Subsea development system

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해양 자원 발 시스템

: Introduction to Offshore Petroleum Production System

Yutaek Seo



Period Contents

1 Week General introduction, outline, goals, and definition

2 Week

Type of reservoir fluids

: Dry gas / Wet gas / Gas condensate / Volatile oil / Black oil

PVT laboratory testing

: Constant mass expansion / Differential vaporization / Compositional analysis /: Oil densities and viscosity / SARA, Asphaltenes, WAT

3 WeekFluid sampling and characterization

: Bottom hole samples / Drill stem test samples / Case studies

4-5 Week

Thermodynamics and phase behavior

: Ideal gas / Peng-Robinson (PR) / Soave-Redlich-Kwong (SRK)

: Peneloux liquid density correction / Mixtures / Properties calculated from EoS

6 WeekSubsea Field Development

: Field configuration / Artificial rift / Well layout

7 WeekWell components

: Well structures/Christmas tree

8 WeekSubsea manifolds/PLEM and subsea connections

: Components / design / installation

9 WeekUmbilical / risers / flowlines

: Design criteria/ analysis

10 WeekFlow regime

: Horizontal and vertical flow / Stratified flow / Annular flow / Dispersed bubble flow / Slug flow

11 WeekFlowline pressure drop

: Frictional losses / Elevation losses / Acceleration losses / Errors in ΔP calculation / Pipe wall roughness

12 WeekLiquid hold up

: Cause / Prediction / Field & experimental data / Three phase flow

13 WeekFlow assurance issues

: Hydrate/Wax/Asphaltene/Corrosion/Scale

14 WeekField operation

: Operational procedures for offshore petroleum production

15 Week Application Example: Offshore platform (Pluto fields), Floating production system (Ichthys fields)

16 Week Final Test





Subsea tree

• A subsea tree is basically a stack of valves installed on asubsea wellhead to provide a controllable interface between the

well and production facilities.

• It is also called a Christmas tree, cross tree, X-tree, or tree.

• Subsea tree contains various valves used for testing, servicing,

regulating, or choking the stream of produced oil, gas, andliquids coming up from the well below.

• The various types of subsea trees are used for either

production or water/gas injection.

• Configurations of subsea trees can be different according to the

demands of the various projects and field developments.



Tree Interfaces that Govern Design



Subsea completion

• Prior to the start of production, a subsea well is to be completedafter drilling. Subsea completion is the process of exposing the

selected reservoir zones to the wellbore, thus letting the

production flow into the well.



• Open hole completion:: Open hole completions involves simply setting the casing in

place and cementing it above the producing formation.

: Then continue drilling an additional hole beyond the casing and

through the productive formation. Because this hole is not cased,

the reservoir zone is exposed to the wellbore.• Set-through completion:

: The final hole is drilled and cemented through the formation.

: Then the casings are perforated with tiny holes along the wall

facing the formations. Thus, the production can flow into the well

hole.



Casing design

• The most important parameters for casing design are wallthickness and length.

• It is a comparatively simple structure.



• As the oil explorations move into deepwater drilling of high-pressure and high temperature wells, it has become more and

more popular and necessary to increase the scope of the

optimization by encompassing more design parameters into the

analysis.

• Consequently, numerous variables can be taken into accountwithin the design spectrum. However, usually it is imperative to

integrate all of the subsea components in the analysis of the

casing design, which we will elaborate on in wellhead reliability

analysis section.



• Normally, a lot of different design parameters are proposedunder the same conditions.

• To counter this problem, a dimensionless parameter called the

wellhead growth index (WHI) has been developed, which

greatly aids the ability to determine the severity of the design

and a means of describing the severity of wellhead growth,without sacrificing any rigor.

• WHI encapsulates the annulus fluid expansion and wellhead

growth and it provides a simple practical way to view the casing

movement and fluid expansion in the annulus during the course

of drilling and also during the production phase of the well. It isdefined as the ratio of the annulus fluid expansion of the casing

to the actual volume of the exposed segment above the top of

the cement.



• The annulus fluid expansion includes the unconstrained volumechange and the annulus volume change due to annulus

pressures. Wellhead growth gives an estimate of the

circumferential and axial strain on the casings.

• With the circumferential and lateral strain, the total volume of

the expansion of all casing string for all casing segments isgiven by:

• The total area of the annulus cross section for each casing

string is given by





• WHI gives a quantitative predictive capability for interpreting the

calculation results. The higher the value of WHI, the higher the

severity of the casing design involved.

• for multiple casing string



Subsea wellhead

• The main function is to serve as a structural and pressure-containing anchoring point on the seabed for the completion

systems and for the casing strings in the well.

• The wellhead system incorporates internal profiles for support

of the casing strings and isolation of the annulus.

• In addition, the system incorporates facilities for guidance,mechanical support, and connection of the systems used to drill

and complete the well.





Function requirement

• Provide orientation of the wellhead and tree system withrespect to the tree-to-manifold connection.

• Interface with and support the Xmas tree system and blowout

preventer (BOP).

• Accept all loads imposed on the subsea wellhead system from

drilling, completion, and production operations, inclusive ofthermal expansion. Particular attention should be given to the

horizontal tree concept where the BOP is latched on top of the

Xmas tree.

• Ensure alignment, concentricity, and verticality of the low-

pressure conductor housing and high-pressure wellheadhousing.

• Be of field proven design, as far as possible, and designed to

be installed with a minimum sensitivity to water depth and sea

conditions.



Operation requirement

• Provide the ability to install the following equipment in the sametrip: the production guide base (PGB), the 36-in. conductor, and

the low-pressure conductor housing. The assembly should be

designed to be preinstalled in the moon-pool prior to being run

subsea.

• Allow for jetting operations for the casing pressure and for thedrill and cement as a contingency case.

• Include provision for efficient discharge of the drill

cuttings/cement returns associated with the drilling operations.

• Provide a bore protector and wear bushings to protect the

internal bores of the wellhead system components duringdrilling, completion, and retrieval operations.

• Ensure that all seals and locking arrangements can be tested in

situ.



• Ensure that the complete seal assembly can be retrieved andreplaced in the even of a failed test.

• Ensure that all permanent seals are protected during the

running phase and remotely energized after landing.

• Be designed such that the running string with wellhead tools

and components will not snag or be restricted when running inor being pulled out of the hole.

• Provide tooling that allows for seal surfaces to be cleaned after

cement operation and prior to setting seal assemblies without

pulling the running string; that is, the tool should allow cleaning

of seal surfaces by circulation prior to pack offsetting.• Be designed to allow for landing of the casing hanger and

installation of the seal assembly and removal of the same (in

case of failure) in a single trip. Multipurpose tools should as far

as possible be used to avoid pulling of the running string for tool

change-outs.









• Normally, a finite element analysis (FEA) and riser fatigueanalysis will be performed to verify the design capacities.

• In addition, thermal analysis is performed to determine the

temperature profiles through the system so that temperature

derating can be accounted for as appropriate.

• A prototype wellhead should be tested to the test pressure aswell as loaded with simulated casing loads and BOP test

pressure with hangers in place simulating the real production

environment in total without experiencing any permanent

deformation.



Intermediate Casing Hanger

• The intermediate casing hanger for the system lands in the firsthanger position in the lower portion of the wellhead.

• Detailed stress analysis and classical calculations should be

performed in fashion similar to the analysis performed for the

intermediate hanger.







Casing Hanger Running Tools

• The intermediate and production casing hanger running toolsrun the casing hangers and set the annulus. These tools

normally are designed using the same technology and in many

cases the same parts as the standard 15-ksi running tool.



BOP test tool

• The BOP test tool is designed with an approach that is similarthat for other components and tools in this system. It is used to

test the BOP in terms of future formation pressure that the

operator is currently drilling into, and is also used to run and

retrieve wear bushings.





Wellhead system reliability analysis

• When drilling a well in deep water, the wellhead will bear theintricate forces from the environment and the drilling operation,

which will affect the integral reliability of the wellhead system.

• Normally an FEA model is built to analyze the wellhead system

reliability in terms of taking all factors into consideration,

including loading from the marine environment and the drift of adrilling vessel or platform, and nonlinear response between

casing string and soil stratum.



Fx is the sum of the external force on the riser in the x direction,

Fy is the sum of the external force on the riser in the y direction,

W is the weight of the BOP and wellhead, and

Fd is the direct wave force on the BOP and wellhead upper seabed





• P (x,y) is determined by



Fundamentals of subsea configuration



Next Class on 3rd April

: Tree type, design, and installation

Homework 5: Preparing a report

Discuss the following issues for designated oil and gas fields

a. Reservoir type

b. Types of host structure

c. Topside facilities

d. Field architecturee. Current status

f. Operational issues





Gullfaks & Tordis fields



Magnolia field





Perdido field



Girassol FPSO



Ormen Lange

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Subsea development system