Published in Energy Northern Perspective, April 2019
Drilling waste management experts, TWMA, offer a full range of drill cutting management options – the most cost effective of which includes cleaning and recycling drilling waste at the source. At the heart of the system is the TCC RotoMill® that breaks cuttings down to oil, water and solids which can be recycled and reused at the drill site.
To find out more about the process, Energy Northern Perspective spoke with Jan Thore Eia, TWMA’s Sales & Business Development Manager in Norway.
“In the North Sea we have demonstrated cost and operational efficiencies through the application of our TCC RotoMill technology,” says Jan Thore Eia. “Rather than transferring the cuttings back to the shore and treating them there, processing at the rig site saves operators significant costs on transportation – and they can reuse the base oil on location. So, it’s very cost-effective.”
“The cost savings are even greater when compared to cuttings reinjection, which is often considered to be the least expensive of the options, because an operator says, ‘we’ve got the injection well already’. In many cases, however, the injection well needs to be drilled first.”
“The trouble is that injection wells don’t last forever – they fill up. When the wells fill, operators encounter many problems for example fractured formations and lost circulation. And, as an operator searches a reservoir for additional reserves, they can start to cross the injection domains,” Eia continues.
“So, in that respect, utilising the TCC RotoMill thermal treatment of the cuttings – and discharging the processed materials to sea in compliance with environmental regulations – becomes significantly less expensive.”
Recycling on site
The TCC RotoMill uses simple physics to do its job, as Eia explains, “It’s not very complicated. In principle, we take raw cuttings, which primarily consist of sand/clay/shale and oil-based drilling fluid – and we make it pumpable.”
“The cuttings – oil-based drilling fluid mixture – consist of barites, inert material, as well as formation clays. The liquid portion may be a mixture, about an 80:20 oil to water ratio, where the water often is emulsified calcium chloride – basically brine.”
“In the TCC RotoMill, an electrical or diesel motor powers the mill to a specific RPM. Inside are rotating ‘hammers’ and the cuttings are pumped into the mill with the mixture generating friction heat,” says Eia.
The process, known as “thermal desorption”, separates liquid from the solids. “We adjust the feed to regulate the temperature inside, which may be 250° C or a little bit higher, depending on what type of base-oil we are treating. This is to ensure that the liquids evaporate, but not so high that it damages the oil, which will be reused.” Eia continues. The evaporated water and oil are transferred to separate condensers and are collected.
According to Eia, “When the cuttings go through the mill, the solids are crushed and ground – from pieces that are 2 to 10 mm or so – down to very dry, very small particles, with oil on solids as low as 0.1-0.2%.” These solids are classed as inert and can be discharged at source. “The clean water output can then be mixed back in with the powder. Then we pump the mixture down to a minimum of about 20 metres below the sea level, and the current takes it away and scatters it.”
“The recovered oil is clean as well, so they can take this base-oil and remix it back into the drilling fluid,” he adds. “It can be repeatedly reused on the rig, saving on the replacement costs and CO2emissions from transport. It’s very cost-effective and very environmentally friendly.”
“The system that we install on our customers’ rigs is always designed to accommodate the maximum desired drilling speeds. High ROP drilling can result in cuttings being produced at rates of over 50 tonnes per hour. We use what we call CSTs – cutting storage and transfer tanks – on deck to store and condition the cuttings so they are ready for us to run through the TCC RotoMill in a continuous process. The rig can continue to drill fast, and we process – and the tanks in between are buffering the whole process.
“TWMA has years of experience with this. We have, by far, the most experience in the market with this technology,” Eia continues. “For example, if we have a one well or six to eight well programme for drilling, we go through them all, prepare a containment plan where we look at how much capacity we have and how much storage we need.”
Treating cuttings at source significantly reduces logistics costs and the likelihood of environmental and safety incidents during “skip and ship” operations – collecting cuttings and fluids for shipment to onshore treatment facilities where there are potential chances of spills on these journeys.
Compared to “skip and ship” operations, processing drilling wastes at source can eliminate up to 95% of the lifting operations. Eia explains, “There’s a significant amount of logistics involved with the transportation of skips. If you are going to ship 350 skips for a well, you need approximately 50 skips on each boat – it’s a lot of vessel trips. Each container must be lifted a minimum of 10 times to get it from the shore and later back to the shore. We’re talking thousands of crane lifts – that’s a safety issue.”
Moreover, decreasing the need for transport – both offshore and onshore – leads to a corresponding reduction in CO2 emissions.
Jan Thore Eia, during his presentation at ONS 2018, pointed out that although the latest drilling rigs have made use of state-of-art technologies to improve efficiency, dealing with the produced drill cuttings remains an issue. “They have all these technologies and people sitting in war rooms, watching every hour of the drilling, but they don’t have enough cuttings handling capacity to drill as fast as they want,” he observes.
“TWMA has years of experience with offshore processing. We have developed a process that works smoothly and safely in the background which allows operators to use the drilling machines efficiently and safely.”