Horizontal Well

Updated on April 22, 2024
Article byKhalid Ahmed
Reviewed byDheeraj Vaidya, CFA, FRM

What Is A Horizontal Well?

A horizontal well is a drilling technique where an oil or gas well is drilled horizontally at an angle more than 80 to 95 degrees from a vertically placed wellbore. It gives easy access to gas and oil reserves that are difficult to reach by vertical drilling. It primarily aims to increase oil and gas production and help reach inaccessible reserves.

Horizontal Well Meaning

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Companies use it to drain big areas from one drill pad. They also use it to enhance and improve the production from fractured reservoirs. Although costly, they are still preferred for successfully extracting gas and oil resources from shale rocks. It has made gas and oil production more economical, albeit the pollution risks.

Key Takeaways

  • Horizontal wells are drilled at angles of more than 80 degrees for easier access to oil and gas reserves which are inaccessible by vertical drilling. The aim is to increase production and reach remote resources.
  • Even though they boost oil and gas production, they are costly to construct and sustain, which indicates both their advantages and disadvantages in resource extraction.
  • The various types of horizontal wells include extended-reach, multilateral, build-and-hold, re-entry, snake, long-radius, short-radius, extended-reach, multilateral, drain hole, and relief wells.
  • The drilling of these wells takes place parallel to reservoir layers, while vertical wells go straight down.

How Does Horizontal Well Work?

A horizontal well is a process of drilling a well turning to a horizontal direction from a vertical wellbore at a specific depth. It deviates by a specified angle from the conventional straight-down drilling approach. It has been in existence since the early 1900s. However, a hydraulic fracturing technique made it a widespread drilling technique.

First, there is the drilling of a vertical well up to a certain depth. Then, when it reaches the targeted rock built-up region, drilling is tilted at more than 80 degrees. Consequently, the well gets bored horizontally. Moreover, the wellbore is flexible enough to turn the well’s direction to any degree. Furthermore, the direction change depends on the desire for the location of the production zone.

Horizontal well drilling involves skilled horizontal well drillers implementing a process where the well’s direction changes from vertical to horizontal, as depicted in a horizontal well diagram below:

How Does Horizontal Well Work

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Such a technique can improve oil and gas recovery, with the extracted resources being stored in a horizontal well pressure tank.

It did have a significant effect on the financial world. It led to an unprecedented rise in oil and natural gas production. Consequently, the oil and gas industry saw a boom in revenues and profits. As a result, their stock prices increased, leading to all-round economic development globally.

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As per different uses, various reservoir shapes, and drilling difficulties, the types of horizontal well differs. They are as follows:

Types of Horizontal wellsDescription and uses
Extended-Reach WellsIt easily reaches distant reservoirs from a single wellpoint is ideal for offshore drilling.
Multilateral WellsIt branches out to numerous reservoirs just from one single wellbore. It has the advantage of efficient resource drainage. 
Build-and-Hold WellsThese wells can be used for horizontal drilling at a particular depth inside a reservoir. One uses it in uniform productions.
Horizontal Re-Entry WellsIt is good for secondary drilling in already existing wells. Old wells start to produce in an enhanced manner. 
Snake WellsThrough difficult formations, it runs in a zigzag manner horizontally. It successfully overcomes geological obstacles.
Long-radius Horizontal wellsFor increasing contact between low permeability and wellbore reservoirs.
Short-radius Horizontal wellsIn high permeability reservoirs, it leads to efficient drainage.
Extended-Reach Horizontal WellsIt gets utilized in reaching farther targets. 
Multilateral Horizontal-wellsThese wells can create numerous sections within a single vertical wellbore. 
Drain hole WellsThe short horizontal wells drilled from existing well bores are made to drain using it.
Relief WellsThese wells seal or relieve pressure from problematic wells through their horizontal intersection.


Let us use a few examples to learn more about the topic.

Example #1

One can observe an instance highlighting the utilization of horizontal wells in the case of the Bakken Formation located in North Dakota. As reported by the US Energy Information Administration, the implementation of horizontal drilling and hydraulic fracturing has led to a significant boost in oil production within the Bakken region. Specifically, oil production escalated from 200,000 barrels per day in 2007 to 1 million barrels per day by 2014.

Example #2

Let us explore the fictitious Sunburst Energy Field, with the pioneering SolarHawk horizontal well. SolarHawk’s horizontal segment stretches 800 feet beneath the Earth’s surface, accessing ample oil reservoirs. By employing state-of-the-art technology, this well optimizes the efficiency of oil extraction. Since its introduction in 2022, SolarHawk has consistently impressed, yielding over 5,000 gallons daily. It stands as a testament to the efficacy of horizontal drilling in uncovering untapped energy reserves.

Advantages And Disadvantages

Let us use the table below to look at its pros and cons:

These wells increase oil and gas production. These wells are highly expensive to build and maintain. 
It prevents seepage of water and gas into the well.The digging and finishing of the well is a complicated process needing skilled and special machinery. 
It is highly cost-effective and affordable than vertical wells.The risk of oil wells collapsing or losing drilling fluids is high here.
It is environmentally friendly as it can be equal to many vertical wellsThis well cannot be dug in every place.
It makes more direct contact with oil and gas reservoirs, allowing more production. It extracts oil and gas from only one layer at a time.

Horizontal Well vs Vertical Well

Let us look at the differences between them:

Horizontal wellVertical well
It is done parallel and sideways to the reservoir rock layers. The well is drilled straight down into the ground. 
It makes good contact with the reservoir owing to the longer path. The well makes lesser contact with the reservoir and is confined to a small vertical area. 
It has a higher production rate. The well has a lower production rate. 
It needs more water, chemicals, and wastewater. The need for water and chemicals is lower.
It has a higher drilling cost.Although the cost of drilling is low, so is the production. 
It reaches difficult zones. In simpler formations, it is generally used.
The pay zone penetration is more.Pay zone penetration in vertical walls is limited.
For effective production, it can penetrate fractures easily.The reach to fractures is not so efficient. 
It helps in relieving of well pressure.Relieving of the well pressure is not supported.
It aids in the installation of utilities where excavation is difficult.Utilities do not get installed using it.

Frequently Asked Questions (FAQs)

1. How far can one drill a horizontal well?

The maximum horizontal reach of a well can vary based on the drilling technique employed and the characteristics of the local geology. Horizontal wells can typically reach drilling depths of up to 10,000 feet. At the same time, instances have occurred where horizontal wells were excavated to depths as substantial as 20,000 feet.

2. Why do we drill horizontal wells?

Drilling horizontal wells enhances the connection between the wellbore and the reservoir, thereby enabling the extraction of a greater amount of gas or oil from the reservoir. Furthermore, horizontal wells reach reservoirs in areas where vertical wells would be impractical.

3. What is the longest horizontal well drilled?

The Zamzama-1 well in Pakistan holds the distinction of being the longest horizontally drilled well to date. In the year 2014, the drilling of this remarkable 20,000-foot-long structure took place.

4. What is the range of short-radius horizontal wells?

The radius of a short-radius horizontal well spans from 40 to 20 feet, while its lateral section extends anywhere from 200 to 900 feet in length.

This article has been a guide to what is Horizontal Well. Here, we compare it with vertical well and explain its examples, types, advantages, and disadvantages. You may also find some useful articles here –

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