Oil and Gas Wells Classifications
By Rabiu Aminu, PhD, FCNA, FMNES
A. Classification Based on Location
Based on the location of oil and
gas wells, the wells can be classified as onshore or offshore, depending on
whether they are located on land or in bodies of water.
1- Onshore Wells
Onshore wells are oil and gas
wells that are drilled on land. These wells are usually located in areas where
there are significant oil and gas reserves, and they can be drilled in a
variety of terrains, including deserts, forests, and mountains. Onshore wells
are typically less expensive to drill and operate than offshore wells because
they do not require the use of specialized equipment and facilities to access
and process the oil or gas.
2- Offshore Wells
Offshore wells are oil and gas
wells that are drilled in the ocean or other bodies of water. These wells can
be located in shallow waters close to shore or in deep waters far from shore.
Offshore wells require specialized equipment and facilities, such as offshore
drilling rigs and offshore platforms, to access and process the oil or gas.
These facilities can be expensive to build and maintain, and the drilling
process can be more challenging due to the ocean environment, such as storms
and waves.
Offshore wells can also pose
additional environmental risks, such as oil spills and pollution, which can
have significant impacts on the ocean ecosystem and local communities. However,
offshore wells can potentially access larger oil and gas reserves than onshore
wells, which can make them more economically valuable.
B. Classification Based on Fluid Production
1- Oil wells
Oil wells are wells that are
drilled to extract crude oil from underground reservoirs. These wells are
typically drilled vertically or at a slight angle to the surface, and they are
often located in areas where there are significant oil reserves. The oil
extracted from these wells can be processed into a variety of products,
including gasoline, diesel fuel, and lubricants, among others.
2- Gas wells
Gas wells are wells that are
drilled to extract natural gas from underground reservoirs. These wells can be
drilled vertically or horizontally, and they are often located in areas where
there are significant natural gas reserves. The natural gas extracted from
these wells can be processed and used as a fuel for heating and electricity
generation, as well as for other industrial processes.
While oil and gas wells can have
similar characteristics, there are some differences between them. For example,
oil wells typically produce a mixture of oil, natural gas, and other
substances, while gas wells typically produce only natural gas. Additionally,
the drilling techniques and equipment used for oil and gas wells can be
slightly different, depending on the specific characteristics of the reservoir
being drilled.
C. Classification Based on Drilling Direction
Based on the drilling direction, wells
can be classified as vertical, deviated, or horizontal, depending on the
direction in which they are drilled.
1- Vertical Wells
Vertical wells, as the name
suggests, are oil and gas wells that are drilled straight down into the ground,
perpendicular to the surface. These wells are the most common type of well, and
they are typically used in areas where the oil or gas reservoir is relatively
shallow and can be accessed with a relatively short wellbore. Vertical wells
are also used when drilling for minerals other than oil and gas, such as coal.
2- Horizontal Wells
Horizontal wells are oil and gas
wells that are drilled at an angle from the vertical so that the wellbore
extends horizontally through the oil or gas reservoir. This allows the well to
access a larger area of the reservoir, which can improve the efficiency of oil
or gas extraction. Horizontal wells are often used in areas where the oil or
gas reservoir is relatively thin or where there are geological barriers that
prevent vertical drilling.
3- Deviated wells
Deviated wells are oil and gas
wells that are drilled at an angle from the vertical, but not to the extent of
a horizontal well. Deviated wells are typically used when the oil or gas
reservoir is located at an angle to the surface or when there are other
geological barriers that prevent vertical drilling. The angle of deviation can
vary depending on the specific circumstances, but typically deviated wells have
a deviation angle of less than 60 degrees from vertical.
D. Classification Based on Production Stage
Based on the production stage:
Wells can be classified as exploration, appraisal or development wells
depending on the stage of production they are in.
1- Exploration wells
Exploration wells are wells
drilled to find new reserves of oil and gas. These wells are drilled in areas
where there is no known oil or gas reserve. These wells are typically drilled
to determine if there are commercial quantities of oil or gas in the area.
Exploration wells are usually drilled to relatively shallow depths and are
often located in remote areas. Exploration wells are also called exploratory
wells.
2- Appraisal well
Appraisal wells are wells used to
determine the size and quality of a discovered reservoir. These type of wells
are drilled after an exploration well has discovered a potential oil or gas
reservoir. The purpose of appraisal wells is to determine the size, shape, and
characteristics of the reservoir, as well as to estimate the potential amount
of recoverable oil or gas. Appraisal wells are typically drilled around the
discovery well and may be drilled to different depths or locations to get a
better understanding of the reservoir. Appraisal wells are also called Step-out
wells.
3- Development wells
Development wells are used to
produce oil and gas from a known reservoir. These type of oil and gas wells are
drilled after an oil or gas reserve has been discovered and appraised. The
purpose of development wells is to extract the oil or gas from the reservoir
and bring it to the surface for processing. Development wells may be drilled
vertically or horizontally, and the number of wells required will depend on the
size and characteristics of the reservoir. The drilling and completion of
development wells may be done in phases over several years or even decades,
depending on the size and complexity of the reservoir.
E. Other Oil and Gas Wells Classifications
1- Wildcats or wildcat wells
Wildcat or wildcat wells are oil
and gas exploration wells that are drilled in areas where there is little or no
known oil or gas reserves. These wells are drilled based on geological and
geophysical data and are typically considered to be high-risk ventures due to
the uncertainty of finding commercial quantities of oil or gas. Wildcat wells
can be expensive to drill and operate, but if successful, they can lead to the
discovery of new oil or gas fields.
2- Discovery wells
Discovery wells are the first
wells drilled in an area to explore and determine if there are any commercial
quantities of oil or gas. These wells are typically drilled based on geological
data and previous exploration findings.
3- Dry hole
A dry hole is a well that is
drilled but does not produce any commercially viable quantities of oil or gas.
This can happen due to a variety of reasons, such as drilling in the wrong
location or encountering a reservoir that has been depleted.
4- Step-out well
Step-out wells are wells that are
drilled outside of the known producing area of an oil or gas reservoir. These
wells are drilled to determine if the reservoir extends beyond the known
boundaries and to discover new producing areas.
5- Production wells
Production wells are wells that
are drilled to extract oil or gas from underground reservoirs. These wells can
be vertical or horizontal, and they are equipped with pumps or other equipment
to bring the oil or gas to the surface for processing.
6- Marginal wells
Marginal wells are wells that
produce oil or gas at a low rate or have been depleted to a point where they
are no longer economical to operate. These wells may continue to produce oil or
gas for many years, but they typically require a lower investment and operating
cost compared to high-producing wells.
7- Injection well
Injection wells are wells that
are drilled to inject fluids, such as water, steam, or chemicals, into
underground reservoirs to enhance oil or gas recovery. These wells are
typically drilled close to production wells and are used to maintain reservoir
pressure and increase the amount of oil or gas that can be recovered.
8- Disposal well
Disposal wells are wells that are
drilled to inject waste fluids, such as saltwater or produced water, into
underground formations where they will not harm the environment or contaminate
groundwater. These wells are used to dispose of the fluids that are produced
along with the oil or gas.
9- Service well
Service wells are wells that are
drilled for purposes other than oil or gas production, such as to monitor
reservoir conditions or to access the wellbore for maintenance or repairs.
10-Stratigraphic well
Stratigraphic wells are wells
that are drilled to explore and analyze the geology and stratigraphy of an
area. These wells can provide valuable information about the rock formations
and can help determine the potential for oil or gas reserves.
11-Abandoned well
An abandoned well is a well that
is no longer in use and has been permanently sealed and abandoned to prevent
environmental contamination or other hazards.
12-Stripper well
Stripper wells are wells that
produce small amounts of oil or gas, typically less than 10 barrels per day.
These wells can be marginally profitable but may continue to produce for many
years, even after larger wells in the area have been depleted.
References
Craft, B. C., Hawkins, M. F., & Terry, R. E. (2012). Applied
petroleum reservoir engineering (3rd Edition). Prentice Hall.
Fahim, M. A., Hasan, M. R., Hossain, M. M., & Islam, M. S.
(2019). Classification of oil and gas wells based on different criteria. Journal
of Petroleum Exploration and Production Technology, 9(4), 3199-3210.
International Association of Oil & Gas Producers. (2018). Drilling
and Well Operations.
https://www.iogp.org/wp-content/uploads/2018/11/2018a-Drilling-and-Well-Operations-Report.pdf
Johnston, D. (2015). Petroleum geology of the North Sea: Basic
concepts and recent advances. John Wiley & Sons.
Khan, M. R., Khattak, M. A., Khan, A. R., & Tariq, M. (2017).
Classification of oil and gas wells based on production stage and formation
lithology: A case study from the northern Potwar, Pakistan. Journal of
Petroleum Science and Engineering, 157, 690-703.
Mukherjee, S., & Agrawal, A. (2015). On the classification of
oil and gas wells. Journal of Petroleum Exploration and Production
Technology, 5(3), 261-270.
Mungan, N. (2014). Oil and Gas Wells: Drilling, Completion, and
Production (2nd Edition). PennWell Books.
Schmidt, J. J. (2018). Petroleum engineering handbook: Drilling
engineering. Society of Petroleum Engineers.
https://doi.org/10.2118/2007-4-30-3
Speight, J. G. (2018). The Chemistry and Technology of
Petroleum (5th Edition). CRC Press.
U.S. Energy Information Administration. (2021). Oil and gas
wells by production type.
https://www.eia.gov/tools/faqs/faq.php?id=709&t=6
U.S. Geological Survey. (n.d.). Oil and gas drilling methods.
https://www.usgs.gov/faqs/oil-and-gas-drilling-methods?qt-news_science_products=0#qt-news_science_products
