Cromwell Development - Xodus Group
Client: Centrica Energy
Location: Offshore Trinidad & Tobago

Providing complete, costed development solutions.

Xodus Group’s integrated team of process, flow assurance, layout and structural engineers outline the technical feasibility of potential Cromwell development options.

The Cromwell development comprises gas fields located in the Block 22 and North Coast Marine Area-4 (NCMA-4) licence areas located offshore, north of Tobago. The project aimed to determine the feasibility of delivering 300 MMscfd of natural gas from these concessions to the Atlantic Liquefied Natural Gas terminal (ALNG) in south-west Trinidad. The requirement was to make up forecasted terminal ullage via a combination of new processing facilities, new pipelines and existing infrastructure.

A total of 16 wells were to be tied back to ALNG via a 111km x 24-in. infield pipeline to either:

  • a brownfield module on the existing Hibiscus platform (located in the NCMA-1 licence area) and exported via the existing NCMA-1 pipeline to ALNG,
  • a new Bridge-Linked Platform (BLP) at Hibiscus and exported via the existing NCMA-1 pipeline to ALNG.

Following concept opportunity studies, Xodus Group was asked to ascertain the technical feasibility of two main development options before progression to the select phase of the project cycle.

Assignment scope
For the BLP and brownfield module options, Xodus carried out:

  • Class 4 cost estimates
  • Level 1 overall concept schedules
  • Technical studies to identify any potential concerns affecting project realisation.

Initial work centred on the integrated flow assurance and compression studies defining the key components of the development. Early definition of these items was critical. The existing subsea pipelines are constrained to a 600# rating and the Cromwell reservoir pressure is expected to deplete rapidly over the first two years.

Steady-state flow assurance studies were carried out using PIPESIM software to assess the 24-in. infield pipeline from Block 22 to Hibiscus and to determine the platform arrival conditions providing input to the conceptual process design. A dedicated outline compression study was performed to determine flexible compressor configurations for high and low pressure arrival to minimise future modifications.

Process layouts were carried out using PDMS software for the BLP option. This was aligned with relevant input for required safety distances to present an As Low As Reasonably Practicable (ALARP) safe process configuration. A 3D layout was produced to give the client clear visualisation of the final topsides.

Structural design of the BLP jacket, bridge and piles was carried out in tandem with the layouts. A key focus was the feasibility and location of the bridge landing onto the existing Hibiscus platform and relocation of the flare boom to the BLP.

The brownfield module concept involved installation of a cantilever to site the new Cromwell slugcatcher, pig receiver, subsea communications equipment, Mono Ethylene Glycol (MEG) regeneration system and waste heat recovery / heating medium system. The necessary topsides facilities / modifications, layouts and preliminary structural design were carried out in addition to an estimate of Hibiscus downtime.

Overall cost estimates were produced for the BLP and brownfield module development options. QUE$TOR was used for the topsides and jacket estimates while Xodus’ proprietary estimating tool was used for the Brownfield concept and subsea infrastructure.


  • Successful execution of 3,500 man-hour / 18 week study
  • HYSYS process modelling and in-house calculation tools used for topsides design
  • PIPESIM used for steady-state transport pipeline analysis
  • PDMS used for 3D platform layout and demonstration
  • Project costs estimated using a combination of QUE$TOR for greenfield costs and Xodus’ in-house brownfield cost estimating tool.