3. Technology for a better society
Varying:
• Ice conditions (sea, subsurface)
• Temperature (air, seafloor)
• Ocean currents
Everywhere:
• Darkness, remoteness, sensitive area
• Short operational windows
• Unknown geology, ground in motion
• Poor wellbore position accuracy
• Cold "tophole" of well and stronger
temperature cycling (on/off production)
Not "one Arctic"
‐ Different well solutions are required
for different Arctic locations
3
J. Bang and T. Torkildsen (2011), "Wellbore Anti‐
Collision Safety: Separation Distances Must Be
Increased Due To Degraded Positioning Accuracy
In Northern Areas", SPE 149699.
Source: AAPG
Arctic ice cap Onshore & offshore permafrost
8. Technology for a better society 8
15 year old well in GoM: 50% probability to leak
United States Mineral Management Service (MMS) survey on sustained
casing pressure (SCP) of 15500 wells in the Gulf of Mexico.
Brufatto et al. (2003), "From Mud to Cement ‐ Building Gas Wells", Oilfield Review.
9. Technology for a better society
38% of temporarily abandoned wells on NCS have issues
9
2 defect barriers
1 defect barrier
1 reduced barrier
No WI issues
PSA, SINTEF & Wellbarrier study of 193 temporarily abandoned wells
O. K. Helgesen (2011), "Stor fare for lekkasje fra forlatte oljebrønner", Teknisk Ukeblad, 3. Oct.
11. Technology for a better society 11
Gap along casing‐
cement interface
Cement
porosity
Degraded casing
Cracks in
cement
Gap along cement‐
formation interface
Based on: Celia et al., Quantitative Estimation of CO2
Leakage from Geological Storage, ICGGCT (2004)
#2: Placement and integrity
of well barriers
16. Technology for a better society
Harsh topside conditions
• Short operational windows
• Speed up operations
• Less frequent repairs
• On/off production
• Need to protect top section of the well
• Iceberg scours down to 400 m water depth
16
Photo: www.123rf.com
C. Teff (Royal Dutch Shell), "Mud Line Cellar Construction for Arctic Wells", Alaska Exploration (2009).
17. Technology for a better society 17
Challenging subsurface conditions
Permafrost
G. Cherkashov, "Russian studies on subsea permafrost and gas
hydrates in the Arctic", VNIIOkeangeologia, St. Petersburg
Gas hydrates
Source: AAPG
? ?
19. Technology for a better society
Why avoid thawing of
gas hydrates?
19
• Trapped gas molecules (often methane)
in a solid framework of water molecules
– Under permafrost
– Beneath sea in outer continental margins
• During thawing, trapped gas is released*
– Pressure build‐up
– Mud gasification
– Poor cement jobs
• Reported consequences**
– Catastrophic subsidence
– Uncontrolled gas release
– Collapsed casings
** Yakushev et al. (1992), "Gas hydrates in Arctic regions: risk to drilling and production", Int. Offshore and Polar Eng. Conf. 1:669‐673
*Tan et al. (2005), "Mechanical and Petrophysical Characterisation and Wellbore
Stability Management in Gas Hydrate‐Bearing Sediments", ARMA/USRMS 05‐833
Image: NOC
Photo: softpedia
21. Technology for a better society
What does cold "top hole" mean?
21
IKU News 1988: Målinger av temperatur i
grunne brønner sør for Svalbard
Beaufort Sea
= Worst case?
South of Svalbard
= Best case?
Xie et al. (2011), "Methodology to Assess Thaw Subsidence Impacts on the
Design and Integrity of Oil and Gas Wells in Arctic Regions", SPE 149740.
22. Technology for a better society
Cold well barrier materials
22
*Reinås et al. (2011), "Hindered Strength Development in Oil Well Cement due to Low Curing Temperature", SPE 149687.
**Limaye et al. (2011), "Contamination Resistante Phosphate Ceramic Cement for Arctic Applications", Int.Offshore and Polar Eng. Conference.
• New environment
= new predicted lifetime
• Cement in the Arctic:
• Freezing of water before setting
• Enhanced permeability
• Poor bonding to formation
• Lower compressive strength*
• Proposed solution: new sealant types**
• Steels in the Arctic:
– Brittle at low temperatures
– Stress‐based design
– Proposed solution: other materials***
***M. Y. Gelfgat et al. (2009), "Aluminium pipes – a Viable Solution to Boost Drilling and Completion Technolgy", IPTC 13758.
Surface casing failure, Alaska
(Anders et al. (2008), "Prudhoe
Bay Well P2‐15 Surface Casing
Failure", SPE 116771)
Cement and steel are
weakest where the
loads are largest!
24. Technology for a better society
• Drilling muds are chosen with respect to
e.g. weight and hole cleaning properties.
• Their effect on the sealing ability of cement
was recently investigated by SINTEF.
Ex. Choices made during drilling
affect long‐term well integrity
24
Interface porosity: sandstone Interface porosity: shale
No mud WBM OBM No mud WBM OBM
N. Opedal et al. (2013), "Leakage of CO2 along cement‐formation interfaces in wellbores", Energy Procedia.