Downsizing wells has environmental benefits. During drilling the volume of cuttings, waste mud and cement are reduced roughly in proportion to the square of the hole diameter at total depth. Once slim wells are accepted in an area, the size of wellheads, blowout preventers, masts, draw works, mud pumps, mud tanks, storage bins, pipe racks, and power systems can all be reduced.

Smaller, multi-skilled crews require smaller camps and logistics become easier.

Slim disposal wells for injection of liquids, slurries and cuttings may also prove to be a cost effective solution.

1 Land drilling

On land a smaller rig translates into a smaller location (depending on production testing burner requirements), no cellar, less visual intrusion, less truck traffic during rig moves and operations, etc.

For exploration drilling in remote and/or environmentally sensitive areas (e.g. jungle, mountainous areas, or national park) the rig can be moved in smaller loads. Large 30-ton trucks normally used to move the draw works and mud pumps of a typical medium-depth rig can be replaced by 10-ton trucks or, in special cases, by four-wheel drive or tracked vehicles. In some cases this may avoid the need to strengthen bridges, or it may be possible to use the same roads as the seismic crews. The smaller loads will facilitate logistical operations involving landing craft or similar devices.

Using a slim rig in helicopter supported operations will drastically reduce the number of lifts required, thereby reducing exposure and fuel consumption.

2 Swamp and inland waters

When drilling in swamp or sheltered inland waters fewer and/or smaller barges are required for logistic support. The smaller hook load, wellhead, blowout preventer stack and weight of drilling equipment means that for a given ship stability criteria, the barge used for drilling needs less beam, whether it operates in floating or sit-on-bottom mode. This means that a smaller location and access canal have to be dredged. In sensitive areas a smaller location can be boomed off against spills. Alternatively, by modifying an existing hull to drill slim it is easier to make it drip tight. For a given canal size "slot barges" could perhaps be replaced with slim-drilling "cantilever barges". In a mature area such as Nigeria or Louisiana, this would permit cluster infill drilling without enlarging existing dredged slots.

In some remote areas, slim land rigs have been used from small barges for part of the year, and in some climates this can drastically increase equipment utilisation rates, thus reducing costs. In the future it may be possible to support the mast and hook load on a driven conductor (complete with baseplate), reducing the size of support equipment still further. Drilling can then take place supported by barges, supply vessels or Self-Elevating Workover Platforms, which were previously considered too small for such duty.

3 Arctic drilling

The delicate ecosystems of the Arctic and Antarctic make slim exploration wells almost mandatory even before consideration of the logistical gains. In some areas of Canada, ice roads and locations are used to protect the tundra and its delicate vegetation. Lighter loads could give more operational flexibility, or less truck traffic. For example, a small rig could operate off barges, ice locations or hover barges. Such flexibility could extend the drilling season significantly, with a dramatic impact on costs per well. Smaller rigs and mud systems give lower total heat transfer into the ice during drilling and require less fuel for operation and heating, leading to a lighter environmental burden.

4 Offshore

For offshore drilling, less marine traffic is required. At offshore locations where cuttings may have to be shipped back to shore for disposal, slimmer holes can greatly reduce the logistical difficulties of allowable deck load, delays due to rough weather, etc. It may make the use of oil-based mud possible to combat drilling problems. Retrofitting existing mobile rig hulls to drill slim may eliminate the need for some shore based materials facilities, especially for single string ventures.