Oil and Gas Well Completions cont 1

Tubing Hanger/Xmas Tree Interface

Adapter Flange

•Cross-over between tubing hanger spool and x-mas tree

•It can receive the extended tubing hanger neck

•Feed through for:

– electrical cables (ESP or sensors)

– hydraulic controllines (sc-sssv)

–sensor lines etc 

Surface Wellhead Connectors

The completed well

Xmas Trees

Primary flow control system for well once in production

Features and access requirements

•Outflow from well - production

•Inflow to well - injection or killing

•Vertical access to tubing - wire line, coiled tubing

Flanged Xmas Tree 

Xmas Tree Components 

•Pressure gauges (accessory)

– safety hazard / potential wrong pressure readings

•Gauge flange or tree cap

–provides seal for top of tree

•Lubricator valve

–isolate pressure, well access for intervention tools

•Flow tee

–used to direct flow, enable thru-tubing access

•Production wing valve

–used to isolate well for most routine operations 

•Kill wing valve

–enables connection of pumping equipment

•Choke (accessory)

–controls rate of flow from well

•Master valves (main isolation valves)

–Upper Master Valve (operational valve), optional: hydraulic / pneumatic controlled
Surface Safety Valve

–Lower Master Valve (back-up valve)

  manually operated

 X-mas tree valve

¥The stem rotates

¥The gate moves up and down

 

 Choke

Categories of Xmas Tree 

Flanged tree

•Several flanged components

– each connection is a potential leak path

•Much more common than monoblock design

•More flexible than monoblock design

•takes up more space (height)

Monoblock construction tree

•Single block construction

•Fewer possible leak paths

•Used in high pressure/leak sensitive locations

 

  Monoblock Xmas Tree

 

Comprises inline or "Y" shaped block of single casting/forging

Valving arrangement

•Lower Master Valve (manual)

•Upper Master Valve (Surface Safety Valve)

•Y piece or side outlet flanges

–houses both production and kill wing valves

•Uppermost valve (manual swab valve)

  Well cluster in shallow water

WELL IN CELLAR

 

 

Tree hook-up

Multiple Completions

Cases where more than one completion string installed

•Each string independently suspended

•Must seal off tubing casing annulus

–either independently or collectively

•Independent control of fluid flow in each string

Multiple Completion Tree

Xmas Tree Selection

produce a listing of the parameters of the anticipated process or 

operating envelope

- Classify the Well Type

  Water Well ( low or medium pressure, Rate )

  Oil Well (low, medium or high pressure, GOR, Rate )

  Gas Well ( low, medium or high pressure, WGR, Rate)

This will be the basis for the design and the selection of equipment 

type and rating

 

KEYWORDS

•tubing suspension

•annulus access

•hanger flange

•boll weevil

•ram type

•LMG, UMG, Swab valve

•production and kill wing valve

•surface safety valve

•flanged and monoblock tree

•pressure rating

 

Oil and Gas Well Completions

Gas Lift Optimization cont 1

Wells that can only Flow under gas Lift

•WTEST can be used to revive a dead well by adding lift gas

•The WIG  is calculated based on the total number of lift gas increments that would give the well the largest ratio of oil production rate to lift gas injection rate (line 

O-A)

•If a well is only just able to flow (at point B), the WDG is calculated based on all the increments (line O-B)

Using the GLO Facility (1)

•Prepare the VFP Tables - VFPPROD

•ALQ = lift gas injection rate (GRAT)

•VFPTABL

•1 = Linear interpolation

•2 = Cubic Spline interpolation

•LIFTOPT keyword

•Activates the GLO facility

•Sets: 

•incremental size for lift gas injection rate

•Min economic gradient

•Min interval between GLOs

•GLO during each of the 1st NUPCOL iterations?

 •WLIFTOPT keyword 

•Well name 

•Is the well to be optimized using GLO? 

•Max lift gas injection rate 

•Weighting factor for preferential allocation of lift gas 

•Min lift gas rate 

•>0 = Min rate unless the well cannot flow 

•<0 = at least enough lift gas to enable the well to flow 

•allocate in decreasing order of weighting factor to group of wells 

•Note: By default, no lift gas is allocated if the group’s target can be met unless the weighting factor > 1.0

•GLIFTOPT keyword (optional)

•group lift gas supply limits

•group lift gas rate = SUM well lift gas rate x efficiency factor

•maximum total (produced + lift ) gas rate for the group

• Group Production Rate Limits

•Lift gas is allocated if a group/field cannot reach its OPR

•subject to lift gas supply limits, other phase limits (unless 

necessary to make the well’s Min lift requirement & the well’s

 weighting factor > 1.0)

•Rates could change if GLO is only in the 1st iteration

•Use with network option

•GLO when the network is being balanced 

•if the network is only balanced in the 1st iteration, GLO is only in the start of the time step

•if the network is only balanced in the 1st NUPCOL iterations, GLO will also be carried out in the 1st NUPCOL iterations

•Computing time increases with (No. wells)2

•effect of lift gas in pipe line:

•item 6 of GRUPNET

•‘FLO’ = add wells’ lift gas to the branch. The total GFR is used in VFP table

•‘ALQ’ = total ALQ = SUM of wells’ ALQs = the total ALQ is used in VFP table

  

•Output

•Gas lift injection rate: FGLIR, GGLIR, WGLIR

•well oil gas lift ratio: WOGLR 

•FGPR & WGPR do not include injected lift gas

•Restrictions

•Do not use

•GLIFTLIM - Max(sum ALQ), Max No. wells on artificial lift

•the lift switching option in WLIFT

•Use GLIFTOPT and WLIFTOPT instead

•Flux Boundary Conditions facility should no be used

•lift gas supplied to wells outside the flux boundary is not taken into account

 

 

Gas Lift Optimization

•A gas-lift system provides production energy by injecting gas into the production fluid column, thereby reducing the hydrostatic pressure and enabling improved reservoir production.

 

Purposes of Gas Lift optimization

•optimizing gas lift to individual wells
What is the optimum amount of lift gas required for a well to achieve its production target?


•optimizing gas lift within a group of wells
How should a limited supply of lift gas be best distributed among the individual wells in order to achieve its group production target?


•optimizing gas lift within a simple network
For sub-sea manifold group of wells, how do the pressure losses in a flow line affect the optimum distribution of lift gas to the wells?
 

Gas Lift without optimization 

 

•VFPPROD -record 1, item 7 - definition of ALQ: GRAT, IGLR, TGLR

•WCONPROD - item 12

•WELTARG - item 2 -LIFT

•WLIFT - item 5 - new ALQ; item 10 incremental of ALQ

 

Optimizing Individual Wells

•Divide the lift gas supply into discrete increments of uniform size

•Examine effect of increasing lift gas to each well by one increment. Calculate the well’s weighted incremental gradient (WIG)

•Examine effect of reducing lift gas to each well by one increment. Calculate the well’s weighted decremental gradient (WDG)

Add lift gas to the well as long as its weighted incremental gradient > the minimum economic gradient (MEG)

 Optimizing Groups

 

•Update the distribution of the lift gas increments currently allocated to the group:

•move an increment from well w2 to w1 if maxWIG(w1)>minWDG(w2)

•until there is no exchange

•Remove from the group any surplus increments

•>production rate limit

•>lift gas supply limit

•well’s WDG<MEG

•Add lift gas increment to the well

•with largest WIG>MEG

•<its own lift gas supply limit 

•<its group’s lift gas supply limit

 

 Optimizing Gas Lift in a Network

 

•Whenever a lift gas increment is added or subtracted,  WIG & WDG must be 

recalculated for all the wells in the field

•reason: change in Q affects THPs of other wells in the network

•Each time WIG & WDG are recalculated, the whole network must be rebalanced

•computation time proportional to square of the no. of wells multiplied by no. of lift gas increments added/subtracted

•recommend to use NETBALAN to decrease the network convergence tolerance 

by a factor of 10.