Subsea compleations-Offshore Engineering

7/29/2019 Subsea compleations-Offshore Engineering

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Alexandria University

Faculty of Engineering

Dept. of Marine Engineering & Naval Architecture

By:

Basem Elsayed Tawfek No 22

Mohamed Abu Elabass No 72


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Introduction:

Subsea well completions are generally used for 2applications:

1- Support to fixed installation as an alternative to a satelliteplatform for recovering reserves located beyond the reach ofthe drill string.2- used in conjunction with a floating production system torecover oil from marginal fields.Subsea completions are useful in deep water but are difficultfor access & maintenance.

1. Subsea development options:

The well head consists of permanent equipments used tosecure & seal the casings & production tubing & to providemounting place for Christmas tree.It may consist of any number of wells, if the developmentconsists of more than 1 well, the wells may be located on atemplate, in clusters feeding back to a manifolds or subseaflowbase.

1.1 templates:

Subsea template field layouts involve a structural frame thatsupports and protects a number of subsea wells together onthe seabed. It may be extremely large, heavy structures, upto 800 ton, which will accommodate a considerable no ofwells, or they may be small & light with provision for just 2or 4 wells.The template provides guides to assist in the location of the

Christmas trees & a manifold arrangement to connect thetrees with the subsea pipeline.A removable structure sits over the structure to protect thetrees from ships anchors & fishermens trawlboards.


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Subsea template

Protection structure

Subsea production templates fall into two broad categories:

a- Unitised templates:

The unitized template is normally modular in concept, andinvolves initially installing a drilling template structure priorto spudding the wells. This drilling template acts as the"temporary" guidebase for the wells. This drilling template


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spaces out wells to the required position, may supportconductor loads and provides the datum on which theproduction equipment is based. Following drilling, theproduction parts of the system are installed, either as

"flowbases" run with the wellhead high pressure housing, oras a separate structure with flowline connection mandrelsand piping installed. Wells can have individual, dedicatedflowlines back to a processing facility, or can be commingledin a manifold arrangement (usually retrievable) andexported together in a common flowline. Typically unitizedtemplates are smaller than integrated templates, withcapacity for between 2 and 8 wells.

b- Integrated templates:

The integrated template is typically more complete prior toload-out than the unitized template. An integrated templatehas well bay inserts or flowbases installed already, andrequires only drilling out and completion before productioncan begin. Template size can be large, with up to 24 wells(or more), several thousand tons in weight, and a significantconstruction project needed to build, test and install thetemplate. A large installation barge can be expected to berequired. Although initial investment in the integratedtemplate can be large, the "per well" cost falls rapidly asmore wells are drilled and completed.


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In addition, the advanced state of completion of thetemplate before load-out allows for extensive integrationtesting and proving prior to the template leaving thefabrication yard.

1.2 Manifolds:

Similar to templates, but the difference being that thestructure containing just a manifold, the Christmas treesbeing located around the structure than within it, often atlocation several hundred meters distant. The manifold isessentially a marshalling point for flow lines & controlumbilicals.

Manifolds are relatively light; the manifold can be installedfrom the drilling rig rather than a crane vessel whichconsiderably reduces installation costs. However the costs of

the additional subsea flowlines & control umbilicalsassociated with manifold can be extremely expensive.The decision whether manifolds or templates will be used isgoverned by the reservoir characteristics & installation &material costs.


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An example for manifold completions there is MENSA, GULFOF MEXICO, USA.It consists of three wells, connected to a subsea manifoldfive miles away, which is in turn tied back via a 63-mile 12in

flowline, to the shallow-water platform West Delta 143. Thisis the longest tieback in the world.

1.3 flowbase:

A flowbase allows one well to be flowed & then commingledwith the output from a second well in what generallydescribed as a daisy-chain arrangement.The Daisy Chain subsea wells consist of two or more subseasatellite wells joined together by a common flowline (and

possibly umbilical). Valving on the flowbases of the daisy-chained wells allows basic manifolding to commingleflowstreams. Each subsea tree may have a choke installed toavoid pressure imbalances in the flows.


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Using daisy chained wells allows combined use of infieldflowlines by more than one well, and may provide acontinuous loop for round trip pigging if needed.

2. Control Umbilicals:

The control umbilical is a bundle containing all the requiredcomponents to operate and serve the subsea equipment.Dependent on which type of subsea control system beingspecified, the control umbilical may contain required fluidconduits (hoses), electrical power/signal conductors,chemical injection lines, vent lines, and required spare lines.If the umbilical is subjected to dynamic loads from waveaction and currents, it may be equipped with steel armoring.

There are five types of control systems which are:

Multiplex Electro hydraulic Sequence hydraulic Piloted hydraulic Direct hydraulic
http://www.titan.snclavalin.com/offshore/norven/images/alcatel3.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls3.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls1.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls5.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls6.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls2.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls2.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls6.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls5.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls1.jpghttp://www.titan.snclavalin.com/offshore/norven/images/controls3.jpghttp://www.titan.snclavalin.com/offshore/norven/images/alcatel3.jpg


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The minimum components required in the umbilicals foreach control system are summarized below:

1-Multiplex

One hydraulic supply line, one electrical power supply line,and one electrical signal line.


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2-Electro Hydraulic

One hydraulic supply line and one electrical power/signal linefor each valve and other component to be operated.

3-Sequence Hydraulic

One hydraulic supply line and one hydraulic signal line.

4-Piloted Hydraulic

One hydraulic supply line and one hydraulic signal line foreach valve and other component to be operated.

5-Direct Hydraulic

One hydraulic supply line for each valve and othercomponents for operations. In case electrical down holeequipment is used, electrical conductors are included in thecontrol umbilical.
http://www.titan.snclavalin.com/offshore/norven/images/cliq2.jpghttp://www.titan.snclavalin.com/offshore/norven/images/cliq2.jpg


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The composition of the control umbilical therefore variesconsiderable from one control system to the next, and it isdetermined primarily by the requirements of the particularsystem being used.

In addition there will be a requirement for spare lines toreplace any damaged or leaking lines. The total number ofspare lines depends on the selected type of control system

and the sparing philosophy chosen for each specific project.


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References:

1- Angus Mather, Offshore engineering: An Introduction

, 2ndEdition, Witherby publishers, London, 2000.

2-www.titan.snclavalin.com/offshore/norven/control_umbilical.htm

3-http://www.offshore-technology.com/projects/mensa/index.html#mensa6

4-www.camerondiv.com/cgi-bin/cam.dll/cam/scripts/products
http://www.offshore-technology.com/projects/mensa/http://www.offshore-technology.com/projects/mensa/http://www.camerondiv.com/cgi-bin/cam.dll/cam/scripts/http://www.camerondiv.com/cgi-bin/cam.dll/cam/scripts/http://www.camerondiv.com/cgi-bin/cam.dll/cam/scripts/http://www.offshore-technology.com/projects/mensa/

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Subsea compleations-Offshore Engineering