reactor). The reaction product from the DME reactor is admixed with recycle gas 23 for temperature adjustment and then converted in further adiabatically operating reactors 24 in the temperature range from 320 to 420 C. to a hydrocarbon/water mixture. From the 435 t/h of methanol used, in this case 191 t of hydrocarbons and 244 t of water are formed. This aqueous hydrocarbon mixture is finally degassed in a degassing unit 25 and added to the untreated heavy crude oil.

(17) According to this example, 435 t of aqueous hydrocarbon mixture having a chain length of predominantly C4 to C12 and not containing any oxygen-containing hydrocarbon compounds are admixed continuously per hour to the untreated heavy crude oil (1088 t/h). In the flowchart, the point of admixture is indicated by the reference sign 26.

(18) The hydrocarbon mixture is admixed before the crude oil/mineral oil-associated gas separation process which takes place within the central oil processing facility 1.

(19) Then the aqueous phase and gaseous components still present, such as nitrogen, carbon dioxide, methane and ethane, are separated off from the diluted crude oil mixture in the central oil processing facility 1. 1004 t/h of treated crude oil having an API 36 are obtained. This can then be transported with pumping stations in conventional transport pipelines 27 over thousands of kilometers without problems. This modified crude oil has a quality such as light crude oil.

(20) The advantage of the further processing or refining of the light crude oil to petroleum is that the special hydrocarbons added to improve the transportability have absolutely no disadvantage on the refining process and become an active component of the petroleum produced, as a result of which the amount of petroleum produced is increased by this share.

EXAMPLE 2

(21) The variant embodiment shown in FIG. 2 differs from the embodiment shown in FIG. 1 in the following process steps.

(22) After the saturator 5, via a first line 28, a first substream (quantitative share about 40%) of the water-saturated desulfurized process gas is mixed with stream and fed at a temperature of about 480 C. to the prereformer 6.

(23) Therein, the process gas is precracked into a mixture of methane, carbon dioxide, hydrogen and carbon monoxide. After further heating up to 520 C., the precracked process gas arrives in a steam reformer 29, an externally heated tube reactor having a nickel catalyst, and is converted therein into a first synthesis gas 30, a mixture of hydrogen, CO and CO.sub.2. This first synthesis gas 30 is returned to the substream (share approximately 60%) conducted in the other, second line 31 of the water-saturated desulfurized process gas, which arises downstream of the saturator 5, mixed therewith, and fed at a mixture temperature of 670 C. to the autothermal reformer 7.

(24) The division of the process gas into two substreams can be performed either upstream or downstream of the saturator 7, or downstream of the prereformer 6.

(25) In the autothermal reformer 7, an adiabatically operating catalytic reactor, the mixed gas, by addition of oxygen 9 heated to 240 C. which oxygen 9 is obtained in an air separation arrangement 8, is completely converted at 980 C. to a second synthesis gas 10 which only contains a very small amount of uncracked methane. This synthesis gas is cooled in the downstream waste-heat system 11.

(26) The synthesis gas present at a pressure of 32 bar is then further treated in a manner analogous to that stated in example 1, in order to produce an aqueous hydrocarbon mixture having a chain length of predominantly C4 to C12, with the sole difference that, downstream of the compressor 12, no synthesis gas substream 19 is branched off and fed to the pressure-swing arrangement (PSA) 18.

(27) With this method variant, it is possible, compared with the procedure according to example 1, to reduce the gas consumption for production of the aqueous hydrocarbon mixture by approximately 10%.