The most accepted theory of hydrocarbon origins is the one known as «organic«. According to this theory, oil comes from particles of organic matter (animal and plant wastes) that, under certain conditions of pressure and temperature, are «cooked» over millions of years.
Hydrocarbons are cooked in what is called a source rock or mother rock. Once «ready», due to different densities and pressures, oil and gas migrate upwards until they meet a natural impediment that prevents them from continuing their journey to the surface; this obstacle is known as a seal. It is from then on, that hydrocarbons accumulate and concentrate in a stored rock.
There are two concepts worth highlighting. Porosity, which is a condition of rocks that consists of the presence of holes through which the hydrocarbon travels; and permeability, meaning that the rock pores are connected, making it easier to move them.
This is what makes up a traditional oil system, but some reservoirs do not cover all the elements of this system; we know them as non-conventional. They are non-conventional resources (oil or gas) because they come from a different system than the traditional one.
A clear example of a non-conventional reservoir is what we usually identify as shale. Here, the mother rock and the storage rock are the same thing; evidently, it is a formation with very low porosity and permeability. In this case, to extract the hydrocarbons that are trapped in the rock, we need to fracture it through a technique that has been in the oil industry for more than 50 years: hydraulic stimulation or fracking.
Mexico’s greatest hydrocarbon wealth (60%) is located precisely in the non-conventional prospective resources, and of the portfolio that we have as a country, the most prolific zones are located in the deep waters (between 500 and 1,500 meters of water) and the ultra-deep waters (more than 1,500 meters of water) of the Gulf of Mexico.
In the next chapter, we will talk about Prospective Resources and Reserves, concepts that are often confused and that certainly involve a good amount of technical elements. We will do it, as always, so as we all understand it. Until then.
By: Sergio Pimentel