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Sinking at sonic speed

Danbar Drilling Services was approached recently by Brownfield Solutions (BSL) regarding its sonic drilling rig capabilities.

BSL is currently undertaking a site investigation contract on a new industrial estate in Sheffield, UK, for an internationally renowned, UK-based technology manufacturer. The task had been proving troublesome with conventional drilling rigs.

The site was previously home to an open-cast coal mine and the workings, which are now backfilled, were more than 60m deep.

The site has been investigated on a previous occasion as part of a larger survey area. Drilling conditions during this previous investigation were found to be extremely difficult as the site had been backfilled with a mixture of mudstone, clay and sandstones.

To overcome this problem, BSL employed cable percussive drilling, with a rotary core follow-on. However, drilling was found to be extremely slow due to the variable ground conditions.

The rotary rigs were required to be on standby in case the cable techniques could not advance through boulders, which was very costly, and significant equipment damage occurred.

Danbar Drilling Services is now working with BSL using its rotary Sonic SDC550-18 rig to core the open-cast backfill. The technique was chosen because it offers high production rates.

The core it produces removes the requirement for a second rotary coring programme, and it is also more likely to reach the final depths required.

Sonic drilling is ideal for this type of geology, as the core barrel does not allow any of the flushing medium to come into contact with the ground being sampled.

When the casing is driven over the top of the core barrel, it keeps the borehole fully cased at all times. This stops the formation collapsing and makes the drilling process much easier than with standard techniques.

Daniel Havard, drilling director at Danbar, reports: “The Sonic rig is an excellent piece of kit that can provide speedy production rates. Many of our clients are surprised at how efficient it is when they see the machine in action.”

The work involves sinking a number of boreholes up to 66m into the underlying strata and collecting cores.

The contract is programmed to take three weeks and should be completed by early June. Progress so far has been swift. The crew have been coring up to 30m per day with standard penetration tests. All of the core runs have provided 100% recovery.

“This is a great achievement considering the variable conditions on this site,” adds Mr Havard. “Slag has also been encountered on this site and the rig has been able to drill through this without delay.”

Danbar Drilling Services is also using sonic drilling techniques on several geothermal projects. Where the geology is favourable, this method can reduce drilling time considerably.
Courtesy Geo Drilling International

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