One of the most expensive and troubling issues with drilling operations is the handling, processing, and circulation of drilling mud along with disposing of the unwanted drill cuttings. The drilling cuttings deposited in the half round tank and are typically removed with an excavator that must move the contents of the waste bin or roll-off box. The excavators are usually rented for this duty and the equipment charges can range from $200-300/day. Add in the cost for the day and night manpower and the real cost for a single excavator can be as much as $1800/day.
Using the excavator method explained above, the unloading of 50 barrels of drill cuttings from the half round can take as long as two hours. This task is mostly performed by the solids control technicians. The prime duty for the solids control technicians is to maintain the solids control equipment in good working order. This involves maintenance for the equipment, screen monitoring and changing, centrifuge adjustments, and retort testing to prepare a daily operational summary of the solids control program.
Operating the excavator takes the technician away from these tasks and can lead to poorly performing equipment. Additionally, the excavator has the potential for abuse as some solids control technicians use the climate-controlled cab as a break area or refuge from the elements. Many times, these guys are found asleep on the job.
One solids control company reported the idle time for the excavator can be more than 8 hours for a 24-hour period with 8 hours of operation and 8 hours of shut down time. Fuel and time lost can cause an economic drag on rig operations. And lastly, there have been several accidents on each rig causing a potential for injury, loss of production, and lost revenue as the excavator must be repaired.
Currently, most onshore drilling rigs dispose of drilling mud by mechanically loading the used drilling mud onto trucks via excavator or hire vacuum trucks to come and transport the mud away. Another method of disposal is by mechanically loading the drilling mud into poly-lined ponds until a threshold is met, before being trucked off for permanent disposal. Both these options are expensive and require a lot of manpower. Conventional pumps cannot move the drilling mud due to the high viscosity of up to 1000 cp and specific gravity of up to 1.9. This, along with the occasional large cuttings cause a nightmare for centrifugal pumps. Most pumps cannot even move the material and the ones that can have their impellers and volutes chewed up by the abrasive nature of the drilling mud, greatly shortening the lifespan of the pump which leads to frequent costly pump repairs coupled with unscheduled operational downtime.
Offshore drilling rigs follow a similar process in which the mud is loaded into empty drums and held on the oil platform. When a certain number of filled drums is met, the drums are then loaded onto barges or vessels which take the drilling mud to the shore to unload and dispose of.
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