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Constructability Suggestions for Offshore and Subsea Installations

Published on 27 Apr 2019 by Nicole Castelli


Constructability Suggestions for Flowline, Flowline Jumper (FJ) & PLET

  • Need to identify stabilization period for flexible and rigid jumper combination for hydrotest.
  • Identify plan to dewater pipeline, specifically gas injection (define dryness criteria). Need to define who handles this task.
  • Consider flexible pipe for entire length of flowline. Consider material compatibility (e.g. MEOH), pigging, reliability, insulation, etc.
  • Consider elimination of gauge pigging after installation of flowline. Check current code for applicability. That would need alternate method to verify no kinks in line.
  • Prepare plan for safe anchoring for future field projects.
  • Consider testing pig-able "y" with the pigs that will be used.
  • Consider definition of functional requirement for insulation. Need qualification criteria for insulation and thermal analysis. The Risk of not meeting a performance spec. has cost implications.
  • Flowlines need to be isolated from compliant tower. Supply Insulation kit for cathodic protection.
  • Make sure there is enough contingency in minimum bend radius for flow line and umbilical installation.
  • Gather temperature data of sea bottom during hazard survey to validate insulation system design.
  • Ensure there is test data on riser available for review.
  • Define acceptable condition that flowlines will be left by contractor.
  • Define acceptable specification for reel lay installation alternative. Make sure minimum requirements associated with each installation method are identified.
  • Need Long BaseLine (LBL) array for accurate positioning of PLET. Alternate is Ultra Short BaseLine (USBL), precision is better with LBL.
  • Use positioning array installed for positioning tower; fixed frame with removable Compatt Transponder, or, field wide acoustic system.
  • Ensure length of flexible FJ meets length required to overcome torsional stiffness. Use mock-up of connection points to verify fit-up.
  • Consider rigid well jumpers in lieu of flexible jumpers. Ensure metrology is proper.
  • Introduce more bend in flow line to take care of thermal growth, simplify PLET design.
  • Consider allowing entire PLET to move relative to seabed vs. fixed with sliding piece. Less weight, can use winged mud mats.
  • Ensure inline tee(s) remain in correct orientation.
  • Confirm dimension of inline tee is compatible with stinger. Design of ITA and PLET are handled by contractor. Need to have a good functional specification to maintain reasonable control.

Constructability Suggestions for Contracting Strategy for Subsea Equipment Vendor (SEV) and Subsea Installation Contractor (SIC)

  • Consider having riser supplier supply both halves of connector. Same applies to manifolds, trees. Attempt to standardize on connectors.
  • Develop coordinated connector system strategy for field (consider free issue of connectors by appropriate contractor). Need to evaluate non-tooled connector vs. tooled connector and optimum sets of tools.
  • Consider separate installation contracts or packages for Subsea contractor A & B, or, C individually or combined.
  • Consider after-market support of equipment (SEV).
  • Need to clarify interface details between SIC and SEV.
  • Need to identify how to interface with facility’s logistics such as laydown area, equipment usage, fuel, water, etc.
  • Need to identify point of delivery for trees.
  • Need to identify requirements for local content.
  • Consider alternate contracting strategies for SEV and/or SIC partnering, alliance, incentives, etc.
  • Consider establishing stand-by rate criteria for specific work that could be interrupted with other priority work / operation. Include in bid packages to avoids risk of higher price for unknown access to contractors' work.
  • Specify the level of your company involvement in Contractors' design and installation.
  • Clearly specify interface points on umbilical, Umbilical Termination Assembly (UTA) between SEV and SIC; and responsibility for controls and testing of completed installation. Whoever supplies umbilical, there needs to be close coordination between both contractors on umbilical, UTA.
  • Ensure design of installation equipment is done by the contractor / party performing the installation or that party has responsibility to review / approve installation equipment design. Need to specify who is responsible / liable for what.
  • Ensure the elements of a project safety management plan are included in bid packages (integrating all governing safety requirements). Ensure JSA's are required.
  • Consider contingency plan in contract for change.

Constructability Suggestions for Manifolds & Well Tie-ins

  • Keep manifolds within project pre-specified installation load (including dynamic load). Ensure risk of bid from contractors coming in with greater dead weight is minimized.
  • Keep manifold foundation within project pre-specified installation load (including dynamic load).
  • Consider use of heave compensator for manifold installation.
  • Investigate how smaller vessels can be utilized for manifold installation.
  • Keep a continuous installation sequence as base case (eliminate multiple mob - demob).
  • Pre-install manifold foundation.
  • Confirm tolerances of well positioning.
  • Coordinate sequence of well drilling with layout of well jumper. Consider retrieval issues. Installation of jumpers can be done independently (one doesn't interfere with next one).
  • Ensure there is numbering system to match suction pile to manifold.
  • Have dual valves: one ROV and one hydraulic activated. Allow replacement of jumper without shutting in entire manifold.
  • Identify functional requirements for complete installed system test. Individual items / components should be hydro tested.

Constructability Suggestions for Subsea Center Layout

  • Reduce height of riser jumper (RJ) by consider adding additional PLET at base of riser.
  • Eliminate doglegs in horizontal portion of RJ.
  • Need vertical clearance above RJ connector for running tools & rigging. Identify installation aids location and expected loads on the tower.
  • Design RJ to avoid use of running tools by possibly using self activating connectors.
  • Direct connect MEOH line straight to tower to avoid the jumper / PLET.
  • Pre-plan anchor points for future accommodation barge(s) and other vessels.
  • Optimize export pipeline layout with future flowline layout.
  • Consider installation of protection over export pipeline to possibly combine with dropped object protection for flowlines. Location of deadman anchors may vary with installation contractor. Thermal expansion needs to be considered for any protection.
  • Consider alternate route for umbilical layout of umbilical that goes to an additional location.

Constructability Suggestions for Umbilical Termination Assembly (UTA) and Subsea Distribution Unit (SDU)

  • Consider making UTA independent of water injection manifold.
  • Address slack loop (over length compensation) consideration on as-built length of umbilical. Vee support concept on water injection manifold further complicates slack length issue.
  • Consider UTA size limitation for reel. Make UTA small enough to fit on reel. Idea implies UTA and SDU are separate. Need to partition the reel.
  • Umbilical needs to be isolated from compliant tower. Make Insulation kit available for cathodic protection.
  • Strap umbilical to coiled tube. This has implications on installation, possible savings on installation time.
  • Include MEOH line in umbilical. Could use less expensive material such as CS.
  • Consider design / installation of hold back anchor to control touchdown point of umbilical.
  • Consider bringing umbilical into center of Subsea Center layout.
  • Develop clear procedure for overboarding UTA. Ensure rigging is workable and does not conflict with other operation or create safety problem.
  • Specify need for umbilical supplier representative onboard vessel during installation.

Constructability Suggestions for Drilling

  • Ensure well head setting height is agreed.
  • Ensure cuttings will not interfere with setting any layout items (mudmats, etc.). Require drilling contractor to level bottom after drilling.
  • Consider setting manifold foundation with drilling rig. Typically want suction pile / conductor installed prior for set-up time (30 days or more).
  • Production wells would be flowed back to rig for cleanup of completion fluids.
  • Need to locate standby (backdown) buoy for anchor vessels.

Constructability Suggestions for SIMOPS & General Installation

  • Ensure there is a fully integrated schedule with SEV, SIC, and project scope.
  • Consider as wide & flexible as possible an installation window for SIC (vs. specified period).
  • Consider safe area for lowering BOP then bringing across over Subsea Centers / tree.



Tags: offshore subsea constructability installation

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