multilateral completions

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.


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


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


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,


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 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.


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)


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


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 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)


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,


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.)


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


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.


References

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