What is HDD?
HDD stands for Horizontal Directional Drilling. There are three specific stages during which HDD is executed:
1 – Pilot Drilling
Drill from entry point to exit point while continuously surveying position.
2 – Reaming & Cleaning
Enlarging the Pilot Hole to the final hole size required for pullback.
3 – Pullback
Installation fo the actual pipeline / bundle in the hole
Phase 1: Pilot Hole Drilling
During this phase, a hole is drilled from entry to exit:
- BHA consisting of drillbit, bent sub, various cross overs.
- A Non Magnetic Drill Pipe is used if the Steering Tool is magnetic.
- Survey every end of the pipe – typically this is 9.7 m.
- The hole can be supported by secondary systems such as:
- Surface Coil
- Beacon / LFB
- An intersect can be made to extend the HDD length or to limit annular pressure and therefore frac-out risk.
Phase 2: Reaming & Cleaning
The hole is enlarged and checked to allow for the Pipeline installation:
- Reaming is done in various steps limited by rig capacity, tooling capacity and mud system capacity.
- Final hole diameter between 1.3 and 1.5time pipe diameter.
- Typically done from exit- to entry side, with drillpipe in tension.
- Drilling fluid is checked to ensure sufficient displacement.
- Forward reaming in shore approaches can be considered.
Phase 3: Pullback
The last phase is the installation of the Pipeline in the HDD Hole:
- Pullback assembly consisting of a swivel, shacklesand pullback reamer will be installed at the end of thedrill string.
- Pullback Assembly will be hooked up to pullheadwelded to the pipeline
- Pipe on rollers in one section.
- Special HDD coating on pipe and joints.
- Holiday tested during installation.
- Post hydro tested for HDD Contractor release.
- Pipe prelaid and tested on seabed.
- Pipe string welded during pull.
- Floating, typically in swamp work.
HDD Shore approach Risk:
HDD projects carry higher risks than conventional crossings, onshore and offshore. Not many HDD projects end up in complete failure though – they end up costing more time and money.