1

Well design and construction I

Adrian AdamsNexen Petroleum UK

2

Agenda

• 11:00-12:00 Well construction

• 12:00-14:00 Lunch

• 14:00-14:50 Well design

• 14:50-15:00 Coffee break

• 15:00-16:00 Design exercise

3

Drill rigs (1): fixed (surface wellheads)

Jack-up Fixed platform

4

Drill rigs (2): floating (subsea wellheads)

Semi-submersible (moored) Drillship (DP)

5

Drill rigs (3): compliant platforms

6

Drill rigs: water depth capability

7

Rig selection

• Semi-submersibles (moored)

- exploration and development wells

- up to 3000 ft water depth for conventional mooring system

• Drillships (dynamic positioning)

- exploration and development wells

- up to 10000 ft water depth

• Jack-ups

- usually development wells (cantilever over wellhead platform)

- up to 400 ft water depth (WD)

• Platforms

- development wells only

- fixed platforms up to 500-600 ft WD, compliant above this

8

Floater drilling: overview

9

Rig systems: hoisting

Derrick Draw-works

10

Rig systems: rotation

Kelly and rotary table Top drive

11

Rig systems: circulation

12

Rig systems: well control

13

Well types

• Exploration

- used to look for oil and gas reservoirs

- aimed at crest of structure

- usually a throw-away well (abandon after drilling)

• Appraisal

- used to determine the extent of a discovery

- aimed at flank of structure

- may be a keeper, otherwise abandoned

• Development

- production (extract oil and/or gas)

- injection (re-pressurise reservoir by injecting water or gas)

- 10 to 20 year service life

14

Well targets

Gas-Oil contact

Oil-Water contact

Seal

Reservoir Rock

Oil

Gas

Fault

Water

15

Typical well schematics

80

405

0

Seabed

RT

MSL

MD BRT TVD BRT

0

80

405

64426” hole20” shoe 642 642

396Top face guidebase 396

All depths in feet

8½” TD 11140 10590

Bottom hole location (final)Lat: 57° 48’ 28.300” NLong: 00° 56’ 14.577” W X: 622,566.69 m EY: 6,409,331.61 m N

Wellhead Vetco SG5 10000 psiFlowbase heading: 315.7º G, 317.5º TTop face bullseye support beam 9 ft ASB

John Shaw

9 5/8” x 7” casing9 5/8” 53.5 lb/ft L80 Vam Top10º internal taper XO7” 29 lb/ft L80 13Cr Vam Top HTPressure tested to 5000 psi in seawater

Surface location (slot #10) (final)Lat: 57° 48’ 02.377” NLong: 00° 56’ 23.438” W X: 622,444.86 m EY: 6,408,525.68 m N

Top Buzzard SST 9652 9206

644

3695 369513 3/8” shoe

17 1/2” hole 3715 3715

9 5/8” x 7” XO 9392 8967

12¼” hole 9412 8985

TOC (theoretical) 8652 8284

7” shoe 11129 10579

Revisions listRev 01 (20/9/06): first issueRev 02 (27/9/06): motor bend for 17½” hole, 13 3/8” test pressure, TD depth revisedRev 03 (29/9/06): 13 3/8” pressure test policy revisedRev 04 (31/10/06): updated for as-built, target, trajectory, and geological tolerance revisedRev 05 (6/12/06): updated for as-built

30” x 20” conductor30” x 1.5” X52 extension BWP up x HD/HT-9030” x 1.5” X52 XO HD/HT-90 x SF-603 jts 30” x 1” X52 SF-6020” 133 lb/ft X56 shoe joint c/w XO to 30” SF-60Final bullseye readings 0.5º forward, 0.5º aftHard cement tagged 20 ft BSB (both funnels),40 bbl top-up both sides

13 3/8” casing18¾” HP housing c/w 21” x 1.25” extension20” x 13 3/8” XO joint13 3/8” 72 lb/ft L80 Vam TopPressure tested to 1800 psi on bump Pressure test to 3000 psi after BOPs set

BJ Lite 115330 bbl 12.5 ppg (250% excess)

62436” hole 624

CCB Class GLead 930 bbl 13.2 ppg (150% excess) Tail 90 bbl 16.0 ppg (15% excess)

CCB Class GTail 105 bbl 16.0 ppg (10%)

87

457

0

Seabed

RT

MSL

MD BRT TVD BRT

0

87

457

20” shoe26” hole 697 697

36” hole 677 677

3478 3478

LiteFIL RHC 408 bbl12.5 ppg

449Top face LP housing 449

All depths in feet

Rugby class GLead 838 bbl 12.5 ppg Tail 167 bbl 16.0 ppg

TOT 2978 2978

12¼” TD 9179 9179

12¼” coringCore Burns sandstone on shows

LoggingAs per logging programme

Bottom hole locationLat: 57° 39’ 03.830” N Long: 00° 52’ 44.929” W X: 626,573.00 m EY: 6,391,987.00 m N

Wellhead Vetco SG5 10M

13 3/8” casingPre-assembled 18¾” WHH assemblySeat protector, SSR and top wiper plug pre-installedApprox 74 joints 13 3/8” 72 lb/ft L80 BTCPressure test on bump to 2000 psi

12¼” holeSmith MA74PX, PDM/ABH 0.78 degDIR/INC/GR/RES/SONICDrill out wiper plug with seawater Displace to 10.0 ppg WBM while drilling cementDrill 10 ft new hole, circulate and condition mudPerform FIT to 15.0 ppg minimumIncrease MW to 11.5 ppg before bottom ChalkDrill ahead 12¼” hole to TD

17½” holeSmith MG02TQc, PDM/ABH 0 degDIR/INC/GRSeawater + high-vis sweeps (8.7 ppg)10.5 ppg displacement mud

30” x 20” conductor30” x 1.5” X52 extension BWP up x HD/HT-90 b/d30” x 1.5” X52 XO HD/HT-90 p/u x SF-60 b/d3 jts 30” x 1” X52 SF-60 pin up x box down20” 133 lb/ft X56 shoe joint c/w XO to 30” SF-60 p/u

36” x 26” hole26” MSDSSHc + 6-point HO, PDM/ABH 0 degDIR/INCSeawater + high-vis sweeps (8.7 ppg)10.0 ppg displacement mud

BOP Hydril 18¾” 15M ChRdRdChAhAl

Abandonment (indicative)5 x 600 ft plugs on bottom2 x 500 ft plugs across shoe Tag and test shoe plugFinal plugs dependent on formations

Sedco 714

9 5/8” casingContingency for hole problems or DST9 5/8” 47 lb/ft L80 New Vam available

Surface locationLat: 57° 39’ 03.830” N Long: 00° 52’ 44.929” W X: 626,573.00 m EY: 6,391,987.00 m N

13 3/8” shoe

Run BOPRun and test BOP to 5000 psi

Top Burns 6504 6504

692

17½” hole 3498 3498

16

Casing strings

36 inchHole

30 inchConductor

26 inchHole

20 inchCasing

17 1/2 inchHole

13 3/8 inchCasing

12 1/4 inchHole

9 5/8 inchCasing

8 1/2 inchHole

7 inchLiner

6 inchHole

5 inchLiner

Typical casing design for central North Sea

• Conductor (30” diameter, 36” for deep water)

- supports weight of inner strings

- cases off soft topsoils

- usually 6 no. 40 ft joints (240 ft)

• Intermediate casing (usually 13 3/8”)

- cases off Tertiary formations

- usually set in top UC Chalk (3500-4000 ft)

• Production casing (usually 9 5/8”)

- cases off Chalks and LC Siltstones

- usually set just above reservoir

• Liner (usually 5½” or 7” diameter)

- set across reservoir

• NB: optimum casing design varies by area (depths, geology, drilling hazards)

17

Typical lithology (central North Sea)

Ekofisk Fm. (3130’)

SeabedHordaland Gp

Beauly Mbr

Tor Fm. (3373’)

Hod Fm. (3727’)

Intra Hod Mkr. (4105’)

Herring Fm. (4938’)

Rødby Fm. (5469’)Sola Fm. (5568’)

Valhall Fm. (6315’)

BCU (8508’)

Plenus Marl (5128’)Hidra Fm. (5175’)

Top Buzzard Sst (9232’)

Base Buzz B4 (9568’)

Top Buzz B1 (9806’)Top Heather (9930’)

18

Casing cementation

• Cement is pumped down the well between the top and bottom plugs

• Once bottom plug bumps, cement is expelled through float valve and up the annulus (i.e., outside the casing)

• The cement volume is disposed such that top of cement (TOC) is at the desired height once the top plug bumps

• TOC height is determined by zonal isolation requirements

• Once the cement has set, the plugs, float and shoe track are drilled out

DisplacementFluid

Top Plug

CementSlurry

Centralizer

Centralizer

Bottom Plug

Float ValveOpen

CasingShoe

Float ValveClosed

Top PlugSeated

DisplacementFluid

Drill Bit

Drillstring

Stabilizer

Stabilizer

19

Drilling fluids

Functions of drilling fluid

• Provides primary well control

• Stabilises open hole (mechanical, chemical)

• Cools and lubricates bit

• Removes cuttings from bit

• Transports cuttings to surface

• Powers the mud motor

• Reduces torque, drag (run/pull DP, casing)

• Provides fluid medium for well logging

Types of drilling fluid

• Seawater plus hi-vis sweeps

• Water based mud (WBM)

• Oil based mud (OBM)

20

Drilling fluid selection (central North Sea)

• 36” section (30” conductor)

- seawater plus hi-vis sweeps

- displace to 10.5 ppg bentonite WBM after drilling

• 17½” section (13 3/8” casing)

- seawater plus hi-vis sweeps

- displace to 10.5 ppg bentonite WBM after drilling

- reactive shales may limit shoe depth

• 12¼” section (9 5/8” casing)

- WBM if reactive shales not a problem, OBM otherwise

• 8½” section (7” or 5½” liner)

- as 12¼”, but drill-in (clear) fluid if risk of formation damage

21

Drill bits

Mill tooth TCI PDC

Tungsten carbide Polycrystalline

insert diamond compact

22

Drill bit selection

• Mill tooth bits

- can only drill soft formations: Quaternary, top Tertiary

- used for tophole (36” section: 26” bit plus 36” hole opener)

• TCI (or “insert”) bits

- can drill all formations, including chert and pyrite

- rate of penetration (ROP) ±10 ft/hr in hard formations

- life limited by bearing wear (750 krevs, 24-36 hours drilling)

- used for 17½” section if chert at Ekofisk/Tor transition

• PDC bits

- can drill up to moderately hard formations (not chert and pyrite)

- ROP 10-100 ft/hr, depending on formation

- life limited by cutter wear (3-5 days if bit correctly chosen)

23

Bottom-hole assemblies (1)

• Essential

- heavyweight DP, drill collar Weight on bit

- drilling jars and accelerator Jar stuck pipe

- non-magnetic DC Allows azimuth measurement

- MWD (instrumentation) Inclination, azimuth, GR

- MWD (telemetry) Real time D&I / GR

- stabilisers Directional control

• Optional

- motor ROP improvement

- AGS / ABH motor / RSS Steering

- LWD (logging while drilling) GR, sonic, resistivity, DN

- PWD (pressure while drilling) BH pressure

- drillstring mechanics Vibration control

24

Bottom-hole assemblies (2)

25

Drilling problems (1)

• Kick: oil or gas flowing into wellbore. Close BOP, circulate out kick to mud-gas separator via choke and kill lines. If not controlled, may develop into:

• Blowout: an uncontrolled release of oil or gas, either underground (between permeable zones), or to surface

• Lost circulation: mud flowing out of well into formation, usually because LOP has been exceeded. Reduce flow rate, and hence BH pressure. If still losing, pump LCM (loss control material) pill.

• Stuck pipe: DP or casing stuck in well, either mechanically (key-seating) or differentially (mud weight too high with respect to formation pressure, pipe pushed against hole wall)

• Parted or twisted-off BHA: fish lost-in-hole assembly. If unsuccessful, cement fish into place, sidetrack well, and redrill lost section.

26

Drilling problems (2)

27

Well evaluation (1): wireline logging

Determine:

• Presence and nature of hydrocarbons

• Formation properties (porosity, permeability)

28

Wireline / e-line log types

Open hole

• GR, sonic, resistivity, DN Reservoir porosity, permeability

• VSP (vertical seismic profiling) Hydrocarbons below hole TD

• RCI pressures Reservoir pressure(s)

• RCI samples Hydrocarbon (HC) samples

• SWC (percussion side wall core) Reservoir rock samples

• RCOR (rotary side wall core) Reservoir rock samples

Cased hole

• CCL / drift Casing connection depths

• PLT (flow rate only) Bottom-hole flow rates

• PLT (samples) Bottom-hole HC samples

• SBT, USIT Cement job competence

29

Well evaluation (2): coring

Determine:

• Formation properties (porosity, permeability)

• Measured from recovered sample

30

Well evaluation (3): testing

• Determine flow rate

• Acquire samples under flowing conditions

• Infer reservoir volume

• Assess reservoir connectivity

31

Completion

Packer

Tubing Hangerc/w 6.187” QN

Safety Valve c/w5.980” QN

7” 29 Lbs/ft Tubing

Nipple c/w5.875” QN

Packer

Nipple c/w5.750” QN

Depth CorrelationSub (DCS)

7” 29 lb/ft Liner

DCS DCS

Tubing connections

32

Construction sequence

Typical exploration well

• Tow to location, run anchors

• Drill 36” hole section

• Run and cement 30” conductor

• Drill 17½” hole section

• Run and cement 13 3/8” casing

• Run BOPs and marine riser

• Drill 12¼” hole section

• Log well on wireline

• Abandon well (set cement plugs)

• Pull BOPs and marine riser

• Cut and pull 13 3/8” x 30”

• Pull anchors

Typical development well

• Tow to location, run anchors

• Drill 36” hole section

• Run and cement 30” conductor

• Drill 17½” hole section

• Run and cement 13 3/8” casing

• Run BOPs and marine riser

• Drill 12¼” hole section

• Run and cement 9 5/8” casing

• Drill 8½” hole section (reservoir)

• Log well on wireline

• Run 7” liner

• Clean-up well, displace to brine

• Run Xmas tree and completion

• Pull BOPs and marine riser

• Pull anchors