Successful drilling in reactive clay
Drilling in highly reactive, sticky clay can be a real challenge. Your reamer may ball up, making it difficult to cut and clean the hole - resulting in a thick cuttings bed that sticks to the drill pipe. The drill pipe may be squeezed by swelling clay, and in the worst situations - the pipe may become stuck during the install.
Testing
Most drillers are aware of the locations with the most reactive clay. Having previously encountered it, they can then prepare tooling and fluids to drill successfully.
If you’re unsure, and there are no geotechnical reports to base decisions on - a sure fire method for testing the reactivity of clay is to break off a small clump of damp clay, and roll it between your hands. If you can roll it out to the thickness of a pencil, it is going to be reactive and swell.
Tools for success
To drill effectively in reactive clay there are only three steps to follow;
Choose an effective reamer;
Choose a fluid system that will break down the clay and stop it from swelling;
Pump sufficient volumes of fluid - the higher the ratio the better
Choosing a reamer
To effectively drill reactive clay, the formation needs to be cut into as smaller pieces as possible, and pumped past the reamer to the exit pit.
The Tornado reamer accomplishes both of these tasks. Each blade cuts the hole incrementally larger, producing a slurry that will be pumped through the large mixing holes in the blades, and back to the pit.
Choosing a fluid system
The RaPiD system is a cost effective solution; for breaking down and inhibiting swelling clays. Composed of Ringfree, Polyplus and Platinum DD; RaPiD will complement the Tornado reamer to produce a non-sticky, pumpable slurry.
Ringfree is a polymeric thinner - it rapidly breaks down clays into small particles that Polyplus can inhibit.
Polyplus is a long chain PHPA polymer - the chains wrap around clay particles, preventing water interacting with them to reduce swelling.
Platinum DD reduces torque and drag, by preventing the clay sticking to the reamer and rods.
Pumping the right volume
Reactive clay requires a higher ratio of drilling fluid to spoil than other formation types. The additives bind to the clay particles, and so are “drawn” out of the system. Pumping a higher ratio means there are sufficient additives to continue to act on newly exposed clay cuttings. In unreactive formations, a ratio of 3 parts fluid to 1 part spoil may be suitable. In reactive clays, a ratio of 5:1 may be required to treat the clay.
When the bore is larger than around 250mm, consider adding Duo Vis to suspend the cuttings.
Reactive clay can be a challenge to drill effectively. Everyone has heard the horror stories. By using a reamer designed for clay, a fluid system to break down and inhibit the clay, and pump at an appropriate ratio, you can get your bores completed on time in the trickiest ground.
Talk to us today about reamers, fluid systems and pumping ratios. Our team is available on 07 849 2366 or email us about effectively drilling in reactive clay.
