METHOD OF USING CONTAMINATED WATER FROM AN OILWELL EFFLUENT STREAM

Abstract

A method of using contaminated water from a well effluent stream produced by oil wells to produce biofuel and/or other biochemical compositions comprises: a) separating the well effluent stream in an oil-water separator assembly into a crude oil stream and a contaminated water stream with capped fractions of contaminants, such as crude oil, salt and metals; b) feeding at least a fraction of the contaminated water stream (1) to an irrigation system (2) of a cascaded series of soil beds (4) in which at least one saline tolerant cellulosic crop (5), such as reed, eucalyptus trees and/or tamaris, is planted, which cascade of soil beds acts as a cascaded biological filter for stepwise further reduction of the crude oil and metals content of the contaminated water stream; c) growing the cellulosic crop or crops (5) on the soil beds, wherein the contaminated water stream (1) is used to irrigate and mature the cellulosic crop or crops (5); d) harvesting a mature cellulosic crop (5) from at least one of the soil beds (4); and e) converting cellulosic material in the harvested mature crop (5) into a compound of a biofuel and/or other biochemical composition by a chemical conversion process.

Description

BACKGROUND OF THE INVENTION

The invention relates to a method of using contaminated water from a well effluent stream produced by oil wells traversing a crude oil and contaminated water containing earth layer.

In many oilfields the produced well effluent streams comprise more water than crude oil. The produced water is often brine, which is contaminated, inter alia, with metals, dissolved salts, organic chemical constituents and hydrocarbons, and which cannot be currently purified economically into fresh water.

It is known to separate contaminated water from a well effluent stream produced by a cluster of oil production wells in a bulk oil-water separator and to subsequently re-inject the contaminated water into the earth.

It is also known to use contaminated water derived from crude oil production for irrigation purposes from SPE paper 88667 “Opportunities for re-use of produced water around desert oil fields” presented by A. C. Sluijterman et al at the 11th Abu Dhabi International Petroleum Exhibition and Conference on 10-13 Oct. 2004.

Various processes are known to convert biomass into biofuels. It is known to convert cellulose-containing biomass into levulinic acid and formic acid by acid hydrolysis. Examples of such processes are disclosed in U.S. Pat. Nos. 4,897,497; 5,608,105; 5,892,107 and 6,054,611. Levulinic acid can be converted into compounds that are suitable as fuel components, e.g. levulinate esters, pentanoate esters or methyltetrahydrofuran (MTHF). U.S. Pat. No. 7,153,996 discloses a process for preparing levulinic acid esters and formic acid esters from biomass and olefins and to use the levulinic acid as a fuel additive.

US patent application US20050171374 discloses a method of preparing levulinic acid esters from alpha-angelica lactone (a levulinic acid derivative) and olefins and the use of the produced ester compositions as fuel additives.

The paper “Das Konzept der Bioraffinerie—Produktion von Plattformchemikalien and Finalprodukten” published by B. Kamm et al. in the magazine “Chemie Ingenieur Technik”, vol. 79, No. 5, May 2007 (2007-5), pages 592-603 (XP002477368) discloses that reed can be converted to biofuels and biochemicals, such as levulinic acid, via a rout involving cellulose and glucose.

A problem with the method described in the above SPE paper of using contaminated water derived from crude oil production for irrigating a reed bed is that the reed crop grown may have a changing composition and may contain contaminants which have thus far inhibited the use of the produced crop for consumption by humans (food) or animals (fodder).

U.S. Pat. No. 4,679,582 discloses a biological living filter system using leachate tolerant plants, such as reed canary grass, for treatment of a sanitary landfill leachate.

International patent application WO2006/030164 discloses a method for treating wastewater in a cascade of soil beds in which plants depollute the wastewater.

It is an object of the present invention to provide a method of using contaminated water from well effluent stream produced by a crude oil production well in such a way that it can be used for irrigating a reed and/or another saline tolerant cellulosic crop, which crop contains a limited amount of contaminants and has a accurately predictable composition such that it can be converted into a biofuel and/or another biochemical product.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a method of using contaminated water from a well effluent stream produced from a crude oil and contaminated water containing earth layer, the method comprising:

a) separating the well effluent stream in an oil-water separator assembly into a crude oil stream and a contaminated water stream with capped fractions of contaminants, such as crude oil, salt and metals;
b) feeding at least a fraction of the contaminated water stream to an irrigation system of a cascaded series of soil beds in which at least one saline tolerant cellulosic crop is planted, which cascade of soil beds acts as a cascade of biological filters for stepwise further reduction of the crude oil and metal content of the contaminated water stream;
c) growing the at least one cellulosic crop on the soil beds, wherein the contaminated water stream is used to irrigate and mature the cellulosic crop;
d) harvesting at least one mature cellulosic crop from at least one of the soil beds; and
e) converting cellulosic material in the harvested mature crop into a compound of a biofuel and/or other biochemical composition by a chemical conversion process.

Optionally, the conversion step e) comprises:

• • milling the harvested matured crop;
  • mixing the milled harvested matured crop with water, thereby forming an aqueous slurry comprising dispersed cellulosic material stemming from the milled harvested matured crop;
  • converting cellulosic material dispersed in the slurry by acid hydrolysis into levulinic acid and formic acid at an elevated pressure and temperature.

The levulinic acid may be converted into a biofuel compound of a biofuel containing fuel composition.

It is preferred that the acid hydrolysis is carried out at a temperature above 180 degrees Celsius and at a pressure above 20 bar.

In accordance with the invention the saline tolerant cellulosic crop is used to purify irrigation water passing through the soil of the bed by biodegrading crude oil and by adsorbing metals contained in the irrigation water.

The irrigation system of the first of the cascade of soil beds may comprise an irrigation water discharge system, in which unused irrigation water that has been passed through the soil of the first soil bed and of which the crude oil content has been reduced during said passage, is collected and is used as irrigation water for irrigating a second reed bed in which a second saline tolerant cellulosic crop is planted, which is less tolerant to irrigation water that is contaminated with crude oil.

Preferably the saline tolerant cellulosic crop is selected from the group of reed, eucalyptus trees, tamaris and/or Phragmites australis, Hordeum vulgare, Leucaena, Atriplex hastate, Hordeum marinum, Sporobolus kentrophyllus, Acacia species, Eucalyptus, Prosopis, Spartina anglica, Aristida species, Phoenix, Tamarix, Zostera species, Aeluropus species, Panicum antidotale, Mangrove.

Optionally the irrigation water stream discharged by the most downstream soil bed of the cascade of soil beds is fed to a water evaporation pond from which salt is collected wherein algae are grown in the water evaporation pond, which algae are collected and subsequently converted into a compound of a biofuel and/or other biochemical composition by a chemical conversion process.

These and other features advantages and embodiments of the method according to the invention are described in the accompanying claims, abstract and the following detailed description of a depicted embodiment in which reference is made to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The general principle of reed bed water purification technology is depicted in FIG. 1.

DETAILED DESCRIPTION OF THE DEPICTED EMBODIMENT

FIG. 1 shows how a flux of wastewater 1 comprising a capped amount of salt, boron and crude oil is fed via a permeable irrigation conduit 2 into the soil 3 of a reed bed 4 on which reed plants 5 are growing and consume irrigation water flowing through the soil 3, as illustrated by arrows 6, towards a pair of permeable drainage pipes 7 that are embedded in the soil 3 above an impermeable liner 8. The roots 5A of the reed plants 5 suck up wastewater 1 and bacteria living in the soil 3 around the roots 5A of the reed plants 5 break down the crude oil and thereby reduce the crude oil content of the wastewater through biodegradation, thereby creating a flux of unused irrigation water with a reduced crude oil content flowing into the drainage pipes 7, such that the unused irrigation water contains such a small amount of crude oil that it can be fed to an irrigation system for irrigating for example eucalyptus trees, which are less tolerant to irrigation water contaminated with crude oil than reed plants 5.

Reed plants 5 are halophytes, meaning plants that grow well in saline environments. The wastewater 1 is introduced at the top of the reed bed via a set of perforated irrigation conduits 2. Moisture probes 8 are used to ensure no leakages occur from the reed bed 4 into to surrounding soil layers 9.

The location of the reed bed 4 is chosen such that the soil depth is sufficiently large and the soil is sufficiently porous. Also, due to the oil present in the reed bed 4, it has to be made sure that no leakages to the surroundings can occur. The reed bed 4 will treat the water for hydrocarbons and metals.

Produced waste water at the inflow of the reed bed 4 produced at the NIMR oil field in Oman, where the pilot Reed bed experiment described in the above SPE paper took place, have an average oil in water concentration of 250 ppm. Salinity of the wastewater is around 6,000 ppm. With an inflow of 45,000 m³ waste water per day, this will lead to 270 ton salt per day and 11,250 litres of oil per day (equivalent to 71 barrels a day). Salt volumes remaining in the soil and taken up by the reed plants 5 will be negligible, due to constant leaching and limited storage volume in the biomass.

After treatment, at the outflow in the drainage pipes 7, oil in water concentrations will be below 5 ppm. Using a reference evapo-transpiration varying between 4 and 11 mm per day, the outflow volume and salt concentration of the effluent can be calculated. The salinity of the effluent will limit, but not totally restrict the use of this water as irrigation water for another crop, which is less tolerant for irrigation water contaminated with crude oil, such as eucalyptus trees.

It is known that biochemical and/or biofuel products that may be generated from non-food or non-fodder crops, and/or from cellulose based is described as the so-called second generation biofuels. Reed is an example of a non-food source of biomass. Reed is a lignocellulosic material, and can be converted in materials that are suitable for blending with gasoline or diesel.

Lignocellulosic materials contain cellulose, hemicellulose and lignin. Cellulose can be converted into levulinic acid. Through esterification, this levulinic acid can be converted into a levulinate ester, for example Ethyl Levulinate, which can be blended with both diesel as gasoline.

After pre-treatment of the reed 4 (milling, slurring, etc), the following processes take place: Hydrolysis of cellulose results in glucose. After this, during a high pressure (at about 30 bar) and steam heating (at about 230° C.) process, the C6 sugars are converted into Levulinic Acid and Formic Acid. In reaction with ethanol, the Levulinic Acid will be converted into Ethyl Levulinate.

As one example of such technology is a process described in U.S. Pat. No. 5,608,105, where Lignin stays as it is and contains solids. The lignin provides energy for boiling and heating.

It is also known that through esterification, levulinic acid can be converted into Ethyl Levulinate and that Ethyl Levulinate can be mixed with both gasoline as diesel as well. Wastewater produced by the oil industry is a globally rising issue.

Given the high environmental and financial costs relating to disposal of this produced wastewater, re-use options for this water must be defined. Because re-use options of water produced at oil drilling activities are limited to non food purposes, the method according to the invention uses production water associated with crude oil production to produce bio fuels and/or biochemicals.

A suitable process of producing biofuel from production water can be divided in the following steps:

I) Contaminated wastewater production.
II) Contaminated wastewater treatment. Biological treatment by reed beds has proven to be a cost efficient and environmentally-friendly alternative to the current method of disposing produced contaminated water, which is deep well disposal.
III) Biomass production. Reeds have been identified as a good option for growing biomass.
IV) Levulinic acid production. Levulinic acid production has been identified as a good option for converting reeds into useful compounds.

A cost benefit analysis, performed on the costs and benefits of the steps described above and related nature preservation costs, carbon credits and avoided deep well disposal costs, has led to the conclusion that using 45,000 m³ or more of production water associated with crude oil production from the NIMR oil field in Oman per day to produce Levulinate Acid is economically, environmentally and socially feasible. On the short term, 9,400-14,000 tonnes biomass dry feedstock produced by using a gross affluent contaminated water of 45,000 m³ per year will be delivered from reed beds fed by wastewater produced at the NIMR oilfield in Oman to the levulinic acid production plant. However, on the long term, if the testing period has been completed successfully, the water re-use might be maximised, resulting in a higher area of reed production, thus in higher yield. Also, other areas in Oman and other countries might implement the re-use of water by growing biomass. Furthermore, the levulinic acid production process makes it possible that also inputs from other sources may be used (such as municipal waste, agricultural waste, etc). This implies that on the long term a far larger quantity of Levulinate Acid may be produced.

Claims

1. A method of using contaminated water from a well effluent stream produced from a crude oil and contaminated water containing earth layer, the method comprising:

a) feeding the contaminated water to an irrigation system of a cascaded series of soil beds in which at least one saline tolerant cellulosic crop is planted, which cascade of soil beds acts as a cascade of biological purification filters for stepwise further reduction of the crude oil and metal content of the contaminated water stream;

b) growing the at least one cellulosic crop on the soil beds, wherein the contaminated water stream is used to irrigate and mature the cellulosic crop; and

c) harvesting at least one mature cellulosic crop from at least one of the soil beds;

d) separating the well effluent stream in an oil-water separator assembly into a crude oil stream and a contaminated water stream with capped fractions of contaminants, such as crude oil, salt and metals; and

e) converting cellulosic material in the harvested mature crop into a compound of a biofuel and/or other biochemical composition by a chemical conversion process.

2. The method of claim 1, wherein step e) comprises:

milling the harvested mature crop;

mixing the milled harvested mature crop with water, thereby forming an aqueous slurry comprising dispersed cellulosic material stemming from the milled harvested mature crop;

converting cellulosic material dispersed in the slurry by acid hydrolysis into levulinic acid and formic acid at an elevated pressure and temperature.

3. The method of claim 2, wherein the levulinic acid is converted into a biofuel compound of a biofuel containing fuel composition.

4. The method of claim 2, wherein the acid hydrolysis is carried out at a temperature above 180 degrees Celsius and at a pressure above 20 bar.

5. The method of claim 1, wherein step d) further comprises mixing the contaminated water stream with fresh water such that the commingled contaminated and fresh water streams comprise capped fractions of, inter alia, crude oil, salt and metals.

6. The method of claim 1, wherein the saline tolerant cellulosic crop is used to purify irrigation water passing through the soil of the cascade of soil beds by biodegrading crude oil and by adsorbing metals contained in the irrigation water.

7. The method of claim 6, wherein the irrigation system of the first of the cascade of soil beds comprises an irrigation water discharge system, in which unused irrigation water that has been passed through the soil of the first soil bed and that is purified during said passage such that its crude oil content is reduced, is collected and is used as irrigation water for growing a second crop on the second of the cascade of soil beds, which second crop is less tolerant to irrigation water that is contaminated with crude oil.

8. The method of claim 7, wherein unused irrigation water discharged into the soil of the second of the cascade of soil beds in which the second crop is planted is collected, which unused irrigation water has a crude oil content that has been further reduced through biodegradation in the soil around the roots of the second crop, is used as irrigation water for growing on a third of the cascade of soil beds a third crop, which is less tolerant to irrigation water that is contaminated with crude oil than the cellulosic first and second crops.

9. The method of claim 1, wherein the saline tolerant cellulosic crop is selected from the group of reed, eucalyptus trees and tamaris.

10. The method of claim 1, wherein the saline tolerant cellulosic crop is selected from the group of Phragmites australis, Hordeum vulgare, Leucaena, Atriplex hastate, Hordeum marinum, Sporobolus kentrophyllus, Acacia, Eucalyptus, Prosopis, Spartina anglica, Aristida, Phoenix, Tamarix Zostera, Aeluropus, Panicum antidotale, Mangrove.

11. The method of claim 7, wherein the first cellulosic crop is reed and the second cellulosic crop comprises eucalyptus trees.

12. The method of claim 1, wherein an impermeable liner is arranged below at least one of the soil beds in which the cellulosic crop is planted to inhibit drainage of contaminated water into adjacent soil layers.

13. The method of claim 12, wherein the impermeable liner is arranged at an average depth of less than 1 meter below the upper surface at least one of the soil beds.

14. The method of claim 1, wherein the irrigation water stream discharged by the most downstream soil bed of the cascade of soil beds is fed to a water evaporation pond from which salt is collected.

15. The method of claim 14, wherein algae are grown in the water evaporation pond, which algae are collected and subsequently converted into a compound of a biofuel and/or other biochemical composition by a chemical conversion process.