by Armağan Derman:
After the Shale Revolution in North America in early 2000’s, a huge interest rose all over the world and Turkey, no doubt, is among those countries.
In this article, I will try to explain what unconventional resources are, which caused a revolution particularly in USA and turned this biggest hydrocarbon consuming and importing country into a hydrocarbon exporting one. I will also try to discuss, where in Turkey, might be these resources and how it can contribute to Turkey’s energy independence.
In order to understand what unconventional resources are one must first understand the terminology and how hydrocarbons (a term used both for oil and gas) are formed.
Especially in Turkish community, the term “unconventional” causes confusion. From a fluid type point of view Unconventional Resources are the same oil and gas that we produce conventionally. Actually, the term unconventional refers to the rock type where hydrocarbons are produced and the methodology that is used to extract them. Apart from the term Unconventional Resources, Shale Gas, Shale Oil, Tight Gas, Tight Oil and Self Sourced Resources are used widely in the industry.
In Turkish press or other publications, the term “Rock Gas” is used. Technically it is not correct to use such a term since all hydrocarbons are produced from rocks. So, rather than using “Rock”, we strongly recommend to use the term “shale” which is a type of rock which (if available) is capable to transform in situ organic matter into oil and gas.
What are these resources which is described with such different terms? As mentioned above unconventional resources is not something different from conventional oil and gas. The unconventional side of these resources are the rock from which hydrocarbons are produced and the methodology that is used to extract them.
Conventional oil and gas is produced from certain type of rocks where porosity and permeability is high. In other words, such rocks referred to as reservoirs are capable to transmit oil and gas without any stimulation. In such reservoirs, fluids exist from top to bottom as gas, oil and water.
Unconventional oil and gas, on the other hand, are those hydrocarbons which are produced from the same petroleum system with conventionals, but from a different rock type (Fig.1). These rocks, as stated above, are referred to as shales. If a shale is rich in organic matter it is referred to as Source Rock. Despite conventional reservoirs, it is very difficult to extract oil and gas due to very low transmissibility of fluids. To have economic flow rates, horizontal drilling and hydraulic fracturing is a must.
A less known unconventional resource is called “Basin Centered Gas Systems” or “Pervasive Tight Gas Systems”. The difference from shale gas is that these resources consist of various rock types. These various rocks, are very close to source rock and hence, have high gas saturation values. Despite conventional reservoirs, they exist below free water level and do not need any trap. The fluids exist from top to bottom as water, oil and gas which is just the opposite of a conventional system.