Acording to Act 13 - Feequently Asked Questions by PA DEP the difference between conventional and unconventional wells is explained as follows:
What is a conventional gas well?
A conventional gas well , also known as a traditional well, is a well that produces oil or gas from a conventional formation. Conventional formations are variable in age, occurring both above and below the Elk Sandstone. While a limited number of such gas wells are capable of producing sufficient quantities of gas without stimulation by hydraulic fracturing, most conventional wells require this stimulation technique due to the reservoir characteristics in Pennsylvania. Stimulation of conventional wells, however, generally does not require the volume of fluids typically required for unconventional wells.
What is an unconventional gas well?
An unconventional gas well is a well that is drilled into an unconventional formation, which is defined as a geologic shale formation below the base of the Elk Sandstone or its geologic equivalent where natural gas generally cannot be produced except by horizontal or vertical well bores stimulated by hydraulic fracturing. To view a rock correlation diagram of formations in Pennsylvania , please click here.
Unconventional formations that are currently being targeted or that may possibly be targeted for oil and gas development in Pennsylvania include, but are not limited to, the Marcellus, Utica, Mandata, Huron, Rhinestreet, and miscellaneous Upper Devonian formations such as the Dunkirk, Pipe Creek, Middlesex, Geneseo, and Burkett. There are some shale formations, including the Huron, Dunkirk, and Pipe Creek shales, that are younger than the oldest basal Elk Sandstone section and, therefore, do not meet the Act 13 definition of an "unconventional formation."
Based on DEP's information two factors seem to control the difference; (1) the depth of the formation and (2) the amount of water needed to frac the well.
Outside PA law the difference is even more vague and appears to be based on the drilling techniques used in the process. As newer techniques are used in shallower formations the difference becomes even more blured.
| Conventional | Unconventional | |
| Well Pad Size | 1 to 5 Acres | More than 5 Acres |
| Equipment needed | Small equipment truck mounted drill rig, several trucks small backhoe, buldozer limited amount of pipe Photo |
Large amount of equipment Large drill rig Fracking equipment large waste pits Photo |
| Depth/length | less than 6000 feet | 6000 feet or more |
| Well head pressure | Low | Very high |
| Frac fluid used | Less than 1 million gallons | 4 to 10 million gallons |
| Production volume | A few barrels/day of oil less than ? cfm/day of gas |
High |
| Rock permeability | Porus: less than 0.1 millidarcies | Tight: greater then 0.1 millidarcies |
| Product transport | Trucks for oil small pipeline system before connecting to distribution system. |
Large pipeline system with compressor stations |
Conventional Wells from PGCC
Act 13 - Feequently Asked Questions PA DEP
Act 13 FAQ -PA Public Utilities Commission
New Frontiers: Conventional oil, unconventional, or an Oreo cookie? The pertolium industry definition differs from those of the general public and government.