Conventional resources and unconventional resources are two very different, separate sets of resources that can potentially be extracted. Both refer to some quantity of fossil fuels that could contribute to a reserve if they could be extracted economically.The distinction between a resource and reserve is explored with a diagram known as a McKelvey box. The difference between conventional and unconventional is relatively straightforward, and has to do mostly with the ease the fuels can be extracted with.
Conventional oil or gas comes from formations that are "normal" or straightforward to extract product from. Extracting fossil fuels from these geological formations can be done with standard methods that can be used to economically remove the fuel from the deposit. Conventional resources tend to be easier and less expensive to produce simply because they require no specialized technologies and can utilize common methods. Because of this simplicity and relative cheapness, conventional oil and gas are generally some of the first targets of industry activity.
In contrast to this, unconventional oil or gas resources are much more difficult to extract. Some of these resources are trapped in reservoirs with poor permeability and porosity, meaning that it is extremely difficult or impossible for oil or natural gas to flow through the pores and into a standard well. To be able to produce from these difficult reservoirs, specialized techniques and tools are used. For example, the extraction of shale oil, tight gas, and shale gas must include a hydraulic fracturing step in order to create cracks for the oil or gas to flow through. In the oil sands, in situ deposits must utilize steam assisted gravity drainage to be able to extract thick bitumen from underground deposits. All of these methods are more costly than those used to produce fossil fuels from a traditional reservoir, but this stimulation allows for the production of oil and gas from resources that were previously not economic to extract from. These resources become reserves when they can be utilized economically.
Unconventional resources are being utilized more and more as decades of oil and natural gas production have resulted in extensive use of conventional resources. Because of this, new technologies are constantly being introduced that allows for the more economic extraction of non-traditional oil and gas that may have been previously impossible to obtain. Development of these unconventional resources has significant economic potential as a large portion of oil and gas resources is estimated to exist in unconventional deposits. In Canada, estimates put oil reserves at 174 billion barrels of oil, with 169 billion being in the oil sands - a type of unconventional resource. Similarly, there is far more natural gas in unconventional deposits rather than conventional ones.