A mobile drilling mud cleaning unit

Abstract

A mobile drilling mud cleaning system 1 which is provided with an optimised mud processing capacity whilst at the same time retaining its manoeuvrability. The system is provided with an electrically operated mud treatment apparatus 7 configured to extract contaminants. The apparatus having a vibrating screen separator 15, cyclonic separator 14 and mud pumping means. A pair of mud storage tanks 16 / 17 is mounted on a chassis 2 with a continuous track-based propulsion means 3 that is powered by an on-board power source 4. The mud treatment apparatus is configured to receive electrical power from an external, off-board power supply that is distinct from the on-board power source. There may be extendable stabilising legs 20 and retractable gangways 19.

Description

Field of the Invention The present invention relates to the technology field of on-site drilling mud treatment and in particular a mobile drilling mud cleaning device for processing used drilling mud to remove contaminants so that the drilling mud can be re-used again in drilling operations. Background of the Invention In some drilling operations it is a requirement to use fluid to bring the geological strata (e.g. clay, silt, sand, rock, etc...) through which a drilling tool passes, typically referred to as ‘cuttings’, up to ground level. In addition these fluids, which come in a range of specifications and are generally known as drilling muds, also work to lubricate and cool the drilling tool as it cuts through the subterranean geological formations. The drilling mud can also consolidate the strata surrounding the borehole. During drilling operations drilling mud is pumped down hole to the drilling tool and then recirculated back out of the borehole carrying the cuttings with it. As drilling muds can be expensive to purchase (and also dispose of), during ongoing drilling operations it is common practice to treat and clean used drilling muds so that they can be re-used repeatedly. Essentially used drilling muds need to be filtered and cleaned in order to remove the cuttings carried away from the cutting edge of the drilling tool by the drilling mud. It is established drilling industry practice to deploy drilling mud cleaning systems on the site of ongoing drilling operations so that the drilling mud employed in the drilling work can be used, cleaned and re-used multiple times. Due to the large volumes of drilling mud required (e.g. up to 3m3 of mud per minute of drilling) drilling mud cleaning systems need to have large throughput capacities. As a consequence, drilling projects with high drilling mud requirements require the deployment of static mud cleaning equipment, which can comprise multiple tanks and have a large footprint. Such systems are bulky and have substantial weight which means that they require the use of cranes to position them on site at a drilling location. Once in position on site, these drilling mud cleaning systems are connected to active drilling operations by way of extensive pipe runs that traverse the site. Although the use of large capacity mud cleaning systems is highly beneficial from the point of view of maintaining a steady flow of cleaned drilling mud, their static nature and their reliance on an extensive pipe network to connect them to the various boreholes can obstruct other operations on site. In view of this, mobile mud cleaning systems have been developed. These mobile mud cleaning systems provide much greater flexibility in terms of positioning. They can be moved to operate on different boreholes on a particular drilling site, as well as having a much smaller footprint. However, as a consequence, they have reduced throughput capacities. This is because these mobile systems cannot accommodate as much mud treatment apparatus as the larger, static systems. The reduced treatment rate of existing mobile drilling mud cleaning systems means that, at times, they cannot keep up with the rate at which used drilling muds are generated by the drilling operations active at any one time on a drill site. As a result, sites being serviced by mobile drilling mud cleaning systems are often subject to periodic drilling shutdowns in order to enable the backlog of contaminated drilling mud to be processed. At present, therefore, site operators are required to choose whether their most important requirement is the rate at which drilling muds can be cleaned for re-use or the mobility / flexibility of the drilling mud cleaning system. Summary of the Invention In order to address the issues relating to on-site drilling mud treatment the present invention provides a mobile drilling mud cleaning system according to claim 1. In this regard the mobile drilling mud cleaning system comprises an electrically operated mud treatment apparatus configured to extract contaminants from drilling mud so that such can be re-used, said apparatus having at least one vibrating screen separator, at least one cyclonic separator and mud pumping means; a pair of mud storage tanks, the first tank being configured to receive and store contaminated drilling mud and the second tank being configured to receive and store cleaned drilling mud; wherein the apparatus and the mud storage tanks are mounted on a chassis with a continuous track based propulsion means that is powered by an onboard power source; and wherein the mud treatment apparatus is configured to receive electrical power from an external, off-board power supply that is distinct from the on-board power source. In existing mobile drilling mud cleaning systems the mud treatment apparatus and the propulsion means are driven by a common power source, which typically takes the form of an on-board diesel engine. As such, the diesel engine is operated not only when the mud cleaning system is propelled from one location to another on site but also when the mud treatment apparatus is in operation. As a result the engine can be operated almost non-stop throughout the working day. This increases the carbon footprint of the mud cleaning system unnecessarily as the energy requirement for cleaning the drilling mud is far less than the energy required for propulsion. In addition to the inevitable maintenance challenges, this need to run the diesel engine continuously during operations requires the system to be provided with a substantial on-board fuel storage tank capable of housing sufficient fuel to keep the engine running for a required operating period. By way of the system of the present invention the inventor has sort to reduce the reliance on a single on-board internal combustion engine power source by adopting a twin-power source arrangement in which the mud cleaning apparatus is powered by a separate off-board power supply rather than the on-board power source. In particular, rather than drawing power from a generator driven by an on-board diesel engine, the drilling mud treatment apparatus is configured to receive electricity from a separate electrical power source, which may be a stand-alone portable generator with a much lower power output than an on-board propulsion diesel engine or a direct electrical mains supply that could be fed from a renewable energy source, thereby reducing the carbon impact of the drilling operation. The inventor has determined that, as the various components of the drilling mud treatment apparatus (e.g. vibrating screen separator, cyclonic separator, pumping means) have much lower power requirements than the continuous track based propulsion means used to move the system around, it is much more efficient to employ an alternative off-board power source to run the electrically operated apparatus. By using an alternative off-board power source during the general operation of the drilling mud treatment apparatus it is possible to greatly reduce the size of the on board power source. The on-board power source could preferably take the form of an internal combustion engine with an associate fuel tank or alternatively an electric motor driven by at least one battery could be employed to achieve further environmental benefits. It is envisaged that in both preferred forms of on-board power source, the use of the alternative off-board power source for the drilling mud treatment facilitates a reduction in the size of the on-board power source. In the case of an internal combustion engine power source (i.e. a diesel engine) the size reduction is achieved by using a smaller fuel tank, whereas, in the case of the electric motor arrangement, a size reduction is achieved by employing a smaller battery or batteries. This reduction in the space required for the on board power source frees up space aboard the chassis of the system of the present invention to accommodate drilling mud treatment apparatus with an increased throughput capacity. As a consequence, the mobile drilling mud cleaning system achieves the benefits of a greatly reduced footprint (i.e. on-site flexibility) whilst at the same time retaining the ability to clean drilling muds at a high treatment rate. Preferably the maximum capacity of the on-board fuel tank is 70 litres. Although it is envisioned that fuel tanks with smaller storage capacities could be employed due to the fact that the on-board engine is only required infrequently, a 70 litre capacity is considered to represent the maximum capacity and smaller capacities are preferred. Preferably the mud storage tanks may provide an operating platform that supports one or more mud treatment apparatus components selected from: vibrating screen separator, cyclonic separator and pumping means. By essentially stacking at least part of the mud treatment apparatus on top of the mud storage tanks, which typically have large volumes, it is possible to optimise the use of the limited space provided on the system’s chassis. This, in turn, enables the overall footprint of the mobile system to be kept to a minimum without having to sacrifice the throughput capacity of the drilling mud treatment apparatus. Further preferably a portion of the operating platform may comprise a personnel deck which, in use, enables operator access to the mud treatment apparatus. Once again, it will be appreciated that by using the system’s mud storage tanks to support a platform it is possible to optimise the operational benefits of the system. Preferably the system may further comprise at least one chassis mounted retractable gangway that runs adjacent to storage tanks and, in use, enables operator access to the mud treatment apparatus, mud storage tanks and / or the internal combustion engine. By way of the retractable gangways, which can be stowed away when the system is being moved from one location to another, operators of the system can have full access to the various components of the system during the normal day to day running of the system without sacrificing the manoeuvrability of the system when the time comes to relocate it. Preferably the system may further comprise a set of retractable stabilizing legs mounted on the chassis. The stabilizing legs help to ensure the system retains a stable footing, particularly when the gangways are extended away from the main body of the system. Preferably the mud treatment apparatus may comprise a pair of vibrating screen separators. The provision of multiple vibrating screen separators, which is made possible at least by the reduced size of the on board power source, helps to deliver a greater throughput of drilling mud through the mud treatment apparatus. Each vibrating screen separator comprises twin mesh screens arranged one above the other. Further preferably each vibrating screen separator may co-operate with a separate cyclonic separator array. Once again, this facilitates the provision of a greater rate of throughput through the apparatus. In addition, providing the vibrating screen separators and cyclonic separator arrays in pairs means that they can be operated independently of one another, which provides greater operational flexibility. For example, having two separate treatment pathways in the system means that one pathway can continue to operate even when the other is off-line for maintenance. Brief Description of the Drawings The present invention will now be described with reference to the preferred embodiment shown in the drawings, wherein: Figure 1 shows a front perspective view of a preferred embodiment of the mobile drilling mud cleaning system of the present invention in a ‘transit’ mode; Figure 2 shows a side view of the mobile drilling mud cleaning system shown in Figure 1; Figure 3 shows a front perspective view of the preferred embodiment of the mobile drilling mud cleaning system of the present invention in an 'operation' mode; and Figure 4 shows a rear perspective view of the mobile drilling mud cleaning system shown in Figure 3. Detailed Description of the Preferred Embodiment It is known to process drilling mud to remove contaminants, such as cuttings brought up from a borehole by the drilling mud, so that the mud can be recycled and used again, as are the processes and separation apparatus typically used to extract the contaminants. The recycling of drilling mud is commonly carried out on the same site as the drilling is taking place so as to keep transport and storage costs to a minimum. It is will be appreciated that, if it is possible to re-use a quantity of drilling mud multiple times by simply cleaning it to extract the contaminants that accumulate therein, the operator of the drilling site can make more efficient use of, what is, a bulk material. At present, this process of cleaning drilling mud is typically carried out using static machines capable of processing a high volume of mud in a relatively short period of time. These machines employ vibrating shaker screens to separate out large contaminants from the used drilling mud. Once the larger contaminants have been removed and disposed of, cyclonic separation is used to separate out smaller contaminant particles from the drilling mud to make it suitable for re-use in a drilling operation. Although the high processing capacity of static drilling mud recycling machines is highly desirable, the size and scale of these machines means that they can only usually be moved using cranes and other specialist moving equipment. As a result, these machines are usually only placed on-site once after which they are connected to each drill location in turn via an extensive pipe network that transports the drilling mud to and from the machine. The need to run pipework around an active site causes obstructions that can impact the efficient working of the site. In the light of the problems associated with these bulky static drilling mud recycling systems, mobile drilling mud recycling systems have been developed. These mobile units have the advantage that they are relatively quick and easy to redeploy around a site to better service different drill locations without the need for extensive pipework being trailed across the site. As with the static drilling mud recycling systems these mobile units also employ shaker screens and cyclonic separation to extract contaminants (i.e. cuttings) from the drilling mud so that it can be re-used. Unfortunately, as a result of the trade-off between their size (and thus mobility) and the amount of on-board mud processing apparatus that can be accommodated, mobile drilling mud recycling machines have much lower processing speeds that their large static counterparts. As a result, during intensive drilling operations, it is often necessary to pause drilling to enable the build-up of contaminated drilling mud to be processed. This can lead to unnecessary delays on site. The mobile drilling mud cleaning systems of the present invention seek to strike a better balance between the flexibility of existing mobile units and the processing power of the larger static machines as well as reducing the environmental impact. As such, it will be appreciated that a number of the separation processes and apparatus employed by the systems of the present invention are similar to those already in use. Turning now to Figures 1 to 4, the preferred embodiment of the present invention will now be described. Figures 1 and 2 show the mobile drilling mud cleaning system of the present invention in a ‘transit’ mode, whereas Figures 3 and 4 show the system in an ‘operation’ mode. Common reference numbers are used throughout to help identify their status in both the ‘transit’ and ‘operation’ modes. As will be appreciated from at least Figure 1, the mobile drilling mud cleaning system 1 essentially comprises a chassis 2 mounted upon a continuous track based propulsion means 3, which is provided with a pair of tracks running in parallel along the length of the system 1. The continuous track based propulsion means 3 spreads the weight of the chassis 2 and the rest of the system’s components mounted thereon. The propulsion means 3 are driven using an on-board internal combustion engine 4, which is preferable a diesel engine and further preferably a tier 5 diesel engine. The fuel for the internal combustion engine 4 is supplied by an on-board fuel storage tank 5, which is mounted adjacent the engine 4 on the chassis 2. In contrast to existing mobile drilling mud recycling units, which rely on the power from an on-board diesel engine to drive both the propulsion system and the mud cleaning apparatus, the engine 4 provided on board the system 1 of the present invention is provided primarily to power the propulsion means 3. However, it is envisaged that the on-board power source, which in this embodiment is an engine, could also be used to power other infrequently used components that do not form part of the cleaning apparatus (e.g. retractable stabilising legs 20) In view of this, it is envisaged that the engine 4 will generally be operated infrequently, because the propulsion means are only required when the system needs to be moved from one location to another. By removing the need to operate the engine 4 for extended periods of time (i.e. both during transit and during cleaning operations), it has been discovered that it is possible to greatly reduce the size of the on-board fuel tank without impacting the mud cleaning operations of the system. By reducing the size of its on-board fuel tank 5, the inventor of the present invention has been able to accommodate additional and / or larger mud cleaning components on the chassis 2 of the mobile system 1, thereby achieving great processing capacity than might otherwise have been possible using existing mobile units with their similar footprints. The drilling mud cleaning apparatus 7 is provided on top of the twin storage tank housing 6, which is in turn mounted on the chassis 2 of the system 1. This arrangement is considered particularly preferable because it optimises the use of the limited floor space available on the chassis 2. As is best appreciated from the side view shown in Figure 2, the twin mud storage tank housing 6 comprises a first storage tank 16, which receives and stores contaminated drilling mud, and a second storage tank 17, which receives and stores cleaned drilling mud. The two distinct storage tanks 16, 17 are defined by way of an inclined internal partition within the twin mud storage tank housing 6, which is represented diagrammatically by a dashed line in Figures 2 and 4. The first tank 16 is positioned towards the rear of the housing 6 such that it is positioned below the mud cleaning apparatus 7, whereas the second tank 17 is positioned towards the front of the housing 6. The area above the second tank is provided with a platform that provides user access to the mud cleaning apparatus 7. The system 1 is provided with a network of conduits that transport the drilling mud between the twin mud storage tank housing 6 and the various components of mud cleaning apparatus 7. With reference to Figure 1, the conduits are identified as follows. Inlet conduit 8 is configured to be connected to the source of used drilling mud (i.e. drilling site). This inlet conduit 8 is connected in fluid communication with the twin contaminated mud supply conduits 9, which deliver the used drilling mud to the vibrating screen separators 15 positioned above the twin storage tank housing 6. Used drilling mud from mud supply conduit 9 is dispersed onto the lower screen 15a of the vibrating screen separator using a spreader plate. The lower screen 15a, which is inclined upwards towards the back of the system 1, comprises a mesh configured to filter out the larger cuttings held in the used drilling mud. As the lower screen 15a is vibrated the mud and the smaller contaminants (e.g. sand particles) pass through the mesh and fall into the first mud storage tank 16, which is arranged directly below the vibrating screen separators 15. Those contaminants that are too large to pass through the mesh of the lower vibrating screen 15a travel up the incline and eventually drop off the system into a waiting receptacle (not shown) via chute 18. The partially cleaned mud held in the first mud storage tank 16 is then pumped via the twin secondary mud supply conduits 10 to an array of cyclonic separation units 14 (e.g. four are provided for each vibrating screen separators in the preferred embodiment shown). The cyclonic separation units 14 are positioned above the vibrating screen separators 15 so that they can discharge onto the upper screen 15b thereof. Within the cyclonic separation units 14 the partially cleaning mud is further cleaned by removing the remaining smaller contaminant particles (e.g. sand). Each separation unit 14 is provided with two outlets, wherein the majority of the cleaned mud is discharged via the first outlets and the contaminant particles (and possibly some mud) are discharged via the second outlets. The contaminant particles and mud discharged from the second outlets of the cyclonic separation units falls on to the upper vibrating screen 15b, which is inclined upwards towards the back of the system and comprises a smaller mesh than the lower screen 15a. As with the lower vibrating screen 15a, the mud and contaminants either fall through the mesh or travel along the upper vibrating screen 15b and drop off the system 1 into a waiting receptacle (not shown) via chute 18. The material that falls though the upper screen 15b also passes through the lower screen 15a, which has a larger mesh, and returns to the first storage tank 16 so that it can be processed again. The cleaned mud discharged by the cyclonic separation units feeds into twin cleaned mud conduits 11, which delivers the mud to the second storage tank 17. The outlet conduit 12 of the system 1 is connected to the second storage tank 17 so that the drilling mud cleaned by the system is drawn by a pump on the drilling rig for re-use. In addition to the mud cleaning apparatus 7, the system 1 is also provided with a mud mixing hopper 13 which facilitates the blending of drilling mud materials. The hopper 13 is provided in fluid communication with the second mud storage tank 17 so that an operator can not only supplement the cleaned mud held on board the system 1 but can also use the system 1 to mix up the drilling mud prior to the start of a drilling operation. It will be appreciated that on-board pumping means (not shown) are provided to facilitate the movement of the mud, in its various states, around the system 1. As explained above, the mud cleaning apparatus 7 of the system 1 of the preferred embodiment is arranged as a pair of self-contained operational units, with each unit comprising its own vibrating screen separators 15, cyclonic separators 14 and conduit network 9, 10, 11. Although not essential (a single larger unit could be employed without departing from the general inventive concept), this arrangement of paired units is considered beneficial because it allows for the units to be operated either in unison or in isolation. For example, one unit could be operated on its own if the other unit were to be undergoing maintenance. Another example would be when the required rate of mud cleaning was reduced, at which time running a single unit may be sufficient. As noted above, the preferred embodiment of the present invention is provided with the ability to transform between a ‘transit’ mode, which is optimised from movement around a drilling site, and an ‘operation’ mode, which is optimised for the system’s main function of processing drilling mud. The transforming function of the system 1 is best appreciated from Figures 1 and 3, which show the system in its two modes from the same view point. As a first point it will be appreciated that chute 18, via which extracted contaminants are discharged from the system into a suitable receptacle (not shown), is mounted on the back of twin storage tank housing 6 by way of hinging means so that it can be folded back against the housing when the system is in the ‘transit’ mode. In this way the manoeuvrability of the system is improved. The system 1 is also provided with retractable gangways 19 that run along its length from front to back and provide a walkway for operators to use whilst accessing the various areas of the system 1. Once again, the retractable gangways are mounted via hinging means, this time to the chassis 2, so that they can be folded back against the sides of the system 1 when it enters into the ‘transit’ mode. The gangways 19 are preferably provided with safety rails and an access ladder. The system 1 is also provided with a plurality of stabilizing legs 20, which a configured to extend down from at least the corners of the chassis 2 to engage the ground increase the stability of the system overall while it is in use. Various mechanisms for extending and retracting the stabilizing legs 20 will be readily appreciated by the skilled person. The system 1 is also provided with a lighting mast 21, which can be extended when in the ‘operation’ mode and retracted when in the ‘transit’ mode. It is envisioned that the actuation of the various retractable components (i.e. chute 18, gangway 19, legs 20 and mast 21) could be powered. In this regard, as these components are only required either immediately before or after the propulsion means is used it is considered preferable that the on-board engine 4 could also be used to power their actuation. In contrast to existing mobile units, the various components of the drilling mud cleaning apparatus 7 (i.e. the vibrating screen separator and the cyclones) and the pumps are not powered by the on-board diesel generator / engine. Instead, these components are configured to draw their power from an off-board electrical power supply. This may take the form of a portable generator or simply the mains power supply. It has been discovered that, because the power levels required to operate the various components of the drilling mud cleaning apparatus is much less than the power output of the on-board internal combustion engines of existing mobile mud cleaning units, the mud cleaning function of the mobile mud cleaning system of the present invention can be delivered by using a separate, lower power energy source. By using separate power sources for the mobile unit’s propulsion system and the mobile unit’s mud treatment apparatus, that is, by adopting a twin-power source arrangement, it has been possible to greatly reduce the size of the on-board fuel tank of the on-board internal combustion power source and thereby free up more space for the mud treatment apparatus. As the on-board generator / engine of the mobile system of the present invention is only required infrequently (i.e. when the system is in transit or possibly transforming between modes) the system can not only be operated more efficiently, but also in a more environmentally friendly manner. In this regard, it is appreciated that the not only does the use of smaller portable generator to power the mud cleaning apparatus reduce the level of exhaust gases being created, but it also reduces the level of noise pollution being generated. Indeed, in those embodiments where the apparatus can be connected to the mains power, this local pollution can be almost completely eliminated. This is considered highly desirable to personnel working in close proximity to the mobile drilling mud cleaning system of the present invention. Although the on-board power source employed in the preferred embodiment of the invention shown in the Figures takes the form of an internal combustion engine (e.g. diesel engine), it is envisaged that the in an alternative embodiment the on-board power source may be provided in the form of an electric motor with an associated battery. In this regard it is should be appreciated that, with the exception of the engine and its associated fuel tank, all of the above described features could also be adopted in a mobile drilling mud cleaning system that employs an electric motor as its on-board power source. In this alternative embodiment, the electric motor can drive the propulsion system directly or use an electrically driven hydraulic pump to drive the propulsion system. In that format the unit could be run entirely from a renewable energy source via the mains grid supply and self-contained rechargeable battery. In addition this again reduces the carbon footprint, direct exhaust emissions and noise. It will be appreciated that just as the size of the fuel tank required to supply the engine can be reduced, so too can the battery required to supply the electric motor. 5 As a result in both embodiments additional space is freed up to accommodate drilling mud cleaning apparatus with an increased capacity.

Claims

1. A mobile drilling mud cleaning system, said system comprising:an electrically operated mud treatment apparatus configured to extract contaminants from drilling mud so that such can be re-used, said apparatus having at least one vibrating screen separator, at least one cyclonic separator and mud pumping means;a pair of mud storage tanks, the first tank being configured to receive and store contaminated drilling mud and the second tank being configured to receive and store cleaned drilling mud;wherein the apparatus and the mud storage tanks are mounted on a chassis with a continuous track based propulsion means that is powered by an on-board power source; andwherein the mud treatment apparatus is configured to receive electrical power from an external, off-board power supply that is distinct from the on-board power source.

2. The system of claim 1, wherein the on-board power source is selected from:a) an internal combustion engine with an associated fuel tank; orb) an electric motor driven by at least one battery.

3. The system of claim 2, wherein the maximum capacity of the on-board fuel tank is 70 litres4. The system of claim 1, 2 or 3, wherein the mud storage tanks provide an operating platform that supports one or more mud treatment apparatus components selected from: vibrating screen separator, cyclonic separator and pumping means.

5. The system of claim 4, wherein a portion of the operating platform comprises a personnel deck which, in use, enables operator access to the mud treatment apparatus.

6. The system of any one of the preceding claims, further comprising at least one chassis mounted retractable gangway that runs adjacent to storage tanks and, in use, enables operator access to the mud treatment apparatus, mud storage tanks and / or the internal combustion engine.5   7. The system of any one of the preceding claims, further comprising a set ofretractable stabilizing legs mounted on the chassis.

8. The system of any one of the preceding claims, wherein the mud treatment apparatus comprises a pair of vibrating screen separators.

9. The system of claim 8, wherein each vibrations screen separator feeds a io separate cyclonic separator.

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