HDD
Powerful pumps – the heart of HDD maxi-rig spreads It’s common to think of horizontal directional drilling (HDD) spreads in terms of rig size, but the true workhorse is in fact the mud pumps – a high efficiency positive displacement piston pump. Without it, drilling fluid cannot be pumped into the bore to the jet or motor drill, and the bore would not have any stability.
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f the pumps are down, the drilling stops In the Australian HDD sector there is a limited number of available maxi-rigs and powerful mud pumps. Having ready access to additional maxi-rigs and powerful mud pumps is a key means to maintaining project productivity and mitigating the impact of unscheduled repairs. If the pumps are down, the drilling stops. Mud pressure is lost as it moves through the surface piping and a lot more as it moves down the drill string. Most of the pressure is expended in a jet stream at the drill bit and as it passes through the stages of a downhole motor if being used. At this point the mud pump needs to provide additional pressure to push the mud back along the annulus to the
Gardner Denver PZ8.
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surface, while maintaining an operational long term duty cycle. It is also important that the mud pump is sized appropriately to adequately cope with the volumes of drilling fluid required and to maintain adequate annular velocity in the borehole to ensure cuttings remain in suspension in the drilling fluid until the fluid exits the borehole. The capacity of the mud pumps is commonly misunderstood and misrepresented. It is common for people to promote their mud pumps as having a 500gpm (1,892lpm) capacity and a 500 psi pressure rating. While both numbers may be on the spec sheet, promoting the pumps as a 500 gpm pump at 5000 psi is almost certainly incorrect.
For example: A common HDD pump such as the EWECO 446 – a good all-round pump for smaller projects – is often quoted as having an output of 56 5gpm with pressure rating of 5000 psi. While both numbers are true, they are not true together. The spec sheets show that the pump will do 565 gpm at 1200 psi at 440 rpm max with 6-inch diameter liners. Or, if the liners are changed to 3-inch diameter, the pump will output 5000 psi, but even at a max of 440 rpm, the flow output is only 141 gpm. For a long duration longevity on a project, it is good drilling practice to limit the operation to 60 per cent – 70 per cent of the capacity,
