Wellbore: What it is, How it Works, Examples

What Is a Wellbore?

A wellbore is a hole drilled to aid in the exploration and recovery of natural resources, such as oil, gas, or water. It can be encased with materials like steel and cement or left uncased. The primary purpose of drilling a wellbore is to extract oil or gas over an extended period.

Key Takeaways

• A wellbore is a borehole used for oil or gas extraction.
• Boreholes can also serve purposes like mineral extraction, environmental assessment, and temperature measurement.
• Wellbores are generally vertical shafts and may or may not be encased with cement and steel.
• A wellbore’s main objective is to extract oil and gas for an extended period.

Understanding a Wellbore

A wellbore is a type of borehole, which is a narrow shaft drilled into the ground to extract water, petroleum, or gases. Boreholes can be drilled horizontally or vertically and fulfill various purposes, including mineral exploration, environmental site assessment, and temperature measurement. Resource extraction companies use wellbores to access natural resources, typically oil and gas. A wellbore is a straight vertical shaft that allows for the recovery of natural resources and includes the open hole and uncased sections of the well.

Examples of a Wellbore

The diagram below illustrates an oil wellbore encased in steel and cement. The wellbore represents the actual drilled hole, which can refer to the inner diameter of the wellbore wall or the rock face that forms the hole. Casing materials are used to enhance the wellbore’s stability and operational efficiency.

Borehole and wellbore are often used interchangeably, although borehole sometimes refers specifically to the open diameter of the hole itself, while wellbore encompasses the casing between the opening and the surrounding rock or earth walls.

It is essential to clean wellbores before and after production to minimize operating costs and mitigate safety and environmental risks associated with mud or debris. Drilling wellbores is a complex process requiring specialized training, tools, and equipment. A successful wellbore enables the extraction of oil and gas over an extended period.

Although commonly associated with oil drilling, wellbores can be used for any type of well. Throughout history, drilling rigs, whether operated manually or mechanically, have facilitated the creation of wellbores. The choice of machinery and techniques depends on geological conditions and the intended purpose of the well. For offshore drilling, floating units or platforms supported by the seafloor are employed.

Chinese miners have been creating wellbores since at least the Qin Dynasty (221–206 BC). Initially, these wells reached depths of up to 30 meters, which later increased to 1,000 meters by the 1800s.

According to K.S. Tom, the Chinese method of deep drilling involved a team of men alternately jumping on and off a beam to impact the drilling bit, while buffalo and oxen rotated the boring tool. Early oil extraction in California during the 1860s and beyond used this technique, known as "kicking her down."