OVERVIEW
Believed to be a world record in the field of horizontal directional drilling at the time, Clear Solutions supplied the drilling fluid for the successful installation of two 324 mm diameter steel gas pipelines between the UK Mainland and the Isle of Wight. The project was part of a scheme by Southern Gas Networks to replace the existing gas supply pipelines which had been laid just after the Second World War.
Challenge
At 3926 m (12,880 ft) and 3930 m (12,894 ft) respectively, these were believed to be the two longest pipelines installed by HDD in the world at the time. Each crossing used two 508 mm pilot holes connected by intersection techniques at a depth of 63 m below the seafloor. Both 508 mm pilot holes involved drilling through variable and highly reactive clays from the Headon & Totland Formations, together with the highly permeable and unconsolidated Becton Sand Formation.
Solution
Clear Solutions worked closely with the Principal Contractor, LMR Drilling UK Ltd, to test the viability of the crossing. The Environment Agency approved Clear Solutions environmentally friendly, water-based drilling fluid system; comprising of Ultrabore® a high-performance bentonite drilling fluid to which Pure-Bore® was added to modify the fluid properties thus enabling the drilling fluid to stabilise the challenging geological conditions and to clean the borehole, ensuring the success of both crossings.
The result was a highly inhibitive fluid providing exceptional hole cleaning, stability, effective clay inhibition and a slick gauge borehole. The results were outstanding, with drilling for crossing #1 being completed in 50 days and for crossing #2 in just 45 days with only 37 tonnes of pull back force.
Conclusion
Two record breaking pipelines were successfully installed by HDD using a Pure-Bore based drilling fluid which provided exceptional stability despite the highly reactive clay formations. Both boreholes were completed with drilling and pullback forces lower than predicted value models.
