A wellbore is a hole drilled down into the Earth to aid in the exploration and recovery of natural resources such as oil, gas, or water. This is the primary structure that forms a well. Wellbores might be encased with materials like steel and cement to provide structural integrity or may be left uncased for different reasons. The primary goal behind drilling a wellbore is typically to extract oil or gas over an extended period.
Key Takeaways
- Resource Extraction: A wellbore is a type of borehole specifically used for extracting oil or gas.
- Versatility: Boreholes can also serve purposes like mineral extraction, environmental assessment, and temperature measurement.
- Structure: Wellbores typically consist of vertical shafts that can be either uncased or encased with materials such as cement and steel.
- Longevity: Their primary purpose is to enable the long-term extraction of valuable resources like oil and gas.
Understanding a Wellbore
A wellbore is essentially a narrow shaft drilled horizontally or vertically into the Earth. Its primary function is to access natural resources such as water, petroleum, or gas. Resource extraction companies drill wellbores to tap into these resources effectively. Typically, wellbores are vertical shafts that are drilled to provide adequate access to the desired natural resources. They encompass the entirety of the drilled hole, including both the open and uncased portions of the well.
Examples of a Wellbore
Here’s a comprehensive look at an oil wellbore encased in steel and cement:
In this example, the wellbore refers to the drilled hole, whether it denotes the inside diameter of the wellbore wall or the rock face surrounding the hole. Often, the wellbore is cased with materials to enhance stability and optimize resource recovery.
While the term ‘borehole’ is sometimes used interchangeably with ‘wellbore,’ borehole typically refers to the open diameter of the drill hole itself. In contrast, wellbore includes the complete structure, casing, and all.
Cleaning wellbores before and after production is crucial to avoid increased operational costs and safety or environmental risks stemming from mud or debris accumulation. Given that drilling a wellbore is complex, it demands specialized training, tools, and equipment. When successfully executed, a wellbore can facilitate resource extraction for many years.
Although commonly associated with oil drilling, wellbores are applicable for various types of wells. Historically, humans have used drilling rigs or even manually-operated rigs to dig wells for thousands of years. The tools and methodologies for creating wellbores change based on geological conditions and the intended use. Offshore drilling employs floating units or seafloor-supported platforms for its operations.
Interestingly, Chinese miners have been making wellbores since at least the Qin Dynasty (221–206 BC). Initially, these wells only reached depths of 30 meters, but by the 1800s, they could reach up to 1,000 meters.
As described by K.S. Tom, “The Chinese method of deep drilling involved a team of men jumping on and off a beam to impact the drilling bit while the boring tool was rotated by buffalo and oxen.” This method continued to be used in early oil extraction in California in the 1860s, known colloquially as “kicking her down.”
Related Terms: borehole, well casing, horizontal drilling, vertical drilling, resource extraction.
References
- John K. Warren. “Evaporites: A Geological Compendium”. Spring, 2016.
- K. S. Tom. “Echoes from Old China: Life, Legends, and Lore of the Middle Kingdom”. University of Hawaii Press, 1989.
