As the meaning of "well" includes "origin", "spring" or "spilling out", "well" tends to be used for a drilling hole from which water, oil or gas is derived, or expected in the industry. Since scientific drilling such as IODP drilling is not aiming to produce oil and gas, the term "hole" is used. "Borehole" means just "not cased (no casing set) condition" of a hole.

Well, hole and borehole are commonly used in O&G industry to refer to same object. But the O&G well in a general sense is a complex object. You should pay attention to the specifics of the database you work with as there are quite a few subtleties to well description. As an example a "well" can have several attached "boreholes" accidental (when drilling with sequential drilling runs the drill bit "erred") or on purpose (to maximize surface of contact / position contact to formation in specific locations). In some instance a well might in fact be... several wells originating from similar surface locations or targeting similar downhole locations. Conventions widely differ from location to location. The database you are working with probably has some attached definitions. You should consider them with care.

There is no difference in the three names hole, well and borehole as long as we all know what are we talking about. When you want to drill an oil well, you start with a hole, then you continue until you reach the target depth, you could complete it with multiple boreholes such as multilateral but having one Christmases tree, wellhead, of which you could give a well number

There is no difference between well, hole, and borehole in a scientific sense. "Hole" is usually used as a shortened form of "borehole." A "well", however, is typically used for extractive purposes, where as a hole or borehole is used for scientific purposes and is not completed for production of any resource.

Offshore oil and gas wells can have several lateral or directional sections drilled from a common vertical section of the well. Each unique lateral or directional section is drilled in a different direction and/or to a different target interval. each of those wells can have unique or related names. This type of well geometry is used where the cost of drilling a new tophole section is higher than drilling multiple laterals.

The ODP and IODP typically drills vertical boreholes for cost and engineering reasons. The drillships used are not typically designed to intentionally drill lateral wells or wells that are significantly deviated from vertical.

There is no difference between well, hole and borehole in the sense of the words.

A well is a man-made hole deeper than the water table. It is the name given to a hole in the ground to access groundwater and bring it to the surface. The most common type consists of a vertical steel pipe that has an open section at the base opposite the most productive water-bearing layer.

A hole is a hollow place in a solid body or mass; a cavity; a hole in the ground.

A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid (such as petroleum) or gases (such as natural gas), as part of a geotechnical investigation, environmental site assessment, mineral exploration, temperature measurement or as a pilot hole for installing piers or underground utilities.

A well is a hole of one or more boreholes.

In O&G, a well is a borehole that have been completed for hydrocarbon production or any other O&G purpose. A borehole is a hole made by boring (drilling) and not yet completed. A hole in O&G Drilling Engineering) could mean a rat hole or mouse hole used for any purpose (like placement of Kelly) except hydrocarbon production or fluid injection

Borehole collectively describes all of the various types of holes drilled as part of a geotechnical investigation or environmental site assessment. Well is a hole or borehole from which water, crude oil or gas are extracted.

For someone outside the Oil and Gas Industry, the three words can mean practically the same. However, for oilfield workers and practitioners the three words can have different shades of the same . A well is the complete and final state of a surface to reservoir conduit.Designed and developed to produce Gas, Oil or water from below the earth surface. A wellore is the term used to discuss this conduit before its actually drilled or developed and the term hole can be used to describe in more general way any depression or aperture created in the earth surface, usually vertical.

I confess not to have read all previous responses. The words are commonly used interchangeably, but there is a distinction. A "borehole" is just the drilled hole. Many "borings" can be done for sampling, only (e.g., geotechnical, stratigraphic). A "well" must be "completed." This is done in various ways (e.g., open-hole, slotted screen, perforated casing). The purpose of a "well" is to produce fluid (gas, oil, water). For more information see "Groundwater and Wells" (Johnson Screens).

Many thanks for your nice answers, I appreciate that! based on all answers, I just can say that there are still diverse opinions on this matter. Thanks again.

There is a lot of nice answers for your question. In the DSDP/ODP jargon, the words mean the same thing.

A well is the complete and final state of a surface to reservoir conduit including Designed and developed to produce Gas, Oil or water from below the earth surface.

A borehole is the generalized term for any narrow shaftbored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water or other liquid, such as petroleum or natural gas, as part of a geotechnical investigation, environmental site assessment, mineral exploration, temperature measurement or as a pilot hole for installing piers or underground utilities. Also boreholes can be made for geothermal installations. As well as pumping petroleum from an underground well through a borehole, liquid or gas can be pumped into it, for that process, or for underground storage of unwanted substances. e.g. in Carbon capture and storage.

hole can be used to describe in more general way any depression or aperture created in the earth surface, usually vertical.

Though a well, borehole and a hole have the same literal meaning yet there are some differences in them with respect to use in Petroleum Engineering. A well is a term used for a boring in the earth designed to use for bringing the hydrocarbons, oil and gas to the surface. This involves steps like planning,drilling, completion, production and abandonment.

A borehole is also a narrow boring but it is done mainly to take out small sample from the earth's surface in order to check temperature of the site or geotechnical investigation, emvironmental assesment of the field.

A hole in the context of petroleum industry is an excavation done in the sea floor in order to protect the wellhead equipment on petroleum wells from iceberg or ice.

Well, Hole and Borehole all have the same meaning in petroleum industry and its scientific literature.

Mohammad is correct, they are all the same. University Professor will use the term Oil Well, field Engineer prefers Borehole. 

I had a doubt that, if all the terms are same why do we have both well code code and well bore code in API number? @ Benjamin C. Burke

@Ali Al-Bemani?

Well is always used by an Oil-drilling engineer,but borehole is used by a Geo-drilling engineer instead. we always say that we get samples and cuttings from borehole by drilling in Geo-drilling.

Hello,

I would like to share a viewpoint about this question to Gery Herbozo.

As I read above, a few commenters gave a very good point in highlighting the semantic context behind these words. In Portuguese, it is somewhat difficult to translate the meaning of "wellbore" and "well", for instance, in distinct ways. Hence, we could think of it as synonyms. However, for English speakers, they seem to have slightly different interpretations.

Herbozo's question seems to fit into drilling engineering context. To complement what Jonathan Lucas Jee and Mahmoud I. Abdou have already commented, I would add the following specificity:

- "Hole" is a widely generic term meaning simply an "aperture" or "orifice". We could use this word in a "slangy" and "loose" way to refer to the "void" space open in the rock after a drilling operation, but it sounds to me too much generic if you wish to be formal.

- "Borehole" and "wellbore" are, in my opinion, the best formal synonyms for the "void" space aforementioned. That is to say, it refers to a rock formation that was only drilled. It is free of all the mechanical apparatuses.

- "Well", in my opinion, is the best formal term to use when we talk about the "all thing equipped", i.e. ready for completion and production.

Roughly speaking, think of "borehole/wellbore" as a nude body and "well" as clothes and beauty accessories. Perhaps, this is not the best comparison, but it may help you to understand the meaning.

This is a little odd... But, as I said, in my language, there is only a word to refer to "borehole" and "well". Then, I really understand why Mr. Herbozo asked such a thing, which seems to be elementary. Well, it is a semantic issue, like this last "well".

I hope this helps.

Best wishes to all!

Reference: https://www.glossary.oilfield.slb.com/en/Terms/w/wellbore.aspx

What about the early oil industry hand-dug pits? It appears they must be named wells because they were "cased" and equipped for production.

Were they wells?

Best to all