GB2459776A

GB2459776A - Gelling drilling waste

Info

Publication number: GB2459776A
Application number: GB0907821A
Authority: GB
Inventors: Bruce Rae Ewen
Original assignee: SCOMI OILTOOLS
Current assignee: SCOMI OILTOOLS
Priority date: 2008-05-09
Filing date: 2009-05-06
Publication date: 2009-11-11
Anticipated expiration: 2029-05-06
Also published as: GB2459776B; GB0808473D0; GB0907821D0; GB2459776A9

Abstract

The invention concerns the treatment of drilling spoils so as to facilitate the storage and conveyance of the drilling waste to distant locations for disposal in accordance with industry regulations. The disclosure provides a method of treating oilfield drilling waste to facilitate the handling and transport thereof, the method comprising providing drilling waste by drilling an oil well bore using a drilling fluid, adding a gelling agent to the drilling waste and inducing the waste to gel as a semi-solid, thereby immobilising any solid cuttings as a suspension in the gel, the gelled waste being capable of reverting to a free flowing state when subjected to sufficient shearing. The gelling agent may be pseudo plastic liquid, typically comprising oil and an organoclay. The gelling agent composition is activated by shearing and heating of the composition above a threshold temperature.

Description

Treatment of cuttings from oil well drilling The present invention concerns the field of drilling oil wells, for example on offshore oilrigs. The invention particularly concerns the treatment of drilling spoils so as to facilitate the storage and conveyancing of the drilling waste to distant locations for disposal in accordance with industry regulations.

The drilling of well bores in oil fields is usually carried out by using a drilling fluid or mud to lubricate the drill work head and to remove drill cuttings to the surface. The drilling fluid also provides an hydraulic pressure balance which helps prevent the bore collapsing as well as preventing the ingress of pore fluid into the well bore. Drill cuttings are typically rock chips or other solids cut away during drilling.

Drilling fluids may be oil-based or aqueous. Often the oil-based fluids may be in the form of an inverted emulsion where oil is the continuous phase with an aqueous discontinuous dispersed phase. The cuttings are typically separated from the drilling fluid at the surface and the cuttings together with adhering drilling fluid may together be termed drilling waste.

The disposal of drill cuttings created by drilling a well bore is a significant consideration. Drill cuttings from of [shore oil rigs may not be discharged into the sea unless regulatory standards are met, for example the hydrocarbon (oil) content must be less than 1% by mass.

If the spoil does not reach the required low level of oil content, then alternative methods must be used to deal with the spoil. These methods include: 1) Processing the spoils at the rig site to reduce the proportion of oil.

2) Transporting the spoil from the rig site to shore-based processing plants where the oil may be separated from the cuttings and the cuttings disposed of in landfill.

3) The cuttings and drilling fluid are macerated and injected into sub-surface rock strata at the drilling site.

An alternative approach involves the use of oil-free aqueous drilling fluids so that oil is not present in the spoils and does not therefore have to be removed.

Frequently however oil based drilling fluids are preferred and must be used.

Transporting waste cuttings to shore-based processing plants is the most used solution for mobile drilling rig operations, and involves the ferrying of thousands of tonnes of drilling waste from rigs to land by means of ships.

The method typically involves filling multiple skips, each with a capacity of 4 to 5 tonnes and transferring the waste batch wise in the skips to an oilfield service vessel. As an average well would typically generate in excess of 1000 tonnes of oil-contaminated drilling waste, the transportation of waste to the shore is a major undertaking involving multiple skips, complex materials handling equipment, cranes and multiple sea journeys between the rig and shore. Material handling is necessary both from the rig to ship as well as from ship to shore-based storage vats.

Attempts have been made to simplify the transfer of drilling waste by pumping the waste from rig to ship via a flexible pipe, but with limited success. Problems arise because the waste can vary from being somewhat dry and having a high proportion of large particles (up to and beyond 25mm) to essentially liquid with very little solids content. This means that the waste can be difficult to pump reliably. For essentially dry drilling waste air driven pump systems have been used, but these typically are only capable of transferring about 40 tonnes per hour.

Quite apart from the transfer problem, cuttings tend to consolidate during storage, either in tanks on the rig before transfer, or in the skips at sea during transfer.

These cuttings become compacted as layers in the storage vessels so that it is then difficult to remove from the tanks or vessels, especially by means of a pump. This applies to waste stored on the rig, shore or in skips as the waste is ferried. Cuttings compaction and solidification can also result in difficulty in emptying skips by inversion. Compaction can be such that when a skip is turned upside down, the cuttings remain immobile.

There is therefore a need for a method of improving the ease with which drill waste may be handled and transferred back to shore.

GB-A-2 330 600 (Bailey) discloses in general terms a method for transporting oily drill cuttings in which the drill cuttings are mixed with a mud-based thixotropic carrier fluid to form a slurry. Agitation means are provided to keep the solids in suspension. The slurry is transported to the shore from a marine well site for treatment ashore. No specific details are given in relation to the composition of the carrier fluids, or what agitation means should be used.

The present invention seeks to address the problem of transporting oil field cuttings and to provide a method of treating cuttings which render them more easily

transportable.

According to one aspect of the invention there is provided a method of treating oilfield drilling cuttings to facilitate the handling and transport thereof, the method comprising providing drilling waste by drilling an oil well bore using a drilling fluid, adding a gelling agent to the drilling cuttings and inducing or allowing the waste to gel as a semi-solid, thereby immobilising any solid cuttings as a suspension in the gel, the gelled waste being capable of reverting to a free flowing state when subjected to sufficient shearing, wherein the gelling agent is pre-treated by shearing and heating to a temperature level which activates the gelling ability of the liquid.

According to another aspect of the invention there is provided a method of treating oilfield drilling cuttings to facilitate the handling and transport thereof, the method comprising providing drilling cuttings by drilling an oil well bore using a drilling fluid, adding a gelling agent composition to the drilling waste and inducing or allowing the waste to gel as a semi-solid, thereby imrnobilising any solid cuttings as a suspension in the gel, the gelled waste being capable of reverting to a free flowing state when subjected to sufficient shearing, wherein the drilling cuttings and gelling agent composition are treated by shearing and heating to a temperature level which activates the gelling ability of the liquid thereby to induce gelling.

The methods hereinbefore described provide a generally stable gel in which are immobilised and dispersed cuttings solids. Thus the prior art requirement for continuous agitation, per Bailey, is avoided. In addition the gel may be disrupted by shearing, with then renders the gel into flowable liquid. This considerably improves handling of cuttings waste as it allows easy discharging of the cuttings by pumping from a storage vessel.

Suitable gelling agent compositions include liquids which are pseudoplastic in nature. The required functionality is that the viscosity should be low under shear conditions so that the mixture can readily flow, but the viscosity should rise in the absence of shear so that the immobile liquid gels as a semi-solid. Such liquids may also be termed thixotropic although strictly speaking these liquids have a viscosity which reduces over time under a constant shear rate, whereas a pseudo plastic material has a viscosity which reduces in response to an increasing applied shear. Pseudoplastic materials may also be termed "shear thinning" materials.

The gelling agent is typically a pseudoplastic liquid which may conveniently comprise an organophillic clay, such as dimethyl dihydrogenated tallow arnmoniuin bentonite amongst others. Organoclays are already part of typical drilling fluid formulations, so their presence creates no regulatory or contamination problems. Their function in drilling fluids is to increase viscosity by similar interaction but their gelling potential is inhibited by the presence of surfactants in oil based drilling fluids.

Moreover, high gelling character is generally undesirable in drilling fluids. Hence drilling fluids would not gel to a semi-solid state when not under shear.

The pseudo-plastic liquid preferably further comprises oil. The oil may be a mineral base oil. Some suitable mineral oils are those which have a boiling temperature of about 200 to 250 Centigrade.

The pseudo-plastic liquid may further comprise an activator such as water, typically added in small amounts, such as less than 2% and preferably about 1%.

This is added as a thixotropic activation agent which interacts with the organo-clay to induce gelling. Other suitable agents will be known to the skilled person. One is propylene carbonate.

Thus the pseudo-plastic liquid may have a similar composition to a conventional oil-based drilling fluid.

To activate the gelling agent it is necessary to provide a mixing and heating step. Thus in one aspect of the invention there is provided a method wherein the gelling agent is pre-treated by shearing and heating to a level which activates the gelling ability of the liquid. In the case of an organo-clay the heating may be up to above a threshold temperature. The threshold temperature is typically 40 degrees Centigrade. In one embodiment a target temperature is 75 degrees Centigrade. The heating and shearing step can be conducted after mixing of the gelling agent with the cuttings, although the energy required to heat and mix will be considerably higher than if the gelling agent composition is activated before it is added to the cuttings.

In yet another aspect of the invention there is provided treated oilfield drill cuttings obtainable by the methods as hereinbefore described.

According to yet another aspect of the invention there is provided a gelling agent composition for use in treating oil field cuttings to facilitate transport thereof, obtainable by providing liquid oil and admixing a gelling agent, heating and shearing the mixture above a threshold activation temperature so as to activate the gelling ability of the mixture.

The gelling agent composition may comprise an organo-clay in a weight amount that is less than lOOg per litre of oil. An amount of water activator added to the composition is preferably less than 2 wt%.

In a further aspect of the invention, there is provided a method of conveying drilling waste comprising providing treated drilling cuttings obtained by a method as hereinbefore described, optionally storing the treated waste, and then transferring the cuttings to a distal location by a method which involves shearing the waste so as to permit flow of the waste through a conduit to the distal location.

The distal location may be a seagoing vessel, such as a ship or boat. Alternatively the location may be a shore-based waste processing plant. The conduit may be a flexible pipe which provides liquid communication with a sea going vessel, or it may be a pipeline communicating directly with the shore. The shearing may be provided by mechanical working such as mixing. However, preferably, the shearing is provided by the action of a pump to displace the gelled drilling waste and cause it to flow.

Distal locations can include both an intermediate transportation means (such as a boat/ship or land vehicle such as a train or lorry) as well as a cuttings treatment site. The treated cuttings can then be further transported for treatment at thermal plants where the oil is desorbed prior to cuttings disposal in a landfill or other dispersal site.

Any solid cuttings present in the treated cuttings may during subsequent processing be separated from the waste.

To do this a standard shale shaker may be used to provide the shear necessary for the gelling agent to flow away and allow the collection of solids from the shaker screen. The remaining cuttings will typically comprise oil and organo-clay, thus being suitable f or re-use as a gelling agent, or for use as a drilling fluid/mud. So the waste liquid may be re-used and effectively acts as a re-useable carrier for transfer of solid cuttings.

Following is a description by way of example only and with reference to the figures of the drawings of one method of putting the present invention into effect.

In the drawings: Figure 1 is a series of photographs which show the effect of increased organo clay loading on the appearance of the pseudo-plastic liquid.

Figure 2 is a graph showing the pseudo plastic behaviour of one pseudo-plastic liquid composition according to the invention at three different shear rates.

Figure 3 is a photograph of a tub containing waste cuttings before treatment.

Figure 4 is a photograph of one jar containing raw waste cuttings and another jar containing a combination of cuttings and pseudo-plastic gelling agent.

Figure 5 shows one jar having separated drill cuttings and one jar with separated pseudo-plastic liquid.

Specific embodiment A liquid pseudo-plastic gelling agent is prepared as follows: An organophillic clay (dimethyl dihydrogenated tallow ammoniuxn bentonite) is added to mineral base oil in an amount of 60g per litre of oil. The combination is mixed thoroughly. ithout 1 wt% water is added as an activator.

The mixture is sheared by mixing and heated to 75 degrees centigrade which causes the viscosity to increase markedly and irnmobilise as a soft gel which, in the absence of shearing, will not readily flow.

Figure 1 shows three beakers each filled with gelling agent having different organoclay loadings. From left to right the loading varies from 43 to 86 gIL. The higher the loading the more viscous the liquid. The liquid needs to be viscous enough to hold the waste cuttings in suspension without significant settling over time. The liquid also needs to maintain its pseudo-plastic properties so that flow is possible. Figure 2 shows the pseudo plastic behaviour of a typical liquid according to the invention.

The liquid gelling agent is then added to drilling waste derived from well bore drilling. The amount of gelling agent added can vary according to the characteristics of the cuttings in the drilling waste, which will in turn depend upon the geology of the well site. However the amount of liquid gelling agent added to the drilling waste will typically be, by volume, less than the amount of drilling waste.

Once gelling agent has been added the combination is mixed so that the cuttings are distributed as a suspension in the gelling agent. This prevents the cuttings from settling and consolidating, either during storage at the rig or during transit. At the rig, the stabilised waste is stored in a large container ready for transfer to a ship for ferrying to the shore.

The gelled cuttings can optionally be lightly mixed by a mixing auger to improve homogeneity in the gel.

When it is desired to move the stabilised drilling waste a conventional progressive cavity pump is used to drain the container and convey the waste to a waiting ship via a flexible pipeline. The shearing of the waste induced during pumping is enough to reduce its viscosity, so that the waste readily flows through the pipeline. Once in a container in the ship the shearing is absent and the waste reverts to the stabilised gel form and the suspension of cuttings is maintained without settling of the cuttings. The waste may then, on arrival at a shore-based facility, be pumped out of the ship to a storage container on shore. Pump rates of 200 tonnes per hour may be obtained, and in certain circumstances up to 500 tonnes per hour can be attained. This represents a significant improvement over batchwise skip transfer or

air driven pumping of the prior art.

When it is desired to treat the waste to remove solid cuttings, the stabilised waste is pumped to a standard oilfield shale shaker. The shaking causes shearing of the cuttings mixture and thereby causes the viscosity of the gelling agent to fall rapidly so that it may flow away and be collected from under the shaker. The shaker screen (in one example with a 100 micron standard sieve) collects the cuttings which comprise particles of rock removed during drilling. These may be processed to remove the oil by thermal desorption and the solids subsequently disposed of in landfill. The collected liquid gelling agent may be contaminated with drilling fluid, but since this typically includes mineral oil and organoclay, there is no incompatibility. In fact the gelling agent may be re-used -either as a gelling agent or as a drilling fluid itself. Figure 3 shows two beakers -one on the left hand side containing cuttings from the 100 micron screen and the beaker of the right hand side holding gelling liquid collected from under the shaker screen.

The present invention allows drilling waste to be transferred efficiently from a rig site for disposal in accordance with industry regulations. The invention is counter-intuitive because it relies upon adding a further notional contaminant to the waste (including oil in certain embodiments). However, by taking advantage of a thixotropic effect the liquid gelling agent as well as residual drilling fluid, may be easily separated from the solid cuttings. An environmental advantage arises from re-use of the carrier liquid as outlined above.

In surrimary, the invention particularly concerns the treatment of drilling spoils so as to facilitate the storage and conveyancing of the drilling waste to distant locations for disposal in accordance with industry regulations. The disclosure provides a method of treating oilfield drilling cuttings to facilitate the handling and transport thereof, the method comprising providing drilling cuttings by drilling an oil well bore using a drilling fluid, adding a pre-activated liquid gel to the drilling waste thus transforming it to a semi-solid, thereby irnrnobilising any solid cuttings as a suspension in the gel, the gelled waste being capable of reverting to a free flowing state when subjected to sufficient shearing. The gelling agent may be pseudo plastic liquid, typically comprising oil and an organo-clay. The gelling agent composition is activated by shearing and heating of the composition above a threshold temperature.

Claims

Claims 1. A method of treating oilfield drilling cuttings to facilitate the handling arid transport thereof, the method comprising providing drilling waste by drilling an oil well bore using a drilling fluid, adding a gelling agent composition to the drilling cuttings and inducing or allowing the waste to gel as a semi-solid, thereby immobilising any solid cuttings as a suspension in the gel, the gelled waste being capable of reverting to a free flowing state when subjected to sufficient shearing, wherein the gelling agent composition is pre-treated by shearing and heating to a temperature level which activates the gelling ability of the liquid.
2. A method of treating oilfield drilling cuttings to facilitate the handling and transport thereof, the method comprising providing drilling cuttings by drilling an oil well bore using a drilling fluid, adding a gelling agent composition to the drilling waste and inducing or allowing the waste to gel as a semi-solid, thereby imrnobilising any solid cuttings as a suspension in the gel, the gelled waste being capable of reverting to a free flowing state when subjected to sufficient shearing, wherein the drilling cuttings and gelling agent composition mixture is treated by shearing and heating to a temperature level which activates the gelling ability of the liquid thereby to induce gelling.
3. A method as claimed in claim 1 or claim 2 wherein the temperature of heating is 40C or greater.
4. A method as claimed in any preceding claim wherein the gelling agent composition is a pseudo-plastic liquid.
5. A method as claimed in any preceding claim wherein the gelling agent comprises an organophillic clay.6. A method as claimed in claim 5 or claim 6 wherein the organophillic clay is dimethyl dihydrogenated tallow arnmonium bentonite.
6. A method as claimed in any preceding claim wherein the gelling agent composition further comprises oil.
7. A method as claimed in claim 7 wherein the oil is a mineral based oil.
8. A method as claimed in any of claims 2 to 6 wherein the gelling agent composition further comprises a thixotropic activation agent, such as water or propylene carbonate.
9. A method as claimed in any preceding claim wherein the drilling fluid is an oil-based drilling fluid.
10. Treated oilfield drilling cuttings obtainable by the method of any of claims 1 to 9.
11. A method of conveying drilling cuttings comprising providing treated drilling cuttings by a method according to any of claims 1 to 9, optionally storing the treated waste, and then transferring the waste to a distal location by a method which involves shearing the waste so as to permit flow of the waste through a conduit to the distal location.
12. A method as claimed in claim 11 wherein the distal location is a seagoing vessel or a shore-based waste processing plant.
13. A method as claimed in claim 11 or claim 12 wherein the shearing to induce flow comprises pumping of the treated waste.
14. A method as claimed in any of claims 10 to 12 wherein at least a portion of the solids in the cuttings is subsequently separated from the cuttings.
15. A method as claimed in claim 14 wherein the solids are separated by sieving so that solids above a threshold size are separated.
16. A method as claimed in claim 14 or claim 15 wherein after separation of the solids the remaining liquid portion is re-used as a gelling agent composition.
17. A method as claimed in claim 14 or 15 wherein after separation of the solids the remaining liquid portion is conveyed to a drilling site for use as an oil-based drilling fluid.
18. A gelling agent composition for use in treating oilfield cuttings to facilitate transport thereof,obtainable by providing liquid oil and amixing a gelling agent, heating and shearing the mixture above a threshold activation temperature so as to activate the gelling ability of the mixture.
19. A gelling agent composition as claimed in claim 18 wherein the gelling agent is an organophillic clay.
20. A gelling agent as claimed in claim 18 or claim 19 further comprises an activator such as water or propylene carbonate.
21. A gelling agent composition as claimed in claim 19 or claim 20 wherein the amount of organo-clay is less than bOg per litre of oil.
22. A gelling agent composition as claimed in claim 20 or claim 21 wherein the amount of activator is less than 2 wt%.