A multilateral well is a well with two or more laterals (horizontal, vertical, or deviated) drilled from a main mother well. This allows one well to produce from several reservoirs. Multilateral wells are suitable for complex geology where drilling more new wells to penetrate to those reservoirs is not economical. Lateral sections may be used to produce from a separated section in depleted, faulted, layered and heavy oil reservoirs.
Figure 1 – Multilateral Well Bashkiria drilled in 1953 (Credit – http://www.drillingcontractor.org)
Figure 2 shows how multilateral wells fit with several geological structures.
Figure 2 – Multilateral well with different geological structure
A multilateral well is ranked by its complexity and the ranking system is called “Technology Advancement Multi Laterals” or “TAML” The complexity of multilateral wells is classified into 6 categories.
TAML Level 1
TAML Level 1 is suitable for formations with hard rock in main bore, at junction, lateral. Additionally, a lateral section should have homogeneous fluids and pressures.
Figure 3 – TAML Level 1
Description for TAML Level 1
Main bore – Open hole with no casing support or slotted liner hang in the open hole
Lateral section – Open hole with no casing support or slotted liner hang in the open hole
Junction – No pressure integrity
Advantages of TAML Level 1
- Stable in strong formation
- Less complexity
Disadvantages of TAML Level 1
- No pressure integrity at junction
- Unable to shut off unwanted water/gas production
- Not suitable for unconsolidated formations
- Extremely limited re-entry capability
TAML Level 2
TAML Level 2 is suitable for hard laterals & hard junctions with low potential for cross flow. Furthermore, TAML Level 2 has a limited possibility to re-entry and production isolation between a main bore and laterals.
Figure 4 – TAML Level 2
Description
Main bore – Cased and cemented
Lateral section – Open hole with no casing support or possible slotted liner hang in the open hole
Junction – No pressure integrity
Advantages of TAML Level
- Multiple lateral from a main bore
Disadvantages of TAML Level
- No pressure integrity at a junction
- Limit on unwanted fluids (water/gas) shut off
TAML Level 3
TAML Level 3 is suitable for softer junction and laterals with moderate potential for cross flow control.
Figure 5 – TAML Level 3
Description
Main bore – Cased and cemented
Lateral section – Cased but uncemented laterals. Slotted liner is set in lateral sections and anchored back into a main wellbore.
Junction – No pressure integrity
Advantages of TAML Level 3
- Junction is partially protected from sand production
- Multiple multi laterals
Disadvantages of TAML Level 3
- No pressure integrity at a junction
TAML Level 4
TAML Level 4 is suitable for unconsolidated or unstable laterals and junctions with potential cross flow control.
Figure 6 – TAML Level 4
Description
Main bore – Cased and cemented
Lateral section – Cased and cemented
Junction – No pressure integrity
Advantages of TAML Level 4
- Open hole support in lateral section(s)
- Multiple laterals
- Production isolation from lateral and main bore is achievable.
- Cement protects the junction from sand infiltration and potential collapse.
- Allow selective through tubing re-entry in both a main bore and a lateral (laterals)
Disadvantages of TAML Level 4
- No pressure integrity at a junction
TAML Level 5
The TAML Level 5 has a similarity in a wellbore construction to the TAML Level 4. However, pressure sealing capability is achieved by using the integrity of tubing strings and packers in order to isolate the junction. This is suitable for an unconsolidated junction with pressure integrity at a junction.
Single bore packers are set in both main bore and lateral below the junction. Above the junction, two tubing strings are connected to a dual bore packer. Therefore, pressure integrity at a junction can be achieved by using tubing and packers.
Figure 7 – TAML Level 5
Description
Main bore – cased and cemented
Lateral section – cased and cemented
Junction – pressure isolation is achieved by completion string and packer
Advantages of TAML Level 5
- Allow production from a main bore and lateral at the same time
- Wellbore support
- Junction integrity
- Easy access to a main bore and a lateral
- Easy and effective for zonal isolation
Disadvantages of TAML Level 5
- Large wellbore required
TAML Level 6
TAML Level 6 is suitable for a weak and unstable junction. For TAML Level6, cementing junction the same way as TAML Level4 is not acceptable, so the Level 5 uses a premanufactured junction. Two separate wells are drilled from a main wellbore and a premanufactured junction is installed downhole.
Figure 8 – TAML Level 6
Description
Main bore – cased and cemented
Lateral section – cased and cemented
Junction – pressure isolation is achieved by casing or liner to seal the junction.
Advantages of TAML Level 6
- Easy and effective for zonal isolation
- Adaptable for all formation types
- Allow both separate or comingle production
- Allow independent production/injection of each production zone
Disadvantages of TAML Level 6
- Large wellbore required
- Limited pressure differential rating
References
Adam, J, 1986. Applied Drilling Engineering (Spe Textbook Series, Vol 2). Society of Petroleum Engineers.
Drillingcontractor.org, (2011), Multilateral Well Bashkiria drilled in 1953 [ONLINE]. Available at: http://www.drillingcontractor.org/wp-content/uploads/2011/07/ml03.jpg [Accessed 6 June 2017].
Gabolde, G, 2006. DRILLING DATA HANDBOOK 8TH (IFP Publications). 8. Editions Technip.
http://petrowiki.org. 2017. Multilateral completions. [ONLINE] Available at: http://petrowiki.org/Multilateral_completions. [Accessed 6 June 2017].
http://tehtsk.ru/, (2010), Multilateral Well [ONLINE]. Available at: http://tehtsk.ru/upload/iblock/45d/45d8cd0448f144a2eff6ef74704be14c.png [Accessed 1 June 2017].
Inglis, T, 2010. Directional Drilling (Petroleum Engineering and Development Studies). 1987. Springer.
TAML website online. 2010. TAML website. [ONLINE] Available at: http://taml-intl.blogspot.com/. [Accessed 6 June 2017].
