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

Installation of an 880 m long 48″ pipe string under the Turian Chai in Azerbaijan.

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
  • Onshore:
    • Pipe on rollers in one section.
    • Hydrotested.
    • Special HDD coating on pipe and joints.
    • Holiday tested during installation.
    • Post hydro tested for HDD Contractor release.
  • Offshore:
    • 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.