In oil and gas industry, the term “Unconventional” refers to hydrocarbon resources that are or could be exploited with processes and techniques of drilling and production other than those commonly used by the upstream industry all over the world..
The term unconventional has been subject to different definitions, and various agencies or industry companies may have developed their own definition.
The Society of Petroleum Engineers (SPE), for instance, defines “Unconventional Resources” as petroleum accumulations that are prevalent throughout a large area and that are not significantly affected by pressure exerted by water (hydrodynamic influences); they are also called “continuous-type deposits” or “tight formations.”
An energy industry firm – Schlumberger – uses the term “Unconventional” referring to oil and gas reservoirs whose porosity, permeability, fluid trapping mechanism, or other characteristics differ from conventional sandstone and carbonate reservoirs.
Another energy industry company, IHS, defines “Unconventional” as a term which refers to hydrocarbon resources that cannot be produced at economic flow rates or that do not produce economic volumes without particular activities and operations such as stimulation, special recovery processes and advanced technologies.
The existence of unconventional resources has been known for many years, but, it is in the last decade that, a combination of economic and geopolitical factors, together with advances in directional drilling and well stimulation technologies, has made them commercially exploitable on a large scale.
In particular, the last two decades have seen an increase in the price of crude oil and natural gas, and this aspect has led companies to focus on developing hydrocarbon resources whose production would formerly have been judged to be uneconomic.
The emergence of unconventional oil & gas has had a great impact on the global energy system, and their development has been supported by several factors such as a favourable regulatory regime in some countries, the previously cited issue of high prices of conventional resources, the significant technological advancements in areas of horizontal drilling, of thermal EOR processes (TEOR), and of hydraulic fracturing (fundamental for their exploitation).
Resource Triangle (Master & Gray – 1979)
There are many different kind of hydrocarbon unconventional resources, among them it is useful to mention and briefly describe:
Map of basins with assessed shale oil and shale gas formations, as May 2013
Oil Sands Sample
Typical CBM Production Curve (IEA)
Schematic section of CBM exploitation (IGas)
Left – Natural gas hydrate burning
Right – The structure of methane hydrate. Molecules of methane are trapped within a ‘cage’ of water ice molecules
Hydrate Phase Diagram (Oilfield Review)
Map of global hydrate distribution
Red dots show locations where hydrate has been found on continental margins (Oilfield Review)