Conventional versus Unconventional Oil and Gas
Conventional Resources are concentrations of oil or gas that occur in discrete accumulations or pools. Rock formations hosting these pools traditionally have high porosity and permeability and are found below impermeable rock formations.These impervious layers form barriers to hydrocarbon migration resulting in oil and gas being trapped below them. Conventional oil and gas pools are developed using vertical well bores and using minimal stimulation.
Conventional oil and gas pools fall into several categories based on the mechanism responsible for the trapping or pooling of the hydrocarbon:
- Structural traps whereby broad folds and/or faults lead to concentrations of hydrocarbons;
- Dome-like structures related to diapiric rise of underlying sediments;
- Stratigraphic traps where a change in the rock type creates a barrier; and
- Multiple combinations of the previous processes.
Prior to 2006, conventional oil and gas pools were the primary exploration targets in Western Canada.
Unconventional Resources are oil or gas-bearing units where the permeability and porosity are so low that the resource cannot be extracted economically through a vertical well bore and instead requires a horizontal well bore followed by multistage hydraulic fracturing to achieve economic production.
Unconventional resources fall into two broad categories:
- A widespread, low-permeability and -porosity gas- or oil-charged horizon. If the horizon is composed primarily of shale, it is a “shale gas” or “shale oil” resource; and,
- Low-permeability and -porosity portions of an oil or gas pool that cannot be developed through conventional drilling and completion processes
Currently, virtually all wells being completed in the province are classified as unconventional. This is because the exploration industry can economically develop these widespread resources through the application of horizontal drilling and multi-stage hydraulic fracturing.