Water well drillers WB&AD Morgan have produced a tailormade solution to the problem of dealing with the waste that arises from drilling boreholes in an environmentally friendly, efficient way. Built to their own specification, their innovative MC80 Mud Trailer system provides the answer to a long-standing problem.
The ‘arisings’ are a combination of drilling mud and suspended debris resulting from drilling operations. Containing and recovering fluids traditionally necessitated the use either of excavated settlement lagoons, or a series of skips to hold and allow settlement of the arisings, prior to recycling fluid down the drill string.
Both of these methods create problems:
An excavated lagoon needs a large area of ground. And when work is completed, this must be reinstated. Open lagoons raise health and safety concerns: they should not be deeper than a metre, with battered sides for ease of access should someone fall in.
An impervious liner is usually needed to prevent excessive leakage, and at the end of the project material must be excavated to remove the liner, enabling ground to return to its original condition. Creating a lagoon impacts upon space, and is expensive.
Using of a series of skips creates its own problems too—containers of sloppy waste that are difficult to manage and expensive to dispose of.
While the waste disposal industry can readily handle solids or liquids, a mixture of the two presents difficulties.
Neither lagoons nor skips utilise any mechanical action and are inefficient, and will not return adequately cleansed quantities of drilling fluid for boring operations.
Mobile mud cleaning
Over the summer of 2005, in conjunction with Lloyd Engineering, Morgans designed and constructed a unique mud cleaner. This is a self-contained mobile unit which allows the drill cuttings to be separated from the drilling fluids. Cuttings are disposed of directly to a skip, and the fluids recycled.
Mounted on a 14-metre long trailer, the unit is based around a highly efficient PSD MC80, so the need to specially install mud cleaning equipment on each site is eliminated.
The MC80 is a high performance mud cleaner employing a double deck screening system, mounted on a hollow section steel frame with underflow tank and mud feed chute.
Mechanical particle recovery
Larger particles such as gravels and coarse sands are removed first using a Rigtech VSM 300 fifth-generation shaker. This is a high performance, linear motion and double motor shaker with inverter speed control. In the top deck pre-tensioned screens, usually 10 to 30 mesh and held in place by pneumatic bladders.
Fine particles are removed at the lower deck, which uses four pre-tension stainless steel fine 84 to 250 mesh screens with pneumatic clamping for ease of use.
Screens in both sections vibrate, with oscillation rates controlled by the operator via the inverter speed control.
Fluids are passed through a Sveldala 100 x 75 centrifugal hydrocyclone feed with a 22kw motor, and four 5-inch hydrocyclones which help recover more waste.
Fluid ready to return to the drilling rig is transferred from the MC80 to the holding tank via a high volume (100m3/hr) 6m head CD100M 5.5kw horizontal end suction pump. This is powered by a super-silenced JS88k 88kw generator mounted at the front of the trailer, which also powers shaker motors and pumps.
Finally, fluids are pumped to a 20 cubic metre holding-and-settlement tank fitted with three internal weirs/baffles which progressively reduce the velocity of flow, allowing remaining fine residual material to settle.
Cleaned fluids are returned to the drill rig via a diesel-driven CL100 horizontal end-suction pump. This is powered by a direct-coupled diesel Perkins 84kw 1104C-44TA engine. This has distinct advantages—an electrically driven unit would have required a much larger and heavier larger generator with a loss of fuel efficiency.
The main tank itself is easily cleaned, and incorporates removable side panels. A high pressure jetting system is coupled to a 1500 psi Triplex Bean pump. This pump can also be used for cleaning purposes, mixing polymer or bentonite muds, and grouting or deep hole drilling if required.
Safety issues paramount
The health and safety of operatives has been a major consideration throughout the design. For example rather than using open ladders, stairs with handrails are incorporated wherever possible.
The top working area has collapsible hand rails that fold away for transportation. Generated power on board also provides lighting to illuminate the entire working area, rather than just the trailer.
Technology benefits customers
Says WB&AD Morgan’s Brian Morgan: ‘The technology is working extremely well, and there is a considerable benefit to our customers: we can set up rapidly, and leave a site clean. Disposal costs for drilling waste and fluids are minimised, these are now separated into a fluid with a very low level of suspended solids, and a dry waste.’