Pile Top Drilling Works on the below principle:
OCS employs Drilling off The Boom (DOTB) technique. The drilling assembly (comprises of the power swivel, drill string and bottom hole assembly) is connected to the vessel crane. Control tugger winches is connected to the power swivel to maintain the power swivel orientation during the swivelling operations.
Drilling off the Boom technique eliminates the requirement of an extensive drilling rig spread. The drilling assembly can be mobilized and set-up on the main installation vessel in the event of a pile refusal and/or relief drilling is expected. The key working principal for Drilling off the Boom comprises off;
- Drilling assembly rigged up onto the vessel crane and lowered into the pile top.
- The Bottom hole assembly rotating bit cuts and breaks up the soil plug formation.
- Cuttings from the formation is airlifted to the surface.
Principle equipment for Drilling:
- Drill String, Bottom hole assembly centralisers, roller cutters.
- Power Swivel and Hydraulic power pack.
- Drill string make up frames.
- Airlift system
- Access platform on top of the pile
OCS Drilling Spreads consists of the following:
1. Drilling Equipment assembly
- 1 unit Power Swivel and Crossover
- Hydraulic Power Pack
- 13-3/8” Drill Pipe Strings. Mobilized length to suit water depth and drill depth
- Bottom hole assembly with drilling bit, BHA cross over, BHA collar
2. DOTB tool make up assembly
- DOTB make up frame (designed by OCS, fabricate and installed by client)
- HT100 Tongs and Hydraulic Jack
- Pipe elevator / clamps to lift up drill strings
3. Air lift system
- High pressure – high volume air compressor
- High pressure – high volume air receiver tank
- Air hoses connecting air lift system to the power swivel