WO2004013455A1

WO2004013455A1 - Decontamination of drill cuttings and other waste material

Info

Publication number: WO2004013455A1
Application number: PCT/GB2003/003389
Authority: WO
Inventors: Kenneth Stuart Killham; Graeme Iain Paton
Original assignee: Remedios Limited
Priority date: 2002-08-02
Filing date: 2003-08-04
Publication date: 2004-02-12
Also published as: GB2406873A; GB0501796D0; GB2406873B; GB0217928D0; AU2003267535A1

Abstract

Drill cuttings (2) are delivered from a hopper (3) onto a conveyor belt (4) which moves in the direction of the arrow (A). Steam is passed under pressure from a steam nozzle (8) through the conveyor (4) and the drill cuttings carried thereon. The steam is generated in an oil fired boiler (9). Thereafter the drill cuttings are subjected to a bioremediation step. A C:N:P ratio of the drill cuttings is monitored at least one during the method and the ratio optionally altered to provide an optimum C:N:P ratio for microorganism activity. Steam treatment drives off mobile oil fractions in the drill cuttings and additionally conditions the waste material for the performance of either indigenous microorganisms or subsequently added innoculum.

Description

DECONTAMINATION OF DRILL CUTTINGS AND OTHER WASTE MATERIAL

Technical Field of the Invention

The invention relates to a method and apparatus for decontaminating drill cuttings.

Background of the Invention

Drill cuttings produced from oil and gas exploration and production contain high volumes of hydrocarbon based toxic waste, usually derived from oil in the well or the drilling fluids used to extract it. As new environmental legislation precludes dumping at sea, such waste needs to be managed and treated in a sustainable manner. Even after conventional treatment, drill cuttings may still include contaminants, which are generally disposed of in landfill sites. This is obviously undesirable.

It is an object of the invention to overcome at least some of the above disadvantages. Disclosure of the Invention

According to the invention, there is provided a method of decontaminating drill cuttings comprising the step of passing steam through the drill cuttings. A method according to the invention has the effect of melting and dispersing parts of many, if not all, fractions of oil contaminants in the drill cuttings. Additionally, steam treatment can enhance the physiological status of some of the indigenous microorganisms in the drill cuttings. Moreover, steam has been surprisingly found to successfully wet the drill cuttings. This is an important part of the invention as water is required by microorganisms for degrading contaminants in the drill cuttings. Heretofore, water has been used to wet the drill cuttings, however, this has not been successful due to the hydrophopicity of the hydrocarbon contaminated drill cuttings. The use of steam has been found to overcome this wetting problem. Additionally, steam has been found to be more successful at permeating through drill cuttings.

In one embodiment of the invention, the steam is low temperature steam.

In this specification, the term "low temperature steam" should be taken to mean steam having a temperature which is sufficiently raised to activate microorganisms in the drill cuttings without resulting in heat induced inactivation. Generally, the temperature of the low temperature steam is between 30 and 80 degrees C, typically between 40 and 70 degrees C and preferably between 50 and 60 degrees C. In one preferred embodiment of the invention, low temperature steam is produced in a low temperature steam generator, the details of which will be known to a person skilled in the art.

In a preferred embodiment of the invention, the steam-treated drill cuttings, optionally combined with inoculated microorganisms, are bioremediated for a period of time which is sufficient to allow microorganisms (either indigenous, innoculated or both) in the drill cuttings to degrade contaminants therein. Typically, the drill cuttings are bioremediated for a period of between 6 and 12 weeks. Suitably, the drill cuttings are bioremediated in biopiles which ideally are covered to retain moisture. Preferably, the drill cuttings are aerated during bioremediation by turning or other means, suitably on a periodical basis, such as, for example, six times over an eight-week period.

Typically, the drill cuttings are placed on a platform such as a perforated conveyor and the steam is passed through the drill cuttings on the conveyor. Typically, the steam is passed through the perforations in the conveyor from below. In one embodiment of the invention, the steam is passed through the conveyor and drill cuttings at pressure or under vacuum. Although the preferred embodiment of the invention involves the use of a continuously moving conveyor, it is envisaged that the conveyor may operate in a discontinuous manner in which it moves into stationary position over a steam generator where it remains for a given period of time during which the drill cuttings are treated before moving the treated drill cuttings onto a further treatment station.

In a preferred embodiment of the invention, the C:N:P ratio of the drill cuttings is monitored at least once during the process and the ratio altered to provide an optimum C:N:P ratio for microorganism activity. The optimum C:N:P ratio depends to a large extent on the composition and bulk density of the drill cuttings, however the ratio will generally be in the range of 250:10:1 to 400:10:1. Thus, in one preferred embodiment of the invention, augmentation of the drill cuttings takes place after steam treatment and prior to bioremediation, during which the steam treated drill cuttings may be augmented with one or more of: a nitrogen source such as urea or ammonium nitrate; a phosphorus source such as ground rock phosphate or triple super phosphate, a bulking agent such as chipped wood; trace nutrients and water. In addition, the microbial population of the drill cuttings may be augmented with an innoculum of microorganisms. Typically, the innoculum may be derived from hydrocarbon contaminated wastes such as soil, dredgings, drill cuttings, or drill cuttings which have been steam- treated and bioremediated according to the present invention. Alternatively, the innoculum may be derived from another source. In this regard, the degradation potential of the drill cuttings may initially be measured by means of a suitable assay. If the potential is found to be too low, an innoculum may be added to the drill cuttings prior to bioremediation.

In one embodiment of the invention, the process includes a steam recovery system wherein steam which has been passed through the drill cuttings is extracted and treated to remove contaminants. Ideally, the steam recovery system includes passing the steam through one or more of : an activated carbon trap to remove volatile organic carbon; a condenser; desalinating equipment; and a filter to remove particulate material. Suitably, water produced in the steam recovery system is returned to the low temperature steam generator. In a preferred embodiment of the invention, the process includes the step of collecting oily water which falls from the perforated conveyor, separating the oil from the water in a separator, and optionally returning recovered water to the steam treatment step. Oil recovered during the process may be returned to a steam generator.

In one embodiment of the invention, the process involves an initial step of pulverising the drill cuttings until a suitable consistency of source material is obtained. However, in a preferred embodiment of the invention, the drill cuttings are initially aggregated, suitably by means of an aggregating agent such as, for example, woodchips . Typically, the aggregating agent is added to the drill cuttings in an amount of between 10 and 30% (v/v) . Aggregation allows for easier aeration and wetting of the drill cuttings. Typically, the aggregating agent is mixed with the drill cuttings for between 10 and 40 minutes. Suitably, the mixing takes place in a FARESIN TMB PRO mixer. Typically, the drill cuttings are delivered from a hopper onto a conveyor at a desired rate. The conveyor belt is preferably made of stainless steel . Suitably, the perforations in the conveyor have a mesh size of at least 2mm. Ideal movement of the conveyor should be such as to result in agitation of the drill cuttings thereon. During an initial stage of the conveyor excess oily water which drains through the conveyor may be collected and discarded. In one embodiment of the invention, the process includes at least two steam treatment steps. In one embodiment, the temperature of the air above the drill cuttings is measured during steam-treatment . When the air temperature reaches a pre-determined reading, steam- treatment of. the cuttings is stopped either by moving the cuttings away from the steam with the conveyor or by cutting off the supply of steam. The pre-determined temperature depends on the hydrocarbon content of the cuttings, the fabric of the cuttings matrix, the conductivity of the material, and the microbial biomass of the cuttings. In one embodiment of the invention, the drill cuttings are treated prior to steam treatment to ensure that the bulk density of the cuttings of between 1.0 and 1.2 g/cm3.

The invention also relates to an apparatus for decontamination of waste material such as drill cuttings comprising a perforated conveyor and at least one steam generator adapted for passing steam through the perforated conveyor. Typically, the steam generator is adapted for passing steam through the perforated conveyor under pressure. Preferably, the apparatus includes at least one steam treatment means comprising a vacuum pump adapted for extracting steam which has passed through the conveyor and one or more of:- an activated carbon trap adapted for removing volatile organic carbon; a condenser; desalinating means; and a filter adapted for removing particulate. Ideally, the apparatus includes collection means adapted for collecting condensed oily water which falls from the conveyor and, preferably, a conduit which is adapted to convey condensed oily water to an oil/water separator. Suitably, the apparatus includes means for conveying water separated in the oil/water separator to the steam treatment means downstream of the condenser.

The invention also relates to the use of steam in the decontamination of drill cuttings. The invention also relates to bioremediated material obtainable according to the process of the invention, suitably for use as an innoculum in a drill cutting decontamination process.

The invention also relates to a method of decontaminating waste material comprising the steps of passing steam through the waste material and bioremediating the steam-treated waste material. In this specification, the term "waste material" should be understood as including hydrocarbon contaminated effluents, sludges, tailings, dredgings, drill cuttings, and soils.

In one embodiment of the invention, the steam is low temperature steam. Generally, the temperature of the low temperature steam is between 30 and 80 degrees C, typically between 40 and 70 degrees C and preferably between 50 and 60 degrees C. In one preferred embodiment of the invention, low temperature steam is produced in a low temperature steam generator, the details of which will be known to a person skilled in the art.

In a preferred embodiment of the invention, the steam-treated waste material, optionally combined with inoculated microorganisms, is bioremediated for a period of time which is sufficient to allow microorganisms (either indigenous, innoculated or both) in the waste material to degrade contaminants therein. Typically, the waste material is bioremediated for a period of between 6 and 12 weeks. Suitably, the waste material is bioremediated in biopiles which ideally are covered to retain moisture. Preferably, the waste material is aerated during bioremediation by turning or other means, suitably on a periodical basis, such as, for example, six times over an eight-week period.

Typically, the waste material is placed on a platform such as a perforated conveyor and the steam is passed through the waste materialon the conveyor. Typically, the steam is passed through the perforations in the conveyor from below. In one embodiment of the invention, the steam is passed through the conveyor and waste material at pressure or under vacuum. Although the preferred embodiment of the invention involves the use of a continuously moving conveyor, it is envisaged that the conveyor may operate in a discontinuous manner in which it moves into stationary position over a steam generator where it remains for a given period of time during which the waste material is treated before moving the treated waste material onto a further treatment station.

In a preferred embodiment of the invention, the C:N:P ratio of the waste material is monitored at least once during the process and the ratio altered to provide an optimum C:N:P ratio for microorganism activity. The optimum C:N:P ratio depends to a large extent on the composition and bulk density of the waste material, however the ratio will generally be in the range of 250:10:1 to 400:10:1. Thus, in one preferred embodiment of the invention, augmentation of the waste material takes place after steam treatment and prior to bioremediation, during which the steam treated waste material may be augmented with one or more of: a nitrogen source such as urea or ammonium nitrate; a phophorus source such as grand rock phosphate or triple super phosphate, a bulking agent such as chipped wood; trace nutrients and water. In addition, the microbial population of the waste material may be augmented with an innoculum of microorganisms. Typically, the innoculum may be derived from hydrocarbon contaminated wastes such as soil, dredgings, waste material, or waste material which have been steam- treated and bioremediated according to the present invention. Alternatively, the innoculum may be derived from another source. In this regard, the degradation potential of the waste material may initially be measured by means of a suitable assay. If the potential is found to be too low, an innoculum may be added to the waste material prior to bioremediating.

In one embodiment of the invention, the process includes a steam recovery system wherein steam which has been passed through the waste material is extracted and treated to remove contaminants. Ideally, the steam recovery system includes passing the steam through one or more of: an activated carbon trap to remove volatile organic carbon; a condenser; desalinating equipment; and a filter to remove particulate material. Suitably, water produced in the steam recovery system is returned to the low temperature steam generator. In a preferred embodiment of the invention, the process includes the step of collecting oily water which falls from the perforated conveyor, separating the oil from the water in a separator, and optionally returning recovered water to the steam treatment step. Oil recovered during the process may be returned to a steam generator.

In one embodiment of the invention, the process involves an initial step of pulverising the waste material until a suitable consistency of source material is obtained. However, in a preferred embodiment of the invention, the waste material is initially aggregated, suitably by means of an aggregating agent such as, for example, wood chips. Typically the aggregating agent is added to the waste material in an amount of between 10 and 30% (v/v) . Aggregation allows for easier aeration and wetting of the waste material. Typically, the aggregating agent is mixed with the waste material for between 10 and 40 minutes. Suitably, the mixing takes place in a FARESIN TMB Pro mixer. Typically, the waste material is delivered from a hopper onto a conveyor at a desired rate. The conveyor belt is preferably made of stainless steel. Suitably, the perforations in the conveyor have a mesh size of at least 2mm. Ideal movement of the conveyor should be such as to result in agitation of the waste material thereon. During an initial stage of the conveyor excess oily water which drains through the conveyor may be collected and discarded. In one embodiment of the invention, the process includes at least two steam treatment steps. In one embodiment, the temperature of the air above the waste material is measured during steam-treatment . When the air temperature reaches a pre-determined reading, steam- treatment of the material is stopped either by moving the material away from the steam with the conveyor or by cutting off the supply of steam. The pre-determined temperature depends on the hydrocarbon content, the fabric, the conductivity, and the microbial biomass, of the cuttings.

In one embodiment of the invention, the drill cuttings are treated prior to steam treatment to ensure that the bulk density of the cuttings of between 1.0 and 1.2 g/cm3.

The invention also relates to an apparatus for decontamination of waste material such as waste material comprising a perforated conveyor and at least one steam generator adapted for passing steam through the perforated conveyor. Typically, the steam generator is adapted for passing steam through the perforated conveyor under pressure. Preferably, the apparatus includes at least one steam treatment means comprising a vacuum pump adapted for extracting steam which has passed through the conveyor and one or more of:- an activated carbon trap adapted for removing volatile organic carbon; a condenser; desalinating means; and a filter adapted for removing particulate. Ideally, the apparatus includes collection means adapted for collecting condensed oily water which falls from the conveyor and, preferably, a conduit which is adapted to convey condensed oily water to an oil/water separator. Suitably, the apparatus includes means for conveying water separated in the oil/water separator to the steam treatment means downstream of the condenser .

The invention also relates to bioremediated material obtainable according to the process of the invention, suitably for use as an innoculum in a waste material decontamination process.

Brief Description of the Figures

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings in which:

Fig. 1 illustrates a process for decontaminating drill cuttings according to the invention;

Fig. 2 illustrates a process for decontaminating drill cuttings according to an alternative embodiment of the invention; Fig. 3 illustrates a steam recovery system forming part of the process for decontaminating drill cuttings illustrated in Fig.2;

Figs. 4 and 5 are graphs showing the relationship between bulk density of drill cuttings and the % of hydrocarbons removed from the drill cuttings during steam treatment; and

Figs. 6a and 6b are chromatograms showing the fractions of oil present in untreated (6a) and treated (6b) drill cuttings, respectively.

Detailed Description of the Invention

Referring to the drawings, and initially to Fig. 1, there is illustrated a method of treatment of drill cuttings according to the invention and indicated generally by the reference numeral 1. In an initial step of the process, drill cuttings 2 are delivered from a hopper 3 onto a conveyor belt 4 which moves in the direction of the arrow indicated by the reference numeral A. In a steam treatment step, steam is passed under pressure from a steam nozzle 8 through the conveyor 4 and the drill cuttings carried thereon. The steam is generated in an oil fired boiler 9 before being passed to the nozzle 8.

Referring to Figs. 2 and 3, an alternative method of treating drill cuttings according to the invention is illustrated in which parts identical to those illustrated with reference to Fig. 1 are assigned the same reference numerals. Referring initially to Fig. 2, the drill cuttings 2 are delivered from a hopper 3 unto a conveyor belt 4 which moves in the direction of the arrow marked A. Although not illustrated, the drill cuttings are initially aggregated by mixing with 25% (v/v) wood chips for 10 minutes in a FARESIN TMB PRO mixer. The steam treatment step is identical to that described with reference to Fig. 1.

The process illustrated with reference to Fig. 2 additionally includes a steam recovery system associated with the stream treatment step, the system comprising a hood 12 in communication with a vacuum pump 13. The remaining steps of the recovery system, indicated by the reference numeral 15, are described in more detail below. The oily water recovery system 18 is arranged underneath the conveyor 4 and hopper 3 to collect any excess oily water which drains therefrom.

After the drill cuttings have been treated with steam, the conveyor 4 delivers the cuttings to a second conveyor 20. In this step of the process, the steam treated drill cuttings are augmented with additional materials which will aid in the bioremediation and activation of the indigenous drill cutting microorganisms. Thus, the hoppers 21 to 24 contain urea or ammonium phosphate, ground rock phosphate or triple super phosphate, water and an innoculum respectively. The innoculum is provided in the form of hydrocarbon contaminated waste such as soil, dredgings, drill cuttings or drill cuttings which have been treated and bioremediated according to the present invention.

The determination of which additional products need to be added to the drill cuttings can be carried out at any stage of the process. In this embodiment, the drill cuttings which arrive from off-shore are initially assayed for C:N:P ratio, total carbon content, water content, most probable number of degraded organisms and toxicity. Based on these measurements further components may be added to the drill cuttings from the hoppers 21 to 24 as required before the conveyor 20 delivers the treated drill cuttings to a hopper 28.

The treated drill cuttings are then delivered from the hopper 28 to biopiles (not shown) wherein the drill cuttings are bioremediated for six to twelve weeks at operational temperatures. During bioremediation, the contents of the biopiles are turned, usually about once every two weeks. During bioremediation, indigenous microorganisms and innoculum in the drill cuttings degrade hydrocarbons in the drill cuttings.

Referring now to Figure 3, the steam recovery system mentioned above is described in more detail in which parts similar to those described with reference to Fig. 2 are given the same reference numerals. In this system, extracted steam is first passed through a condenser 31 which is also connected to an activated carbon trap 30 for removal of volatile organic carbon. Condensate from the condenser 31 is optionally passed to a boiler 32 where the condensate is desalinated. The condensate is finally passed through a filtration unit 33 which removes particular matter prior to delivery of clean water to the low temperature steam generator 9. Although it is not illustrated in Fig. 2, the clean water can alternatively be delivered to a storage tank. Steam which condenses on the stainless steal conveyor 4 is collected in an oily water collection system 36 and delivered to a sump 37 for delivery to an oil water separator 40. Water which is separated in the separator 40 is delivered to the steam recovery system via the boiler 32, and the separated oil is delivered to the boiler 32.

Referring to Figs. 4 and 5, the relationship between bulk density of the drill cuttings, and % of hydrocarbons removed during steam treatment, is illustrated graphically with respect to light hydrocarbon fractions (Fig. 4) and all fractions (Fig. 5) . It has been dicsovered that a bulk density of between 1.0 and 1.2g/cm3 enables a cost effective level of bulking to be combined with enhanced remediation.

Referring to Figs. 6a and 6B, it can be seen that steam treatment according to the invention has the effect of removing a portion of the complete suite of drill cuttings present in the drill cuttings. It was predicted that only the light fractions would be removed, however, this has not proven to be the case.

Generally, the process described herein provides a means whereby drill cuttings (and other waste material) can be processed through a steam generator to drive off the mobile oil fractions and additionally condition the waste material for the performance of either indigenous microorganisms or subsequently added innoculum. The drill cuttings may then be optimised (if required) with respect to carbon to nitrogen to phosphorus ratios and optionally biopiled to support maximum biodegradation of organic pollutants in the cuttings over a six to 12 week period. Previous attempts to degrade organic pollutants in drill cuttings with inoculations of exogenous microorganisms have not been successful as the exogenous microoganisms do not prosper in the oily toxic environment of the drill cuttings, as they cannot degrade in the absence of water and oxygen. As mentioned previously, steam treatment has been found to effectively wet the waste material.

Although the process of the present invention is described almost exclusively with reference to drill cuttings, it is intended that the process may be applied to the treatment and decontamination of other waste materials including, for example, beach and harbour sediment produced as a result of oil spills and materials produced by the dredging industry. The invention is not limited to the embodiments hereinbefore described which may be varied without departing from the spirit of the invention.

Claims

1. A method of decontaminating drill cuttings comprising the step of passing steam through the drill cuttings.

2. A method as claimed in Claim 1 in which the steam-treated drill cuttings are bioremediated

3. A method as Claimed in Claim 2 in which the drill cuttings are bioremediated for a period of between 6 and 12 weeks .

4. A method as claimed in Claims 2 or 3 in which the the drill cuttings are bioremediated in biopiles.

5. A method as claimed in Claim 4 in which the biopiles are covered to retain moisture.

6. A method as claimed in any of Claim 2 to 6 in which the drill cuttings are aerated during bioremediation.

7. A method as claimed in any preceding Claim in which drill cuttings are placed on a platform such as a perforated conveyor and the steam is passed through the drill cuttings on the conveyor.

8. A method as claimed in Claim 7 in which the steam is passed through the conveyor and drill cuttings at pressure or under vacuum.

9. A method as claimed in any preceding Claim in which a C:N:P ratio of the drill cuttings is monitored at least once during the method and the ratio optionally altered to provide an optimum C:N:P ratio for microorganism activity.

10. A method as claimed in Claim 9 in which the ratio is in the range of 250:10:1 to 400:10:1.

11. A method as claimed in any of Claim 2 to 10 in which augmentation of the drill cuttings takes place after steam treatment and prior to bioremediation, during which the steam treated drill cuttings may be augmented with one or more of: a nitrogen source such as urea or ammonium nitrate; a phosphorus source such as ground rock phosphate or triple super phosphate; a bulking agent such as chipped wood; trace nutrients; and water.

12. A method as claimed in any of Claims 2 to 11 in which a microbial population of the drill cuttings is augmented with an innoculum of microorganisms.

13. A method as claimed in Claim 12 in which the innoculum is derived from one or more of hydrocarbon contaminated wastes such as soil, dredgings, drill cuttings, or drill cuttings which have been steam- treated and bioremediated according to the present invention.

14. A method as claimed in any preceding Claim in which a degradation potential of the drill cuttings is initially measured by means of a suitable assay.

15. A method as claimed in any preceding Claim in which steam which has been passed through the drill cuttings is extracted and treated to remove contaminants .

16. A method as claimed in Claim 15 in which the steam recovery system includes passing the steam through one or more of : an activated carbon trap to remove volatile organic carbon; a condenser; desalinating equipment; and a filter to remove particulate material.

17. A method as claimed in Claim 15 or 16 in which water produced in the steam recovery system is returned to the low temperature steam generator.

18. A method as claimed in any preceding Claim including a step of collecting oily water which drains from the drill cuttings, and separating oil from the water in a separator.

19. A method as claimed in Claim 18 in which recovered water is used to generate steam.

20. A method as claimed in Claim 18 or 19 in which recovered oil is returned to a steam generator.

21. A method as claimed in any preceding Claim in which the drill cuttings are initially aggregated.

22. A method as claimed in Claim 21 in which the drill cuttings are aggregated by means of a suitable aggregating agent.

23. A method as claimed in Claim 22 in which the aggregating agent is woodchip.

24. A method as claimed in any of Claims 21 to 23 in which the aggregating agent is added to the drill cuttings in an amount of between 10 and 30% (v/v) .

25. A method as claimed in any preceding Claim in which the drill cuttings are treated prior to steam treatment such that the bulk density of the cuttings is between 1.0 and 1.2 g/cm3.

26. An apparatus for decontamination of drill cuttings comprising a perforated conveyor and at least one steam generator adapted for passing steam through the perforated conveyor.

27. An apparatus as claimed in Claim 26 in which the steam generator is adapted for passing steam through the perforated conveyor under pressure.

28. An apparatus as claimed in Claim 26 to 27 including at least one steam treatment means comprising a vacuum pump adapted for extracting steam which has passed through the conveyor.

29. An apparatus as claimed in Claim 28 in which the steam treatment means further includes and one or more of : - an activated carbon trap adapted for removing volatile organic carbon; a condenser; desalinating means; and a filter adapted for removing particulate.

30. An apparatus as claimed in any of Claims 26 to 29 further including collection means adapted for collecting condensed oily water which drains from the conveyor.

31. Use of steam in the decontamination of drill cuttings .

32. Bioremediated material obtainable according to the process of any of Claims 2 to 24