The present invention relates to apparatus and a method for processing drill cuttings generated by the drilling of a well into a formation.

Background

Drilling of a well for oil or gas or water into a formation generates drill cuttings in the form of particles of rock and sand etc. which are recovered from the wellbore during drilling. Drill cuttings arriving at the surface are permeated with naturally occurring hydrocarbons from the formation, and are also usually contaminated with hydrocarbon-based drilling mud, which is pumped through the string into the well to lubricate and cool the bit during drilling, and to wash drill cuttings back up the annulus between the string and the hole toward the surface for recovery. Before being disposed of, drill cuttings must be treated to reduce the levels of hydrocarbons and other contaminants in the cuttings, in on- or off-site treatment facilities that are specialised for this purpose, for example, cuttings generated from offshore wells are transported by ship to land-based treatment facilities. Before transport to the treatment facility, cuttings are stored in storage tanks on the drilling facility (e.g. platform), and are conveyed to and from the storage tanks by pumps. Cuttings can be stored in tanks on the drilling facility for 24-36 hours typically, and in that time the contents of the tank are stirred (manually by operators) to keep the cuttings suspended within the fluid.

Existing systems for mixing drill cuttings are known from WO2015/160374, WO20 11/063463, and CN112252978, which are useful for understanding the claimed invention.

Summary

The invention provides a method of processing drill cuttings generated from a well, the method comprising: conveying the cuttings to a tank, the tank having a cuttings inlet for passage of drill cuttings into the tank, a cuttings outlet for passage of drill cuttings from the tank, a gas supply for supply of gas into the tank, and at least first and second gas outlets connected to the gas supply and spaced apart from one another within the tank; wherein the method comprises flowing gas from the first and second gas outlets in a sequence wherein gas flows from the first gas outlet into the tank before gas flows from the second gas outlet into the tank.

The invention also provides a drill cuttings processing tank adapted to process drill cuttings generated from a well, the tank comprising: a cuttings inlet for passage of drill cuttings into the tank, a cuttings outlet for passage of drill cuttings from the tank, a gas supply for supply of gas into the tank, and at least first and second gas outlets connected to the gas supply and spaced apart from one another within the tank; a gas injection controller adapted to control the flow of gas from the first and second gas outlets in sequence, such that gas flows from the first gas outlet into the tank before gas flows from the second gas outlet into the tank.

The invention also provides a gas outlet assembly for a drill cuttings processing tank, the gas outlet assembly comprising: first and second plates arranged mutually parallel and spaced apart from one another, and having a gas outlet adapted for connection to a gas supply line, the gas outlet being disposed between the first and second plates.

Optionally the gas outlet assembly has a feed pipe extending through one of the plates, and opening into the space between the plates to form the outlet. The plates are optionally circular, and optionally have the same diameter. The space between the plates (e.g. along a vertical axis) can be varied to adjust the size of the bubbles generated from gas outlet assembly, and the inter-plate spacing is typically in the range of 25mm-40mm; particularly useful results were obtained with inter-plate spacing in the range of 30mm-35mm, e.g. 30mm. In one aspect, the inter-plate (vertical) spacing is related to the diameter, e.g. inner diameter, of the gas supply line, and is optionally 100-130% e.g. 110-120% of the ID of the gas supply line. In one aspect, with a gas supply line of 1 inch (25.4mm), the inter-plate spacing is 30mm (112% of the ID of the gas supply pipe), which provides a useful size of bubble in the examples shown.

Optionally the gas outlet is arranged at the centre of the circular plates, optionally equidistant from all plate edges, optionally oriented toward the bottom wall of the tank, and passing through the upper plate. Each gas outlet assembly is typically adapted to be submerged within the fluid in the tank, and to permit passage of gas from the outlet into the fluid surrounding the submerged outlet assembly.

Optionally the tank has more than two gas outlets, depending on the size and configuration of the tank, for example, 3, 4, 5, 6, 7, 8, 9, 10 or more gas outlets can be provided. Optionally the gas outlets are connected to a common gas supply, but could be connected to separate gas supplies if desired. Optionally the gas outlets (or sets of gas outlets if there are more than two) have valves that can be selectively actuated to open or close the valve, and optionally the valves are actuated by a control mechanism, such as a programmable logic controller (PLC). Optionally the gas outlets are connected to a gas manifold, which can be supplied by a central gas line, and can control via valves the gas directed to the different gas outlets. Optionally the gas outlets can be connected in sets to one or more manifolds, and arranged to emit gas in those sets. Optionally the gas outlets are connected to a common gas supply, but could be connected to separate gas supplies in some aspects. Optionally the gas can be compressed air.

Optionally flowing gas from an outlet submerged in the fluid suspension of drill cuttings creates a bubble in the fluid which rises through the fluid and mixes it, maintaining the cuttings in suspension within the fluid as a result.

Optionally gas flow from the first outlet stops before gas flow from the second outlet starts. Optionally the sequence of gas flow incorporates a delay between the valve for the first outlet closing the valve for the second outlet opening. Optionally the first and second valve outlets are open for the same time period. Thus, there is optionally a delay in the sequential flow of gas from the first and second outlets. Optionally the delay between the sequential first and second outlet “valve open” configurations (the delay time) can be at least the same length of time as the length of time between the valve open and valve closed period for each of the outlets (the open time). Optionally the delay time can exceed the open time. For example, the valve for the first outlet can be open for a first open period of 80-1 OOmS, and the valve for the second outlet can be open likewise for a second open period of 80- 100mS, optionally with a delay period of at least 80-200mS between the first and second open periods, although in some cases, the second valve can optionally open before the first valve has closed.

Optionally the gas outlets each comprise at least one plate assembly comprising a pair of parallel plates with a nozzle adapted to emit gas between the plates. Optionally the plates in each plate assembly are horizontal, i.e. arranged parallel with a horizontal axis of the tank. Optionally the plates extend radially from the nozzle, and are optionally circular, with the nozzle disposed at a common centre of the circular plates, such that each point on a periphery of the plates is the same distance from the nozzle. Optionally each plate has the same diameter. Diameters between 100mm and 500mm are suitable, and between 200mm and 400mm are good examples, for instance, 300mm, using a typical 1 inch (25.4mm). Optionally the inter plate spacing in each plate assembly (along a vertical axis) is uniform. Optionally the plates are supported against vertical movement with respect to the tank by an optional support member extending between the plates and by a further optional support member between the lower plate and the bottom of the tank, optionally in the form of a skirt extending at least partly around the lower plate. Optionally in each plate assembly, the plates are divided by spacers, which space the plates apart by an equal distance, and circumferentially divide the space between the plates into a number of segments. Optionally there are three spacers, and three segments, but different combinations could be used. The spacers optionally divide the gas injected between the plates circumferentially so that multiple discrete bubbles are emitted from the plate assembly when gas is emitted from the outlet. Optionally the multiple discrete bubbles are emitted from the plate assembly simultaneously, and remain as discrete bubbles as they rise in the fluid. Optionally as the bubbles rise in the fluid, they expand, and optionally diverge from one another in a radial direction with respect to the plates.

Optionally the outlets are laterally spaced apart from one another in the tank. Lateral spacing of the outlets in relation to one another is selected to achieve at least 90%, and optionally 100% coverage of the surface area of the fluid in the tank, taking into account the expansion of the bubbles during transit between the submerged plate assemblies and the surface of the fluid in the tank. Optionally lateral spacing of the outlets is in a regular pattern; in other words, each outlet is spaced from its neighbouring outlet by the same amount. Optionally lateral spacing of plates can be varied with the surface area of the tank, e.g. at the bottom of the tank. Typically each outlet (e.g. each plate assembly) is spaced from adjacent plate assemblies in a horizontal plane by at least the diameter of the plate assemblies, and typically by more than said diameter. Typically each bubble expands to an extent sufficient to overlap on the surface of the fluid with bubbles emitted from neighbouring plate assemblies. Typically each bubble expands by a factor of at least 200% per metre of change in depth, optionally up to 400%.

Optionally bubbles emitted from the first and second outlets are the same size. Since they are emitted from the first and second outlets at different times, they typically reach the surface of the fluid in the tank at different times, and generally the bubble from the first outlet will be at a different depth than the bubble from the second outlet throughout its travel from the outlet to the surface. Optionally the sequence repeats so that subsequent bubbles emitted from the first outlet in a repeated cycle of the sequence will be released after the emission of a bubble from the second outlet in a previous iteration of the sequence. This feature optionally creates a staggered array of bubbles rising in the fluid in the tank between the first and second outlets. Optionally each outlet in each set of outlets in the tank releases a bubble in one cycle before the sequence repeats for the second cycle. Optionally there can be one set of outlets in the tank, in which case each outlet in the tank releases at least one bubble in each cycle of the sequence, or there can be more than one set of outlets in the tank, in which case, each outlet in the set releases at least one bubble in each cycle before the sequence repeats; hence some other outlets in the same tank but in a different set (for example in a different area of the tank) might not necessarily release a bubble in that sequence. Optionally sequentially adjacent outlets in a single set are spatially adjacent in the tank.

Optionally bubbles have a convex upper surface and optionally a concave lower surface. Optionally bubbles ascend through the fluid in the tank on a deviated, non vertical path, optionally as a result of the lateral expansion of different adjacent bubbles released from the same outlet at the same time.

Optionally the gas injection is controlled (e.g. the gas injection controller is programmed) to emit at least some bubbles from spatially adjacent outlets in the tank at adjacent times in the sequence. For example, the sequence could be: outlet 1 emits bubble 1; outlet 2 (adjacent to outlet 1) emits bubble 2; outlet 3 (adjacent to outlet 2) emits bubble 3 etc. In other words, spatially adjacent outlets in the tank can emit respective bubbles at adjacent steps in the sequence.

Optionally the valves are electronically actuated (opened and closed). Optionally the valves are solenoid-actuated. Optionally the open time is less than 200ms, optionally less than 150ms, optionally less than 100ms, e.g. 80ms. Optionally the delay time is more than the open time, optionally more than 100ms, optionally more than 150ms or 200ms. Optionally the delay time is at least 500-2000ms, and could be longer.

Optionally the tank has bottom and side walls and optionally a top wall, and optionally at least a portion of the bottom wall is non-horizontal, for example, a portion of the inner surface of the bottom wall can be inclined at an angle to a horizontal axis. Optionally the cuttings outlet can intersect a low point in the inner surface of the bottom wall. Optionally the bottom wall inner surface is canted, optionally having first and second inclined sections with the cuttings outlet disposed at or near an intersection between the first and second inclined sections.

Optionally the gas outlets are arranged at or near the bottom of the tank, such that gas emitted from the gas outlets form bubbles which rise vertically through the tank. Optionally the outlet is in contact with the bottom wall of the tank, i.e. the inner surface of the bottom wall of the time, such that the bubble released from the outlet rises through substantially the whole of the depth of the fluid suspension, mixing the cuttings and fluid substantially across the whole of the depth of the fluid suspension.

Optionally at least one first gas outlet is spaced further from the cuttings outlet than at least one second gas outlet. Optionally other gas outlets (third, fourth etc.) are arranged to open in sequence in a similar manner to the first and second gas outlets, and can optionally be disposed closer to the cuttings outlet in the tank than gas outlets earlier in the sequence. The outlets, and optionally the gas supply lines, are fixed in position in the tank, for example, rigidly connected to walls of the tank, so that the distance between the outlets is fixed during the process. Optionally the sequential flow of the gas through the first, second and optionally further outlets moves the cuttings within the tank in a horizontal plane, optionally toward the outlet. Optionally piles of cuttings accumulating in corners of the tank are circulated and move toward the outlet by the sequential flow of the gas.

Optionally gas flow from each of the first and second gas outlets in the fluid in the tank is intermittent, for example, gas flows from the first outlet into the fluid for a first “open” period of the first outlet when the corresponding valve controlling gas flow to the first outlet is open; flow from the first outlet then ceases during a “closed” period when the corresponding valve is closed. The valve remains closed, thereby restricting or preventing flow from the first outlet for the duration of that closed period, following which the valve optionally opens once more and flow recommences from the first gas outlet. This generates a sequence of discrete gas bubbles in the fluid at a frequency determined by the open and closed periods of the valves. The first and second outlets typically operate at the same frequency, but as indicated previously, are staggered such that the first outlet opens (and optionally closes) before the second outlet.

The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect can typically be combined alone or together with other features in different aspects of the invention. Any subject matter described in this specification can be combined with any other subject matter in the specification to form a novel combination.

Various aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, each example herein should be understood to have broad application, and is meant to illustrate one possible way of carrying out the invention, without intending to suggest that the scope of this disclosure, including the claims, is limited to that example. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. In particular, unless otherwise stated, dimensions and numerical values included herein are presented as examples illustrating one possible aspect of the claimed subject matter, without limiting the disclosure to the particular dimensions or values recited. All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa.

Language such as "including", "comprising", "having", "containing", or "involving" and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Thus, throughout the specification and claims unless the context requires otherwise, the word “comprise” or variations thereof such as “comprises” or “comprising” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of”, "consisting", "selected from the group of consisting of”, “including”, or "is" preceding the recitation of the composition, element or group of elements and vice versa. In this disclosure, the words “typically” or “optionally” are to be understood as being intended to indicate optional or non- essential features of the invention which are present in certain examples but which can be omitted in others without departing from the scope of the invention.

References to directional and positional descriptions such as upper and lower and directions e.g. “up”, “down” etc. are to be interpreted by a skilled reader in the context of the examples described to refer to the orientation of features shown in the drawings, and are not to be interpreted as limiting the invention to the literal interpretation of the term, but instead should be as understood by the skilled addressee.

Brief description of the drawings

In the accompanying drawings:

Figure 1 shows a perspective view (from above and one side) of apparatus for processing drill cuttings in the form of a drill cuttings processing tank;

Figure 2 shows a perspective view of the Fig 1 tank (from beneath and the other side);

Figure 3 shows a front view of the Fig 1 tank;

Figure 4 shows a plan view of the Fig 1 tank showing internal detail of the gas supply system;

Figure 5 shows a side view of the tank showing the same internal detail as shown in Fig 4;

Figure 6 shows a schematic view of the gas supply in the tank;

Figure 7 shows a perspective view of the Fig 1 tank showing internal detail of the gas supply system;

Figure 8 shows a perspective view of a gas outlet plate assembly;

Figure 9 shows a front view of the gas supply nozzle and plate assembly of Figs 8 &

9;

Figures 10-12 show front, plan (in section) and front (in section) views of the tank with detail of the gas supply system;

Figure 13 shows an end view of Fig 10 showing the internal details of the tank;

Figure 14 shows a front view of the tank illustrating the emission of bubbles from the gas supply system;

Figure 15 shows a schematic side view of bubbles rising in a tank from a plate assembly of Fig 9; Figure 16 shows a plan view of bubbles rising from a plate assembly as shown in Fig 15;

Figure 17 is a schematic side view of the tank showing the stagger between bubbles emitted from adjacent outlets as they rise;

Fig 18 is a side cutaway view of a second example of a tank; and Fig 19 is a close up view of the bottom of the Fig 18 tank.

Referring now to the drawings, a drill cuttings processing tank 10 is supported by a frame 11, and has side walls 12s, end walls 12e, a bottom wall 13, and a top wall 14 with one or more inlet hatch 15 for the passage of drill cuttings into the tank 10. The tank is generally rectangular in plan view, with side walls 12s being longer than the end walls 12e. The tank 10 has a cuttings outlet 20 for passage of drill cuttings out of the tank 10 in the bottom wall 13. The bottom wall 13 is non-horizontal, and in this example is formed by two flat base plates set at a declining angle from the short end walls 12e toward the centre of the tank 10 to form a sump 13s at a low point of the tank 10. The drill cuttings outlet 20 is located in the sump 13s, optionally to one side of a central seam where the two flat base plates are connected (e.g. welded). Material contained within the tank such as drill cuttings recovered from a well is passed through the cuttings outlet 20 into an outlet hopper 21 , optionally to an auger or other conveyor mechanism, for transport to a processing facility, optionally at a local site near the tank 10 or via another tank on a vehicle to a remote treatment facility. The tank 10 optionally comprises a storage tank, adapted to process the drill cuttings and maintain them in suspension within fluid 5 in the tank 10, to facilitate their passage from the tank 10 when required, for example, for offloading onto a transport tank for transfer to a more specialised treatment facility, e.g. onto a vessel for transport from an offshore drilling platform to a shore-based treatment facility.

The tank 10 has at least two, and in this example, at least four gas outlets arranged near the bottom of the tank 10 and connected by gas supply lines 30 to gas manifolds 40, which are typically supplied by a common gas feed. In this example, two separate manifolds 40a, b supply respective outlets in the form of gas outlet assemblies 25 on opposite sides of the tank. Each gas outlet assembly 25 comprises a bank of two outlet heads 26 and is connected via a respective gas supply line 30 to one of the four outlets on the manifolds 40a, b. Each gas supply line 30 is opened and closed by a valve in the manifold that is independently actuable, so the relevant manifold can direct gas from the common gas feed supplying the manifold 40 to any one of the gas lines 30 leading to the gas outlet assemblies 25. In this example, the pair of outlet heads 26 in each of the outlet assemblies 25 is arranged parallel to the longitudinal axis X of the tank, connecting the short end walls 12e, but could equally be arranged perpendicular to the axis X in other examples. The pipework, manifolds and outlets are optionally formed from steel, and are optionally fixed to the tank as permanent fixtures, e.g. by welding, bolting of flanges etc.

As best seen in Figs 5&6, each of the gas outlet assemblies 25a-h is fed by a respective individual gas supply line 30 from one or other of the manifolds 40a, b. The manifolds 40a, b are optionally fed from the same master gas supply as best shown in Fig 6. The manifolds are controlled by a common controller 60, typically in the form of a PCB, which electronically controls solenoid or other valves on the manifolds through control lines 61a, b, allowing the manifolds 40a, b to direct gas to one or more of the outlets 25a-h or 25s.

Gas outlet assemblies 25a and 25b are spaced apart along the axis X (further from the cuttings outlet 20) as compared with gas outlet assemblies 25c and 25d, which are arranged closer to the sump 13s. Gas outlet assemblies 25e and 25f are likewise spaced apart along the axis X (further from the cuttings outlet 20) as compared with assemblies 25g and 25h. While in this example each gas supply line 30 supplies a set of two outlet heads 26 in each assembly 25, in other examples, each outlet head could have its own gas supply line 30, or sets of more than two outlet heads could be supplied by one gas supply line 30. As well as being spaced apart along the axis X, it can be seen from Fig 5 that different sets of outlets are spaced apart across the axis X. For example, outlet pairs 25a/25b; 25c/25d; 25g/25h; and 25e/25f are spaced apart from one another across the axis X, on opposite sides thereof. A further gas outlet is provided in the sump 13s, in the form of sump gas outlet assembly 25s, disposed within the drill cuttings outlet 20, and in the same plane as the sump 13s. The sump gas outlet assembly 25s is an optional feature that is intended to displace clumps of drill cuttings accumulated in the sump 13s and potentially blocking the cuttings outlet 20. The spacing between the different outlets and the possibility of flowing gas through different outlets 25 at different times permits different patterns or sequences of firing of outlets, with useful effects, as will be described below.

In this example, each gas outlet 25 comprises a pair of outlet heads 26, each comprising a plate assembly comprising parallel and horizontal circular plates 27a, b best seen in figs 8&9, coupled by a short horizontal pipe to a common supply line 30. Spacers 28 located vertically between the plates 27a, b space them apart by a uniform distance in each pair (in this case by 30mm). The spacers 28 are also distributed at regular (optionally equal) angular distances around the centre of the plates, and as best seen in Figs 8&9, in this example comprise flat rectangular steel blocks disposed in a vertical plane on a radius of the plates 27, adjacent to the edges, such that they divide the outer radial portions of the plates into three generally equally-sized angular segments. The plates 27 in this example are uniformly circular and have the same dimensions, with a diameter of 250mm-350mm e.g. 300mm and a thickness of 10mm. While the plates in each gas outlet are parallel and horizontal, they are not generally set at the same depth in the tank 10, as best seen in Fig 9, but instead are generally set in the tank 10 at a generally uniform distance from the bottom wall 13 (which declines at an angle from each end wall 12e toward the sump 13s). The plates 27 are generally suspended by the supply pipe 30 above them, typically to a depth of at least 1m, and typically the supply pipe extends to a higher height than the maximum depth of material in the tank in order to reduce the risk of ingress of material from the tank 10 into the pipe 30 through the gas outlet 25.

Optionally a skirt 29 welded below each lower plate 27b rests on (or can be welded to) the bottom wall 13 of the tank. Optionally the skirt 29 can be tapered vertically to match the angle of the bottom wall 13, as best seen in Fig 9. Generally the plates 27 are set in the tank at a depth that is as low in the tank as possible, i.e. as close as possible to the bottom wall 13, so that the lower plate 27b closest to the nearest end wall 12e is almost touching the bottom wall 13 and at that location, the section of skirt approaches a minimum vertical extension downwardly from the lower plate 27b. The supply pipe 30 connects with the upper plate 27a at the centre as best see in Fig 8, and opens into the space between the plates 27a, b. The upper and lower plates 27a, b are therefore non-identical, the lower plate 27b having no central opening, so that gas released from the supply pipe 30 is diverted laterally by lower plate 27b.

Gas (optionally compressed air @ 7bar (700 KPa) pressure) released from the supply pipe 30 into the space between the plates 27a, b expands radially in a horizontal plane under the constraints of the two plates 27a, b and is circumferentially divided by the three spacers 28 to emerge from the sides of the plates 27a, b as three separate bubbles 50 at substantially the same instant. The bubbles 50 rise together through the fluid 5 in the tank, expanding as they do so. The movement of the bubbles vertically through the fluid creates local pressure gradients in the fluid column and suspends the sold particles of cuttings within the fluid, as best seen in fig 14. The bubbles 50 produced are of a generally consistent size as a result of the parallel plates 27 and the circumferentially regular arrangement of the spacers 28. Each bubble 50 is typically emitted at the same moment from a different position around the circumference of the plates 27. Bubbles 50 emitted from the gas outlet 25 initially expand to approx. 200% of the plate 27 diameter, and continue to expand by approx. 450% (relative to the plate diameter) as they reach the surface 5s of the fluid in the tank 10.

Optionally gas is injected in bursts through the outlet 25, for example, in one sequence, gas is injected for a 80 millisecond burst with a delay of e.g. 1s before a subsequent burst through the same gas outlet 25.

The controller 60 is programmed in this example to inject gas through the outlets 25 in a sequence which enables movement of the material laterally within the tank. Optionally the sequence can be adapted to focus bursts of gas into piles of material located in specific areas of the tank, e.g. in corners.

Each gas outlet assembly 25 is connected to one of the manifolds 40 mounted beneath the tank 10 which are arranged to regulate the flow of gas to the individual gas outlets 25. Each gas outlet 25 in this example has its own gas supply line 30, enabling injection of individual bursts of gas through each gas outlet 25, under the control of the controller 60. The controller 60 is programmed to inject gas through the manifolds 40a, b in parallel, series or individually, and the sequence can be varied dependant on where the material enters the tank 10. Prior to operations the heads 26 in the gas outlets 25 are submerged in a low viscosity lubrication fluid circulating within the tank under gravity.

As shown in Figure 15, the bubbles 50 are released from the outlet heads 26 as discrete bubbles 50, rather than a stream of air. The bubbles 50 expand as they rise in the fluid 5 in the tank 10, each discrete bubble adopting a convex domed top surface and optionally having a general mushroom shape, optionally with a slightly concave lower surface which arises because of the slight pressure changes in the fluid 5 as the bubble rises through the fluid. Further, as shown in Fig 16, each time the valve is opened to emit gas from the outlet 25, each outlet head 26 emits three bubbles simultaneously from the radially spaced segments defined by the spacers 28. Each bubble 50 emitted from the outlet heads 26 forms separately from the others simultaneously emitted, and rises separately through the fluid 5 in the tank 10. The formation of the discrete bubbles 50, their expansion during their ascent, and the domed shape naturally adopted as shown in Figs 15 and 16 illustrate a useful advantage of the invention, which is that the bubbles emitted at the same time from an outlet rise in layers while remaining separate from one another, thereby increasing the mixing effect obtained. Further, as the discrete bubbles expand in the same layer while rising, they diverge naturally laterally from the vertical axis passing through the outlet heads 26, pushing laterally away from one another. Also, the natural expansion of the bubbles as they ascend through the fluid 5 means that practically all of the upper surface of the fluid in the tank is mixed by rising bubbles, and the domed upper surface naturally adopted by the rising bubbles 50 means that fluid 5 in front of a bubble 50 (e.g. above the bubble) is rolled laterally to the sides of the bubble as the bubble 50 reaches the surface, as shown in Fig 15, which moves the fluid 5 vertically and laterally within the tank, 10, and enhances the mixing effect in the tank 10, by encouraging different layers of fluid 5 in the tank to mix more thoroughly. This enhances the suspension of cuttings in the fluid 5 and means that more cuttings are conveyed out of the tank for treatment.

In one trial, the rate of expansion of the bubbles in a deeper tank were tested with a gas supply line having an ID of 25.4mm supplying gas to an outlet in a tank with a 4m depth, wherein the outlet comprised a plate assembly as per outlet head 26, with a diameter of 300mm; peak rates of bubble rise and expansion were obtained in depths below 1m, above which depth, the rate of expansion of the bubbles rising through the fluid, and their apparent speed of ascent, tended to plateau. The following table shows how the apparent diameter of bubble in the fluid varies with the distance of upward travel of the bubble from the outlet at the bottom of the tank:

Distance Diameter of bubble

0m 600 mm

1m 1,200 mm

2m 1,500 mm

3m 1,688 mm

4m 1,721 mm

Examples of the invention will now be illustrated.

Example 1

Drill cuttings enter the tank 10 through a hatch, in this case, immediately above the gas outlet 25a. The controller 60 fires bursts of compressed air through the gas outlets in the following sequence:

Step Gas outlet Duration (ms)

1 25a 80

1a - 1000

2 25b 80

2a - 1000

3 25c 80

3a - 1000

4 25d 80

4a - 1000

5 25s 80m

Optionally in a modification to example 1, the gas outlets on the opposite side of the tank 10 can also be fired at the same time as the above outlets as per the following sequence:

Step Gas outlet Duration (ms)

1 25a/25e 80

1a - 1000

2 25b/25f 80

2a - 1000 3 25c/25g 80 3a 1000

4 25d/25h 80

4a 1000

5 25s 80

In these examples, there is a delay between each step 1-5, for example, a delay step of 1a lasting at least as long as the open period of 80ms, and in this case, between 100 and 2000ms (e.g. 1000ms) interposed between the cessation of the burst in step 1 and the commencement of the burst in step 2, and similar delays of the same (or optionally a different) duration are interposed as additional steps in the sequence between steps 2&3, 3&4, and 4&5. During the delay steps 1a, 2a, etc. no valves are open, and no gas enters the tank through any of the gas outlets 25. The gas injection sequence moves the drill cuttings within the tank 10 from the entry point above gas outlet 25e to the outlet bowl below gas outlet 25s through a rolling motion created by the bubbles 50 rising in sequence within the fluid 5 in the tank 10. The delay steps 1a, 2a, 3a, 4a, etc. in this example are optional.

As the skilled reader will understand, steps 1-4a of example 1 can be optionally be repeated sequentially to circulate the drill cuttings within the tank 10 and move them towards the cuttings outlet 20 until suitable transport is available to receive material from the cuttings outlet 20. Thus in a modification of example 1, steps 1-4a are repeated in sequence, optionally with step 5 included in each repeat, while the cuttings outlet 20 is closed, to circulate drill cuttings in the tank 10 and maintain them in suspension. Optionally this continues until substantially all of the cuttings in the tank are sufficiently suspended to be discharged from the tank 10.

The sequences shown above are especially useful if the cuttings are piled up on the floor of the tank near the inlet hatch above outlet 25e. In the event of the cuttings being admitted into the tank through another inlet hatch, for example, the hatch above gas outlet 25h, the sequence can optionally be different, for example:

Step Gas outlet Duration (ms)

1 25e 80 1a 1000

2 25f 80 2a - 1000

3 25g 80

3a - 1000

4 25h 80

4a - 1000

5 25s 80

In other words, gas outlets further from the outlet are typically fired before others in the sequence that are closer to the outlet. Similar modifications (relating to delays and cascades etc.) as indicated above can be made to this sequence.

Example 2

The protocol is the same as described for example 1, but without a delay between adjacent steps 1-5, so that the valve(s) on the manifold controlling outlet 25b (or outlets 25b/25f) opens to inject gas in step 2 synchronously with the closure of the valve controlling gas outlet 25a (or 25a/25e); otherwise, the same procedure as outlined in example 1 is followed.

Example 3

The protocol is the same as described for example 1, but with no delay as in example 2, and with a continuous cascading sequence wherein the valve(s) on the manifold controlling outlet 25b (or outlets 25b/25f) opens to inject gas in step 2 after the opening (but before the closure) of the valve controlling gas outlet 25a (or 25a/25e); otherwise, the same procedure as outlined in example 1 is followed.

Example 4

Drill cuttings enter the tank through a hatch immediately above the gas outlet 25a as previously described. The controller 60 fires bursts of compressed air through the gas outlets in the following sequence:

Step Gas outlet Duration (ms)

1 25a/25b 80

1a - 1000

2 25c/25d 80

2a - 1000

3 25s 80 In this example, the valves controlling outlets 25a and 25b at one end of the tank 10 are opened simultaneously, followed by simultaneous opening of the valves controlling outlets 25c and 25d, creating a wave of material parallel with the axis X and moving toward the cuttings outlet 20, where it can then optionally discharge from the tank 10. In possible modifications of example 4, delays can be omitted as described in example 2, and/or continuous cascades can be used as described in example 3. In another possible modification of example 4, the gas outlets 25e-g, at the opposite end of the tank can be fired as per the modification to example 1. Optionally in a further modification to this example, the gas outlets 25e-f at the opposite end of the tank can be fired instead of gas outlets 25a-d, as in example 1.

Example 5

Drill cuttings enter the tank through a hatch immediately above the gas outlet 25a as previously described. The controller 60 fires bursts of compressed air through the gas outlets to move the cuttings in the tank from one side to the other, in the following sequence:

Step Gas outlet Duration

1 25a 80

1a - 1000

2 25b 80

2a - 1000

3 25d 80

3a - 1000

4 25c 80

4a - 1000

5 25g 80

5a - 1000

6 25h 80

6a - 1000

7 25f 80

7a - 1000

8 25e 80

8a - 1000

9 25s 80 (optional) After step 9 (optionally after step 8) the sequence can be operated in reverse to return to the starting point. Step 9 can optionally be included in each cycle of the sequence, or can be included only in the sequence prior to discharge of the cuttings into a transportation tank for further processing at another facility. Delay steps are optional.

Example 6

Drill cuttings enter the tank through a hatch immediately above the gas outlet 25a as previously described. The controller 60 fires bursts of compressed air through the gas outlets to move the cuttings in the tank from one side to the other, in the following sequence:

Step Gas outlet Duration

1 25a/b 80

1a - 1000

2 25c/d 80

2a - 1000

3 25g/h 80

3a - 1000

4 25e/f 80

4a - 1000

5 25s 80 (optional)

This generates a wave in the tank, which tends to move the cuttings from left to right as shown in the drawings. After step 5 (optionally after step 4) the sequence can be operated in reverse to return to the starting point, sending the wave in the opposite direction. Step 5 can optionally be included in each cycle of the sequence, or can be included only in the sequence prior to discharge of the cuttings into a transportation tank for further processing at another facility. Delays are optional.

A side view of example 6 is shown in Fig 17, which schematically illustrates only one of the plate assemblies 26 from each of the outlets 25, and shows the staggered release of the bubbles 50 as the wave passes from left to right in the tank 10. In Fig 17, bubbles 50.1-50.8 are released in sequence (50.1 before 50.2, 50.2 before 50.3 etc.) and expand as they travel from the outlets 25 to the surface 5s of the fluid 5 in the tank. For clarity in Fig 17m, only one bubble 50 is shown being emitted from each outlet 25 during each step, but as will be appreciated from the above discussion, each outlet 25 has two plate assemblies 26 each of which will be emitting separate bubbles 50, and each plate assembly 26 emits three bubbles simultaneously, so the overlap in the bubbles will be greater than is actually shown in Fig 17. However, Fig 17 conveniently shows the staggered feature of the bubbles 50 rising in the tank 10 towards the surface 10s. The same staggering effect is achieved on the bubbles in other examples as will be appreciated by the skilled reader, although the pattern of release will be different as shown in the various examples. This staggering effect enhances mixing of the cuttings in the fluid 5 in the tank 10.

Example 7

Optionally drill cuttings already in the tank 10 can be continuously circulated in the tank without the addition of more cuttings using the following exemplary sequence: Step Gas outlet Duration

1 25a 80

1a - 1000

2 25b 80

2a - 1000

3 25c 80

3a - 1000

4 25d 80

4a - 1000

5 25s 80 (optional)

5a 1000 (optional)

6 25h 80

6a 1000

7 25g 80

7a 1000

8 25f 80

8a 1000

9 25e 80

After step 9, the sequence can be operated in reverse to return to the starting point. Thus cuttings in the tank 10 can be circulated indefinitely in the tank 10 without being removed therefrom, and the cuttings can be kept in suspension until ready for offloading into a transportation tank for further processing at another facility. Delays are optional.

Example 8

In a similar manner to example 5, continuous circulation within the tank 10 without addition of drill cuttings into the tank 10 can follow the continuous wave sequence from left to right as described in example 4 as follows:

Step Gas outlet Duration

1 25a/25b 80

1a - 1000

2 25c/25d 80

2a - 1000

3 25s 80 (optional)

3a 1000 (optional)

4 25g/25h 80 4a 1000

5 25e/25f 80

After which the sequence can optionally reverse to drive the drill cuttings in a wave in the opposite direction from right to left (as shown in the drawings) for example:

Step Gas outlet Duration

6 25g/25h 80

7a - 1000

8 25s 80 (optional) 8a 1000 (optional)

9 25c/25d 80 9a 1000

10 25a/25b 80

This sequence can then repeat until the contents of the tank 10 are ready for discharge. In all possible modifications of examples 5 & 6, delays can optionally be omitted as described in example 2, or continuous cascades can be used as described in example 3. In any example, the firing of outlet 25s might be omitted in circulation mode, where the objective is to maintain the cuttings in suspension without discharging any material from the tank 10. In any example, gas can be injected through outlet 25s prior to the discharge of any material from the tank, or at any convenient time before that, to maintain cuttings in suspension.

Optionally in any example, should drill cuttings accumulate in one area of the tank 10, for example in a corner, the relevant valve can be isolated and the gas outlet 25 fired for longer periods to initially free any settled particles before changing to a sequence to move the material towards the cuttings outlet 20.

Referring now to Figs 18 and 19, a second drill cuttings processing tank 110 has various shared features to the tank 10. The various shared features are referred to herein by the same reference number but increased by 100, and will be only briefly described herein, since the reader can readily understand the structure and function of the shared features from the previous examples. The tank 110 has a frame, side walls, end walls, a bottom wall 113, and optionally a top wall with one or more inlet hatches as previously described, and a cuttings outlet 120, comprising a sump as previously described. Passage of the drill cuttings to and from the tank 110 is the same as described in relation to the tank 10. The tank 110 has in this example five gas outlet assemblies 125 at or near the bottom of the tank and connected by a respective gas supply line 130 to one or more gas manifolds. In this example, the difference resides in the arrangement of the gas outlet assemblies and the gas supply lines.

In this example, each gas outlet assembly 125 comprises a row of either two or three outlet heads 126 which are connected together with a respective gas supply line 130. Each gas supply line 130 is typically opened and closed by a valve in the manifold that is independently actuable, so the relevant manifold can direct gas from the common gas feed supplying the manifold to any one of the gas outlet assemblies 125a-e as in the previous examples. In this example, the outlet heads 126 in each of the outlet assemblies 125 are arranged in a line or row perpendicular to the longitudinal axis X of the tank. The pipework, manifolds and outlets are optionally formed from steel, and are optionally fixed to the tank as permanent fixtures, e.g. by welding, bolting of flanges etc. The gas supply lines extend through the bottom 113 of the tank 110 in this example. Each of the gas outlet assemblies 125a-e is fed by a respective individual gas supply line 130, from manifolds which are arranged and controlled as previously described. Gas outlet assemblies 125a-e are spaced apart along the axis of the tank, as previously described, with gas outlet 125a being furthest from the cuttings outlet 120, gas outlet 125e being closest to the cuttings outlet 120, and gas outlets 125b-d being spaced apart therebetween, optionally at regular intervals, but as seen in the drawings, the axial spacing between adjacent gas outlet assemblies 125a-e does not need to be regular. All the outlet heads 126 in each assembly 125 are typically arranged in a straight line with equal spacing across the axis between adjacent heads 126 in each assembly 125 in this example, but this can optionally be varied in different examples. A further gas outlet is optionally provided in the sump as previously described. The outlet heads 126 typically comprise plate assemblies as previously described. The heads 126 in gas outlet assembly 125a are typically on a shelf at the opposite end of the tank to the cuttings outlet 120, whereas the heads 126 in the remaining assemblies 125b-e are arranged on or near the bottom of the tank 113 as previously described.

Examples of the invention using the second tank 110 will now be illustrated.

Example 9

Drill cuttings enter the tank 110 through a hatch, in this case, immediately above the gas outlet 125e, but the inlet for the cuttings can be at any location without affecting the results. The controller fires bursts of compressed air through the gas outlets in the following sequence:

Step Gas outlet Duration (ms)

1 125a 80 1a 1000

2 125b 80 2a 1000

3 125c 80 3a 1000

4 125d 80 4a 1000

5 125e 80m Optionally in a modification to example 9 similar to the modification to example 1 , the tank outlet can be located at the centre of the tank 110, and gas outlets optionally provided on each side of the outlet can be fired at the same time. Optionally an additional gas outlet can be provided in the sump as previously described, which can optionally be fired at the end of the sequence, during discharge. Optionally steps 1- 5 can be repeated sequentially to generate a wave from right to left and to circulate the drill cuttings within the tank 110 and move them towards the cuttings outlet 120 until suitable transport is available to receive material from the cuttings outlet 120, without necessarily opening the cuttings outlet 120 during the circulation of the cuttings. Thus in a modification of example 9, steps 1-5 are repeated in sequence, while the cuttings outlet 120 is closed, to circulate drill cuttings in the tank 110 and maintain them in suspension. Optionally this continues until substantially all of the cuttings in the tank are sufficiently suspended to be discharged from the tank 110. As previously described, gas outlets further from the cuttings outlet 120 are typically fired before others in the sequence that are closer to the cuttings outlet 120.

Example 10

The protocol is the same as described for example 9, but without a delay between adjacent steps 1-5 as described in example 2 above.

Example 11

The protocol is the same as described for example 9, but with no delay as in example 10, and with a continuous cascading sequence wherein the valve(s) on the manifold controlling outlet 125b opens to inject gas in step 2 after the opening (but before the closure) of the valve controlling gas outlet 125a etc.; otherwise, the same procedure as outlined in example 9 is followed.

Example 12

Drill cuttings already in the tank 110 can be continuously circulated in the tank optionally without the addition of more cuttings using the following exemplary sequence:

Step Gas outlet Duration

1 125a 80

1a - 1000

2 125b 80 2a 1000

3 125c 80

3a 1000

4 125d 80

4a 1000

5 125e 80 (optional)

5a 1000 (optional)

6 125d 80

6a 1000

7 125c 80

7a 1000

8 125b 80

8a 1000

9 125a 80

After step 9 (optionally after step 8a), the sequence can be repeated. Thus cuttings in the tank 10 can be circulated indefinitely in the tank 10 without being removed therefrom, and the cuttings can be kept in suspension until ready for offloading into a transportation tank for further processing at another facility. Delays are optional.

In any example, the firing of gas outlets in the sump might be omitted in circulation mode, where the objective is to maintain the cuttings in suspension without discharging any material from the tank 110.