Running head: MULTILATERAL DRILLING & COMPLETIONS
Multilateral Drilling & Completions
Syed Zeerak Abbas Abdi
The University of Texas at Austin
MULTILATERAL DRILLING & COMPLETIONS 2
Abstract
Multilateral wells unlock the production potential in reservoirs of all sizes. Extending
multiple laterals from the main wellbore allows for a greater sweep volume due to
increased contact with the reservoir. Multilateral wells are more cost-effective and have a
smaller environmental impact than separate wells. However, multilateral wells are
difficult to drill and complete. There is a small margin for error when drilling
directionally. Furthermore, the completions process requires investment in expensive
technologies that allow for remote control of production. Therefore, there needs to be
considerable research and development of multilateral technology before widespread
implementation.
MULTILATERAL DRILLING & COMPLETIONS 3
Table of Contents
Abstract 2
List of Figures 4
Executive Summary 5
History of Multilateral Drilling 7
Levels of Classification 8
TAML Level 1 9
TAML Level 2 9
TAML Level 3 9
TAML Level 4 9
TAML Level 5 10
TAML Level 6 10
TAML Level 6s 10
Multilateral Configurations 11
Intelligent Completions 11
Benefits 13
Drawbacks 14
Conclusion 14
References 16
MULTILATERAL DRILLING & COMPLETIONS 4
List of Figures
Figure 1. The First Multilateral Well 8
Figure 2. TAML Levels 10
Figure 3. Most Common Multilateral Configurations 11
Figure 4. Schlumberger’s Intelligent Completions System 13
Figure 5. Halliburton’s Intelligent Completions System 13
MULTILATERAL DRILLING & COMPLETIONS 5
Executive Summary
Multilateral technology, while sophisticated and complex, has been in
development for over 50 years. The first multilateral well was drilled by the USSR in
1953. This pioneer well proved the theory that increased reservoir exposure would lead to
increased production by showcasing a 1,700% increase in production. The greatest
advantage of multilateral wells is their cost-effectiveness. The first multilateral well,
drilled by Alexander Mikailovich Grigoryan, consisted of 9 laterals and only cost 1.5
times more than a regular vertical well. This incredibly low cost-to-benefit ratio is the
reason for advancements in multilateral technologies.
The process of drilling laterals is similar to that of directional drilling. Through
the use of a whipstock, the drill bit is positioned to the correct angle. This process is
repeated for other laterals as well. Alternate drilling methods can also be adopted
depending on reservoir geology. In softer formations, pressurized fluids coupled with a
retractable hose can be used to make horizontal laterals.
Multilateral Completion is a longer process and has a very small margin of error.
Since each lateral is unique in its geometry, completion solutions are custom tailored.
The most important decision regarding multilateral completions is the amount of support
needed for each lateral at the junction. This ultimately depends on the formation pressure
and the risk tolerance for a company. The amount of support needed is classified by the
Technology Advancement for Multilaterals (TAML) and ranges from no mechanical
support to maximum possible support. In simple laterals with sturdy geological
surroundings, TAML level 1 and TAML level 2 completions can be implemented.
However, with softer formations, such as the Austin chalk, more advanced lateral support
is required. Such solutions are significantly more expensive and can only be implemented
by operators with larger budgets. It is important to realize that for lower TAML levels,
MULTILATERAL DRILLING & COMPLETIONS 6
there is no support provided for at the laterals. Therefore, a collapsed lateral is certainly a
possibility.
There are numerous benefits to multilateral wells aside from their cost-
effectiveness. Since multilaterals enable access to multiple reservoirs, it is economically
viable to produce from older, formerly depleted wells. Re-entry is also a key feature of
multilateral drilling. Plugged wells can be re-entered and by drilling laterals, oil can be
produced from previously unprofitable reservoirs.
The future of multilateral technology ultimately lies in the hands of oil & gas
prices. Intelligent completion solutions developed by service companies are expensive
but also required in off-sea ventures. Intelligent completions essentially allow for remote
monitoring and control of production. If prices remain low, there would be no reason to
further an unprofitable technology. Without intelligent completions, drilling for
multilateral wells is even riskier. Therefore, multilateral wells, while very profitable, will
continue to remain at a steady pace of usage for the next decade.
MULTILATERAL DRILLING & COMPLETIONS 7
Multilateral Drilling and Completions
As oil & gas recovery becomes more difficult, research has led to the
development of increasingly complex and efficient ways of augmenting production, with
one of them being multilateral drilling. While conventional vertical drilling releases
hydrocarbons that lie under the surface of the work pad, multilateral drilling enables the
production of hydrocarbons that are distant from the vertical wellbore (Turcich, 1998).
By drilling laterals from the main wellbore, production can be obtained from multiple
wells. Laterals are horizontal extensions from the wellbore and can run up to 900 meters.
Completion of successfully drilled laterals is equally important for production. This paper
will discuss the history of multilateral drilling, the various configurations that laterals can
be placed in, the levels of classifications for completions, the benefits & drawbacks of
this type of drilling and finally, intelligent completions.
History of Multilateral Drilling
Industry history books show that multilateral drilling and completions have been
attempted as early as the 1930s. However, it wasn’t until 1941 that the first successful
directional well was drilled. Inspired by the USSR’s policy of maximizing production,
Alexander Mikailovich Grigoryan, a Soviet drilling engineer, completed the first
directional drilling job without the use of a whipstock or modern technology (Bosworth
et al., 1998). With this experience, Grigoryan theorized that extending an additional
lateral from the wellbore would increase production. In 1953, Grigoryan successfully
drilled the first multilateral well in Bashkortostan, Russia. By using downhole turbodrills
and halting the drill string’s rotation, Grigoryan was able to create 9 lateral branches,
with each branch extending up to 300 meters. A sketch of the first multilateral well is
shown in Figure 1. Grigoryan was able to produce 17 times more oil while only spending
1.5 times the original budget.
MULTILATERAL DRILLING & COMPLETIONS 8
Following Grigogyran’s achievements in multilateral completions, the USSR
drilled 110 lateral wells over the next 27 years. While
very productive, multilateral drilling was incredibly
difficult to accomplish, especially in thin pay zones.
The true explosion in popularity did not happen until
the advent of the modern computer. Research and
development was greatly aided due to the computer’s
ability to run simulations. The second generation of
multilateral completions occurred in 1997 and
established the use of advanced lateral support. As a
final stamp of approval, statistics showed that in 2001
and 2002, multilateral completions had a failure rate
of only 1.9%, which was less than half of the failure
rate from 1993 to 2002 (Oberkircher, Smith, &
Thackwray, 2004).
Levels of Classification
The process of making a well ready for production is called completion.
Completing a regular vertical well is a fairly simple process. Casing, liners, and cement
are used to solidify and protect the rock formation around the well from leakage.
Completions become more complicated when dealing with laterals, mainly due to the
change in geometry. There are a variety of different levels of completions that can be
applied on a multilateral well. These variations have been simplified into a set of
classifications by the Technology Advancement for Multi-Laterals (TAML). These
classifications are organized into six levels by the amount of mechanical support
Figure 1: The First Multilateral Well (Bosworth et al., 1998)
MULTILATERAL DRILLING & COMPLETIONS 9
provided to the laterals (TAML Complexity Ranking, 2012). A general summary of the
levels is provided in Figure 2 below.
TAML Level 1
This is the simplest level of multilateral completions and is completely dependent
on the natural stability of the wellbore. The wellbore and lateral are unsupported,
meaning that there is no cementing or casing present. Since there are no control options
present in level 1, there is no possibility of selective production. Due to the
aforementioned reasons, TAML level 1 is an obsolete form of multilateral completions
and is often viewed as risky and impractical.
TAML Level 2
In this level the wellbore is completely cemented and cased whereas the laterals
are still openhole. While there is no support for the lateral along its flowing axis,
mechanical support is provided at the junction by cement and casing. Hydraulic isolation
is present in this level, as well as in level 1. Since there is no support for the lateral along
its axis, there is a possibility for collapse.
TAML Level 3
Similar to level 2, level 3 consists of a cased and cemented wellbore, in addition
to a cased lateral. An alternate version of TAML level 3 replaces the lateral casing with
an anchored slotted liner that provides the same structural support as casing. Unlike level
2, there is no hydraulic isolation due to the support provided at the laterals’ flowing axis.
This forces the production to be commingled between each lateral.
TAML Level 4
This level provides casing and cementing to the wellbore as well as each lateral.
The cementing increases stability at the junction and prevents the flow of sand and
MULTILATERAL DRILLING & COMPLETIONS 10
cutting along with production. It is important to realize that cementing at the junction
does not provide support against large amounts of pressure.
TAML Level 5
This level is the same as level 4 with the addition of packers that provide support
against large pressure. The packers, which are placed above and below the lateral allow
for zonal isolation, and therefore more control over production.
TAML Level 6
The second-to-last level classified by TAML consists of only casing at the
junction. Furthermore the junction is pre-manufactured and is assembled downhole,
providing increased structural and pressure integrity. Level 6 is considered to be the
safest completion options. It provides support to the lateral and maintains zonal isolation.
TAML Level 6s
The last level of structural integrity, level 6s is not very common, but very
interesting. The addition of a splitter around the lateral junction essentially forces the
main wellbore into becoming two separate laterals. By splitting a wellbore into two,
engineers gain precise control over production.
Figure 2: TAML Levels (Guidry, Pleasants, & Sheehan, 2011)
MULTILATERAL DRILLING & COMPLETIONS 11
Multilateral Configurations
There are many different types of
configurations that laterals can be arranged in given
a target area. Laterals can be created in both the x-
and y- planes. The most common lateral
configuration is dual-opposed. As shown in Figure
3, two laterals are positioned 180o from each other
in the x-plane (Joshi, 2012). . The dual-opposed
configuration is useful in naturally fractured
formations with low permeability since two or more
laterals can intersect more fractures than a single
lateral. Another common type of configuration for
laterals is the horizontally-fanned position. Similar
to dual-opposed, the horizontal-fanned configuration targets a single zone to maximize
production, usually from shallow, low-pressure oil fields. The most common lateral
configuration in the y-plane is the vertically-stacked position. This configuration is
mostly used in layered reservoirs. By commingling the laterals, hydrocarbon recovery
increases dramatically. Other multilateral configurations are a combination of the
aforementioned positions. For example, dual-opposed laterals can be combined with
vertically-stacked laterals in order to maximize production.
Intelligent Completions
Intelligent Completions allow for remote reservoir monitoring and well control in
real time. An intelligent completion system combines a variety of sensors and monitoring
systems with the ability to remotely control the production from the laterals (Montaron &
Vasper, 2007). Halliburton developed the first intelligent completion system in 1997.
Figure 3: Most Common Multilateral Configurations (Bosworth et al. 1998)
MULTILATERAL DRILLING & COMPLETIONS 12
Called SmartWell, it provided a combination of zonal isolation devices, monitoring
systems, downhole control systems and interval control devices (Multilateral Solutions,
2015). A similar intelligent completions system offered by Halliburton is depicted in
Figure 5 below. Schlumberger’s IntelliZone Modular Company System is a pre-
assembled and pre-tested 30-foot long system that is placed at the lateral junction
(Multilateral Completion Systems, 2015). It sends real time updates to the control panel
and allows the engineer to control production flow by adjusting the flow control valves
(FCVs). Schlumberger also claims that its system only takes 8-10 weeks of delivery time
in order to reach the well site. Even though this time is fairly long compared to the time
its takes to drill a well, it is significantly less than the time required by Schlumberger’s
competitors. A system similar to IntelliZone is depicted in Figure 4 below.
It is important to realize that intelligent completion systems are custom built for
each well. There are simply too many factors and constraints to create a general model.
Furthermore, subsea ventures require sophisticated planning and engineering due to the
increased demands in completions for formations under water. Adjusting production at
the wellhead is not recommended for subsea operations, therefore requiring intelligent
completions as they allow for remote control and shutoff. Nonetheless, intelligent
completions are still a niche technology. They are expensive, limited to mainly subsea
operations, and in most multilateral cases, unnecessary (Langley, 2011). For multilateral
wells, an intelligent completions system can cost significantly more due to the increased
amount of control lines. Each control line serves a junction. Therefore, in a multilateral
well with many junctions, it is necessary to use a more complex intelligent completions
system, which will also cause an increase in price. Due to these reasons, intelligent
completions are used primarily by larger companies. Ismail Nawaz, a product line
manager at Schlumberger, expects his company’s system to become purely electric,
MULTILATERAL DRILLING & COMPLETIONS 13
resulting in a cheaper price (Oberkirche et al., 2004). With future developments,
intelligent completions should become more accessible for smaller companies.
Benefits
The benefits of multilateral wells are numerous. Multilateral wells allow a
significant increase in production with a minute increase in price. Instead of having one
vertical well and two horizontal wells each with their own wellbore, they can be
combined into one wellbore for a fraction of the price. One of the greatest benefits of
multilateral drilling is that it essentially combines the production of multiple wells. This
makes it economically viable to drill towards a less productive reservoir with the goal of
combining it with another small reservoir. In net terms, the total production would exceed
a single vertical well. Re-entry is also possible with multilateral drilling, making it
possible to drill for previously uneconomical reservoirs in a certain region (Turchich,
1999). Engineers have also used multilateral drilling for exploration wells, in order to
Figure 4: Schlumberger's Intelligent Completions System (Montaron & Vasper, 2007)
Figure 5: Halliburton's Intelligent Completions System (Multilateral Solutions, n.d.)
MULTILATERAL DRILLING & COMPLETIONS 14
survey the geology of an area without having to have separate wellheads (Bosworth et al.,
1998).
Drawbacks
The biggest drawback of using multilateral wells is the risk involved in drilling
multiple laterals. Even though 10% of all fields are candidates for multilateral drilling,
many companies opt out due to the rising prices of TAML level 3 and higher junctions.
Due to the growing complexity of newly discovered reservoirs, pressure stability is
required in the wellbore. In order to attain that pressure stability, level 5 or 6 junctions are
required, which also correspond with a higher price. According to Joe Sheehan, a product
line manager from Baker Hughes, the main drawback of multilateral completions is the
sheer amount of multidisciplinary work required to attain basic goals (Langley, 2011).
While not necessarily drawbacks, there are many challenges associated with multilateral
drilling that make it undesirable. For example, it is incredibly difficult to service and
repair a multilateral well, especially after decades of use. Laterals with different pressures
and geologic features will require more service than similar laterals experiencing a
consistent pressure (Joshi, 2012). Another challenge associated with multilateral
production is determining which lateral to produce from at a given time. Since laterals are
usually close to each other, it is easy for one’s flow to interfere with another. As
explained by Darcy’s Law, each lateral will experience transient flow when hit by a
pressure front caused by an opposing lateral. Therefore, making the decision of
commingling production from laterals is tough, since hitting a transient flow boundary
will significantly slow down operations.
Conclusion
It is unfortunate to say that the demand for multilateral wells has decreased in the
past few years, especially with the oil & gas price collapse. Engineers now favor certainty
MULTILATERAL DRILLING & COMPLETIONS 15
over high-risk and high-reward. Instead of developing more innovative junctions,
engineers prefer to use simple junctions such as TAML level 2 and level 3 in order to
complete their laterals. This is cost-effective and finalizes the project. Considerable
development in junction technology still has to occur in order to optimize structural
integrity. For example, research is being conducted to determine the best chemical sealant
for TAML level 6 junctions. Further research is being conducted on how to minimize
wellbore damage and debris pileup in the construction of downhole laterals. Despite this
grim outlook, it is important to realize that multilateral drilling still holds the key to
tapping into some the world’s largest oil & gas reserves. In addition to being the key for
larger plays, multilaterals are the leading method of increasing production. They have the
largest return on investment, and pay for themselves in a short time period (Hussain et al.,
2011). Furthermore, multilateral technology makes it possible to re-enter old wells and
make them profitable. With growing technology enabling intelligent completions, the
trend of abandoning sophisticated and risky technology for cheaper alternatives will
surely reverse. Until then, engineers still have a long way to go in order to perfect
multilateral drilling.
MULTILATERAL DRILLING & COMPLETIONS 16
References
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