Directional Drilling Types

There are many types of directional wells. These types are discussed below

Horizontal Drilling

Drilling a wellbore of 90° from the vertical is called horizontal drilling. Drilling this type of wellbores allows increasing the contact between the well and the reservoir that can improve the productivity. Using horizontal drilling can also help to overcome the problem of water and gas coning. Horizontal wellbore can be drilled through thin reservoirs with good vertical permeability. The trajectory starts vertically, and then is kicked off to starts the build section at a planned depth from 0° to 90°, and finally the horizontal section is drilled through the formation of interest. The horizontal drilling is categorized according to the buildup rate to short radius, medium radius and long radius.

Short radius has approximately 60 feet of buildup section and from 100 feet to 800 feet of horizontal section. Small diameter holes can be drilled from the same wellbore. The short radius is drilled with special deviating systems and unconventional tubulars. The equipment is weaker due to their small diameter and more likely to fail. The rate of penetration while drilling this type of horizontal wells is very restricted in hard formations and directional control can be a problem.

Medium radius is characterized by a buildup angle from 6° to 35°/ 100 feet with a buildup section from 200 to 700 ft. The horizontal section can be from 1000 to 3500 ft. It is applied when drilling through fractured reservoirs and potential water and gas coning reservoirs. 

Long radius is deviated mainly in the open holes. The buildup rate can be from 1° to 06°/100ft. The horizontal section can reach the level of 5000 ft. It is used in offshore and inaccessible locations. They are characterized by larger holes sizes and susceptible to high torque and drag due longer open hole sections. Larger holes allow for using larger positive displacement motors with higher horsepower.

Fig 01- Horizontal Drilling Types

Multilateral Drilling

This type of wells is based on drilling many branches of wellbores from a single wellbore that is called the trunk. This profile has many advantages; the reservoir exposure increases that leads to production increase. It also reduces the surface well equipment and the cost of the surface facilities. There are many applications of drilling multilateral wells; it can be used in tight reservoirs where the permeability is very low. In this case, the production can be increased by increasing the contact area by drilling multiple branches. It can allow for performing injection and producing from the same well. Drilling multilateral wells can be also a good option when drilling through complex drainage reservoirs. Many issues have to be considered when drilling this type wells. Junction design, well control issues and completion program have to be well planned to make multilateral drilling more effective. 

Fig 02-Multilateral Wells

Extend Reach Drilling (ERD)

Looking for oil in new complex areas pushes the drilling engineering to new limits. An extended reach well (ERW) can be defined in many ways, but in general there is one main factor that is used to define an ERW: depth ratio. The depth ratio is the horizontal departure divided by the vertical depth, if this ratio is greater than 2, then the well can be considered as ERW. Drilling an ERW is a real challenge at all levels. Drilling technology and personal competency are the most important issues. Planning an ERW can involve many issues. BHA design, casing program, hole cleaning, ECD management, and directional control can be considered as obstacles which have to be overcome. There are many advantages and benefits of drilling an ERW, they can be me summarized: reducing environmental impacts, recover more oil from larger area, maximizing the drainage capability and productivity.

Fig 03- extended Reach Drilling

Coiled Tubing Drilling (CTD)

Coiled tubing drilling is used as reentry drilling to discover hydrocarbons pockets in the main reservoir. The tubing used in CTD ranges from 0.75 in to 3.5 in and spooled on the tubing reel. The coiled tubing length depends on the pipe diameter and tubing reel size, it can reach the level of 15000 ft. Coiled tubing drilling can be performed from a drilling derrick, or smaller rig. The CTD unit consists of: injector head, tubing reel, control cabin and power unit. The CTD has many advantages: 

- It allow faster and safer drilling because no pipe connection is needed. 

- The mobilization and rig-up will be a simple issue

- Allows circulation when running in or pulling out of the hole

- Reducing non-productive time due to reducing the tripping time 

Fig 04- Coild Tubing Drilling

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