This document provides an overview of well design and construction. It begins with an agenda and then covers topics such as different types of drill rigs used for various water depths, rig systems for hoisting, rotating, circulating, and well control, well types (exploration, appraisal, development), typical well schematics, casing strings, typical lithology for the central North Sea, casing cementation, drilling fluids, drill bits, bottom-hole assemblies, drilling problems, and well evaluation using wireline logging. The document provides essential information on the key aspects and considerations for well design and construction.

1. Well design and construction I
Adrian Adams
Nexen Petroleum UK
1

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
2

3. Drill rigs (1): fixed (surface wellheads)
Jack-up Fixed platform
3

4. Drill rigs (2): floating (subsea wellheads)
Semi-submersible (moored) Drillship (DP)
4

5. Drill rigs (3): compliant platforms
5

6. Drill rigs: water depth capability
6

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
7

8. Floater drilling: overview
8

9. Rig systems: hoisting
Derrick Draw-works
9

10. Rig systems: rotation
Kelly and rotary table Top drive
10

11. Rig systems: circulation
11

12. Rig systems: well control
12

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
13

14. Well targets
Gas-Oil contact
Gas
Fault Oil-Water contact
Oil
Water
Reservoir Rock
Seal
14

15. Typical well schematics
Surface location (slot #10) (final)
Surface location Lat: 57° 48’ 02.377” N
Lat: 57° 39’ 03.830” N All depths in feet Long: 00° 56’ 23.438” W All depths in feet
Long: 00° 52’ 44.929” W X: 622,444.86 m E
MD BRT TVD BRT MD BRT TVD BRT
X: 626,573.00 m E Y: 6,408,525.68 m N
Y: 6,391,987.00 m N RT 0 0 RT 0 0
Sedco 714 John Shaw
MSL 87 87 MSL 80 80
BOP
Hydril 18¾” 15M Wellhead
ChRdRdChAhAl Vetco SG5 10000 psi
Flowbase heading: 315.7º G, 317.5º T
Wellhead Top face LP housing 449 449 Top face bullseye support beam 9 ft ASB Top face guidebase 396 396
Vetco SG5 10M Seabed 457 457 Seabed 405 405
30” x 20” conductor
36” x 26” hole LiteFIL RHC 30” x 1.5” X52 extension BWP up x HD/HT-90
26” MSDSSHc + 6-point HO, PDM/ABH 0 deg 30” x 1.5” X52 XO HD/HT-90 x SF-60 BJ Lite 115
408 bbl 330 bbl 12.5 ppg (250% excess)
DIR/INC 12.5 ppg 3 jts 30” x 1” X52 SF-60
Seawater + high-vis sweeps (8.7 ppg) 20” 133 lb/ft X56 shoe joint c/w XO to 30” SF-60
10.0 ppg displacement mud Final bullseye readings 0.5º forward, 0.5º aft 36” hole 624 624
36” hole 677 677 Hard cement tagged 20 ft BSB (both funnels), 20” shoe 642 642
30” x 20” conductor 20” shoe 40 bbl top-up both sides 26” hole 644
692 644
30” x 1.5” X52 extension BWP up x HD/HT-90 b/d 26” hole 697 697
30” x 1.5” X52 XO HD/HT-90 p/u x SF-60 b/d
3 jts 30” x 1” X52 SF-60 pin up x box down
20” 133 lb/ft X56 shoe joint c/w XO to 30” SF-60 p/u Rugby class G CCB Class G
Lead 838 bbl 12.5 ppg Lead 930 bbl 13.2 ppg (150% excess)
13 3/8” casing
Tail 167 bbl 16.0 ppg Tail 90 bbl 16.0 ppg (15% excess)
17½” hole 18¾” HP housing c/w 21” x 1.25” extension
Smith MG02TQc, PDM/ABH 0 deg 20” x 13 3/8” XO joint
DIR/INC/GR 13 3/8” 72 lb/ft L80 Vam Top
Seawater + high-vis sweeps (8.7 ppg) TOT 2978 2978 Pressure tested to 1800 psi on bump
10.5 ppg displacement mud Pressure test to 3000 psi after BOPs set
13 3/8” shoe 3695 3695
17 1/2” hole 3715 3715
13 3/8” casing
Pre-assembled 18¾” WHH assembly
Seat protector, SSR and top wiper plug pre-installed
Approx 74 joints 13 3/8” 72 lb/ft L80 BTC Revisions list
Pressure test on bump to 2000 psi 13 3/8” shoe 3478 3478 Rev 01 (20/9/06): first issue
Rev 02 (27/9/06): motor bend for 17½” hole,
17½” hole 3498 3498 13 3/8” test pressure, TD depth revised
Run BOP Rev 03 (29/9/06): 13 3/8” pressure test policy
Run and test BOP to 5000 psi revised
Rev 04 (31/10/06): updated for as-built,
12¼” hole target, trajectory, and geological tolerance
Smith MA74PX, PDM/ABH 0.78 deg revised
DIR/INC/GR/RES/SONIC Rev 05 (6/12/06): updated for as-built
Drill out wiper plug with seawater
Displace to 10.0 ppg WBM while drilling cement
Drill 10 ft new hole, circulate and condition mud
Perform FIT to 15.0 ppg minimum
Increase MW to 11.5 ppg before bottom Chalk
Drill ahead 12¼” hole to TD
12¼” coring
Core Burns sandstone on shows
Logging
As per logging programme
Top Burns 6504 6504
9 5/8” casing
Contingency for hole problems or DST TOC (theoretical) 8652 8284
9 5/8” 47 lb/ft L80 New Vam available
9 5/8” x 7” XO 9392 8967
12¼” hole 9412 8985
Abandonment (indicative)
5 x 600 ft plugs on bottom 9 5/8” x 7” casing
2 x 500 ft plugs across shoe 9 5/8” 53.5 lb/ft L80 Vam Top
Top Buzzard SST 9652 9206
Tag and test shoe plug 10º internal taper XO
Final plugs dependent on formations 7” 29 lb/ft L80 13Cr Vam Top HT
Pressure tested to 5000 psi in seawater
CCB Class G
Bottom hole location Tail 105 bbl 16.0 ppg (10%)
Lat: 57° 39’ 03.830” N
Long: 00° 52’ 44.929” W
X:
Y:
626,573.00 m E
6,391,987.00 m N 12¼” TD 9179 9179
Bottom hole location (final)
Lat: 57° 48’ 28.300” N
Long: 00° 56’ 14.577” W
X:
Y:
622,566.69 m E
6,409,331.61 m N
15 7” shoe
8½” TD
11129
11140
10579
10590

16. Casing strings
Typical casing design for central North Sea
• Conductor (30” diameter, 36” for deep water)
36 inch 30 inch
Hole Conductor - supports weight of inner strings
- cases off soft topsoils
26 inch
Hole
20 inch
Casing
- usually 6 no. 40 ft joints (240 ft)
• Intermediate casing (usually 13 3/8”)
17 inch
1/2 3
13/8 inch
- cases off Tertiary formations
Hole Casing
- usually set in top UC Chalk (3500-4000 ft)
• Production casing (usually 9 5/8”)
12 inch
1/4
9 /8 inch
5
- cases off Chalks and LC Siltstones
Hole Casing
- usually set just above reservoir
• Liner (usually 5½” or 7” diameter)
8 inch
1/2
7 inch
Hole Liner - set across reservoir
• NB: optimum casing design varies by area
6 inch 5 inch
Hole Liner (depths, geology, drilling hazards)
16

17. Typical lithology (central North Sea)
17

18. Casing cementation
Displacement • Cement is pumped down
Fluid
the well between the top
Top Plug and bottom plugs
Displacement
Fluid • Once bottom plug bumps,
Centralizer cement is expelled through
float valve and up the
annulus (i.e., outside the
Cement Drillstring
Slurry casing)
Stabilizer • The cement volume is
Top Plug
disposed such that top of
Seated cement (TOC) is at the
Bottom Plug
desired height once the top
Float Valve Float Valve plug bumps
Open Closed
• TOC height is determined
Centralizer by zonal isolation
requirements
Casing
Shoe Stabilizer • Once the cement has set,
the plugs, float and shoe
Drill Bit
track are drilled out
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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)
19

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
20

21. Drill bits
Mill tooth TCI PDC
Tungsten carbide Polycrystalline
insert diamond compact
21

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)
22

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
23

24. Bottom-hole assemblies (2)
24

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.
25

26. Drilling problems (2)
26

27. Well evaluation (1): wireline logging
Determine:
• Presence and nature of hydrocarbons
• Formation properties (porosity, permeability)
27

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
28

29. Well evaluation (2): coring
Determine:
• Formation properties
(porosity, permeability)
• Measured from
recovered sample
29

30. Well evaluation (3): testing
• Determine flow rate
• Acquire samples under flowing conditions
• Infer reservoir volume
• Assess reservoir connectivity
30

31. Completion
Tubing Hanger
c/w 6.187” QN
Safety Valve c/w
5.980” QN
7” 29 Lbs/ft Tubing
Nipple c/w
5.875” QN
Packer
Tubing
Nipple c/w connections
5.750” QN
Depth Correlation
Sub (DCS) DCS DCS
7” 29 lb/ft Liner
31 Packer

32. Construction sequence
Typical exploration well Typical development well
• Tow to location, run anchors • Tow to location, run anchors
• Drill 36” hole section • Drill 36” hole section
• Run and cement 30” conductor • Run and cement 30” conductor
• Drill 17½” hole section • Drill 17½” hole section
• Run and cement 13 3/8” casing • Run and cement 13 3/8” casing
• Run BOPs and marine riser • Run BOPs and marine riser
• Drill 12¼” hole section • Drill 12¼” hole section
• Log well on wireline • Run and cement 9 5/8” casing
• Abandon well (set cement plugs) • Drill 8½” hole section (reservoir)
• Pull BOPs and marine riser • Log well on wireline
• Cut and pull 13 3/8” x 30” • Run 7” liner
• Pull anchors • Clean-up well, displace to brine
• Run Xmas tree and completion
• Pull BOPs and marine riser
• Pull anchors 32